(Ill "AR0 1403311 LAND DEVELOPMENT AND THE NATURAL ENVIRONMENT ESTIMATING IMPACTS Dale L. Keyes THE URBAN INSTITUTE izx Safaris SEYMOUR DURST When you leave, please leave this book Because it has been said "Ever thing comes t' him who waits Except a loaned book." Avery Architectural and Fine Arts Library Gift of Seymour B. Durst Old York Library LAND DEVELOPMENT AND THE NATURAL ENVIRONMENT: ESTIMATING IMPACTS Dale L. Keyes in The research for this report was made possible through a research grant from the Office of Policy Development and Research of the U.S. Department of Housing and Urban Development under the provisions of Section 701(b) of the Housing Act of 1954, as amended, to The Urban Institute. The publication of this report was supported by the Ford Foundation. The findings and con- clusions presented in this report do not represent official policy of the Department of Housing and Urban Development, the Ford Foundation, or The Urban Institute. THE URBAN INSTITUTE Library of Congress Catalog Card Number 76-10104 U.I. 195-214-4 ISBN 87766-158-8 REFER TO URI 13500 WHEN ORDERING Available from: Publications Office The Urban Institute 2100 M Street, N.W. Washington, D.C. 20037 List Price $4.95 Printed in the United States of America First printing, April 1976 FOREWORD This is one of a series of reports by The Urban Institute's Land Use Center which discuss the evaluation of land developments and their economic, environmental, and social impacts. Increasingly, local governments are turning to formalized impact evaluation requirements in order to ascertain the" likely effect of permitting land to be developed in various ways at specific locations. The degree to which this approach can improve land use decision making is largely dependent on the ability to ac- curately estimate a wide variety of potential impacts. The first report in this series, Measuring Impacts of Land Development: An Initial Approach, established an overall framework for evaluation and suggested a series of measures which could be used to estimate impacts for a wide range of economic, social, and environmental concerns. Proce- dures for actually making impact estimates were also outlined, although in a general and preliminary fashion. The concluding report in the series, Using an Impact Measurement System for Evaluating Land Developments, reexamines the overall framework and describes potential problems and pros- pects for implementing an impact measurement system. This latter report thus provides a general per- spective on this as well as the other reports in this series. This report treats only those impacts related to the natural environment (primarily air quality, water quantity — including flooding — and water quality, wildlife and vegetation, and noise). In addi- tion, natural disasters and scarce resources are discussed briefly. The discussion of environmental im- pacts focuses on data collection and analysis procedures, with special attention given to assessing the costs and data requirements and reliability of specific analytical techniques appropriate for making es- timates in the various impact categories. It can be best described as a reference document for those who find themselves directly involved with the impact evaluation process. These would include planners, developers, and others actually making the estimates as well as decision makers and inter- ested lay persons who wish to learn more about the costs, assumptions, and general considerations which underlie the estimates. Companion reports in this series treat methodological issues in the following areas — fiscal bal- ance (local revenues and the cost of public services), the private economy (employment and property values), public services (the quality and level of service), and social effects (aesthetic considerations and the perceptions and behavior patterns of local residents). Taken together, these reports offer de- tailed guidance in the structuring and operation of a comprehensive impact evaluation system appro- priate for use by local governments. Even with improved information concerning the probable effects of proposed developments, arriving at decisions regarding specific projects will remain a difficult task. Rarely are the impacts so one-sided that no one is adversely affected or that no one is benefitted. Rather, decision makers must sort out and compare impact estimates which are often incommensurable and then balance the inter- ests of various affected parties, some of whom may be future generations. The task is an unenviable one and subject to much speculation. By using a well-documented and highly visible approach to im- pact analysis as is recommended here and in the companion reports, some of these difficulties may be mitigated. Land use conflicts will surely remain, but some of the obscurity and confusion which sur- rounds them may be reduced. Worth Bate man, Executive Director Land Use Center The Urban Instiute iii CONTENTS Foreword iii Acknowledgments ix Advisory Group x Summary xi GENERAL INTRODUCTION 1 A. Comprehensive Impact Evaluations — An Approach 2 1. Impacts on Man 2 2. Comprehensiveness 3 3. Impacted Populations ("Clientele Groups") 3 4. Impact Categorization 3 B. Implementing Impact Evaluation Procedures — Major Issues 4 1. Comprehensive versus Incremental Review 4 2. The "Spillover" Problem 4 3. Proposal Alternatives 5 4. Planning Department/Line Agency Interrelationships 5 5. Applicable Federal. State, and Local Laws 5 C. Needed Research 6 Part 1. AIR QUALITY 7 I. Introduction and Background 9 A. Health and Welfare Effects 9 1. Human Health Effects 9 2. Vegetation and Materials Effects 11 B. Applicable State and Federal Laws 11 C. Emissions and Atmospheric Dispersion: Fundamental Principles 13 1. Emissions and Emission Sources 13 2. Atmospheric Dispersion 13 a. Principal Factors Affecting Dispersion 13 b. Removal and Transformation Processes 14 D. Air Quality Impacts of Land Development 14 II. Methodological Approaches 15 A. Measures, Standards, and Indices 15 1. Measures and Standards 15 2. Indices 16 B. Measurement/Estimation Procedures 17 1. Measuring/Estimating Current Emissions 17 a. Point Sources 17 b. Stationary Area Sources 18 c. Mobile Area or Line Sources 18 d. Estimation Problems 18 2. Estimating Future Emissions 19 a. Aggregate or Large Area Analysis 19 b. Small Area Analysis 19 c. Individual Development Analysis 20 d. Estimation Problems 21 3. Measuring/Estimating Current Ambient Concentrations 21 a. Quantitative Measurement 21 b. Measurement Problems 22 c. Vegetative Indicators 22 4. Estimating Future Ambient Concentrations 22 a. Types of Models 23 Theoretical versus Empirical Models 23 Simple versus Complex Models 25 Source versus Receptor Models 25 iv Models Based on Type of Source 25 Models Based on Type of Pollutant 25 Models Based on Scale of Application 25 b. Description of Individual Models 26 Rollforward Models 26 Miller/Holzworth Model 28 Hanna/Gifford Model 29 California Highway Model 31 ERT/MARTIK Model (Modified AQDM) 31 TASSIM 33 Climatological Dispersion Model (CDM) 34 APRAC Model 35 Other Models 36 c. Summary and Comparison of Models 36 5. Measuring/Estimating Odor and Smoke Problems 38 a. Odor Problems 38 b. Smoke Problems 40 6. Measuring/Estimating Exposure of People to Pollution 40 a. Intensity and Duration 40 b. Number of People Exposed 41 7. Measuring/Estimating Damage in Monetary Units 42 III. Conclusions and Recommendations 45 A. Planning versus Project Review 45 B. Specific Recommendations and Conclusions 46 Part 2. WATER QUALITY AND QUANTITY 49 I. Introduction and Background 51 A. Health, Safety and Welfare Effects 51 1. Flooding 51 2. Water Pollution 51 3. Water Consumption 52 B. Applicable Federal and State Laws 52 1. Flooding 52 2. Water Pollution 54 3. Water Consumption 54 C. Fundamental Hydrologic Principles 54 1. Physical Hydrology 54 2. Biological Hydrology 55 D. Water-Related Impacts of Land Development 55 1. Flooding 55 2. Water Pollution 57 3. Water Consumption 57 II. Methodological Approaches 59 A. Impacts on Flooding 59 1. Impact Measures 59 2. General Analytical Approaches 60 3. Estimating Impacts on Stream Flow 60 a. Analytical Techniques 61 Rational Method 61 Flood Frequency Analysis 61 Other Simple Techniques 62 Complex Hydrologic Models 63 b. Comparison and Summary 65 4. Estimating Impacts on the Extent of Flooding 67 a. Analytical Techniques 67 5. Estimating Impacts in Terms of Damages and Risks 67 B. Impacts on Water Pollution 69 1. Measures, Standards, and Indices 69 2. Measuring/Estimating Current Discharge Levels 70 3. Measuring Current Ambient Concentrations 71 v 4. Estimating Future Discharge Levels 71 a. Point Sources 71 b. Nonpoint Sources 72 5. Estimating Future Ambient Concentrations 72 a. General Considerations 72 b. Surface Water Models 74 Streeter-Phelps 74 Simplified EPA Model 74 Auto-Qual 74 HSP, Water Quality Component 75 Other Models 75 c. Groundwater Models 75 d. Comparison and Summary 76 6. Estimating the Number of People Affected 76 7. Estimating Monetary Benefits 76 C. Impacts on Water Consumption 78 1. Impact Measures 78 2. Measuring/Estimating Impacts on Storage and Yield 78 a. Surface Water 78 b. Groundwater 79 3. Measuring/Estimating Salt Water Intrusion 79 III. Conclusions and Recommendations 81 A. Planning versus Project Review 81 B. Specific Recommendations and Conclusions 82 Part 3. WILDLIFE AND VEGETATION 85 I. Introduction and Background 87 A. Human Welfare 87 B. Fundamental Ecological Principles 88 C. Definitions and Terms 89 II. Methodological Approaches 91 A. Measures and Indices 91 B. Measuring/Estimating Current Conditions 92 1. Vegetation 92 a. Assessment of Areal Extent 92 b. Assessment of Vegetation Quality and Quantity 92 c. Methods of Field Measurement 94 2. Wildlife 95 a. Habitat Analysis 95 b. Population Census 95 C. Estimating Future Conditions 98 1. Vegetation 98 2. Wildlife 98 a. Key Considerations 98 b. Research Findings 99 Birds 99 Mammals 99 Amphibians and Reptiles 100 c. Estimation Procedures 100 III. Conclusions and Recommendations 101 A. Planning versus Project Review 101 B. Alternative Data Collection Approaches 101 C. Specific Recommendations and Conclusions 102 Part 4. NOISE 103 I. Introduction and Background 105 A. Health and Welfare Considerations 105 B. Fundamental Principles 106 vi II. Methodological Approaches 109 A. Measures, Standards, and Indices 109 B. Analytical Techniques Ill 1. Construction-Related Ill 2. Transportation-Related 113 a. Specific Examples 113 HUD Noise Assessment Guidelines 113 TSC Methods 114 NCHRP Report 1 17 Method 114 Other Techniques 114 b. Summary and Comparison 115 III. Conclusions and Recommendations 117 A. Planning versus Project Review 117 B. Specific Recommendations and Conclusions 117 Part 5. OTHER TYPES OF IMPACT: NATURAL DISASTERS AND SCARCE RESOURCE PREEMPTION 119 I. Introduction 121 II. Natural Disasters Other Than Floods 123 A. Landslides and Subsidence 123 B. Earthquakes 124 C. Other Types of Disasters 124 III. Scarce Resource Preemption 127 A. Agricultural Land 127 B. Mineral Deposits 128 C. Unique Natural Features 128 Tables 1. Suggested Direct Measures of Development Impact on the Environment xii 1-1. A Summary of Human Health-Air Pollutant Relationships 10 1-2. National Ambient Air Quality Standards 11 1-3. A Summary of Air Pollution Effects on Vegetation, Materials, and Man (Aesthetic and Nuisance Concerns) 12 1-4. Comparison of Atmospheric Dispersion Models 37 1-5. Results of Model Evaluation Using S0 2 Data 39 1-6. Results of Model Evaluation Using Particulate Data 39 1- 7. Planning and Project Review Considerations for Each of the Major Air Pollutants 46 2- 1. Principal Water Pollutants and Water Quality Indicators 53 2-2. An Illustrative Format for Presenting the Effect of a Development on Risks from Flooding 60 2-3. Results of a Flood Frequency Analysis 62 2-4. Comparison of Techniques Used to Estimate Change in Stream Flow 66 2-5. An Illustrative Format for Presenting the Effects of Development on Water Use 70 2-6. Urban Runoff Quality Models (for Estimating Discharges from Nonpoint Sources) 73 2-7. Assessment of Water Quality Models 77 2-8. Levels of Analysis Applied to the Various Hydrologic Impact Areas 82 4-1. A Summary of Human Health and Nuisance Relationships to Environmental Noise .... 106 4-2. Recommendations of Sound Levels in Various Spaces 110 4-3. Tabular Presentation of Noise Impacts for a Hypothetical Development Ill 4-4. Approximate Noise Levels for Construction Equipment Ill 4-5. Comparison of Predicted and Actual Noise Levels at Selected Sites 115 4-6. Summary of Three Noise Estimation Techniques 115 Figures 1-1. Schematic Representation of the Gaussian Model 24 1-2. Summary of the Miller/Holzworth Model 28 vii 1-3. Summary of the Hanna/Gifford Model 29 1-4. Flow Diagram of the California Highway Model 32 1- 5. The Use of Frequency Distributions to Estimate Exposure Intensity and Duration 42 2- 1. The Hydrologic Cycle 55 2-2. Material and Energy Flows in an Aquatic Ecosystem 56 2-3. An Example of Hydrograph for a Hypothetical Watershed 63 2-4. Flow Chart of Computations for a Complex Hydrologic Model 64 2-5. Representations of the Extent and Depth of Flooding 68 2- 6. An Illustration of Saltwater Intrusion 80 3- 1. Example Formats for the Presentation of Estimated Impacts on Species Abundance and Diversity 93 3- 2. A Chart for Cataloging Baseline Data on Habitat Quantity 97 4- 1. Loudness Range of Common Sounds 107 4-2. Map Presentation of Noise Impacts for a Hypothetical Development 112 viii ACKNOWLEDGMENTS The research supporting the impact evaluation study of which this work is a part was sponsored by the Office of Policy Development and Research of the U.S. Department of Housing and Urban Development. The encouragement of Wyndham Clarke and Allen Siegel from this office and the specific suggestions of James Hoben, the HUD project manager, at various points in the overall study are greatly appreciated. The research was carried out under the general direction of Worth Bateman, Executive Director of The Urban Institute's Land Use Center. Philip Schaenman was the project manager. Their valuable insights, comments, and overall guidance are gratefully acknowledged. Kathleen Christensen of The Urban Institute and Harry Feldman of the Indianapolis Department of Parks and Recreation made substantive contributions to the report. Ms. Christensen provided valuable background material and text to the noise discussion, while Dr. Feldman wrote a paper on urbanization and wildlife/vegetation, parts of which were incorporated into the discussion of the same subject. The author is extremely appreciative of all who critiqued early drafts of this study and provided valuable suggestions: Roger Betson, Tennessee Valley Authority (Water Systems Development Branch); Eugene Darling, U.S. Department of Transportation (Transportation Systems Center); Aelred Geis, U.S. Fish and Wildlife Service; Donald Hey, Hydrocomp, Inc.; Michael McCarthy, University of Arizona (School of Renewable Natural Resources); Curt Miller, University of Michigan (Department of Landscape Architecture); J. A. Smedile, Northeast Illinois Planning Commission; Ethan Smith, U.S. Geological Survey (RALI Program); and Forest Stearns. University of Wisconsin-Milwaukee (Department of Botany). Members of the Advisory Group also assisted in reviewing early drafts. Staff members from the Department of Community Development in Indianapolis and the Maryland National Capital Park and Planning Commission in Montgomery County, Maryland, are acknowledged for their cooperation and the insights they provided into impact evaluation procedures used by local governments. The participation of the following individuals in a survey of air dispersion model users is also acknowledged: Steven Albersheim, NUS Corporation; W. Brian Crews, Oregon Department of Environmental Quality; Richard Hawthorne, Oregon Department of Environmental Quality; and Richard Thuillier, San Francisco Bay Area Air Pollution Control District. i\ ADVISORY GROUP TIMOTHY A. BARROW / Mayor, Phoenix, Arizona KURT W. BAUER / Executive Director, Southeast Wisconsin Regional Planning Commission, Waukesha, Wisconsin FRANK H. BEAL / Director for Research, American Society of Planning Officials, Chicago, Illinois MELVIN L. BERGHEIM / Councilman, Alexandria, Virginia, and National League of Cities-U.S. Conference of Mayors RICHARD F. COUNTS / Zoning Administrator, Planning De- partment, Phoenix. Arizona CARL D. GOSLINE / Director of General Planning, East Central Florida Regional Planning Council, Winter Park, Florida BERNARD D. GROSS / Planning Consultant, Washington, D C. HARRY P. HATRY / Director. State and Local Government Re- search Program. The Urban Institute, Washington. D C. TED KOLDERIE / Executive Director, Citizens League, Minne- apolis, Minnesota DENVER LINDLEY, JR. / Commissioner, Bucks County, Doyles- town, Pennsylvania JACK LINVILLE. JR. / Deputy Executive Director, American Institute of Planners. Washington. D C. ALAN H. MAGAZINE / Supervisor, Fairfax County Board. Fair- fax, Virginia, and Project Director, Contract Research Center, International City Management Association, Washington, D.C. ROBERT H. PASLAY / Planning Director. Planning Commission, Nashville. Tennessee RICHARD A. PERSICO / Executive Director. Adirondack Park Agency. Ray Brook. New York JAMES R. REID / Director. Office of Comprehensive Planning. Fairfax County, Virginia E. JACK SCHOOP / Chief Planner, California Coastal Zone Con- servation Commission, San Francisco, California DUANE L. SEARLES / Special Counsel on Growth and Environ- ment, National Association of Home Builders. Washington, D.C. PHILIP A. STEDFAST I Planning Director, Department of City Planning. Norfolk. Virginia DAVID L. T ALBOTT / Director of Planning, Falls Church, Virginia RICHARD E. TUSTIAN / Director of Planning. Maryland National Capital Parks and Planning Commission . Silver Spring. Maryland F. ROSS VOGELGESANG / Director, Division of Planning and Zoning, Indianapolis. Indiana THORNTON K. WARE / Planning Director, Rensselaer County, Troy, New York JOSEPH S. WHOLEY / Member, Arlington County Board, Arling- ton, Virginia, and Program Evaluation Studies Group. The Ur- ban Institute, Washington. D.C. FRANKLIN C. WOOD / Executive Director, Bucks County Plan- ning Commission, Doylestown, Pennsylvania X SUMMARY That land development may adversely affect the natural environment or, conversely, that the natural environment may pose problems for development is no longer in question. Attention has now turned to designing methods for mitigating these conflicts. The use of impact evaluation to detect ex- isting and potential problems is a valuable step in this process. This report discusses ways to estimate impacts associated with proposed development. Purpose and Scope The objective of this report is to provide information on (1) key issues and considerations in eval- uating the impacts associated with proposed development, and (2) the relative merits of alternative techniques for estimating impacts, in light of the costs, skills, and data required by each technique and the validity of the results, where information on these topics has been found. (Wherever a tech- nique was discovered to have been used by a local government or in a specific community, that fact is noted.) The report discusses development impacts on man associated with or operating through the nat- ural environment (air quality, water quality and quantity, noise, and scarce resource use preemption), impacts on the natural environment (wildlife and vegetation), and impacts from the natural environ- ment (flooding and other natural disasters). Simple manual estimation procedures as well as complex, computerized assessment techniques are examined for each impact category (except for scarce resources and disasters other than flooding) and for three types of development — residential, com- mercial, and industrial. The treatment of scarce resource use preemption and natural disasters other than flooding is considerably reduced in scope and detail in comparison with the other impact areas. This is largely due to the relatively primitive nature of impact estimation techniques in these areas and to the exis- tence of an extensive body of literature documenting what is currently known. Throughout the discussion, the emphasis is on quantification and estimation of end impacts on man, rather than intermediate effects. For example, information on the number of people exposed to new ambient concentrations of pollutants is preferred to simply knowing what the new concentrations will be. For each impact category, measures incorporating these concepts are suggested for use in as- sessing the impacts of proposed development. For certain impacts, however, the preferred measures are impractical, at least for routine use. Either the requisite analytical techniques are lacking, or the costs of data collection and analysis seem prohibitively high. For these cases, alternative or fallback measures are specified. These measures typically incorporate expressions of intermediate effects such as development output (e.g., emission levels) or they reflect qualitative assessments. Even where the preferred measures seem practical, alternatives are offered for those governments which may prefer a less detailed, albeit less satisfactory, approach. Table 1 lists preferred and fallback measures. Rarely will a single development require detailed assessment in all areas. Evaluators must deter- mine the type of impacts which are likely to be significant at the initial screening stage, perhaps em- ploying the '"target" planning approach suggested in the report and summarized below. Intended Audience The report is intended primarily for planners and other key local government staff members responsible for preparing impact evaluations. Elected officers and interested lay persons may also find selected sections of value, especially the introduction and summary sections for each of the five impact categories. Findings and Recommendations The state of the art of impact evaluation regarding the natural environment is very unevenly ad- vanced across the various impact categories. For some types of impact, fairly accurate and inexpen- sive techniques appear to be available for routine use. For others, the desired tools are only at the re- search and development stage or are still too expensive for most local governments. For still others, analytical methods necessary for quantified estimates of end impacts on man have not yet been developed. xi Table 1. SUGGESTED DIRECT MEASURES OF DEVELOPMENT IMPACT ON THE ENVIRONMENT IMPACT CATEGORY PREFERRED MEASURES FALLBACK MEASURES AIR QUALITY Health Change in the ambient concentration of each pol- lutant, the frequency of exposure, and the number of people at risk Change in the ambient concentration of each pollutant (relative to standards) Nuisance Change in the number and frequency of problems caused by smoke plumes, odors, and haze, and number of people affected Change in the likelihood that aesthetic/ nuisance problems will occur or change in severity WATER QUALITY AND QUANTITY Flooding Change in the number of people endangered by flooding and the expected property damage (or value of the property endangered) Change in flood frequency or severity Water pollution Change in the permissible or tolerable uses of the water in question and the number of people affected Change in the ambient concentration of each pollutant (relative to standards) Water consumption a. Change in the total duration and/or severity of expected shortages and the number of people affected b. Change in the concentrations of those drinking water constituents important to health and the number of people affected Change in the likelihood of a water short- age and the number of people affected WILDLIFE AND VEGETATION Change in the number of rare and endangered species: change in the population size and diversity of common species Change in the extent and quality of vege- tation and wildlife habitat NOISE Change in the level of noise, the frequency with which it occurs, and the number of people affected in the area surrounding the development OTHER NATURAL DISASTERS Change in the likelihood of the disaster and the number of people and the value of the property endangered SCARCE RESOURCE USE PREEMPTION The type and value of the scarce resource and the degree of preemption (such as farming, mining, and recreation) To some extent this unevenness reflects the importance that the federal government and, to a lesser extent, state governments have attached to the various types of impacts. Thus, flood prediction is much more advanced than the estimation of impacts on wildlife and vegetation. Recent air and water pollution legislation has spurred research in these areas, although affordable and accurate esti- mation techniques are available only for a limited number of situations. Noise legislation is likewise expected to improve the status of noise prediction models. Following are this report's specific findings and recommendations: 1. Quantitative estimates of end impacts on man appear to provide the most useful information to the decision maker. At the same time it is important to use recognized standards or other reference points in interpreting the quantified and often technically specified estimates in sev- eral of the impact categories. Local governments should consider using the measures suggested in this report (or similar ones) as part of their impact evaluation programs. 2. Comprehensive land use planning and the review of individual projects can and should be coordinated. Where a few large developments or many small ones have communitywide ef- fects, the impacts (ambient air and water quality, flooding) can be related to development out- xii put (emissions or effluents) or even to design characteristics (impervious ground cover) and targets or budgets established. Individual reviews in many cases may be reduced to com- paring the target with the output from or characteristic of the proposed development when added to the current levels. For example, the estimated emissions from a new development can be added to those from all existing developments in that part of the community for which an emission budget has been prepared. If the budget will not be exceeded even with the new development, then no further analysis of air quality impacts will probably be needed. We rec- ommend that communities consider incorporating targets or budget values of air emissions, water effluents, and impervious cover in their comprehensive plans. 3. Even though questions regarding the cost and validity of many techniques remain incom- pletely answered, several of the techniques reviewed seem superior to some of the currently popular rough approximation methods and are unquestionably better than purely qualitative or judgmental approaches. Following is a general appraisal of existing techniques for esti- . mating impacts (using the suggested measures) in each of the major categories. a. Air Quality — Air dispersion models applicable to a limited number of pollutants and types of development are available for health assessments, although the reported accuracies are quite low. Generally, the accuracy of the estimates increases as the models become more complex. For communitywide estimates of long-term average pollutant concentrations due to overall growth, relatively simple and, in some cases, manual techniques are available. Accuracy for a few of the latter is good. Nuisance impact evaluations do not require highly accurate estimates and thus are not difficult to make. b. Water Quality and Quantity — The estimation of impacts in this category frequently re- quires the use of more than one technique or model. Simple techniques for estimating flood frequency and volumes are available but tend to be unreliable. Complex models are presumably more accurate but also more expensive. Translating flood volumes into water levels requires a complex model of uncertain cost and accuracy. Water pollution impacts can be estimated fairly accurately for a very few pollutants and under limited conditions. Estimates of values for the preferred measure require the use of a complex model, and judgments (based on limited evidence) of the implications for water use. Some produce relatively accurate results; all are presumably expensive. Assessments of the supply aspects of water consumption are analogous to flood frequency and volume assessments for sur- face water. Only qualitative assessments are normally possible for underground sources. Water quality assessments are made with water pollution techniques. It should be noted that certain complex models can be used for combined assessments of flooding, water pol- lution, and water consumption (water quality); thus some economies of scale can be achieved. c. Wildlife and Vegetation — Although accurate baseline documentation of existing condi- tions is possible (although often expensive), techniques for producing quantitative esti- mates of impacts are not available. Instead, informal judgments of experts familiar with the local environment are usually necessary. d. Noise — At least one simple and accurate model is currently available for estimating noise levels. However, it is not reliable under all conditions. Another simple technique is also available but produces estimates of unknown accuracy. e. Other Natural Disasters and Scarce Resource Use Preemption — Although specific esti- mation techniques were not reviewed in detail, existing estimation procedures appear to provide only general approximations of the degree of risk from disasters or the value of certain scarce resources. 4. Data on costs, skill level requirements, and accuracy of the various techniques examined were extremely difficult to obtain in some cases and impossible in others. Few attempts at comparative testing and assessment of models have been made. Where the developers of individual techniques have undertaken validation studies the tests were often based on too few comparisons of estimated and observed values, and under conditions which were too similar, for validity to be established. In addition, different and frequently incomparable mea- sures of accuracy were sometimes used. We recommend that the federal government greatly xiii expand its limited testing program for impact estimation techniques. In the meantime, local governments should be cautious about accepting the results of unvalidated or poorly vali- dated models. 5. If some of the more complex computerized models are employed, the user should expect that initial start-up and calibration costs will be high, perhaps tens of thousands of dollars. Re- ' peated applications of the model for project reviews (or for planning purposes) should be much less expensive, typically hundreds of dollars for computing plus some additional data collection costs. Users will generally find three sources for computerized models: those of- fered by a consultant, those offered by the federal government together with some user as- sistance, and those available in the literature but without assistance and often poorly docu- mented. Regardless of the type selected, model users should seek to obtain data on costs of start-up, as well as continued use, from the model developer or others familiar with its appli- cation. Previous users are often the best sources for these data. 6. Where simpler techniques are used, costs may be reduced substantially. However, even though computerized techniques are not available for making estimates of impacts on wildlife and vegetation, estimates made by simple inferences will require relatively expensive field surveys (perhaps ten to twenty thousand dollars for a fifty-acre site) if the estimates are to be quantitative. More detailed findings and assessments of current analytical methods appear in the report itself. Tables comparing the various analytical techniques are found in the summary sections for each im- pact category. xiv GENERAL INTRODUCTION Impacts on, from, or operating through the nat- ural environment have long been a primary concern in land use decision making but have attracted vastly increased attention and concern in recent years. This report, one of a series on impact evaluation tech- niques published by The Urban Institute's Land Use Center, focuses on ways to estimate the impacts of residential, commercial, and industrial development. The intent is to provide urban planners and others concerned with evaluating the impacts of land devel- opment with basic information on the state of the art. However, this report should not be considered a man- ual or "cookbook" for evaluating impacts. In almost every case the referenced documents must be con- sulted for details of the data collection and analysis procedures. Likewise, a complete discussion of the relevant physical/biological processes which charac- terize the complex natural systems being assessed is not included. Instead, a brief, simplified overview of basic scientific principles related to each specific im- pact category is presented, followed by a discussion of impact measures and alternative data analysis pro- cedures. References to original sources and additional readings are also given. The objective is to provide information which can be used in designing and im- plementing an impact evaluation program and in as- sessing the analytical products being promoted by pri- vate consulting firms for evaluating environmental impacts. More specifically, the report should be of value in deciding: 1. Which impact categories to include in a planning and/or project evaluation program, 2. Which measures to use within the constraints of time and available funds, and 3. Which techniques to employ, based on their identified strengths and weaknesses. We have discussed in detail those impact areas for which several estimation techniques are currently available — air quality, water quality and quantity (in- cluding flood hazards), and noise. We have also des- cribed in some detail approaches to estimating im- pacts on wildlife and vegetation, even though specific analytical techniques for making estimates are not currently available. The relative unfamiliarity of most planners with wildlife and vegetation and the scarcity of relevant information justifies a more detailed dis- cussion here. We have discussed to a much lesser ex- tent the estimation of impacts on certain scarce resources such as prime farmland and from natural disasters in addition to floods. The more superficial treatment of these last two impact areas should not be interpreted to mean that they are unimportant. The existing analytical techniques in these areas are in a relatively primitive state of development and since what we do know about estimating these types of im- pacts is discussed quite well in the literature, the dis- cussion here serves to highlight general approaches to making impact estimates and to identify key refer- ences. The detailed treatment of estimation procedures in- cludes a discussion of general procedures as well as specific techniques. Where individual techniques or models are treated explicitly, those in the public do- main are emphasized. A few exceptions have been made, but only where the technique is extremely innovative or the model readily available at an at- tractive price. Although no attempt has been made to review every existing technique or model, the ones included are broadly representative of the field in each impact category. In analyzing the comparative strengths and weak- nesses of the available techniques, the focus is on inputs and outputs — what the techniques require (dollars, skills, and data) and what they produce (de- tail and accuracy of results). The question of accu- racy is extremely important. All too often numbers appear in impact evaluations with no indication of the range of error. 1 This is not to say that information on the accuracy of the various techniques is readily available. An extensive literature search, combined with a limited survey of both developers and users of identified techniques, has produced a base of infor- mation, but a base which is far from complete. Exten- sive validation of both simple and complex tech- niques is urgently needed. Data on the costs of using the various techniques were similarly difficult to find. In addition to its support of this project, the U.S. Department of Housing and Urban Development has sponsored a related and complementary study of pro- cedures for estimating impacts — Interim Guide For Environmental Assessment, HUD Field Office Edi- tion, prepared by Alan M. Voorhees Associates, Inc., et al., for the HUD Office of Policy Development and Research, Washington. D.C., June, 1975. The In- terim Guide was prepared primarily for use by HUD personnel reviewing the impacts of HUD-assisted projects; however, much of the information is appro- priate for use by local planners as well. The Interim Guide lays out a system for the initial screening of development impacts to determine if spe- cial in-depth evaluations of specific impacts are re- quired. Procedures are outlined for making initial judgments regarding the significance of potential ef- fects for each of 79 "environmental components."' The use of national standards and rules of thumb in the screening process are emphasized. This report. Land Development and the Natural Environment: Estimating Impacts, focuses on tech- niques which could be utilized in the detailed level analyses. The two reports thus tend to complement each other and the reader is encouraged to use both in designing and implementing an impact evaluation program. A. COMPREHENSIVE IMPACT EVALUATIONS— AN APPROACH The emotionalism which has accompanied the use of the term "impact evaluation" in environmental de- bates has led to the notion that the words represent 1. In this connection, two questions are relevant: what is the probability that the impact will occur; and if it does, how confident are we that the estimated magnitude is correct? an innovative idea in decision making. A closer exam- ination reveals that the term is fundamental to the very process of making decisions. Few would dis- agree that most, if not all, decisions are based on their likely outcomes, or impact. No decision to ap- prove a subdivision, grant a variance, or amend a zoning plan is made in a vacuum. Each is based on some analysis of the impact of making and imple- menting that decision. What is suggested here is a more comprehensive impact analysis procedure ap- plied systematically to land use decisions. Rather than introducing a new idea, we are suggesting the expansion of an old one. This is not to say that the suggestion is not some- what disturbing. The usual constraints of time, money, and knowledge, compounded by an intriguing web of vested interests, hidden agendas, and political pressures militate strongly against procedures which may increase costs, tax knowledge and abilities, or improve the visibility of public decision making. However, a more comprehensive and systematic im- pact evaluation procedure, painful as it may be in cer- tain situations, holds the potential for improving the allocation of a scarce resource — land. 1. Impacts on Man Further discussion of "the land use problem" and the rationale which underlies our suggested approach can be found in the overview volumes of this series. 2 The preliminary concept presented in those volumes is that the utility of impact evaluations would be in- creased if the impacts were specified in terms of end impact on man rather than in terms of intermediate effects. The fact that additional pollutants will appear in the air or water or that wildlife habitats will be destroyed are merely descriptions of changes, not im- pacts. It is only as these changes affect man physi- cally or psychologically (e.g., an increase in emphy- sema, prohibition of swimming at a local beach, the presence of foul-smelling air), that impacts become interpretable. It also seems likely that the utility of the analysis is increased if impacts can be quantified. Knowledge of changes in the number of people exposed to hazard- ous air or changes in the probability of flooding are preferable to knowing that conditions will "improve" or "deteriorate." Even a rough approximation of magnitude is better than none. The suggested impact measures presented reflect 2. Philip S. Schaenman and Thomas Muller, Measuring Impacts of Land Development: An Initial Approach (Washington, D.C.: The Urban Institute, 1974); Philip S. Schaenman, Using a Mea- surement System For Evaluating Land Development (Washington, D.C., The Urban Institute: forthcoming. 1976). Land Development and the Natural Environment this philosophy — they are designed to specify end im- pacts and are phrased in quantitative terms. Unfortu- nately, the state of the art is not yet advanced enough in each of the impact areas to justify the use of every "preferred" measure. Consequently, we have in- cluded alternative (fallback) measures as well. These, typically, are expressions of intermediate effects and/or are phrased in more qualitative terms. For ex- ample, the suggested fallback measure for air quality is "change in ambient concentration of each pollutant (relative to standards);" while that for wildlife and vegetation is "change in the amount and quality of wildlife habitat altered (quality rating by animal type)." Even where the preferred measure is techni- cally feasible, the time or resources available for data collection and analysis may necessitate use of the fall- back measure. 2. Comprehensiveness Let us turn for a moment to the issue of compre- hensiveness. The comprehensive master plan ap- proach has long been both a conceptual tenet and a source of consternation for professional planners. Since the world is composed of a highly intercon- nected set of elements, the best way to measure the impact of any perturbation is to embrace a holistic, systematic view of the world. Unfortunately, as the scope of analysis increases both the depth of treat- ment and the accuracy of the output tend to decrease, at least when resources for data collection and analy- sis are limited. In view of the difficulties inherent in a comprehen- sive approach, we advocate comprehensiveness only at the initial project screening level. This translates into a comprehensive checklist, the use of which would help assure that no significant type of impact would be ignored. A subset of important categories can then be investigated in greater depth. The amount of time and funds available for analysis will probably play as much a role in selecting this subset as the characteristics and setting of the development under consideration. 3. Impacted Populations ("Clientele Groups") It is often desirable to divide the population at risk (or to benefit) into several distinct but not necessarily mutually exclusive groups if the impacts will not be shared equally by all community residents. One pos- sible division is between residents or workers in the development to be evaluated and their counterparts in the surrounding community. We are primarily con- cerned with the latter group, since the greatest number and most severe impacts usually occur to the surrounding community. We believe that the factors most relevant to new residents or workers (e.g., building design, unit layout, site landscaping) are best assessed by the private market. Of course, some im- pacts affect the entire community by acting through new residents, and these have been included in our discussion. For example, to the extent that a develop- ment endangers new residents' health or safety, the public-at-large may be required to provide specific types of relief. An example of such a danger is the lo- cation of a development in a flood plain. The public cost can be measured in terms of monetary and in- kind subsidies to those persons in the development, if and when a flood occurs. 3 The "surrounding community" group can be fur- ther divided into localized (i.e., immediate vicinity) and nonlocalized (the rest of the community) sub- groups. This is an important differentiation for those impacts which tend to have corresponding spatial components. The impact of a regional shopping center on access roads, for example, is typically far different from its impact on the entire highway net- work of a city. Alternative disaggregations of the population can be made on the basis of special inter- ests, socio-economic characteristics, jurisdiction of residence, type of employment, and other attributes. 4 Disaggregating impacts by clientele group is often necessary to detect important impacts that may be masked if only community-wide effects are consid- ered. 4. Impact Categorization Impacts from land development can be grouped into several somewhat arbitrary and overlapping categories: Local Economy, Natural Environment, Aesthetics and Cultural Values, Public Services, and Social Conditions. Only the natural environment cat- egory is discussed in this report. 5 One danger in di- viding and compartmentalizing, however, is the tend- ency to ignore interrelationships among the parts. Some analysts, for example, may see a change in fiscal balance as a consideration unrelated to impacts on water quality, transportation effects, or changes in neighborhood attractiveness. This results in a false picture of reality. Deterioration of water quality or overcrowding of public roads may necessitate addi- tional expenditures of public funds for new treatment facilities or highways. The attractiveness of the neigh- 3. Consumer protection from unsafe construction is usually cov- ered by local health building and fire codes, although these are not universal nor always adequate. 4. See Schaenman and Muller, op. cit., Chap. IV, for further dis- cussion of clientele groups. 5. The others are dealt with in the companion reports in this series. General Introduction 3 borhood will be reflected in property values, which in turn will affect public revenues. In a system where everything tends, either directly or indirectly, to affect everything else, analysis can proceed only if most variables can be controlled while a few are manipulated, or if only a few variables are clearly dominant. Thus, fiscal impact analysis often assumes that a certain level of services will be main- tained and, tacitly, that a certain threshold of envi- ronmental damage will not be exceeded. The impacts of land development are then measured in terms of changes in public revenues and expenditures needed to maintain those threshold levels. Of course, as- sumed levels may be changed and another analysis performed. But the point is that expenditures and service/quality levels are not varied simultaneously. Likewise, impact assessments in the other areas usually assume constant expenditures and measure impact by changes in levels of services, environ- mental quality, and, in the case of social impacts, changes in community activities and perceptions. A second level of interrelatedness exists — that among impacts within the same category. For ex- ample, sulfur dioxide emitted into the atmosphere by a power plant may eventually become dissolved in nearby lakes and streams, producing dangerously acidic water conditions. These interrelations are dis- cussed within the individual impact categories. B. IMPLEMENTING IMPACT EVALUATION PROCEDURES— MAJOR ISSUES Beyond the technical questions of measurement procedures and analytical methods to which this report is addressed lie more fundamental issues con- cerning the philosophy and strategy of implementa- tion: (a) How can incremental decisions be coordi- nated with planning? (b) How can short-run outcomes be balanced against long-run concerns? (c) Is the only alternative to a specific proposed development no development? (d) Who should conduct the evalua- tions — specialists or generalists? 1. Comprehensive versus Incremental Reviews Urban planners will argue, rather persuasively, that evaluating the impact of individual projects is no sub- stitute for comprehensive planning. At best, individ- ual evaluations capture the incremental effects of one or possibly a few large developments. The combined effects of many developments over a period of sev- eral years are not easily seen when the incremental approach is used. Even if every project, large and small, were evaluated, individual developments tend to be mutually reinforcing and synergistic. Thus, ad- ditional levels of activity from older projects may be induced by new development. Although the focus here is on incrementally applied evaluations, we recognize the complementary need for comprehensive planning. In discussing the con- cerns associated with each impact category, we have attempted to identify and differentiate between those aspects of the evaluation which are more appropri- ately addressed by the development of comprehen- sive land use and zoning plans and those which are better treated through a project review process. For example, problems created by those air pollutants which have slow decay rates and are thus dispersed throughout the community may be more amenable to solution by setting limits on the number and location of pollution sources through large-scale analysis and the adoption of zoning plans than by individual pro- ject review. On the other hand, smoke and odor problems are typically localized in their impact and are best assessed and solved on an individual project basis. If generalizations can be made, perhaps the com- prehensive planning/project review dichotomy can be clarified by considering the extent to which impacts have a community-wide versus a localized origin or effect. Sewage effluent which is collected community- wide but treated and discharged at one geographical point, air pollutants with slow decay rates and uni- form dispersal patterns, and electricity generated at a single power plant for the entire community would af- fect community-wide pollution levels. These large- scale, long-term problems are usually best addressed by comprehensive planning. Impacts which are spe- cific to the spatial locations of development are more appropriately treated on a case-by-case basis. Of course, many developments generate impacts which are neither purely site-specific nor purely community- wide. Here, the interface between comprehensive planning and project review is much less clearly de- fined. And even where a comprehensive plan based on environmental considerations has been imple- mented, a more detailed incremental evaluation of proposed developments consonant with the plan may occasionally be desirable, at least as a check on the adequacy of the plan. 2. The "Spillover" Problem Jurisdictional boundaries typically do not coincide with other manmade or natural boundaries. This leads to "spillover" of pollution from one jurisdiction to another. Not only are air pollutants blown across boundaries, but mobile sources generated by a devel- opment in one jurisdiction may be driven consider- 4 Land Development and the Natural Environment able distances in surrounding communities as well. Thus, "spillover" refers to sources as well as to the pollutants themselves. Where the governmental unit in which the effects of pollution are experienced does not also control pol- lution sources, redress of grievances may not be sat- isfactorily achieved. In fact, it may clearly be to one jurisdiction's advantage to "export" its pollution while reaping the benefits of its pollution-generating activities, usually measured in terms of additional jobs and tax revenues. Control of regional "spillover" problems depends on both technical and institutional solutions. Large- scale models which simulate the movement of pol- lutants and chemical reactions in atmospheric or aquatic environments are needed to estimate the location and magnitude of regional-scale pollution problems. Once the problem has been identified and so- lutions in terms of source and/or land use controls proposed, regional bodies must be organized and em- powered to act. The federal government is now either assuming this role or mandating regional coopera- tion. 6 For communities where the problems are defined more in terms of individual shopping centers, planned unit developments, or industrial plants than in terms of large industrialized areas, state or federal media- tion is much less likely. For these situations we urge that project evaluations include the other affected communities as "clientele groups." This certainly does not insure resolution of the conflict, but it would serve to heighten the level of the debate and may help to reduce suspicion and mistrust. 3. Proposal Alternatives One of the most difficult tasks in preparing specific impact evaluations is to identify realistic alternatives to the project under review. Ideally, several propos- als for a single tract of land would be submitted simultaneously. Decision makers would then be able to select on a comparative basis. Typically, however, the only alternative is no development. No develop- ment is not synonymous with no effect, however. Care must be exercised to gauge the effects in all impact categories of diverting the demand for the proposed activity to other sites. The difficulties in attempting this, however, are enormous. Who can 6. An insightful, although sobering, examination of one area's approach to regionalizing the analysis and solution of environ- mental problems caused by urbanization is documented in B. A. Ackerman et al.. The Uncertain Search for Environmental Quality (Riverside, N.J.: The Free Press, 1974). predict with any degree of confidence where, for example, ten thousand new residents will choose to reside if the project being evaluated is rejected? Still, the reality of rejection must be described, if only in the most general and qualitative way. 4. Planning Department/Line Agency Interrelationships Comprehensive planning departments are usually charged with conducting evaluations of proposals for variances, rezonings, special zone adoptions, and other types of land use changes. Yet the technical ex- pertise required for a competently conducted impact evaluation may well reside in line agencies. The qual- ity of the evaluations produced is thus dependent on the extent to which this expertise can be marshaled and coordinated. The comprehensive planning staff should make a special effort to find out what tools exist (and their limitations) in the line agencies and to work with the agency staff in developing a checklist of measures and formats for expressing the results. 5. Applicable Federal, State, and Local Laws The development of local impact evaluation pro- grams occurs within the context of federal, state, and local laws which relate to and, at times, overlap with comprehensive evaluation requirements. Federal legislation now exists in the areas of air, water, and noise pollution. Although the thrust of this legislation is towards control at the source, the air and water laws also contain explicit language re- garding land use planning and evaluation. Other rel- evant areas for which federal legislation exists in- clude flood hazards and transportation, the former through the flood insurance program and the latter as a product of extensive federal support of highway programs. State activities related to land development typi- cally include granting permits for water and sewage treatment facilities (both community-wide and on- site), for activities which affect the level or location of surface waters, and for new sources of air emis- sions or water effluents. At the local level, government review activities em- phasize the application of building and subdivision codes. Some communities have broadened their ap- proach by adopting ordinances such as those re- quiring "adequate public facilities." This represents a major step toward comprehensive evaluation. Before any evaluation program is developed, a thorough inventory should be made of relevant legis- lation and activity at all levels of government. Simply adding one more layer to the already bewildering General Introduction 5 array of overlapping requirements which guide the developers' application process does little to advance orderly and efficient land development. Coordination is an overworked but pertinent word. In many cases the successful application for federal, state, or local development permits can substitute for the submis- sion of additional data. Where the scope of the permits is more limited, additional data will be neces- sary at the time of impact evaluation. C. NEEDED RESEARCH The results of the methodological review reported in this volume reveal that the state of the art of im- pact evaluation is unevenly advanced in the various impact categories. Predictive techniques are not available for estimating impacts on wildlife and vege- tation, as they are under certain conditions for air and water pollution. But even for the latter, additional vali- dation of available techniques is sorely needed. Ade- quate validation should be based on carefully per- formed (and usually expensive) retrospective studies of individual developments (such as the power plant impact study in progress at the University of Wiscon- sin 7 ), as well as less ambitious studies on the ability of a technique to estimate current conditions. Until such studies are made, progress toward developing improved techniques will be slow and the accuracy of many impact estimates will remain suspect. This is not to say that the use of any current impact esti- mation model is unjustified. Some produce results clearly superior to purely qualitative approaches or "quick and dirty" quantitative methods. But without better information on the accuracy of many of the more complex mathematical models, cost/benefit de- cisions on their use are most difficult to make. 7. D. E. Willard. Preliminary Documentation of Environmental Change Related to the Columbia Electric Power Generating Site, Working Paper II (Madison: Institute for Environmental Studies, University of Wisconsin, May, 1973). 6 Land Development and the Natural Environment PART 1 AIR QUALITY I. INTRODUCTION AND BACKGROUND The word "pollution 1 ' is tightly tied to the con- cept of impacts on humans. Only to the extent that emissions and resulting ambient concentrations of certain substances from either natural or manmade sources negatively affect the health or welfare of man are substances considered pollutants. 1 Thus, carbon dioxide (CO2) is not considered a pollutant while sul- phur dioxide (SO2) is, even though the former is gen- erated by natural processes and human activities and subsequently emitted to the atmosphere in much larger quantities than the latter. 2 A. HEALTH AND WELFARE EFFECTS The effects of air pollution on human health and welfare 3 can be categorized as follows: 1. Effects on health (morbidity and mortality). 2. Effect on other living organisms (which then im- pact upon man). 1. "Ambient" refers to the surrounding atmosphere to which man. plants, and other receptors are exposed. The ambient concentration of any pollutant depends on the quantity emitted and the degree of dispersal. 2. Carbon dioxide may yet prove to be a pollutant if the long- term effect of increasing concentration on a global scale is an in- crease in climatic temperature. This is a subject of considerable de- bate among meteorologists. 3. For further discussion of this subject, see Lester Lave and Eugene Seskin. "Air Pollution and Human Health." Science 69 (1970): 723-33; The National Academies of Sciences and Engineer- ing, Air Quality and Automobile Emission Control, vols. 2 and 4. Senate Committee on Public Works (Washington. D.C.: Govern- ment Printing Office. September. 1974); and George L. Waldbott. Health Effects of Environmental Pollutants (St. Louis: C. V. Mosby Co.. 1973). 3. Effects on materials (e.g., soiling and corro- sion). 4. Aesthetic and nuisance effects (e.g., odors and smoke plumes). 1. Human Health Effects Data that bear on the health effects of air pollution are obtained from laboratory studies of animals, clin- ical observation and limited human experimentation, studies in controlled, nonlaboratory settings (e.g., industrial plants), and epidemiological studies of large populations. The highly controlled environment of a laboratory is ideal for manipulating the level of a single pollutant while holding all other pollutants and environmental conditions constant. However, ani- mals must usually substitute for human subjects and only short-term (acute) effects can be measured. In addition, the possible exacerbation of existing disease conditions by air pollution is difficult to test in the laboratory. Epidemiological studies (at the other extreme) focus on the "real world" — ambient pollutant con- centrations and man in his normal setting. But even when correlations between health and exposure levels are found, it is often difficult to prove a causal rela- tionship. Urban activities may produce air pollution, but they may also create stressful situations which, in turn, cause an increase in morbidity and mortality. Thus, in spite of much effort, there remains consider- able uncertainty about the hazard actually presented by various suspect pollutants. Table 1-1 briefly summarizes current knowledge of 9 air pollutant health relationships, and the major development-related sources for each pollutant. These relationships are only probabilistic. It is known that exposure to high levels of S0 2 will cause ill health in some people. But for any individual the probability of becoming ill is influenced by present health, genetic susceptibility, duration and frequency of exposure, presence of other pollutants, and a host of other factors. Air quality standards based on cur- rent knowledge of health/air pollution relationships are listed in Table 1-2. The strongest case for unambiguous effects on health can probably be made for S0 2 and particulates, for which a statistical relationship between ambient concentration and mortality rate (aggregated on a na- tional basis) has been ascertained. 4 Evidence for the 4. Lave and Seskin. op. cit. Table 1-1. A SUMMARY OF HUMAN HEALTH-AIR POLLUTANT RELATIONSHIPS 3 SUSCEPTIBLE POLLUTANT MAJOR SOURCES HEALTH EFFECTS POPULATIONS COMMENTS Carbon Transportation, industrial Reacts with hemoglobin re- Persons with cardiovascular Past knowledge was based on study monoxide processes ducing mental attentiveness, disease and others of high exposure for short periods (CO) physical exertion, and ex- with healthy, young individuals. acerbating cardiovascular New data show possible health disease symptoms effects for susceptible persons at CO levels in the blood found in urban populations. Nitrogen Transportation, space heat- Interfere with respiratory Persons with respiratory or Conclusions are based on limited oxides (NO x ) ing/cooling, power functions producing long- cardiac disease, the young exposure of healthy adults to low generation term (chronic) disease and the elderly doses, extensive animal studies, symptoms and only limited data relevant to ambient conditions. Hydro- Transportation and indus- See photo-oxidants See photo-oxidants Indirectly polluting through the pro- carbons trial processes duction of photochemical oxidants (HC) upon reaction with NO and N0 2 in the presence of sunlight. Photo- See nitrogen oxides and Interfere with respiratory oxidants hydrocarbons functions and cause eye (Ox) irritations Persons with chronic respi- Ozone (0 3 ) is the most common ratory diseases, especially type and the key indicator for bronchial asthma photo-oxidants. Health effects are based on limited and inadequate data. Particulates 11 Power generation, space Interference with respiratory Persons with respiratory dis- The effects of particulates are diffi- heating/cooling. industrial functions, possible contribu- ease, the young and the cult to separate from those of processes, soil erosion tion to lung cancer elderly sulfur dioxide. Sulfur Power generation, space Little effect in the pure gas Persons with respiratory or Sulfur dioxide is readily converted oxides (SO x ) heating/cooling, industrial form: similar effects as par- cardiovascular disease, the to S0 3 and then to sulfuric acid (a processes ticulates when combined young and the elderly particulate). Determining which with them effects are due solely to S0 2 is difficult. Heavy Power generation, industrial Specific to each pollutant metals, processes radioactive agents, others Specific to each pollutant Pollution from these agents can be intense at the source, but tends not to be widespread. a. Information in this table is based primarily on the following references: National Academies of Sciences and Engineering, op. cit.. vol. 2: Health Effects of Air Pollution: Waldbott, op. cit.: J. D. Williams, et al.. Interstate Air Pollution Study. Phase II Project Report, VI. Effects of Air Pollution (Cincinnati, Ohio: Public Health Service, U.S. Department of Health. Education, and Welfare, December, 1966). b. Particulates, also known as aerosols, are either solids or fine liquid droplets which vary by size, shape, and composition. Sulfuric acid formed from S0 2 is one of the most biologically significant particulates. Some particulates such as dust can be rather innocuous considered alone, but become lethal transport agents when toxic gases are adsorbed to their surfaces. c. For a more complete discussion of other pollutants see. for example, Waldbott, op. cit. 10 Land Development and the Natural Environment Table 1-2. NATIONAL AMBIENT AIR QUALITY STANDARDS PRIMARY SECONDARY STANDARD STANDARD PERIOD OF POLLUTANT MEASUREMENT Mg/m 3 ppm /ag/m 3 l . Carbon monoxide (CO) 8 hours g 1 hour 40.000 35 Same Same 2. Hydrocarbons (HC) (nonmethane) 3 hours 160 0.24 Same Same 3. Nitrogen dioxides (NO^ Year 100 0.05 Same Same 4. Photochemical oxidants (O x ) 1 hour 160 0.08 Same Same 5. Sulfur oxides (SO x ) Year 80 0.03 None None 24 hours 365 0.14 None None 3 hours None None 1.300 ' 0.5 6. Total suspended particulates (TSP) Year 75 60 24 hours 260 150 SOURCE: Federal Register, Vol. 36. No. 84 (April 30, 1971). NOTES: Concentrations are averaged over each period of measurement. The annual TSP concentration is a geometric mean of 24-hour samples: all other concentrations are arithmetic mean values. Standards for periods of 24 hours or less may not be exceeded more than once per year. Units of measurement are micrograms per cubic meter (/zg/m 3 ) and parts per million (ppm). Primary standards are designed to protect human health. Secondary standards are designed to protect human welfare (i.e.. eliminate damage to vegetation and materials and aesthetic problems). other pollutants is highly suggestive. Extreme levels are known to cause illness and even death, but these levels are much higher than normal ambient concen- trations. The effects of long-term exposure to lower concentrations are still highly speculative. 2. Vegetation and Material Effects Table 1-3 summarizes the known or suspected im- pact of air pollution on vegetation, materials, and man in terms of aesthetic and nuisance concerns. Much of the data for vegetation and materials impact is based on laboratory or controlled field studies. As with health effects, sorting out causative agents and mechanisms of action is difficult. Vegetative damage can be mimicked, masked, or exacerbated by a vari- ety of factors, such as rainfall, plant disease, and sun- light. Impact on materials is likewise a complex phe- nomenon. Aesthetic and nuisance effects are more easily identified, although the seriousness of effect is open to considerable question. B. APPLICABLE STATE AND FEDERAL LAWS The federal government has assumed major respon- sibility for the maintenance of air quality in the United States. Pursuant to the 1970 amendments to the Clean Air Act, the Environmental Protection Agency (EPA) has promulgated both primary and secondary ambient air standards (Table 1-2) together with an elaborate list of policies, guidelines, and re- quirements for their implementation. The primary ambient air standards were established by identifying the lowest concentration for which health effects have been observed (usually in clinical situations among patients with respiratory or cardio- vascular illnesses) and then reducing this level by a "safety factor." The secondary standards were estab- lished using data on damage to plants, animals, and materials. State governments are required to designate geo- graphic areas which fail to meet the standards (air quality control regions) and to submit implementation plans for stationary source emission and transpor- tation management controls adequate to solve the problem by 1975-77. 5 These requirements were de- signed to satisfy the letter of the law, but two highly significant court decisions have greatly expanded EPA's role, thrusting the federal government fully into land use planning. The first decision resulted from a challenge to EPA by the Sierra Club (May 30, 1972) regarding EPA's practice of allowing the deterioration of air in rela- tively clean areas. As a result, no significant deteri- 5. More specifically, the control plans may include emission lim- itation, relocation of sources, economic (dis)incentives. changes in operating procedures and schedules of sources, motor vehicle emission control and inspection, limitations in motor vehicle use. expansion of mass transportation, and other unspecified land use and transportation measures. In addition. EPA will establish new- source emission standards for all stationary source categories deemed to endanger public health or welfare. Air Quality: Introduction and Background 1 1 Table 1-3. A SUMMARY OF AIR POLLUTION EFFECTS ON VEGETATION, MATERIALS AND MAN ' (AESTHETIC AND NUISANCE CONCERNS) POLLUTANT VEGETATION MATERIALS AESTHETICS/NUISANCES Carbon monoxide (CO) None None None Nitrogen oxides (NO,) Reduction in growth of plants with broad leaves (e.g., beans, tomatoes) Accelerated deterioration of dyes and paints Creation of a brownish coloring in urban air Photo-oxidants (Ox) Severe reduction in growth and even- tual death of leafy vegetables, field and forage crops, shrubs, fruit and forest trees caused by ozone and PAN b Ozone causes the cracking of rubber and the accelerated deterioration of nylon, rayon, dyes, and paints Ozone has a distinct although not terribly offensive odor Hydrocarbons (HC) None None None Particulates Reduction in plant growth by physical blockage of light when deposited on leaf surface Soiling of fabrics and buildings and corrosion of metals when combined with S0 2 Creation of smoke plumes, scattering of sunlight to produce haze and color- ful sunsets, and formation of hydro- scopic nuclei to produce fog Sulfur oxides (SO x ) Reduction in growth of plants with broad leaves Corrosion of iron metals, accelerated deterioration of building stone, cotton, paper, leather, paints and other finishes Scattering of sunlight to produce haze, production of unpleasant odors Others Floride causes long-term damage to selected field crops (and animals) Tarnishing of metals by hydrogen sulfide Hydrogen sulfide produces extremely unpleasant odors a. The information in this table is taken primarily from Public Health Service. The Effects of Air Pollution (Washington. D.C.: U.S. Department of Health, Education, and Welfare. 1967). b. Peroxyacylnitrate. an oxidation product of hydrocarbons. c. Other pollutants, such as hydrochloric acid and ammonia, are present in small quantities on a national basis and are not discussed. oration in these areas will be allowed in the future. 6 At issue now is the definition of "significant deteriora- tion." Although final regulations had not been pro- mulgated, EPA's expressed intention was to shift the definitional burden to the states. The draft regulations would allow the states to place planning areas (pre- sumably analogous to air quality control regions) into one of three categories, which range from "no deteri- oration allowed" to "deterioration allowed up to a large fraction of the national standards." Regardless of how literally "significant" is interpreted, it is clear that new development in atmospherically clean as well as degraded areas must be controlled in order to minimize air pollution. Thus, state and designated local governments will have to review land use plans as well as individual projects for their impact on air quality. The second court decision was a product of a chal- lenge to EPA-certified state implementation plans (January 1, 1973). The Natural Resources Defense Council, Inc., successfully asserted that the imple- mentation plans addressed only the issue of remedial actions to be taken in areas presently violating na- tional standards. The plans did not assure that air quality would be maintained once the standards were achieved. In response, the EPA is applying two new approaches. Indirect Source Review 7 and the devel- opment of Air Quality Maintenance Plans (AQMPs). 8 Under the first approach, states, or preferably local governments, must review all new developments (above certain thresholds) which threaten to cause new or exacerbate existing violations of the national standards by inducing transportation-related emis- sions. 9 These developments include parking facilities, shopping centers, airports, and sports arenas. Where such developments are estimated to cause the speci- fied deterioration in air quality, they are to be pro- hibited. The second approach requires states to designate areas which, due to projected growth rates, present threats to the continued maintenance of national stan- 6. The Court of Appeals for the District of Columbia reaffirmed a lower court's order and the Supreme Court could not reach a de- cision, thus allowing the original order to stand. 7. See Federal Register, vol. 39, no. 38 pp. 7269-92 (February 25, 1974). 8. See Federal Register, vol. 38. no. 116. pp. 15834-37 (June 18, 1973). 9. The thresholds are expressed in terms of number of cars. 12 Land Development and the Natural Environment dards. These areas are to be known as Air Quality Maintenance Areas (AQMAs). Once the nature and magnitude of the problems have been ascertained, air quality maintenance plans are to be developed speci- fying preventative measures. These are primarily land use and transportation control measures, including emission-density zoning and a requirement for envi- ronmental impact evaluations antecedent to and serving as a basis for decisions on requests for land use changes. 10 Aside from implementing various aspects of the Clean Air Act, states may, and in some cases have, specified standards and implementation programs more stringent than the federal ones (e.g., California). In every state and in many local communities, public agencies have been designated to implement and en- force federal and state air pollution laws. Some states, such as Florida, have also added air quality impact evaluation requirements to the review of cer- tain large-scale developments. 11 A few of the larger cities, such as New York, have also established region-specific standards and regulations. 12 C. EMISSIONS AND ATMOSPHERIC DISPERSION: FUNDAMENTAL PRINCIPLES 1. Emissions and Emission Sources 13 Virtually every substance now identified as a pollu- tant is produced to some extent by natural processes. These background levels are the product of oil and coal field leaks, volcanic eruptions, weathering of rock, biological production and decay, sea spray, forest fires, and a variety of other occurrences. In some situations background levels may be high enough to be a cause of concern. Typically, however, manmade emissions far exceed the natural ones. Man-related emission sources are numerous and varied. The general categories in Table 1-1 refer to the type of development-related activity which pro- duces the emission. Concentrating on physical as- pects of emission sources, most air pollution mete- orologists recognize three types of sources: point, 10. For further information on the designation of AQMAs see, Environmental Protection Agency, Guidelines for Air Quality Maintenance Planning and Analysis, vol. 1: Designation of Air Quality Maintenance Areas (Research Triangle Park, N.C.: EPA, September, 1974). 11. The Environmental Land and Water Management Act, Chapter 380, Florida Statutes, 1972. 12. See "Air Pollution Control News," The American City (August, 1972). 13. For additional information, see National Academies of Sci- ences and Engineering, op. cit. , vol. 3 and The California State Air Resources Board, Current Methodologies for Determining the Spa- tial Distribution of Air Polluting Emissions (Sacramento: CSARB, July, 1974) (NTIS No. PB-237864). area, and line. Point sources are those which are sta- tionary, can be readily identified and located, and usually are substantial contributors to total pollutant loads in the atmosphere. Power plant smokestacks are an obvious example. Area sources are either sources of considerable areal extent (e.g., a burning landfill site) or combinations of small, difficult-to- identify stationary or mobile sources averaged over an area (e.g., residential structures). Line sources are transportation corridors through which mobile sources pass and, over time, can be represented as a continuous source in the shape of a line. 2. Atmospheric Dispersion 14 The escape of noxious materials from point, area, and line sources is only the first stage in the develop- ment of air pollution problems. In the path from source to receptor (who or what is exposed to or "receives" the pollution), atmospheric gases and aerosols are driven by forces with disparate origins, magnitudes, and directions. The actual path that the materials take will largely determine their strength at the receptor and thus their effect on man. The forces which control atmospheric dispersion are the product of differential heating of the earth's surface by the sun and gravitational attraction between the earth and atmospheric constituents. These forces are most conveniently categorized by the scale of effect. Synoptic or large-scale forces pro- duce major weather events and affect large land and water areas, me so or medium-scale forces produce conditions which affect air quality for an entire com- munity (or subarea thereof), and micro or small-scale forces create localized conditions in the immediate vi- cinity of a source. The most dramatic impacts from development will normally be localized and thus con- trolled to a large extent by micro factors. However, cumulative effects and extreme conditions (i.e., those producing the hazards) are caused by factors at all three scales. a. Principal Factors Affecting Dispersion Ambient concentration of pollution at any point in space is largely dependent on the extent to which pol- lutants have mixed with surrounding "clean" vol- umes of air. This in turn is a function of wind speed (the greater the speed the faster the removal from the source and the greater the dilution) and mixing depth. The latter is an expression of the vertical distance from the ground to the inversion layer or area of 14. For more information, see Brian J. L. Berry et al., Land Use, Urban Form, and Environmental Quality, Research Paper No. 155 (Chicago: Department of Geography, University of Chi- cago, 1974). Air Quality: Introduction and Background 13 warmer air aloft and represents the volume of air available for pollutant dispersal. When inversions are located close to the ground (i.e., the depth is small), pollutants are trapped in relatively small volumes of air and ambient concentrations are consequently in- creased. 15 The average mixing depth and the potential for low-level inversion formation (and thus the poten- tial for dangerous pollutant build-ups) can be pre- dicted from historical records. Published data are available on mixing depths on a rather gross scale na- tionally. 16 More disaggregated information is also available, at least for the state of California. 17 Wind speed and direction are determined by forces at all three scales (i.e., synoptic, meso, and micro). More specifically, prevailing winds, storm systems, urban heat-island effects, 18 topographic features, and manmade structures combine to create net move- ments of air at any point in space. The "concrete canyons" created by rows of tall buildings produce special effects. Eddy currents concentrate internally generated pollutants, while the "canyon" walls retard flushing by crosswinds. b. Removal and Transformation Processes Once emitted and dispersed, the fate of atmo- spheric pollutants is an important but poorly under- stood story. Some pollutants, such as CO, S0 3 , nitrogen oxides to some extent, and particulates are removed by precipitation. Some particulates are also removed by gravitational settling, depending on their size. Some, such as NO, N0 2 , and hydrocarbons are either nonsoluble or participate in long-term chemical reactions, being transformed into nonsoluble gases in the process. These nonsoluble gases are presumed to 15. Inversions can occur when warmer air masses descend, when air near the ground cools more rapidly than that above, and. in effect, creates an inversion (as typically happens in urban areas at night), or when cooler air underflows warmer air (as typically happens in valleys at night). 16. George C. Holzworth. Mixing Heights. Wind Speeds, and Potential for Urban Air Pollution Throughout the Contiguous United States (Research Triangle Park, N.C.: EPA. January. 1972). 17. California State Air Resources Board. Meterological Param- eters for Estimating the Potential for Air Pollution in California (Sacramento: CSARB, July. 1974) (NTIS No. PB-237 869). 18. Urban areas are net producers of heat. This creates a "con- vection cell" whereby warm air in the city rises, moves out over the cooler countryside, cools, descends and returns to the city at ground level. This may produce a "recycling" of pollutants. "decay" by adsorption to solid surfaces, absorption by vegetation, or dilution by increasingly larger vol- umes of the atmosphere. 19 The transformation pro- cesses depend on pollutant concentrations, mete- orological conditions, topography, and ground cover. Tracing the fate of these pollutants is important not only from an air pollution perspective — they also af- fect water and "land" pollution. For example, pollu- tants such as S0 3 and N0 2 produce caustic acids when dissolved in water. Heavy metals, if deposited in surface water from the atmosphere, may present health hazards for many years. Radioactive materials present serious health problems regardless of their eventual place of deposition. 20 D. AIR QUALITY IMPACTS OF LAND DEVELOPMENT Air quality impacts resulting from land develop- ment differ by phase (site preparation, construction, occupancy) and type (residential, commercial, indus- trial). In addition, air quality impacts can be distin- guished on the basis of source location — on-site or off-site. For all types of developments the most significant impacts will normally be associated with the occu- pancy phase. Site preparation and construction tend to be relatively transitory activities and the resulting pollution (largely in the form of particulates) rather localized. 21 Consequently, attention will be focused on air quality impacts generated once the development has been occupied. For residential and commercial developments the emission of pollutants will be caused by on-site space heating, by off-site electrical power production, and by the generation of both on-site and off-site trans- portation. For industrial developments one additional source will be the manufacturing processes them- selves. The combustion of fuel, as well as the han- dling of gaseous materials, can lead to significant emissions. 19. Existing evidence indicates that vegetation plays a relatively minor role in removing gaseous pollutants, although it may be ef- fective in removing particulates. See George Hagevik. Daniel R. Mandelker, and Richard K. Brail, Air Quality Management and Land Use Planning (Washington, B.C.: Praeger Publishers, 1974). 20. Waldbott, op. cit. (see fn. 3). 21. However, for development occurring over extended periods of time in already developed areas, this may not be insignificant. 14 Land Development and the Natural Environment II. METHODOLOGICAL APPROACHES Central to the problem of estimating the impact of land development on air quality is the relationship between emissions and ambient concentrations. Most impact assessments, no matter how crude they may be, are based on the measurement or estimation of emissions with and without the development in ques- tion and a translation of this difference into the change in ambient concentration. Since this transla- tion is dependent on highly variable meteorological factors, the fidelity with which the translation tech- nique represents local meteorological conditions will largely determine the accuracy of the results. The general steps in calculating the impact of pro- posed land developments on air quality are as follows. 1 1. Measure/estimate current emissions. 2. Estimate future emissions. 3. Measure/estimate current ambient concentra- tions. 4. Estimate future ambient concentrations. 5. Measure/estimate exposure of man, vegetation, and materials. These steps are necessary in order to establish baseline conditions for comparison purposes and, for some techniques, to make future estimates. After a I. For retrospective analyses of existing developments, simply compare the emission levels and ambient concentrations before construction with those after it has been completed. discussion of impact measures and related topics, the remaining portion of this chapter will discuss avail- able techniques for each step. A. MEASURES, STANDARDS, AND INDICES 1. Measures and Standards Measures of air quality impacts should preferably reflect changes in (a) risk or damage to human health and possibly vegetation and materials, and (b) aes- thetic and nuisance problems. Following is a list of al- ternative measures, with the preferred one listed first in each category: Health 2 1. Change in the ambient concentration of each pollutant, the frequency of exposure, and the number of people at risk. OR 2. Change in the ambient concentrations of each pollutant (relative to standards). Aesthetic /Nu isa n ce 3. Change in the number and frequency of prob- 2. These measures could be expanded to include the exposure of vegetation (areal extent and vegetation type) and materials (amount and type) most likely to be severely affected. An alternative mea- sure is "new emissions as a percentage of the budgeted amount" meaning that a budget has been prepared for the entire community or the area in question. See Part 1. Ill, Section A for a more de- tailed discussion. 15 lems caused by smoke plumes, odors, haze, and the number of people affected. OR 4. Change in the likelihood that aesthetic/nuisance problems will occur or change in severity. Measures 1 and 3 are most directly related to the end impact on man and thus are the preferred mea- sures. Each is a quantitative assessment of changes in ambient pollutant concentrations, including likely new levels and their frequency of occurrence. In ad- dition, these measures suggest that a detailed estima- tion be made of who (or what) will be exposed to which levels and how often. Measures even more re- flective of the end impact on man could be specified. We could speak of changes in morbidity or mortality rates or changes in the monetary value of property damaged by air pollution. However, values for these measures could not be obtained for individual com- munities due to the present lack of knowledge regarding health and damage effects of air pollution. Measures 2 and 4 are much less desirable expres- sions of impact but may be more practical in certain situations. They are more general indications of changes in area-wide pollutant levels, relying on long- term concentration averages rather than the more de- tailed data needed for measures 1 and 3. These should thus be considered proxy measures. One important consideration in choosing between measures is the probable magnitude of the impact. If one or more new developments have the potential of significantly degrading air of currently acceptable quality (based on a cursory qualitative assessment), then a detailed and comprehensive analysis may be justified, unless the initial assessment clearly shows an unambiguous violation of a standard. Small devel- opments, or those located in relatively noncritical areas, on the other hand, probably do not warrant the expense of an elaborate evaluation. Data collection and analysis procedures appear to be available for all of the measures listed, although the accuracy of values generated remains an impor- tant and, in some cases, an unknown quantity. Issues related to the cost and accuracy of impact evaluations are discussed in the next section. The four measures are intended to be objective statements of impacts on the affected population. However, citizen perceptions of annoying or unpleas- ant air pollutants are needed to define reference stan- dards for interpreting the impacts, in addition to knowledge of pollutant concentration/aesthetic rela- tionships based on controlled condition experiments. Where detailed impact evaluations are not feasible, data on current citizen satisfaction with air quality may also be used to infer the general impact of future developments. The subject of measuring perceptions of air quality and other neighborhood attributes is dis- cussed in another report in this series. 3 Interpretation of values generated for the measures is usually made by reference to historical values or standards. In the case of the latter, federal standards are the most popular (and now mandated) reference point. Unfortunately, the relationships between pollu- tant concentration and health typically do not display threshold characteristics with a single value sep- arating completely safe levels from hazardous ones. 4 As mentioned earlier, hazard is best measured as a probability of deleterious effect which depends on current health, inherited susceptibility, length and fre- quency of exposure, the presence of other pollutants, and other factors. Thus, single standards for each pol- lutant, convenient as they may be to apply, do not adequately represent the physical and biological pro- cesses involved. The point is not that the federal stan- dards are invalid, but that they should be viewed as merely the best available knowledge on a complex and imperfectly understood subject. Local govern- ments may well decide to specify more stringent stan- dards as a protection against uncertainty. Once a set of standards or targets has been speci- fied, they can be used to interpret the results of the analysis. Since impact depends on both ambient con- centration and the frequency of occurrence, the stan- dards and the results could be expressed as the "total number of days (or, less adequately, the number of times) a certain concentration is reached." Impact can then be described as the "total number of days or the number of times the standard is exceeded (or closely approached)." 2. Indices For the purpose of comparing one development or plan with another it is sometimes desirable to express "air quality" by a single number. Several air quality indices have been developed to "sum up" or inte- grate the changes in concentration of the various pol- lutants. 5 These are typically root-sum-squares or summations of ratios between observed concentra- 3. K. Christensen, Social Impacts of Land Developments (Washington, D.C.: The Urban Institute, forthcoming). 4. For documentation of the nature of this relationship, see Na- tional Academies of Sciences and Engineering, op. cit., vols. 2 and 4. 5. For a discussion of several indices, see James W. Curlin, Na- tional Environmental Policy Act of 1969: Environmental In- dices — Status of Development, Pursuant to Section 102(2) (B) and 204 of the Act, Senate Committee on Interior and Insular Affairs (Washington, D.C.: December, 1973) and Berry et al., op. cit. 16 Land Development and the Natural Environment tions and the standards. 6 Indices can also be devel- oped to reflect the number of times the standard is exceeded within a specified period of time. However, indices have several inherent problems. The weighting schemes used are often arbitrary, and the numbers which result are difficult to interpret in terms of the severity of the problem. Although higher numbers for each of the various indices tend to indi- cate greater pollution, differences in scores between individual cities show wide variation, depending on the index used. 7 Also, those using an index may be unaware of the weighting. Another problem is that indices tend to blur distinc- tions among pollutants. The same numerical score can be obtained from a vast number of different com- binations of pollutants. Thus, low concentrations for several pollutants could overshadow a high concen- tration for one. We believe that expressing the results separately for each pollutant provides more usable in- formation for the decision maker. B. MEASUREMENT/ESTIMATION PROCEDURES In order to obtain values for these measures, a number of discrete data collection and analysis opera- tions are necessary. These operations were sum- marized in the introduction to this section and will now be discussed in detail. 1. Measuring/Estimating Current Emissions All dispersion models used to estimate the air qual- ity impact of development need values for the total level of emission — current levels plus those added by the proposed development. Consequently, accurate estimates of current emissions will improve the accu- racy of the projected impact. 6. The following are formulas for root-mean-square and linear summation indices, respectively: I = (a£ (CA)) b where I = index value, C = recorded concentration, S = standard, i = 1, 2, . . .n time periods (e.g., 8 hours, 24 hours) or, alternatively, pollutant,. pollutant 2 , . . .pollu- tant„. a and b = scaling factors chosen so that the numerical val- ues of the index fall within desired ranges (e.g., I = 1 for the situation where no standards are ex- ceeded). These can be used to weight the concentrations of one pollutant for different averaging times or the concentrations of different pollu- tants for a single averaging time. 7. See Berry et al.. op. cit. The acquisition and assemblage of current data on point, area, and line source emissions are formidable and costly tasks. Even with a substantial investment of time and money, the results are often less than sat- isfactory, or worse yet, are inaccurate to an unknown degree. However, since an inventory of current emis- sions is a prerequisite for air quality impact evalua- tions at any scale, the expenditure of the necessary funds to make estimates of emissions is probably jus- tified. 8 For most large metropolitan areas it is re- quired under the Clean Air Act. Both the EPA and, to a lesser extent, the U.S. De- partment of Transportation (DOT) have been active in developing guidelines, analytical procedures, and mathematical models for use in preparing emission inventories. 9 Rather than repeating what is covered in these reports and others they reference, only the gen- eral approaches will be described. a. Point Sources The most accurate method of ascertaining the type and quantity of emissions from a point source is to place a monitoring device in the effluent stream. However, the cost of applying this approach to every smokestack of every industrial firm and power plant in a metropolitan area is usually prohibitive. At a minimum, instrumentation can provide an accurate test for other less direct approaches. A second, more practical approach is based on the quantity and type of fuel consumed or raw materi- als used. When multiplied by emission factors (pollu- tants per unit of activity) 10 , these indicators will pro- vide estimates of aggregate emissions. If information on the timing of emissions is desired, however, schedules of operation must be obtained. Data on fuel and raw materials can be collected from surveys of each point source (or a sample of sources if many are similar). If this level of detail is not available, records of local fuel and raw material distributions can be probed. Failing this, statewide 8. The EPA estimates that approximately three man-years are required to inventory current emissions in a city the size of Wash- ington. D.C. (personal communication with a member of the Con- trol Programs Development Division). 9. See the EPA, Guide for Compiling a Comprehensive Emis- sion Inventory (Research Triangle Park, N.C.: EPA, June, 1972); EPA, Compilation of Air Pollution Emission Factors (Research Triangle Park, N.C.: EPA, April, 1974); Federal Highway Adminis- tration, Urban Transportation Planning and Air Quality, Highway Planning Technical Report No. 33, and Federal Highway Adminis- tration, Special Area Analysis (Washington, D.C: Department of Transportation, August, 1973). 10. The emission factors relate the quantity of pollutants emitted to levels of polluting activity (e.g., x pounds of S0 2 per y tons of coal) and are specific to the type of emission control device (if any) in use at individual sources. Air Quality: Methodological Approaches 17 data on fuel and raw material consumption (collected by such organizations as the U.S. Bureau of Mines or state pollution control agencies) can be allocated to a local community, based on the community's state- wide share of the polluting activity. Likewise, community-wide data can be appor- tioned to subareas using the same concept. It is clear, however, that these approaches are several times re- moved from the physical measurement of emission levels; and with the loss in specificity comes a con- comitant loss in accuracy. 11 The measurement of smoke plumes presents a slightly different problem. The most common param- eter measured is opacity, and the most frequently used measuring device is the Ringelmann Smoke Chart. 12 b. Stationary Area Sources Most area sources are groups of point sources which are too small to investigate individually. Sec- ondary sources of information are then typically used. For residential area sources, local fuel distribu- tors can be consulted to obtain information on the amount and mix of fuels used for space heating. A characteristic emission factor for each fuel is then ap- plied to obtain total emissions. Depending on the ultimate utilization of the inven- tory, spatial disaggregation may be desirable. Alloca- tion methods similar to those mentioned for point sources are appropriate here as well. Alternatively, small point sources (e.g.. individual homes) in dif- ferent areas of the community can be sampled and heating bills used to obtain information on fuel con- sumption. Total consumption for each area is then calculated by multiplying the average unit consump- tion by the number of units in that area. If changes over time (e.g.. seasonal variations) are to be considered, additional analysis by type of area source is necessary. For example, the average number of degree-days 13 by season will provide an in- dication of daily residential fuel consumption over the year. Estimates for large area sources, such as fuel depots (evaporative losses), landfills (trash burning), 11. If data on fuel and raw material consumption are to be used on a scale larger than individual sources, then the utilization of emission control devices must also be aggregated and averaged — another possible source of error. 12. R. Kudlich. (rev. by C. R. Burdick). Ringelmann Smoke Chan, Information Circular 7718 (Washington, D.C.: Department of the Interior, Bureau of Mines, August. 1955). 13. "Degree-days" is an expression of heating load and is nu- merically equivalent to the outside temperature expressed as the average number of degrees below a threshold temperature for a given day. The threshold is that temperature which, when reached, will require some indoor heating (usually 65°F.). building fires, and construction sites (dust) are ob- tained as detailed in the previously cited EPA reports (see page 17). c. Mobile Area or Line Sources A moving source of emissions is conveniently de- picted as a line source. However, most emission inventories and most dispersion models treat line sources as area sources by aggregating and then uni- formly distributing the line sources throughout the areal unit of analysis. The data base for estimating emissions from line sources is usually much richer than that for point or area sources. Most medium to large size communities have transportation departments which maintain de- tailed data on street capacities, traffic volumes, and sometimes vehicle mixes (both by type and age). This allows calculation of vehicle miles of travel at various speeds at various times of day. Knowing in addition the average mix (light duty and heavy duty) and the age distribution of vehicles allows calculation of the level of emissions. The analytical procedures are de- tailed in the EPA and DOT publications previously cited (see page 17). Again, if this level of detail is not available or appropriate, indirect data can be used. These include data on total gasoline sales for the community (obtainable from state tax departments) and on motor vehicle registrations (obtainable from state motor ve- hicle departments). It must be remembered that increasing aggregate data usually means decreasing accuracy when these data are disaggregated and allo- cated to individual communities. d. Estimation Problems Potential sources of error in an emission inventory are obviously numerous. If every source could be physically monitored, then only instrumentation errors would be present. Unfortunately, except for a few large point sources, this is not practical for most local governments today. Once secondary and ter- tiary sources of data are used, four possible error types multiply rapidly: 1. Errors in collecting and recording the secondary/tertiary data. 2. Inherent errors in using surrogate data (e.g., how accurately do gasoline sales reflect vehicu- lar emissions?). 3. Inherent errors in using aggregate data (e.g.. how accurately can statewide data on fuel con- sumption be allocated to local communities?). 4. Errors in ascertaining the effectiveness of pollu- tion control equipment. 1 8 Land Development and the Natural Environment Information on the first type of error is typically nonexistent. The second type of error relates to the use of emission factors and other coefficients which relate tertiary indicators (e.g., gasoline consumption) to secondary data (e.g., vehicle miles). EPA has em- ployed a combination of approaches in deriving its emission factors for various pollutant-generating activities, from detailed source testing to engineering appraisals. 14 Consequently, individual factors vary in accuracy as reflected by qualitative rankings attached to each factor. These rankings are undoubtedly useful for judging the relative believability of the results but cannot be used to specify confidence intervals or other quantitative measures of accuracy. How believ- able is "believable" remains an unanswered ques- tion. The situation for coefficients other than emis- sion factors is even worse. Typically, average values for relationships between tertiary and secondary vari- ables are used with no indication of how local condi- tions may vary from the mean. Errors of the third type are likewise extremely diffi- cult to gauge. In selecting a method for allocating shares of aggregated data, data availability and common sense become the yardsticks. Determining the efficiency of pollution control equipment (the fourth type of error) is affected by many factors, including meteorological conditions, maintenance practices, age of the equipment, and the mix of pollutants in the effluent stream. Errors which result from these factors are difficult at the present time to ascertain, due to a lack of data. Presumably, as experience with pollution control equipment in- creases, knowledge about the relative magnitude of these effects will improve. Presently, however, we can do little more than acknowledge the existence of these potential errors. In any one situation the aforementioned errors will obviously not be of equal importance. Some a priori knowledge about local conditions should be brought to bear when the inventory procedure is designed. Where the major problem is associated with point sources, a greater investment of resources to inven- tory these sources would be appropriate. Where motor vehicles are the primary agents, additional funds for obtaining transportation data would be justi- fied. If major problems occur during rush hours, accurate data on the time distribution of traffic vol- umes would prove useful. In this way some of the problems associated with uncertainty in the data can be reduced. In a similar vein the ultimate use of the data will influence the relative emphasis placed on different 14. EPA. Compilation of Air Pollution Emission Factors, 2d ed (Research Triangle Park, N.C.: EPA. April. 1973). types of data collection. If the inventory is to be used for comparison with future emission levels, data of a fairly aggregated nature can be used. On the other hand, estimating the effects of single developments requires data on spatially differentiated emission sources. 2. Estimating Future Emissions Much of what has already been said about current emission inventories applies equally well to estima- tions of future emissions. a. Aggregate or Large Area Analysis It is often useful to consider the effects of individ- ual developments along with those from growth in general (much of which may not require rezoning or similar changes from the existing plan and thus could not normally be prevented). For large developments with long construction times, impacts can be esti- mated only by adding the emissions to those from all other relevant developments at the point of ultimate occupancy. Techniques for estimating overall increases in emissions are detailed in at least two EPA publica- tions and will be briefly summarized here. 15 First, emissions from existing sources are modified to re- flect future mandated reductions, if appropriate. 16 Second, growth factors for the various categories of point and stationary area sources are derived from the land use plan being evaluated and/or current growth rates of suitable surrogates (i.e., population, total earnings, and manufacturing earnings). These growth factors, modified by applicable new source emission standards promulgated by EPA, are then ap- plied to the current level of activity within each cate- gory to obtain emissions in the desired future year. Mobile area sources can be projected in a similar manner, except that the effects of EPA-mandated source controls for new vehicles must also be taken into account. 17 Power plants, due to their importance as emission sources, are projected separately, using data obtained from individual companies. Jb. Small Area Analysis Large area analysis may be adequate on a "first look" basis, but it does not allow the assessment of 15. EPA, Guidelines for Air Quality Maintenance Planning and Analysis, vol. 1: op. cit., and ibid., vol. 7: Projecting County Emis- sions. 16. The state implementation plans for AQCRs specify planned reductions necessary to achieve the national ambient standards by 1975-77. 17. The total effect is the combination of increasingly effective controls and the attrition of older vehicles over time. EPA- mandated controls utilized after 1968 also affect the level of current emissions. Air Quality: Methodological Approaches 19 air quality impacts caused by alternative spatial distri- butions of future development within the community. The projection of future emissions for each subarea can be based on (a) distribution of aggregate growth, or (b) estimation of growth for each individual sub- area. The basis for distributing growth (and also for sub- area delineation) can be as simple as reference to a comprehensive plan. Aggregate growth is assumed to be channeled to those areas which by designation can receive it. This approach, together with variations on the theme, was investigated by the Argonne National Laboratory as part of a general air pollution study of Chicago. 18 Since a comprehensive plan is but a rough approximation of the future, analysts have relied on simulation modeling techniques for more reasonable approximations. 19 These are based on the theoretical behavior of firms and households, observed develop- ment patterns for the test community over a period of time or in analogous communities, or a combination of the two. 20 c. Individual Development Analysis Project plans for major point sources (e.g.. power plants and factories) are usually sufficiently specific so that the techniques outlined for estimating current emissions can be applied. That is, emissions are esti- mated from the manufacturing processes to be used. In fact, new point source emissions are strictly regu- lated by state and local pollution control agencies as mandated by EPA. For proposed residential and commercial develop- ment, the primary effects are power plant and transportation-induced emissions. Procedures for es- timating electrical energy demands of new develop- ments are outlined in another report in this series. 21 These new demands must be translated into addi- tional fuel consumption and then into increased emis- 18. Allen S. Kennedy et al.. Air Pollution — Land Use Planning Project Phase I. Final Report (Argonne. 111.: Argonne National Laboratory. November, 1971). 19. The flexibility of community zoning plans is rather no- torious. Perhaps they can be more appropriately thought of as but one constraint on the pattern of future development. 20. An overview and critique of land use models can be found in Ira Lowry, "Seven Models of Urban Development: A Structural Comparison.'* in Urban Development Models. Highway Research Board. Report No. 97, 1967; William Goldner. " The Lowry Model Heritage.'' Journal of the American Institute of Planners (March. 1972): 100-09; and California State Air Resources Board, Air Qual- ity, Land Use, and Transportation Models (Sacramento: CSARB. July 1974). 21. See the "Energy Services" chapter in: Philip S. Schaenman. Dale L. Keyes. and Kathleen Christensen, Estimating Impacts of Land Development on Public Senices (Washington. D.C.: The Urban Institute, forthcoming). sions. However, this is a question that must be ad- dressed at the regional level. Increased power plant capacities are planned to match regional growth rates, and the impact of expanding capacity is a product of plant location, fuel type and composition, and the de- gree to which new capacities are created by bor- rowing from neighboring electric power grids. Indi- vidual power companies should be consulted on their future plans and the impact of individual develop- ments estimated in the context of projected regional growth. The inducement of transportation-generated emis- sions by new development is usually a much more im- portant consideration for individual projects. The ef- fects on air quality are frequently localized and thus project-specific. The following component parts of the problem can be specified: (1) Number of trips generated (per day). (2) Modal split (i.e., the choice of mode for each trip). (3) Time distribution of trips (hourly). (4) Spatial distribution of trips. (5) Average speed of vehicles on each link or for each zone. (6) Vehicle emission rates. In support of the new indirect source regulations pro- mulgated by EPA, a series of documents has been prepared specifying approaches to estimating the im- pact of indirect (i.e., vehicle-generating) sources. 22 As a basis for these estimations the manuals provide in- formation from which calculations for most of the above data can be made. However, only traffic pat- terns in the immediate vicinity of the facility are con- sidered. In addition, residential developments are ex- cluded. The chapter on transportation in the public and pri- vate service report 23 explicitly treats the issues not covered by the EPA indirect source documents. Methods for estimating trips generated by residential developments and trip distributions for various types of land developments are outlined. The spatial distri- bution of trips is perhaps the most difficult aspect of 22. Scott D. Thayer. Kenneth Axetell. Jr.. and Jonathan Cook, Vehicle Behavior In and Around Complex Sources and Related Complex Source Characteristics, vols. I-VI (Shopping Centers. Airports, Sports Stadiums. Parking Facilities. Amusement Parks. Major Highways. Recreational Areas) (Research Triangle Park, N.C.: EPA, Office of Air and Water Program, Office of Air Quality Planning and Standards, August-November. 1973). See also Kevin G. Croke, et. al.. The Relationship of Automobile Pollutants and Commercial Development. (Argonne, III.: Argonne National Labo- ratory, 1975). 23. Schaenman, Keyes, and Christensen, op. cit. 20 Land Development and the Natural Environment these calculations. It requires detailed information about the future inhabitants and the origins and desti- nations of their trips. In addition, rather complex sim- ulation models are required to assign these trips to links in the highway network. Fortunately, only the largest 24 developments will impact significant portions of the entire network. Once the number of new trips has been estimated and distributed, emission levels can be projected using the EPA emission factors and knowledge of ve- hicle age, speeds, and volumes on specific highway links. 25 d. Estimation Problems Although the uncertainty in predictions may be high (and in many cases is itself unknown), consid- ering an extension of past trends and/or other plau- sible futures is useful for estimating future air quality. However, if growth projections are to be used as any- thing more than qualitative descriptions they should be generalized spatially and cover a limited interval of time, perhaps no more than ten years. However, the primary focus of this report is on individual developments and short-time horizons. Even here, though, considerable uncertainty exists regarding the factors which will determine ultimate impact — vehicle miles of travel induced and energy requirements — which, in turn, are related to a host of other factors, such as population density, character- istics of new residents/customers/employees, and building construction features. But even where un- certainty exists, a range of estimates can be consid- ered — the lowest, average, and highest value at each step in the calculation procedure (if these values are known). The final estimate can then be expressed in the same terms (lowest, average, highest) even though the probability of obtaining these values cannot be specified. In other words, the sensitivity of the estimates to the assumptions can be stated. 26 The concern about data precision, valid as it may be, must be conditioned by the ultimate use of the study results. Great accuracy is not needed to predict trends or make initial assessments, especially when initial assessments show that conditions will be far 24. "Large" is a relative term. The size of the development (in terms of the number of trips generated) must be compared with the size of the surrounding community. 25. EPA. Compilation of Air Pollution Emission Factors (Re- search Triangle Park. N.C.: EPA. Office of Air and Water Pro- grams, Office of Air Quality Planning Standard. April, 1973) (Re- port No. AP-42). 26. For a good discussion of the way errors propagate through multistep calculations, with illustration for air quality assessment, see Hagevik. Mandelker. and Brail, op. cit. below or above preselected standards or targets. On the other hand, if future emissions will produce am- bient concentrations approaching threshold levels, then more accuracy may be needed. 3. Measuring/Estimating Current Ambient Concentrations Although data on emissions constitute a valuable and necessary base of information, ambient pollutant levels must be measured in order to assess the impact of the new emissions. The measurement of ambient concentrations remains a difficult and costly activity, despite continued federal involvement and financial support. 27 a. Quantitative Measurement Pollutants in the atmosphere show variations in both time and space. This has important implications for the design and operation of an air monitoring net- work. The number and placement of stations and the frequency of recordings must be planned to capture the concentration variations. EPA's recommen- dations are a compromise between scientifically based design criteria and the problems of the real world. 28 Recognizing that the costs of an ideal system are prohibitive, the EPA guidelines emphasize place- ment of the sampling stations where the potential for pollution problems is the highest. The "hot spot" cri- teria include such factors as population distribution, suspected ambient levels, location of sources, and areas of future growth. Other practical considerations are presence of power supplies and security from vandalism. Thus, the number and actual location of stations may be far from ideal. The Clean Air Act defines ambient air as "that por- tion of the atmosphere external to buildings to which the general public has access." Thus, measurements of air quality should logically be made at a height of five to six feet. EPA suggests a height of three to six meters (approximately ten to twenty feet), while actual locations are often at roof level. The literature on monitoring instrumentation is well developed and will not be reviewed here. 29 Worthy of 27. EPA estimates that approximately ten man-years of effort are required annually to maintain a monitoring network the size of the one found in Washington. D.C. (personal communication with a member of the Contract Programs Development Division). 28. R. A. McCormick. Air Pollution Measurements (Research Triangle Park, N.C.: EPA, National Environmental Research Center, February, 1972) (NTIS No. Com-73-10016); and EPA, Guidelines: Air Quality Sun eillance Networks (Research Triangle Park. N.C.: EPA, Office of Air Programs, May. 1971) (Publication No. AP-98). 29. For a summary of available methods and techniques, see Na- tional Academies of Sciences and Engineering, op. cit.. vol. 3. Air Quality: Methodological Approaches 21 note, however, is research on measuring ambient concentrations using airborne sensors. Advances in these techniques may significantly improve the accu- racy of the measurements. 30 b. Measurement Problems Despite the existence of more than 7,000 federal, state, and locally operated monitoring stations throughout the country, 31 knowledge of ambient con- ditions remains rather primitive. Even if all the sta- tions recorded each of the major pollutants, there are simply too few stations to reflect geographical varia- tions adequately. With the possible exception of Chi- cago and New York, the number of stations for any one city is insufficient to allow satisfactory interpola- tion between stations and the construction of iso- pleths (lines of equal concentration). Thus, diffusion models will be needed in most communities to ob- tain isopleths of current ambient concentrations or to obtain estimates for areas within the community which are not located near monitors. (Diffusion models are discussed in the next section.) Aside from problems of location, there remains a serious concern regarding data reliability. Variations in station operation and maintenance, combined with poor quality control procedures, especially for sta- tions requiring manual chemical analysis, has ren- dered the data recorded for many cities of question- able accuracy. The inappropriate height of many stations further hampers meaningful interpreta- tion. 32 There is also some evidence that the EPA- recommended sampling frequency is too low for the desired degree of certainty in the results. 33 Compared with the other problems, however, this seems to be of lesser importance. What then can be said about the concentration of pollutants in the atmosphere? Certainly the data from even a single station are useful, not as a definitive statement about air quality for a city, but at least as an indicator of a potential or general problem. Con- 30. L. J. Duncan. E. J. Friedman. E. L. Keitz, and E. A. Ward. An Airborne Remote Sensing System for Urban Air Quality (Wash- ington. DC: The Mitre Corporation. February. 1974). 31. EPA, Inventory of Air Pollution Monitoring Equipment Operated by State and Local Agencies (Research Triangle Park. N.C.: Air Pollution Technical Information Center. 1971). 32. Even New York has recently recognized the inadequacy of its network. Forty-five new CO monitoring stations placed at a height of five to eight feet above street level will be added to the sixteen presently in operation. See Richard Severo, "City to Aug- ment Monoxide Gauges," New York Times, 20 April 1975, p. 42. 33. Harold E. Neustadter and Steven M. Sidik. On Evaluating Compliance with Air Pollution Not to be Exceeded More Than Once Per Year (Cleveland: Lewis Research Center, June. 1974) (NASA No. N74-25879). versely, if ambient concentrations at a single station at a "hot spot" during the worst meteorological con- ditions are satisfactory, then probably no part of the city faces a serious problem. These data may also be useful in answering questions regarding planning at a community-wide level. (E.g., is any additional devel- opment within city limits feasible?) But for other as- sessments there is no substitute for accurate data on the variable conditions found in different parts of the community, which must be obtained from properly located, well-maintained, and competently operated stations. Diffusion models can be used, but their vali- dation depends on the existence of a good profile of current conditions. A series of simple procedures for calculating the current ambient levels in localized areas (i.e., several blocks) using simple mathematical relationships is outlined in a recent HUD-sponsored report. 34 c. Vegetative Indicators For many communities the quantitative monitoring of ambient air quality is simply too expensive, while for others one or a few sampling points must suffice. In order to obtain an objective, albeit very qualitative "sense" of community-wide or subarea air quality, strategically placed vegetative test plots may offer one alternative. Although plant damage from air pol- lution remains a poorly understood phenomenon, carefully controlled field studies continue to provide information by which various plant species can be rated for sensitivity. 35 Local governments interested in utilizing plants as pollution indicators should con- tact state air pollution agencies for additional infor- mation and assistance. 4. Estimating Future Ambient Concentrations The next step in the analytical procedure involves the estimation of future ambient concentrations for each of the various pollutants. In a sense, this is the culmination of all preceding calculations. Data on current and future emissions and current ambient levels are combined with meteorological and surface feature inputs to produce the net change in future am- bient levels. The analysis can be performed at varying levels of sophistication and complexity. Manual tech- niques as well as those requiring computer support are available. The various techniques for estimating future am- 34. T. M. Briggs, Air Pollution Considerations in Residential Planning, vol. I: Manual (Cincinnati: PEDCO-Environmental Spe- cialists, Inc.. July, 1974). 35. See Atle Habjorg, Air Pollution and Vegetation II (Research Triangle Park. N.C.: EPA. June. 1974) (NTIS No. PB-237-880-T). 22 Land Development and the Natural Environment bient concentrations will be discussed both generally and specifically. The material to be presented is partly a synthesis and recombination of information and ideas contained in other overviews. 36 However, only the Darling report contains specific information on the cost and accuracy of individual dispersion models. 37 The information presented here is designed to supplement the Darling report. The emphasis is on models which have wide geographic applicability and which are used routinely by planning or pollution control agencies. a. Types of Models There are many ways to differentiate approaches to estimating the transport and dispersion of atmo- spheric pollutants. The various typologies described below highlight different yet important aspects of dis- persion models. Theoretical versus Empirical Models — "Theoret- ical" models are those which are grounded on basic principles of the physical sciences. They are rigorous, and only a few purely theoretical models have ad- vanced beyond the research stage. Empirical models are derived purely from observed patterns over time or for different settings. Models which embody em- pirically justified modifications of theoretical relation- ships are in the middle. Theoretical air dispersion models are based on the conservation of mass law, which, in simplified mathe- matical terms, is: 38 Q = T, + Dj + R s + Qi where: Q = the change in concentrations of pollutant i over time in a small volume of air T i = the net transport of i into or out of the small volume Rj = the amount of i created in the volume by photochemical reaction 36. See Eugene M. Darling. Jr.. Computer Modeling of Trans- portation-Generated Air Pollution (Cambridge. Mass.: U.S. De- partment of Transportation, Transportation Systems Center, June, 1972) (NTIS No. PB-2 13013): Joe J. Mathis and William L. Grose, A Review of Methods for Predicting Air Pollution Dispersion, (Washington, D.C.: NASA Langley Research Center, 1973) (NTIS No. N73-20658); Harry Moses, Mathematical Urban Air Pollution Models (Argonne, 111.: Argonne National Laboratory. April, 1969) (NTIS No. ANL-ES-RPY-001); R. A. Papetti and F. R. Gilmore, Air Pollution (Santa Monica, Calif.: The Rand Corporation, Feb- ruary. 1971). 37. Darling surveyed private research and consulting firms regarding the mathematical underpinnings and technical aspects of their dispersion models. 38. Or more formally: 0£i = -V • (VQ + V • (K V d) + Rj + Qi Dj = the change due to turbulent diffusion of i out of the volume Q i = the amount of i emitted directly into the small volume from outside With the improved understanding of the way turbu- lent diffusion varies with wind speed, temperature, humidity, sunlight, and surface roughness, and with the advent of high-speed computers, the mass conser- vation equation is now being used as the basis for recently developed dispersion models. The obvious advantage is that, in theory, all emission sources (including photochemical generation) and time varia- tions can be represented, along with data on surface roughness. The disadvantage is that the theoretical models tend to be costly to operate. The next category (semi-theoretical, semi- empirical) includes a family of models derived from the Gaussian dispersion equation, which is depicted schematically in Figure 1-1. 39 This equation repre- sents the concentration at any point in space of a single puff of pollutant i which is transported by local winds and diffuses three-dimensionally in a Gaussian or normal manner in the process. 40 The extent to which the puff will continue to disperse in horizontal and vertical directions is related to the stability of the atmosphere. Turner has developed empirical relation- ships between stability categories and the standard where: C, = concentration of pollutant i t = time V = change with respect to the x, y, and z directions in space V = wind velocity with components in the x, y, and z direction K = turbulent diffusivity with components in the x, y, and z direction Ri = rate of generation or removal of pollutant i by photo- chemical reaction Qi = rate of emission of pollutant i 39. The mathematical representation is as follows: Q = ., . exp - [(x - ut) 2 + (27r) 3/2 o\ cr y cr z I 2 o- y 2 J where: Q = concentration of pollutant i at time t after emission at any point in space Q = amount of pollutant emitted x,y,z = distances in 3-dimensional space u = mean wind speed cr x , a-y, o- z = standard deviation of the distribution of concentration in the x. y, and z directions H = height at which the pollutant is emitted exp = e raised to the expression which follows 40. A Gaussian or normal distribution when graphed is the famil- iar bell-shaped curve. Air Quality: Methodological Approaches 23 FIGURE 1-1 SCHEMATIC REPRESENTATION OF THE GAUSSIAN MODEL a. Gaussian Puff Representation b. Gaussian Plume Representation NOTES: H = height at which emissions are released X = downwind distance SOURCE: Modified from Darling, op. cit. deviations of dispersion. 41 However, atmospheric sta- bility is but one factor, albeit a very important one, which influences the degree and rate of dispersion. Mechanical turbulence from surface roughness is an- other, but the roughness dispersion relationship has 41. D. Bruce Turner, Workbook of Atmospheric Dispersion Esti- mates (Cincinnati: Department of Health, Education and Welfare, Rev. 1970) (NTIS No. PB 191 482). The standard deviations are the parameters which determine the rate of puff expansion. not yet been quantified. The selection of appropriate values for a given local situation remains a serious weakness in the utilization of Gaussian dispersion models. Similarly, the model is not easily adapted to reflect photochemically produced pollutants or pollutant re- moval processes. On the other hand, the puff model retains the conservation of mass model's ability to re- flect changes in wind speed, wind direction, and emissions over time. In order for the instantaneous Gaussian puff model to reflect a realistic urban setting (i.e., continuous emissions from many sources), the equation is mathe- matically integrated over time and summed for each source. 42 The result is an integrated puff or a Gaus- sian plume model. 43 The third category of models embraces those which are empirically derived, that is, those which at- tempt to explain observed data in the simplest way. The most obvious example is the use of regression equations to relate changes in ambient concentrations with such variables as emission levels, meteorological conditions, and terrain. 44 In fact, attempts at repro- ducing the results obtained from more sophisticated models have proven quite successful. 45 The obvious advantage of such an approach is its simplicity and built-in validation properties. By defi- nition, unless the regression equation "explains" a considerable amount of the variance in the dependent variable, it will not be used. Thus, fairly high agree- ment with observed data is assured. However, since regressions only reveal associations and not causal relationships among the data, future patterns may be significantly different from present ones. Another empirically based, simplified dispersion 42. C,= f" C,dt = - — 2 exp _[-j£_| £ _ ■£> q n = the total number of sources toear (K,e, W year Here Q is the average community-wide ambient concentration for some time period (usually one year), e ( is the aggregate emissions from all sources, and K, is a constant which reflects meteorological conditions, surface features, and other factors related to dispersion. 54. "Release height" is a function of both stack height and plume rise, the latter due to the buoyant effect of a hot gas. sources by sector. The K values are then modified to reflect the frequency with which the wind blows from various directions. Thus, those portions of the con- centric zones which normally lie upwind from point A are weighted more heavily. The rollforward models thus far discussed are ap- plicable only to nonreactive pollutants where the am- bient concentration is linearly related to the emission level. For pollutants which undergo photochemical reactions this assumption of linearity does not hold. Smog chamber experiments reveal that a complex re- lationship exists between ambient concentrations of oxidants and the emission level of their precursors (nitrogen oxides and reactive hydrocarbons). How- ever, at least one attempt to apply the rollforward model to reactive pollutants has been reported. 55 In other words, proportionality was made slightly non- linear for these pollutants. The advantages and disadvantages of the various rollforward models are as follows: Advantages 1. These models are the least complicated and least expensive to use of all dispersion models. 2. Current emissions and meteorological data re- quired are available from local or state pollution control agencies and Weather Bureau stations located at all major airports. Disadvantages 1. The models are unvalidated. 2. The point chosen as being representative of the community must be the location of an existing monitoring station and, therefore, may not be truly representative. 3. The lack of spatial disaggregation means that all present emissions are assumed to increase in a proportional manner and maintain their present spatial distribution in the future. (This is some- what less of a problem for the location version.) 4. Meteorological and surface roughness factors are either ignored or treated simplistically. (Complete atmospheric mixing is assumed.) 5. The models are not applicable to short-lived pollutants (such as CO) unless their half-life is comparable to their travel time across the com- munity at the predominant wind velocity. 56 6. Reactive pollutants have not yet been routinely 55. Mikolowsky. et al.. op. cit. As with all applications of the roll-forward model to date, the accuracy of the results is unknown. 56. "Half-life" is the amount of time required for half of the pol- lutant to be removed from the atmosphere by deposition, interac- tions with vegetation, or other processes. Air Quality: Methodological Approaches 27 FIGURE 1-2 SUMMARY OF THE MILLER/HOLZWORTH MODEL NOTES: The community is visualized as being composed of an infinite number of infinitely long line sources of uniform strength. Pollutants from each line source are presumed to disperse in a Gaussian manner until the plume reaches the top of the mixing layer. Thereafter, the contribution from that source is uniformly mixed in the box. These line sources are integrated in the direction of the wind to obtain an aggregate concentration value for the downwind edge. Average, community-wide values are obtained by a process similar to averaging the concentrations of the upwind and dow nw ind edges. treated by rollforward models, although some initial attempts have been made. In general, the rollforward models are attractive and widely used because of their relative simplicity. Gen- eralized emission data inputs and desk calculators are used for computations. However, a reduction in accuracy is the cost of simplicity. It is worth re- peating that these models are completely unverified. Although the rollforward model is typically identi- fied with the assumption of linearity, it should be noted that many of the simpler models to follow also assume linearity between emissions and ambient con- centrations. Thus, rollforward models should be con- sidered as one type of linear model, the distinguishing characteristic of which is its application to commu- nity-wide and long-term estimation problems. Miller IHolzworth Model — This model is relatively simple (it does not require the use of a computer), theoretical (although based on empirically validated relationships), receptor-oriented, and designed to be used with area sources and most pollutants. 57 It also treats line and point sources by assuming they behave as uniformly dispersed area sources. A summary and schematic depiction of the model appears in Figure 1-2. The model is based on the 57. Marvin E. Miller and George C. Holzworth. "An Atmo- spheric Diffusion Model for Metropolitan Areas." Air Pollution Control Association Journal 17 (January. 1967): 46-50. Gaussian dispersion equation for an infinite cross- wind line source emitting at ground level. 58 This is then integrated across the length of the entire commu- nity in the direction of the prevailing wind to obtain the highest ambient concentration (which will occur along the down-wind edge of the community). How- ever, it does not assume that the vertical dispersion of the plume is relatively constant with distance trav- eled. Instead, when integrating the basic equation, two terms are produced, one which represents up- wind sources close to the receptor, the plumes from which have not had time to disperse throughout the mixing layer, and one which represents more distant sources, the plumes from which are uniformly mixed within the "box." 59 In order to obtain average values for the community as a whole (not just at one point), the values at all points are averaged by additional in- tegration. In order to facilitate calculations using their model. Miller and Holzworth have prepared graphs and tables which relate the normalized concentration (C/Q) 60 to wind speed 61 (the greater the speed, the lower the C/Q value), mixing depth d (the greater the depth, the lower the C/Q value), and community size (the smaller the community and thus the fewer the sources, the lower the C/Q value). Once these values are specified, the actual C value is then obtained by substituting the appropriate Q value (the estimated average emission density previously computed) for the community in question. Actual calculations are V27T (T 2 U where: C = the downwind ambient concentration Q = emissions per unit time and per unit length of the source Decomposers' Detritus' Meat Eaters Zooplankton Benthos" Fish Man Outputs Energy Thermal Chemical (Fixed Org. Matter) Latent Heat (Evapor.) Dissolved Nutrients Sediment a. Organisms living at or on the bottom of bodies of water. b. Fungi and bacteria. c. Small particles of organic matter. SOURCE: D. C. Watts and O. L. Loucks, Models for Describing Exchange Within Ecosystems (Madison: Institute for Environmental Studies. University of Wisconsin, 1969). example, deeply rooted plants, such as trees or native grasses, are typically replaced by lawn grass with shallow roots. Less frequently, old fields may be re- placed by ornamental trees and shrubs. The result is a change in the amount of water stored in the soil and subsequently transpired by plants, leading in most cases to increased amounts of surface runoff. Thirdly, development is frequently accompanied by topographical changes and often by a reduction in average slope. These often increase the rate of water percolation through soil and decrease the rate of sur- face runoff, although the removal of topsoil may negate or reverse the effect. Urban storm drainage systems may replace natural drainage channels with culverts and storm sewers. The net effect is a decrease in the time it takes sur- face runoff to reach local streams and lakes. Finally, as a large area or region becomes urban- ized, slight changes in climate may be noticed. Although changes in temperature, wind velocity. humidity, and solar radiation may be observed, the most relevant effect is on precipitation. Some cities with large point sources of air pollution have been as- sociated with increased precipitation. 13 The net effect of these changes will depend on the local hydrology, physiography, and soil conditions, on the extent of urbanization (both absolute and rela- tive to the watershed), on land uses, and on the spe- cific location of the development. It will also depend on the severity of the storm. (Since surface runoff will increase with severity, most precipitation becomes runoff once the soil is saturated, relatively reducing the effect of development.) However, most studies of urbanization have shown that the percentage of pre- cipitation which appears as surface runoff increases, and the time lag between onset of precipitation and 13. Presumably, particulates emitted from these sources act as condensation nuclei for atmospheric moisture. See William P. Lowry, ••Project METROMEX: A Review of Results," Bulletin of the American Meterological Society 55 (February, 1974): 86-121. 56 Land Development and the Natural Environment occurrence of peak stream discharge decreases. Con- sequently, floods increase in both frequency and severity. 2. Water Pollution Water pollution refers to the quality of water bodies which are affected by wastes generated by or associated with development. Residential and com- mercial developments will produce additional quan- tities of sewage and related wastes, while industrial plants often discharge a wide array of harmful wastes associated with various industrial processes. In addition to pollutants discharged from point sources (i.e., sewage treatment plants or industrial plants), water pollution can result from nonpoint source discharges — general stormwater runoff. This type of pollution is due to natural processes as well as human activities. In natural areas the death and sub- sequent decay of plants and animals, natural erosion processes, leaching of soil minerals, and generation of animal wastes account for most pollutants. In agricul- tural areas the use (or overuse) of fertilizers, the hus- bandry of large numbers of animals, and the exposure of soil stripped of natural cover can contribute to a substantial increase in pollutant loadings above the natural condition. In urban areas the pollutants found in runoff derive from such sources as leaf litter, an- imal feces, lawn fertilizer, automobile residue, and air pollution. On a national basis, the order of land uses (or land cover) from most polluting to least polluting based on total solids, nitrates, and phosphates is as follows: cropland, urban land (considering only residential land use), grassland, and forest. Urban stormwater runoff is the major contributor of a variety of pollu- tants during storms, and even on an annual basis it rivals sewage plant effluent in total loadings. 14 For ex- 14. James D. Sartor, Gail Boyd, and Franklin J. Agardy. "Water Pollution Aspects of Street Surface Contaminants," Journal of Water Pollution Control 46 (1) (March 1974): 458-67; and James D. Sartor and Gail Boyd, Water Pollution Aspects of Street Surface Contaminants (Washington, D.C.: EPA, November, 1972) (EPA-R2-72-081). ample, urban stormwater runoff contributes from 40 to 80 percent of the total national BOD (biological ox- ygen demand) discharged to surface water. 15 Thus, urbanization not only increases the amount of polluting material deposited in developed areas and ultimately washed off, it also eliminates natural areas where these materials could be "recycled" before reaching bodies of water. Forests and grasslands are very successful in accomplishing this recycling. 3. Water Consumption A new development (or urbanization in general) will place additional demands on a community's- or neighboring households' water supply. Residential and commercial developments will need water for do- mestic and other uses (e.g., lawn sprinkling), while industries may need large quantities for cooling and related purposes. Since our primary concern is for water used for drinking purposes, our interest in other uses will extend only insofar as they compete with personal consumption for the same supply. Development may also interfere with the replenish- ment or inflow of water to underground sources. Placing impervious materials on land which pre- viously allowed aquifers to be recharged is an ex- ample. Large developments which use underground sources may also remove water at too great a rate, causing water levels in surrounding wells to drop and total available volumes to decrease. Finally, land development may decrease the pre- treatment quality of water due to additional quantities of pollutants discharged from point sources, from stormwater runoff, or from septic tank leach fields. This may either increase the cost of purification or decrease the quality of the water after treatment. The withdrawal of fresh water from underground sources in coastal areas may also lead to salt water intrusion by reducing the hydraulic pressure that formerly acted as a barrier. 15. Anne M. Vitale and Pierre M. Sprey, Total Urban Water Pollution Loads: The Impact of Storm Water (Rockville, Md.: En- viro Control, Inc., 1974) (NTIS No. PB-231 730). Water Quality and Quantity: Introduction and Background 57 II. METHODOLOGICAL APPROACHES The conceptual framework and the individual analytical techniques for estimating water quality and quantity impacts are specific to the various impact areas. Thus, flooding, water pollution, and water con- sumption will be discussed separately. The sections on flooding and water pollution em- phasize the use of generalizable mathematical for- mulas which relate the areal extent and type of devel- opment (among other factors) to stormwater runoff. A broad range of approaches, from simple linear approximations to complex computerized models, will be discussed. The water pollution section also discusses sewage generation. Finally, the analytical treatment of water consumption impacts will focus on methods of estimating total supplies and the use of coefficients which reflect usage rates for different types of development. A. IMPACTS ON FLOODING With the full implementation of the Flood Disaster Protection Act discussed previously the exposure of new structures to flood hazards will be vastly re- duced, although the few future proposals for flood plain development will still require careful review. However, a flood-related problem will remain — the effect of changes in stormwater runoff patterns caused by new development to existing structures within flood hazard areas. This effect can be de- scribed in terms of increased damage to structures already at risk and increased risk to structures cur- rently safe, meaning those located just beyond pres- ent flood plain boundaries. 1. Impact Measures Two alternative measures of flood problems are suggested: 1 1. Change in the number of people endangered by flooding plus the change in the expected property damage (or the value of property endangered). OR 2. Change in flood frequency or severity. Measure 1 best expresses the end impact on man and is thus preferred. It is also the most difficult and ex- pensive to obtain values for. Measure 2 is the fallback measure. Values for Measure 2 are used to compute values for Measure 1 , but they can also be used to re- flect changes in the probability of flooding alone. In this connection one speaks of a flood which can be expected to occur on the average of once in two, five, ten, fifty, 100 or 500 years. (This corresponds to a probability of occurrence of fifty, twenty, ten, two, one and 0.2 percent for any one year.) Obviously, as the frequency decreases the magnitude increases. Since a number of dimensions are suggested by Measure 1, a tabular display of the results may be suitable. An example is shown in Table 2-2. The re- sults are expressed as the additional number of peo- 1. A third alternative would be "the amount of impervious ground cover relative to the budgeted amount" where budgets have been prepared for the watershed in question. See section A-3 of this chapter and section A of part 2. Ill, for a more detailed dis- cussion. 59 Table 2-2. AN ILLUSTRATIVE FORMAT FOR PRESENTING THE EFFECT OF A DEVELOPMENT ON RISKS FROM FLOODING FLOOD FREQUENCY OR MAGNITUDE ADDITIONAL PEOPLE JEOPARDIZED Within Outside Development Development ADDITIONAL PROPERTY VALUE JEOPARDIZED* 1 Within Outside Development Development Floods Worst in 10 years Worst in 50 years Worst in 100 years 1.000 3.000 3.000 (millions of dollars) $10 $40 $40 $.5 $.5 a. Alternatively, the expected property damage could be used (this would be less than the total in jeopardy, as in a case where worth $100,000 is put in jeopardy, but where the likely damage to it may be $25,000). property pie at risk and the expected damage caused by floods of various frequencies. It may also be desirable to display the maps delineating flood plains for the ten, fifty, 100 and 500-year floods. This is extremely effec- tive in communicating the impact on individual properties. 2. General Analytical Approaches In order to measure the hydrologic changes that have occurred as a result of urbanization in a given watershed (i.e., retrospective analysis), one can either trace and relate the hydrologic and develop- mental changes over time (controlling for all other variables), or compare the changes with those ob- served in an "identical" watershed which has not experienced land development. The first approach is limited by the difficulty in accounting for all nondevelopment-related factors which could affect the watershed's hydrology. This is especially true for climatic factors, which can display extreme variabil- ity from year to year. In some cases simple models have been used to estimate the fraction of observed hydrologic changes due to climatic factors alone, the residual then being attributed to land use changes. The second approach is limited by a similar problem. No two watersheds are identical. Thus, dif- ferences must be carefully measured and accounted for. These differences include physiography, soil structure, vegetation, land use, and watershed size, as well as climate. In assessing the impact of future developments pre- dictive techniques calibrated to local conditions are frequently employed. Alternatively, analogies to simi- lar watersheds can be drawn. If the latter approach is used, one must again be careful to account for dif- ferences between the test and the reference situa- tions, as in retrospective analysis. Flood analyses which involve the use of predictive techniques or models are typically comprised of two parts, a hydrologic analysis and a hydraulic analysis. The first estimates rainfall/runoff/stream flow rela- tionships; the second routes the runoff into existing channels and estimates flood levels for bodies of sur- face water in the watershed. A few of the more com- plex models accomplish both types of analyses. The sections to follow present descriptions of alter- native techniques and. where possible, evaluations of them.- The last few years have witnessed a dramatic proliferation of the more complex hydrologic models. Selection of the techniques reviewed here was based primarily on their current popularity or represent- ativeness of alternative approaches. Unfortunately, the dearth of information on input requirements and accuracy of the various techniques reduces our ability to appraise the various approaches. Where possible we have attempted to survey both the developers and users of particular techniques, in order to gain at least qualitative insights. 3. Estimating Impacts on Stream Flow The extent to which a proposed land development will cause significant changes in the flow of local streams is dependent on numerous characteristics of both the development and the watershed in which it is to be located. In determining whether a particular development is large enough to justify an individual assessment, the most meaningful and widely used fac- tor is "percent imperviousness." That is, the amount of land to be covered with impervious material, such as concrete or asphalt, is expressed as a per- centage of the land on the site and as a percentage of the entire watershed. However, in order to determine 2. For more inclusive treatment see, for example, J. W. Brown et al., Models & Methods Applicable to the Corps of Engineers Urban Studies (Vicksburg. Miss.: Army Corps of Engineers, June, 1974): and Ray K. Linsley, A Critical Review of Currently Avail- able Hydrologic Models for Analysis of Urban Stormwater Runoff (Palo Alto, Calif. Hydrocomp International, August, 1971). The first is particularly relevant to the subject here as individual models are described and to some degree evaluated systematically. 60 Land Development and the Natural Environment how large these percentages must be to justify an as- sessment, the sensitivity to imperviousness of indi- vidual watersheds within the community must be as- certained. This can be done through retrospective analyses (as discussed above) or by applying analyti- cal techniques to the watersheds and observing the effect that hypothetical degrees of imperviousness have on estimated stream flow. 3 a. Analytical Techniques The following techniques differ in base data re- quired, complexity of computation, type of results generated, and applicability to different types of watersheds. The simpler techniques will be presented first. Each technique is used to estimate water flow in streams and/or lakes. Rational Method — One of the most widely but, in many cases, inappropriately used techniques is the Rational Method. 4 It is a straightforward and simple computational procedure applicable to streams and based on the following relationship: Q = CiA where: Q = peak (short-term) runoff rate (or stream flow) in cubic feet per second C = a constant dependent on basin character- istics i = average precipitation intensity in inches/hour (different values are used for storms of different degrees of severity) A = drainage area in acres The coefficient C is dependent on many watershed variables, such as shape, slope, soil moisture content and capacity, ground cover, and terrain, as well as on the severity of the storm. 5 (As noted previously, development can affect many of these variables.) Suc- cess in assigning appropriate values to C which re- flect all of these factors has not been obtained. Typ- ically, the total effect of urbanization is represented by "percent imperviousness," although the extent of storm sewerization is implicitly included as well. 3. This is further discussed in Part 2, III. under the heading. "Planning versus Project Review." 4. For additional information, see American Society of Civil Engineers, "Design and Construction of Sanitary and Storm Sewers," Manuals and Reports on Engineering Practices, No. 37 (Washington, D.C., 1969); S. E. Rantz, Suggested Criteria for Hy- drologic Design of Storm-Drainage Facilities in the San Fran- cisco Bay Region, California (Menlo Park, Calif.: U.S. Geological Survey, November 24, 1971); and James K. Searcy, Design of Roadside Drainage Channels, Hydraulic Design Series #4. Bureau of Public Roads (Washington, D.C.: Government Printing Office. May, 1965). 5. Runoff as a percent of precipitation increases as the soil be- comes saturated and the surface depressions are filled. Rantz provides rules of thumb and some empirical data (from the San Francisco area) which can be used to relate various types of development to "percent imperviousness" and thus to determine C. 6 A pro- posed development will change the "percent impervi- ous" and thus values for estimated stream flow through changes in C. As mentioned previously, the Rational Method is one of the most popular techniques for estimating stream flow, especially for watersheds undergoing ur- banization. It is simple and provides estimates of peak stream flow — a quantity directly pertinent to flooding. However, it is limited in application to small watersheds of no more than a few square miles and preferably less, a fact not recognized by all users. 7 In addition, there have been few attempts to compare computed with observed values. In at least two vali- dation studies, errors were as large as 60 percent. 8 Another test showed that only 35 percent of the esti- mates were within 25 percent of the observed values. It is thus of dubious utility for anything more than gross estimates. Flood Frequency Analysis — As the name implies, this technique estimates stream flow during flood in- cidents from actual flood data. 9 These data are then related by empirical analysis of watersheds in the region under study to climatologic, topographical, and if possible, land use characteristics. The impact of a new development is then estimated, using these empirical relationships. More specifically, data on peak stream flow are compiled for all streams within the region on which gauging stations are located. 10 These data are then 6. The relationship between land use categories and "percent imperviousness" for other geographical areas can be found in: Water Resources Engineers and the Hydrologic Engineering Center, Corps of Engineers, Management of Urban Storm Runoff (New York: American Society of Civil Engineers, May, 1974); George Dempster, Jr. Effects of Floods in Dallas, Texas Metropoli- tan Area (Austin, Texas: Geological Survey, January, 1975); and Joachin Tourbier and Richard Westmacott, Water Resources Pro- tection Measures in Land Development — A Handbook (Newark: Water Resources Center. University of Delaware. April. 1974). 7. Some have suggested the the upper limit be 200 acres (approximately V3 square mile). See Wright-McLaughlin Engineers, Urban Storm Drainage Criteria Manual (Denver: Denver Regional Council of Governments, 1969). 8. Error values are observed-estimated differences as a percent- age of the observed. These occurrences were for watersheds of less than fifty acres. See D. Earl Jones, Jr.. "Urban Hydrology — A Re- direction," Civil Engineering (August, 1967): 58-62; and J. C. Schaake, J. C. Geyes, and J. W. Knopp, "Experimental Examina- tion of the Rational Method," Journal of the Hydraulics Division Proceedings of the American Society of Civil Engineers (No- vember. 1967): 353-70. 9. For additional information, see Rantz, op. cit. 10. Gauging stations are manmade structures designed to mea- sure stream flow. Water Quality and Quantity: Methodological Approaches 61 organized into frequency distributions for each stream according to standard statistical procedures. 11 Values for stream flow for floods of various recur- rence intervals (typically, two, five, ten, fifty and 100 years) are then mathematically related to the basin characteristics of the test watersheds. 12 If the set of test watersheds shows wide variation in these charac- teristics (e.g., the gauged basins include large as well as small ones, urbanized as well as natural ones, ones with high levels of precipitation as well as dry ones), these factors can be analyzed for their effect on stream flow. If not, relationships developed for other regions can possibly be substituted if interregional dif- ferences are not too great. The natural basin charac- teristics and forecasted land use changes (either gen- eral growth or single large developments) are then used to estimate flow levels for the stream in ques- tion. Measures of development are typically very gross, such as "percent urbanization" as measured by areal extent of structures, lawns, pavements, etc. Thus, this technique is best applied only where the new development represents a large increase in a watershed's degree of urbanization. Again, more de- tailed guidelines can be found in the Rantz report. 13 Table 2-3 shows the results of a Flood Frequency Analysis of forty watersheds in the San Francisco region. Storms of various recurrence intervals are re- lated to several basin variables (only precipitation and basin size proved significant) and correlation coeffi- cients reported. 14 As shown, the technique is highly successful in reproducing past events, although future events can only be estimated accurately to the extent that future hydrologic relationships are similar to past ones. 11. The data are fitted to a Pearson Type III distribution. See Water Resources Council, Hydrology Committee, A Uniform Technique for Determining Flood Flow Frequencies, Bulletin No. 15 (Washington. D.C.; December. 1967). 12. These relationships are determined by regression analysis, typically using an equation of the form: Q = ax b y c . . . where: Q = flow x, y . . . = are variables such as watershed area and pre- cipitation a, b, c . . . = are constants, the values for which are deter- mined by analyzing the data for Q, x, y, etc.. collected for various watersheds 13. Rantz, op. cit. 14. Correlations measure the agreement between data. Values of signify no agreement while values of 1.0 indicate perfect agree- ment. Values about 0.7 reflect "good" agreement. Correlation coefficients as applied to stream flow data must be interpreted with caution. The specific coefficient values are a function of the ade- quacy of the stream gauging program, as well as the accuracy of the technique. In addition, other measures of validity can be, and for some techniques have been used. (Correlation coefficients cited in this report are the statistic "r" unless otherwise noted.) Table 2-3. RESULTS OF A FLOOD FREQUENCY ANALYSIS (For Illustration Purposes Only) RECURRENCE COEFFICIENT INTERVAL MULTIPLE REGRESSION OF MULTIPLE (YEARS) EQUATION CORRELATION 2 Q 2 = 0.069A 9,3 P' 965 0.964 5 Q 5 = 2.00A O 92s P' 206 0.976 10 Q,o = 7.38A 922 P° 928 0.977 25 Q 25 = 16.5A 09 ' 2 P° 797 0.950 50 Qso = 69.6A 847 P° 5 " 0.902 SOURCE: Rantz. op. cit. NOTES: Q = stream flow, in cubic feet per second A = drainage area, in square miles P = mean annual basinwide precipitation, in inches These results are specific to the unusual hydrological and climato- logical features of various watersheds in the San Francisco Bay area. Other Simple Techniques — Most other techniques which do not involve the use of computerized hydro- logic models are refinements of the methods already presented. 15 For example, the Unit Hydrograph Tech- nique expands the Flood Frequency Analysis by esti- mating the time distribution of runoff from a storm rather than just peak discharge. 16 (A hydrograph for a hypothetical basin is shown in Figure 2-3.) This infor- mation is useful if certain flood control devices are employed in a watershed. Total, rather than just peak flows, are needed to estimate the effectiveness of storage facilities, such as levees and dams. Hydro- graphs are also useful for showing the impact of ur- banization on the timing of peak discharge. In addi- tion, Rantz has reported a slight improvement in accuracy for estimates of peak discharge values as compared to the Flood Frequency Analysis, although the computation procedures are considerably more involved. A recent study sponsored by EPA further documents the utility of this method. 17 Each of the techniques discussed thus far which es- timate short-term fluctuations in flow (i.e., peak flow) use a single measure to reflect the hydrologic effects of urbanization. Even though this measure is fre- quently called the "percent of imperviousness" it often encompasses the other major hydrologic-related 15. For a discussion of other simple techniques which may be used to estimate runoff, see EPA, Water Quality Management for Urban Runoff (Washington, D.C.: EPA, December, 1974) (NTIS PB241689/AS). 16. For much information see Rantz, op. cit., or any standard hydrologic text such as Linsley. Kohler, and Paulhus, op. cit. 17. E. F. Brater and J. D. Sherill, Rainfall-Runoff Relations on Urban and Rural Areas (Cincinnati: EPA, Office of Research and Development, May, 1975). 62 Land Development and the Natural Environment FIGURE 2-3 AN EXAMPLE OF HYDROGRAPH FOR A HYPOTHETICAL WATERSHED a. Actual Hydrograph TIME b. Mathematical Abstraction factor as well — the extent to which natural drainage channels have been modified or replaced by storm sewers. It would, of course, be useful to know the relative effect of each so that the proposed develop- ment could be characterized by each separately. Luna Leopold has compiled and presented in tabu- lar and graph form the results of flood frequency studies of the effects of both factors on stream flows. 18 Since the individual studies were undertaken in different geographic regions the combined results are national averages and may or may not be appli- cable to specific areas. However, they could possibly be used to suggest when the other techniques may give low or high estimates when applied to specific developments. If the new development will be sewered to an unusually high or low extent when compared with the developments used to calibrate or particularize the technique, the estimates could be ad- justed up or down, perhaps by a factor equal to those in the Leopold reference. The resulting estimate would still be approximate but to a lesser degree. 18. Luna B. Leopold, Hydrology for Urban Land Planning — A Guidebook on the Hydrologic Effects of Urban Land Use, Geologi- cal Survey Circular 554 (Washington, D.C.: Geological Survey, 1968). Another factor not accommodated well by these techniques is the influence of site design. Since the options for diverting or detaining runoff through landscaping and the construction of special facilities are numerous, it is unlikely that the impact of future development on flood potential can ever be estimated with a high degree of certainty using these methods. However, rough approximations of the mitigating ef- fect of runoff detention devices can be made, using design specifications found in relevant engineering reports. 19 Complex Hydrologic Models — The relatively sim- ple techniques discussed so far are simple because they abstract only the more important features of the hydrologic cycle while ignoring the rest. The Rational Method, for example, does not treat evapotranspira- tion, soil moisture replenishment, or subsurface water flow explicitly (see Figure 2-1). Rather, it relies on empirical measurements of rainfall intensity and the coefficient C, which presumably encompasses the lo- cally important variables. Likewise, the Flood Fre- quency Analysis attempts to associate presumed causes (e.g., basin configuration, precipitation, and land use) with effects (floods of various severity) but with no direct analysis of hydrologic processes. Complex hydrologic models, on the other hand, at- tempt to simulate more elements in the hydrologic cycle. "Event models" are used to estimate stream flow during single events or storms. They are consid- erably more complex than the simple techniques, but stop short of simulating the complete hydrologic cycle. "Continuous models" are based on a detailed accounting procedure which traces the fate of precipi- tation within a given watershed on a daily, hourly, or even subhourly basis. Figure 2-4 is a flow chart for one representative continuous model. In order to compute stream flow according to this procedure, short-term data on temperature, precipitation, hours of sunlight, topography, vegetation, soil type, and land cover are necessary. Many of the complex models also employ stream routing routines which assign surface and subsurface runoff to natural and artificial channels in various portions of the watershed. The technique used to route the flows is one of the main points of differen- tiation among the various models. Once the precipitation has been translated into sur- face and subsurface flows, which in turn have been routed into existing waterways, and the overall model 19. American Public Works Association, Practices in Detention of Urban Stormwater Runoff, Special Report No. 43 (Chicago, 1974) (NTIS No. PB-234-554). See also, Tourbier and Westmacott, op. cit. ; and Meta Systems, Inc., Land Use Environmental Quality- Relationships (Washington, D.C.: EPA, forthcoming). Water Quality and Quantity: Methodological Approaches 63 FIGURE 2-4 FLOW CHART OF COMPUTATIONS FOR A COMPLEX HYDROLOGIC MODEL SOURCE: Modified from R. Linsley and N. Crawford, "Continuous Simulation Models in Urban Hydrology, "Geophysical Research Letters, No. 1 (May, 1974): 59-62. a. This diagram refers to the "lands" module of the Hydrocomp Simulation Program. Land Development and the Natural Environment calibrated for a similar watershed with stream flow records, estimates of past and/or future flows are made for the watershed in question. The results are expressed in terms of continuous stream flow hydro- graphs for each of the stream reaches into which the stream has been divided. The past or future impact of changes in land cover (e.g., due to development, reforestation, conversion to agricultural uses), in channel configuration, or in flood control facilities can then be simulated. This description is generally applicable to all con- tinuous hydrologic models but especially those based on or modified from the Stanford Watershed Model. 20 An abbreviated evaluation of complex models, as well as simple hydrologic techniques, appears in the next section in tabular form to aid in comparative as- sessment. 21 In summary, these models are much more satis- fying from a theoretical perspective, although evi- dence for purposes of accuracy comparison is lacking. Most have the capacity to estimate short- term changes in flow and the effects of site design features, including changes to the drainage system. One additional approach worth noting is the simula- tion of long-term stream flow by a mathematically produced stochastic process. 22 The concept is quite simple — hydrologic processes exhibit many features of a random series of events and could be simulated by an appropriately synthesized stochastic process. This requires the use of a digital computer. In addi- tion, the results have not been as accurate as was hoped. For short-term stream flow prediction and for estimation of the impact of changing land use pat- terns, other approaches seem more desirable. b. Comparison and Summary A discussion of the comparative advantages and disadvantages of hydrologic techniques cannot pro- ceed much beyond the obvious. The simple tech- niques are less expensive and produce less informa- 20. See N. H. Crawford and R. K. Linsley. Digital Simulation in Hydrology; Stanford Watershed Model IV, Department of Civil Engineering Technical Report No. 39 (Palo Alto, Calif.: Stanford University, 1966). 21. Numerous events and continuous models are available. Re- cently, several comprehensive reviews of many of these have been published. See, for example, Marsalek. op. cit. ; and A. Brand- stetter. Comparative Analysis of Urban Stormwater Models (Rich- land. Wash.: Pacific Northwest Laboratories, Battelle Memorial Institute, 1974). See also the description of SWMM and STORM (two federally developed runoff models which can also be used to estimate stormwater runoff quality) in Table 2-4. 22. Leo R. Beard, Simulation of Daily Streamflow, Technical Paper No. 6 (Davis, Calif.: Army Corps of Engineers. Hydrologic Engineering Center, 1967); and Linsley, Kohler, and Paulhus, op. cit. tion with less accuracy than the complex ones. The almost total lack of reported information on costs and accuracy necessitates reliance on theoretical consid- erations as the basis for appraisal. We have already mentioned the primary difference between complex hydrologic models and most simple techniques, but it is worth noting again. It is basically the difference between specifying relationships based on observed statistical associations and the simula- tion of underlying, empirically tested processes which are responsible for the observed associations. Both can be equally accurate for reproducing past events for the calibrated watershed, but the second approach is theoretically far superior for estimating future events, or events in a watershed to which the model has not been calibrated. Confirmatory empirical evi- dence is generally lacking, however. Table 2-4 repre- sents an attempt to organize and present descriptive material on the various techniques in a standard format. For the planner seeking to select from among the available techniques (especially in the absence of spe- cific cost and accuracy figures), a very qualitative as- sessment may be valuable. All of the simple tech- niques described can be used in-house by planners who have some familiarity with them. In addition, flood frequency studies for individual watersheds may have already been undertaken by the local U.S. Geological Survey (USGS) field office. The more complex techniques will require the use of a com- puter and often a consultant. These will most likely give better results, but to an unknown degree. All of the techniques require climatologic and hy- drologic data as input. The National Weather Service (NWS) maintains daily precipitation records for various periods of time at 10,000 locations nationwide and hourly records at 2,500 of these. Hourly records of a variety of other meterological data for seventy years are available at approximately 600 first-order stations. 23 Local data, including that produced by the volunteer observer network, may greatly expand the official NWS system. The National Weather Records Archives are another rich source of meteorological data. 24 The USGS operates most of the stream-gauging 23. These data are available in the following Weather Bureau publications or data sets: regional Hydrological Bulletins, Climato- logical Data and Hourly Precipitation. These are available at Weather Bureau offices and at field offices of such agencies as the Corps of Engineers, Bureau of Reclamation, and Soil Conservation Service. 24. Environmental Data Services, National Weather Records Archives, Environmental Science Services Administration, Federal Building, Asheville, N.C. 28801. Water Quality and Quantity: Methodological Approaches 65 2 z £ w P 2 s _ lit 4 8 2 8" •= •- T3 ^ 1 i ~ S I ca o E O 4> o 3 H C "3, .5 — 60 ■- U U 3 c 3 H J= 2 O "S "9 3 -a •£ s &|£ - E g - u -o 2 S 8 •E w 2 B M -a • - ca oo > u o Id.: 1 g a o ■« cu § C C « 00 as ?J 5 « PC Q. D. £ I S" £0 o §1 U g a « "g fa C 3 o O SI E ii S 155 © CL S - 6 P S M U U V a c a u >Soi"c S Z ^ u © 7 3 « £ y § - * c id C D 1) ~ 2P -b 2 m . c oo .b — ?P ^ 28 2 2 3 S £ 2 5 £ £ £ ■■= is ft-' o -o — 5 o o c u ,o 5 E £ E — ' "3! £ I -S * f o o. <-> : c ^ S a o E E a 2 j- ; 00 aj -o ¥ 2 u n # P », « '1 ii •r O O . | | 1 | "O a c« — a > -O E D3 - t U ^3 3 3 — — \C "c is c o. a &- IS Q o eu a, s ^ .2 > o oo U U ■c 'S £ D C .E Z < V E » V 12 1 sa -2 o O ES C ^ s ■a £ £ z w -S oc II S 1 u 5 | § "Qui: g « g. g c S E 3 'a -5 P, 03 H 5 c O ; -ss 4=S £ > 10 as 5'0 t. "5 ; ^11 IO Ej — QS on r — T3 w >i? s I = xS d ^' Q I Z •o 1! * •5 Water Quality and Quantity: Methodological Approaches demand (BOD), the number of physical and biological processes involved may number as many as fourteen. Water quality models can also be classified by other characteristics. The simpler models represent a hydrologic environment as a steady state system, thus ignoring the dynamic elements such as changes in water flows, solar insolation, and changes in pollu- tant discharge with time. Others are time-varying. Some models represent each event in the water qual- ity system as a probabilistic event, while others are deterministic and assume that an event will always occur if the precursor conditions are satisfied. Models are also characterized by the type of water body to which they apply and the extent to which they are spatially disaggregated. As with several other types of water models, the fundamental equation upon which most water quality models are based is the conservation of mass or mate- rial balance relationship: 46 Q, = N, + S, + A, where Qj = the change in the quantity of pollutant i in a small volume of water over time Nj = the net movement of i into or out of the small volume Sj = the summation of sources and sinks (sources of removal) for i in the volume A, = the amount of i added directly into the small volume from outside (i.e.. pollu- tant discharge) The manner and extent to which the various terms are represented mathematically will determine each model's complexity and fidelity to the real world. b. Surface Water Models Here we are again faced with the difficult task of selecting among a profusion of water quality models developed in recent years. As before, the criteria of representativeness and popularity have been utilized for discrimination purposes. In addition, our prefer- ence has been for the better documented models. A number of recent reviews can be used to supple- 46. More formally: Vj ^ = J U A, + V,S U + W u where: C (J = the concentration of pollutant i in segment j V, = the volume of segment j J u = the net flux of i in segment j Aj = the interfacial area of segment j S,] = the summation of sources and sinks of i in j W„ = the direct input of i to j. Furthermore. J depends on the diffusion of pollutant i and the ad- vective transport of i as determined by the flow velocity. ment the information presented here. 47 The review by J. W. Brown et al. is especially useful in describing the characteristics of individual models. Even here, through information on cost and accuracy is sparse. Streeter-Phelps — A number of water quality models have been based on the Streeter-Phelps equa- tion first published in 1925. 48 This is a highly simpli- fied version of the conservation of mass equation; it considers only the DO depletion due to the discharge of BOD containing effluent (and subsequent bacterial oxidation) and the replenishment of DO through sur- face reaeration. The model is also time-invariant (i.e., steady-state) and deterministic, and assumes com- plete, instantaneous mixing. DO concentrations are computed as a function of distance downstream from the outfall. It is basically an easy and inexpensive, but highly simplistic and inaccurate, approach to esti- mating water quality. Simplified EPA Model — This model depends on re- latively gross or averaged input data, rules-of-thumb. generalized relationships between watershed pa- rameters and water quality, and a ''worst condition" philosophy. 49 For example, the degree of stream reaeration is approximated by describing the depth of water relative to the size of bottom rocks, and analy- ses are typically made for points near outfalls and during low flows — the locations and times of lowest quality. Due to the simplicity and manual nature of the model it is very attractive. Unfortunately, it is limited in applicability and may be misleading. Only average relationships between watershed parameters and water quality are used and are assumed constant in time and throughout the water body. The EPA has made an effort to limit distribution to those who are either knowledgeable in water quality analysis or who have attended special training courses. Auto-Qual— The EPAs Middle Atlantic Region III has developed a water quality model which can be 47. J. W. Brown, et al.. op. cit.; Martin E. Harper. Assessment of Mathematical Models Used in Analysis of Water Quality in Streams and Estuaries (Pullman. Wash.: Washington State Water Research Center. June, 1971): and Pio S. Lombardo, Critical Re- view of Currently Available Water Quality Models. (Palo Alto. Calif.: Hydrocomp. Inc. July. 1973) (NTIS No. PB-222265); and Systems Control. Inc.. Use of Mathematical Models for Water Quality Planning (Olympia: Washington Department of Ecology, June. 1974) 48. H. W. Streeter and E. B. Phelps. "A Study of the Pollution and Natural Purification of the Ohio River." Public Health Bulletin 146 (Washington, D.C.: Public Health Service. 1925). (reprinted by HEW. 1958). For a description of other DO-BOD models, see Harper, op. cit. 49. For documentation, see Hydroscience. Inc. and Mitre Cor- poration, op. cit. 74 Land Development and the Natural Environment run in either a steady-state or a quasi-dynamic mode. 50 The model has a hydraulic component which is applicable to any body of water (except stratified lakes or impoundments) whose length is considerably greater than its width (i.e., rivers and many es- tuaries). The model estimates values for nonreactive pollutants and DO-BOD. The computations are based on the conservation of mass equation as applied to a series of points or junc- tions evenly dispersed along the direction of flow. Quality variables are estimated at each junction, while the hydraulic (flow) variables are used to characterize the transport of substances between junctions. Although the dynamic mode of operation allows for changes in pollutant and quality indicator values over time, the use of average or net daily flows "smooths out" the rapid response of these variables due to storm surges or tidal oscillations. However, the loss in fine tuning is compensated for by the model's com- patibility with EPA's Water Quality Information System. 51 HSP, Water Quality Component — This is the set of water quality routines used in conjunction with the HSP hydrologic model described previously. 52 Rivers are segmented into an unlimited number of reaches and lakes or impoundments into several layers. The water quality within each segment is estimated on a continuous basis, using the conservation of mass equation as an organizing framework and laboratory estimates of the various reaction rates to predict val- ues for individual pollutant or quality indicators. The model is extremely comprehensive. In addition to several nonreactive pollutants, various forms of N and P, temperature, coliform bacteria, and micro- scopic plant and animal organisms can be modeled. The DO-BOD system is also represented comprehen- sively. Since the model is run with a surface runoff compo- nent (see Table 2-6), the contribution to water pollu- tion from urban and agricultural nonpoint sources can be modeled. On balance, the HSP system including the water quality submodel appears to be a comprehensive and well-integrated package. However, no quantitative in- 50. Robert L. Crim and Norman L. Lovelace, Auto-Qual Modelling System, Technical Report No. 54 (Annapolis. Md.: EPA, March', 1973) (NTIS No. PB-227 032). EPA has developed alternative water quality models as well (e.g.. HARO 3 and SNSM). 51. For more information contact the Monitoring and Data Support Division. Office of Air and Water Programs, EPA, Wash- ington. D.C. 52. Hydrocomp, Inc., Hydrocomp Simulation Programming Mathematical Model of Water Quality Indices in Rivers and Im- poundments (Palo Alto, Calif.: Hydrocomp. Inc.. n.d.). formation on accuracy for the quality component is in hand, although initial applications on the Green River in Washington are reported to have produced "rea- sonable" results. 53 The cost of operation is also un- known, although it probably is in the neighborhood of that reported for the hydrologic component of HSP (up to $10 per acre for small watersheds, less for larger ones). Other Models — A number of advanced modeling efforts during the 1970s have been undertaken as part of the International Biological Program and as part of EPA's research and development. The ongoing EPA- sponsored projects are listed in Lombardo's review. Although most of these modeling studies are of a purely research nature, significant advances in the understanding of hydrologic and ecologic processes should ultimately result in improved operational models. Analysts involved in water-related planning and evaluation should contact the sponsoring agencies for descriptive and evaluative information as it becomes available. c. Groundwater Models Groundwater hydrologists have been involved with estimating the capacity of underground sources for several decades. The quantitative modeling of groundwater quality, on the other hand, has received only slightly more than passing attention. The most dominant factor in explaining the non- aqueous components of underground water is the mineral composition of the aquifer (i.e., the water- bearing strata of rock or unconsolidated earth mate- rial). Since the movement of groundwater is often extremely slow (perhaps only a few hundred feet a year), the mineral content is usually high despite the slow dissolution rate of most minerals. Human factors are increasingly important. Since surface water and groundwater are most realistically viewed as an interconnected system, degradation of rivers and lakes can also lead to groundwater deterio- ration. Pollutants from cropland, septic tank fields, and sanitary landfills are additional sources of degra- dation. The degree to which a potential source will be pol- luting is largely dependent on the ground material overlying the aquifer and through which the pollutant- bearing water must pass. Properly managed, a liquid waste disposal site such as a septic tank leach field can be used to recycle nutrients with little or no net production of N or P. Soil particles are also effective in destroying bacteria and viruses. Improperly man- 53. Lombardo. op. cit. Water Quality and Quantity: Methodological Approaches 75 aged or operated in areas with inadequate soil charac- teristics (e.g., too fast or too slow percolation, too wet, too shallow), liquid or solid waste disposal sites can be severely polluting. Once polluted, aquifers may take years or decades to regenerate owing to their slow rates of flow. Techniques for estimating groundwater quality must consequently consider both the overlying unsaturated material and the water- filled aquifer, as well as direct communication between surface and groundwater. Unfortunately, the movement of aqueous pollutants in media other than surface water is still not well enough understood to support the development of operational models. One of the most ambitious at- tempts to further the research in this area was re- cently undertaken by investigators from the Univer- sity of Florida. 54 They coupled a surface water model, an unsaturated zone model, and a groundwater model in an attempt to simulate the entire hydrologic regime for a small Florida lake basin. Unfortunately, their set of models could not be validated due to data limita- tions. In the absence of operational predictive techniques, estimates of causal relationships must rest on inferen- tial evidence. Groundwater quality (as measured from well samples) should be correlated with land develop- ment activities and associated soil characteristics to the extent this is possible. 55 The relationships gen- erated will obviously be general and approximate. Most new developments should not present addi- tional groundwater problems, since the majority will be serviced by sanitary sewers. In fact, they may cause an improvement in quality if older housing units with septic tanks are being replaced or if agri- cultural land is being developed. A unique groundwater problem faced by communi- ties in coastal areas is that of salt water intrusion. As this is a problem primarily related to water consump- tion it will be discussed in the next section. Water Supply. d. Comparison and Summary Various aspects of the previously described water quality models are summarized and compared in Table 2-7. These represent only a limited, albeit rep- resentative, sampling of extant models. As with the other water models discussed in Part 2, those which are based on or simulate the fundamental 54. Armando [. Perez, et al.. A Water Quality- Model for a Con- junctive Surface-Groundwater System (Washington. D.C.: EPA. May, 1974) (EPA-600/5-74-013). ' 55. In the case of confined aquifers with specific recharge areas, detailed knowledge of the location and nature of the recharge areas is a prerequisite for any correlation-type analysis. ecological interactions of living organisms and their environment should deliver more accurate results. Thus, the more complex models should provide more reliable predictions. Although the available data on accuracy tends to bear this out, much more extensive testing in a variety of lakes, streams, and estuaries is needed. The same can be said for operating costs. In some cases we have even experienced resistance on the part of the model developer to divulging whatever cost and accuracy documentation exists. Even if reliable operating cost data were available, the question of costs for model start-up, validation, and calibration would remain. Lombardo reports that these costs for the HSP (quality component) model were in the neighborhood of $50,000 and $100,000 for Denver and Seattle, respectively. 56 Thus, any com- munity which contemplates employing a water model should be prepared to expend the necessary and con- siderable funds for preparation. The justification for the utilization of any model should be made on its long-run benefits, in order to capture economies to be realized from long-term application. 6. Estimating the Number of People Affected The number of people engaged in various water- related activities can be approximated using either direct observation survey techniques or written/ telephone surveys of likely users. More detailed discussions of recreational survey techniques can be found in other references. 57 7. Estimating Monetary Benefits If the estimated water quality impacts of land development appear to be substantial in terms of the number of people affected and/or the types of other developments impacted, the local government may want to estimate the monetary value of the clean water benefits being reduced (or the "costs" of the additional deterioration). The principal approaches in- clude the following: (1) Willingness to pay — determining how much the affected individuals or firms are willing to pay for clean water. (2) Expenditure method — determining the expendi- tures made by those using clean water. (3) Cost method — determining the cost to ame- liorate the pollution-caused damage. 56. Lombardo, op. cit. 57. See, for example. The Urban Institute. How Effective Are Your Community Recreation Services? (Washington. D.C.: Bureau of Outdoor Recreation, Department of the Interior, April, 1973). 76 Land Development and the Natural Environment Water Quality and Quantity: Methodological Approaches (4) Local economy method — determining the effect in terms of reduced output. (5) Property value method — determining the effect of clean water in terms of increased property values. These methods are obviously not completely or perhaps even partially substitutable. Thus, results ob- tained by using one are not necessarily comparable to those obtained by using another. This fact, plus the difficulties involved with deriving reliable data regardless of the method employed, makes an eco- nomic analysis of water quality impacts a formidable task. Discussions of the conceptual and technical problems, as well as examples of local studies, can be found in the references cited. The EPA is actively engaged in benefit research at the present time. Pre- sumably, improvements in methodology as well as es- timates of benefits (or damages) on a regional scale will be forthcoming. C. IMPACTS ON WATER CONSUMPTION Concern for the impact of new development on community water supplies, by and large, involves a consideration of quantities available and quantities consumed. In addition, problems of replenishment and salt water contamination are of concern for a small but growing number of communities. 1. Impact Measures Following are suggested measures for both the quantity and quality aspects of the problem: 58 Water Quantity 1. Change in the total duration and/or severity of expected shortages and the number of people af- fected. OR 2. Change in the likelihood of a water shortage and the number of people affected. Water Quality I. Change in the concentration of those drinking water constituents that are important to health and the number of people affected. 59 58. An alternative measure is "the amount of water to be con- sumed relative to the budgeted amount" where a budget has been prepared for the community. See Part 2. III. Section A for a more detailed discussion. 59. For a specification of drinking water standards, see HEW. Public Health Drinking Water Standards, Revised, (Washington. D.C.: Government Printing Office. 1962). The first measure of water quantity best expresses the various aspects of the impact on man and is thus preferred. Measure 2 is the fallback measure. It is based on a largely qualitative rating of "likelihood" and is thus much less difficult to use. The drinking water quality measure is quite similar to those suggested for water pollution. The concern here is for those health- or aesthetic- (color, odor, taste, clarity) related pollutants generated by the new development which may appear in the community or neighboring households' water supply, assuming the same level of purification. (Increased costs for purifi- cation necessitated by the development should be considered in its fiscal impact analysis.) 60 The dis- cussion of standards and their use which appears in the water pollution chapter applies here as well. 2. Measuring/Estimating Impacts on Storage and Yield Any analysis of impacts on water supply should consider existing and potential supplies. These are most conveniently divided into surface water and groundwater categories. a. Surface Water In many ways the estimation of water supply is analogous to flood prediction. In this case, though, the rare event to be predicted is low flow (or low vol- ume) rather than peak flow. Thus, the general discus- sion and many of the specific techniques for esti- mating flood events apply here as well. A river/reservoir system introduces a number of complicating factors, especially if the reservoir is used for purposes in addition to drinking water storage (e.g., flood control, irrigation, power genera- tion, recreation) and if flows in the drainage system are influenced by water rights. Detailed discussions of both conceptual and technical aspects of the problem can be found in selected Corps of Engineers publications and many hydrologic texts. 61 Where the probabilities of various low flows or storage volumes have been determined (i.e., the two, five, ten, fifty, 100, 500 year low flow/volume), the impacts can also be estimated probabilistically. The expected water use from the new development is added to the current use levels during the low flow 60. For a detailed discussion of the issues and methods involved in fiscal impact analysis, see Thomas Muller, Fisc al Impact Analy- sis (Washington, D.C.: The Urban Institute. 1975). 61. See, for example. Leo R. Beard, Methods for Determination of Safe Yield and Compensation Water from Storage Reservoirs, Technical Paper No. 3 (Davis, Calif.: Army Corps of Engineers. Hydrologic Engineering Center, 1965) and Linsley. Kohler, and Paulhus. op. cit. 78 Land Development and the Natural Environment period (obtained from the local water utility), and this new value is compared with the various low flows. The proposed development could then be said to cause a shortage during a five-year or greater low flow, for example (or a shortage with occurrence probability of 20 percent in any one year). Where adequate data on low flow frequency is not available or cannot be computed, qualitative descriptors such as "most likely" or "unlikely" will have to be used. The duration and severity of shortages would ap- pear to be more difficult to estimate. A rough esti- mate of duration could possibly be based on historical records of low flow duration for the various degrees of low flow. Severity could be expressed as the pos- sible consequences of a shortage (e.g., no lawn- sprinkling, no swimming in pools, rationing of drinking water). Local water utility personnel may have useful data if past shortages have occurred. The experience of other communities in similar situations may also be useful. b. Groundwater The problem here is conceptually the same as that for surface water. Total inflows, outflows, and storage should be estimated with and without the land development in question. More realistically, "safe yield" from an aquifer is measured against demand with and without the new development. "Safe yield" may be defined in several ways: 62 1. Maximum sustained yield — the maximum rate at which water can be withdrawn perennially from a particular source. 2. Permissive sustained yield — the maximum rate at which water can economically and legally be withdrawn perennially from a particular source for beneficial purposes without bringing about some undesired result, such as salt water intru- sion. 3. Maximum mining yield — the total volume of water in storage that can be extracted and uti- lized. 4. Permissive mining yield — the maximum volume of water in storage that can economically and legally be extracted and used for beneficial pur- poses, without bringing about some undesired result. Most communities are interested in maintaining "per- missive sustained yield," since this implies perpetual availability. Unfortunately, the calculation of permis- 62. American Society of Civil Engineers, Groundwater Basin Management, Manual of Engineering Service, No. 40 (Washing- ton. D.C.. 1961). sive sustained yield does not involve the simple com- parison of inflows with outflows, even assuming that the characteristics of all recharge and discharge areas and the total amount of withdrawal were known. The mechanisms of underground water transmission are numerous and complex, and without complete and detailed information on the local hydrologic regime estimates of the effects of additional withdrawal re- main of uncertain validity. 63 This is not to say that approximations cannot be and are not made. By tracing the relative changes in precipitation, groundwater level, total withdrawal (usually from well logs), and natural discharge (usually by factoring out the surface and interflow 64 contributions to stream flow records), estimates of permissive sustained yield can be made. 65 Due to the delayed response of groundwater systems and the re- sulting difficulty in ascertaining when permissive sus- tained yield has been exceeded, the accuracy of this approach is difficult to specify. Once the yield has been determined the impact of a proposed development is estimated by adding ex- pected new demand to current demand and com- paring the total to the estimated yield. However, since aquifer systems may be related to rainfall in a way that is difficult to understand, and since safe yield is difficult to determine, it is unlikely that the impact can be expressed in probabilistic terms, at least at this time. In addition to the consumptive demand created by the new development, its location with respect to groundwater recharge areas should also be consid- ered. These are areas where geologic structures allow precipitation to reach underground reservoirs. Most aquifers have rather extensive recharge areas, but for those confined by impermeable rock layers the areas of surface/underground communication may be lim- ited and must be protected from coverage by imper- meable materials. The local planner must depend on geologists from local, state, or federal agencies to conduct the requisite surveys of bedrock formations and overlying unconsolidated earth material from which the recharge areas can be mapped. 3. Measuring/Estimating Salt Water Intrusion Salt water movement into fresh water aquifers is a phenomenon which may occur in coastal areas due to 63. A brief description of an attempt to couple a surface water, an unsaturated zone, and a groundwater model appears in the sec- tion on water pollution. Part 2, 1(B). 64. "Interflow" is water which flows under but close to the sur- face and is not considered part of the groundwater. 65. See Patrick A. Domenico, Concepts and Models in Ground- water Hydrology (New York: McGraw-Hill, 1972). Water Quality and Quantity: Methodological Approaches 79 FIGURE 2-6 AN ILLUSTRATION OF SALTWATER INTRUSION Sea level / _ -7 Confining / material JiUUUlliUliilliiiillili^^ Seawater 7_-_-_-/p7 > wedge ! IllimiliiinilliUUiiiiiiiii ^^Fresh water Q Sea level / _j Seawater wedge Confining material .■■iiiummilillllUllllllii ^llll»HMIIIlljl^ lllllll llt|||ll lUi11 Fresh water (b) SOURCE: Adapted from Patrick A. Domenico. Concepts and Models in Groundwater Hydrology (New York: McGraw-Hill Inc.. 1972). (Used with permission of McGraw-Hill Book Co.) NOTE: The vertical shaft represents a well and Q. the withdrawal of fresh water. The height of freshwater in the well represents the pressure due to the freshwater in the aquifer. excessive fresh water withdrawal. This is illustrated in Figure 2-6. The Domenico text contains an excellent descrip- tion of the phenomenon and a discussion of various fluid dynamic-based methods of quantifying it. 66 A few examples of applications are also included, although a discussion of results is lacking. In the absence of information on the accuracy of specific analytical techniques, a qualitative approach is justified. Where the occurrence of intrusions has been observed it is safe to conclude that additional withdrawal will be exacerbating. However, the ef- fects may possibly be ameliorated if additional cor- rective measures are taken, such as: 67 1. A reduction or rearrangement of pumping pat- terns elsewhere. 2. Artificial fresh water recharge of the aquifer. 3. Establishment of a pumping trough along the coast, thus limiting the intrusion to the trough area. 4. Formation of a pressure ridge along the coast. 5. Construction of a subsurface barrier imper- miable to salt water. Details of these approaches can be found in the refer- ence cited. 66. Ibid. 67. H. O. Banks and R. C. Richter, "Sea Water Intrusion Into Groundwater Basins Bordering the California Coast and Inland Bays," Transactions of the American Geophxsical Union 34, (1953): 575-82. 80 Land Development and the Natural Environment III. CONCLUSIONS AND RECOMMENDATIONS A. PLANNING VERSUS PROJECT REVIEW The relationship between planning and project re- view has emerged as one of the key considerations in an impact evaluation program. Planning can greatly facilitate the evaluation of certain types of impacts re- sulting from individual developments. On the other hand, large-scale planning does not capture the idio- syncrasies of single projects, and the approximate re- lationships between impacts and development charac- teristics used to produce the plan may not be terribly accurate. These and other related points will now be elaborated on for each of the impact areas. For those hydrologic considerations which are rela- tively insensitive to development design character- istics (e.g., sewage generation) the planning approach is decidedly superior. The review at the proposal stage then becomes almost perfunctory — for ex- ample, does adequate treatment capacity exist? For water-related project outputs which are more sensi- tive to design features the ability to minimize hydro- logic impact through long-range planning is consider- ably reduced. Storm water runoff, for example, is a function of landscaping and retention facilities (e.g., ponds) as well as the extent of impervious ground cover and the degree of sewerization. Thus, it is diffi- cult to develop zoning classifications based on a single generalizable factor, such as impervious ground cover. A rather detailed site plan review is re- quired in order to ascertain the actual volume and rate of runoff for various types of storms. Impervious ground cover can be used, however, as an early warning indicator or target in comprehensive plans. That is, allowable degrees of "percent impervi- ous ground cover" can be specified for different areas within a watershed based on acceptable or desirable degrees of flooding. (One of the simpler stream flow techniques could be used for this purpose.) These val- ues can then be incorporated in comprehensive plans as targets. Once the target had been reached for an area the runoff-related problems in the vicinity would have to be investigated in greater detail, and develop- ment proposals would have to be carefully scrutinized on an individual basis before new development would be allowed. 1 A similar analysis for all hydrologic im- pact areas appears in Table 2-8. It is clear that the planning activities outlined for water pollution of surface waters (sewage, industrial effluents, and, to some extent, stormwater runoff) are being or will be assumed by the special area-wide planning organizations as established by the WPCA. Existing city, metropolitan area, or county planning agencies are expected to cooperate with these special planning organizations and to implement the plans developed. Although individual local governments are responsible for flood plain planning and control, the process is controlled by HUD through the Flood Disaster Protection Act. Development outside the 1. A pervasive problem which typically attends the application of land use controls is the lack of public authority to require detailed site plans from developers at the point of variance or rezoning re- quest. This argues strongly for the inclusion of quantifiable indica- tors in the general plan as the best way to control negative impacts. The higher the correlation between the indicator and the impact, the better. Thus, in the runoff example, "percent impervious ground cover" is superior to "housing density." 81 Table 2-8. LEVELS OF ANALYSIS APPLIED TO THE VARIOUS HYDROLOGIC IMPACT AREAS PLANNING PROJECT REVIEW Flooding Water pollution: Sewage Specification of allowable development intensity based on watershed characteristics and expressed in terms of general- izable indicators such as "percent impervious ground cover" and "percent of the area served by storm sewers" (1) Specification of allowable effluent volumes based on hy- drologic characteristics of receiving water body, uses to which it is subject, and degree of treatment to be used: (2) possible allocation of remaining volume to future land use categories Assessment of (I) ground cover and sewerization variables. (2) mitigating design features such as retention ponds, and (3) potential for localized flooding problems Assessment of available treatment capacity Same as for sewage plus specification of additional treatment levels of unusual pollutants Same as for sewage plus assessment of special processing facilities if appropriate Stormwater Specification of allowable development intensity based on runoff watershed characteristics and general runoff loadings for development types, again expressed in terms of general- izable indicators such as "percent impervious ground cover" Assessment of ( 1 ) ground cover variable. (2) mitigating design features such as retention ponds, and (3) planned management practices such as street cleaning Water con- Specification of maximum flow available for consumption sumption (and other uses) and possible allocation of remaining supply among future land use categories Assessment of (I) available supply and (2) localized problems such as salt water intrusions or reduced availability of water for those in immediate vicinity floodplain but within the watershed is not covered, however. Variance applications for locations within the flood plain must also be evaluated. In the area of water consumption, long-range planning is often con- ducted by the Corps of Engineers, especially if drinking water is provided by river regulation or im- poundment. It would thus appear that a complementary planning/project review system could be designed and implemented. Where planning is based on the specifi- cation of targets, reviews of individual projects could be significantly simplified. Most plans, of course, do not use the target con- cept. Even worse, some comprehensive plans have been developed with very little regard for the conse- quences of development to water quality and quan- tity. In these cases the local government may wish to evaluate these or other alternative plans for hydro- logic impacts. The impact measures we have suggested would seem to be applicable to this type of evaluation as well. In selecting techniques and methods to be used in computing values for the measures, we have tried to offer some general guidance. 2 To obtain target figures for use in comprehensive plans or to evaluate existing plans the simpler and presumably less accurate large- scale techniques are probably adequate. On the other 2. Additional assistance in writing requests for proposals and in negotiating with contractors for the use of water models can be found in Systems Control. Inc., op. cit. hand, where a watershed or other community subarea is being developed quite rapidly and potential conse- quences may be quite severe, it may be preferable in the long run to utilize a complex model to specify more accurate targets. For evaluations of individual developments the selection of simple versus complex methods should be based on the size of the develop- ment (or more accurately, the potential severity of its impacts) and the ultimate cost of evaluation. Even for very large developments, the cost of using com- plex, computer-assisted models may not be justified. However, their application to watershed-wide evaluations — in a planning analysis — may be justi- fied on the basis that the specification of accurate targets may greatly reduce the need for individual evaluations. Although we have not been able to provide suffi- cient cost data for the various methods reviewed, we have tried to indicate which techniques could be used on an "in-house" basis, which ones require computer support, which ones would probably necessitate the use of a consultant, and which ones are supported to some extent by the federal government through user services. B. SPECIFIC RECOMMENDATIONS AND CONCLUSIONS 1. Local governments should consider specifying runoff-, emission-, and water consumption- related "targets" in their land use or zoning S2 Land Development and the Natural Environment plans, based on analyses of flooding hazards, desired levels of water quality, and available water supply. At a minimum, evaluations of individual developments would simply estimate future levels of such things as imperviousness, emissions, and consumption associated with each development. These values would then be added to the running sum kept for all develop- ments and compared with the targets. 2. Where developments will cause targets to be ex- ceeded or where special localized problems are likely, (or simply as a check on the assumptions used in preparing the plan), detailed evaluations of individual proposals should be undertaken. 3. The detailed evaluations should utilize the pre- ferred measures suggested here (or similar ones) where possible, and the fallback measures at other times. In choosing between the measures, the potential magnitude of impact and the time and funding available for evaluation will prob- ably be the most important considerations. 4. A variety of both simple and complex tech- niques exist for establishing the relationships between land development and flooding/water quality on a watershed-wide basis (e.g., for spe- cifying targets). Calculations of surface water supply can be made with techniques similar to those used for flood hazard calculations. The more complex techniques are presumably more accurate than the simpler ones. 5. For conducting the detailed evaluations of indi- vidual developments the same watershed-wide techniques can be used. "Before and after" ef- fects are calculated by using the technique to es- timate flooding/water quality with and without the development. 6. Localized effects are estimated using detailed engineering procedures and/or experts in the appropriate disciplines. 7. Every technique reviewed needs additional veri- fication. Assessment of accuracy for most of the models has been based on theoretical consider- ations or on extremely limited validation. Water Quality and Quantity: Conclusions and Recommendations 83 PART 3 WILDLIFE AND VEGETATION I. INTRODUCTION AND BACKGROUND A. HUMAN WELFARE Although concern for the environmental effects of urbanization has frequently focused on air and water pollutants, public interest in other environmental- related problems has been increasing. We now recog- nize that many plant and animal species are facing national and global extinction at an alarming rate. On a more local scale, natural areas rich in common plant species and frequently providing habitat for large numbers of interesting forms of wildlife are rapidly disappearing. The concern here extends beyond first- hand experiences with wildlife and vegetation. Some people feel a moral commitment to furthering the ex- istence of all living things. In this sense the loss of any natural area or wildlife habitat is important, at least for those who hold these values. At the very least, the maintenance of natural life forms in devel- oped areas permits people to become better ac- quainted with natural processes which then places them in a better position to make decisions related to environmental matters. Although the primary subject of this part of the re- port is man's enjoyment of wildlife and vegetation and the way land development may affect the oppor- tunity for such enjoyment, we should not lose sight of the fact that the presence of natural areas is inti- mately related to air quality, water quality, flooding, and noise. On a local, regional, and even global scale, the extent and distribution of vegetated areas may have pronounced climatic effects which in turn will affect temperature, humidity, precipitation, and wind patterns. Vegetation may also help to cleanse air of certain pollutants and is known to have a significant effect on the quantity and quality of stormwater run- off. Certain types of plants may also serve as noise bar- riers. These and other roles which natural areas play in maintaining high levels of environmental quality are discussed further in other parts of this report. Estimating impacts on man's opportunity to enjoy wildlife and vegetation will consist in large part of es- timating how the abundance of various species will change. However, another important factor to con- sider is the value of this type of experience to the local population. In communities where residents value the nonmanmade environment highly this im- pact area should receive additional weight in deci- sions on land development. It must also be recog- nized, though, that some types of vegetation and wildlife in urban areas are undesirable or even a health hazard and that some people dislike many forms of natural life. 1 In these situations decision makers must face the unenviable task of balancing the desires of a subset of the current population with those of other subsets and with the interests of future populations. 1. See the results of an attitude survey conducted in Wa- terloo, Ontario, in Ann Dagg, "Reactions of People to Urban Wild- life," Proceedings of a Symposium on Wildlife in an Urbanizing Environment (Springfield. Mass.: Cooperative Extension Service, November 27-29, 1973) [hereafter cited as Proceedings of Sympo- sium on Wildlife}. 87 B. FUNDAMENTAL ECOLOGICAL PRINCIPLES 2 Ecology is most generally the study of the interre- lationships of organisms to one another and to the environment. All living organisms are seen as existing with their living and nonliving environments in a state of dynamic equilibrium, drawing from them suste- nance (food and water), shelter, and the opportunity for reproduction and, in turn, being used by other components of the system. Within this dynamic equi- librium structure each organism has a position or niche determined by the function it performs. The most common and important types of organisms are the following: food producers (green plants); plant eaters (herbivores); first and second level meat eaters (carnivores); plant and meat eaters (omnivores); para- sites; dead animal and plant eaters (scavengers); bac- teria, yeasts, molds, and fungi which decompose dead organic material into basic chemicals (decomposers); and microorganisms which convert nutrients into compounds usable by green plants (transformers). The complex set of interactions among the con- sumed and the consumers (sometimes known as the food web) can be characterized by the flow of nu- trients and energy. Nutrients (water, minerals, and organic compounds) are continuously recycled by an ecosystem. Energy flow, on the other hand, is pyra- midal. That is, the simple green plants which are the basic food producers are very efficient at converting the sun's energy into food. From this level on up the pyramid of prey and predator relationships there is a loss of useful energy at every step. By the time food reaches man at the top of the pyramid large quantities of energy have been used in its production. As a result of the interdependence of ecosystem components, plants and animals tend to associate in a complementary fashion. Thus, ecologists speak of associations (groups of species) and communities (groups of associations). The type of biotic commu- nity found in any area at any given point in time is de- pendent on soil, moisture, and climatic characteristics as well as the biotic history of the area (what lived there in the past). This leads to another fundamental ecological con- cept, that of succession. A biotic community changes over time, generally progressing toward an assem- blage of climax species. In theory, the climax life forms which occur under a given set of environmental conditions will remain, unless disturbed by outside influences. However, it is often difficult to predict 2. For further information see any standard text on ecology, such as. Robert L. Smith. Ecology and Field Biology (New York: Harper & Row, 1974). A less technical discussion of general envi- ronmental principles is contained in Kenneth E. F. Watt, Princi- ples of Environmental Science (New York: McGraw-Hill Book Company, 1973). which species will be present during the climax stage. In addition, climax associations are rarely observed, since succession is frequently interrupted by human intervention and such natural disturbances as floods, fires, droughts, and insect invasions. Tolerance and adaptation are other key concepts. Individual plant and animal species are known to tol- erate a range of environmental conditions. In some situations they have even been known to adapt to conditions far beyond the normal range. Ecologists usually characterize an ecosystem by such features as its productivity (i.e., the amount and rate of living matter or biomass produced), by the types and magnitudes of energy and chemical flows, and by the abundance and variety of plants and an- imals. Diversity is the term used to describe the latter and is generally considered to be the best indicator of ecosystem stability. A diverse ecosystem is one which can withstand numerous perturbations because many of its species are at least partially substitutable. Thus, elimination of certain components will not destroy the entire system. The implications of these principles for impact evaluation are several. First, the interconnectedness of the ecological system means that secondary and tertiary effects are the rule rather than the exception. What at first appears to be the rather innocuous pri- mary impact of land development (e.g., the mowing of fields or the dredging of a pond) may result in an unexpected and dramatic reduction or increase in a particular species (e.g., loss of field birds or water- fowl). A second but related point is that disturbances which affect organisms located near the bottom of the energy pyramid generally have far-reaching effects in terms of impact on other organisms. DDT is a case in point. Small organisms ingested and concentrated the chemical until levels toxic to susceptible bird species have been reached in insects and other prey. Thirdly, impacts should also be viewed as changes in the direction or rate of natural succession. In this sense, "environmental preservation" may be a mis- leading term. Lakes, for example, often become over- fertilized and fill in as part of natural processes, although the time scales are usually quite long. If the current lake condition is the desired state, then envi- ronmental manipulation may have to be undertaken. Developments which interfered with the natural pro- cesses of lake aging would then be considered to have favorable impacts. Finally, the response to a given disturbance should be estimated with regard to the ability of many species to adapt to new environments. Ideal and tolerable environments may differ substantially. Squirrels and raccoons are good examples of wild- 88 Land Development and the Natural Environment life species which have adapted quite well to man's presence. C. DEFINITIONS AND TERMS The following terms will be used throughout the re- mainder of the discussion: 1. Wildlife is a collective term which refers to all nondomestic animals of a size to be seen and appreciated by the public. We have extended the usual definition to include fish. 2. Open Spaces are areas of the natural or nonbuilt-up environment, including forests, grasslands, deserts, agricultural land, parks, lawns, and bodies of surface water (with empha- sis on their living constituents). 3. Natural Areas are open spaces which are rela- tively unmanaged. 4. Wildlife Habitats are areas which provide food, shelter, and general living space for wildlife. The term "natural area" is used here in a slightly more general way than it appears in some of the liter- ature. That is, "natural area" is used to designate any unmanaged "open space," regardless of quality, while elsewhere it frequently means a high-quality vegetated area of special scientific interest. On the other hand, "open space" usually includes manmade spaces as well as natural ones. Although "wildlife habitat" includes either open spaces or manmade environments which will support a wildlife popula- tion, the more desirable species are associated with open spaces. Wildlife and Vegetation: Introduction and Background 89 II. METHODOLOGICAL APPROACHES Although common and well-accepted techniques exist for characterizing existing natural areas and habitats, the estimation of impacts on wildlife and vegetation from proposed land development rests largely on inference. Simple techniques analogous to simple air or water pollution estimation models are not yet available. The explanation lies in man's lim- ited knowledge of a very complex subject. In addi- tion, standards (analogous to air and water quality standards) against which impact estimates could be gauged do not exist. Instead, the impacts are viewed in the context of how highly local residents (or in the case of rare and endangered species, state and na- tional citizens) value wildlife and vegetation. A. MEASURES AND INDICES Measures of impact on wildlife and vegetation should reflect changes in the amount and kind of veg- etation and wildlife added or lost. As indicated, quan- titative estimates of change are difficult to make. Consequently, a simpler alternative measure is suggested together with the preferred one: 1. Change in the relative abundance and variety of vegetation and wildlife expressed as: (a) change in the number(s) of rare or endangered species. (b) change in the population size and diversity of common species (number of species, amount of cover, and possibly a diversity index score). OR 2. Change in the extent and quality of vegetation (including the number of mature trees added or lost) and wildlife habitat (quality rating by an- imal type). The first measure most directly reflects the number of species added or lost and is thus preferred. Diver- sity and abundance are the key variables. 1 The sec- ond measure is obviously simpler and should be used where detailed surveys of vegetation and wildlife are not feasible. The change in extent is expressed as the number of acres of open space. The impact on wild- life is inferred from changes in the quantity of habitat of a given quality. The terms "quality" and "diversity" imply that rating scales and indices are to be considered. As with the pollution indices, these assessment schemes are designed to combine many factors into one or a few numerical scores. Unlike air and water pollution, however, there are no commonly accepted standards against which the scores can be compared. A more detailed discussion of rating scales and indices ap- pears in the following section. Communities should also consider measuring local residents' attitudes toward, and perceptions of, wild- life and vegetation. Questions on this subject could perhaps be included in a general survey of residents' 1. Other characteristics of vegetation can also be measured, such as cover (a product of abundance and massiveness), density, dominance (relative areal extent of various species), and productiv- ity (the rate of production of living matter). Diversity is probably a better indicator of changes which will affect the experience of ob- serving vegetation and wildlife. 91 perceptions and attitudes. For additional discussions of issues and methods of estimating citizen percep- tions in the context of a social impact analysis, see a companion report in this series. 2 A further consideration is the degree of public access to the areas affected. Total public access would imply that the "clientele group" is the commu- nity at large. However, accessibility is usually related to distance of residence from the area in question. It may thus be useful to identify those people within walking distance separately from those beyond for publicly accessible areas. For private areas the clien- tele group can be more accurately determined. Even for private areas, however, spillover affecting persons other than those with access to the area can occur. This is especially true for bird habitat areas or for pri- vate areas which are visible to a larger audience. Consideration should also be given to the way eval- uation results are presented to the decision makers. Analysis of impacts on open space readily lends itself to map presentation. "Before" and "after" develop- ment maps reflecting open space changes would ap- pear to communicate the information well. The loca- tion of natural areas could be identified on these maps together with their quality ratings (if the preferred measure is used). If species lists have been compiled, a tabular presentation of impact is probably most suit- able, as illustrated in Figure 3-1. B. MEASURING/ESTIMATING CURRENT CONDITIONS This section discusses ways to inventory predevel- opment conditions in and around the proposed devel- opment site. This is necessary in order to determine the amount and the quality of the resource to be im- pacted. Although the need to utilize experts in the various substantive areas throughout the impact evaluation process has been noted in other parts of this report, it is especially noteworthy in the areas of wildlife and vegetation. There is no substitute for expertise in identifying the various species of plants and animals. What follows, then, is a discussion of key factors which may suggest the type and degree of impact and, to a lesser extent, of techniques used by bi- ologists to characterize natural environments. The latter is included so that the reader may develop an appreciation for the detailed types of ecological anal- yses which are frequently required to develop quanti- tative estimates of impact. 2. K. Christensen. Estimating the Social Impacts of Land Development (Washington. D.C.: The Urban Institute, forthcom- ing). See also, Dagg. op. cit. 1. Vegetation Natural vegetation is important both as habitat for wildlife and as a resource itself. The latter, in turn, can be considered from a social/psychological perspective (i.e.. "open" space) and from an aesthetic/educational perspective (i.e., attractive or interesting combinations of vegetation). a. Assessment of Areal Extent Measuring the amount of open space is a straight- forward operation. Change in cover areas currently in a natural state are readily estimated, if all or most of the site is to be altered (e.g.. cleared or filled for home sites). Assessment of the current stock can be made from black and white or color aerial photos of the community and site in question. The segregation of open spaces into cover categories (forest, grass- land, water, etc.) should be performed at this point if this information is to be used in the actual evaluation. An inventory of mature trees at the site might also be taken if there are relatively few and an areal descrip- tion seems less appropriate. Sources of aerial photos include the National Aeronautics and Space Adminis- tration, the Soil Conservation Service and the Agri- cultural Stabilization and Conservation Service (U.S. Department of Agriculture), the U.S. Geolog- ical Survey (U.S. Department of the Interior), state departments of transportation, and private en- gineering/planning firms. Developers often obtain aerial photos for their own use, and these also may be available. In measuring the extent of open space from aerial photos, a simple planimeter (i.e.. an area measuring device) can be employed. Alternatively, a slightly more sophisticated and possibly more accurate point sampling approach can be used but is probably unnecessary unless open space is interspersed with developed areas. 3 b. Assessment of Vegetation Quality and Quantity A simple approach to the inventorying of natural areas is to use a quality rating scheme and data taken from aerial photos and/or obtained from brief field surveys. When available, color infrared photographs are especially useful, since the amount of infrared en- ergy reflected from leaf surfaces during each season provides information on the type and general charac- 3. Points are distributed over the photo according to a sampling design. The percentage of points falling on open spaces equals the percentage of land in open space in the community. See Brian J. L. Berry and Alan M. Baker, "Geographical Sampling. " in Brian J. L. Berry and Duane F. Marble. Spatial Analysis, (Englewood Cliffs. N.J.: Prentice-Hall. Inc.. 1968). 92 Land Development and the Natural Environment FIGURE 3-1 EXAMPLE FORMATS FOR THE PRESENTATION OF ESTIMATED IMPACTS ON SPECIES ABUNDANCE AND DIVERSITY NATURAL AREA "X" Species Present Abundance Future Abundance Diversity Trees Shrubs Grasses & sedges Aquatics Others (e.g., mosses, ferns, herbs, etc.) (Typical entry for one line) (Typical entry for one line) 150 individuals very numerous or covering 3 acres probably 25-50 indi viduals or sparse or covering 1/2 acre (Typical entry for entire column) Present Simpson diversity index score is approximately 20, future score is expected to be 10-15 (where 20 is "very diverse," 15 is "diverse," and 10 is "fairly diverse") 3 Many species with evenly distributed populations now, fewer species with more uneven distributions expected WILDLIFE HABITAT "V Species Present Abundance Future Abundance Diversity Birds (See above) (See above) (See above) Mammals Amphibians Reptiles Fish NOTE: It may be desirable to present impacts on terrestrial (land based) and aquatic habitats separately or to discuss the latter as part of the water quality analysis. a. Simpson's index is a mathematical expression of diversity. See footnote 8. teristics of vegetation. 4 The identification of types of vegetation (both from photos and brief field assess- ment) is based primarily on identifying certain indi- cator species. Where the area under investigation is small (e.g., one hundred acres or less), interpretation of aerial photos may be almost as time-consuming as field studies. Judgments of resource quality are based on the current general understanding of resource value, health, and degree of disturbance. Several rating schemes have been proposed for assessing the quality of natural areas. 5 In general, these are based on the following considerations: (a) The number of distinct plant communities. (b) The uniqueness of each plant community (in the locality/region/state/nation). (c) The presence of subareas which have been re- cently disturbed (e.g., by clear cutting, culti- vating or grazing, burning, bulldozing). (d) The accessibility of the area. Values for these factors can be presented sepa- rately or, as suggested in references in Footnotes 4 and 5, be combined in order to assign a rank or score to individual areas. Although the mathematical manip- ulations differ among the various schemes, higher scores are generally assigned to areas which (a) have a greater number of or rarer plant communities, (b) are undisturbed, and (c) are accessible. Relevant data sources on locally important* 5 plant communities can be obtained from local universities and park departments and from state departments of natural resources or their analogs. The latter should also be consulted regarding the regional and statewide scarcity of community types. A more detailed, more accurate analysis can be made using field surveys by trained observers. Through a sampling procedure the population of 4. For more information see Michael M. McCarthy. Richard A. Boots, and Bernard J. Niemann, Jr., 'Remote Sensing of Infrared Energy: Critical Data for Land-use Decision Makers," Landscape Architecture (January. 1973): 133-47: D. M. Carneggie and D. T. Laver, "Uses of Multiband Remote Sensing on Forest and Range Inventory," Photogrammeteria 21 (1966): 115-41; and Lewis M. Cowardin and Victor I. Myers, "Remote Sensing for Identification and Classification of Wetland Vegetation," Journal of Wildlife Management 38 (April. 1974): 308-14. 5. See, for example. Peter A. Isaacson, "Aquatic and Terrestrial Consideration in Power Plant Siting" (Albany: Office of Environ- mental Planning, State Department of Public Service. 1974): Ber- nard J. Niemann, et al.. Recommendations for a Critical Resource Information Program (CRIP) for Wisconsin. Phase III Report. (Madison: Institute for Environmental Studies, University of Wis- consin, February, 1974); and William Tans. "Priority Ranking of Biotic Natural Areas." The Michigan Botanist 13 (1974): 31-39. 6. Important plant communities are not necessarily rare. Impor- tance refers as well to representativeness, quality, robustness, and aesthetic qualities. plants by species, species within plant communities, and communities within the area can be ascertained. This information can be used to either refine the simple quality assessment previously discussed or to provide baseline data for quantitatively estimating the impact of land development on species' abundance and diversity. Field surveys can also provide data on the presence of rare or endangered species. Their presence would obviously increase the quality rating. If the results of the field investigations are to be used for quantitative estimates of diversity, then a suitable diversity expression should be used. 7 The concept of diversity encompasses (a) the number of species in a community, and (b) the distribution of individuals among the species present. The greater the number of species and the more equal the distri- bution of individuals among the species, the higher the diversity. Although the number of individuals and species can be used alone, it may be useful to employ a mathematical expression which combines both ele- ments. 8 For areas with more than one plant commu- nity the diversity scores for the individual communi- ties can be summed. Since the diversity index scores have little meaning by themselves (and indeed can be misleading if popu- lation sizes are not also specified), it would be useful to "calibrate" the index by applying it to a variety of natural areas in the local community. Subjective ratings of diversity by a trained observer could then be compared with the index score for each area so that a reference scale relating the two could be developed. c. Methods of Field Measurement Various standard methods of recording the pres- ence of plants and measuring their various character- 7. A useful scheme for organizing the results of a field study is as follows: trees, shrubs, vines, grasses and sedges, aquatic vegeta- tion, and others (e.g.. herbs, mosses, ferns, lichens). 8. A number of diversity expressions have been developed. See, for example, Isaacson, op. cit.; C. E. Schannon and W. Weiner, The Mathematical Theory of Communication (Urbana: University of Illinois Press. 1963); and M. O. Hill, "Diversity and Evenness: A Unifying Notion and its Consequences." Ecology 54 (1973): 427-32. One of the simplest is Simpson s Index (E. H. Simpson, "Measurement of Diversity," Nature 163 [1949]: 688): _ N(N - 1) U M 2 n.45dB Urban residential (indoors) Speech interruption indoors (interruptions of normal conversations at distances up to 2 meters) >55B Urban residential (outdoors) Speech interruption outdoors (interruption of normal conversations at distances up to 2 meters) >60dB Urban residential and residential near airport (outdoors) Average community reaction: Complaints and threats of legal action >70dB Industrial settings (indoors) and very noisy urban residential (outdoors) Hearing loss a. These thresholds are based on the summary findings of the Environmental Protection Agency in Information on Levels of Environ- mental Noise . . . (Washington, D.C.: EPA, March, 1974). b. These noise levels are approximations and may be subject to change given variations in such factors as the frequency of noise and the intermittency of occurrence. These are outdoor day-night noise level averages, or average levels for twenty-four hour periods with night noise given increased weighting due to its sleep interruption characteristics. See p. 1 1 1 for a further discussion. 106 Land Development and the Natural Environment FIGURE 4-1 LOUDNESS RANGE OF COMMON SOUNDS (Measured at Source or Indicated Distance) Sound Source Carrier Deck Jet Operation Jet Takeoff (200 feet) Discotheque Auto Horn (3 feet) Riveting Machine Jet Takeoff (2000 feet) Shout (0.5 feet) N.Y. Subway Station Heavy Truck (50 feet) Pneumatic Drill (50 feet) Freight Train (50 feet) Freeway Traffic (50 feet) Air Conditioning Unit (20 feet) Light Auto Traffic (50 feet) Living room Bedroom Library Soft Whisper (15 feet) Broadcasting Studio (background level) Response Criteria Painfully Loud 130 Limits Amplified Speech 120 Maximum Vocal Effort 110 100 Very Annoying --90 Hearing Damage (8 hours) 80 Annoying 70 Telephone Use Difficult Intrusive 60 -- 50 Quiet 40 30 Very Quiet 20 10 Just Audible Threshold of Hearing the source and the point in question, and character- istics of both the intervening land and atmosphere. Noise attenuates in amplitude exponentially with dis- tance. A doubling in distance will reduce the ampli- tude by a factor of four, everything else held con- stant. Additional attenuation can be accomplished by wind and temperature fluctuations and by the pres- ence of vegetation "screens" and physical barriers. 8 The latter two are by far the most important factors. The degree of attenuation will depend on the size, type, and location of the screen or barrier with respect to the source and receiver. For example, tall trees with many branches and thick foliage are quite effective in reducing sound levels. Reverberation from reflecting surfaces, such as highrise buildings found in many central cities, repre- sents a complicating factor. Any method used to esti- mate noise levels in these locations should be care- fully calibrated in order to account for these effects. 8. For further information on atmospheric effects, see B. A. Kugler and A. C. Piersol, Highway Noise — A Field Evaluation of Traffic Noise Reduction Measures, NCHRP Report No. 144 (Washington. D.C.: Federal Highway Administration. Highway Research Board. 1973). For further information on vegetation and barrier effects, see B. K. Huang. An Ecological Systems Approach to Community Noise Abatement — Phase I (Raleigh: North Caro- lina State University. June. 1974) (NTIS No. PB 234-311). SOURCE: Council on Environmental Quality. Environmental Quality, The First Annual Report (Washington. D.C.: CEQ. August, 1970). Noise: Introduction and Background 107 II. METHODOLOGICAL APPROACHES A. MEASURES, STANDARDS, AND INDICES The suggested measure of noise impact is as follows: 1. Change in the level of noise, the frequency with which it occurs, and the number of people af- fected in the area surrounding the development. Estimates of noise levels and frequencies of occur- rence produced by proposed developments could be based on analogies to other similar developments (and in similar settings) or on detailed calculations of noise sources and the subsequent propagations of sound into surrounding areas. Since the suggested measure requires an estimation of the number of peo- ple affected, noise levels should be estimated for a variety of locations around the development. Noise is a multifaceted problem which resists re- duction to a few simple rules of thumb. Nevertheless, the EPA has attempted to relate hearing damage and activity interference to levels of exterior and interior noise. 1 Although the recommended standards do not represent inviolable breakpoints, they can and should be used as points of reference. 2 The Swedish National Board of Urban Planning has also specified interior and exterior standards for various types of structures, while the Federal Highway Administration (FHWA) has developed design guidelines which contain stan- 1. EPA, Information on Levels of Environmental Noise. . . ■ 2. EPA refers to these standards as "guidelines"' since they are not legally binding. dards for different types of land uses. 3 HUD has is- sued standards applicable to outdoor noise for HUD- sponsored residential developments. 4 Table 4-2 lists standards suggested by still others. One of the basic problems in developing standards is to capture the most significant aspects of noise variability: pitch, magnitude, frequency of occur- rence, compatibility. Reference has already been made to the dBA scale, which reflects both pitch and magnitude. Some sets of standards (e.g., the FHWA guidelines) are specified directly in terms of the dBA scale. In order to capture frequency of occurrence, standards are typically specified in terms of L 10 — the level which is exceeded 10 percent of the time. 5 This is true for the FHWA guideline. The HUD Standards are in terms of L 33 and L 4 . The EPA standards, on the other hand, refer to L eq values. This is a scale which expresses patterns of intermittent noise as equivalent constant-level noise. L eq is thus dependent on the dis- tribution of noise levels over time and can be easily converted to L 10 values. 6 The compatibility factor has 3. Sten Ljunggun. A Design Guide for Road Traffic Noise (Stockholm: National Swedish Building Research, 1973) (NTIS No. PB-227-258); and Federal Highway Administration. Interim Noise Standards and Procedures for Implementing Section 109(i) of Title 23, U.S.C.. FHWA PPM 90-2 (Washington. D.C.. n.d.). 4. HUD, (1390.2 chp. 1). 5. Similarly. L 50 and L s0 are levels which are exceeded 50 and 90 percent of the time, respectively. 6. In order to translate L eq to L 10 values, the distribution of noise levels over time and the standard deviation of this distribution must be known. See EPA, Information on Levels of Environmental Noise. . . . 109 5 s 25 35-45 25 35-45 35-50 35-50 : 2 r ss I n 2 9 a Hi s s I 3 I I = 3 t t c c nn SS 3 55 42-52 38-47 50 42-52 60 si ill a 3 1121 mi ni R S III g s s il 30-40 40-50 35-45 I 33 R P s 3 R 3 1 I 5 lA lii P lid r s 5 ss nil" a i HUH s 'I urn i i sii is ft huh nil" i HUH 1 ll \\im\\i\i\ till Land Development and the Natural Environment been used in designing still another scale of noise levels — L dn . This is basically a day-night or 24-hour Lgq scale with nighttime noises weighted more heavily to reflect their intrusive nature. Additional indices which attempt to integrate the various noise considerations in other ways include Table 4-3. TABULAR PRESENTATION OF NOISE IMPACTS FOR A HYPOTHETICAL DEVELOPMENT 3 Table 4-4. APPROXIMATE NOISE LEVELS FOR CONSTRUCTION EQUIPMENT NUMBER OF RESIDENTS EXPOSED b NOISE LEVEL (L 10 in dBA) >65 55-65 45-55 <45 Local standards: >65 — clearly unacceptable 55-65 — potentially unacceptable 45-55 — normally acceptable <45 — clearly acceptable a. Another table should be prepared showing the levels to which the population groups are currently exposed. Changes in the num- ber of people exposed to the various levels could then be calculated. b. Socioeconomic and demographic data can be obtained from the census. Supplemental information on individual units such as nursing homes can be used to further refine the population distri- bution data. the Community Noise Equivalent Level (CNEL), the Composite Noise Rating Method (CNR), the Noise Exposure Forecast (NEF), and the Noise Pollution Level (NPL) 7 . Although any one of these indices may be best suited for a given situation, they tend to cor- relate well with one another. They can also be readily translated into L eq values. 8 A local government may well desire to use different standards in different parts of the community. Citi- zens presumably desire quieter residential than work- ing or shopping environments. Determining the ap- propriate standards, however, is not a trivial task. Eliciting preferences, assigning levels of accept- ability, and translating these into statistical values for noise levels require a considerable survey effort. Regardless of which standards or categories of acceptability are used, a map format becomes ex- tremely useful for an intermediate, if not a final, display of information. If estimates are made for enough geographical points (perhaps fifty. 100. 200, and 300 feet back from the roadway and every 100 feet along the roadway), then 7. For further information, see ibid.; and Bolt. Beranek, and Newman, Inc., Noise Assessment Guidelines, Technical Back- ground, No. TE/NA 172 (Washington. D.C.: HUD. n.d.). 8. See EPA, Information on Levels of Environmental Noise .... for specific instructions. TYPE OF EQUIPMENT TYPICAL SOUND LEVEL dBA AT 50 FT. Dump truck Portable air compressors Concrete mixer (truck) Jackhammer Scraper Dozer Paver Generator Piledriver Rock drill Pump Pneumatic tools Backhoe 87 89 70 101 98 76 85 85 SOURCE: Federal Register 39 (121) (June 21, 1974): 22298. noise contour lines can be interpolated. By over- laying these on maps showing population by block or some other spatial unit, approximate values for the number of people exposed to various levels of noise can be obtained. Figure 4-2 illustrates a pop- ulation and noise distribution map. Once these values for both the "with" and "without development" situations have been ob- tained from such a map overlay process, they could be displayed in a tabular format, as illustrated in Table 4-3. It may also be desirable to indicate the impact on especially susceptible population groups (e.g., older persons, persons living in poorly insulated homes, or, from an equity perspective, disadvantaged groups), as shown. At a minimum, the location of noise sensitive activities or facilities, such as schools and hospitals, should be noted in the map presenta- tion. B. ANALYTICAL TECHNIQUES A new development will generate noise in several different ways. Depending on the type and number of buildings constructed and the degree of terrain mod- ification required, significantly high construction- related noise levels may be attained. After occu- pancy, commercial and residential developments will produce transportation-related noise. Industrial de- velopments will also produce various on-site noises specific to each type of industry. 1. Construction-Related The degree to which objectionable levels of noise will be produced during the construction stage is largely dependent on the type of equipment and machinery to be used. Table 4-4 presents average Noise: Methodological Approaches l l l FIGURE 4-2 MAP PRESENTATION OF NOISE IMPACTS FOR A HYPOTHETICAL DEVELOPMENT" 55 dBA 65 dBA Local standards (based on a survey): >65 — clearly unacceptable 55-65 — potentially unacceptable 45-55 — normally acceptable <45— clearly acceptable a. This displays the estimates for noise levels with the proposed development. A similar map should be prepared for the existing condi- tions so that the change in noise levels can be calculated. For this example, the loudness (dBA) estimates are given at the L 10 levels. b. The residents are assumed to be evenly distributed throughout each spatial unit (e.g.. the block or block group). noise levels for various types of construction equip- ment at a distance of fifty feet. Rough estimates of total noise generated by the construction of a pro- posed development could be made simply by esti- mating the number and different types of machinery required and adding the noise generated by those that will be used at the same time. 9 The estimates should reflect changes in noise by time of day and by phase 9. The noise produced by several sources is calculated by adding the sound pressure levels rather than the decibels. Thus, two cranes each producing 80 dBA of noise would produce 83. not 160 dBA. together. 112 Land Development and the Natural Environment of construction. (The duration of each construction phase should also be noted.) Estimates for distances other than fifty feet can be made, based on the fact that sound pressure changes exponentially with a change in distance from the source. 10 The effects of terrain, barriers, and possibly meteorology can be sim- ulated according to techniques found in references cited in the next section. 2. Transportation-Related The discussion here will be limited to vehicular traffic. Noise from aircraft and trains is covered in numerous other sources. 11 Residential, commercial, and industrial developments will all cause an increase in traffic at least on the surrounding streets, if not on a significant portion of the entire road network. The degree of impact will be determined by the type and number of vehicles added (by time of day), the average speed and ■'stop-and-go'* nature of the trips, the physical characteristics of the streets (e.g.. eleva- tion, grade, natural or manmade barriers), and the distance from source to receptor. The noise levels once the development has been constructed are then the sum of existing levels and the increment added by the development. 12 Besides data on traffic generation, information on population distribution is needed to select the points where estimates should be made and to specify the number of people affected. For residential popula- tions the census provides population data on a census tract, block group, and individual block basis. (In most cases the smaller units will allow more accurate estimates.) Population dot maps would also prove useful if they are available on a large-map scale. For daytime nonresidential populations local transpor- tation studies of trip origins and destinations are a po- tential source of information. Rarely, however, is the data available for small areas. (Traffic zones are usually a square mile or more.) Planning departments or assessment offices may have data on office and re- 10. Mathematically, the relationship is: where: P, = pressure level at distance "1" P 2 = pressure level at distance "2" d, = distance "1" d 2 = distance "2" This translates into an approximate decrease of 6 decibels with a doubling of distance. 11. See. for example. Bolt. Beranek. and Newman. Inc.. op. cit. 12. For a discussion of methods for estimating traffic levels as- sociated with proposed developments, see the chapter on transpor- tation in P. Schaenman. D. Keyes. K. Christensen. Estimating the Impacts from Land Developments on Public Senices (Washing- ton. D.C.: The Urban Institute, forthcoming). Noise: Methodological Approaches tail space for smaller areas which could be used to supplement the transportation data. a. Specific Examples The available techniques for making transportation- related noise estimations range from simple approxi- mation based on the use of tables and graphs to rather complex computer models. Three of the more promis- ing and/or popular of these techniques will be dis- cussed. HUD Noise Assessment Guidelines — Bolt. Bera- nek, and Newman. Inc. have developed a set of simple procedures to estimate the suitability of poten- tial settings for proposed HUD-sponsored develop- ments. 13 That is. proposed sites are rated for their current acceptability, based on noise emanating from the surrounding environment. For estimating noise impacts from a development on the community, the same procedures can be used, but at several geo- graphic points. Although the guidelines deal with aircraft and railroad as well as with automobile and truck noise, our concern is largely with the lat- ter two. In order to use the guidelines the following must be specified: 1. The mix of cars and trucks. 2. The average flow (number per hour) and speed of the vehicles. 3. Whether the flow is continuous or "stop and go." 4. The road grade (i.e., percent slope). 5. The existence and position of large reflective barriers (e.g.. billboards, buildings). 6. The distance from each of the street lanes to the geographic points where estimates are desired. The noise levels are then estimated by using a series of nomographs and charts. The impact due to the new development would thus be based on the ad- ditional number and type of vehicles generated, their effect on traffic speeds and volumes, and changes to noise barriers. 14 In order to estimate the total impact on the community estimates should be made for a number of points at various distances along each side of every street affected, with the points chosen to re- flect the distribution of population and the location of especially sensitive facilities, such as hospitals. The results are expressed as one of four levels of acceptability (from clearly acceptable to clearly unac- 13. Bolt. Beranek. and Newman. Inc.. op. cit. 14. The development may also reduce noise levels by adding barriers or other sound dampening devices. 113 ceptable), rather than in terms of decibels. Thus, the HUD standards are built-in. If desired, the levels of acceptability can be adjusted to reflect local stan- dards. A modification of this type is presumably a straightforward operation. However, we know of no one who has attempted it. 15 Unfortunately, no data on accuracy are provided in the user manual or supporting document. The only re- lated notation that does appear concerns the fact that the technique does not estimate noise levels from more than one source very well. This lack of infor- mation on accuracy levels detracts considerably from what otherwise appears to be an extremely simple ap- proach to noise estimation. TSC Methods — Two versions of a technique for es- timating highway-associated noise have been devel- oped by the FHWA's Transportation Systems Center (TSC). 16 Similar to the HUD guidelines, the simple version of the technique specifies parameters which characterize the traffic and the environment, with es- timates being derived from nomographs. However, fewer parameters are used and thus the results are less sensitive to variations in traffic and other vari- ables. The effects of "stop-and-go" flow and street grade are ignored. As with the HUD guidelines, the impact from a development would be described by estimating the noise levels at numerous locations on either side of each street where significant additions to traffic vol- umes are expected. The actual number of estimates required depends on initial results (i.e.. low estimates near the street eliminate the need to estimate levels at greater distances) and the uniformity of the environ- mental and street characteristics. The results of the simple version are L 10 values and are reported to be within 3 dBA of measured values. 17 However, validation experiments for the presumably more accurate complex version (discussed below and in the Summary and Comparison section) would indi- cate that this is an overstatement of accuracy. The more complex version allows a greater number of input variables to be used (and thus allows for a more detailed description of the area), produces esti- mates in terms of various statistical measures (e.g.. L 50 . L 1() ) and indices (e.g.. Noise Pollution Level), and increases very little in cost as the number of points at which estimates are to be made increases. 15. The acceptability categories can be related to statistical ex- pressions of noise levels (dBA) in a general way from Figure 29 in Bolt. Beranck. and Newman. Inc.. op. cit. This graph plus those found in Part 4 of this report provide the basis for recalibration to locally determined levels of acceptability. 16. J. E. Wesler. Manual for Highway Noise Prediction (Cam- bridge, Mass.: DOT, TSC. March. 1972) (NT1S No. PB 226088). 17. Ibid. The model is sensitive to such factors as the noise spectrum 18 of different types of vehicles, the heights of the source and the receptor, and various types of ground cover (trees, shrubs, high grass), as well as to the variables used as input to the simple version. Thus, the results should be more accurate than those produced by the simple version. Validation experi- ments, however, indicate that the accuracy even of the more complex version is disappointing. (See the Summary and Comparison section.) NCHRP Report 117 Method— Bolt, Beranek, and Newman, Inc., as part of the National Cooperative Highway Research Program (NCHRP), have devel- oped a guide to be used by highway engineers in de- signing highways for noise minimization. 19 Much of the input data and many of the relationships under- lying the calculations are the same as those for the HUD noise guidelines. In this case, however, the technique was designed to estimate impacts of in- creased traffic levels due to a proposed development at selected sights in the surrounding neighborhoods rather than existing noise from the neighborhood at a proposed site for development. The analysis involves the use of charts and tables to relate the input values to levels of noise at each point specified, a new analysis being required for each point. One relevant application of this technique was the analysis of noise impacts from increased traffic levels due to new high-rise office buildings in San Francisco. 20 A discussion of the advantages and disadvantages from this and other applications ap- pears in the Summary and Comparison section. Other Techniques — Since the degree of roadway, traffic, and environmental characterizations neces- sary to make accurate noise-level estimates tends to be necessarily large and to involve numerous calcula- tions, several efforts are now underway to develop computer models of noise generation and propaga- tion. One such model, albeit a relatively crude one — the TSC model — has already been discussed. Another promising but as yet unverified example is the Noise-Environment-Ecology System Model under development at North Carolina State University. 21 Approximately the same level of detail is required for 18. The noise spectrum is the relative magnitude of noise pro- duced at various pitches or frequencies. The spectrum of new ve- hicles can presumably be altered in such a fashion that those noises which are irritating to man are reduced. 19. C. G. Gordon et al.. Highway Noise — A Design Guide for Highway Engineers. NCHRP Report 117 (Washington, D.C.: Highway Research Board. 1971). 20. David M. Dornbusch & Co., Inc., Intensive Commercial and Residential Development Impact Study, San Francisco. Phase I Report (San Francisco: Dornbusch & Company, Inc., n.d.). 21. Huang, op. cit. 114 Land Development and the Natural Environment descriptive data on roadway and traffic character- istics, but the required descriptions of factors af- fecting propagation are much more refined. The latter include the type and density of grass, shrub, and tree zones, atmospheric temperature and pressure, and wind patterns. The computations are based on rela- tionships derived from extensive field studies on the effect of these factors on propagation of sound. Noise levels can be expressed as h 10 , L 50 , Lgo and Noise Po- lution Level values, each of which in turn can be plotted as isopleths on maps of the area under inves- tigation. 22 Although the cost of operation is unre- ported and the accuracy of the results remains to be determined, the model seems promising. b. Summary and Comparison Three operational techniques for estimating the noise impact of increased traffic have been described. The key considerations from an application perspec- tive are the relative cost and accuracy of these tech- niques. Perhaps the simplest measure of accuracy is the difference between estimates from observed values under a variety of field conditions. Table 4-5 shows the results of several such experiments by an inde- pendent organization. As shown, the NCHRP 117 Method proved to be considerably more accurate than the computerized version of the TSC Method (average deviation of 1.8 versus 7.2 dBA), 23 although the investigators report that the TSC model was 22. Isopleths are lines connecting points of equal values. 23. The reader should recall that noise is perceived to double with a 10 dBA increase. An error factor of ± 7.2 could easily make a difference between acceptable and unacceptable levels if the esti- mate is close to a threshold. Table 4-5. COMPARISON OF PREDICTED AND ACTUAL NOISE LEVELS AT SELECTED SITES PREDICTIVE TECHNIQUES MEASURED TSC NCHRP 117 SITE 3 DISTANCE dBA dBA DIFF. dBA DIFF. 1 50' 77.1 80.3 +3.2 79.0 + 1.9 100' 74.7 78.7 +4.0 74.9 + 0.2 200' 71.3 76.5 + 5.2 69.6 -1.7 2 50' 71.4 76.7 +5.3 74.4 + 3.0 100' 65.4 75.0 + 9.6 71.1 + 5.7 200' 58.4 67.9 +9.5 60.0 + 1.6 400' 55.4 67.6 + 12.2 57.1 + 1.7 3 50' 74.6 79.4 +4.8 76.7 + 2.1 100' 68.5 75.8 +7.3 70.7 +2.2 200' 64.8 73.7 +8.9 66.4 + 1.6 400' 60.6 70.9 + 10.3 60.6 4 50' 75.5 80.1 +4.6 78.5 + 3.0 100' 72.0 77.8 +5.8 73.5 + 1.5 200' 68.4 75.0 +6.6 68.4 400' 59.5 70.8 + 11.3 61.5 + 2.0 SOURCE: E. W. Babin, Highway Noise Study (Baton Rouge. Loui- siana: Louisiana Department of Highways, Research and Develop- ment Section, May. 1974). a. Sites are various highways. better adapted to making large numbers of estimates and to situations where roadway geometries became more complicated (e.g., interchanges). Additional val- idation studies of NCHRP 1 17 produced deviations ±3 dBA or less for observed versus estimated reduc- tions in noise levels due to barriers. 24 However, the best-drawn line through plots of observed versus esti- 24. The reductions were due to physical shields and to roadway configurations. Kugler and Piersol, op. cit. Table 4-6. SUMMARY OF THREE NOISE ESTIMATION TECHNIQUES TECHNIQUE Ol'TPIT COST ACCURACY COMMENTS HUD noise assessment guidelines Noise level as one of four acceptability categories Inexpensive, although repeated appli- cations are tedious (a new calculation is required for each point for which an estimate is desired) Unreported This is an extremely simple technique whose utility is limited by the unknown accuracy and the already interpreted nature of the estimates. TSC method L 10 for the manual ver- sion; L 10 , L 50 , Lso, "noise pollution level" for the more computer- ized version Same as for the HUD guidelines (for the manual version); more expensive for the computerized version but to an undetermined degree Suspect for the The manual version should be used only simple version , a for very rough approximations; the corn- fair for the puterized version is probably better than computerized the NCHRP 117 method only for corn- version plex roadway configurations. Neither version of TSC is applicable to stop- and-go traffic. NCHRP 117 L 10 , L 50 , Lgo, "noise pollution level" Inexpensive, although the computa- tions are not as quickly performed as with the HUD guidelines Good This appears to be the most widely applicable of the three methods reviewed here. a. The accuracy should be less than that for the computerized version but was reported to be fairly good by one investigator. Noise: Methodological Approaches 115 mated values often deviated significantly from the ideal 45° line. 25 The authors of the study report that, in general, the NCHRP 117 method tends to overpre- dict reduction in noise levels due to barriers at points distant from the roadway and to underpredict reduc- tions for trucks. No validation efforts have been re- ported for the HUD guidelines. Information from these and other sources is used to summarize the three methods in Table 4-6. NCHRP 25. If on the average the observed and estimated values were equal, then a line drawn through plotted points would be at a 45° angle to each axis. 1 17 would appear to be the most accurate but TSC (computerized version) the most practical for impact evaluation where large numbers of estimates are needed. If the TSC method is used, the analyst should anticipate a consistent pattern of overpredic- tions for continuous traffic and unknown accuracies for stop-and-go traffic. 26 Regardless of which tech- nique is employed accuracies should be determined locally, since the reported accuracies are only for a limited range of conditions. 26. Stop and go traffic tends to produce louder but more inter- mittent noise levels than continuous traffic of the same speed. 116 Land Development and the Natural Environment III. CONCLUSIONS AND RECOMMENDATIONS Much has already been said, either implicitly or explicitly, about the utilization of measures and tech- niques for estimating noise impacts. This chapter will attempt to tie together some loose ends and offer fur- ther guidance to those in local governments responsi- ble for impact evaluation. A. PLANNING VERSUS PROJECT REVIEW Unlike the situation for many of the other types of impact, advanced planning does not appear to offer great potential for impact mitigation in the case of noise. Of course, some areas will be more or less pre- disposed to noise problems owing to topographical features or vegetative cover, and planners can encourage the segregation of noise-producing activi- ties. In general, downtown areas will be noisier than mixed central city residential/commercial areas, which will be noisier than suburban residential areas, which will be noisier than rural areas. Noise mitiga- tion thus lies primarily in source controls and project design. Impact evaluations of individual developments can be used to (1) assess the seriousness of the additional increment added by the development (perhaps by ref- erence to some set of standards), and (2) determine the effect of special design features used to reduce noise levels (e.g., physical barriers or trees). Baseline noise studies (not necessarily part of a planning activ- ity) can be used to identify those areas where noise is either currently a severe problem or where noise is an increasing but not yet severe problem (and thus where the impact of new development should be care- fully evaluated). Quiet areas can also be identified for the purpose of preservation, if this is desired. It is worth reemphasizing that in the process of deter- mining problem areas communities may wish to use different standards, or "targets," in different areas. B. SPECIFIC RECOMMENDATIONS AND CONCLUSIONS Following are recommendations and conclusions regarding the estimation of noise impacts from land development: 1. Local governments should consider using im- pact measures similar to the ones suggested here. Where practical, they should be quantita- tive and reflect the number of people affected. 2. Standards should be used to interpret the esti- mated noise levels. Standards suggested by various experts (such as the EPA standards) can be employed for the purpose, although commu- nities may wish to establish their own levels of acceptability, based on surveys of the local resi- dents. Different areas of the community may thus have different standards. 3. Success in reducing noise or in maintaining low levels will probably depend on the incorporation of barriers, buffer zones, and other noise- abating features in the project design. 4. Analytical techniques appear to be available for use in quantitatively estimating noise impacts. 5. Much remains to be done in the area of tech- nique development and validation. 117 PART 5 OTHER TYPES OF IMPACT: NATURAL DISASTERS AND SCARCE RESOURCE PREEMPTION I. INTRODUCTION Although the discussions in the preceding parts of this report have been wide-ranging, a few topics have not been covered fully or have been left untouched. Among the many types of natural disasters, for in- stance, only floods have been mentioned thus far. (See Part 2.) As for topics not yet broached, problems associated with the substitution of development uses for other types of land use is an obvious candidate for discussion. Hence, this part of the report deals with natural disasters and scarce resource preemption. The man- ner in which new developments may (a) create dis- aster hazards for the occupants or other commu- nity residents, or (b) preclude other valuable uses of the land will be highlighted. Key considerations for impact evaluation will be noted. Since many of the salient issues have been discussed elsewhere, the treatment here will be of a summary and reference nature. The relatively superficial treatment given these topics compared to other impact areas in this report should not be misinterpreted. Natural disasters and scarce resource preemption are extremely serious problems for specific communities. But the quantita- tive methods for evaluating the impacts occurring to or caused by land development is generally less ad- vanced for these types of impacts. In addition, what we do know about impact estimation is reasonably well documented elsewhere, although this informa- tion is contained in many diverse documents. We have elected to highlight key considerations and ref- erence primary sources of information. 121 II. NATURAL DISASTERS OTHER THAN FLOODS In spite of improvements in our understanding of natural processes and in our technical ability to cir- cumvent undesirable events, man still is seriously af- fected by natural disasters, such as earthquakes and landslides. Many developments are built in or near hazardous areas in the absence of clear identification of the risks involved. Whether to allow development of land when the risks are known is another matter left to local or higher governmental judgment. The reader should also keep in mind that the subject of this report — estimating the impacts associated with land development — is but one small aspect of a com- prehensive disaster prevention program. 1 The factors which lead to natural disasters are often localized geographically. Earthquakes occur near fault lines; landslides in areas of steep, unstable slopes; forest fires on forested land. In order to esti- mate damage to future inhabitants (and thus to reduce the potential monetary impact on the population as a whole), the hazard potential in the locality of the pro- posed development should be evaluated. Impact measures for any type of disaster can be patterned after that suggested for flooding: Change in the likelihood of the disaster and the number of people and the value of the property endangered. 1. For a discussion of key issues involved in the design of disaster prevention and relief programs, see Gilbert F. White and J. Eugene Haas, Assessment of Research on Natural Hazards (Cam- bridge, Mass.: The MIT Press, 1975) and Office of Emergency Preparedness, Disaster Preparedness — A Report to the Congress, (Washington, D.C., Executive Office of the President, January, 1972). It is difficult to specify quantitatively the probability of occurrence for most disasters other than floods and, in some cases, earthquakes. The discussion of data needs and procedures for estimating people and property at risk which appears in Part 2 applies equally to other types of natural disasters. A. LANDSLIDES AND SUBSIDENCE Landslides are the result of forces exerted on earth material located on sloping bedrock and can be due to the characteristics of the soil or to weaknesses in the bedrock. Subsidence is the vertical collapse of the ground due to underground mining, overpumping of groundwater, cavern formation, and other causes. The scale and location of a development and, to some extent, the degree of landscape alteration, will largely determine the potential for landslides or subsidence. The basic procedure involves determining the haz- ard potential at the development site from geologic and hydrologic evidence and from records of past landslides or subsidence episodes in the area or in other areas of similar topographic, geologic, hydro- logic, and soil characteristics. 2 In order to reduce the 2. For information on specific data requirements and methods of landslide hazard assessment, see E. B. Eckel, ed., Landslides and Engineering Practice (Washington, D.C.: Highway Research Board, 1958): Building Research Advisory Board, Methodology for Delineating Mudslide Hazard Areas (Washington, DC. National Academies of Sciences and Engineering, 1974): and John H. Sorensen, et al., Landslide Hazard in the United States: A Re- search Assessment (Boulder, Col.: Institute of Behavioral Science, University of Colorado, 1975). 123 need to evaluate each proposed development on a site-by-site basis, regional hazard maps can be pre- pared using similar data and assessment methods but at a smaller geographic scale. For example, a land- slide hazard map has been prepared for the San Cle- mente area of California based on a geologic model which relates landscape stability to (1) background factors (e.g., critical angle of natural slope and type of vegetation), (2) energy factors (e.g., amount of pre- cipitation and fire potential), and (3) special factors (e.g., presence of swelling clays and adverse geologic structures). 3 B. EARTHQUAKES Numerous areas within the United States are sub- ject to earthquakes. The West Coast in particular has been the site of significant episodes of seismic activity, although some of the largest earthquakes in history occurred in the Midwest and on the East Coast. In conducting an earthquake impact analysis the key questions are these: Will the new development be in a high risk zone? What is the frequency of expected earthquakes of various magnitudes? And what is the expected loss of life and property damage? In order to predict the frequency and severity of future earth- quakes, past records of seismic activity are combined with geological information in the vicinity of the site in question. Future damage is also a function of the size, nature, and method of construction of the pro- posed development. Earthquake risk maps should be a starting point for the analysis. Although the National Seismic Risk Map does not contain information on the probability of fu- ture earthquakes, it does indicate what the severity may be and can be used where other risk maps are unavailable. 4 The U.S. Geological Survey (USGS) is completing a national risk map which incorporates both the frequency and severity factors. This is ex- pected to be available sometime in 1976. Techniques have also been developed by USGS and HUD which provide a basis for more detailed mapping. 5 Where a proposed site is located in a high risk zone, a site-level evaluation should be conducted. This is based on detailed information concerning the 3. California Division of Mines and Geology. "Mudslide and Landslide Prediction." California Geology 25 (June 1975): 136. 4. National Seismic Risk Map, Department of Commerce. Envi- ronmental Science Services Administration. Coast and Geodetic Survey, circa 1969 (also contained in HL'D's Minimum Property Standards). 5. USGS, Studies for Seismic Zonation of the San Francisco Bay Region. Professional Paper 941-A (Washington, D.C.: U.S. Department of the Interior, 1975). location of fault lines, soil type and depth, bedrock type, and water table conditions. Detailed guidelines regarding the site-level assessment of risk are found in various federal agency publications. 6 The estimation of expected damage should be based on detailed information regarding the location, design, and construction of the proposed develop- ment. Several reports by various federal government agencies provide relevant information for damage as- sessments and hazard reduction through improved construction practices. 7 This highly abbreviated discussion may create the impression that earthquake hazard assessment is a simple, straightforward operation. Quite the contrary is true. These calculations require the collection of considerable quantities of data and are fraught with uncertainty. The error in estimating the expected damage for a single building may be 100 percent and for several hundred structures, 50 to 75 percent. 8 Before undertaking an assessment of earthquake impacts for proposed developments, it is recom- mended that the USGS be contacted regarding the ex- tensive body of research on the subject. Many communities in seismically active areas now have special building codes designed to mitigate earthquake damage. New development in these com- munities must meet these codes, thus reducing some- what the need for special attention to impact evalua- tion. However, improved earthquake resistance is only a partial solution. 9 C. OTHER TYPES OF DISASTERS Hurricanes, tornadoes, avalanches, and forest fires all extract a toll in human life and property damage. In some cases the high risk areas are so widespread and the forces of destruction so great that few pre- 6. See, for example. Walter W. Hays, et al.. Guidelines for Developing Design Earthquake Response Spectra (Champaign, III.: Army Construction Engineering Lab. June 1975) (NTIS No. AD-A012 728/2GA). 7. See. for example, The National Bureau of Standards, Building Practices for Disaster Mitigation, NBS Building Science Series #46 (Washington. D.C.: U.S. Government Printing Office, 1973) and National Oceanic and Atmospheric Administration. A Study of Earthquake Losses in the San Francisco Bay Area (Washing- ton, D.C.: Government Printing Office. 1972). Additional informa- tion can be obtained from Charles Culver at the National Bureau of Standards. 8. Personal communication with Charles Thiel of the National Science Foundation. 9. Improvements in our ability to predict earthquakes may re- duce the safety hazard if not the property damage. See. Frank Press. "Earthquake Prediction," Scientific American 232 (May, 1975): 14-23; and Christopher N. Scholtz. "Toward Infallible Earthquake Prediction," Natural History 83 (May 1974): 54-59. 124 Land Development and the Natural Environment ventative measures can be taken. Tornadoes are a case in point. 10 Forest fires and avalanches, on the other hand, are more localized. Damage from the latter can thus be minimized by preventing develop- ment in the high-risk areas and, in the case of forest fires, undertaking certain preventative maintenance activities, such as removal of dead plant material in forest fire-prone areas and clear-cutting of trees in corridors to be used as barriers to the propagation of fire. 11 10. Even for tornadoes, attempts at identifying high risk zones have met with some success. See Illinois Emergency Services Agency, Hazard Analysis for the State of Illinois (Springfield, 111.: October, 1975). 11. For a discussion of factors which can be used to estimate the potential for or risk from forest fires, see R. D. Nelm, B. Neal,andL. For hurricanes the key considerations involve build- ing strength and potential evacuation problems for those likely to be affected. For example, one argument for limiting development in the Florida Keys is based on potential evacuation problems caused by too few bridges linking the Keys with the mainland. In order to provide local governments in hurricane hazard areas with more information on the extent and severity of the problem, the National Oceanic and Atmospheric Ad- ministration is planning to publish about 185 storm evacuation maps showing the potential flood zone areas. 12 Tayler, A Fire Hazard Severity Classification System for California Wildlands (Sacramento: California State Division of Forestry, April 1, 1973) (NTIS No. PB-237 951/9WV). 12. Raymond Wilcove. ""The Mapping of Hurricane Alley," Water Spectrum (Summer 1975): 18-25. Other Types of Impact: Natural Disasters Other Than Floods 125 III. SCARCE RESOURCE PREEMPTION For every parcel of land used for urban develop- ment, alternative uses must be foregone. In some cases the preemption of alternative uses may carry with it significant social costs which are borne by the population as a whole or large portions thereof. This may be the case when certain scarce resources, such as agricultural land, land overlying mineral deposits, and land with unique natural features are used for res- idential, commercial, or industrial development. The suggested impact measure is as follows: The type and value of the scarce resource and the degree of the preemption. Although the calculation of the costs of preemption in monetary terms is far from a straightforward process and is not practical for routine evaluations at the present time, an articulation of the land uses being preempted by development will allow decision makers to consciously formulate value judgments about these costs. Descriptions in terms of land area, and perhaps qualitative assessments of "value," are more practical. A. AGRICULTURAL LAND Recent food shortages in various parts of the world have heightened the concern of many for the conver- sion of agricultural land to other uses in metropolitan areas. Although much of the land converted to urban uses tends to be well-suited for crop production, the impact of these conversions on total food production is far from clear. Improvements in technology and the reclamation of farmland elsewhere in the country may render urban preemption relatively insignificant. 13 Still, metropolitan farmland may affect the local price of certain agricultural products. In assessing the value of farmland to be converted, the following factors should be considered. 14 1. Productivity — this can be expressed directly as yield (by crop type) or indirectly as soil fertility, topography, and available moisture. 2. Specialty crops — certain land may be uniquely suited for the production of certain specialty products, such as cranberries or seed potatoes. 3. Viability — even productive land is of limited value if its size is too small or if support indus- tries have left the community or region. These factors could be used to specify a qualitative measure of resource "value." The impact of develop- ment could then be expressed as amount of land of the specified value converted to other uses. 13. For a discussion of these issues, see George E. Peterson and Harvey Yampolsky , Urban Development and the Protection of Met- ropolitan Farmlan d (Washington, D.C.: The Urban Institute, 1975); and Richard L. Barrows, et al., Wisconsin Natural Resource Policy Issues: An Economic Perspective, Working Paper No. 6 (Madison: Center for Resource Policy Studies and Programs, School of Natural Resources, University of Wisconsin, July 1973). 14. For additional elaboration see, Bernard J. Niemann, Jr., et al., Recommendations for a Critical Resource Information Pro- gram (CRIP) for Wisconsin, Phase III Report, (Madison: Institute for Environmental Studies. University of Wisconsin, February, 1974). 127 B. MINERAL DEPOSITS Less well-publicized but certainly as important is the preemption of mineral extraction by urban devel- opment. The loss of gravel pits on Long Island, for example, has reportedly cost New York State $30,000,000 per year in increased building costs. 15 This is not to say that the value to society of develop- ing land overlying mineral deposits is not equal to or even greater than the value of the deposits them- selves. But investigation of this issue prior to devel- opment is certainly in order. Mineral resources encompass nationally scarce fossil and nuclear fuels and metallic minerals, as well as less scarce but locally significant construction min- erals, such as sand and gravel. Key considerations in any planning study or impact evaluation include scar- city, quality and size of the deposit, ease of extrac- tion, and (usually) the availability of water. 16 Unfortu- nately, an adequate assessment of these variables fre- quently requires costly test borings. Even though po- tential deposits can be inferred from general geologic data, only about 1 percent of potentially valuable deposits are economically exploitable. Where the po- tential mineral is extremely valuable and the pro- posed development represents a sizable investment, test borings might be conducted. The impact of the development should be measured not only by direct physical interference with mining activity. Development in close proximity may effec- tively preclude future mining activity, since mine 15. E. Dale Trower. "Land Use and Mineral Industry" (Paper presented at the Annual Meeting of the American Association for the Advancement of Science, January 30. 1975). 16. For a further description of these variables and their applica- tion to various types of minerals, see Niemann et al.. op. cit. operators may well decide to close their operations rather than spend the money necessary to reduce the level of noise and pollutant output in a manner appropriate for residential or commercial areas. Un- less the proposed development will be compatible with surface or deep mining operations (e.g., heavy industry), a buffer area should be secured sufficient to screen the mine and to mitigate accompanying noise and dust. C. UNIQUE NATURAL FEATURES Unique natural features are those geologic or physi- ographic features which are of scientific, educational, or aesthetic interest. 17 They include such items as waterfalls, canyons, natural bridges, mountain ranges, escarpments, or simply combinations of more com- mon features which provide a scenic view. Many states have undertaken an inventory of these resources as part of critical area or other programs. The relevant state agencies should be consulted for this information. If planning or inventory studies have not been conducted at the state or local level an as- sessment of the impacted environment should be made as part of the impact evaluation of individual developments. Criteria to use as basis for these as- sessments can be found in the literature. 18 A further discussion of aesthetic evaluation appears in another volume of The Urban Institute's land use series of re- ports. 19 17. Biological features (i.e., natural areas and wildlife habitats) have already been discussed. See Part 3 of this report. 18. See. for example, Niemann, et al., op. cit. 19. K. Christensen, Estimating the Social Impacts of Land Developments (Washington D.C.: The Urban Institute, forthcom- ing). 128 Land Development and the Natural Environment THE URBAN INSTITUTE BOARD OF TRUSTEES Charles L. Schultze, Chairman Senior Fellow, The Brookings Institution, Washington, DC Kingman Brewster, Jr., President, Yale University, New Haven, Conn. John H. Filer, Chairman, AEtna Life & Casualty, Hartford, Conn. Eugene G. Fubini, President, E. G. Fubini Consultants, Limited, Arlington, Va. William Gorham, President, The Urban Institute, Washington, D C. Katharine Graham, Chairman of the Board, The Washington Post Company, Washington, D.C. Robert V. Hansberger, Chairman and Chief Executive, Futura Industries Corporations, Boise, Idaho Vernon E. Jordan, Jr., Executive Director, National Urban League, New York, N Y. Richard Llewelyn-Davies, President, Llewelyn-Davies Associates, New York, N.Y., and London, England Bayless A. Manning, President, The Council on Foreign Relations, New York, N Y Stanley Marcus, Executive Vice President, Carter Hawley Hale Stores, Inc., Dallas, Texas Robert S. McNamara, President, International Bank for Reconstruction and Development, Washington, D.C. Arjay Miller, Dean, Graduate School of Business, Stanford University, Stanford, Calif. J. Irwin Miller, Chairman, Cummins Engine Co., Inc., Columbus, Ind. John D. Rockefeller IV, Charleston, West Virginia William D. Ruckelshaus, Partner, Ruckelshaus, Beveridge, Fairbanks & Diamond, Washington, D.C. Herbert Scarf, Professor of Economics, Yale University, New Haven, Conn. Franklin A. Thomas, President, Bedford-Stuyvesant Restoration Corp., Brooklyn, N Y. Cyrus R. Vance, Partner, Simpson, Thacher & Bartlett, New York, N Y James Vorenberg, Professor, School of Law, Harvard University, Cambridge, Mass.