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 No. 9024 
 
 
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Bureau of Mines Information Circular/1985 
 
 Feasibility of Water Diversion 
 and Overburden Dewatering 
 
 By Noel N. Moebs and Michael L. Clar 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 75 
 
 *f/NES 75TH AV 5 ^ 
 
Information Circular 9024 
 n 
 
 Feasibility of Water Diversion 
 and Overburden Dewatering 
 
 By Noel N. Moebs and Michael L. Clar 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
I 
 
 As the Nation's principal conservation agency, the Department of the Interior 
 has responsibility for most of our nationally owned public lands and natural 
 resources. This includes fostering the wisest use of our land and water re- 
 sources, protecting our fish and wildlife, preserving the environmental and 
 cultural values of our national parks and historical places, and providing for 
 the enjoyment of life through outdoor recreation. The Department assesses 
 our energy and mineral resources and works to assure that their development is 
 in the best interests of all our people. Thg*«ftSB3cTOe»i also has a major re- 
 sponsibility for American Indian reseryrf^&£ommunira£i\ind for people who 
 live in Island Territories under U.S. 
 
 Library of Congress Cataloging in Publication Data: 
 
 Moebs, Noel N 
 
 Feasibility of water diversion and overburden dewatering. 
 
 (Information circular / United States Department of the Interior, 
 Bureau of Mines ; 9024) 
 
 Bibliography: p. 47-49. 
 
 Supt. of Docs, no.: I 28.27:9024. 
 
 1. Mine drainage. 2. Mine water. 3. Coal mines and mining- 
 Appalachian Region. I. Gar, Michael L. II. Title. III. Series: In- 
 formation circular (United States. Bureau of Mines) ; 9024. 
 
 TN295.U4 [TN321] 622s [622'. 334] 84-600364 
 
n 
 
 \3 
 
 o-S CONTENTS 
 
 £^ Page 
 
 c 
 
 Abstract 1 
 
 Introduction 2 
 
 Acknowledgments 4 
 
 Impacts of mine water 4 
 
 Health and safety 4 
 
 Production 6 
 
 Environment 6 
 
 Costs 7 
 
 Sources of inflow to underground mines 8 
 
 Ba ckg round 8 
 
 Water entrance into mines 9 
 
 Coal and water-bearing strata 10 
 
 Water in shallow mines 13 
 
 Surface seepage 13 
 
 Surface water inrush 14 
 
 Water entrance through fractures 15 
 
 Joints 16 
 
 Faults and fracture zones 16 
 
 Mine subsidence fractures * 17 
 
 Abandoned deep mines 18 
 
 Barrier pillars 18 
 
 Interconnections 19 
 
 Boreholes, wells, and shafts 20 
 
 Water control practices 21 
 
 Siting surface facilities and openings 22 
 
 Surface runoff diversion 22 
 
 Surface regrading 22 
 
 Soil sealing 24 
 
 Stream channel modifications 24 
 
 Grouting 25 
 
 Borehole sealing 25 
 
 Subsurface soil sealing 26 
 
 Mine sealing 27 
 
 Well dewatering 28 
 
 Ground water pumping directly to the surface 29 
 
 Gravity drainage to the mine 29 
 
 Gravity drainage into lower aquifers 30 
 
 Costs 31 
 
 Case study 32 
 
 Summary of water control practices 32 
 
 Analysis of three water control projects 33 
 
 Technical effectiveness 38 
 
 Case study 1 38 
 
 Case study 2 41 
 
 Case study 3 41 
 
 Costs 42 
 
 Case study 1 42 
 
 *OCase study 2 42 
 
 Case study 3 42 
 
 5 
 
 — : 
 
11 
 
 CONTENTS— Continued 
 
 Page 
 
 Other considerations 43 
 
 Conclusions 44 
 
 Impacts of mine water 44 
 
 Sources of inflow to underground mines 45 
 
 Water control methods 45 
 
 Current engineering practices 45 
 
 Recommendations 46 
 
 References 47 
 
 Appendix A. — Case study 1 50 
 
 Appendix 8. — Case study 2 60 
 
 Appendix C . — Case study 3 66 
 
 ILLUSTRATIONS 
 
 1 . Summary of cost analysis 7 
 
 2. Matrix of mine water controls versus mine water sources 21 
 
 3 . Ground water pumping systems 30 
 
 4 . Gravity drainage into mine 30 
 
 5. Gravity drainage into underlying aquifers 31 
 
 6. Map of Nemacolin Mine 41 
 
 A-l. Location map of Lancashire No. 20 Mine and pilot well dewatering site.... 50 
 
 A-2. Generalized stratigraphic column, case study 1 51 
 
 A- 3 . Water transport system 54 
 
 A-4 . Average daily flows to treatment plant 54 
 
 A- 5 . Main G study area 55 
 
 A-6 . Average mine inflow in Main G study area 56 
 
 A-7. Location map of dewatering and observation wells 56 
 
 A-8. Average daily mine inflow, July 1977 57 
 
 A-9. Average daily mine inflow, September 197 7 58 
 
 B-l . Planned and ongoing mine operations 60 
 
 B-2. Generalized stratigraphic column, case study 2 61 
 
 B-3. Site cross section 62 
 
 TABLES 
 
 1. Relationship between mine depth and well dewatering 7 
 
 2. Representative costs for surface regrading and restoring 24 
 
 3. Representative costs for constructing various types of mine seals 29 
 
 4. Summary of water control practices 34 
 
 5. Summary of water control costs 36 
 
 6. Comparison of geologic conditions at three case study sites 39 
 
 7. Comparison of hydrologic conditions at three case study sites 40 
 
 B-l . Beaver Run inflows 64 
 
 B-2 . Gobbler ' s Knob inf lows 64 
 
 B-3. Big George inflows 65 
 

 UNIT OF MEASURE ABBREVIATIONS 
 
 USED IN THIS 
 
 REPORT 
 
 cm 
 
 centimeter 
 
 
 
 km 
 
 kilometer 
 
 cm 2 /s 
 
 square 
 
 centimeter per second 
 
 km 2 
 
 square kilometer 
 
 ft 
 
 foot 
 
 
 
 
 L 
 
 liter 
 
 ft 2 
 
 square 
 
 foot 
 
 
 
 lb/in 2 
 
 pound per square inch 
 
 ft 3 
 
 cubic foot 
 
 
 
 lb/ton 
 
 pound per ton 
 
 ft 3 /s 
 
 cubic i 
 
 :oot per 
 
 second 
 
 
 L/d 
 
 liter per day 
 
 gal 
 
 gallon 
 
 
 
 
 L/s 
 
 liter per second 
 
 gpd 
 
 gallon 
 
 per day 
 
 
 
 m 
 
 meter 
 
 gpd/ft 
 
 gallon 
 
 per day 
 
 per foot 
 
 
 m 3 
 
 cubic meter 
 
 gpd/ft 2 
 
 gallon 
 
 per day 
 
 per square 
 
 foot 
 
 mg/L 
 
 milligram' per liter 
 
 gpd/mi 2 
 
 gallon 
 
 per day 
 
 per square 
 
 mile 
 
 mi 2 
 
 square mile 
 
 gpm 
 
 gallon 
 
 per minute 
 
 
 pet 
 
 percent 
 
 h 
 
 hour 
 
 
 
 
 ppm 
 
 part per million 
 
 hp 
 
 horsep< 
 
 Dwer 
 
 
 
 t 
 
 metric ton 
 
 in 
 
 inch 
 
 
 
 
 ton/yr 
 
 ton per year 
 
 in/h 
 
 inch p 
 
 ar hour 
 
 
 
 tpy 
 
 metric ton per year 
 
 kg/m 2 
 
 kilogram per square meter 
 
 
 yd 3 
 
 cubic yard 
 
 kg/t 
 
 kilogram per metric ton 
 
 
 yr 
 
 year 
 

FEASIBILITY OF WATER DIVERSION AND OVERBURDEN DEWATERING 
 
 By Noel N. Moebs and Michael L. Clar 
 
 ABSTRACT 
 
 The Bureau of Mines studied the feasibility of water diversion and 
 overburden dewatering for underground coal mines in the Appalachian re- 
 gion. All relevant published literature pertaining to the occurrence 
 and control of surface and ground water in underground coal mines was 
 reviewed, and the impacts of mine water with respect to health and 
 safety, production, environment, and costs were assessed and are de- 
 scribed in this report. The report also identifies the sources of wa- 
 ter inflow into underground coal mines, and gives a summary description 
 and evaluation of techniques that can be used to reduce the amount of 
 water entering these mines. Engineering practices currently used by 
 operating coal mines in the Appalachian region to prevent the movement 
 of ground and surface water into active coal workings were reviewed 
 and are summarized. Major emphasis has been placed on the identifica- 
 tion of geologic and hydrologic conditions of the site, the water con- 
 trol methods used, and an evaluation of their technical and cost 
 effectiveness. 
 
 geologist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 ^vice president, Hydro-Terra, Inc., Columbia, MD . 
 
INTRODUCTION 
 
 This report presents the results of a 
 study undertaken by the Bureau of Mines 
 to determine the feasibility of water 
 diversion and overburden dewatering tech- 
 niques in advance of underground coal 
 mining operations in the Appalachian coal 
 districts. 
 
 The presence and, in particular, the 
 ponding of water in the active workings 
 of underground coal mines can be very 
 detrimental to health and safety, produc- 
 tion, costs, and the environment. The 
 negative impacts that a wet mine has 
 in these areas are generally well recog- 
 nized. However, there exists no com- 
 prehensive and quantitative reporting 
 of these impacts in the published 
 literature. 
 
 In the Appalachian coal districts, 
 where major underground mine expansions 
 are anticipated, drainage in the coal 
 mines is extremely variable. The volume 
 of water to be handled, which is typical- 
 ly expressed in terms of tons of water 
 pumped out of the mine for every ton of 
 coal mined, can range from an average of 
 5 tons in the Pennsylvania bituminous 
 mines to 36 tons in the anthracite 
 region. 
 
 Several approaches have been proposed 
 either to dewater the mine area in ad- 
 vance of mining or to substantially re- 
 duce the amount of water reaching the 
 mine area by diverting or reducing the 
 infiltration of surface waters. Many of 
 these methods, however, address hypothet- 
 ical conditions rather than actual situ- 
 ations. Some of the literature treats 
 special situations such as preventing wa- 
 ter from entering through boreholes, sub- 
 sided or stripped areas, or surface 
 streams entering through old mine open- 
 ings. Some researchers have addressed 
 water diversion and well dewatering tech- 
 niques as control measures and proposed 
 routing and rechanneling of surface flow 
 as an effective method of excluding water 
 from mines. 
 
 Although the methodology for imple- 
 menting these approaches is not new, to 
 date both the application and the success 
 
 of these methods in underground coal 
 mines have been limited. Consequently, 
 these methods have not found widespread 
 use in the coal industry in the United 
 States. The most common approach to 
 handling water in underground mines con- 
 sists of collecting the water by gravity 
 and pumping the water back out to the 
 surface where treatment is provided if 
 needed, prior to discharging to the re- 
 ceiving streams. 
 
 The still recent Surface Mining Control 
 and Reclamation Act (SMCRA) and the ensu- 
 ing permanent regulatory program of the 
 Office of Surface Mining (OSM) represent 
 an additional consideration. Several 
 general requirements are stipulated that 
 are related to the effects of underground 
 coal mining activities on the hydrologic 
 balance: 
 
 Section 817.41 Hydrologic Balance: 
 General Requirements 3 
 
 (a) Underground mining activities 
 shall be planned and conducted to 
 minimize changes to the prevailing 
 hydrologic balance in both the mine 
 plan and adjacent areas, in or- 
 der to prevent long-term adverse 
 changes in that balance that could 
 result from those activities. 
 
 (b) Changes in water quality and 
 quantity, in the depth to ground 
 water, and in the location of sur- 
 face water drainage channels shall 
 be minimized so that the approved 
 postmining land use of the permit 
 area is not adversely affected. 
 
 (c) In no case shall Federal 
 and State water quality statutes, 
 
 ^U.S. Code of Federal Regulations. Ti- 
 tle 30 — Mineral Resources; Chapter VII-- 
 Office of Surface Mining Reclamation and 
 Enforcement, Department of the Interior; 
 Subchapter K--Permanent Program Perform- 
 ance Standards; Part 81 7--Underground 
 Mining Activities; July 1, 1981. 
 
regulations , standards or effluent 
 limitations be violated. 
 
 (d) Operations shall be conducted 
 to minimize water pollution and, 
 where necessary, treatment methods 
 shall be used to control water 
 pollution. 
 
 (1) Each person who conducts un- 
 derground mining activities shall 
 emphasize mining and reclamation 
 practices that prevent or minimize 
 water pollution. Changes in flow 
 shall be used in preference to the 
 use of water treatment facilities. 
 
 (2) Acceptable practices to con- 
 trol and minimize water pollution 
 include, but are not limited to — 
 
 (i) Stabilizing disturbed areas 
 through land shaping; 
 
 (ii) Diverting runoff; 
 
 (iii) Achieving quickly germinat- 
 ing and growing stands of temporary 
 vegetation; 
 
 (iv) Regulating channel velocity 
 of water; 
 
 (v) Lining drainage channels with 
 rock or vegetation; 
 
 (vi) Mulching; 
 
 (vii) Selectively placing and 
 sealing acid-forming and toxic- 
 forming materials; 
 
 (viii) Designing mines to prevent 
 gravity drainage of acid waters; 
 
 (ix) Sealing; 
 
 (x) Controlling subsidence; and 
 
 (xi) Preventing acid mine 
 drainage. 
 
 (3) If the practices listed at 
 paragraph (d)(2) of this section 
 
 are not adequate to meet the 
 requirements of this part, the per- 
 son who conducts underground mining 
 activities shall operate and main- 
 tain the necessary water treatment 
 facilities for as long as treatment 
 is required under this part. 
 
 As the above clearly indicates, any 
 method proposed for use must include a 
 thorough assessment of the impact it may 
 produce on the hydrologic balance of the 
 mine site and will require the approval 
 of this new regulatory agency (OSM) or 
 the appropriate State agency. 
 
 The combined concerns for environmental 
 protection and for a safe and productive 
 workplace demand additional studies and 
 research on the feasibility of water di- 
 version and overburden dewatering to ad- 
 vance the state of the art. The perform- 
 ance characteristics of 'these methods 
 need to be evaluated and documented. It 
 is unlikely that widespread use of such 
 methods will occur until sound quanti- 
 tative data that justify their use are 
 presented. 
 
 This Bureau research project was under- 
 taken to study the feasibility of water 
 diversion and overburden dewatering in 
 advance of mining in underground coal 
 mines in the Appalachian coal districts. 
 This basic objective was accomplished 
 through — 
 
 1. A review of the literature relative 
 to preventing surface or shallow ground 
 water from entering underground coal 
 mines. The literature evaluation focused 
 on three major areas: (1) the impacts of 
 mine water, (2) sources of water inflow 
 to underground mines, and (3) available 
 water control practices. 
 
 2. An on-site review and analysis of 
 current engineering practices. Three in- 
 dividual case studies are presented in 
 appendixes A, B, and C. 
 
 The combined results of the literature 
 evaluation and on-site review are summa- 
 rized in this report. 
 
ACKNOWLEDGMENTS 
 
 The authors are grateful for the coop- 
 eration of numerous coal mining companies 
 who contributed information for this 
 study. In particular, the authors wish 
 to thank the Barnes and Tucker Co. , Jones 
 and Laughlin Steel Corp. , and Mettiki 
 Coal Corp. , for information used in com- 
 piling the case studies. John J. Ferran- 
 dino and Connie Bosma of Hittman Associ- 
 ates, Inc. , contributed substantially to 
 the text and data collection. 
 
 Figures A-3, A-4, A-5, A-6, A-7, A-8, 
 and A- 9 were adapted from illustrations 
 by W. A. Wahler in "Dewatering Active 
 Underground Coal Mines: Technical As- 
 pects and Cost Ef f eciveness" (38) . 4 Fig- 
 ures 3, 4, and 5 were adapted from il- 
 lustrations by H. L. Lovell and J. W. 
 Gunnett in "Hydrological Influences in 
 Preventative Control of Mine Drainage 
 From Deep Coal Mining" (19). 
 
 IMPACTS OF MINE WATER 
 
 An understanding and a quantification 
 of the extent to which water can bene- 
 fit or impede underground coal mining 
 operations is a prerequisite to conduct- 
 ing an assessment of the effectiveness 
 of available water control practices. 
 For the purposes of this study, the ef- 
 fects of mine water have been organized 
 into four categories: (1) health and 
 safety, (2) production, (3) environment, 
 and (4) costs. 
 
 Most recent publications underemphasize 
 the health, safety, and productivity 
 problems associated with water in under- 
 ground mines, and instead focus on the 
 environmental effects of mine water. In 
 underground mines in the Pennsylvania 
 anthracite region, 36 tons of water are 
 pumped out of the mine for every ton 
 of coal mined. In the bituminous coal 
 mines , this average is between 5 and 6 
 tons of water for every ton of coal. 
 
 Regardless of the water source, the de- 
 terminants of the water problems in a 
 mine are (1) the rate of inflow, (2) the 
 mode and location of inflow, and (3) pro- 
 visions to handle the inflow. A uniform 
 rate of inflow will not normally present 
 severe problems in designing a pumping 
 plant. However, unforeseen high inflow 
 rates have the potential to cause major 
 disruptions in normal activities. 
 
 Water seeping into the mine at loca- 
 tions far removed from the active work- 
 ings can be directed to suitable sumps 
 and pumped out of the mine. When the in- 
 flow is in the active workings and is a 
 slow seepage, the water can be allowed to 
 accumulate and can then be pumped out to 
 
 a section sump using portable pumps. Wa- 
 ter problems tend to become critical when 
 high inflow rates are generated in ac- 
 tive workings by the advance of the work 
 itself. 
 
 HEALTH AND SAFETY 
 
 In defining the significant effects 
 of water on health and safety in the 
 workplace, the following factors must 
 be considered: (1) inrushes of water, 
 (2) ventilation, (3) roof conditions, 
 (4) maintenance problems, (5) corrosion, 
 and (6) miscellaneous effects. 
 
 Inrushes of Water . - The Appalachian 
 coal districts are the oldest coal mining 
 districts in the country. New mines in 
 these districts are often adjacent to 
 and/or below older abandoned mines. 
 Since these older abandoned mines are of- 
 ten flooded, they behave as underground 
 water reservoirs, and the potential for 
 inrushes of water must be considered in 
 siting new mines. This concern is likely 
 to increase in the future as the number 
 of new mines grows, particularly since 
 these new mines will often be sited in 
 the deeper seams underlying the older wa- 
 terlogged workings. The Bureau has de- 
 veloped guidelines to prevent and control 
 the inrush of mine waters. These guide- 
 lines include the work by Wardell ( 40 ) 
 and Skelly and Loy (32). 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding the appendixes. 
 
Ventilation . - Water can affect a 
 mine's ventilation in three ways: It can 
 aggravate the heat and humidity problem, 
 increase the methane emission, and block, 
 the ventilating airways. 
 
 Roof Conditions. - Several studies have 
 been performed on the influence of humid- 
 ity on roofs in underground mines. These 
 studies indicate that roofs composed of 
 soft shales or some form of clay, with 
 mud partings , are most vulnerable to 
 failure. Sometimes an effort is made to 
 recover an upper seam that was not mined 
 before a lower seam was extracted. In 
 this case, the subsidence in the overly- 
 ing strata, as a result of the lower seam 
 mining, can cause roof control problems. 
 Cracks and fissures in the broken strata 
 may be filled with mud and clay. When 
 the upper seam is developed for mining, 
 water tends to wash into these fillings 
 and create weakened roof conditions. Wa- 
 ter seeping through strata is indicative 
 of poor strata conditions. 
 
 Roof collapses are often associated 
 with the presence of water in conjunction 
 with geologic unconformities. Water will 
 act as a lubricant to decrease frictional 
 resistance to movement of rock strata. 
 Lubrication of a slip surface, such as a 
 slickenside, requires only small volumes 
 of water or moisture, although the pre- 
 cise amount has yet to be quantified. It 
 is known, however, that the moisture sup- 
 plied by the mine ventilation system is 
 sufficient to cause failure in weak shale 
 roofs. 
 
 Maintenance Problems . - Water in mines 
 creates special problems in the operation 
 of electrical equipment. Whereas perma- 
 nently located electrical equipment can 
 be adequately protected from water, mo- 
 bile equipment cannot be so easily pro- 
 tected. Trailing cables and trolley 
 wires are of greatest concern from a 
 safety point of view. Defective splices 
 and breaks in the insulation of cables 
 have been responsible for severe shocks 
 and burns [Mason ( 21_) ] . Trailing cables 
 of all types are used at or near the coal 
 face, where they are most likely to be 
 damaged. Trailing cables are continually 
 being handled, in many cases under wet 
 conditions; therefore, there is always 
 
 the danger of electrical shocks should a 
 fault arise. 
 
 Water tends to carry dirt and clay 
 into exposed bearings, sockets, conveyor 
 chains, and other machinery parts, in- 
 creasing the frictional resistance to 
 movement. In addition to the increased 
 wear and tear, this can result in exces- 
 sive heat generation. If unattended for 
 long periods of time, the frictional heat 
 can cause a fire. 
 
 Corrosion . - Although most corrosion of 
 mining equipment is minor, serious cor- 
 rosion can occur under certain circum- 
 stances. This problem is discussed in 
 detail in papers by White (4_1_) and Kenny 
 ( 16) . According to White, mine water can 
 be classified as follows: 
 
 Type pH 
 
 1— Highly acid i 1.5- 4.5 
 
 2 — Soft, slightly acid 5.0- 7.0 
 
 3 — Hard, neutral to alkaline... 7.0- 8.5 
 
 4 — Soft, alkaline 7.5-11.0 
 
 5 — Highly saline 6-9 
 
 6 — Soft, acid 3.5- 5.5 
 
 In laboratory tests, it was found that 
 water fitting the description of types 1 
 and 5 causes corrosion. Type 1 water is 
 most corrosive because of the free sul- 
 furic acid and ferric ions. Usually py- 
 rite in the coal seams is the source for 
 this water. Type 5 water contains a high 
 concentration of dissolved salts, partic- 
 ularly sodium chloride. The salt may 
 come from the strata and is highly corro- 
 sive as a result of the high electrical 
 conductivity and of the interference to 
 the rust-forming process. 
 
 Miscellaneous Effects . - The accumula- 
 tion of water in the mine makes it un- 
 pleasant to work, and cuts down on work 
 time and efficiency. More importantly, 
 it may lead to an Increase in accidents. 
 
 Although dangers from water account for 
 a relatively small portion of accidents 
 resulting in injuries and deaths, there 
 
is always the possibility of serious dis- 
 asters when mining activity is in the 
 vicinity of large bodies of water. Even 
 if the existence of a water body is 
 known, its exact location and the volume 
 and head of water are usually not well 
 defined. 
 
 Owing to the variety of problems that 
 can occur, it is impossible to form one 
 set of rules that can be uniformly ap- 
 plied in all cases. However, there are 
 several general preventive measures that 
 must be taken: 
 
 • The potential water danger must be 
 studied and surveyed on a mine site, 
 area, and regional basis to assess the 
 full extent of the danger. 
 
 • Adequate sumps and gravity flow 
 paths into them should be established as 
 early as possible. 
 
 • A plan must be formulated to ensure 
 that workers are withdrawn safely in the 
 event of an inrush. 
 
 PRODUCTION 
 
 The productivity of a mining system has 
 been expressed as a function of a number 
 of major independent variables [Stefanko 
 (34) , Manula, Bouillot, Rivell, and Sand- 
 ford (_20), Suboleski ( _35) ] . Excluding 
 the mechanical equipment and the human 
 element, these independent variables in- 
 clude (1) roof quality, (2) methane lib- 
 eration, (3) bottom quality, (4) water, 
 (5) grades, (6) hardness and strength of 
 seam, (7) seam height, and (8) depth of 
 seam. 
 
 To some extent these all are interre- 
 lated with the presence of water; howev- 
 er, each can also be a factor independent 
 of others — for example, the roof may sim- 
 ply be weak and the floor may have little 
 bearing strength even when dry. 
 
 ENVIRONMENT 
 
 Underground coal mines can have an im- 
 pact on both the quantity and quality of 
 surface and ground waters. The impact 
 on water quality has long been recognized 
 and regulated by both State and Federal 
 
 agencies. These regulations generally 
 require that mine waters be treated to 
 neutralize and remove pollutants prior to 
 discharge to receiving streams. Conse- 
 quently, some information is available 
 related to the technology of controlling 
 this impact. 
 
 All of the water pumped from the mine 
 will generally require treatment. A num- 
 ber of dewatering schemes have been pro- 
 posed based on the assumption that by 
 intercepting the ground water before it 
 contacts the mining operation, the re- 
 quirement for treatment and the related 
 cost could be avoided. 
 
 The impacts of underground coal mines 
 on water quantity can be short term or 
 long term and can occur both during ac- 
 tive mining and after abandonment. The 
 two most noticeable and immediate impacts 
 are changes in water levels and ground 
 water flow. Lowering of the water table 
 level or a decrease in ground water flow 
 can result in the dewatering of shal- 
 low wells and the loss of ground water 
 supplies. 
 
 The mechanisms that cause these hydro- 
 logic impacts include (1) the removal of 
 the coal seam, resulting in underground 
 cavities that serve as broad sinks or un- 
 derdrains , which receive ground water 
 percolating downward from overlying 
 strata, (2) the fracturing and separation 
 of overlying strata resulting from the 
 removal of the coal seam, and (3) the re- 
 moval of the water from the mine by grav- 
 ity drainage in jthe case of updip drift 
 mining or by pumping in downdip drift, 
 slope, or shaft mining. 
 
 It must be pointed out that use of a 
 dewatering technique will also result in 
 changes (lowering) of water levels and 
 will reduce ground water flows. Thus, 
 the same type of hydrologic impacts will 
 be experienced during mining. The dewa- 
 tering techniques will not prevent the 
 development of the mechanisms discussed 
 above. Consequently, the hydrologic im- 
 pacts will continue to be experienced af- 
 ter the mining operation is completed. 
 
 A recent investigation suggests that 
 the hydrologic impacts of underground 
 mines may be less severe in the future. 
 An inventory of water levels in domestic 
 wells in Marion County, WV, showed that 
 
TABLE 1. - Relationship between mine 
 depth and well dewatering 
 
 Mine depth, 
 Ft 
 
 Effect on wells completed 
 above mining zone 
 
 <200 All wells permanently 
 
 dewatered. 
 200 to 250.... Most wells permanently 
 
 dewatered. 
 250 to 300.... Some wells occasionally 
 
 dewatered. 
 >300 No wells dewatered. 
 
 Source: 
 (30). 
 
 Sgambat, Labella, and Roebuck 
 
 variations in long-term dewatering are 
 related to mine depth [Rauch {21) ] . A 
 similar investigation (table 1) found 
 that when the mine depth exceeded 300 ft 
 (91 m) , no wells completed above the min- 
 ing zone were dewatered. A recent survey 
 of 325 operating sections in Appalachia 
 revealed that 92 pet of the surveyed sec- 
 tions were 300 ft (91 m) deep or more. 
 The average depth was 600 ft (183 m) , and 
 the most frequently reported depth was 
 500 ft (152 m) . These data suggest that 
 dewatering of wells by underground mines 
 may not be a frequent occurrence in the 
 future. 
 
 COSTS 
 
 Mine water can affect mining costs in 
 both direct and indirect ways. The di- 
 rect costs associated with mine water in- 
 clude costs for — 
 
 • Water handling (collection, treat- 
 ment, and disposal). 
 
 • Coal preparation (additional costs). 
 
 • Miscellaneous wet and waterproof pay 
 items (such as blasting agents) . 
 
 The indirect costs include — 
 
 • Additional costs of time lost owing 
 to health and safety aspects: venti- 
 lation, floods and inrushes, and roof 
 support. 
 
 • Productivity losses. 
 
 • Cost associated with additional 
 maintenance requirements. 
 
 The literature review revealed that 
 there is very little information avail- 
 able on the direct costs associated with 
 mine water and even less on the indirect 
 costs. Mining companies do not normally 
 separate water-related costs from other 
 costs in much detail. To date, water 
 treatment costs are the only direct cost 
 that has been thoroughly investigated. 
 (The available data on water treatment 
 costs are too extensive to summarize in 
 this report, but selected references were 
 reviewed and are given in the reference 
 list at the end of this report.) 
 
 Figure 1 presents a comprehensive sum- 
 mary of water-handling costs experi- 
 enced by an underground mine in central 
 
 FIGURE 1. - Summary of cost analysis of water 
 handling at one mine (38). 
 
Pennsylvania and serves to illustrate the 
 major cost components (38) « The water- 
 handling costs for this mine were gener- 
 ated as part of a study to evaluate the 
 effectiveness of dewatering an active 
 mine from the surface, which represents a 
 rare situation where cost data have been 
 reported. The practicality of establish- 
 ing standard figures for the industry is 
 questionable because of the great varia- 
 tion in physical factors such as depth, 
 water quality, size of mine, geology, and 
 engineering methods. However, examina- 
 tion of costs incurred by mines within 
 local mining districts operating in the 
 same coal seam might yield useful plan- 
 ning guidelines. 
 
 Information on the indirect costs of 
 mine water was very scarce. The indi- 
 rect costs associated with the effects of 
 mine water on health and safety and with 
 
 additional maintenance requirements have 
 yet to be quantified. A partial assess- 
 ment of the indirect cost resulting from 
 the impact of mine water on production 
 can be generated based on the work of 
 Suboleski (35). 
 
 According to Suboleski, a reduction in 
 the range of 32 to 50 tons (29 to 45 t) 
 of coal per shift might be experienced 
 between a mining section with a dry, hard 
 floor and a section with a wet, rutted, 
 and slippery floor. Assuming that the 
 section operates three shifts per day, 
 and 220 days per year, a decrease in pro- 
 duction ranging from 21,120 to 33,000 
 ton/yr (18,000 to 29,700 tpy) per section 
 would result. Assuming a selling price 
 of $20 per ton, a potential production 
 loss ranging from $422,400 to $660,000 
 annually per section would be suffered. 
 
 SOURCES OF INFLOW TO UNDERGROUND MINES 
 
 BACKGROUND 
 
 Problems associated with water inflow 
 into underground coal mines have an im- 
 portant effect on the cost and progress 
 of the mining operations. Greater knowl- 
 edge and increased efficiency in reducing 
 the risk of sudden water inflows, in im- 
 proving stability, and in reducing dewa- 
 tering and mining costs are goals at many 
 underground operations. To identify the 
 best approaches to mine water control, it 
 is necessary, as a first step, to identi- 
 fy the sources of water infiltration into 
 the mine. Once the sources are identi- 
 fied for any given mine, the potential 
 solutions to reduce or control the water 
 problem can then be developed. 
 
 Water may enter mine workings via a 
 number of different avenues. Water-bear- 
 ing strata that are in contact with the 
 coal seams can be sources of inflow. 
 These strata include sandstones and lime- 
 stones, which are associated with the 
 coal seams, and any unconsolidated de- 
 posits, such as sand and gravel, which 
 may lie above the coal seams . In addi- 
 tion, the coal seams themselves may con- 
 tribute water to the mining environment 
 
 and, therefore, deserve consideration as 
 a source. 
 
 The development of an underground mine 
 alters the natural ground water flow 
 patterns. The extent of the alteration 
 is dependent on the geohydrology of the 
 site and the type of mining system used. 
 These aspects are briefly reviewed. 
 
 Water may also enter shallow coal mines 
 via seepage from surface water bodies 
 or through general surface infiltration. 
 The amount of water entering the mine 
 will depend upon the nature of the strata 
 above the mine and the depth to the mine. 
 
 Earth fractures, such as faults, frac- 
 ture zones, joint systems, and subsidence 
 fractures, also allow water to enter un- 
 derground mines. These fractures tend to 
 localize inflow and destroy the confining 
 effect of any relatively impermeable beds 
 above the coal. They are the prevalent 
 avenue by which water enters underground 
 coal mines in the Appalachian coal 
 region. 
 
 Water may also enter underground mines 
 through manmade pathways. Abandoned deep 
 mines and active and abandoned strip 
 mines can serve as sources of water accu- 
 mulation and infiltration. Water from 
 
these sources can enter the mine workings 
 directly through barrier pillars and in- 
 terconnections, or these pathways may fa- 
 cilitate the entry of surface runoff into 
 the ground water system, which eventually 
 works its way into an underground mine. 
 In addition, boreholes, abandoned wells, 
 shafts, and mine openings also serve as 
 water collection points and direct con- 
 duits to underground mines by tapping 
 overlying aquifers and collecting surface 
 waters. 
 
 WATER ENTRANCE INTO MINES 
 
 The quantity of water varies with local 
 conditions during the construction or 
 later development of many mines. Some 
 mines are dry, while in others the weight 
 of water to be removed is many times that 
 of the coal raised to the surface. For 
 example, at the Colver Mine in West Vir- 
 ginia, the pumping load averages approxi- 
 mately 31 tons of water per ton of coal 
 produced, while the Sonman Mine in West 
 Virginia pumps 33 tons of water per ton 
 of coal produced [Coal Age (8^)]. 
 
 Water may enter mine workings in sev- 
 eral ways: 
 
 1. From water-bearing strata that are 
 in contact with coal seams; 
 
 2. Through shallow mines from surface 
 seepage; 
 
 3. Through faults and fractures in 
 coal seams and adjacent strata; 
 
 4. Through active sections from aban- 
 doned workings. 
 
 There is considerable overlap in the 
 ways that water enters the mine workings. 
 For example, water may enter simultane- 
 ously through water-bearing strata in 
 contact with the coal seams and through 
 faults and fractures from the same over- 
 lying strata. Water may also enter from 
 the surface via percolation or through 
 faults and fractures that run through to 
 the surface. Also, percolated water from 
 
 the surface may be the source of water 
 for faults and fissures, which may later 
 feed the mine. Here, these pathways will 
 be dealt with separately, but under 
 natural conditions water may enter the 
 mine workings through any means possible, 
 no matter where it originates. 
 
 In considering the problem of water 
 passing into the mine workings, it is es- 
 sential to take into account: 
 
 1. The prevailing geologic and hydro- 
 logic conditions , including the composi- 
 tion and permeability of the associated 
 coal strata and the presence of any dis- 
 continuities such as faults, joints, or 
 igneous intrusions. 
 
 2. The depth of the mine workings and 
 thickness of the coal seam being mined. 
 
 3. The mining system employed and its 
 effect on the prevailing geologic 
 conditions. 
 
 Underground coal mines can create a 
 measurable change in water levels and 
 ground water flow as a result of removal 
 of water, coal, and rock from the mine. 
 The removal of the water occurs by grav- 
 ity drainage in the case of updip drift 
 mining or by pumping in downdip drift, 
 slope, or shaft mining. 
 
 Ground water movement through aquifers 
 from areas of higher piezometric pressure 
 to regions of lower piezometric pressure 
 has been described as follows [Wilson, 
 Mathews , and Stump (43) ] : When a mine 
 shaft sinks into water-bearing strata, it 
 creates a region of lowered piezometric 
 pressure, causing water to flow from the 
 strata to the mine shaft, which in turn 
 drains water from the pores and crevices 
 in the strata. If pumping is started to 
 remove the water, the flow into the shaft 
 continues as the piezometric pressure in 
 the shaft is lowered. As pumping contin- 
 ues, the water level is artificially de- 
 pressed and assumes the shape that a 
 stretched membrane would have if punched 
 downward with a stick. The water table 
 has the shape of a flat, inverted cone 
 with its apex at the shaft, known as the 
 
10 
 
 cone of depression. However, it is not a 
 true cone, since its sides, when viewed 
 in cross section, are not straight lines, 
 but curves that steepen toward the shaft. 
 
 The flow of water into a mine shaft is 
 heaviest when sinking begins. If sinking 
 of the shaft is halted and pumping con- 
 tinues at a steady rate, the flow into 
 the shaft gradually decreases and after 
 some time becomes virtually constant, 
 equaling the rate of recharge. Accord- 
 ingly, the cone of depression assumes a 
 shape that is practically stable, as the 
 flow of water into the shaft reaches a 
 state of equilibrium with the supply of 
 water entering the aquifer and percolat- 
 ing through it. If shaft sinking is re- 
 sumed, the process is repeated; the new 
 cone is deeper and requires a higher rate 
 of pumping to keep it drained. 
 
 If a drift is extended from the bottom 
 of the shaft, the cone of depression is 
 no longer a symmetrical cone; what was 
 formerly the point of the cone is elon- 
 gated into a horizontal line, with the 
 water table sloping upward from it at 
 both sides and at the ends. If closely 
 spaced crosscuts are driven from the 
 drifts, the cone assumes the form of a 
 bathtub with flat-sloping sides. If up- 
 per levels are now driven from the shaft, 
 they will encounter little water until 
 they are out far enough to reach the 
 sides of the cone. They will then begin 
 to tap the water reservoir, diminishing 
 the flow that enters the deepest 
 workings . 
 
 The creation of the cone of depression 
 by shaft sinking provides piezometric 
 highs and lows and allows for the flow of 
 water into the mine when the shaft is 
 lowered through water-bearing strata. 
 
 Detecting water-bearing strata and mea- 
 suring water levels and water movement 
 are being increasingly recognized as a 
 necessity for determining the economics 
 of mining. Drilling is a means of accom- 
 plishing this. Water levels and water 
 movement can be delineated and studied by 
 plotting the data on water level contour 
 maps, water level change maps, and well 
 hydrographs. 
 
 Gallaher of the U.S. Geological Survey 
 performed a study in West Virginia that 
 included the drilling of 28 boreholes 
 
 (43). In addition, 137 other private and 
 public wells were investigated. The 
 study determined the effect of deep min- 
 ing on ground water movement. The data 
 were correlated with information gathered 
 from seasonal and areal distribution of 
 precipitation, and the conclusions were — 
 
 1. No two mines are expected to be 
 alike in environment, hydrology, source 
 of pollution, or treatment. 
 
 2. Mining can affect speed, course, 
 and quality of water moving through the 
 mining area. 
 
 3. Mining accelerates the natural flow 
 and hydrogeological conditions already 
 existing in the area basins. 
 
 4. Water under pressure as a result of 
 flow through strata located at elevations 
 above the mine workings can enter the 
 mine from all directions, including the 
 floor. 
 
 5. The chemistry of the ground water 
 depends primarily on the composition 
 of the minerals with which it comes in 
 contact. 
 
 6. Water samples collected at differ- 
 ent depths varied widely in quality. 
 Samples taken at shallow depths were less 
 mineralized than those taken at great 
 depths. 
 
 COAL AND WATER-BEARING STRATA 
 
 The strata most frequently found im- 
 mediately above or below coalbeds are 
 shales, clays, and sandstones. These may 
 form either the roof or bottom and the 
 hanging and foot walls in pitching seams. 
 Conglomerates are rarely found in contact 
 with the coal but are frequently part of 
 the rock group associated with coalbeds. 
 This is also true of limestone beds. The 
 water-bearing capacity of these rocks 
 will depend on their depth, since the ca- 
 pacity of a rock to store and transmit 
 water will decrease with depth, owing to 
 the increasing pressure of the overlying 
 strata. 
 
11 
 
 Shales are generally the desired roof 
 materials when coal is mined. This is 
 because they are aquitards, having only 
 minor ground water leakage through them. 
 An exception to this condition is when 
 clay veins or similar structures are 
 present. Clay veins are slickensided 
 wedges of indurated clays and silts that 
 penetrate the coalbed from either above 
 or below. They can be vertical or form 
 an angle of about 45° with the vertical. 
 Clay veins encountered in mines are usu- 
 ally crooked and angular and interfinger 
 with the coal. They have thicknesses 
 ranging from 1 in (2.54 cm) to several 
 feet (a few meters) and may be hard 
 enough to damage mining equipment. Clay 
 veins generally extend into the strata 
 immediately overlying the coalbed, break- 
 ing up the lateral continuity of the lay- 
 ered roof strata, causing roof instabil- 
 ity. Water can then flow into the mine 
 through these zones. 
 
 Coal itself acts as a minor aquifer 
 since it possesses a fracture permeabil- 
 ity, although transmissivities appear to 
 vary from well to well by a factor of a 
 hundred or more. Transmissivities range 
 from less than 100 gpd/ft (0.14 cm 2 /s) to 
 over 10,000 gpd/ft (14 cm 2 /s). An impor- 
 tant aquifer characteristic of this unit 
 is its widespread continuity. 
 
 Sandstone is formed chiefly by accumu- 
 lation of sands in shallow water adjacent 
 to land from which stream action carries 
 the material. Many of the massive sand- 
 stones are extensively jointed. Even a 
 rock that has little or no water-bearing 
 capacity may yield water from joint 
 openings . 
 
 In Pennsylvania, the Allegheny Sand- 
 stone yields from 50 to 300 gpm (3.2 to 
 19 L/s), while the Pottsville Sandstone 
 yields from 100 to 400 gpm (6.3 to 25 
 L/s). The Pocono Formation of Pennsyl- 
 vania has also yielded from 300 to 600 
 gpm (19 to 38 L/s) in some places. The 
 Triassic sandstones of Pennsylvania, par- 
 ticularly those incorporating conglom- 
 erates and f anglomerates , yield as much 
 as 200 to 300 gpm (13 to 19 L/s). The 
 Pottsville in West Virginia has also 
 yielded over 250 gpm (16 L/s). On the 
 average, sandstone aquifers yield 50 gpm 
 (3.2 L/s) and are an excellent source of 
 
 water for communities throughout the Ap- 
 palachian region [Lohman ( 18) ; Doll, Mey- 
 er, and Archer (11)]. 
 
 Limestone is a hard sedimentary rock 
 composed chiefly of calcium carbonate, a 
 calcareous sediment that may at first 
 contain a large proportion of intersti- 
 tial space; however, subsequent solution 
 and recrystallization accompanying com- 
 paction may ultimately produce a lime- 
 stone with very little original porosity. 
 A seemingly impermeable rock may be rend- 
 ered permeable by joints or fractures, or 
 by the development of solution passages. 
 Solution passages in limestone result 
 from the solvent action of circulating 
 ground water charged with carbon dioxide 
 and usually follow preexisting joints or 
 bedding planes. 
 
 When the rock is deeply buried and the 
 ground water circulation is sluggish, or 
 when the rock has not been long subjected 
 to solvent action, the solution passages 
 may be few and small. If, however, the 
 topography and geologic structure have 
 favored rapid circulation, and conditions 
 have been stable over long periods, the 
 rock may be rendered cavernous. Some so- 
 lution passages are large enough to carry 
 the entire flow of a stream. The term 
 "lost river" has been applied to a stream 
 that disappears completely underground in 
 limestone terrain. Large springs are 
 frequently found in limestone areas. 
 
 This solution of limestone proceeds 
 most rapidly above the water table, where 
 downward movement of the water is rela- 
 tively vigorous and the supply of carbon 
 dioxide is adequate. Below the water ta- 
 ble, the content of dissolved carbon di- 
 oxide, and consequently the solvent power 
 of the water, becomes depleted. The 
 largest yields are obtained from lime- 
 stone that has been depressed with rela- 
 tion to the water table, so that its up- 
 per, cavernous areas become submerged and 
 saturated. Ultimate development of a 
 limestone terrain forms a karst region 
 where subterranean drainage through the 
 limestone creates large ground water 
 reservoirs . 
 
 In Pennsylvania, both the Cambrian and 
 Ordovician limestones and dolomites yield 
 abundant supplies of ground water. These 
 rocks are more or less fractured, and 
 
12 
 
 solution channels have been created. 
 Most of the wells yield adequate supplies 
 ranging from 100 to 1,000 gpm (6.3 to 
 63 L/s). Boiling Springs, in Cumberland 
 County, is the largest spring in Pennsyl- 
 vania and yields 13,500 to 20,600 gpm 
 (850 to 1,300 L/s). Bellefonte Spring, 
 in Centre County, yields roughly 14,000 
 gpm (880 L/s). The Devonian age Helder- 
 berg Limestone also yields moderate to 
 large supplies of water in Pennsylvania, 
 while the springs of the Mississippian 
 age Greenbrier Limestone of West Virginia 
 yield more than 140 gpm (9 L/s) (18). 
 
 As previously stated, while they remain 
 intact, the shales and clays immediate- 
 ly above and below the coal will not al- 
 low water to infiltrate the mine work- 
 ings. Occasionally though, the shale 
 above the coal or the underclay is ab- 
 sent. Then sandstone, and less frequent- 
 ly limestone, is adjacent to the coal. 
 This may result in the transmission of 
 many thousands of gallons of water into 
 the mine, depending on the depth of the 
 mine. In the Cahaba Coalfield of Alabama 
 [Johnston, Foster, and Howard (15)], con- 
 glomerates and porous strata directly 
 above the coal seams transmit water into 
 the mines, resulting in the need to es- 
 tablish a pumping system to keep the mine 
 dry. In central Pennsylvania [Parizek, 
 Sgambat , and Clar ( 24 ) ] , when the shale 
 above the coal pinches out and sandstone 
 lies on the coal, it is usually fractured 
 into blocky shapes and is very difficult 
 to support. 
 
 Unconsolidated deposits of glacial, ma- 
 rine, and alluvial origin can store and 
 transmit huge quantities of water and can 
 cause problems when in proximity to any 
 coal workings. Ninety percent of all 
 developed aquifers consist of these types 
 of deposits [Todd (36); UOP, Inc. (37)]. 
 They are widely distributed and have 
 caused considerable trouble to miners in 
 the past. The anthracite region of Penn- 
 sylvania has been especially plagued with 
 this type of problem and deserves mention 
 here, even though it is not part of the 
 Appalachian bituminous coal region. It 
 is estimated that the northern anthracite 
 field of Pennsylvania contains 10 billion 
 tons (9.1 billion t) of these deposits, 
 
 or a sufficient quantity to cover the 176 
 mi 2 (450 km 2 ) of coal area to a depth of 
 about 26 ft (8 m) [Bunting (_7 ) ] . These 
 deposits overlying coal measures attain 
 a maximum depth of more than 300 ft (91 
 m) . The materials vary widely in parti- 
 cle size and degree of sorting, with a 
 corresponding variation in their water- 
 yielding capacities. However, many are 
 often saturated to the point of being 
 semifluid. It is this condition of flu- 
 idity that limits the mining of coal 
 seams cropping in these deposits or in 
 close proximity to them. 
 
 A considerable number of inrushes have 
 occurred because mine workings were too 
 close to these deposits (_7, 40) . 
 
 • In 1882, the workings at the Maltby 
 Mine in Swoyersville, PA, broke into sand 
 and water, which filled the mine and 
 shaft to within 65 ft (20 m) of the top 
 in a few hours. 
 
 • In 1884, an inrush of sand and wa- 
 ter filled the slope of the Fuller Mine 
 at Swoyersville, PA, to the shaft level, 
 a vertical distance of almost 100 ft 
 (30 m). 
 
 • In 1885, the inrush of a culm bank 
 with sand and water completely filled the 
 gangways in the vicinity in less than 1 h 
 at the No. 1 Slope Mine in Nanticoke, PA. 
 The accident took the lives of 26 men. 
 
 • In 1912, an inrush of sand and water 
 broke into the workings at the Superba- 
 Lemont Mines in Stanton, PA, killing four 
 miners. 
 
 • In 1914, an inrush of approximately 
 19,600 yd 3 (15,000 m 3 ) of semifluid sand 
 and clay filled several thousand feet 
 (a couple of thousand meters) of gang- 
 ways and tunnels, and required months to 
 clean up. The accident occurred at the 
 Sugar Notch No. 9 Mine in Sugar Notch, 
 PA. 
 
 • In 1917, an inrush of sand and water 
 broke into the Wilkeson Mine workings in 
 Wilkeson, PA, killing six miners. 
 
13 
 
 © In 1927, an inrush due to a break- 
 through into 200-ft (60-m) thick gravel 
 beds killed seven miners in Carbonado, 
 
 WA. 
 
 • In 1959, an inrush of water killed 
 12 miners at the Lehigh Valley Coal Co.- 
 Dillston Coal Co. in Pennsylvania when 
 the workings broke into the alluvial de- 
 posits of the Susquehanna River. 
 
 The coal seams that are being mined 
 currently are deep enough so that they do 
 not come into contact with these types of 
 deposits. However, the huge quantities 
 of water contained in these deposits may 
 be tapped by means other than direct con- 
 tact with coal workings. These means 
 will be examined in other sections of the 
 report. 
 
 WATER IN SHALLOW MINES 
 
 Strata will tend to store and transmit 
 less water with increasing depth, as the 
 porosity of the strata is affected by the 
 increased confining pressure resulting 
 from the weight of the overburden [Ash, 
 Dierks, and Miller (3); Miller and Thomp- 
 son ( 2_2 ) ; Wrathers , Swanson, and Langill, 
 (_44) ] • This pressure also tends to close 
 up any fissures and cracks that exist. 
 At depths of less than 300 ft (92 m) , it 
 is comparatively easy for water to perco- 
 late to a certain varying depth as a con- 
 sequence of the porosity of the surface 
 rocks, according to Miller and Thompson. 
 The coal measures are generally very wet 
 to work at these shallow depths. There 
 is a marked difference between the quan- 
 tity of water pumped in summer and in 
 winter in the areas where water can per- 
 colate rapidly into the mine workings. 
 
 Surface Seepage 
 
 The volume of water seeping into mine 
 workings during and after any period of 
 rainfall varies greatly in adjoining ba- 
 sins and even in adjoining mines in the 
 same field because of differences in the 
 condition of the strata as affected by 
 the progress of coal extraction [Ash (1), 
 Ash, Dierks, and Miller (3); Ash and Link 
 
 (4_ ) ; Ash, Link, and Romischer (_5_ ) ; Ash 
 and Whaite ( 6_) ] . The ratio between run- 
 off and seepage varies for each period of 
 rainfall in any given area because of 
 variables in (1) the rate of rainfall, 
 (2) duration of storms, (3) rate of evap- 
 oration (depending on temperature and 
 humidity) , (4) transpiration (depending 
 on the season and amount of vegetation) , 
 (5) status of the water table, (6) frost 
 that seals crevices in the ground, 
 (7) presence of anchor ice sealing stream 
 bottoms, (8) distribution of rainfall, 
 (9) topography, and (10) surface soil 
 condition and type. 
 
 Surface water entering underground coal 
 mines may originate either at a surface 
 body or through general surface infiltra- 
 tion. Any bodies of surface water may 
 contain a sufficiently large volume of 
 water so that significant seepage into 
 underground workings could occur. Howev- 
 er, the most important avenue of surface 
 water seepage is that of streambed seep- 
 age into underground waterways. 
 
 Most streams that cross coal measures 
 usually lose some of their water, which 
 eventually enters underground mine work- 
 ings. It is usually impossible, except 
 in small streams, to accurately measure 
 the amount of seepage that will require 
 the use of corrective measures. This is 
 because the loss at any particular point 
 is usually very small, and the distance 
 between the point where the water left 
 the stream and the point where it entered 
 into the mine workings may be great. 
 
 Many different factors affect the vol- 
 ume of water infiltrating mine workings. 
 The following factors play a significant 
 role in the inflow to mines from streams 
 (3-6): (1) quantity of water flowing in 
 streams, (2) velocity of the water flow- 
 ing in streams, (3) nature of material 
 composing the stream channel, (4) wetted 
 perimeter of stream channels, (5) weather 
 conditions, (6) gradient or slope of 
 streams, and (7) fractures in the coal 
 measures underlying the streams. 
 
 Stream seepage will not increase sig- 
 nificantly unless the volume of water 
 added to the stream is enough to appreci- 
 ably increase the cross section of the 
 stream channel in contact with the water. 
 
14 
 
 A noticeable increase in the depth of wa- 
 ter flowing in the channel of a river or 
 stream after a heavy rain indicates an 
 increase in seepage due to the increase 
 in the wetted perimeter of the stream 
 channel O ) . When streams are in flood 
 stage, water spreading out beyond normal 
 streambanks further increases seepage. 
 
 The anthracite region of Pennsylvania 
 serves as a classic example of stream 
 seepage into underground mines. Many of 
 the smaller streams in the region lose 
 all of their water soon after crossing 
 the outcrop of the lowest anthracite bed, 
 where they enter the area that overlies 
 the coal measures. These streams carry 
 water throughout their original length 
 only during periods of heavy runoff. For 
 the greater part of the year, their en- 
 tire flow seeps into the mine workings. 
 This flow can range from a few gallons to 
 several thousand gallons per minute (3). 
 
 A study of larger streams indicated a 
 marked decrease in flow between the point 
 where they intersect the coal outcrops 
 and the point where they flow into the 
 main stream. This was true at almost all 
 periods when relatively low water levels 
 permitted comparable observations. How- 
 ever, at the same levels of water, such 
 decrease did not occur when the bed of 
 the stream was sealed by anchor ice. 
 Consequently, a project is being under- 
 taken in western Maryland to reline a 
 streambed for a distance of approximate- 
 ly 4-1/2 miles (7-1/4 km) in order to re- 
 duce infiltration. Water currently in- 
 filtrates through the streambed at a rate 
 of roughly 15,000 gpm (990 L/s). This 
 water is entering abandoned underground 
 mines, causing the stream to dry up dur- 
 ing the summer months. The project in- 
 volves putting down a clay bottom, topped 
 by a layer of sand and a layer of riprap. 
 The estimated cost of the project is $3.5 
 million. 
 
 Natural surface seepage is also a prob- 
 lem in permeable areas where the infil- 
 tration rate is so great that some oper- 
 ating companies have dug ditches and 
 built flumes to divert the runoff into 
 natural stream channels. In addition, 
 mining operations have changed the con- 
 figuration of the terrain, thereby 
 
 affecting the original drainage patterns 
 of the region. The continued increase in 
 the number and size of culm banks, cinder 
 dumps , and unreclaimed spoil banks has 
 blocked the normal flow of water to the 
 surface streams so much that water now 
 collects in many low places and eventual- 
 ly seeps into the ground. In addition, 
 denuding woodlands destroys a control of 
 runoff, and solids from breakers and 
 banks pollute and choke stream channels. 
 The dry beds of thousands of small former 
 watercourses are evidence of the general 
 disturbance of the surface (3-_6 ) . 
 
 Surface Water Inrush 
 
 In considering the problems of water 
 passing from a surface source into mine 
 workings, the proximity of mining to a 
 given body of water is a vital factor in 
 the risk of inundation. Another impor- 
 tant factor is that the height of a roof 
 fall can be in part related to the height 
 of workings and in part to the nature of 
 the solid strata between the workings and 
 the streambed. 
 
 Studies in the anthracite region of 
 Pennsylvania are presented here to pro- 
 vide a clearer picture of the quantity of 
 water capable of entering underground 
 coal mines via stream and surface seep- 
 age. One study involved the Lackawanna 
 Basin and the Wyoming Basin of the North- 
 ern Field, the Western Middle Field, and 
 the Southern Field (3-6.) • 
 
 The Lackawanna River and its tribu- 
 taries drain a troughlike area of 347 
 mi 2 (900 km 2 ). The synclinal axis of 
 this trough lies within the coal mea- 
 sures. For 1948, the U.S. Weather Bureau 
 recorded 44.9 in (114 cm) of rainfall, 
 indicating that there were 135 billion 
 gal (510 billion L) of runoff from the 
 Lackawanna River drainage area. This is 
 approximately three times the volume of 
 water pumped for this area in 1948. Be- 
 cause of the pervious condition of the 
 strata overlying the mine workings, ap- 
 proximately one-third of the total runoff 
 in the Lackawanna River area becomes mine 
 water. Approximately 22 pet of this wa- 
 ter arrives underground as a result of 
 direct surface seepage. In addition, an 
 
15 
 
 equal volume seeps into the mine workings 
 through the pervious beds of 52 streams. 
 The remaining 56 pet of the pumped water 
 seeps underground through the bed of the 
 Lackawanna River. 
 
 Similarly, the Susquehanna River and 
 its tributaries drain an area of 169 mi 2 
 (437 km 2 ) overlying the Wyoming Basin. 
 Even though this is slightly less than 
 half the size of the Lackawanna River 
 drainage area, the total volume of water 
 pumped to the surface is 21 pet more than 
 in the Lackawanna Basin. The average 
 volume of water pumped per year is 112 
 billion gal (425 billion L) , which corre- 
 sponds to more than 214,300 gpm (13,500 
 L/s) pumped against an average hydro- 
 static head of 394 ft (120 m) . It is 
 difficult to achieve good runoff because 
 of the relatively flat terrain created 
 by the wide floodplain in the Wyoming 
 Valley. Consequently, much of the sur- 
 face water seeps directly into the 
 ground, eventually ending up in the mine 
 workings . 
 
 Approximately 30 pet of the seepage wa- 
 ter is direct surface seepage, while 
 another 21 pet seeps through the pervious 
 beds of 59 streams. The remaining 49 pet 
 seeps through the bed of the Susquehanna 
 River. 
 
 In contrast to these two basins, the 
 Western Middle Field and the Southern 
 Field do not have major rivers overlying 
 them. Therefore, there is a higher per- 
 centage of mine water from surface seep- 
 age. In 1951, 36 billion gal (136 bil- 
 lion L) were pumped to the surface from 
 the Western Middle Field, while 17 bil- 
 lion gal (64 billion L) were pumped from 
 the Southern Field. This corresponds to 
 roughly 67 pet and 34 pet of the total 
 runoff into the respective drainage 
 areas. The general surface seepage in 
 the coal areas is 90 and 92 pet, respec- 
 tively. The remaining 10 and 8 pet are 
 seepage from the streambeds. 
 
 In the bituminous region, surface res- 
 toration and stream reconstruction have 
 also been underway to check water inflow 
 due to seepage. A project involving the 
 construction of a new channel on Little 
 Sandy Run in north central Pennsylvania 
 was undertaken in 1974 [Klingensmith , 
 
 Miorin, and Saliunas (17) ] . The channel 
 was to be constructed approximately 1,000 
 ft (305 m) over underlying mine workings. 
 A significant loss of streamflow had been 
 noted here during earlier watershed in- 
 vestigations. The area was cleared and 
 grubbed; the new channel was excavated; 
 the existing channel was filled; a layer 
 of sand and bentonite was placed as an 
 impermeable membrane in the new channel; 
 riprap protection was provided for the 
 impermeable membrane; two underdrains 
 were laid to convey acid water from new 
 mine pool overflows (possibly caused by 
 Hurricane Agnes in June 1972) into the 
 new channel; and the affected area was 
 graded, limed, fertilized, and seeded. 
 This work was completed in September 
 1974, at a total construction cost of 
 $96,545.97. This channel also success- 
 fully carried the runoff from Hurricane 
 Eloise in September 1975.' No maintenance 
 has been necessary since construction was 
 completed. An estimated average infil- 
 tration of 400,000 gpd (1.52 million L/d) 
 of water was prevented from entering the 
 underlying mine workings. 
 
 Another project involved the recon- 
 struction of the streambed of a headwa- 
 ter's branch of Morris Run (17) . The re- 
 constructed streambed was first lined 
 with a layer of locally available clay, 
 which was then covered by a protective 
 filler blanket and quarry stones. The 
 entire area was then limed, fertilized, 
 and seeded. The total construction cost 
 of this project, which was completed in 
 October 1975, was $453,925.20. This 
 project, together with the reclamation of 
 two adjacent strip mines, has prevented 
 an estimated average daily infiltration 
 of 1.25 million gpd (4.73 million L/d) of 
 water into underlying mine workings. 
 
 These data indicate that huge quanti- 
 ties of water can enter mine workings as 
 a result of seepage , and because of the 
 seriousness of this problem, preventative 
 measures must be taken. 
 
 WATER ENTRANCE THROUGH FRACTURES 
 
 Earth fractures, such as faults, frac- 
 ture zones, joint systems in rocks, and 
 fractures caused by surface subsidence, 
 
16 
 
 allow water to enter underground mines 
 in various quantities. They are a major 
 avenue of water entrance into underground 
 mines, because coal measures are usually 
 overlain by impervious strata consisting 
 of shales. No water will enter the mine 
 from the surface or from any aquifer 
 above the coal seam if these strata re- 
 main intact. 
 
 Fracture flow, which tends to local- 
 ize inflows, is prevalent within the 
 eastern margins of the bituminous coal 
 region. These zones of fracture concen- 
 trations show up on the surface as frac- 
 ture traces. These fracture traces have 
 been used to locate highly productive 
 water wells with aerial photography, and 
 more recently, with remote sensing. 
 Here, subtle lines are present on the 
 Earth's surface; indicators include more 
 lavish vegetation due to ground water in 
 decomposed rocks, surface sags and de- 
 pressions, and stream valley alignments. 
 There is often an abundant supply of wa- 
 ter where two or more of these fracture 
 traces intersect. Wells drilled at these 
 intersections have yielded up to 3,000 
 times more water than wells drilled at 
 random. 
 
 Joints 
 
 A joint is a fracture in a rock in 
 which there is no observable relative 
 movement between the sides. A series of 
 parallel joints is called a joint set, 
 while two or more sets intersecting pro- 
 duce a joint system. 
 
 Joints are important because they lo- 
 cally control drainage patterns and be- 
 cause they provide a passage through 
 which water may penetrate deeply into a 
 rock mass, thus allowing weathering to 
 take place. This is especially evident 
 in limestone, where the end result of 
 this weathering is karst scenery. In ad- 
 dition, joints increase the porosity and 
 permeability of a rock mass, thereby cre- 
 ating aquifers in previously impervious 
 strata. If they are developed enough, 
 the joints can also tap overlying aqui- 
 fers and water sources, and provide flow 
 paths to the mine workings. 
 
 The intergranular permeability of shale 
 is relatively low because the rock is 
 
 fine grained and lithified. Shales have 
 a high porosity relative to most sand- 
 stones, but the interstitial spaces are 
 so minute that the water movement is re- 
 stricted. For this reason, shales usual- 
 ly provide an excellent means for keeping 
 water out of underground mines . Howev- 
 er, where shales are jointed, they have 
 provided significant water supplies to 
 users. In many rocks, shales and joints 
 are the principal means by which the wa- 
 ter is stored and transmitted. 
 
 Wells penetrating strata whose water 
 capacity is determined by joints yield 
 up to 200 gpm (13 L/s), with most wells 
 yielding 50 gpm (3 L/s). Pre-Cambrian 
 rocks of southeast Pennsylvania, consist- 
 ing of schists, slates, and crystalline 
 rocks, yield up to 100 gpm (6 L/s), while 
 the rocks in the lower Cambrian sand- 
 stones, quartzites, and conglomerates 
 yield up to 200 gpm (13 L/s) (18). 
 
 Joints tend to close and heal with 
 depth, resulting in a decreasing yield 
 of ground water. Closed joints are some- 
 times called latent, blind, or incipient. 
 The majority of open joints are close to 
 the ground surface, and significant flows 
 are encountered, usually in the first 100 
 ft (30 m) of excavation (44) . With in- 
 creasing depth, the increased confining 
 pressure caused by the overburden weight 
 tends to limit the space created by 
 jointing. At depths greater than 300 ft 
 (90 m) , the water storage capacity of 
 joints becomes less significant. Howev- 
 er, the presence of higher differential 
 heads in deep mines tends to negate the 
 advantage of lower permeabilities created 
 by this healing, resulting in the inflow 
 of stored water into the mines. 
 
 Faults and Fracture Zo nes 
 
 Faults can cause water problems in un- 
 derground coal mines by (1) acting as a 
 water reservoir, releasing water when 
 tapped by the mine workings, and (2) act- 
 ing as a conduit, hydraulically connect- 
 ing a water source, such as an aquifer 
 or surface water body, to the mine work- 
 ings. Faults and fracture zones can also 
 cause very bad roof conditions, espe- 
 cially if a significant amount of water 
 is present. As a rule, jointing and 
 
 
17 
 
 faulting tend to coincide in folded re- 
 gions. No real distinction is made be- 
 tween faults and joints since both act as 
 conduits, transmitting water from other 
 sources to the mine workings. 
 
 The most noteworthy example of how 
 faults can be a cause of inundations is 
 the flooding of the Higashisome Colliery 
 in Japan in 1915. (Although collieries 
 in Japan are outside the scope of this 
 report, they serve as excellent examples 
 of how costly, in both production and 
 safety, a fault zone can be.) On April 
 12, 1915, an estimated 10.5 million ft 3 
 (0.3 million m 3 ) of water flooded the en- 
 tire mine in 2 h , killing 237 workers. 
 The source of the flooding was a fault 
 that acted as a hydraulic connection be- 
 tween a seabed above the workings and the 
 workings themselves. The fault extended 
 155 ft (47 m) through a sandstone bed, 
 and another 83 ft (25 m) through an allu- 
 vial deposit of clay and sand (40) . 
 
 Japanese collieries have been known 
 to be susceptible to flooding through 
 faults. In 1934, 54 lives were lost when 
 the Matsushima Mine was flooded. Here 
 the fault penetrated over 200 ft (61 m) 
 of cover to a surface seabed. In 1942, 
 183 miners were killed when the Chosei 
 Mine was flooded by seawater penetrating 
 119 ft (36 m) through a fault (40). 
 
 In the United States, fracture-domi- 
 nated flows have not been as severe. In 
 some cases , especially where the fault 
 zone is serving as a storage reservoir 
 and the recharge to the fault zone is 
 limited, water inflow is virtually negli- 
 gible. Republic Steel's North River No. 
 1 Mine in Berry, AL, exemplifies this. 
 Here, the major source of water is from 
 water-bearing fractures. The workings 
 are dry, except when occasional water- 
 bearing fracture zones are penetrated by 
 mine openings. The initial penetration 
 of water-bearing openings usually re- 
 leases a large inflow averaging 200 to 
 300 gpm (12.6 to 18.9 L/s). This would 
 be a problem should this inflow remain 
 constant. However, after a period of 
 time, the flows decrease to a trickle, 
 indicating that the water storage system 
 is very restricted both vertically and 
 laterally [Shotts, Sterett, and Simpson 
 (31)]. 
 
 The Lancashire No. 20 Mine near Car- 
 rollton, PA, illustrates another feature 
 of fracture-dominated flows (38) . Here, 
 baseline monitoring of water quantities 
 established that the flows responded rap- 
 idly to wet and dry conditions in spite 
 of a depth of over 500 ft (152 m) . This 
 rapid response indicated that the frac- 
 ture zones had a hydraulic connection to 
 the surface. It was even possible to 
 recognize recharge from individual rain- 
 storms. Geologic investigations indi- 
 cated that the fracture zones consisted 
 of steeply dipping fractures that inter- 
 sected the surface, permitting rapid 
 recharge from precipitation and from 
 streams or ponds on the surface. It was 
 noted that secondary aquifers also fed 
 the fracture zones. 
 
 Mine Subsidence Fractures 
 
 Mine roof fracturing and the resulting 
 surface subsidence following the removal 
 of mine roof supports such as pillars and 
 blocks is one primary cause of water en- 
 trance into deep mines. Here, water de- 
 scends on fractures resulting from the 
 subsidence of mined-out ground. Such 
 fissures form direct conduits that carry 
 water. It has been found that as pil- 
 lars are removed, the cost of pumping in- 
 creases greatly. In some of the Pratt 
 Mines (Alabama), where pillars were 
 robbed as the entries were driven to the 
 boundary, from 10 to 15 tons of water 
 were pumped for each ton of coal produced 
 U5). 
 
 Whittaker, Singh, and Neate (42) have 
 attempted to quantify the effects of 
 subsidence on the increased permeability 
 of these zones in England. Although this 
 work was done in England and not in the 
 Appalachian coal region of the United 
 States , it is the only current investi- 
 gation that quantifies the effects of 
 subsidence. One of the studies was per- 
 formed in the East Midlands Coalfields, 
 involving the deep soft seam. The re- 
 treating longwall mining method was em- 
 ployed in the study. The mine was 1,970 
 ft (600 m) deep and had a longwall face 
 width of 690 ft (210 m) , and the seam was 
 31 in (80 cm) thick. The results showed 
 that the closer the stratum was to the 
 
18 
 
 coal seam, the more the permeability was 
 increased by caving. 
 
 A second site investigated by Whit- 
 taker, Singh, and Neate (42) was the 
 Yorkshire Coalfield. Here, the shallow 
 Wood Seam at Wentworth was being rained 
 by the retreating longwall method. The 
 depth of the seam was rather shallow at 
 175 ft (53 m) . Results showed that a 
 discernible change in the waterflow was 
 taking place at 164 to 197 ft (50 to 60 
 m) ahead of the face line. This flow in- 
 creased in marked steps, indicating the 
 opening and closing of near-surface 
 cracks and fissures. The flow curve set- 
 tled to a constant value of about 98 to 
 131 ft (30 to 40 m) behind the face line. 
 The onset of permeability change occurred 
 significantly ahead of the face line with 
 the upper test strata in comparison with 
 the lower test strata. 
 
 A third site investigated ( 42 ) was the 
 Lyneraouth Mine. Here, the seam under 
 consideration was the Brass Hill Seam. A 
 retreating longwall method was being used 
 on a 3.3-ft (1-m) seam. The face length 
 was 600 ft (183 m) . Static head measure- 
 ments were taken at six different depths 
 in two boreholes. The lowest test sec- 
 tion showed the largest change in static 
 head, with the higher sections displaying 
 progressively less change. However, per- 
 meability changes occurred first in the 
 higher test section. 
 
 All test results show a marked increase 
 in the permeability of the strata as a 
 result of subsidence. Marked increases 
 in flow rates were also observed. It is 
 important to compare the quantity of wa- 
 ter flowing when a possible aquifer is 
 tapped by the fracturing, with that flow- 
 ing when only the immediate roof , con- 
 sisting of relatively impervious strata, 
 is tapped. 
 
 Another example of water inflow in un- 
 derground deep mines that was due to sub- 
 sidence occurred at the Jones and Laugh- 
 lin Steel Corp.'s Shannopin's Section No. 
 1 Mine in Greene County, PA [Doyle, Chen, 
 Malone, and Rapp (12)] . The Pittsburgh 
 Coal Seam was being mined. It has a min- 
 able thickness of about 6.6 ft (2 m) . 
 Section 1 underlies Dooley Run drainage 
 basin, which during the investigation 
 had no flow. The method of mining was 
 
 retreat room-and-pillar , which resulted 
 in surface subsidence and fracturing of 
 the overlying rock strata. The overbur- 
 den thickness of 350 ft (107 m) was not 
 sufficient to prevent the total loss of 
 streamflow. The river flow was estimated 
 at 1 ft 3 /s (28 L/s), which corresponds to 
 a loss of 650,000 gpd. The researchers 
 concluded that essentially all precipita- 
 tion within the drainage basin (less the 
 loss through evapotranspiration) is per- 
 colating into the mine through subsidence 
 fractures and fissures. This is an exam- 
 ple of mine subsidence capturing most of 
 the precipitation falling in the drainage 
 basin. 
 
 ABANDONED DEEP MINES 
 
 Flooding of abandoned mines is a major 
 factor affecting the future of the coal 
 industry. The proximity of these flooded 
 mines to active workings results in the 
 infiltration of water either through bar- 
 rier pillars, which separate the aban- 
 doned workings from the active workings, 
 or through interconnections [Ash, Cassap, 
 Eaton, Hughs, Romischer, and Westfield 
 (2); Peters, (26)]. Therefore, the aban- 
 donment of a mine and suspension of pump- 
 ing in that mine tends to increase pump- 
 ing costs for adjacent mines. Adjoining 
 mines must prepare to handle more water 
 seeping through barrier pillars or main- 
 tain the water in the abandoned mine at 
 such an altitude that the barrier pillar 
 will not fail or allow excessive seepage. 
 Thus, the operating mines gradually as- 
 sume the pumping loads of all abandoned 
 mines in their basin. This is impossible 
 in some mines so mine pumps have been in- 
 stalled in abandoned mines to prevent the 
 flooding of active mines. 
 
 Barrier Pillars 
 
 Coal mines are usually separated by 
 barrier pillars, which are formed by 
 leaving part of a coal seam unmined along 
 the lines of adjoining mining properties, 
 or between mines or parts of mines. The 
 principal function of barrier pillars 
 is to act as a dam to confine accumu- 
 lating mine water and prevent it from 
 seeping, flowing, or breaking into an 
 
19 
 
 adjacent mine and causing loss of life 
 and property [Ash, Cassap, Eaton, Hughs, 
 Romischer, and Westfield (2 ) ; Dierks, 
 Eaton, Whaite, and Moyer (10) ] . 
 
 A barrier pillar should be designed to 
 hold water in abandoned mines under high 
 head, since the pressure may be suffi- 
 cient to force water through the strata 
 either above or below the otherwise ade- 
 quate barrier pillar. The size of these 
 barrier pillars is based on (1) the ex- 
 tent of waterlogged workings and accumu- 
 lation of water, (2) physical-mechanical 
 properties of coal, (3) presence of geo- 
 logical disturbances, and (4) head of wa- 
 ter against the proposed drivages [Gulati 
 and Singh (14) ] . 
 
 The path of seepage in the vicinity of 
 a coal barrier will depend on the flow 
 gradient and position with relation to 
 major circulation. In downward circulat- 
 ing zones , seepage tends to occur along 
 and under the coal, with a smaller amount 
 over the coal. In upward circulating 
 zones, seepage tends to occur along and 
 over the coal, with perhaps a smaller 
 amount under the coal. The underclay 
 significantly prevents seepage below the 
 coal (22). 
 
 Investigations have revealed that the 
 extent of damage to many barrier pillars 
 during subsidence cannot be anticipated 
 since many are too small, or are partly 
 removed, punctured, or encroached upon 
 (_32_) . The extent of bridging of roof 
 rock above a mined coal will affect the 
 ability of a barrier to restrict seepage. 
 Undisturbed permeability in roof rock 
 will be limited to a wedge of unfrac- 
 tured rock above the barrier. A highly 
 permeable bed close to the level of the 
 coal will also decrease the effectiveness 
 of seepage restriction by a barrier, es- 
 pecially in the presence of subsidence 
 fractures. In addition, barrier pillars 
 often are punctured by passageways in 
 which masonry or concrete dams are con- 
 structed to resist hydrostatic pressure. 
 However, a masonry dam can fail even be- 
 fore the barrier pillar itself collapses 
 if the barrier pillar is unstable. 
 
 The abandoned flooded portion of the 
 Republic Steel Corp.'s Clyde Mine, in 
 Washington County, PA, is the largest 
 source of water infiltration to Bethlehem 
 
 Steel Corp.'s Marianna No. 58 Mine to the 
 west. The Clyde Mine is higher up, and 
 the impounded water behind the barrier 
 pillar that separates the two mines seeps 
 through fractures. Percolation reduction 
 would require at least 9,600 ft (3,000 m) 
 of grout curtain to seal the fractures 
 
 (j_2). 
 
 At Jones and Laughlin Steel Corp.'s 
 Shannopin Mine Complex in Greene City, 
 PA, sections 1 and 2 experience water in- 
 filtration of about 750,000 gpd (30 L/s) 
 from the worked-out sections of the Maid- 
 en Mine. The water infiltrates through 
 barrier pillars (12). 
 
 Present-day problems would be much sim- 
 pler if the need for and value of barrier 
 pillars had been understood 75 yr ago, 
 when mining at depth was getting under- 
 way. Unfortunately, particularly in the 
 anthracite coal region of Pennsylvania, 
 lands were not generally controlled in 
 large blocks by one company or individ- 
 ual; because of the irregular shape of 
 holdings, the quantity of coal that would 
 have had to be left for adequate barrier 
 pillars was too great to be considered. 
 In the past, barrier pillars were not es- 
 tablished soon enough. Excavations were 
 made too close to property lines before 
 there was any attempt to establish a 
 barrier pillar. 
 
 Interconnections 
 
 Abandoned deep coal mines are usually 
 not completely separated from the active 
 workings by barrier pillars. Great min- 
 ing activity with the resultant abandoned 
 and waterlogged workings results in the 
 connection of both active and abandoned 
 workings by shafts, boreholes, cross- 
 measure drifts, and in-seam roads. These 
 interconnections permit water from inac- 
 tive mines to enter the active workings. 
 Unreliable old mine maps compound the 
 problem, because the extent of the water- 
 logged workings is not always known. 
 
 Large quantities of surface water are 
 often collected by nonregraded surface 
 mines. These mines usually consist of 
 open pits with no surface exit point for 
 this water. Water collecting in these 
 pits can then infiltrate into any near- 
 by underground mines. Many active and 
 
20 
 
 abandoned underground mines also out- 
 crop into areas that have been contour- 
 stripped. This provides a direct hydrau- 
 lic connection into an underground mine. 
 In addition, water collected by a surface 
 mine on the updip side of an underground 
 working can enter the working through a 
 permeable coal seam, either directly or 
 by entering the ground water system. 
 
 Recontouring and revegetation of the 
 strip mines located above an underground 
 mine should control and reduce ground wa- 
 ter infiltration. Improved contouring 
 for surface drainage would favor surface 
 runoff. Vegetation will hold water and 
 increase evapotranspiration. The addi- 
 tion of limestone to the cover, in con- 
 junction with revegetation, would improve 
 the quality of water seeping into the wa- 
 ter table. Draining the strip pits would 
 accompany recontouring and would lessen 
 vertical leakage. The pits could be 
 drained with ditches without recontouring 
 or by installing pumps and piping. 
 
 At the Beech Creek Mine in northern 
 Pennsylvania, the restoration of an aban- 
 doned strip mine reduced the amount of 
 water flowing into the underground work- 
 ings to approximately 36,000 gpd (2 L/s). 
 The work included backfilling and regrad- 
 ing, providing ditches and flumes to con- 
 vey surface water across the restored 
 strip mine, liming, fertilizing, and 
 seeding the area (17) . 
 
 Another site where waters were entering 
 underground mines through the surface 
 mines was near Williamsport , PA, at the 
 Tioga River (17) . Here, an inactive 16- 
 acre (6.5-hectare) strip mine partially 
 full of water was restored, a streambed 
 running across the mine was recon- 
 structed, and the entire area was limed 
 and fertilized. Also, an 80-acre (32- 
 hectare) portion of an inactive strip 
 mine was restored and graded to blend 
 into an adjacent, previously restored 
 strip-mined area. This has prevented an 
 estimated daily infiltration of 1.23 mil- 
 lion gpd (50 L/s) of water into underly- 
 ing deep mine workings. 
 
 Active strip mines have also been known 
 to create water problems for underground 
 coal mines. In Great Britain, the Aber- 
 pergum Colliery had its main returns 
 blocked when water from the Maesgwyn Cap 
 
 Opencast Site entered them in 1963 [Dav- 
 ies and Baird (9_) ] . On December 30, 
 1974, the pumps at Tower No. 4 Shaft of 
 Tower-Ferhilt Mine were overwhelmed by 
 water after the pillar that had separated 
 old workings in the 9-ft (3-m) seam at 
 Tower from the disused workings of Rhigos 
 Mine had been penetrated by the Dunraven 
 Opencast Coal Site. The result was over- 
 flowing sumps and flooded roadways, and 
 the obstruction of one roadway serving 
 as a return from a longwall face. When 
 opencast operations are allowed to en- 
 croach on old workings connected with 
 working mines , there is a risk of inun- 
 dation. The likelihood of flooding in- 
 creases during periods of high rainfall. 
 
 Boreholes, Wells, and Shafts 
 
 Boreholes and abandoned wells act as 
 water collection points and conduits to 
 underground mines. They are usually ver- 
 tical, or near vertical, and tap overly- 
 ing aquifers and surface waters. They 
 are usually drained when the holes are 
 penetrated during mining. 
 
 Shafts and mine openings are very simi- 
 lar to boreholes and abandoned wells 
 since they act as water collection points 
 and conduits to underground mines by tap- 
 ping overlying aquifers and collecting 
 surface waters. The difference is that 
 they are usually an integral part of 
 the mining operation, and therefore can- 
 not be sealed. An example of this is 
 the Shidler Air Shaft located in an 
 abandoned section of Marianna No. 58 Mine 
 in Washington City, PA. The air shaft 
 provides some ventilation of active 
 operations, and sealing the shaft would 
 affect mine ventilation (32). 
 
 It is evident that there are a consid- 
 erable number of avenues by which water 
 may enter underground coal mines. Most 
 of these avenues are interrelated in that 
 any one source could feed any number of 
 other sources; for example, seepage could 
 feed faults, aquifers, abandoned mines, 
 or the mine itself. The danger of a sud- 
 den influx of water from an overlying 
 flooded mine, as strata are disturbed by 
 pillar extraction in the lower bed, can- 
 not be overemphasized. 
 
21 
 
 Knowledge of the various sources of wa- 
 ter inflow will assist the mining engi- 
 neer in identifying sources of inflow to 
 a specific mine, in the planning and de- 
 sign stages. Early identification of the 
 sources of water inflow together with the 
 
 information on water control practices 
 provided in the following section will 
 enable the mining engineer to evaluate 
 and select the most effective method(s) 
 of water control. 
 
 WATER CONTROL PRACTICES 
 
 This section discusses practices that 
 have been used, or proposed for use, to 
 control the inflow of surface and ground 
 water into active underground coal mines. 
 This compilation was obtained by review- 
 ing the available literature and select- 
 ing those practices that are designed to 
 be preventative in nature, rather than 
 prescriptive. Thus, the common objective 
 of all of the practices described is to 
 prevent or reduce the inflow of water in- 
 to active mines for the implicit purpose 
 of reducing the costs of coal production 
 by improving one or all of the three cat- 
 egories previously discussed: (1) health 
 and safety, (2) production, and (3) the 
 environment. 
 
 Ten water control practices are de- 
 scribed. Although each practice is de- 
 scribed separately, they can be grouped 
 according to whether they are designed to 
 control surface or ground water inflow. 
 Figure 2 is a matrix listing the 10 con- 
 trol practices and indicating which of 
 the sources of water inflow, previously 
 discussed, can be controlled by the use 
 of these practices. The first five prac- 
 tices described in this section are suit- 
 able primarily for controlling surface 
 water inflow, while the last five prac- 
 tices described are suitable primarily 
 for the control of ground water inflows. 
 
 The water control practices presented 
 are not universally applicable, and the 
 choice of a particular technique to use 
 for a given situation will ultimately de- 
 pend on the cost effectiveness of the 
 technique. The cost effectiveness of the 
 technique will depend on the hydrogeo- 
 logical conditions in the area and the 
 benefits derived from the use of the 
 practice with respect to health and safe- 
 ty, production, and the environment. 
 Unfortunately, the literature evaluation 
 revealed that the technical feasibility 
 
 and cost effectiveness of many of these 
 practices have yet to be determined. 
 Many of these practices were selected be- 
 cause they represented the best, and in 
 some instances the only, available con- 
 trol technology. However, provisions 
 were seldom incorporated to monitor the 
 short- or long-term performance of these 
 controls. 
 
 For example, an interim report prepared 
 by Schmidt and Ahnell (28) for the Bureau 
 describes the tasks necessary for the ap- 
 plication of a mine dewatering strategy 
 and the implementation of a dewatering 
 scheme at a mine in Preston County, WV. 
 Results of the mine dewatering efforts 
 were inconclusive, partly because of 
 problems encountered in attempting flow 
 measurements inside the mine. The depth 
 
 s 
 
 
 Surfoce woter controls 
 
 Ground water controls 
 
 ^ x Water controls 
 
 N 
 
 o 
 o 
 
 3 C 
 
 en O 
 
 *o S o> 
 o*5.| 
 
 "o 
 
 4) o 
 
 3 2 
 
 c 
 
 T3 
 P O* 
 
 O..E 
 
 "£ TD 
 3 C 
 CO O 
 
 c 
 
 o 
 
 o rz 
 
 4) T3 
 
 $> E 
 
 Reduce 
 permeability of 
 overlying strata 
 
 E 
 
 is 
 11 
 
 
 \ 
 
 Water sources \ 
 \ 
 \ 
 \ 
 
 c 
 '5 
 
 o 3 
 
 c C 
 
 3 3 
 O O 
 
 O 
 
 CD 
 
 8 
 
 a 
 
 if 
 
 ■"=> o 
 
 3 A) 
 
 in Si 
 
 
 Cool ond contact- 
 ing water-bearing 
 strata 
 
 Strata associated 
 with coolbeds 
 
 
 
 
 
 
 • 
 
 
 
 
 • 
 
 Other strata serving 
 as a woter source 
 
 
 
 
 
 
 • 
 
 • 
 
 
 • 
 
 
 Surfoce water body 
 seepage 
 
 
 
 
 
 
 
 
 
 
 
 Surfoce woter 
 entrance 
 
 General surfoce 
 seepage 
 
 • 
 
 • 
 
 • 
 
 • 
 
 
 
 
 • 
 
 
 
 
 Surface water inrush 
 
 
 • 
 
 • 
 
 • 
 
 • 
 
 
 
 
 
 
 
 Joint system in rocks 
 
 
 
 
 
 
 • 
 
 
 
 
 • 
 
 Water entronce 
 through fractures 
 
 Foults and fracture 
 zones 
 
 
 
 
 
 • 
 
 • 
 
 
 
 
 • 
 
 
 Mine subsidence 
 fractures 
 
 
 
 • 
 
 • 
 
 • 
 
 • 
 
 
 • 
 
 
 • 
 
 
 Abandoned under- 
 ground mines (barrier 
 pillars, interconnections) 
 
 
 
 
 
 
 • 
 
 
 
 • 
 
 
 Constructed 
 pathways 
 
 Abandoned ond active 
 surfoce mines 
 
 
 
 
 
 
 
 
 • 
 
 
 
 
 Borings, boreholes, 
 gos ond oil wells 
 
 • 
 
 • 
 
 • 
 
 
 
 
 • 
 
 
 
 
 
 Shafts ond 
 
 mine openings 
 
 • 
 
 • 
 
 • 
 
 
 
 • 
 
 
 
 • 
 
 
 • Indicates that water control techniques can be used to control the water source 
 
 FIGURE 2. - Matrix of mine water controls 
 versus mine water sources. 
 
22 
 
 of cover at this time ranged from 100 
 to 300 ft (31 to 92 m) , considerably 
 shallower than the average depth of min- 
 ing in the Appalachian region, which is 
 approximately 600 ft (183 m) . A cost 
 analysis of this dewatering was not 
 available. 
 
 SITING SURFACE FACILITIES AND OPENINGS 
 
 A considerable amount of water can be 
 prevented from entering underground mine 
 workings simply by proper siting of sur- 
 face facilities and mine openings. Im- 
 portant considerations in siting sur- 
 face facilities and openings are access, 
 surface rights , power and water avail- 
 ability, government and municipal re- 
 strictions, material availability, sur- 
 face space, topography, wind direction, 
 floods, slides, and costs. All of these 
 considerations may have an effect on 
 how much water may enter the mine. Bore- 
 holes, shafts, and other mine openings 
 should not be located in floodplains, 
 naturally depressed areas, or other low- 
 lying areas that retain surface runoff, 
 since water accumulating in these areas 
 will enter the mine through these open- 
 ings. In addition, surface facilities 
 located in these areas will tend to pud- 
 dle water, enabling it to infiltrate into 
 the mine via surface water-body seepage 
 and general surface seepage. 
 
 SURFACE RUNOFF DIVERSION 
 
 The amount of water with potential to 
 enter an underground mine can be con- 
 trolled by reducing the amount of surface 
 runoff that enters the area overlying 
 a mine. Surface runoff can infiltrate 
 the soil and eventually enter the mine 
 through surface water-body seepage and 
 general surface seepage. Ponding of sur- 
 face runoff may also cause water to en- 
 ter an underground mine via surface wa- 
 ter inrush. In addition, surface runoff 
 can collect and enter abandoned and ac- 
 tive surface mines, borings, boreholes, 
 gas and oil wells, and shafts and mine 
 openings , thereby finding direct access 
 into underground mines in many instances. 
 Surface runoff diversion is the process 
 
 of intercepting and channeling the sur- 
 face runoff to natural watercourses be- 
 fore it reaches these potential infil- 
 tration sources. 
 
 Methods for diverting surface runoff 
 include ditches, trench drains, flumes, 
 pipes, and dikes. Diversion ditches are 
 frequently used to divert surface water 
 around the mine area. Flumes and pipes 
 are used to convey water across surface 
 cracks and subsidence areas. Dikes can 
 be used for the same purpose as ditches; 
 however, they are often used together, 
 with the excavated material from the 
 ditch used to form the downslope dike. 
 
 Advantages of surface runoff diversion 
 methods include low maintenance require- 
 ments, relatively low cost, a potential 
 for a high degree of effectiveness, and a 
 long service life. 
 
 The disadvantages include the need for 
 surface restoration once mining is com- 
 plete and the need for obtaining 
 access to the surface land required for 
 construction of the diversion facilities. 
 Underground mining companies may not own 
 all of the surface land needed for diver- 
 sion facilities and, consequently, may 
 not have ready access to modify the sur- 
 face drainage patterns. An additional 
 disadvantage may be that the diversion of 
 surface runoff into streams, especially 
 during maximum flow conditions, can ag- 
 gravate flooding and erosion problems 
 downstream. 
 
 In most cases, the cost of surface wa- 
 ter diversion will be less than the costs 
 involved in treating an equal volume 
 of mine water to meet acceptable stan- 
 dards. Surface water diversion costs 
 will vary depending on the following 
 factors: topography, availability of 
 equipment, type and condition of soil, 
 size of area, and quantity of water 
 expected. 
 
 SURFACE REGRADING 
 
 The amount of water available to infil- 
 trate the soil and, eventually, the 
 underground mine can be decreased by in- 
 creasing surface runoff over the overly- 
 ing surface area. Surface runoff can be 
 increased by regrading selected areas to 
 
23 
 
 provide a better drainage configuration, 
 thereby limiting the amount of surface 
 water-body seepage, general surface seep- 
 age, and surface water inrush that can 
 occur. Areas suitable for regrading are 
 those that retard the flow of surface 
 runoff, thereby providing the opportu- 
 nity for water to enter the soil strata. 
 These areas include natural depressions, 
 depressions caused by subsidence, or non- 
 regraded surface mines. Nonregraded sur- 
 face mines are a common source of under- 
 ground mine water in the Eastern United 
 States where coal outcrops are contour- 
 stripped. Depressions occurring around 
 borings, boreholes, gas and oil wells, 
 and shafts and mine openings are particu- 
 larly important in that a considerable 
 amount of water can freely enter an un- 
 derground mine through these avenues. 
 
 The effectiveness of a particular ap- 
 plication of surface regrading will 
 depend on the site hydrology. On-site 
 evaluations are necessary to determine 
 the amount of infiltration caused by cor- 
 rectable situations. This amount can be 
 estimated by using flow measurements and 
 by comparing the infiltration capacity at 
 similar adjacent undisturbed areas. 
 
 The amount of water that can be pre- 
 vented from infiltrating the soil as a 
 result of regrading depends on the fol- 
 lowing factors: the size of the drainage 
 area that is tributary to the depressed 
 area, annual precipitation rates, and the 
 change in runoff coefficients caused by 
 the filling and grading activities. 
 
 Strip mines can intercept underground 
 mine workings along the highwall. If in- 
 terception takes place on the updip side 
 of an underground mine, a significant 
 amount of surface runoff can be conveyed 
 to the underground mine workings. The 
 regrading method should be designed to 
 divert surface runoff from the highwall. 
 In addition to regrading, ditches and 
 flumes can be constructed to aid in in- 
 creasing surface runoff. Impervious 
 materials or spoil material can be com- 
 pacted against highwalls before backfill- 
 ing to prevent water from flowing into 
 adjacent mines. 
 
 The advantages of surface regrading are 
 similar to those for surface runoff 
 
 diversion: low maintenance requirements, 
 relatively low cost, a potential for a 
 high degree of effectiveness, and a long 
 service life. An additional advantage is 
 the restoration of abandoned areas. 
 
 The disadvantages include the need for 
 obtaining access to the use of the sur- 
 face land and the possibility that the 
 increase in surface runoff into streams, 
 especially during periods of maximum 
 flow, could aggravate flooding and ero- 
 sion problems downstream. An additional 
 disadvantage for regrading and restoring 
 surface mines involves assessing the re- 
 sponsibility for performing the work. 
 The mining company involved with surface 
 mining may not be the same company in- 
 volved with underground mining. 
 
 The costs of surface regrading and re- 
 storing depend on factors such as the 
 length and height of the highwall, the 
 number of cuts made, the size of the af- 
 fected area, the degree of regrading nec- 
 essary, the method of revegetation, and 
 whether surface mining reclamation activ- 
 ities are included in the mining opera- 
 tion or take place sometime after mining 
 activities have stopped. The costs for 
 surface regrading and restoration may in- 
 clude clearing and grubbing, backfilling, 
 grading, revegetation, establishing mine 
 access, diversion ditches, flumes, and 
 seals. 
 
 A project to control water infiltration 
 by regrading a surface mine was under- 
 taken in the Roaring Creek-Grassy Run wa- 
 tersheds near Elkins, WV [Scott and Hays 
 (29) ] . The contour method of regrading 
 was used when the highwall was fractured 
 and unstable, and the pasture and swal- 
 lowtail regrading methods were used when 
 the highwall was stable. Also included 
 in this project was sealing of an opening 
 in the highwall to prevent water from in- 
 filtrating through the opening and into 
 an adjacent underground mine. Represen- 
 tative costs for this reclamation are 
 shown in table 2. 
 
 The actual effectiveness of this re- 
 grading project was difficult to deter- 
 mine because of cost overruns, and in- 
 complete reclamation and sealing of a 
 large underground mine. A preliminary 
 evaluation, however, revealed that flow 
 
24 
 
 in streams adjacent to the regraded area 
 was increasing, which indicates an in- 
 crease in surface runoff and a decrease 
 in the amount of water entering the soil 
 strata. 
 
 SOIL SEALING 
 
 Another method of increasing surface 
 runoff and, subsequently, reducing the 
 amount of water infiltration is to reduce 
 the permeability of the surface soil. 
 The permeability can be reduced by seal- 
 ing the soil with an impermeable mate- 
 rial, which will limit the amount of 
 surface water-body seepage and general 
 surface seepage. Soil sealing may also 
 be effective in cases of potential inrush 
 occurring from surface runoff. Mine sub- 
 sidence fractures extending to the sur- 
 face may also be partially sealed at the 
 surface. Soil sealing can also be used 
 on soils in active and abandoned surface 
 mines to limit the seepage of water pond- 
 ing in these mines into underground 
 mines. Materials that have been investi- 
 gated for soil-sealing purposes include 
 clay, asphalt, concrete, rubber, and 
 plastic. 
 
 Soil sealing is often used in conjunc- 
 tion with other water infiltration con- 
 trol methods. For example, areas that 
 have subsided because of mining activi- 
 ties are often filled and graded to pro- 
 vide better surface drainage patterns. 
 In addition to filling and grading, im- 
 permeable materials can be placed in the 
 area, compacted, and graded to increase 
 the rate of surface runoff. Another 
 
 example is the placement and compaction 
 of impermeable materials against the 
 highwall of a surface mine during regrad- 
 ing and restoration activities. These 
 materials will prevent ground water from 
 penetrating the highwall and entering an 
 adjacent underground mine. 
 
 The advantage of soil sealing is its 
 potential effectiveness in reducing wa- 
 ter infiltration. A disadvantage of soil 
 sealing is that, depending on the type of 
 sealant, the future use of the land may 
 be severely limited for activities such 
 as agriculture, industry, and recreation. 
 Other disadvantages include the need for 
 obtaining access to the land and the po- 
 tential for aggravating downstream flood- 
 ing and erosion problems by increasing 
 surface runoff. 
 
 Reported costs range widely, as 
 follows: 
 
 Concrete $42.30-$84.60 per cubic yard 
 
 Clay.... 2.80- 8.50 per cubic yard 
 
 Rubber.. .70- 1.40 per square foot 
 
 Asphalt. .30- .80 per square foot 
 
 STREAM CHANNEL MODIFICATIONS 
 
 A stream that flows over highly perme- 
 able areas may be a significant source of 
 underground mine water. Such streams can 
 lose water to underground mines through 
 their streambeds by surface water-body 
 seepage or surface water inrush. Verti- 
 cal fractures and subsidence of strata 
 
 TABLE 2. - Representative costs for surface regrading and restoring 
 
 Item 
 
 1975 dollars 
 
 1980 dollars 
 
 
 Per acre 
 
 Per hectare 
 
 Per acre 
 
 Per hectare 
 
 Clearing and grubbing... 
 Backfilling and grading: 
 
 $500 
 
 2,000 
 
 1,800 
 
 $500- 550 
 
 1,800-3,800 
 1,500-3,400 
 
 $1,235 
 
 4,938 
 
 4,445 
 
 $1,235-1,358 
 
 4,445-9,383 
 3,704-8,395 
 
 $700 
 
 2,820 
 
 2,540 
 
 $700- 775 
 
 2,540-5,350 
 2,115-4,790 
 
 $1,740 
 6,950 
 
 
 6,260 
 
 
 $1,740- 1,910 
 
 Regrading: 
 
 6,260-13,220 
 
 
 5,220-11,830 
 
 includes lime, fertilizer, seeding, and mulch. 
 
 Source: Scott and Hays (29). 
 
25 
 
 overlying underground mines can also pro- 
 vide openings through which surface 
 streams can penetrate. A stream flowing 
 over such areas may allow water to infil- 
 trate into mines at rates 1,000 times 
 higher than those of an adjacent area. 
 Streams flowing through abandoned and ac- 
 tive surface mines can also, owing to the 
 more permeable soils at the mine, allow 
 water to infiltrate the underground mine. 
 
 Advantages of channel modification are 
 the potential for a high degree of effec- 
 tiveness in reducing mine water inflow, a 
 long service life, low maintenance re- 
 quirements, and relatively low costs com- 
 pared with pumping and treating mine 
 water. 
 
 The disadvantages include the need for 
 obtaining surface access to construct the 
 facilities, determining the party respon- 
 sible for restoring abandoned surface 
 mines and subsidence areas, and the po- 
 tential for aggravating downstream ero- 
 sion and flooding problems. 
 
 The costs of channel modification will 
 normally be much less than pumping and 
 treatment costs of an equal volume of 
 mine water. The costs of channel excava- 
 tion are estimated to range from $1.40 to 
 $4.20 per cubic yard ($1.85 to $5.50 per 
 cubic meter). Lining the channel bottom 
 with clay costs from $1.40 to $2.80 per 
 square yard ($1.70 to $5.10 per square 
 meter). The cost of stabilizing the 
 channel with riprap or with a vegetative 
 cover should also be included in estimat- 
 ing channel modification costs. The to- 
 tal cost of reconstructing a channel is 
 estimated to range from $14.00 to $35.25 
 per linear foot ($46.25 to $115.60 per 
 linear meter). These cost estimates are 
 in 1980 dollars and are based on data de- 
 veloped by Scott and Hays (29) . 
 
 GROUTING 
 
 The process of grouting consists of 
 injecting fluid materials into perme- 
 able rock and/or soil formations to fill 
 pore spaces and allowing the material to 
 set, forming a stiff gel or hardened 
 cement-type material. The purpose of 
 grouting is to reduce the permeabil- 
 ity of the grouting medium by sealing 
 
 fissures, fractures, and other permeable 
 formations. 
 
 An impermeable barrier formed by grout- 
 ing is called a grout curtain. Grout 
 curtains are used to control leakage 
 around underground hydraulic seals, to 
 stabilize outcrop areas, and to reduce 
 water infiltration through subsidence 
 areas and through fracture zones. Grout 
 curtains are also used to reduce water 
 infiltration through barrier pillars, 
 around mine openings, and during shaft 
 sinking by reducing the permeability in 
 these areas. 
 
 In addition, grout retainers consisting 
 of large bags made from materials such as 
 cloth or plastic can be placed in large 
 openings (e.g., mine shafts) and filled 
 with grouting materials. 
 
 The advantages of grouting are its con- 
 venience and effectiveness for sealing 
 fissures, cracks, and permeable forma- 
 tions. Grouting can also increase the 
 strength and load-bearing properties of 
 ground formations. 
 
 The greatest disadvantage of grouting 
 is its requirement for skilled labor 
 knowledgeable in grouting materials, 
 equipment used, and geological forma- 
 tions. Additionally, some grouting mate- 
 rials are toxic and present a potential 
 safety hazard to personnel. 
 
 BOREHOLE SEALING 
 
 Boreholes are vertical or near-vertical 
 holes, usually drilled during mineral ex- 
 ploration activities, which are often 
 used later for supplying power to under- 
 ground equipment or for discharging wa- 
 ter pumped from the underground mine 
 workings. ^The boreholes that intercept 
 mines act as conduits and are capable of 
 transmitting large volumes of water to 
 the mine from surface water sources and 
 from overlying aquifers. 
 
 Boreholes can be effectively plugged to 
 prevent the passage of water. The bore- 
 holes can be sealed by placing packers 
 and injecting a cement grout, or by fill- 
 ing the hole with rock over which a con- 
 crete or clay plug is installed. 
 
 When the boreholes are sealed with ce- 
 ment grout, the packers should be placed 
 
26 
 
 below the aquifers overlying the mine to 
 prevent subsurface water infiltration. 
 These packers should, however, be located 
 well above the mine roof to guard against 
 roof collapse from additional water pres- 
 sure. Boreholes can also be sealed by 
 filling the hole with rock until the mine 
 void directly below the hole is filled to 
 the roof, then placing successive layers 
 of increasingly smaller stone above the 
 rock, and installing a clay or concrete 
 plug. The remainder of the hole can then 
 be either filled with rock or capped. 
 
 Boreholes can be sealed from the sur- 
 face or from below in an active under- 
 ground mine. It is usually more diffi- 
 cult to seal a hole from the surface. In 
 many instances, the holes must be cleared 
 of debris prior to sealing. 
 
 An advantage of borehole sealing is 
 that the seals will prevent not only the 
 passage of water into the underground 
 mine but also the discharge of mine water 
 pollutants from a flooded abandoned mine 
 having a water level above the borehole 
 elevation. An additional advantage is 
 that little operation and maintenance is 
 required after the sealing is complete. 
 
 A disadvantage of borehole sealing from 
 underground is that the roof strata lose 
 their support as coal is removed during 
 mining, which increases the danger of 
 roof collapse. If roof collapse occurs, 
 the sealing operation may be rendered 
 ineffective. An additional potential 
 disadvantage may be the determination of 
 responsibility for sealing a borehole 
 for an abandoned mine. Borehole sealing 
 should be conducted as part of a mine 
 closure and sealing program. 
 
 During 1973, the Pennsylvania Drilling 
 Co. installed a borehole seal to elimi- 
 nate the flow of water from the Lower 
 Freeport Coal Seam to the Lower Kittan- 
 ning Coal Seam at the Tanoma Complex, 
 Upper Crooked Creek, Indiana County, PA 
 (29). 
 
 The 10.25-in (26-cm) diameter borehole 
 was sealed in the following steps: A 
 packer was hydraulically set at 323 ft 
 (98.5 m) by pumping water through a 7-in 
 (17.8-cm) steel casing at pressures up 
 to 1,000 lb/in'- (703,000 kg/m 2 ); cement 
 grout was then pumped through ports to 
 the outside of the casing until the 
 
 cement rose to the Lower Freeport open- 
 ing; a top cementing plug was then pumped 
 into place; a threaded cap was placed on 
 top of the casing; and a plate was tack- 
 welded between the existing borehole cas- 
 ing and the steel casing. 
 
 The completed seal cost a total of 
 $8,611 and successsfully stopped the 
 leakage between the coal seams. 
 
 SUBSURFACE SOIL SEALING 
 
 Subsurface soil seals can be applied to 
 control surface seepage above underground 
 coal mines and in abandoned and active 
 surface mines. They may also have lim- 
 ited use in controlling mine subsidence 
 fractures occurring near the surface. 
 Subsurface seals are formed by injecting 
 an impermeable material into the soil 
 strata to control subsurface water move- 
 ment. Materials that may be used for 
 this purpose include asphalt, cement, and 
 gel. Various latexes, water-soluble pol- 
 ymers, and water-soluble inorganics have 
 been demonstrated to be effective in lab- 
 oratory and field tests. Grouting mate- 
 rials injected below the surface can be 
 an effective method of soil sealing; how- 
 ever, in severely fractured areas, the 
 grout does not fill the void space and, 
 consequently, the sealing efficiency is 
 reduced. 
 
 Placing a seal below the surface has 
 several advantages over using a surface 
 seal: (1) A subsurface seal is less 
 affected by mechanical and chemical ac- 
 tions , (2) the future land use of the 
 area would not be as severly restricted, 
 and (3) the seal could be located in an 
 area of lower natural permeability. 
 
 The disadvantages of subsurface soil 
 sealing include a significant reduction 
 in sealing efficiency if the material is 
 injected in a severely fractured area, 
 the lack of large-scale applications dem- 
 onstrating the success of this technique, 
 and the need to obtain access and disturb 
 the surface area overlying the mine. 
 
 Although many laboratory and small- 
 scale field tests have been conducted on 
 subsurface sealants, there has been no 
 full-scale application of this technique 
 to demonstrate its feasibility. 
 
27 
 
 MINE SEALING 
 
 Abandoned underground mines are a po- 
 tential water source to nearby active un- 
 derground mines. As such, the abandoned 
 mine not only contributes to the water- 
 handling problems in the active mine but 
 also poses a safety hazard to mine work- 
 ers owing to the possibility of a sudden 
 inrush of large quantities of water. 
 
 To reduce these potential problems, the 
 following preventive measures can be im- 
 plemented as part of the mine closure op- 
 eration: (1) leaving safety pillars or 
 barriers, (2) providing a standby sub- 
 merged pump facility, (3) constructing 
 water dams, (4) erecting bulkhead doors, 
 and (5) maintaining records concerning 
 the mine. 
 
 Implementation of these measures may 
 not be entirely successful in preventing 
 water from exfiltrating from the aban- 
 doned mine perimeter. Pumping the mine 
 water to the surface would also not be 
 entirely successful if additional water 
 infiltrates the abandoned mine and would, 
 furthermore, incur considerable operating 
 expenses. In order to effectively pre- 
 vent water from escaping an abandoned 
 mine, all of the potential sources of 
 water exfiltration must be sealed. Mine 
 sealing involves the closure of mine en- 
 tries, drifts, slopes, shafts, subsidence 
 holes, fractures, and any other openings. 
 
 There are two kinds of seals that can 
 be used for water seepage control: 
 
 1. Dry seals: The purpose of dry 
 seals is to prevent air and water from 
 entering underground mines. These seals 
 are used only when mining is in the down- 
 dip direction and when there is little 
 or no flow and little danger of a hydro- 
 static head developing. Dry seals are 
 installed in openings on the high side of 
 a mine. Suitable materials for dry seals 
 include masonry block, clay, concrete, 
 and soil. 
 
 2. Hydraulic seals: The purpose of 
 hydraulic seals is to cause and maintain 
 flooding of the mine. In hydraulic seal- 
 ing, the mine creates an impoundment 
 and the entire mine acts as an under- 
 ground reservoir. The effectiveness of a 
 
 hydraulic seal depends largely on the 
 location of the sealing area relative to 
 ground water levels and the extent of 
 fracturing in the surrounding strata. 
 Seals placed above ground water levels 
 create a hydraulic head that the sur- 
 rounding strata must be able to contain. 
 If these surrounding strata contain a 
 number of fractures or a good aquifer, 
 the ground water flow will increase as 
 the mine floods. 
 
 The entire dam area must be able to 
 withstand the water pressure, which can 
 be in excess of 1,000 ft (300 m) . Miner- 
 al barriers left along mineral outcrops 
 and between adjacent mines are often the 
 weakest link in the underground impound- 
 ment. These barriers are usually of non- 
 uniform thickness and frequently cannot 
 withstand water pressure. ' 
 
 The first step in hydraulic sealing is 
 to conduct an examination of the geo- 
 logic, hydrogeologic, and mine extent and 
 condition perimeters to identify the hy- 
 draulically unsound areas. These areas 
 may include surface-mined outcrops, sub- 
 sidence holes, boreholes, and fractured 
 mineral barriers. If feasible, these 
 areas should be improved by sealing or 
 grouting. If this is not feasible, the 
 mine pool elevation should be lowered or 
 the sealing project abandoned. The ef- 
 fectiveness of mine sealing is often de- 
 termined primarily by the physical and 
 mining framework and less by the actual 
 effectiveness of the sealing technology. 
 
 The hydraulic seals most often used for 
 mine sealing are the single and double 
 bulkhead seals. These seals can be made 
 from concrete, quick-setting cement mate- 
 rial, or grouted aggregate and are formed 
 by either injecting the material through 
 vertical boreholes or by placing the ma- 
 terial directly within the mine opening. 
 The single bulkhead seal could also be 
 made from masonry block or brick. In ad- 
 dition to the bulkhead seals, gunite, 
 clay, and grout bags can be used to hy- 
 draulically seal mine openings. 
 
 The seals should be anchored into the 
 mine openings. Additionally, to ensure 
 effectiveness of the seal, a grout cur- 
 tain may need to be placed directly adja- 
 cent to the seal. Vertical shafts and 
 
28 
 
 surface breaks can be filled with imper- 
 vious materials such as compacted clay, 
 earth cover, or cement. 
 
 Mine sealing can be an effective tech- 
 nique for controlling a potential water 
 source for a nearby active mine. It also 
 reduces potential safety hazards by re- 
 ducing the possibility of a large inrush 
 of water into the active mine. Another 
 advantage of mine sealing is that after 
 the initial capital expenditure, assuming 
 that the sealing is effective, no addi- 
 tional operating and maintenance costs 
 would be incurred. 
 
 The disadvantages of mine sealing are 
 
 (1) if the roof strata lose their support 
 (as a result of mining) and collapse, the 
 sealing operation would be ineffective, 
 
 (2) it is difficult to locate and, subse- 
 quently, seal all of the water leaks, be- 
 cause of inadequate records kept by min- 
 ing companies and because of backfilling 
 operations that cover evidence of frac- 
 ture, and (3) seals lose their effective- 
 ness with time, depending on the method 
 of construction and any change in the 
 strata surrounding the seal. Another 
 problem is the inability to successfully 
 anchor the seal into the surrounding mine 
 strata, resulting in leakage around the 
 seal. Other disadvantages involve sec- 
 ondary effects of mine sealing. A hy- 
 draulic seal placed in a mine in Pennsyl- 
 vania created sufficient head to cause 
 ground water levels to rise and flood 
 cellars and damage foundations. The 
 sealed mine was subsequently opened to 
 relieve the ground water pressure. 
 
 A double bulkhead seal was constructed 
 in the drift entry of an abandoned mine 
 in the Kittanning Coal Seam in West Vir- 
 ginia (29). The front and rear bulkheads 
 were constructed with quick-setting ce- 
 ment. Grout pipes and limestone were 
 placed in front of the rear bulkhead, 
 which was located in front of an existing 
 air seal. The limestone was stabilized 
 and rendered impermeable by grouting with 
 light cement. Prior to sealing, the 
 average rate of discharge from the mine 
 was 74 gpm (4.7 L/s). 
 
 One week after the sealing was com- 
 plete, the head behind the seal was 
 3.20 ft (0.98 m) and an opening near the 
 
 seal was observed to be leaking. After 
 placing a permeable aggregate seal in 
 this opening, the head behind the seal 
 stabilized at 3.8 ft (1.2 m) . 
 
 Approximately 2 yr after the sealing 
 was complete, the seal was inspected. 
 Although there was some flaking off of 
 the front bulkhead, no seepage was ob- 
 served. The total cost of constructing 
 this seal was $9,463. 
 
 A grouted, aggregate, double bulkhead 
 seal was developed for sealing inaccessi- 
 ble mine entries in the Middle Kittanning 
 Coal Seam in Butler County, PA. Between 
 February 1969 and August 1971, this seal 
 was constructed in the openings of 19 
 mines. 
 
 Double bulkhead seals were constructed 
 by placing coarse, dry aggregate through 
 vertical drill holes and then grouting 
 the boreholes to form solid seals. Water 
 was pumped from the space between the 
 bulkheads and replaced with a center plug 
 formed by poured concrete. Curtain 
 grouting was performed for a minimum of 
 50 ft (15 m) from both sides of the seal 
 at each mine entry. 
 
 This sealing program had the follow- 
 ing effects on mine water discharges: 
 (1) Eight mines had no flow, (2) one mine 
 had an average flow less than 1 gpm (0.06 
 L/s), (3) eight mines had reduced flow 
 rates, (4) one mine had the same flow 
 rate, and (5) one mine had a 1.5-gpm 
 (0.095-L/s) increase in flow rate. 
 
 The water level in the mines ranged 
 from 1 to 5 ft (0.3 to 1.5 m) , which 
 fluctuated with precipitation and in- 
 filtration. The head behind the seals 
 ranged from less than 1 ft (0.3 m) up to 
 38 ft (11.6 m). 
 
 The costs of the seals ranged from 
 $8,308 to $58,437, with an average cost 
 of $19,480 per seal. Approximately 61 
 pet of this cost was attributable to cur- 
 tain grouting. Representative costs for 
 constructing various types of mine seals 
 are shown in table 3. 
 
 WELL DEW ATE RING 
 
 Aquifers situated both above and di- 
 rectly below an underground mine are po- 
 tential sources of water infiltration 
 
29 
 
 TABLE 3. - Representative costs for construct 
 
 Seals 
 
 DRY SEALS 
 
 Masonry block 
 
 Placement of clay seals 
 
 Construction of clay bulkheads 
 
 HYDRAULIC SEALS 
 Double bulkhead seals: 
 
 Grouted aggregate (with grout curtain) 
 
 Quick-setting (no grouting) 
 
 Grouting around seal and curtain grouting of 
 adjacent strata. 
 
 Single bulkhead seals (with grouting) 
 
 Gunite seals 
 
 Clay seals 
 
 Grout bagseals 
 
 Shaft seals: 
 
 Backfilling shafts [from 100 to 300 ft (30 to 
 100 m)]. 
 
 Concrete seals 
 
 Gel materials (AM-9 chemical grout) 
 
 Curtain grouting: 
 
 Vertical curtains 
 
 Horizontal curtains 
 
 ing various types of mine seals 
 
 Est. 1980 dollars 
 
 Per 
 
 $3,520 -$4,230 
 
 2.80- 5.60 
 3.70- 7.40 
 3,520 - 6,340 
 
 14,100 
 
 -42,270 
 
 21,150 
 
 -25,360 
 
 
 28,180 
 
 7,050 
 
 -14,100 
 
 
 18,300 
 
 2,800 
 
 - 5,600 
 
 14,100 
 
 -21,150 
 
 9,860 
 
 -49,300 
 
 28,200 
 
 -35,200 
 
 
 12,700 
 
 49 
 
 113 
 
 160 
 
 370 
 
 16,900 
 
 -28,200 
 
 41,750 
 
 -69,600 
 
 Seal. 
 
 Cubic yard. 
 Cubic meter, 
 Seal. 
 
 Do. 
 Do. 
 
 Do. 
 
 Do. 
 Do. 
 Do. 
 Do. 
 
 Do. 
 
 Do. 
 Do. 
 
 Linear foot. 
 Linear meter, 
 Acre. 
 Hectare. 
 
 Source: Scott and Hays (29). 
 
 into the mine. In addition, joint sys- 
 tems, faults, fracture zones, and subsi- 
 dence fractures can be potential sources 
 of water in an underground mine. To re- 
 duce these potential water infiltration 
 sources, well dewatering sysems have been 
 suggested to intercept the aquifers and 
 to control the movement and ultimate dis- 
 charge of the ground water. 
 
 Three basic well dewatering systems 
 have been suggested in documented lit- 
 erature. These systems are (1) ground 
 water pumping directly to the surface, 
 
 (2) gravity drainage to the mine, with 
 subsequent discharge at the surface, and 
 
 (3) gravity drainage into underlying 
 aquifers. These systems, which are all 
 in a developmental stage, are discussed 
 in greater detail below. 
 
 Ground Water Pumping Directly 
 to the Surface 
 
 This type of well dewatering sys- 
 tem, which is illustrated in figure 3, 
 
 involves installation of closely spaced 
 wells that are drilled from the land 
 surface and tap aquifers lying above and 
 below the mine. The wells are cased 
 above the source bed. The ground water 
 is then pumped to the surface and can be 
 either discharged to a nearby stream or 
 used for water supply purposes. Since 
 the ground water does not enter the mine 
 environment, the quality of the water is 
 maintained and treatment should not be 
 required. 
 
 In figure 3, ground water pumping sys- 
 tems are illustrated for dewatering aqui- 
 fers located above and below the mine. 
 In the cases shown, it would not be fea- 
 sible to try to force the water into low- 
 er rock units. 
 
 Gravity Drainage to the Mine 
 
 This system, which is illustrated in 
 figure 4, is similar to the ground water 
 pumping system except that the ground wa- 
 ter drains by gravity to the underground 
 
30 
 
 Surface, 
 
 Initial water level 
 
 
 £fe 
 
 Confining 
 bed 
 
 — »- Deep mine 
 
 Source beds located above deep mines 
 
 -Deep mine in regional 
 ground water discharge 
 
 
 ^r!vl-i— r 4^l:"U-^".. 'Source bed 
 
 Source beds below mines located in ground water 
 discharge areas 
 
 FIGURE 3. - Ground water pumping systems. 
 
 mine and is then pumped to the surface 
 for disposal. This system eliminates the 
 need for a pump in each dewatering well. 
 Instead, it requires a central collection 
 and pumping system within the mine, which 
 is already common practice in many under- 
 ground mines. The collection and con- 
 veyance system, however, would consist 
 of a piping arrangement whereby the water 
 would not come into contact with the 
 pyrite-bearing rock and would, conse- 
 quently, not require treatment prior to 
 discharge. 
 
 In updip mining from drift or slope en- 
 tries, a gravity drainage system could be 
 installed whereby the overlying aquifer 
 is drained into the mine and the water is 
 drained by gravity to the slope of the 
 drift opening. 
 
 Surface 
 
 '.'•■.—" i*?-:-;— *| |*7- :: -*i i*t" Source bed-'. ■■■'A 
 •" ' •'."•'■• I . !■"•'•'■ ••:••■"•' ■ [■'■'■' '■ ■'••■'!■ !• ■•.'. : . '••.-•'-■ ■•':'■■.'•. ■-. : 
 
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 i\ Seepage 
 face 
 
 — Mine 
 drainage 
 
 FIGURE 4. - Gravity drainage into mine. 
 Gravity Drainage Into Lower Aquifers 
 
 This system, shown in figure 5, is sim- 
 ilar to the ground water pumping system 
 except that the ground water drains by 
 gravity through wells drilled through the 
 underground mine and, eventually, into a 
 deeper aquifer. The mine roof rock and 
 the mine opening should be cased and 
 grouted to prevent water from entering 
 the mine and to prevent contaminated mine 
 water from entering the underlying aqui- 
 fer. Double casings and grout may be 
 needed to prevent corrosion of the steel 
 casing within the mine. 
 
 This system requires the availability 
 of favorable geologic conditions reason- 
 ably close to the mine area. Both a re- 
 gional recharge area and a deep aquifer 
 system have to be present for the system 
 to work. A hydrogeologic setting where 
 two to three distinct water tables and 
 rock beds occur is ideal. The ground wa- 
 ter flow must be downward. This system 
 is not feasible for high fluid volumes in 
 excess of 3 million gpd (130 L/s). In 
 the Appalachian region, this factor alone 
 may create limitations, as the aquifer 
 must be capable of accepting the antici- 
 pated flow. 
 
 A possible alternative to installing 
 separate dewatering systems for each mine 
 would be to construct a regional drainage 
 system designed to reduce the flow of wa- 
 ter into several mines within a given 
 drainage basin. One such system, the 
 
31 
 
 Surface 
 
 FIGURE 5. 
 aquifers. 
 
 Gravity drainage into underlying 
 
 Hoffman Tunnel, was constructed in the 
 Georges Creek Basin water province in Al- 
 legany County, MD [Slaughter and Darling 
 (33)]. 
 
 The Hoffman Tunnel, which was con- 
 structed in the early 1900' s to drain the 
 Pittsburgh Coal Seam, has a total length 
 of 10,646 ft (3,245 m) with approximately 
 2,600 ft (800 m) of auxiliary tunnels and 
 26,700 ft (8,100 m) of ditches draining 
 to it. The drainage area covers roughly 
 14 mi /i (36 km ? -) , which extends north from 
 Midland to Zihlman. The mean flow of the 
 tunnel in the late 1950' s averaged about 
 940,000 gpd/mi 2 (16 L/s for each square 
 kilometer of surface area) . During low- 
 flow periods , the tunnel can divert near- 
 ly all of the flow of the upper third of 
 Georges Creek, which is a tributary of 
 the Potomac River. 
 
 The potential benefit of well dewater- 
 ing systems is that they are preventa- 
 tive, rather than prescriptive, tech- 
 niques that rely on natural geochemical 
 and hydrogeological systems. Other ad- 
 vantages are a reduction in the amount 
 of mine water that must be treated and 
 a possible reduction in pumping and 
 
 maintenance costs. Additionally, if the 
 local need for water becomes sufficient 
 in the future, the dewatering wells can 
 be converted to water supply wells. 
 
 Well dewatering systems are still in 
 the developmental stage, and large-scale 
 applications of these systems have not 
 been shown to be cost effective in the 
 United States. Since it is usually not 
 possible to completely eliminate water 
 infiltration into the mine, the dewater- 
 ing system just reduces, does not elimi- 
 nate, the water-handling requirements in 
 the mine. Depending on the character of 
 the rock, a dewatering system may not 
 produce noticeable results for more than 
 a few hundred feet from the wells and it 
 may take several months before results 
 are noticed. 
 
 Prior to implementing a dewatering sys- 
 tem, the impact on neighboring land uses 
 must be considered. If the system will 
 threaten local water supplies, the yield 
 of the well system must either be reduced 
 or used to supplement the water supply. 
 The possibility of well plugging is 
 another potential problem. If the aqui- 
 fer contains ferrous iron, precipitation 
 of iron oxyhydroxide and growth of iron- 
 oxidizing bacteria around the wells could 
 reduce the permeability of the aquifer 
 and decrease well efficiency. 
 
 Costs 
 
 The cost effectiveness of a well dewa- 
 tering system will depend on a comparison 
 of the cost of pumping and treating mine 
 water with the cost of the dewatering 
 system. The cost of a dewatering system 
 will depend on the the number and spacing 
 of wells, the well depth and diameter, 
 casing requirements, and depth to static 
 and pumping levels. The cost will in- 
 clude hydrogeologic evaluations, drill- 
 ing, casing, piping, and possibly grout- 
 ing to control leakage through the mine 
 roof. 
 
 The total annual costs per well in dol- 
 lars per million gallons of water a day 
 delivered to the surface are estimated as 
 follows: 
 
32 
 
 Well yield, gpm 
 
 75 , 
 
 230 , 
 
 760 , 
 
 Annual cost, 
 per million gpd 
 
 $36,970 
 19,460 
 13,430 
 
 These estimates assume a 25-yr service 
 life for the well and equipment. 
 
 Mine water treatment costs are esti- 
 mated to range from $0.10 to $2.45 per 
 1,000 gal ($0.02 to $0.64 per 1,000 L) 
 depending on the water quality and on the 
 effluent discharge limitations. The low- 
 er estimate is for water containing 2 
 to 3 ppm iron and up to 20 ppm acidity. 
 The higher estimate is for water with 500 
 to 700 ppm iron and 2,000 to 5,000 ppm 
 acidity. 
 
 The cost estimates in this section were 
 taken from a Pennsylvania State Univer- 
 sity research report prepared by Parizek 
 (23) , and adjusted to 1980 dollars. 
 
 Case Study 
 
 A pilot dewatering program was con- 
 ducted at the site of the Lancashire No. 
 20 Mine, near Carrolltown, PA (38). The 
 objectives of this program were to assess 
 the impact of a well dewatering program 
 on the quantity and quality of mine water 
 inflows, to evaluate the potential effec- 
 tiveness of the well dewatering tech- 
 nique, and to conduct an economic evalu- 
 ation of the program. 
 
 A total of seven wells were drilled and 
 used for dewatering. A pumped-well sys- 
 tem was selected for dewatering because 
 pumped wells provide more information and 
 create fewer mining disruptions and safe- 
 ty hazards than the other dewatering sys- 
 tems considered. 
 
 Some of the conclusions of this program 
 were — 
 
 1. Fracture-dominated flow systems 
 usually prevail where large mine water 
 inflows are experienced. Ground water 
 
 flows into the subject mine were concen- 
 trated along two fracture zones that 
 appeared to intersect at the area of 
 greatest inflow. 
 
 2. Flows responded rapidly to wet and 
 dry periods in spite of the 500-ft (152- 
 m) mine depth, indicating that the frac- 
 ture zones had hydraulic connections to 
 the surface. 
 
 3. Dewatering with three wells was 
 performed continuously for 14 days with 
 an average well effectiveness, initially, 
 of 45 pet (i.e., 45 pet of the pumped wa- 
 ter was diverted from mine inflow). The 
 average well effectiveness increased to 
 55 pet at the end of the test, and it was 
 projected that it would increase to 80 
 pet after 120 days of pumping with no re- 
 charge. The well effectiveness for full- 
 scale mine dewatering was estimated to 
 range from 50 to 80 pet. 
 
 4. The wells in this study were not 
 cost effective unless the average well 
 yield was increased from 3 to 4 times. 
 The cost of well dewatering was estimated 
 to be at least twice as great as water 
 removal and treatment costs. If, how- 
 ever, the acidity of the mine water were 
 higher, i.e., 500 to 1,500 ppm (500 to 
 1,500 mg/L) and if the coal seam were 
 less than 150 ft (45 m) deep, the dewa- 
 tering system would have been cost ef- 
 fective. Three significant variables in 
 the cost comparison were depth of the 
 well system, the acidity level of the wa- 
 ter, and ground water flow patterns. 
 Additionally, if the wells had been lo- 
 cated along the fracture zones, a higher 
 well yield could have been obtained, 
 which would have increased the cost ef- 
 fectiveness of the dewatering system. 
 The cost-effectiveness analysis did not 
 consider the indirect benefits of dewa- 
 tering (e.g., increase in productivity, 
 more stable roofs, and reduced safety 
 hazards) . 
 
 SUMMARY OF WATER CONTROL PRACTICES 
 
 Table 4 is a summary of the water con- 
 trol practices previously discussed. 
 (The siting of surface facilities and 
 
 openings is not included because there is 
 not enough information on this practice 
 as a method of controlling water inflow.) 
 
33 
 
 Table 5 shows equivalent water control 
 costs. These tables list information on 
 each practice's applicability, limits of 
 control, field experience, and costs. 
 The limits of control and the field ex- 
 perience taken together give an indica- 
 tion of each practice's effectiveness. 
 Thus, a preliminary attempt can be made 
 to assess the cost effectiveness of most 
 of the control practices listed. This is 
 important since it is the cost effective- 
 ness of a control method for a given sit- 
 uation that should determine the choice 
 of that measure. 
 
 As indicated in table 4, all of the 
 surface control measures listed and all 
 but two of the ground water control mea- 
 sures have some information available re- 
 garding their cost effectiveness in con- 
 trolling inflow into underground mines. 
 Only subsurface soil sealing and well 
 dewatering lack sufficient data on 
 effectiveness . 
 
 Of the control practices that have 
 available performance information, only 
 soil sealing is considered to be unsatis- 
 factory. The performance data on soil 
 sealing indicate that its use would be 
 very costly, on the order of $30,500 to 
 $61,000 to seal an acre of land with rub- 
 ber. This should be compared with sur- 
 face regrading and restoring, which costs 
 roughly $1,800 to $3,800 for the equiva- 
 lent conditions of applicability. Al- 
 though the literature evaluation has pro- 
 vided information on the effectiveness of 
 these practices in controlling water in- 
 flow in underground coal mines, a quanti- 
 tative analysis is needed to accurately 
 determine the cost effectiveness of these 
 measures. The quantitative analysis 
 should include the benefits and drawbacks 
 associated with the use of each prac- 
 tice, taking into account factors such as 
 health and safety, the environment, and 
 production. 
 
 ANALYSIS OF THREE WATER CONTROL PROJECTS 
 
 The water control practices considered 
 for evaluation were identified through a 
 combination of literature review and per- 
 sonal conversations with a large number 
 of knowledgeable individuals, State and 
 Federal agencies, and private and public 
 organizations associated with the coal 
 mining industry. These water control 
 practices have been described in the pre- 
 ceding sections. It must be emphasized, 
 however, that most of these practices 
 have been used principally to control wa- 
 ter problems associated with abandoned 
 coal mines. 
 
 Discussions with personnel of both 
 State agencies and mining companies in 
 Appalachia made it very clear that the 
 only widely accepted method of dewater- 
 ing underground coal mines is to collect 
 the water in sumps and pump it up to the 
 surface, where treatment is provided, as 
 needed, prior to discharge to receiving 
 streams. Personnel of both the State 
 regulatory agencies and mining companies 
 indicated very limited, if any, knowledge 
 of the application of dewatering tech- 
 niques in advance of mining in the Appa- 
 lachian coalfields. In fact, the inves- 
 tigations identified only three cases 
 
 where dewatering in advance of mining was 
 either being considered or applied. 
 
 Of these three cases, only one repre- 
 sented an actual documented demonstration 
 of the feasibility of dewatering in ad- 
 vance of mining. This particular demon- 
 stration evaluated an attempt to dewater 
 a section of a mine using a series of de- 
 watering wells drilled from the surface. 
 
 The second of the three cases was a 
 preliminary feasibility study to deter- 
 mine whether dewatering in advance of 
 mining using dewatering wells would be 
 technically and economically feasible for 
 a new mining operation. 
 
 The third case represents an ongoing 
 attempt to control water problems in the 
 last working section of an old mine. 
 Subsidence is being induced in the area 
 of heaviest inflow in order to concen- 
 trate the mine drainage in a system of 
 sumps, which will then allow the safe ex- 
 traction of the remaining coal. 
 
 The three case studies differed marked- 
 ly. Case study 1 was a federally funded 
 demonstration project, which spanned a 
 period of approximately 33 months. This 
 study provides the most comprehensive and 
 detailed data available to date on the 
 
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36 
 
 TABLE 5. - Summary of water control costs 
 
 Water control practice 
 
 Cost item 
 
 Cost 
 
 Per 
 
 Surface water controls: 
 Runoff diversion.... 
 
 Surface regrading and 
 restoring. 
 
 Soil sealing, 
 
 Stream channel 
 modification. 
 
 Construction of diver- 
 sion ditch. 
 Construction of dikes.. 
 
 Dumped rock 
 
 Riprap 
 
 Clearing and grubbing. . 
 
 Backfilling: 
 
 Contour 
 
 Terrace. 
 
 Revegetation 
 
 Regrading: 
 
 Contour 
 
 Terrace 
 
 Concrete 
 
 Clay 
 
 Rubber 
 
 Asphalt 
 
 Channel excavating 
 
 Clay-lining bottom 
 
 Channel reconstruction. 
 
 $0.70- 
 
 2.30- 
 
 .55- 
 
 .75- 
 
 3.50- 
 
 4.60- 
 
 17.70- 
 
 23.00- 
 
 700 
 1,740 
 
 2,540 
 6,260 
 2,115 
 5,220 
 42.30- 
 55.00- 
 2.80- 
 3.70- 
 .70- 
 7.60- 
 .30- 
 2.80- 
 1.40- 
 1.85- 
 1.40- 
 1.70- 
 14.00- 
 46.25- 
 
 $2.80 
 
 9.25 
 
 1.15 
 
 1.50 
 
 10.60 
 
 13.80 
 
 44.25 
 
 60.20 
 
 700 
 
 1,740 
 
 2,820 
 6,950 
 2,540 
 6,260 
 775 
 1,910 
 
 5,350 
 
 13,220 
 
 4,790 
 
 11,830 
 
 84.60 
 
 110.00 
 
 8.50 
 
 11.00 
 
 1.40 
 
 15.15 
 
 .80 
 
 8.50 
 
 4.20 
 
 5.50 
 
 2.80 
 
 5.10 
 
 35.25 
 
 115.60 
 
 Linear foot. 
 Linear meter. 
 Cubic yard. 
 Cubic meter. 
 Cubic yard. 
 Cubic meter. 
 Cubic yard. 
 Cubic meter. 
 Acre. 
 Hectare. 
 
 Acre. 
 
 Hectare. 
 
 Acre. 
 
 Hectare. 
 
 Acre. 
 
 Hectare. 
 
 Acre. 
 Hectare. 
 Acre. 
 Hectare. 
 Cubic yard. 
 Cubic meter. 
 Cubic yard. 
 Cubic meter. 
 Square foot. 
 Square meter. 
 Square foot. 
 Square meter. 
 Cubic yard. 
 Cubic meter. 
 Square yard. 
 Square meter. 
 Linear foot. 
 Linear meter. 
 
TABLE 5. - Summary of water control costs — Continued 
 
 37 
 
 Water control practice 
 
 Cost item 
 
 Cost 
 
 Per 
 
 Ground water controls: 
 
 
 
 
 
 Grouting and grouting 
 
 
 $50 
 
 $113 
 
 Linear foot. 
 
 curtains. 
 
 
 160.30- 
 
 370 
 
 Linear meter. 
 
 
 Horizontal curtains.... 
 
 16,900 
 
 28,200 
 
 Acre. 
 
 
 
 41,750 
 
 69,600 
 
 Hectare. 
 
 
 
 14 
 
 28 
 
 Linear foot. 
 
 
 
 47 
 
 93 
 
 Linear meter. 
 
 
 Sealing with cement 
 
 21 
 
 28 
 
 Linear foot. 
 
 
 grout. 
 
 69 
 
 93 
 
 Linear meter. 
 
 Subsurface soil 
 
 
 2.80- 
 9.25- 
 
 4.30 
 13.90 
 
 Linear foot. 
 
 sealing. 
 
 
 Linear meter. 
 
 
 
 2.80- 
 
 6.35 
 
 Bag. 
 
 
 
 2.80- 
 
 5.60 
 
 Pound. 
 
 
 
 6.20- 
 
 12.40 
 
 Kilogram. 
 
 
 Fly ash 
 
 11.30- 
 12.40- 
 
 28.20 
 31.00 
 
 Ton. 
 
 
 
 Metric ton. 
 
 
 Horizontal grout 
 
 16,900 
 
 56,360 
 
 Acre. 
 
 
 curtain. 
 
 41,750 
 
 L39,160 . 
 
 Hectare. 
 
 
 Dry seals: 
 
 Masonry block seal... 
 
 
 
 
 
 3,520 
 
 4,230 
 
 Seal. 
 
 
 
 2.80- 
 
 5.60 
 
 Cubic yard. 
 Cubic meter. 
 
 
 
 3.70- 
 
 7.40 
 
 
 
 3,520 
 
 6,340 
 
 Seal. 
 
 
 Hydraulic seals, double 
 
 
 
 
 
 bulkhead: 
 
 
 
 
 
 Grouted aggregate. . . . 
 
 14,100 
 
 42,270 
 
 Do. 
 
 
 
 21,150 
 
 25,360 
 
 Do. 
 
 
 Seal and curtain 
 
 
 28,180 
 
 Do. 
 
 
 grouting. 
 
 
 
 
 
 Hydraulic seals, single 
 
 7,050 
 
 14,100 
 
 Do. 
 
 
 bulkhead. 
 
 
 
 
 
 Curtain grouting: 
 
 
 
 
 
 Vertical curtains.... 
 
 49 - 
 
 113 
 
 Linear foot. 
 
 
 
 160 
 
 370 
 
 Linear meter. 
 
 
 Horizontal curtains.. 
 
 16,900 
 
 28,200 
 
 Acre. 
 
 
 
 41,750 
 
 69,600 
 
 Hectare. 
 
 
 
 
 36,970 
 
 Year, per 
 million gpd. 
 
 
 
 
 
 19,460 
 
 Do. 
 
 
 
 
 13,430 
 
 Do. 
 
38 
 
 technical and economic performance of a 
 dewatering system in Appalachia. Conse- 
 quently, a very heavy emphasis has been 
 placed on the results of case study 1. 
 
 Case study 2 was a preliminary feasi- 
 bility study conducted by a private min- 
 ing company to evaluate the advantages 
 and disadvantages of dewatering a new 
 mine in advance of mining. Both techni- 
 cal and legal factors were considered in 
 this study; however, the major considera- 
 tion was whether the additional costs in- 
 curred by the dewatering system would be 
 recovered through a reduction in unit 
 production costs. It was concluded that 
 legal factors alone made the project un- 
 feasible. In addition, the complexities 
 of the technical problems resulted in 
 both a technical approach and related 
 high costs that made the project prohibi- 
 tive to implement. 
 
 Case study 3 involved an ongoing at- 
 tempt by a mining company to control wa- 
 ter inflow in the last working section of 
 an old mine. This situation occurs with 
 some frequency in Appalachia and often 
 results in substantial amounts of coal 
 left unmined because of difficult mining 
 conditions. The approach being attempted 
 consists of inducing subsidence in the 
 area of heaviest inflow to concentrate 
 the mine drainage in a system of sumps, 
 which will then allow the safe extraction 
 of the remaining coal. This demonstra- 
 tion will not be completed in time to in- 
 clude a discussion of the actual effec- 
 tiveness in this report. This method 
 does, however, appear to represent a 
 practical approach to the problem, and it 
 provides an interesting comparison with 
 the other two case studies. 
 
 The geologic conditions of the three 
 study sites are compared and summarized 
 in table 6. The parameters compared are 
 (1) the coal seam mined, including depth 
 and thickness, (2) the mining method 
 used, (3) the surface geology, (4) the 
 subsurface geology, and (5) the major 
 structural features. 
 
 The hydrologic conditions of the three 
 study sites are compared and summa- 
 rized in table 7. The parameters com- 
 pared are divided into three categories: 
 surface water, ground water, and mine 
 
 water. The surface water parameters 
 include (1) drainage basin, (2) water- 
 courses, and (3) springs. The ground wa- 
 ter parameters include (1) aquifer(s) and 
 (2) aquifer properties. The mine water 
 parameters include (1) sources, (2) in- 
 flow rate, and (3) method of control. 
 
 TECHNICAL EFFECTIVENESS 
 
 Case Study 1 
 
 The technical effectiveness of case 
 study 1 is described in detail in appen- 
 dix A. As the data show, the dewatering 
 operation had little impact on controll- 
 ing the quantity of water flowing into 
 the mine; only a 34-pct decrease in mine 
 inflow was realized. The following de- 
 scription of the area's ground water con- 
 ditions offers an explanation as to why 
 the dewatering operation was ineffective. 
 
 The inflow rate at the test site was 
 estimated to range from 100 to 150 gpm 
 (6.3 to 9.5 L/s), yet the geologic and 
 ground water conditions of the area indi- 
 cate that aside from the Saltsburg Sand- 
 stone, no discernable aquifer units ex- 
 ist. In addition, a rapid response to 
 heavy rainfall was observed in the well 
 water levels and in the mine inflow. 
 This indicates that the ground water sys- 
 tem is fracture controlled. Since most 
 of the water is located in the fracture 
 zones, wells that do not intersect any of 
 these water conduits will do little to 
 relieve the water problem in the mine. 
 The study demonstrated this very well. 
 The wells could only intercept some of 
 the ground water storage space, while the 
 major avenue of water infiltration into 
 the mine was never dealt with. As a re- 
 sult, only a small decrease in the mine 
 inflow was achieved. It must still be 
 demonstrated technically that dewatering 
 in advance of mining can be achieved when 
 the ground water conditions are fracture 
 controlled. The fractures must be well 
 delineated and their hydraulic character- 
 istics well defined, so that wells can be 
 properly located. This is not beyond the 
 technology available today. Parizek and 
 Tarr (25) have demonstrated that water 
 supply wells sometimes can be located via 
 
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 s 
 
 
 
 
 
 
 
41 
 
 fracture analysis. However, the impact 
 of this technology on mine water inflow 
 has yet to be demonstrated. 
 
 Case Study 2 
 
 The technical effectiveness of case 
 study 2 is described in detail in appen- 
 dix B. In this case, dewatering in ad- 
 vance of mining was considered primarily 
 because of the high cost of tramming 
 within the mine under wet conditions. 
 Each mine in this area receives inflows 
 of approximately 10,000 to 20,000 gpd 
 (37,850 to 75,700 L/d) in the first year 
 alone. This amount increases as more 
 mine area is exposed. Dewatering in ad- 
 vance of mining was also considered be- 
 cause the region is artesian. Unfortu- 
 nately, test wells drilled to evaluate 
 aquifer characteristics showed that the 
 sandstone unit above the coal seam was 
 not permeable enough to pump, yield- 
 ing only 2 to 3 gpm (0.13 to 0.19 L/s). 
 These results indicated that dewatering 
 in advance of mining would be difficult 
 and expensive, owing to the number of 
 wells necessary for effective dewatering 
 and the cost of drilling these wells. 
 Also, the mining cycle would advance too 
 rapidly for dewatering to be effective. 
 
 In addition, it was found that the nat- 
 ural water in the area has a pH of 4.0 to 
 4.5. State regulations require that wa- 
 ter in this pH range be treated before 
 being returned to the environment, which 
 eliminates one of the major advantages of 
 dewatering prior to mining. 
 
 After considering these and other 
 facts, it was decided that dewatering in 
 advance of mining would be technically 
 and economically impractical for this 
 area. 
 
 Case Study 3 
 
 Water has caused significant problems 
 in the operation of the Nemacolin Mine 
 (fig. 6). The inflow of water into the 
 working section of the mine was so great 
 that it disrupted face operations even 
 with an adequate dewatering system of 
 pumps and sumps. To remedy this problem, 
 the mine engineers decided to vary the 
 direction of mining by 90° , advancing the 
 
 FIGURE 6. - Map of Nemacolin Mine. 
 
 operations away from the Monongahela 
 River, which borders the mine, instead of 
 paralleling it. This brought some ini- 
 tial relief, but with time the problem 
 returned. 
 
 The mine engineers decided that the 
 best way to prevent the disruption of 
 face operations was to dewater the over- 
 burden before the water reached the face 
 operations. They are second-mining the 
 area just north of the 90° turn and down- 
 dip of the Monongahela River, thereby 
 creating a huge sump where water will 
 collect. This water can then be pumped 
 out of the mine. 
 
 This system is basically a modification 
 of the gravity drainage and mine pump- 
 ing system of dewatering the overburden 
 above a mine (fig. 4). Instead of using 
 drilled holes to collect water, the water 
 is collected by fracturing the confining 
 bed and part of the source bed so that 
 the water will run along the fractures 
 into the mine. 
 
It would seem that this type of over- 
 burden dewatering system is very well 
 suited for this kind of situation, since 
 most of the water entering the workings 
 is traveling along bedding planes from 
 the Monongahela River. Although it has 
 yet to be demonstrated that this type of 
 system can adequately drain the overbur- 
 den, the system is technically and eco- 
 nomically feasible in this situation. As 
 already stated, it would be necessary to 
 second-mine an area of coal in order to 
 implement this system. This would actu- 
 ally generate more income, since the coal 
 could then be put on the market. In ad- 
 dition, no roof support would have to be 
 instituted. The area would need less up- 
 keep after retreat mining, resulting in a 
 more economical, stable, and water-free 
 environment. 
 
 COSTS 
 
 included well drilling and aquifer test- 
 ing, they decided that this approach 
 would not be cost effective for the fol- 
 lowing reasons: 
 
 • The aquifer unit feeding water to 
 the mine is not permeable enough to pump. 
 Maximum well yield is only 2 to 3 gpm 
 (0.13 to 0.19 L/s). In order to dewa- 
 ter the mine using wells, the wells 
 would have to be placed on 100-ft (30-m) 
 centers. 
 
 • If the water table or hydrologic 
 balance is altered, a potable water sup- 
 ply must be made available by the mining 
 company for the area's landowners. 
 
 • The natural water in the area has a 
 pH of 4.0 to 4.5, which is not potable. 
 By law, this water must be treated before 
 being returned to the environment. 
 
 Case Study 1 
 
 The cost effectiveness of this demon- 
 stration project is detailed in appen- 
 dix A. The overall conclusion of this 
 specific project was that individually 
 pumped wells constructed from the surface 
 do not appear to be cost effective in 
 controlling water quality at the specific 
 demonstration site, unless the average 
 well yield can be increased from the 30 
 gpm (1.9 L/s) used in the analyses. On 
 the average, the cost of well dewatering 
 at this study site appeared to be at 
 least twice that of present water removal 
 and treatment methods. 
 
 In addition to the requirements for 
 higher flow rates as described above, two 
 other factors were offered to improve the 
 cost effectiveness of this approach: The 
 acidity concentration of the mine water 
 should be in the range of 500 to 1,500 
 ppm (500 to 1,500 mg/L) , and the coal 
 seam depth should be less than 150 ft (46 
 m) . 
 
 Case Study 2 
 
 Mine engineers studied the possibil- 
 ity of using individually pumped wells 
 constructed from the surface to control 
 water flowing into the mine. After a 
 period of information gathering, which 
 
 • The company would need to purchase 
 surface rights for access, power lines, 
 etc., needed for the wells. 
 
 • The cost of drilling in hard and 
 fractured rock is extremely high. 
 
 Case Study 3 
 
 No cost data are available for this 
 situation since the mining company did 
 not investigate the use of individually 
 pumped wells constructed from the surface 
 to control inflowing mine water. Most 
 of the company's mine property has been 
 mined out, except for a small 1-1/4— mi 2 
 (3.24—km 2 ) area, which is currently ex- 
 periencing water problems. It is not to 
 the company's benefit to expend large 
 amounts of money on well development and 
 testing. However, it would be beneficial 
 for the company to extract the existing 
 coal, since it represents a considerable 
 market value. Company officials have 
 therefore decided to dewater the overbur- 
 den by retreat mining the area between 
 the water source and the workings , there- 
 by creating a large sump where the water 
 can be collected and pumped out of the 
 mine. This type of system is extremely 
 cost effective under conditions such as 
 those at this mine. 
 
43 
 
 OTHER CONSIDERATIONS 
 
 Well dewatering systems are not de- 
 signed to control or influence sudden in- 
 rushes of water. Sudden inrushes are 
 usually associated with one of the three 
 following situations: (1) flood waters 
 entering a mine opening located in the 
 floodplain, (2) subsidence or caving be- 
 low a large water body, or (3) breaching 
 of an underground pool of water such as 
 abandoned and flooded mine workings. Al- 
 though a dewatering well can be used to 
 drain abandoned flooded mine workings 
 when they are identified, inrushes are 
 usually associated with unidentified and 
 unexpected underground pools. Conse- 
 quently, well dewatering systems cannot 
 be credited with providing any benefits 
 in this area. 
 
 Roof collapses, which are a reflection 
 of poor roof conditions, are often asso- 
 ciated with the presence of water in con- 
 junction with geologic unconformities. 
 Water will either soften claystone roof 
 or act as a lubricant to decrease the 
 frictional resistance to movement of rock 
 strata. It has been postulated that well 
 dewatering systems may aid in the control 
 of roof problems by reducing the volume 
 of water entering the working section. 
 However, since dewatering systems have 
 been demonstrated to intercept less than 
 50 pet of the inflow to a given section, 
 their benefit with respect to roof con- 
 trol is questionable. Reducing inflow to 
 a working section from 100 to 50 gpm (6.3 
 to 3.2 L/s) is not likely to improve roof 
 conditions significantly. Lubrication of 
 a slip surface, such as a slickenslide, 
 requires only small volumes of water or 
 moisture, although the precise amount is 
 variable. Thus, it would appear that in 
 order to improve roof control problems, a 
 dewatering system would have to intercept 
 virtually all of the water coming in con- 
 tact with slip or failure planes. Simi- 
 larly, only small amounts of water are 
 necessary to cause a softening of under- 
 clays, which leads to floor heave and 
 pillar punching. 
 
 Ventilation problems associated with 
 the presence and flow of water include 
 increases in heat and humidity, and ven- 
 tilation system blockages. The potential 
 
 effect of well dewatering on heat and 
 humidity has not been explored to date. 
 However, with respect to ventilation sys- 
 tem blockages, well dewatering systems do 
 not appear to offer any advantages over 
 conventional drainage systems. 
 
 In summary, the use of a well dewater- 
 ing system in the Appalachian coalfields 
 is not likely to provide any substantial 
 advantage over conventional drainage sys- 
 tems with respect to health and safety. 
 
 An underground coal mine has the poten- 
 tial to substantially alter both the 
 quantity and quality of surface and un- 
 derground water. The impact of coal 
 mines on water quality has been the focus 
 of many research projects in the past. 
 Regulation of the impact of coal mines on 
 the quantity of both surface and ground 
 water is a more recent development. 
 
 The use of dewatering wells to control 
 the contamination of water by underground 
 coal mines is particularly attractive 
 from an environmental standpoint because 
 it eliminates the need for treatment pri- 
 or to discharge to surface waters. For 
 those underground mines involved in the 
 handling, pumping, and treatment of large 
 volumes of contaminated water, it might 
 prove cost effective to intercept the 
 mine inflow prior to contamination and 
 release the uncontaminated water directly 
 to surface streams, thus avoiding the 
 cost of treatment. 
 
 This practice is not directly ap- 
 plicable in Appalachia for a number of 
 reasons. There are wide variations in 
 the characteristics of natural waters 
 throughout the Appalachian coalfields. 
 Simply because ground water is "natural" 
 does not imply that State regulatory 
 agencies will allow its discharge to sur- 
 face streams without treatment. For ex- 
 ample, the ground water encountered in 
 case study 2 was derived from an acidic 
 sandstone and displayed a natural pH in 
 the range of 4.0 to 4.5. Consequently, 
 this water would have to be treated to 
 obtain a pH in the range of 6.0 to 9.0 
 prior to release. In addition, the natu- 
 ral ground water may be objectionable 
 with respect to its iron, manganese, or 
 dissolved salts concentrations. 
 
44 
 
 A second major constraint to the suc- 
 cessful application of this approach in 
 Appalachia is the failure to demonstrate 
 that it can result in well effectiveness 
 (the ability to intercept a certain per- 
 centage of the mine drainage inflow) ex- 
 ceeding 50 pet [Fink (13)]. This method 
 would require the use of two separate 
 dewatering systems at the mine: the 
 standard approach to mine dewatering, 
 previously discussed, and the well dewa- 
 tering system itself. 
 
 Well dewatering systems appear to be 
 more advantageous at shallower depths. 
 In order to obtain a well effectiveness 
 of 80 pet, the depth of the mine would 
 have to average less than 220 ft (67 m) 
 for the system to be cost effective ( 13). 
 The average depth of underground coal 
 mines in Appalachia is approximately 600 
 ft (183 m) , and this value is expected to 
 increase in the future. Consequently, it 
 is unlikely the high well-effectiveness 
 values can be achieved at this time, and 
 the likelihood decreases in the future as 
 the depths of mines increase. 
 
 There is very little information avail- 
 able on the cost effectiveness of well 
 dewatering systems in Appalachian under- 
 ground coal mines. In fact, the only 
 
 information available is that provided in 
 case study 1, which represents the only 
 known and reported demonstration of such 
 a system. 
 
 The results of this demonstration pro- 
 gram indicate that the cost of well dewa- 
 tering appears to be, on the average, /at 
 least twice that of present water removal 
 and treatment practices. The case study 
 suggests that dewatering with individual- 
 ly pumped wells could be cost effective 
 if the coal seam is less than about 150 
 ft (45 m) deep. As previously discussed, 
 the average depth of underground mines in 
 Appalachia is approximately 600 ft (183 
 m) , and that figure is expected to in- 
 crease. There are very few underground 
 mines with depths of less than 150 ft 
 (45 m) in Appalachia. 
 
 The case studies suggest that addition- 
 al indirect benefits of dewatering, such 
 as reduction of production losses due to 
 high water inflows and unstable roofs, 
 could enhance the effectiveness of well 
 dewatering systems. However, the volume 
 of water intercepted by the dewatering 
 systems has not been demonstrated to in- 
 crease productivity any more than conven- 
 tional drainage methods. 
 
 CONCLUSIONS 
 
 IMPACTS OF MINE WATER 
 
 The effects of mine water fall into 
 four major categories, as follows: 
 
 1. Health and Safety 
 
 system can cause failure in weak shale 
 roofs. 
 
 • Mine water increases the maintenance 
 requirements for both electrical and me- 
 chanical equipment. 
 
 • The concern for inrushes of mine wa- 
 ter in Appalachia is likely to increase 
 in the future as the number of new mines 
 increases, particularly since these new 
 mines will often be sited in the deeper 
 seams, adjacent to and/or underlying the 
 older water-logged workings. 
 
 • Mine water can affect a mine's ven- 
 tilation in two ways: it can (1) aggra- 
 vate the heat and humidity problem and 
 (2) block the ventilating airways. 
 
 • Mine water seeping through the roof 
 and moisture supplied by the ventilation 
 
 • The presence of mine water, particu- 
 larly when strongly acidic or alkaline, 
 can accelerate the corrosion of mining 
 equipment. 
 
 2. Production 
 
 • A survey of 325 working sections in 
 the Appalachian region revealed that 56 
 pet of the sections had floor conditions 
 in the wet to damp category. Thirty-nine 
 percent of these sections displayed floor 
 conditions with some degree of rutting 
 and probable rolling resistance exceeding 
 100 lb/ton (51 kg/t). 
 
45 
 
 • A correlation of these floor con- 
 ditions with production suggested that 
 a section would experience a decrease 
 on the order of 16 to 25 tons (14.5 to 
 22.7 t) per shift per drop in bottom 
 classification. Thus, a difference in 
 the range of 32 to 50 tons (29 to 45 t) 
 per shift might be experienced between 
 a section with a dry, hard floor and a 
 section with a wet, rutted, and slippery 
 floor. 
 
 3. Environment 
 
 • The mechanisms that cause hydrologic 
 impacts include (1) the removal of the 
 coal seam, which results in underground 
 cavities that serve as broad sinks or un- 
 derdrains , which receive ground water 
 percolating downward from overlying 
 strata, (2) the fracturing and separation 
 of overlying strata resulting from the 
 removal of the coal seam, and (3) the re- 
 moval of the water from the mine by grav- 
 ity drainage and pumping. 
 
 • Recent inve 
 hydrologic impact 
 of domestic wel 
 be a frequent oc 
 for two reasons 
 mining zone were 
 mine depth excee 
 (2) the average 
 in Appalachia is 
 and this figure 
 future. 
 
 stigations suggest that 
 s , such as dewatering 
 Is, are not likely to 
 currence in the future 
 : (1) wells above the 
 not dewatered when the 
 ded 300 ft (91 m), and 
 depth of existing mines 
 already 600 ft (183 m) , 
 will increase in the 
 
 4. Costs 
 
 • A difference in coal sales ranging 
 from $422,400 to $660,000 per mining sec- 
 tion per year can be experienced between 
 a section with a dry, hard floor and a 
 section with a wet, rutted, and slippery 
 floor. 
 
 • Existing information on the effects 
 of mine water on health and safety, pro- 
 duction, environment, and costs is gen- 
 erally qualitative. Very little quan- 
 tification of these impacts has been 
 attempted to date, which precludes the 
 determination of associated costs. 
 
 SOURCES OF INFLOW TO UNDERGROUND MINES 
 
 In order to assess conditions where wa- 
 ter diversion and overburden dewatering 
 might be feasible, it is necessary to 
 briefly evaluate the characteristics of 
 the aquifers associated with coal seams 
 at mine sites in Appalachia. However, 
 the literature survey revealed that there 
 is a general lack of such data. This 
 study also indicated that there is a gen- 
 eral lack of information on sources of 
 water inflows in underground mines. 
 
 The literature survey and consulta- 
 tions with mine personnel revealed that 
 fracture-dominated flow systems are the 
 major source of water inflow in under- 
 ground mines, especially with large mine 
 inflows of ground water. Fracture zones 
 associated with faulting, jointing or 
 subsidence are the avenues 'for the larger 
 inflows . 
 
 WATER CONTROL METHODS 
 
 Several methods were identified for 
 controlling surface and ground water in- 
 flow to underground mines , but the liter- 
 ature evaluation revealed that the tech- 
 nical feasibility and cost effectiveness 
 of many of these methods have yet to 
 be determined. A number of practices re- 
 ported were developed or adapted for use 
 in controlling water problems associ- 
 ated with abandoned underground mines. 
 Many of the practices were selected be- 
 cause they represented the best, and in 
 some instances the only, available con- 
 trol technology. Provisions were seldom 
 made, however, to monitor the short- or 
 long-term performance of these control 
 measures. 
 
 CURRENT ENGINEERING PRACTICES 
 
 Consultation with mine personnel re- 
 vealed only one widely recognized and ac- 
 cepted approach to managing the influx of 
 water into underground coal mines in Ap- 
 palachia. This approach consists of col- 
 lecting the water that builds up within a 
 section with one or more portable pumps 
 and transferring it through a combination 
 of conduits (either pipes or ditches), 
 
46 
 
 sumps, and pumps back to a surface hold- 
 ing facility for treatment and discharge 
 to surface waters. As a consequence of 
 this approach, the preferred method of 
 planning an underground coal mine to min- 
 imize water problems consists of develop- 
 ing the mains along the strike of the 
 coal. Panels are driven on the downdip 
 during advance and on the updip during 
 retreat. The investigations conducted 
 during this project did not identify any 
 new basic approaches that could replace 
 the standard approach to mine dewatering 
 described above. 
 
 The use of water diversions and over- 
 burden dewatering methods is not likely 
 to control the flow of water into under- 
 ground mines sufficiently to alleviate 
 the need to develop a traditional system 
 of gravity drainage and pumpage. These 
 methods should not be viewed as alterna- 
 tives, but rather supplements to tradi- 
 tional methods of handling water in un- 
 derground mines. 
 
 To justify the application of water 
 diversions and overburden dewatering, it 
 is necessary to identify and quantify the 
 
 benefits derived from the use of these 
 control practices. These benefits must 
 be greater than the benefits provided by 
 the standard dewatering approach to jus- 
 tify the additional expense. 
 
 On the basis of reported data, the use 
 of dewatering wells alone, drilled from 
 the surface in advance of mining, does 
 not appear to be a cost-effective method 
 of dewatering underground coal mines in 
 Appalachia, except under unusual condi- 
 tions. These conditions include an aver- 
 age depth of overburden above the coal 
 seam not exceeding 200 ft (67 m) , inter- 
 ception of 80 pet of the normal mine wa- 
 ter inflow, and an acidity concentration 
 in contaminated mine waters in the range 
 of 500 to 700 ppm (500 to 700 mg/L). 
 
 These are rather unusual circumstances 
 in underground Appalachian coal mines, 
 which average approximately 600 ft (183 
 m) , a value which is projected to in- 
 crease in the future. On this basis, it 
 is concluded that the use of dewatering 
 wells drilled from the surface in advance 
 of mining is not practical at this time 
 in Appalachia. 
 
 RECOMMENDATIONS 
 
 Methods of predicting water inflow to 
 underground mines should be standardized 
 and simplified. The regulatory require- 
 ments of the Office of Surface Mining re- 
 quire that a permit application for an 
 underground coal mine include a determi- 
 nation of the probable hydrologic conse- 
 quences of the proposed mine plan area 
 and adjacent area, with respect to the 
 hydrologic regime and quantity and qual- 
 ity of water in surface and ground water 
 systems under all seasonal conditions 
 [30 CFR 780.21(c)]. Particular emphasis 
 should be placed on the feasibility of 
 developing empirical values and constants 
 on a regional or subregional basis, such 
 as a drainage basin, to facilitate and 
 simplify these computations. 
 
 The Bureau's Bulletin 570, "Ameri- 
 can Standard Recommended Practice for 
 Drainage of Coal Mines (M6. 1-1955, UDC 
 622.5)," needs to be updated. This pub- 
 lication, published in 1957, provides the 
 latest in formal guidelines for drainage 
 practices of coal mines. The guidance 
 provided should be reviewed and reas- 
 sessed in order to incorporate any devel- 
 opments that have occurred over the past 
 23 yr and, in particular, to assess the 
 compatibility of the recommended drainage 
 practices with new regulatory require- 
 ments such as those implemented by the 
 Office of Surface Mining. 
 
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49 
 
 31. Shotts, R. Q. , E. Sterett, and 
 T. A. Simpson. Site Selection and Design 
 for Minimizing Pollution From Underground 
 Coal Mining Operations (U.S. EPA contract 
 68-03-2015, Univ. AL, University, AL). 
 EPA-600/7-78-006, Jan. 1978, 98 pp. 
 
 32. Skelly and Loy. Guidelines for 
 Mining Near Water Bodies. Phase III. 
 Recommended Guidelines for Mining Under 
 Surface Waters (contract H0252083) . Bu- 
 Mines OFR 29-77, 1976, 193 pp.; NTIS PB 
 264 728/ AS. 
 
 33. Slaughter, T. H. , and J. M. Dar- 
 ling. The Water Resources of Allegheny 
 and Washington Counties. MD, Dep. Geol. , 
 Mines and Water Resour. , Bull. 24, 1962, 
 408 pp. 
 
 34. Stefanko, R. Coal Mining Tech- 
 nology - Theory and Practice. Soc. Min. 
 Eng. AIME, Littleton, CO, 1983, 402 pp. 
 
 35. Suboleski, S. C. Effects of Phys- 
 ical Conditions on Continuous Mine Pro- 
 duction in Underground Coal Mines. Ph.D. 
 Thesis, PA State Univ., University Park, 
 PA, 1978, 362 pp. 
 
 36. Todd, D. K. Ground Water Hydrol- 
 ogy. Wiley, 1959, 336 pp. 
 
 37. UOP, Inc. , Johnson Division (St. 
 Paul, MN). Ground Water and Wells. 4th 
 ed. , 1975, 440 pp. 
 
 38. Wahler, W. A., and Associates. 
 Dewatering Active Underground Coal Mines: 
 Technical Aspects and Cost Effectiveness 
 (U.S. EPA contract). EPA-600/7-79-124, 
 July 1979, 124 pp. 
 
 39. Walton, W. C. Leaky Artesian 
 Aquifer Conditions in Illinois. IL State 
 Water Surv. , Rep. Invest. 39, 1960, 
 27 pp. 
 
 40. Wardell, K. , and Partners. Guide- 
 lines for Mining Under Surface Waters. 
 Phase III and Final Report (contract 
 H0252021). BuMines OFR 30-77, 1976, 67 
 pp.; NTIS PB 264 729/ AS. 
 
 41. White, P. E. Corrosion Research 
 and Corrosion Resistance Fasteners. Min. 
 Eng. (London), v. 127, No. 92, May 1968, 
 pp. 463-473. 
 
 42. Whittaker, B. N. , R. N. Singh, and 
 C. J. Neate. Investigation and Evalua- 
 tion Studies of Surface and Subsurface 
 Drainage Pattern Changes Resulting From 
 Longwall Mining Subsidence. Paper in 
 Mine Drainage (Proc. 1st Int. Mine Drain- 
 age Symp., Denver, CO, May 1979). Miller 
 Freeman Publ. , Inc., 1979, pp. 161-183. 
 
 43. Wilson, L. W. , N. J. Mathews, and 
 J. L. Stump. Underground Coal Mining 
 Methods To Abate Water Pollution: A 
 State of the Art Literature Review (U.S. 
 EPA, project 14010 FKK, Coal Res. Bureau, 
 Morgantown, WV). Dec. 1970, 178 pp. 
 
 44. Wrathers , R. J., A. W. Swanson, 
 and R. F. Langill. Investigation and 
 Analysis of Subsurface Conditions for 
 Coal Mine Development in Eastern Ken- 
 tucky. Paper in 19th U.S. Symposium on 
 Rock Mechanics (Stateline, NV, May 1978). 
 Univ. NV-Reno, 1978, pp. 151-158. 
 
50 
 
 APPENDIX A. —CASE STUDY 1 
 
 INTRODUCTION 
 
 The interception of ground water in- 
 flows to active coal mines was the sub- 
 ject of a study conducted by W. A. Wahler 
 and Associates for the Environmental Pro- 
 tection Agency (38). 1 The study involved 
 the construction and operation of a pilot 
 well dewatering system, to collect and 
 analyze both technical and cost data. 
 The study site for this pilot dewatering 
 program was the Lancashire No. 20 Mine, 
 located near Carrolltown, PA, and owned 
 by the Barnes and Tucker Co. (fig. A-l). 
 The Lancashire No. 20 is a moderately 
 deep slope mine, and the Lower Kittanning 
 (B) coal of the Allegheny Group is the 
 only seam mined. The coal seam averages 
 60 in (152 cm) in thickness and is lo- 
 cated at depths ranging from 500 to 550 
 ft (152 to 168 m) in the vicinity of the 
 
 1 Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding this appendix. 
 
 PA 
 
 r^\. 
 
 Mine property boundary 
 
 v.r'Vh'a'g 
 
 Carrolltown , 
 ^(study site)( 
 
 Study area 
 
 ^Eastern working 
 I n face 
 
 &J 
 
 Scale, miles 
 
 FIGURE A-l. - Location map of Lancashire 
 No. 20 Mine and pilot well dewatering site. 
 
 study area. The "B" coal is metallurgi- 
 cal-grade, low-sulfur, low-volatile coal. 
 The longwall method of mining is used. 
 
 The objectives of the pilot study were 
 (1) to determine the impact of the dewa- 
 tering operation on the quantity and 
 quality of inflows in the limited area 
 of the mine under study, (2) to evaluate, 
 by extrapolating the results of this pro- 
 gram, the potential effectiveness of the 
 dewatering technique for the mine as a 
 whole, and (3) to perform an economic 
 evaluation of the technique. 
 
 GEOLOGIC ENVIRONMENT 
 
 Surface Geology 
 
 Unconsolidated materials cover most of 
 the surface of the area and include qua- 
 ternary alluvium, colluvium, and seden- 
 tary soil. Sedentary soil and colluvium 
 make up the greater percentage of this 
 cover and typically consist of silty sand 
 to silty clay. They form a soil cover 
 over bedrock units that varies widely in 
 thickness. Quaternary alluvial material 
 consists chiefly of sandy silt and sand. 
 This alluvium is restricted to the flood- 
 plain and channel of Laurel Lick Run, 
 which runs across the mine property. 
 
 All rocks exposed on the surface are 
 of Pennsylvanian age and belong to the 
 Glenshaw Formation of the Conemaugh 
 Group. They generally consist of thinly 
 to thickly bedded sandstone and shale. 
 Sandstones are generally quartzose and/or 
 argillaceous, fine to very fine grained, 
 moderately hard to very hard, moderate- 
 ly weathered, and iron oxide stained. 
 Shales are gray to gray brown, moderately 
 hard, and moderately to severely weath- 
 ered. The outcrops of sandstone and 
 shale are relatively few in number and 
 are generally covered by soil units. 
 
 Subsurface Geology 
 
 A generalized stratigraphic column of 
 the units encountered is shown in fig- 
 ure A-2. All rocks in the subsurface 
 are from Pennsylvanian period and are 
 
51 
 
 DEPTH, ft 
 O-i 
 
 100- 
 
 Lithology Description 
 
 200- 
 
 300- 
 
 - : : - 
 
 ?: :- 
 
 600- 
 
 -"- 
 
 
 
 a. 
 
 c 
 o 
 
 
 
 
 
 o 
 
 o 
 
 
 O 
 
 E 
 
 
 f 
 
 .? 
 
 
 o> 
 
 
 
 3 
 O 
 
 F 
 
 3 
 
 
 s> 
 
 in 
 
 
 
 
 
 o 
 
 
 
 o 
 
 O 
 
 s 
 
 
 
 _ 
 
 
 
 £ 
 
 
 
 >- 
 
 
 
 to 
 
 
 
 z 
 
 
 
 < 
 
 
 
 z 
 < 
 
 
 
 
 
 > 
 
 
 
 _j 
 
 
 
 >- 
 
 
 o 
 
 CO 
 
 
 
 z 
 
 
 o 
 
 z: 
 
 
 b 
 
 111 
 a. 
 
 
 £ 
 
 
 a. 
 
 o 
 
 
 3 
 
 a. 
 
 
 o 
 
 a> 
 
 
 — 
 
 a> 
 
 
 o 
 
 it 
 
 
 >> 
 
 
 
 
 
 
 a> 
 
 c 
 
 
 c 
 
 o 
 
 
 o> 
 
 
 
 ■ 
 
 a 
 
 
 < 
 
 E 
 
 W 
 
 £ 
 
 — 
 - 
 
 c 
 o 
 
 2 
 
 -^-~r 
 
 Colluvium clayey sand 
 Saltsburg Sandstone 
 
 Shale, limestone 
 
 Buffalo Sandstone, Siltstone 
 Shale 
 
 Brush Creek Marine shale 
 Brush Creek Coalbed 
 Corinth Sandstone 
 
 Shale 
 
 Mahoning Sandstone 
 
 Upper Freeport Limestone 
 
 Interbedded shale, siltstone, 
 
 and sandstone 
 Lower Freeport (D) Coalbed 
 
 Interbedded shale, siltstone, 
 and sandstone 
 
 Upper Kittanning(C) Coalbed 
 Upper Worthington Sandstone 
 
 Shale 
 
 Middle Kittanning(C) Coalbed 
 
 Lower Worthington Sandstone 
 
 Lower Kittanning (B)Coalbed 
 
 FIGURE A-2. - Generalized strat igraph ic 
 column, case study 1 . 
 
 sedimentary in origin. Sandstone, shale, 
 siltstone, limestone, coal, and clay were 
 found. 
 
 The rocks in the subsurface can be di- 
 vided into two stratigraphic groups: the 
 Allegheny and the Conemaugh. The Alle- 
 gheny Group, the older of the two, can 
 be further divided into three forma- 
 tions (oldest to youngest): the Clarion, 
 the Kittanning, and the Freeport. The 
 maximum thickness encountered in the 
 wells for the Allegheny Group was 250 ft 
 (76 m). 
 
 The Conemaugh Group overlies the Alle- 
 gheny and can be divided into two 
 formations: the Glenshaw and the Cas- 
 selman. The Casselman Formation is 
 
 stratigraphiically higher than the Glen- 
 shaw and was not encountered on the 
 surface or in the subsurface. The maxi- 
 mum thickness for the Glenshaw Forma- 
 tion was 328 ft (10° m) . Names of mem- 
 bers for both the Allegheny and the 
 Conemaugh Groups, along with relative 
 thicknesses, are indicated on the strati- 
 graphic column. 
 
 Structurally, the area is generally 
 flat with a gentle dip to the east- 
 southest. Strata lie subparallel to one 
 another except for the lowermost coal 
 seam, the Lower Kittanning (a member of 
 the Kittanning Formation of the Alle- 
 gheny Group) , which dips to the east at a 
 slightly greater angle. No fault fea- 
 tures were identified by correlation of 
 geologic units. 
 
 HYDR0L0GIC CONDITIONS 
 
 Surface Water 
 
 The mine area lies within the drainage 
 basin of the Susquehanna River, whose 
 flow ultimately reaches the Atlantic 
 Ocean. Laurel Lick Run and Chest Creek 
 both cross the mine property. Laurel 
 Lick Run, with a drainage area of 9 mi 2 
 (23 km 2 ), flows into Chest Creek, which 
 in turn flows into the West Branch of the 
 Susquehanna River. 
 
 Laurel Lick Run and Chest Creek are 
 relatively unpolluted and support trout 
 and other aquatic life. In the past, 
 Chest Creek has been used as a source of 
 municipal water and could be used in this 
 manner in the future. Because of the 
 high quality of water in this watershed, 
 treated mine drainage from the Lancashire 
 No. 20 Mine is discharged into the West 
 Branch of the Susquehanna, though Laurel 
 Lick Run is closer. 
 
 Seeps, springs, and other hydrologic 
 features are also present. Springs are 
 few in number and not associated with any 
 given horizon or topographic elevation. 
 Only flows that are continuous year round 
 were designated as springs, and flows for 
 these are generally greater than 5 gpm 
 (0.315 L/s). Seeps, on the other hand, 
 were found to be quite common. Flow is 
 usually less than 1 to 2 gpm (0.063 to 
 
52 
 
 0.126 L/s), occurs intermittently, and is 
 associated with wet periods. Seeps are 
 commonly found in the topographic lows or 
 swales or in areas with a break in slope. 
 
 Ground Water 
 
 Attempts were made to identify the 
 principal water-bearing zones as they 
 were encountered during air-rotary drill- 
 ing. This was achieved by logging both 
 the amount of water airlifted as the 
 holes advanced and the rock types. Each 
 water-bearing zone generally increased 
 the amount of water airlifted as long 
 as circulation was maintained. It was 
 found, generally, that there was little 
 correlation between rock types and the 
 amount of ground water. There appeared 
 to be some perching of ground water in 
 the Saltsburg Sandstone, a member of the 
 Glenshaw Formation of the Conemaugh 
 Group, and possibly in the underlying 
 unidentified limestone. Below this ap- 
 parent perched zone, the bedded rock 
 units could not be separated into dis- 
 tinct aquifers or zones with any degree 
 of consistency. In particular, the vari- 
 ous sandstone beds encountered did not 
 indicate higher permeabilities than even 
 the shales. There were some indications 
 that the coal seams and the Upper Free- 
 port Limestone are relatively permeable, 
 but not with consistency. Also, there 
 were indications that the thin shale bed 
 above the Lower Kit tanning (B) Coal, 
 which forms the mine roof, is relatively 
 permeable. This information, although 
 not conclusive in itself , seems to indi- 
 cate that fractures control the ground 
 water flow. 
 
 Pump test data indicated a very asym- 
 metric drawdown response with the cone of 
 depression around the pumped well elon- 
 gated along fractures, possibly in sev- 
 eral directions. Also, it was observed 
 that there was very rapid response to 
 heavy rainfall both in well water levels 
 and in inflows to the mine, indicating a 
 hydraulic connection of fracture zones 
 with the surface. 
 
 Using time-drawdown data from the 
 pumped wells and distance— drawdown data, 
 the transmissivities were calculated; 
 they ranged between 200 and 300 gpd/ft 
 
 (0.29 to 0.43 cm 2 /s). This was later 
 confirmed using data developed from the 
 pilot dewatering operation. 
 
 In conclusion, the data strongly indi- 
 cate that ground water drains into the 
 study area along narrow, preferred flow 
 paths. These flow paths are controlled 
 by fractures and are directionally ori- 
 ented. Permeabilities across these flow 
 paths may be several orders of magnitude 
 lower than permeabilities along the frac- 
 ture planes. The bedded rock units prob- 
 ably act as secondary aquifers to various 
 degrees and provide both hydraulic inter- 
 connection between fractures and ground 
 water storage space. The fracture zones 
 appear to consist mainly of steeply dip- 
 ping fractures that intersect the sur- 
 face. These permit rapid recharge from 
 direct precipitation and from streams or 
 ponds at the surface. The secondary 
 aquifers also release ground water from 
 storage to the fracture zones. The 
 ground water flow regime is, therefore, 
 quite complex and difficult to model with 
 mathematical techniques because of the 
 severe boundary effects and directional 
 variations in permeability. 
 
 MINE WATER 
 
 The source of water inflow to the mine 
 is ground water in overlying and sur- 
 rounding rocks. Water flows into the 
 mine primarily through the roof and is 
 transmitted predominantly by fractures. 
 There is probably some inflow through the 
 mine floor, but it appears to be rela- 
 tively minor. The mine floor is on an 
 underclay (clay-shale) that restricts up- 
 ward seepage of water. 
 
 Although minor drips and seeps are 
 scatterd throughout the mine, the larger 
 inflows are localized, probably along 
 zones of more intense fracturing. Frac- 
 tures and fracture zones are caused orig- 
 inally by geologic processes and later by 
 the subsidence of rocks overlying the 
 mine openings. Natural fractures were 
 encountered while driving main haulage- 
 ways and while establishing entries and 
 crosscuts during the development of long- 
 wall panels for mining. Unstable roofs 
 are often associated with areas of rela- 
 tively high water inflow. 
 
53 
 
 Inflows to the longwall panels and 
 abandoned areas of the mine are influ- 
 enced both by natural fractures and sub- 
 sidence fractures. The longwall panels 
 are 500 to 550 ft (152 to 168 m) wide and 
 about 3,500 ft long. Normally, all of 
 the coal is extracted in a continuous 
 operation, and the roof support is moved 
 forward with the coal cutting machine, 
 allowing the roof behind the support 
 to collapse. Entries previously driven 
 along the panel partially dewater the 
 panel area, but new fractures associated 
 with roof collapse, along with preexist- 
 ing fractures, promote more drainage into 
 the mine. New fractures may extend to 
 the surface, resulting in drainage of 
 ground water that was not previously 
 tapped. These fractures can result in 
 inflows of water that are large enough to 
 cause handling problems and that have hy- 
 drostatic heads sufficient to affect the 
 caving characteristics of the roof. Both 
 of these problems can affect production. 
 Similarly, additional fracturing can be 
 caused by the slow collapse of abandoned 
 or inactive openings in which roof sup- 
 ports have not been maintained. 
 
 It appears that approximately 40 pet of 
 the water enters through abandoned parts 
 of the mine and 60 pet enters directly 
 into the more recent workings. Inflows 
 are affected by seasonal conditions, and 
 it is even possible to recognize recharge 
 from individual rainstorms. There is a 
 tendency for high inflows to occur be- 
 neath stream channels, which probably 
 tend to follow fracture zones along parts 
 of their courses. Wells and springs 
 overlying the mine may be affected or 
 drained completely, especially where sub- 
 sidence has occurred. 
 
 Water Removal 
 
 Water in the mine is collected and 
 transferred through a series of sumps and 
 conduits and eventually pumped to the 
 surface. Initially, water is collected 
 by small sludge pumps or allowed to drain 
 by gravity into sumps. From there it is 
 pumped from sump to sump through pipe- 
 lines, as shown schematically in figure 
 A-3. Water is pumped to the surface from 
 F-l and F-14 sumps, and the pipelines are 
 
 combined to a single flow at the treat- 
 ment plant, which has a design capacity 
 of 5 million gpd (19 million L/d). Flow 
 to the plant is controlled by pump opera- 
 tors underground, according to water lev- 
 els in the sumps. Logs are kept for each 
 pump and are used to determine flow 
 rates, based on the pump curves for the 
 two sumps. 
 
 Water Inflow Rate 
 
 General 
 
 Figure A-4 is a graph of average daily 
 inflows to the treatment plant. The pat- 
 tern of these flows tend to follow the 
 dry and wet periods for this region. The 
 yearly average flow for the period July 
 
 1976 through June 1977 is 3.4 million gpd 
 (12.9 million L/d). The data after June 
 
 1977 are not reflective of normal flows, 
 owing to the flooding on July 19 and 20 
 and cleanup operations extending well in- 
 to August 1977. 
 
 Underground Study Area 
 
 The underground test site is referred 
 to as the Main G study area and is lo- 
 cated near the northeasternmost limit of 
 workings along Main G heading or (as com- 
 monly referred to in the mine) the left 
 side of Main G, near section G-14. The 
 study area is bounded by the haulageway 
 on the south, by the edge of underground 
 working on the north and east, and by the 
 G-ll entry on the west. Figure A-5 is a 
 map of this portion of the mine. 
 
 This area was selected because it has 
 relatively high ground water inflows [ap- 
 proximately 100 to 150 gpm (6.3 to 9.5 
 L/s)] and because it could easily be sep- 
 arated from other mine drainage and moni- 
 tored. Mining in the immediate area had 
 been temporarily halted because of unsta- 
 ble roof conditions and high ground water 
 inflows, so advancement of the workings 
 would not hamper the progress of the 
 project. 
 
 Water enters the study area of the mine 
 from the roof and from the coal seam. 
 The roof is a gray to dark gray-brown 
 shale-siltstone , which is fractured to 
 intensely fractured. Slickensides and 
 
54 
 
 L-2 
 sump 
 
 Drainage collected from Main G 
 study area 
 
 G-ll 
 sump 
 
 K-12 
 sump 
 
 G-IO 
 sump 
 
 6-9 
 
 sump 
 
 G-7 
 sump 
 
 G-5 
 sump 
 
 K - 7 sump 
 
 F-20 
 sump 
 
 MainH 
 sump 
 
 LT 
 
 F-13 
 sump 
 
 F-17 
 sump 
 
 Slant sump 
 
 I 
 
 Main Fsump, 
 
 old workings 
 
 drainage 
 
 F-14 
 sump 
 
 —Old workings 
 I drainage 
 
 i 4. 
 
 F-l 
 sump 
 
 i 
 
 To treatment 
 
 FIGURE A-3. - Water transport system. 
 
 Main C 
 sump 
 
 Out- 
 drift 
 
 E 
 a. 
 en 
 
 5.0 
 
 CD 
 O 
 
 4.5- 
 
 - 4.0 
 
 UJ 
 
 Unseasonably high flow due \ 
 
 to pumping out mine following \ 
 
 July 19-20, 1977, flood / 
 
 Mar. 
 
 May 
 
 July Sept. 
 
 I976 I977 
 
 FIGURE A-4. - Average daily flows to treatment plant. 
 
55 
 
 L-2 pool. 
 
 Small pond 
 L-4 
 
 11 
 
 n 
 
 i UI| i 
 
 » i 
 
 m. 
 
 \ 
 
 ? 
 
 111 
 
 ^L-2 
 sump 
 
 Section 
 G-14 
 
 o 
 
 tic 
 
 Section 
 G-ll 
 
 G-ll 
 sump 
 
 ^ 
 
 LEGEND 
 i— Light inflow 
 °— "-Moderate inflow 
 *—* Heavy inflow 
 -*-— Direction of uncontained 
 
 flow 
 — —Direction of piped flow 
 M Concrete block dam 
 Pi Pump 
 
 D 
 
 100 
 
 Scale, ft 
 
 FIGURE A-5. - Main G study area. 
 
 polished surfaces are common on much of 
 the rock, and water drains freely from 
 these fractures. Fractures in the roof 
 rock are common throughout this area of 
 the mine. Water inflow, however, tends 
 to be more localized in areal extent. 
 The shale-siltstone roof is about 7 ft 
 (2 m) thick and is overlain by a massive 
 sandstone. Originally, it was thought 
 that this sandstone was acting as an 
 aquifer and was the source of ground wa- 
 ter inflow to the study area. However, 
 drilling and pump testing indicated that 
 this unit is relatively tight, except 
 along fractures. 
 
 The area of greatest mine inflow is 
 along the L-4 heading near the northern 
 face (see figure A-5) where most of it 
 is collected behind a cement block dam. 
 Overflow from the L-4 pond and any addi- 
 tional drainage from the left (north) 
 side of the Main G heading is collected 
 in a low area of the mine floor, forming 
 
 a pool located at the east end of the L-2 
 heading. Prior to establishment of the 
 underground monitoring system, the L-2 
 pool also collected drainage from the 
 right (south) side of the Main G head- 
 ing. Water from both the L-4 pond and 
 L-2 pool is then transferred to the L-2 
 sump, which is formed by a cement block 
 dam and is also located in the L-2 head- 
 ing. Gravity flow is used to drain the 
 L-4 pond, while pumping is required to 
 remove water from the L-2 pool. Water 
 collected in the L-2 sump includes all of 
 the mine inflow to the Main G study area. 
 From the L-2 sump, water is pumped to the 
 G-ll sump where it is combined with wa- 
 ter from adjacent areas and transferred 
 through the mine and eventually to the 
 surface. 
 
 Flow measurements at the underground 
 monitoring station began in the late part 
 of September 1976. Figure A-6 represents 
 typical background flow data for the to- 
 tal water inflow occurring in the Main G 
 study area of the mine. The data shown 
 are average weekly values and the stan- 
 dard deviation for each 7-day period. 
 These data are based on average daily 
 flows derived from individual flowmeter 
 readings and have been adjusted for 
 changes in L-2 sump water levels where 
 appropriate. 
 
 The average inflow rate for the entire 
 period of September 26, 1976, through May 
 31, 1977, was 106 gpm (6.7 L/s), with a 
 standard deviation of 9 gpm (0.57 L/s). 
 As can be seen in figure A-6, the water 
 inflow did vary somewhat over time, but 
 such changes were generally gradual. 
 
 PILOT DEWATERING SYSTEM 
 
 Method of Approach 
 
 The objective of the dewatering program 
 was to intercept a major portion of the 
 ground water inflow to the Main G study 
 area and to analyze the cost effective- 
 ness of mine dewatering as a means of 
 controlling acid mine drainage (AMD). 
 Vertical wells were constructed adjacent 
 to the mine openings to intercept ground 
 water before it could be degraded in the 
 mine. The wells were located along a 
 line parallel to the mine face, in an 
 
56 
 
 e 
 
 Q. 
 
 UJ 
 
 I 
 
 _j 
 
 Li- 
 
 150 
 
 140 
 
 130 
 
 - 120 
 
 10 
 
 100 
 
 90 
 
 80 
 
 'Standard 
 deviation 
 
 Sept. 
 
 Oct. Nov. 
 1976 
 
 Dec. 
 
 Jan. 
 
 Feb. 
 
 Mar. Apr. 
 1977 
 
 May 
 
 June 
 
 FIGURE A-6. - Average mine inflow in Main G study area. 
 
 attempt to create a hydraulic drawdown 
 barrier against ground water movement to- 
 ward the underground study area. 
 
 Results 
 
 The first pilot dewatering started on 
 July 13, 1977, pumping from wells P-l, 
 P-2, and P-3 (shown in figure A-7). The 
 yield of the wells was increased gradual- 
 ly to a maximum total of 45.5 gpm (2.9 
 L/s). This yield was disappointing, be- 
 cause P-l and P-3 were each expected to 
 yield 40 to 50 gpm (2.5 to 3.2 L/s) on 
 the basis of previous pump tests. Well 
 P-2 did not produce much water and was 
 later removed. Pumping continued for 
 about 3 days and was stopped on July 16. 
 During this period, flows in the Main G 
 study area of the mine had decreased from 
 107 to 96 gpm (6.75 to 6 L/s), or 10 pet, 
 as shown in figure A-8. About 24 pet of 
 the water pumped from the wells was in- 
 tercepted or diverted from the mine. 
 These results were somewhat improved 
 by an equipment change. 
 
 A 
 
 u- 
 
 p-4(0B-4) 
 
 P-3 
 
 tr !° B - 3 ^T 
 
 LEGEND 
 • Pumping well 
 o Observation well 
 
 
 
 400 
 
 Scale, ft 
 
 FIGURE A-7. - Location map of dewatering 
 and observation wells. 
 
 The 5-hp pump was removed from P-2 
 and installed in observation well 0B-4, 
 thereafter designated P-4. Pumping 
 
57 
 
 resumed on July 18, and total pumpage was 
 increased to 73.5 gpm (4.6 L/s). On July 
 19, flow in the Main G study area, which 
 had increased to 111 gpm (7 L/s) just 
 prior to restarting the pumps, rapid- 
 ly decreased 23 pet to about 85 gpm (5 
 L/s). This indicated that 35 pet of the 
 water pumped from the wells was diverted 
 from mine inflows. The operation was 
 interrupted by mine flooding, but these 
 results were encouraging because the per- 
 centage of water intercepted should 
 increase with time. 
 
 Dewatering was again resumed on Sep- 
 tember 16, 1977, after the wells were 
 cleaned and the pumps were reset. The 
 average total pumpage was approximately 
 82 gpm (5.2 L/s), ranging from about 95 
 gpm (6 L/s) near the start to about 75 
 gpm (4.7 L/s) at the end of the pumping 
 period. Well OB-1 responded as expected, 
 with generally consistent declines dur- 
 ing pumping except near the end of the 
 period. Well OB-2 declined rapidly at 
 first and then more or less stablized. 
 Water levels in P-2 declined slightly and 
 then rose. Well OB-3 had essentially no 
 response to pumping. 
 
 Inflows to the Main G study area (fig. 
 A-9) decreased rapidly at first but 
 showed only a slight decreasing trend 
 after September 25. Inflows ranged from 
 70 to 76 gpm (4.4 to 4.8 L/s) after this 
 date and quickly recovered to 112 gpm (7 
 L/s) after pumping stopped. The average 
 inflow rate from September 25 through 
 October 6 was 73.2 gpm (4.6 L/s), with a 
 standard deviation of ±1.92 gpm (±0.12 
 
 120 
 
 !l no 
 uT 
 
 < 100 
 £T 
 
 o 
 
 .T 1 90 
 
 90 
 
 Start P-3 and 
 P-4 (0B-4) 
 
 Start 
 
 Start P-l, 
 Start P-3 
 
 Shut off P-l. P-2, 
 and P-3 
 
 Pumping discontinued, 
 mine flooding 
 
 — 
 
 — 
 
 J L 
 
 9 10 II 12 13 14 15 16 17 18 19 20 
 July 
 
 FIGURE A-8. • Average daily mine inflow, July 
 1977. 
 
 L/s). The postpumping monitoring peri- 
 od, after inflows had recovered, from 
 October 8 through October 22, showed an 
 average flow of 110 gpm (6.9 L/s), with 
 a standard deviation of ±4 gpm (±0.25 
 L/s). These values are comparable to 
 all of the other background data, which 
 showed an average inflow rate of 112±9.4 
 gpm (7±0.59 L/s). 
 
 All of the pumping and observation 
 wells, with the exception of 0B-2, were 
 affected by recharge from direct precipi- 
 tation. The pumping and inflow data in- 
 dicate that the mine study area inflow 
 was decreased by about 34 pet, based on 
 average flow rates. This decrease may 
 have been as much as 38 pet, based on 
 measurements at the end of the pumping 
 period and the first inflow measurements 
 after full recovery. These data indicate 
 that 45 pet of the water pumped from 
 wells comprised intercepted or diverted 
 mine inflow, based on average rates for 
 the pumping period. Theoretically, this 
 percentage should increase with time, and 
 at the end of the test, up to 56 pet of 
 the water pumped was diverted from mine 
 inflows. Projection of these data to 120 
 days of pumping indicated that up to 80 
 pet of the water pumped would be diverted 
 from mine inflows. Recharge from storms 
 or streams would reduce these percent- 
 ages. Therefore, for purposes of esti- 
 mating full-scale mine dewatering, it was 
 assumed that 50 to 80 pet of the water 
 yield from dewatering wells would be di- 
 verted from mine inflows. 
 
 During the dewatering operation, well 
 yields were still disappointing. Only 
 well P-3 was close to the maximum avail- 
 able drawdown, and that could not be 
 sustained during the latter part of the 
 pumping period. Well P-l had more than 
 100 gpm (6.3 L/s) of available additional 
 drawdown. The 7.5-hp pump in each of 
 these two wells was not able to produce 
 at Its rated capacity, which was in ex- 
 cess of 40 gpm (2.5 L/s), with a pump 
 lift of 510 ft (155 m). In contrast, 
 the 5-hp pump performed relatively well 
 throughout most of the dewatering program 
 and during earlier pump tests. Howev- 
 er, the yield of well P-4 gradually de- 
 creased, along with a small increase in 
 drawdown. The impellers on the 7.5-hp 
 
58 
 
 Pumping ended 
 Oct. 7, 9a.m. 
 
 /Standard deviation 
 J I I I L_L 
 
 16 18 20 22 24 26 28 30 2 4 6 8 10 12 14 16 18 20 22 24 
 
 Sept. Oct. 
 
 FIGURE A-9. - Average daily mine inflow, September 1977. 
 
 pumps may have been worn, reducing their 
 capacity, or gas blocks may have devel- 
 oped to retard well yield. Although it 
 was detected that all three pumping wells 
 produced methane gas , the volume was not 
 measured. The pumped water obviously had 
 
 Cost 
 
 a large amount of gas entrained in the 
 discharge. 
 
 For the study mine, costs 
 collection and treatment were 
 from company records: 
 
 for water 
 computed 
 
 Collection 
 
 Treatment 
 
 Capital investment $432,000 $430,000 
 
 Operating costs: 
 
 Annual 530,000 209,000 
 
 Per 1,000 gal 1 .468 
 
 'Based on average flow rate of 3.1 million gpd. 
 
 .185 
 
 Of the $530,000 annual operating cost for 
 water collection, approximately 77 pet 
 goes for water collection and transfer 
 costs, and 23 pet for pumping to the sur- 
 face. Major cost contributors to the 
 $530,000 are power, 37 pet, labor, 36 
 
 pet, material, 19 pet, and other charges, 
 8 pet. 
 
 The computed values of treatment plant 
 capital costs ($430,000) and annual oper- 
 ating expenses for treatment ($209,000) 
 compare reasonably well with figures from 
 
59 
 
 published sources for other plants of 
 similar capacity treating water with sim- 
 ilar flow rates and acid levels. 
 
 Individually pumped wells constructed 
 from the surface, as used in this study, 
 do not appear to be cost effective in 
 controlling water quality at the Lan- 
 cashire No. 20 Mine, unless the average 
 well yield can be increased three to four 
 times the 30 gpm (1.9 L/s) used in the 
 analyses. The cost of well dewatering at 
 this mine appears to be, on the average, 
 at least twice as great as present wa- 
 ter removal and treatment costs. If the 
 acidity of the mine water were higher (in 
 the range of 500 to 1,500 ppm — 500 to 
 1,500 mg/L) this dewatering system would 
 be more cost effective. Also, if the 
 coal seam were less than about 150 ft (46 
 m) deep, it appears that it would be fi- 
 nancially feasible to dewater using indi- 
 vidually pumped wells. Conservative well 
 yields were used in the cost analysis 
 based on the assumption that it would be 
 
 difficult to locate wells along fracture 
 zones, where optimum yields could be 
 obtained. If fracture zones can be lo- 
 cated accurately on the surface and pene- 
 trated with wells, then it is quite pos- 
 sible that dewatering with this type of 
 system could be more effective. An aver- 
 age well yield of 30 gpm (1.9 L/s) was 
 assumed in this analysis, but with wells 
 located only in the more intensely frac- 
 tured rocks, yields could average as high 
 as three to four times this amount. In- 
 dividual pumped wells would be cost ef- 
 fective if an average well yield of 90 
 to 120 gpm (5.7 to 7.6 L/s) could be 
 obtained. 
 
 The cost-effectiveness analysis did not 
 consider indirect benefits of dewatering 
 such as reduction of production losses 
 due to high water inflows and unstable 
 roofs. Production losses due to poor wa- 
 ter control can be much more expensive 
 than the acid drainage problems that the 
 water also creates. 
 
60 
 
 APPENDIX B.--CASE STUDY 2 
 
 INTRODUCTION 
 
 Dewatering problems are of prime con- 
 cern to this mine, located in Garrett 
 County, MD. The company, Met tiki Coal 
 Corp. , has decided to mine roughly 9 mi 2 
 (15 km 2 ) of Upper Freeport Coal. Figure 
 B-l shows an aerial view of the planned 
 and ongoing operations. Mining the coal 
 will be quite difficult since the coal 
 seam is part of the North Potomac syn- 
 cline, where dips on the limbs of the 
 syncline pitch up to 18°. 
 
 The mining complex is broken up into 
 three mines: the Beaver Run Mine, the 
 Gobbler's Knob Mine, and the Big George 
 Mine. These mines will produce both met- 
 allurgical and steam coal since the qual- 
 ity of the coal varies within the seam 
 itself. Each mine will use four continu- 
 ous miner units in conjunction with die- 
 sel haulage equipment. Eventually, each 
 mine will have two main sections and two 
 working sections with a total projected 
 production of 2 million clean tons per 
 year. 
 
 Because of the existing conditions, the 
 company investigated the possibility of 
 intercepting the ground water inflow to 
 the mines. The company felt that better 
 mining conditions could be realized in 
 
 keeping the mines dry. They hoped that 
 this would result in higher productivity. 
 
 GEOLOGIC ENVIRONMENT 
 
 Surface Geology 
 
 All rocks exposed on the surface di- 
 rectly above the mine are of Pennsyl- 
 vanian age and belong to the Conemaugh 
 Group. This formation consists of pre- 
 dominantly gray and brown claystones, 
 shales, siltstones, and sandstones. The 
 lower part of the formation is character- 
 ized by several redbeds, calcareous clay- 
 stone, and fossilif erous marine shales. 
 
 In addition to rocks , soil groups ex- 
 posed on the surface include Brinkerton, 
 Cookport, Gilpin, Ernest, Dekalb, and 
 Stony Land. Their properties are summar- 
 ized below. 
 
 Average Permeabil- 
 depth, in ity, in/h 
 
 Brinkerton. 
 
 Cookport, Gilpin, 
 Ernest 
 
 Dekalb, Stony Land 
 
 50 
 
 29-38 
 
 24-36 
 
 0.2-0.63 
 
 1.6-5.1 
 
 2.0 + 
 
 MD 
 
 Kempton 
 
 LEGEND 
 
 Proposed mine 
 opening 
 
 Proposed test-drilling 
 sites, nests of 
 piezometers 
 
 II I I II Approximate area 
 1 II to be undermined 
 
 Scale, miles 
 FIGURE B-l. - Planned and ongoing mine operations. 
 
 Subsurface Geology 
 
 A generalized stratigraphic column of 
 units encountered in the subsurface is 
 shown in figure B-2. All rocks in the 
 subsurface are from the Conemaugh Group 
 (described in the previous section) . The 
 Upper Freeport Coal itself is part of the 
 Allegheny Formation, which is of Pennsyl- 
 vanian age. It is a relatively soft coal 
 containing a shale binder 0.4 to 1.4 ft 
 (12 to 0.43 m) thick near the middle of 
 the seam. 
 
 The immediate roof for the Upper Free- 
 port Coal is the Uffington Shale, which 
 ranges from a few inches to 10 ft (3.1 m) 
 thick. This shale is, in most places, 
 firm and moderately hard, but it is in- 
 terbedded with soft clay near the eastern 
 corner of the property. The main roof is 
 
61 
 
 DEPTH, ft 
 0- 
 
 100— 
 
 Lithlogy Description 
 
 200— 
 
 300- 
 
 -:: — 
 
 500- 
 
 600- 
 
 K : — 
 
 Sandstone, shale, ond soil 
 
 -Upper Hoffman Coalbed, 1.4 ft thick 
 
 Sandstone ond shale 
 -Lower Hoffman Coolbed, 1.9 ft thick 
 
 Shale 
 -Upper Clarysville Coalbed, 0.3 ft thick 
 
 Shole 
 
 Morgantown Sandstone 
 
 Morgantown Shale 
 Barton Sandstone 
 -Elk Lick Coolbed, 8 ft thick 
 Birmingham Shale 
 
 Grafton Sandstone 
 Ames Marine Shale 
 -Harlem Coalbed, 2 ft thick 
 Shale 
 
 Jane Lew Sandstone 
 
 Pittsburgh Shale 
 
 -Upper Bokerstown Coalbed, 0.2 ft thick 
 
 Soltsburg Sandstone 
 -Bokerstown Coalbed, I.I to 6.I ft thick 
 
 Meyersdale Shale 
 
 Buffalo Sandstone 
 
 Brush Creek Shale 
 -Brush Creek Coalbed, 0.5 ft thick 
 Upper Mohoning Sandstone 
 Mahoning Shale 
 — Mahoning Coalbed, 0.9 ft thick 
 Lower Mahoning Sandstone 
 Uffington Shale 
 
 Upper Freeport Coalbed, 8 to 10 ft thick 
 Bolivar Fire Cloy 
 
 FIGURE B-2. - Generalized strat igraphic 
 column, case study 2. 
 
 Lower Mahoning Sandstone, which ranges 
 from 5 to 110 ft (1.5 to 33.5 m) thick, 
 and occurs 7 to 22 ft (2.1 to 6.7 m) 
 above the coal. 
 
 Total thickness of cover above the coal 
 averages more than 500 ft (152 m). How- 
 ever, along the southeastern edge of the 
 property, at the Potomac River, the coal 
 is typically about 450 ft (137 m) deep. 
 
 The floor of Beaver Run Mine consist of 
 at least 2 ft of Bolivar Fire Clay, com- 
 prised of fire clay, claystone, or soft 
 shale. Softest areas are confined to the 
 northwest limb of the syncline. 
 
 The principal structural feature of the 
 mine property is the North Potomac syn- 
 cline, which trends roughly northeast- 
 southwest an average of 6,000 ft (1,829 
 m) north of the North Branch of the Po- 
 tomac River. The basin and southeast 
 limb are relatively flat, with dips of 
 0° to 3°, while dips of up to 18° exist 
 
 near the outcrop of the Upper Freeport 
 Coal on Backbone Mountain. The synclinal 
 structure overlying the proposed mine is 
 depicted in the schematic cross section 
 (fig. B-3). 
 
 Joints and fractures were found to have 
 major trends at N 7° E, N 26° E, N 74° E, 
 and N 11° W, with a minor set at N 43° E. 
 No true geologic faults were detected in 
 the area. 
 
 HYDROLOGIC CONDITIONS 
 
 Surface Water 
 
 The mine area lies within the upper Po- 
 tomac Drainage Basin, whose major river 
 is the North Branch of the Potomac. This 
 river also forms the southeast boundary 
 of the mine area. A. number of smaller 
 streams, all of which drain into the 
 North Branch, are also present on the 
 mine site. These include Sand Run, Lau- 
 rel Run, Chestnut Ridge Run, and Red Oak 
 Run. No larger bodies of water, such as 
 lakes, are present on the property, al- 
 though one spring is known to exist. 
 
 Subsurface Water 
 
 General ground water flow conditions at 
 the mine sites are artesian owing, to 
 the synclinal structure of the site and 
 the presence of thick, impermeable shale 
 units that confine existing aquifers. 
 
 The following is a list of major aqui- 
 fer units in the area: 
 
 Thickness Feet above 
 Sandstone unit range, ft coal 
 
 Lower Mahoning.... 15-110 10 
 
 Buffalo 15- 50 120 
 
 Saltsburg 0-60 190 
 
 Jane Lew 15- 25 280 
 
 Grafton 0-40 310 
 
 Upper Grafton 0- 20 370 
 
 Morgantown 0- 50 470 
 
62 
 
 NW. 
 Backbone Mountain 
 
 SE. 
 
 Surface 
 
 Potomac 
 River; 
 
 
 Total depth 
 (Not to scale) 
 
 7,000 ft 
 
 FIGURE B*3. - Site cross section. 
 
 Since 80 ft of Mahoning Shale overlie 
 the Lower Mahoning Sandstone, most of the 
 ground water flow into the mines will be 
 from this sandstone. The Big George Mine 
 differs slightly from this regime in that 
 the Lower Mahoning Sandstone is almost 
 entirely absent. Instead, an interbedded 
 sandstone and shale unit overlies most of 
 the area. This unit is extremely thick 
 and less permeable than any of the indi- 
 vidual aquifers. 
 
 Permeabilities are as follows: 
 
 Unit 
 
 Lower Mahoning Sandstone. . 
 
 Uffington Shale (roof 
 material) 
 
 Permeability, 
 gpd/ft 2 
 
 0.047 
 
 .015 
 
 Recharge 
 
 Recharge to the Lower Mahoning Sand- 
 stone, which outcrops near the north- 
 ern boundary of the proposed mine site, 
 and to the other aquifers above the coal 
 is contingent upon infiltration from an 
 average annual precipitation of 48 in 
 (122 cm). Some minor infiltration may be 
 expected from Sand Run, Laurel Run, and 
 the North Branch of the Potomac River. 
 
 WATER INFLOW 
 
 Dewatering Rates Versus 
 Time of Development 
 
 Pumping rates anticipated during devel- 
 opment of the mines, in million gallons 
 per day, are as follows: 
 
63 
 
 Walton (39) derived an alternate meth- 
 od of predicting water inflows, which 
 uses a variation of Darcy's law. Walton 
 states: 
 
 QM 
 
 P = 
 
 Aha 
 
 (B-l) 
 
 5 yr 10 yr 15 yr 20 yr 
 
 Beaver Run Mine 0.38 0.94 1.6 1.7 
 
 Gobbler's Knob Mine 83 2.7 4.1 4.9 
 
 Big George Mine 32 .6 .88 .93 
 
 Expected Inflow Rates The entire area of the mine was assumed 
 
 to contribute flow either directly or in- 
 directly. The entire roof area was also 
 assumed to continuously contribute to in- 
 flow from the moment the roof is exposed 
 until the mine is eventually sealed. 
 
 On the basis of these two assumptions, 
 a baseline of equal intervals was con- 
 structed across the mine area. This 
 baseline roughly approximates a time line 
 and can be used to extrapolate to any de- 
 sired time interval. Mine advance paral- 
 lel to the baseline was also assumed to 
 be complete along the lateral width of 
 each area. Therefore, exposed roof areas 
 became the area of each mine segment 
 along the baseline. This particular ar- 
 rangement allows computation of inflow 
 from any one segment or from the entire 
 mine. 
 
 Next, the potential head for the mine 
 was determined. By definition in equa- 
 tion B-l, Ah is the difference between 
 the average head in the first source bed 
 above the mine and the mine roof. It was 
 assumed that the existing artesian system 
 is, or will become, a leaky artesian sys- 
 tem. Therefore, the total piezometric 
 head was considered to approximate the 
 ground surface. The value Ah then ap- 
 proximates the thickness of the roof ma- 
 terial. In the Beaver Run Mine, this 
 value was calculated to be 15 ft (4.6 m) , 
 and for Gobbler's Knob, it was calculated 
 to be 22 ft (6.7 m) . 
 
 The Big George Mine, however, had a 
 slightly different regime. In this mine, 
 the Lower Mahoning Sandstone was almost 
 entirely absent. An interbedded sand- 
 stone and shale unit was present over 
 most of the area. This unit also is ex- 
 tremely thick. Therefore, in the Big 
 George Mine, the ratio of Ah to M was 
 seen to approach 1. 
 
 where P = vertical permeability of the 
 confining beds, gpd/ft 2 , 
 
 Q = quantity of water leaking 
 through the roof rock, gpd, 
 
 M = average thickness of the con- 
 fining bed over the mine, 
 ft, 
 
 Ah = difference between the aver- 
 age head in the first source 
 bed above the mine and the 
 mine roof, ft, 
 
 and a = mine roof area through which 
 leakage will occur, ft 2 . 
 
 Consequently, any parameter can be cal- 
 culated if other parameters can be deter- 
 mined through prior knowledge, experi- 
 mental testing, or hypotheses. In this 
 case, Q, or expected inflow, was the 
 quantity that was unknown and could not 
 be assumed. Therefore, equation B-l can 
 be rearranged to state 
 
 Q = 
 
 PAha 
 M ' 
 
 (B-2) 
 
 This equation could not, however, be 
 applied to all mines or even to all areas 
 within a mine. Values for each mine 
 were derived on a case-by-case basis. A 
 knowledge of the geology of each mine was 
 imperative. 
 
64 
 
 Assumed permeability values were de- 
 rived by reviewing existing literature on 
 permeabilities and by visually inspecting 
 samples of the roof shales. A value of 
 0.015 gpd/ft 2 (0.071 L/s per square me- 
 ter) was assumed for all calculations. 
 Tables B-l, B-2, and B-3 show the com- 
 pleted calculations. 
 
 DEWATERING SCHEMES 
 
 Dewatering in Advance of Mining 
 
 Dewatering in advance of mining was 
 considered primarily because of the high 
 cost of tramming within the mine under 
 wet conditions. Moisture and air convert 
 the 25-ft-thick fire clay bottom into a 
 
 gooey clay. Tramming across this type of 
 floor creates deep ruts and can lead to a 
 loss in productivity. Favorable condi- 
 tions for dewatering in advance of mining 
 were expected since the region is arte- 
 sian, with most of the ground water flow 
 into the mines originating from the Lower 
 Mahoning Sandstone (approximately 10 ft 
 above the Upper Freeport Coal). 
 
 Test wells were drilled to evaluate 
 permeability, yield, and other aquifer 
 characteristics. Results showed that the 
 sandstone rock unit above the Upper Free- 
 port Coal is not permeable enough to 
 pump. It was found to be extremely hard 
 and highly fractured, resulting in ex- 
 tremely poor recharge to the drilled 
 wells (2 to 3 gpm, 0.13 to 0.19 L/s 
 
 TABLE B-l. - Beaver Run inflows 
 
 
 Roof 
 area, ft 2 
 
 M, 1 
 ft 
 
 Inflow 
 
 Area 
 
 Roof 
 area, ft 2 
 
 M, ] 
 ft 
 
 Inflow 
 
 Area 
 
 gpd 
 
 Cumula- 
 
 gpd 
 
 Cumula- 
 
 
 
 
 
 tive, gpd 
 
 
 
 
 
 tive, gpd 
 
 1... 
 
 700,000 
 
 15 
 
 10,500 
 
 10,500 
 
 10... 
 
 6,340,000 
 
 15 
 
 95,100 
 
 940,800 
 
 2... 
 
 5,020,000 
 
 13 
 
 86,900 
 
 97,400 
 
 11... 
 
 5,970,000 
 
 12 
 
 112,000 
 
 1,052,800 
 
 3... 
 
 5,240,000 
 
 11 
 
 107,200 
 
 204,600 
 
 12... 
 
 5,840,000 
 
 9 
 
 146,000 
 
 1,198,800 
 
 4... 
 
 5,470,000 
 
 13 
 
 94,700 
 
 299,300 
 
 13... 
 
 5,840,000 
 
 7 
 
 188,000 
 
 1,386,800 
 
 5... 
 
 5,670,000 
 
 15 
 
 85,100 
 
 384,400 
 
 14... 
 
 5,970,000 
 
 10 
 
 134,300 
 
 1,521,100 
 
 6... 
 
 5,700,000 
 
 14 
 
 91,600 
 
 476,000 
 
 15... 
 
 6,570,000 
 
 13 
 
 113,700 
 
 1,634,800 
 
 7... 
 
 6,340,000 
 
 13 
 
 109,700 
 
 585,700 
 
 16... 
 
 5,290,000 
 
 16 
 
 74,400 
 
 1,709,200 
 
 8... 
 
 6,750,000 
 
 12 
 
 126,600 
 
 712,300 
 
 17... 
 
 1,170,000 
 
 17 
 
 15,500 
 
 1,724,700 
 
 9... 
 
 6,520,000 
 
 11 
 
 133,400 
 
 845,700 
 
 
 
 
 
 
 Im - 
 
 M = average thickness of the confining bed over the mine. 
 NOTE.— P = 0.015 gpd/ft 2 ; Ah = 15 ft. 
 
 TABLE B-2. - Gobbler's Knob inflows 
 
 
 
 Roof 
 area, ft 2 
 
 M, ■ 
 ft 
 
 Inflow 
 
 
 
 Roof 
 area, ft 2 
 
 M, 1 
 ft 
 
 Inflow 
 
 Area 
 
 gpd 
 
 Cumula- 
 tive, gpd 
 
 Area 
 
 gpd 
 
 Cumula- 
 tive, gpd 
 
 1... 
 2... 
 3... 
 4... 
 5... 
 6... 
 7... 
 8.., 
 9.. 
 
 
 700,000 
 4,290,000 
 4,830,000 
 4,830,000 
 4,820,000 
 4,800,000 
 4,780,000 
 4,760,000 
 4,740,000 
 
 11 
 10 
 9 
 7 
 6 
 5 
 4 
 3 
 4 
 
 21,000 
 142,000 
 177,100 
 277,700 
 265,100 
 316,800 
 394,400 
 523,600 
 391,000 
 
 21,000 
 
 163,000 
 
 340,100 
 
 567,800 
 
 832,900 
 
 1,149,700 
 
 1,544,100 
 
 2,067,700 
 
 2,458,700 
 
 10.. 
 
 11.. 
 
 12.. 
 
 13... 
 
 14... 
 
 15... 
 
 16... 
 
 17... 
 
 18... 
 
 
 4,720,000 
 4,710,000 
 4,690,000 
 4,670,000 
 4,650,000 
 4,650,000 
 4,100,000 
 2,830,000 
 2,520,000 
 
 6 
 8 
 9 
 7 
 5 
 3 
 3 
 4 
 7 
 
 260,000 
 194,000 
 172,000 
 220,000 
 307,000 
 512,000 
 451,000 
 233,000 
 119,000 
 
 2,718,700 
 2,912,700 
 3,084,700 
 3,304,700 
 3,611,700 
 4,123,700 
 4,574,700 
 4,807,700 
 4,926,700 
 
 'M 
 
 average thickness of the confining bed over the mine. 
 
 NOTE.— P = 0.015 gpd/ft 2 ; Ah = 22 ft. 
 
65 
 
 TABLE B-3. - Big George inflows 
 
 
 Roof 
 area, ft 2 
 
 Inflow 
 
 Area 
 
 Roof 
 area, ft 2 
 
 Inflow 
 
 Area 
 
 gpd 
 
 Cumulative, 
 gpd 
 
 gpd 
 
 Cumulative, 
 gpd 
 
 2 
 
 3 
 
 6 
 
 8 
 
 700,000 
 5,270,000 
 5,560,000 
 5,020,000 
 4,770,000 
 4,510,000 
 4,240,000 
 4,010,000 
 
 10,500 
 79,050 
 83,400 
 75,300 
 71,550 
 67,650 
 63,600 
 60,150 
 
 10,500 
 89,550 
 172,950 
 248,250 
 319,800 
 387,450 
 451,050 
 511,200 
 
 9 
 
 13 
 
 2,900,000 
 2,760,000 
 2,780,000 
 3,560,000 
 3,650,000 
 3,690,000 
 5,770,000 
 2,620,000 
 
 43,500 
 41,400 
 41,700 
 53,400 
 54,750 
 55,350 
 86,550 
 39,300 
 
 554,700 
 596,100 
 637,800 
 691,200 
 745,950 
 801,300 
 887,850 
 927,150 
 
 NOTE. — Assume: 
 
 Ah 
 M 
 
 - 1; P - 0.015 gpd/ft 2 , 
 
 maximum). These results showed that de- 
 watering in advance of mining may be dif- 
 ficult and expensive. 
 
 Other factors that make dewatering in 
 advance of mining impractical for this 
 area are — 
 
 • The advent of new laws (Office of 
 Surface Mining, State, etc.), which state 
 that if the water table or hydrologic 
 balance is altered, a potable water sup- 
 ply must be made available by the mining 
 company to the area's landowners. 
 
 • The natural water in the area has a 
 pH of 4.0 to 4.5, which is not potable. 
 By law, this water must be treated before 
 being returned to the environment. 
 
 • The mining cycle advances too rapid- 
 ly for dewatering in advance of mining. 
 
 • The cost of drilling in hard 
 fractured rock is extremely high. 
 
 and 
 
 • The mining company has to purchase 
 surface properties and acquire rights-of- 
 way for access, power lines, and pipe- 
 lines in the dewatering wells. The com- 
 pany may also get adverse reactions from 
 preservationists. 
 
 After considering these facts, the min- 
 ing company decided that dewatering in 
 advance of mining would be technically, 
 legally, and economically impractical. 
 
 Dewatering During Mining 
 
 As operations in the mine proceed down- 
 dip, a number of sumps will be estab- 
 lished to collect water. The water will 
 be pumped in three stages. Face pumps 
 will transfer water collected at the face 
 to a main sump, where it will be picked 
 up and pumped out of the mine. 
 
 In approximately 10 yr, the operations 
 will reach the base of the North Potomac 
 syncline, where it is anticipated that 
 wells will be drilled from the surface to 
 main sump areas located at the syncline 
 base. All subsequent dewatering will be 
 accomplished through staged pumping. 
 
 The mining operations should have ex- 
 cellent control over water infiltration 
 since the majority of the mine life will 
 be spent advancing downdip. This, in 
 conjunction with the practice of segre- 
 gating flows and minimizing contact with 
 pyritic materials, will minimize mine 
 water contamination. 
 
66 
 
 APPENDIX C.--CASE STUDY 3 
 
 INTRODUCTION 
 
 The mine used in the third case study 
 has had a history of water problems. The 
 Nemacolin Mine, owned by Jones and Laugh- 
 lin Steel Corp. and located near Nemaco- 
 lin, PA, has a total area of 11,000 acres 
 (4,452 hectares), which generate roughly 
 2 million gpd (7.6 million L/d) of water. 
 Many of the smaller areas within the mine 
 generate between 200 and 300 gpm (12.6 to 
 18.9 L/s). 
 
 The Pittsburgh Coal of the Monongahela 
 Group is the only seam mined. The coal 
 seam averages 8 ft (0.24 m) in thickness 
 and is located at depths ranging from 160 
 to 540 ft (48.8 to 164.7 m) . For the 
 most part, the seam is more than 400 ft 
 (122 m) deep. 
 
 Most of this mine has been excavated. 
 Only a small area of about 1-1/4 mi 2 
 (3.24 km 2 ) has remained unmined. This 
 area is bounded by Muddy Creek on one 
 side, the Monongahela River on another, 
 and by worked-out sections on a third 
 side (figure 6 in the main text). Con- 
 siderable water was generated by the ad- 
 vancement of operations into this area. 
 The amount of water currently being 
 generated is so great that if left un- 
 checked, the company would be forced to 
 shut down the operation. This has caused 
 the company to consider changes in the 
 mining and water-collecting plan to re- 
 duce the water inflow. 
 
 belong either to the Dunkard or Mononga- 
 hela Groups. The formations exposed are 
 the Waynesburg, the Uniontown, and the 
 upper member of the Pittsburgh Formation. 
 The Waynesburg and Uniontown Formations 
 consists of thinly to thickly bedded 
 sandstone, shales, siltstones, and mud- 
 stones, with numerous interbeds of car- 
 bonaceous shale, argillaceous limestone, 
 and coal. Clays tone and limestone are 
 found less frequently. These coalbeds 
 occur in the Waynesburg Formation; the 
 thickest is located at the base in two 
 and, locally, three benches separated by 
 layers of claystone. This coalbed is 50 
 to 80 in (1.27 to 2.03 m) thick. An im- 
 pure coalbed of less than 1 ft (0.31 m) 
 marks the base of the Uniontown Formation 
 (Uniontown Coalbed). In contrast, the 
 upper member of the Pittsburgh Formation 
 consists of four distinct units of argil- 
 laceous limestone separated by muds tone, 
 siltstone, and sandstone units of charac- 
 teristic greenish-gray color. 
 
 All rocks in the subsurface are from 
 the Upper Pennsylvanian and the Lower 
 Permian periods. They can be divided in- 
 to two groups : the Monongahela and the 
 Dunkard. These consist predominantly of 
 interbedded limestone, mudstone, shale, 
 and sandstone. The commercially mined 
 coal bed, the Pittsburgh Coal, is 60 to 
 90 in (1.52 to 2.29 m) thick. 
 
 The slope of the bed does not exceed a 
 half degree over extensive areas. 
 
 GEOLOGIC ENVIRONMENT 
 
 HYDROLOGIC CONDITIONS 
 
 Quaternary alluvium consisting of un- 
 consolidated silt, sand, gravel, and cob- 
 bles is found in, and adjacent to, Muddy 
 Creek and the Monongahela River. Gener- 
 ally, unconsolidated and poorly sorted 
 alluvium composing the Carmichaels Forma- 
 tion is found in ancient, abandoned river 
 channels and on rock terraces related to 
 this ancient drainage network. These de- 
 posits consist of laminated clay, mixed 
 yellowish-brown clay, silt, sand, and 
 well-rounded pebbles , cobbles , and boul- 
 ders of sandstone. 
 
 All rocks exposed on the surface are of 
 Upper Pennsylvanian and Permian age and 
 
 Surface Water 
 
 The active mine area is bounded on the 
 west by Muddy Creek and on the northeast, 
 east, and southeast by the Monongahela 
 River. At the most northern point of the 
 mine area, Muddy Creek flows into the 
 Monongahela River. In addition, the mine 
 property has a number of intermittent 
 streams, which flow into either the Mon- 
 ongahela River or Muddy Creek. 
 
 Springs of variable flows, which yield 
 a few gallons per minute, are numerous 
 along the outcrops of the Lower Limestone 
 Member of the Uniontown Formation. Many 
 
67 
 
 of these springs are true joint or bed- 
 ding plane springs supplied by a distant 
 source and are an indication of the 
 water-yielding capacity of the beds. 
 Others, those springs whose flows are 
 most variable, presumably originate lo- 
 cally in vadose water trapped above one 
 of the impermeable limestone beds. Such 
 springs are not indicative of the water- 
 yielding capacity of the beds. 
 
 Ground Water Conditions 
 
 The Waynesburg Sandstone and the Pitts- 
 burgh Sandstone are the principal water- 
 bearing zones of the area. There are a 
 number of other water-bearing zones that 
 yield limited supplies of ground water 
 from bedding plane conduits. Although 
 they are not deeply buried, they are im- 
 permeable beneath continuous cover. In 
 addition, small perched water zones pro- 
 vide small supplies of water. 
 
 The Waynesburg Sandstone is 20 to 60 ft 
 (6.1 to 18.3 m) thick and is commonly 
 more than 40 ft (12.2 m) thick. The unit 
 is light gray or buff, micaceous, and 
 usually arkosic or feldspathic. 
 
 The upper division is typically cross- 
 bedded and flaggy, although the lower 
 division is generally massive and fri- 
 able and locally coarse grained or even 
 pebbly. The lower division is a bluff 
 maker, and in many places its outcrops 
 are somewhat cavernous. 
 
 The Waynesburg Sandstone, especially 
 the massive and coarser grained lower 
 portion, is by far the outstanding water- 
 bearing member of the entire Permian se- 
 ries and has been extensively developed. 
 
 The coarser facies of the member yield 
 as much as 65 gpm (4.1 L/s) where the 
 member lies below drainage level. The 
 specific yield of individual wells is not 
 known precisely but is approximately 2 
 gpm (0.13 L/s) for each foot of drawdown 
 in wells at the town of Waynesburg lo- 
 cated about 10 miles west of the mine. 
 Water is confined within the member under 
 moderate hydrostatic pressure. It is 
 noteworthy that wells reported to have 
 been drilled to a depth of 200 ft (61 ra) 
 at the flour mill and at the electric 
 light plant at Waynesburg failed to ob- 
 tain water, although borings of that 
 
 depth should have penetrated the Waynes- 
 burg Sandstone. This reported phenomenon 
 has never been observed with the Waynes- 
 burg Sandstone elsewhere, and if authen- 
 tic, points to considerable variations in 
 permeability of the member from place to 
 place. 
 
 The interval between the Redstone and 
 Pittsburgh Coals is in many places occu- 
 pied entirely or partially by the Pitts- 
 burgh Sandstone, which has been called 
 the Upper Pittsburgh. This bed is typi- 
 cally coarse grained, massive to irregu- 
 larly bedded, friable, and buff to dark 
 gray or brown in color. In many local- 
 ities, however, it grades laterally into 
 flaggy or thin-bedded sandstone and into 
 interbedded sandy shales and sandstone 
 lentils. The Pittsburgh Sandstone ranges 
 in thickness from to 70 ft (0 to 21.3 
 m) and generally thickens toward the 
 south. 
 
 The Pittsburgh Sandstone and its equiv- 
 alents are highly permeable over wide 
 areas, but they have been drained wherev- 
 er the underlying Pittsburgh Coal has 
 been mined and the roofs above the aban- 
 doned mine entries have collapsed. Con- 
 sequently, this sandstone is no longer a 
 potential source of water in many of the 
 mining districts, especially in those 
 that have long been worked out and aban- 
 doned. Furthermore, such drainage is 
 likely to become more extensive in the 
 future. In some places, the muddy water 
 that percolates down from the surface 
 along the larger subsidence fractures or 
 "breaks" fills the drainage conduits so 
 that the sandstone may become water bear- 
 ing again after a lapse of several years. 
 It is quite by chance, however, that such 
 puddling takes place, and in most dis- 
 tricts the water-yielding capacity of the 
 sandstone is never fully restored. The 
 member displays its normal water-bearing 
 properties in those districts in which 
 the coal has not been mined. In many 
 mining districts there has been very lit- 
 tle roof collapse and the member has not 
 been completely drained. In these cases, 
 wells of moderate yield may be obtained 
 if care is taken to cease drilling be- 
 fore the well penetrates the mine entry. 
 Where the member lies below drainage lev- 
 el, it is likely to be saturated, have a 
 
68 
 
 moderately high head, and a moderately 
 large yield. Yields range from to 35 
 gpm (0 to 2.2 L/s), the maximum being at- 
 tained where the member lies below drain- 
 age level on the flanks of a syncline. 
 
 WATER INFLOW 
 
 Rate 
 
 The amount of water entering the whole 
 mining operation on any given day has 
 been estimated to be roughly 2 million 
 gpd (7.6 million L/d). Small areas with- 
 in the mine experience inflows of 200 to 
 300 gpm (12.6 to 18.9 L/s). In the one 
 active section, most of the water is gen- 
 erated during the advance cycle of mine 
 development, causing a considerable num- 
 ber of problems in production and mine 
 development. In addition, roof bolt 
 holes have yielded up to 50 gpm (3.2 L/s) 
 of water in many instances. 
 
 Most of this water is found along the 
 contact between the Pittsburgh Sandstone 
 and a shale complex that lies directly 
 above the Pittsburgh Coal Seam. The 
 shale complex consists of an 8-in (0.2-m) 
 coal seam sandwiched between two 2-in 
 (0.05-m) shale beds. The water is held 
 under considerable head; sprays of up to 
 4 ft (1.22 m) from the contact have been 
 observed. 
 
 Water also enters the mine through cer- 
 tain fracture traces; however, their flow 
 is not constant. 
 
 Source 
 
 Most of the water enters the mine 
 through the roof and exterior faces. 
 This water is transmitted primarily by 
 bedding planes and roof bolt holes. A 
 considerably smaller percentage seeps 
 through fractures and through barrier 
 pillars that separate abandoned parts of 
 the mine from the active sections. 
 
 The source of the water infiltrating 
 the mine has not yet been fully deter- 
 mined. Observations show that water is 
 entering the active section along the 
 base of the Pittsburgh Sandstone. Al- 
 though this sandstone is a water sup- 
 plier, it is not capable of supplying 300 
 
 gpm (18.9 L/s) of water. Water wells in 
 the sandstone yield only up to 35 gpm 
 (2.2 L/s), and this is only under the 
 most optimal conditions. In contrast, 
 roof bolt holes have yielded up to 50 gpm 
 (3.2 L/s). In addition to this, raining 
 operations have experienced considerable 
 problems in the areas closest to the Mon- 
 ongahela River. 
 
 Based on these observations, it is be- 
 lieved that most of the water is origi- 
 nating from the Monongahela River. The 
 water is moving along the permeable bed- 
 ding planes and is entering the mine at 
 the point where the mine operations in- 
 tersect these planes. 
 
 DEWATERING SCHEME 
 
 The dewatering scheme in the active 
 section of the underground mine complex 
 first consisted of a conventional series 
 of sumps with pumps transporting the 
 water to main sumps where it was then 
 pumped out of the mine. This system 
 proved to be inadequate since the inflow 
 was so great that it disrupted face oper- 
 ations. As a consequence, mine engineers 
 thought that the water inflow could be 
 decreased by changing the direction of 
 mining by 90°. This had only limited 
 success . 
 
 Since most of the water flowing into 
 the mines was coming from the direction 
 of the Monongahela River, mine engineers 
 decided that in order to prevent disrup- 
 tion of face operations, the water would 
 have to be intercepted before it reached 
 the face. This technique is currently 
 being implemented by second-mining the 
 part of the operation closest to the Mon- 
 ongahela River, thereby creating a huge 
 sump. It is hoped that the water will 
 drain into the sump before reaching the 
 face. The water in the sump will then be 
 pumped out of the mine. This system is a 
 modification of the gravity drainage and 
 mine pumping system to dewater above a 
 mine. Instead of using drilled holes to 
 collect water, the water is collected by 
 fracturing the confining bed and part of 
 the source bed so that the water will run 
 along the fractures into the mine. 
 
 izU.S. GPO: 1985-505-019/20,062 
 
 INT.-BU.OF MIN ES,PGH.,P A. 27979 
 
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