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bridgeport's improved 
 Sewerage System 
 
 BY 
 
 •o 
 
 JAMES A. MCELROY 
 
 CITY ENGINEER. BRIDGEPORT. CONN. 
 
 Reprint From The 
 
 Proceedings of the Connecticut Society of Civil Engineers 
 
 Nineteen Hundred and Twenty 
 

BRIDGEPORT SEWERAGE SYSTEM. 53 
 
 BRIDGEPORT'S IMPROVED SEWERAGE 
 SYSTEM. 
 
 By James A. McElroy, City Engineer, Bridgeport, Conn. 
 
 In 1906 the Common Council of the City of Bridgeport author- 
 ized the mayor to appoint a special commission to investigate the 
 existing sewer conditions and formulate, if possible, a new sewer 
 system to meet the present and future needs of the City. The 
 well known firm of Hering & Fuller was secured by the com- 
 mission, and their report, submitted in the spring of 1908, has 
 served as a guide for all sewers built since that time. 
 
 In the past all sewers in Bridgeport had been built on the com- 
 bined system, that is, the same sewers carried both storm water 
 and house sewage. These sewers, many of which were too 
 small, emptied into the nearest tide water. The Pequonnock 
 River which runs through the center of the city and naturally 
 divides the city into two districts, which are now known as the 
 Eastern and Western Sewage Districts, had about 26 sewers 
 emptying into it, while Ash Creek which runs along the western 
 edge of the city had 4, and Johnsons Creek, the eastern boundary, 
 had 12. There were 8 sewers flowing into Yellow Mill Pond, in 
 the center of the eastern district and 9 into Cedar and Bun- 
 Creek in the western district. 
 
 It was realized that the city could not continue indefinitely 
 emptying sewage into these small streams some of which were 
 hardly more than mud flats at low tide, and that at some time in 
 the future it would all have to be collected and discharged into 
 the sound through long outfalls, either with or without treatment. 
 
 The topography of Bridgeport is such that large areas near the 
 sound are very low, and the Pequonnock River and other streams 
 extend so far into the land at tidewater level, that it would be 
 impossible to collect the sewage and deliver it either to outfalls or 
 disposal work without pumping. To collect large quantities of 
 storm water in combined sewers and then pump it, would add 
 greatly to the cost of construction of the trunk sewers and to the 
 pumping cost, so Hering & Fuller recommended separate sewers 
 for rainwater wherever practicable, with storm water overflows 
 
54 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
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 STARS SHOW OLD SEWER OUTLETS. 
 
BRIDGEPORT SEWERAGE SYSTEM. 
 
 55 
 
 INTERCEPTORS AND PUMPING STATION. 
 
56 THIRTY-SIXTH ANNUAL MEETING. 
 
 in some of the older sections of 'the city where the combined sys- 
 tem would have to be retained. 
 
 They considered the city naturally divided into two districts 
 by the Pequonnock River, and planned a pumping station and 
 system of intercepting sewers for each district. It was their 
 opinion that by carrying the outfall to deep water, i. e., 20 feet 
 to 25 feet, no further treatment would be required; but sug- 
 gested that when sites were acquired for the pumping stations, 
 sufficient land be secured to enable the city to build treatment 
 plants, if desired at some future time. 
 
 By 1916 practically all the interceptors had been completed 
 down as far as the sewage would discharge by gravity. No fur- 
 ther extensions of the interceptors could be made until the pump- 
 ing stations were built. The firm of Hering & Gregory, 
 successors to Hering & Fuller, were asked to review the work 
 done to date and recommend a program for the future. They 
 considered the advisability of bringing the sewage of the entire 
 city to one treatment plant located on Steeplechase Island, but 
 finally decided in favor of the original plan of Hering & Fuller 
 which divided the city into two districts with a complete plant for 
 each district. 
 
 As the Western District was the more important it w T as decided 
 to finish that first; so contracts were let for the construction of 
 the Railroad Avenue and Bostwick Avenue interceptor, and plans 
 were prepared for the Western District Pumping Station at the 
 foot of Bostwick Avenue. 
 
 The consulting engineers recommended "an Imhoff tank sewage 
 treatment plant and designed the pumping station accordingly. 
 But, although the city did not intend to build the treatment works 
 at this time, before letting the contract for the pumping station 
 it was decided to investigate sewage treatment in other cities. 
 So a committee consisting of the City Engineer, the Director of 
 Public Works, the President of the Paving and Sewer Commis- 
 sion and .the chairman of the committee on sewers of the common 
 council, visited a number of plants including Fitchburg, Wor- 
 cester, Rochester, Brooklyn, Baltimore, Plainfield and Wildwood, 
 N. J. It was the opinion of a majority of this committee that 
 the Riensch-Wurl fine screen method of sewage treatment was 
 the most appropriate system for Bridgeport. 
 
R k I DG E P( ) R T S E W E RAGE SYSTE M . 
 
 57 
 
58 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
BRIDGEPORT SEWERAGE SYSTEM. 59 
 
 The report of this committee was submitted to two prominent 
 sanitary engineers, George W. Fuller and George A. Johnson, 
 for their advice. They approved of the committee's report ; so 
 new plans were prepared for the Western District pumping 
 station, including screening and pumping equipment to take care 
 of the present sewage of the district, with provisions for the 
 installation of additional equipment when required in the future. 
 
 The principal reasons which led the committee to decide on 
 the fine screen rather than the Imhoff tank method of treatment 
 was the uncertainty of the action of Imhoff tanks. It was noted 
 that several Imhoff plants, designed by competent engineers, were 
 unsatisfactory, while few of the plants which were giving satis- 
 factory service were handling the amount of sewage for which 
 they were designed. As Bridgeport's Western Treatment Plant 
 was to be located on the southwest edge of a well populated dis- 
 trict, with the prevailing winds coming from the southwest, it 
 was thought best not to run the risk of having another such 
 experience as they had in Plainfield, where they have finally had 
 to install a Riensch-Wurl fine screen ahead of their Imhoff tanks. 
 
 The original Hering & Fuller report recommended disposal of 
 Bridgeport sewage by dilution. The process finally adopted was 
 that of clarification by fine screens, followed by dilution. If fur- 
 ther treatment is desired at some future time, the outfall can be 
 extended, or if necessary additional treatment works can be built 
 on land. 
 
 The flow line of the interceptor at the plant is at elevation ioo, 
 22 feet below the street level and 10 feet below mean low water. 
 Several combinations of screens and pump were studied includ- 
 ing the plan of having high level screens following the pumps, so 
 that the screened effluent would flow by gravity to the outfall. 
 This scheme would have saved something on the cost of construc- 
 tion of the station, but it was discarded mainly because the 
 screens would be more effective if installed ahead of the pumps. 
 
 In the plant finally decided upon, the sewage from the 71 -inch 
 interceptor flows through the sluice gate to a bar screen at eleva- 
 tion 100, thence through a concrete channel to the R-W Screens. 
 The screened effluent flows over an adjustable weir to the sump 
 at elevation 80 and is then lifted by the pumps to the force main 
 at elevation 105. 
 
6o 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
BRIDGEPORT SEWERAGE SYSTEM. 
 
 6 i 
 
62 THIRTY-SIXTH ANNUAL MEETING. 
 
 The plant is designed for three Riensch-Wurl screens, to han- 
 dle a total dry-weather flow of 35 million gallons per day. The 
 estimated population of the district when fully developed is 
 180,000. As the present population of the district is in the 
 neighborhood of 100,000, two screens will be installed now and 
 the third one when needed. The R-W Screen consists of a 
 circular disc 22 feet in diameter inclined at an angle of 15 degrees 
 to the horizontal. A truncated cone 12 feet in diameter, at the 
 base, is centrally mounted on the disc. The surface of both disc 
 and cone consists of a number of removable bronze plates, per- 
 forated with slots two inches long and 3/64 of an inch wide. 
 The lowest point of the disc is set at the elevation of the influent, 
 and the slope is such that about one-third of the disc will be above 
 the surface of the water. 
 
 The sewage flows on to the screen which is revolving at a rate of 
 about one revolution in two minutes. The liquid passes through 
 the perforations in the disc and flows over the weir into the pump 
 sump. The suspended solids, which are retained on the screen 
 are lifted out of the water as the screen" revolves, and are brushed 
 off the screen into the hopper of the screening conveyor system. 
 The brushes are cylindrical and are carried on a revolving spider 
 which is mounted on a shaft parallel with the main disc shaft. 
 These brushes work on the same principle as a street sweeper, 
 which is carried along the street mounted on a truck and at the 
 same time is revolving and brushing the refuse ahead of it. 
 
 The screenings are conveyed from the hopper to the storage 
 tanks by a pneumatic system which does away with the necessity 
 of handling it in open cans or on an open conveyor-belt. From 
 the storage tank which is located 10 feet above the street level, 
 the screenings will be dropped into tank wagons, carted to the 
 town farm and buried. 
 
 The pumping equipment consists of two 20-inch horizontal cen- 
 trifugal pumps each having a capacity of 15 million gallons per 
 day and two 15-inch horizontal centrifugal pumps with a capacity 
 of eight million gallons per day each. These pumps will be 
 direct connected to electric motors, controlled by floats in the 
 pump sump. The floats are adjustable and electrically connected 
 to switches and automatic motor starters, mounted on panels of 
 the main switch board. 
 
BRIDGEPORT SEWERAGE SYSTEM. 
 
 63 
 
64 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
BRIDGEPORT SEWERAGE SYSTEM. 65 
 
 A Venturi tube is to be installed on the outfall, with the record- 
 chart and register located on one of the main switch board 
 panels. The 60-inch gate valve, electrically operated, will be 
 installed in a gate house at the discharge end of the venturi tube. 
 
 The building will contain a complete system of heating, ven- 
 tilating and plumbing, including toilets and shower baths. 
 
 The State Board of Health approved of the plans, for the plant 
 itself, leaving the question of the location of the outfall to he 
 decided later, so construction was started about the first of last 
 year, 1919. The substructure is a reinforced concrete caisson 
 80 feet inside diameter and 45 feet deep. The cylindrical shell 
 forming the outside wall is constructed of a series of rings ten 
 feet high. The rings were cast above ground and after the con- 
 crete in each ring had properly set, the forms were removed and 
 the ring sunk until the top was approximately a foot above 
 ground. The forms were then re-assembled and the next sec- 
 tion cast. When the caisson had reached the predetermined 
 depth the bottom was placed under water. After the concrete 
 bottom had set, the caisson was unwatered, the bottom made 
 smooth and finished to a surface. This part of the work is fin- 
 ished and the inside walls, partitions, beams and floor slabs are 
 now being built. The rectangular superstructure will be con- 
 structed of tapestry brick with stone trimmings and a red tile 
 roof. 
 
 The lowest ring, which contains 475 cu. yds. of 1-2-4 con_ 
 crete and thirty tons of steel, was completed in March of last 
 year. After a few days the forms were removed and set for the 
 second ring. The same forms were used for all five rings. The 
 second, third and fourth rings, each containing 500 cu. yds. of 
 concrete and 16 tons of steel, were finished by June ist, the con- 
 crete being poured in continuous operations of about eight hours 
 for each ring. 
 
 After the first ring had been poured and the forms removed 
 the ring was allowed to sink by excavating the material from the 
 interior. Two three-quarter yard clam-shell buckets on two 65- 
 foot boom stiff-leg derricks, set up on opposite sides of the cais- 
 son, averaged about 200 cu. yds. of excavation a day. One 
 derrick was placed on the north side of the caisson, the other on 
 
66 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
 
BRIDGEPORT SEWERAGE SYSTEM. 
 
 67 
 
 FORMS IN PLACE FOR THIRD RING. SHOWING PUMPS. 
 
68 THIRTY-SIXTH ANNUAL MEETING. 
 
 the south. On the east side, towards Bostwick Avenue were two 
 one-yard mixers and an 8o-foot double hoisting tower from 
 which the concrete could be delivered through chutes to any part 
 of the ring. Just north of the tower was another derrick which 
 supplied gravel and sand to hoppers located above the mixers. 
 As the excavation proceeded levels were taken at frequent inter- 
 vals each day on the top of the shell and if one side was found to 
 be sinking too fast, excavation was stopped on that side and con- 
 tinued near the other side until the ring was level again. At no 
 time was the caisson more than nine inches out of level. At first 
 it was not intended to keep the caisson dry during excavation, but 
 as the work proceeded and it was seen that there was not much 
 water coming in, pumps were installed and the interior was kept 
 dry during this part of the work. 
 
 Several of the engineers who looked over the job before the 
 contract was let said it would be almost impossible to sink- this 
 caisson, as the skin friction on the outside would hold it up. As 
 a matter of fact it went down so easily that the top ring was left 
 off until the caisson was within three feet of the bottom. 
 Progress had been so satisfactory up to this point that an attempt 
 was made to excavate still further and try to lay the bottom in 
 the dry. It was found, however, that the pumps were drawing too 
 much sand, which, flowing in from the outside under the bottom 
 edge of the caisson was undermining the derricks and concrete 
 tower. So the top ring was put on, the caisson was allowed to 
 fill with water, and the excavation was continued until the ring- 
 was down to the predetermined depth and soundings showed that 
 the excavation for the bottom was completed. 
 
 The bottom was then put in under water in one continuous 
 operation. The same gang - worked right through and put in 1800 
 cu. yds. of concrete in thirty-nine hours. The men were allowed 
 to knock off occasionally for rest and refreshment, but the mixers 
 were kept going continuously except when shut down for minor 
 repairs.- There was a two hour delay about noon of the first 
 day. and the plant was shut down for about five hours at different 
 times during the second day. 
 
 The bottom was allowed to stand three weeks, then the water 
 was pumped out. No leaks were found so the floor was finished 
 
BRIDGEPORT SEWERAGE SYSTEM. 
 
 6 9 
 
7° 
 
 THIRTY-SIXTH ANNUAL MEETING. 
 
BRIDGEPORT SKWKK'.V.K SYSTF.M. 7 I 
 
 and work was commenced on the forms for the inside walls and 
 partitions. 
 
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