SANITATION AT WASHINGTON
Specially written for FIRE AND WATER ENGINEERING.
In 1852-53 it was determined to give Washington the benefit of an adequate water supply for the use of its 40,000 people, and the sum of $5,000 was appropriated for that purpose. The source of supply was to be the Great Falls, where a dam was built, with its comb 145 ft. above high tide at Washington. From this dam the water was conducted through a circular conduit of brick 9 ft. in diameter, with a fall of in. to the mile. A receiving reservoir was built by damming the Little Falls branch, a tributary of the Potomac, about five miles from Washington. Its area is a little over fifty acres; its capacity, approximately 85,500,000 gals. It is. used for both sedimentation and storage. The conduit is continued and connected with a distributing reservoir on the heights of Georgetown about two miles from Washington and, also, with a receiving reservoir. The whole system was completed in 1863 and is still .in operation. All hut one mile and one-half of the conduit is laid under the Conduit road, and the Cabin John bridge, the longest but one singlearch stone bridge in the world, carries the conduit over Cabin John run and the Pennsylvania avenue bridge on arches formed hy the two mains leading from the distributing reservoir to the city over Rock creek. The Lydecker tunnel now carries the greater part of the water to a reservoirs on the heights to the north of the city, whence it is pumped into the new filter beds and thence distributed through the city. The filtration plant recently completed cost $3,468,405. It is one of the longest and finest in the world, and is of the English or slow-sand type. The filtration of the water costs $6 per 1,000,000 gals. The plant covers forty-five acres of ground, and the plant proper is divided into twenty-nine compartments of one acre each, each bed holding 3,000,000 gals., the whole having a daily capacity of 75,000.000 gals. The preliminary sedimentation takes place in the Washington city reservoir, near the filterbeds. The reservoir’s capacity is 300,000,000 gals. From it the pumps raise the water to twenty-five of the filterbeds* beginning with the farthest, whence it flows in order into the other beds, always at the top. In each bed there are three ft. of clean, sharp sand and one of gravel. A system of under-drainage and piping delivers the water into an inclosed storage reservoir, with a capacity of 20.000,000 gals., a cement floor and roof supported by cement pillars. Any particular bed may be cut off, without disturbing the supply to the other beds, some four of which are being cleaned all the time by having about three inches of the sand scraped from the surface and an equal amount added. The sand scraped off is afterwards washed, about five inches of the whole being lost every year. A completely equipped bacteriological and chemical laboratory has been established, with experts always testing the water. In process of leveling the site, which presented a considerable grade towards the city, tops of some of the beds were left above the street, and some below it. These were covered with concrete, on which were packed twenty-four inches of earth, the whole tract being then sodded. The disposal of the sewage of the city will be accomplished at a cost of $5,000,000 by raising the entire sewage at k pumping station at the point of collection, a distance of nearly thirty ft., and forcing it Across the river. To collect the sewage are to be built two separate and distinct sewer systems, a lowarea system and one at the usual level. The latter has a great trunk sewer—the B street sewer—two miles and more in length, and with a diameter of from 7 ft. to 18 ft. Into it arc discharged the contents of many small conduits and high-level interceptors. Numerous interceptors and small conduits also discharge into the low-area trunk sewer, running under Pennsylvania avenue. Except when there are heavy rain storms, the contents of the B street trunk sewer will be discharged into a junction chamber on the northeast corner of the pumping station. where gates will divide the sewage and force it round a large sedimentation chamber into a screen-chamber, where all the solids will be removed, and the liquid sewage will flow direct to the immense pumps that are to lift it into the syphon chamber, where mammoth centrifugal pumps will force it through two inverted syphons across the river into the outfall sewer, whence it will flow by gravity to the outlet some miles down the river. When there is a heavy rainstorm, the sewage will flow through the opened gates of the sedimentation chamber direct into that chamber, and not round it into the pumps. Here sticks, stones, sand, etc., will be removed from the sewage before it passes into the screening-room and the pumps. If the rainfall is exceptionally Heavy, gates working automatically will divide into four storm-water tunnels on the east and west sides of the pumping station the storm-water carried down by the big sewers, and whatever water the pumps do not handle will he carried by gravity through these tunnels into the Eastern branch. Still further to protect the low-area district from being flooded, huge stormwater pumps will be built and set to work pumping the storm-water into the river, if there is the slightest sign of a flood. The solids removed in the screening-chamber will be pressed in hydraulic presses and loaded into a train of buckets operated by electricity and run on overhead tracks, carrying their load through a conveyor tunnel round the east and west sides and across the north end of the pumping station to
a crematory. The pumproom floor lies twentyfive feet below the bottom of the river, and in it will be installed thirteen powerful centrifugal pumps, of which eight on the west side, each with a capacity of 65,000,000 gals, per day, will pump the storm-water. Three pumps, each with a daily capacity of 65,000,000 gals., will pump the ordinary sewage from the high-level trunk sewers, and two, each with a capacity of 2,000,000 gals, per day, will pump it from the low-level system—the whole system being designed to handle adequately the sewage of a city with a population of 800,000. One man in the engineroom will be able to control all the sluice-gates, valves, covers and interceptor-gates in the whole system, wherever located. Each of the two syphons that cross the river is 5 ft. in diameter and 1.200 ft. in length. They were laid by divers in 48-ft. sections, four 12-ft. sections being welded together before being let down. Each 48-ft. section was securely fastened to the top of a 50-ft. caisson—an airtight box—which was tipped over, after being towfrd into position; the section of pipe then floated into it. Tbe water was admitted into the caisson by ports opened in it. The caisson, on reaching the bottom, was guided into its place by divers and made fast there. T11 doing so, the divers handled about thirteen tons, as each one of the 12-ft. sections, of which there were four, weighed 14.000 lbs. For the beds of piles on which the syphons rest on the bottom the river was dredged to the proper depth. The pipes go down from the syphon chamber with a steep slope 26 ft. below the water, rising to an equal distance on the other side, and connecting there with the outfall sewer in Maryland. The accompanying illustrations show the interior and exterior of the filterheds, and five views of the progress of the sewerage works (from the Scientific American), including the pumping station, the portals of the twin sewerage tunnels and the outfall sewer.
John C. Sparks. B. Sc., F. C. S., consulting and analytical chemist and water expert, whose office and laboratories are at 16 Beaver street. Manhattan. New York city, makes a specialty of the full chemical sanitary and organic analysis of water for ice-making purposes, also of feed-water for boilers as well as of water for drinking purposes. guaranteeing correctness and promptness in every respect. This work is a special branch of the science and it is always advisable to consult an expert, who is not only able to insure accuracy, but, also, can give valuable advice and help to his clients.