CORRESPONDENCE. THE SANITARY WORKS OF BUENOS AYRES
Minutes of the Proceedings of the Institution of Civil Engineers
Proceedings.] DISCUSSION ON SANITARY WORKS OF BUENOS BYRES. 77 with the subsoil water ; if, therefore, the water was taken from Mr. Parsons. the subsoil, there was always a danger of its being contaminated with sewage. With regard to the proper quantity of flush which Mr. Hawksley and Professor Robinson had alluded to, he thought the amount necessary depended entirely upon the construction of the sewers. If badly constructed, the amount of flush necessary t o keep them clean was large; if, on
... was large; if, on the other hand, they were properly constructed with adequate gradients, then a small quantity only was necessary. I n Buenos Ayres he believed a 2-gallon flush was amply sufficient to keep the sewer in proper working order. CORRESPONDENCE ON THE SANITARY CEnutes of Mr. Bruce. had constructed being only S1 Os. 10d. per 1,000 gallons of storage. In Rosario the rate of filtration was about 75 gallons per square foot per day, or 6 inches per hour, nearly identical with that adopted at Buenos Ayres. The filtering materials were of about; the same thicknesses, but instead of the drains being embedded in the lower stratum, the whole bottom of the filters was laid. with bricks set on edge, covered with others placed flat" forming a continuous drain communicating with a central brick culvert, which discharged into regulating wells, whence it flowed to the clear-water reservoir. The head required, when the filters were clean, was between 4 inches and G inches ; when it exceeded 2 feet G inches the filter was changed, as any greater head was found. liable to cause the bursting of holes through the sand. About 1 inch of the upper surface was scraped off and removed to the sand-washer. When the total thickness of sand was reduced to 12 inches by successive scraping, the original thickness was restored. Sand which had been used and washed was found t o be more efficient than new sand. The cost of cleaning a filter, including sand-washing, was about cent gold per square metro, or 1 cent per 1,000 gallons filtered. Trouble had been experienced, as described by the Author, from the growth of green slime on the surface of the sand in summer, necessitating changing the filters about every two or three weeks, but as the interest on the cost of roofing the filter beds, as wa.5 done at Buenos Ayres, would have exceeded the saving in working expenses by their needing to be cleaned less frequently, it had not been deemed advisable to carry it out. The filters were lined witlr concrete, made of five parts of broken bricks, three of sand, and one of cement, and cost, including filtering materials, 19s. 1Od. per square yard. There being plenty of good sand and gravel on the islands in the Paran&, it was much more easily obtained than at Buenos Ayres; it was all delivered at the company's jetty, and discharged from the boats by an iron bucket hauled up a wire rope by a steam-winch, a t a cost of $0.64 per cubic metre, equal to Is. 3d. per cubic yard. The cost of brickwork and concrete a t Eosario, owing, no doubt, to their having been carried out by administration instead of by contract, and also to natural advantages, were, as shown in the Table on the following page, mucl] less than at Buenos Ayres. At Rosario the period of maxin11111~ consumption in summer was from 4 P.M. to G P.M., and amounted to about two-and-a-half times the mean rate, due to the use of hoses in cooling the Patios. The arrangement of the distribution pipes in Buenos A p e s Downloaded by [ University of Sussex] on [12/09/16]. Proceedings.] WORKS OF BUENOS BYRES.