Land Treatment of Sewagfe. 



of heavy storms sometimes reaches 16,000,000 

 gallons per twenty-four hours. The Water Supply 

 is about 28 gallons per head per diem ; the greater 

 part is obtained from corporation wells in the chalk, 

 the remainder from the Lambeth Water Company 

 (now the Metropolitan Water Board). The average 

 Rainfall is 23"6in., and the Drainage Area of the 

 district sewered is 6,300 acres. Flushing. — The 

 sewers are flushed from large automatic tanks, 

 tipping tanks and flushing vans and hose. The 

 Stay in Sewers is on the average some two hours, 

 the Distance being about 3 miles. The Sewer 

 Capacity, running full (two outfalls), is 5,814 c.f.m. 

 Screens. — The Croydon sewage passes through one 

 of Latham's patent solid sewage extractors. They 



gravel and sand 6 ft. to 12 ft. deep ; iron pan, more 

 or less impervious, appears in parts. Under-drainage. 

 — Only about 100 acres of the farm are under- 

 drained ; the pipes were put in to assist the land to 

 dry after the sewage was taken off. The drains 

 vary in depth from 4 ft. to 9 ft. and from 4 in. to 

 20 in. in diameter ; they are usually very wide 

 apart, but the distances differ. This work was 

 executed about 1886. Subsoil Water and Floods. — 

 There is not much subsoil water on the farm, and it 

 is not subject to flooding. 



The Mechanical Analysis shows the following per- 

 centage composition of the ignited soil and the un- 

 ignited subsoil (this subsoil gave very little loss on 

 ignition) : — 



are in duplicate, worked by a turbine, the sewage 

 itself providing the motive power. The extractor 

 may be briefly described as resembling a circular 

 wire sieve, revolving on a horizontal axis ; the sewage 

 flowing through the meshes leaves the solids in the 

 sieve and a revolving screw passes the solid matter 

 into a trough. The Norbnry and Thornton Heath 

 sewage is screened. Settling Tanks. — The Thornton 

 Heath and Norbury sewage passes through two 

 small settling tanks, each 32 ft. by 9 ft. by 1 ft. 

 average depth, provided with scum boards ; both 

 are used together on the continuous method. The 

 Screenings and Sludge (about 25 tons, wet, weekly) 

 are ploughed or dug into the land. The Analynes, 

 both chemical and bacteriological, of the sewage will 

 be found at the end of this section compared with 

 those of the effluent and of the stream. 



The Soil is from 12 in. to 18 in. 

 deep, varying from loam, inter- 

 spersed with gravel, to land of a 

 somewhat lighter character. The Subsoil is chiefly 



Soil 

 and Subsoil. 



The approximate number of particles in 1 gramme 

 is for soil 368,297,690, subsoil 160,510,970 ; and in 

 1 c.c. for soil 520,776,170, subsoil 295,828,280. 



The Lime (parts per 100,000) dissolved by water 

 in twenty-four hours is for soil 0029, subsoil 0'026 ; 

 and dissolved by water saturated with carbonic acid 

 in forty-eight hours, for soil 0215, subsoil 0-268. 



Aoreagre, 

 Population, &o. 



The total area of the farm is 

 673'5 acres, and of this 420 

 acres are available for sewage 

 treatment. The average area under irrigation at 

 one time is about 70 acres ; the population served is 

 100,000 (Croydon 75,000, Thornton Heath and Nor- 

 bury 25,000), which works out at 238 persons per 

 irrigable acre, or 1,428 persons per acre for the 

 average area irrigated. The normal dry- weather 

 flow is 40 gallons per head per diem. The amount 

 treated per acre for twenty-four hours at the normal 

 rate of flow is 57,120 gallons on the average area 

 irrigated, equal to 9,520 gallons on the whole 

 irrigable area. 



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