12 SEWER DESIGN 



sewer with the 4-foot storm-sewer, each 3000 feet long. Brick sewer re- 

 quires 200 brick per lin. ft. 



6. A pipe lateral system contains 18,000 feet of 8-inch pipe, 2000 

 feet of lo-inch pipe and 600 feet of 1 2-inch pipe. A small section con- 

 taining 100 people is too low to drain into the system, and it is found that 

 to serve this section the system must be lowered an average depth of 

 5 feet, the soil being a hard clay, in which excavation costs 75 cents per 

 cubic yard. Compute the interest at 5 per cent on this additional amount 

 and compare with the cost of pumping the sewage of 100 persons (80 

 gallons per head per day) 5 feet high, if the installation costs $650, and 

 the running expenses are at the rate of 20 cents per million gallons lifted 

 one foot. 



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