SEWERS 93 



must be pumped out before the work can be joined. The 

 ditching is done by pick and shovel. The shovels may be 

 either short-handled or long-handled. The former are 

 generally better, as the men are more familiar with their 

 use. Grade is given by stakes driven on the side of the 

 trench on which the cut from the top of the stake is marked 

 in feet and inches. These stakes are driven every 50 feet 

 except for main ditches, when they should be 25 feet apart. 

 The minimum grade for mains is 1 inch per 100 feet and for 

 laterals 3 inches. The trenches are hollowed out on the 

 bottoms for the collars so that the weight on the tile may 

 not be borne at the ends. Tile drains should be laid 

 below frost and out of reach of rootlets, particularly of 

 willows. Professor Mapes, who is quoted by Colonel 

 Waring, specifies that drains must be 3 feet deep when 20 

 feet apart, 4 feet deep when 40 feet apart, and 5 feet deep 

 when 80 feet apart. 



In backfilling no stones should be placed closer than 6 

 inches to the tile and the subsoil should be thrown in 

 first. Some engineers require that in excavating the trench 

 the topsoil be placed on one side and the subsoil on the 

 other. The backfilling is tamped in 9-inch layers to secure 

 the best results. 



SEWERS 



Line and grade are best given by placing 2-inch by 

 10-inch planks transversely in the ground every 50 feet. 

 These planks do not have to be set at any exact elevation, 

 but they should be firmly embedded and should be of suffi- 

 cient length so that when the trench is excavated they 

 will remain immovable. The center line can be located 

 by driving a tack on top of the plank. After the excavation 

 work is partially finished a 1-inch by 2-inch strip is nailed 



