16 SEWER DESIGN 



take from the office either blue-prints made from the parchment 

 paper, or the bond maps or notes made from them. On these 

 sheets, usually mapping two blocks, are plotted the street, 

 curb, and gutter lines, trees, lamp-posts, hydrants, and catch- 

 basins, the front and side lines of the houses and barns, the 

 existing water- and gas-mains, and all old sewers. The profiles 

 of the streets plotted just below on the same sheet show the 

 street surface, with lines of intersecting streets, depth of rock, 

 and position of all pipes and drains. Cellar-bottoms which 

 might govern the depth of the sewer are plotted. These last 

 are easily obtained by reading the level-rod on the house-sill 

 outside and then adding the inside measurements of the cellar 

 height. 



The reasons for these requirements are self-evident. It 

 is for the city's interest to have the sewer laid in another part 

 of the street from the water or gas, first because thereby dangers 

 of breakage during construction are lessened, and second 

 because future repairs to any of the lines will be more easily 

 accomplished in separate trenches. If the sewer has to be laid 

 in a trench along the middle of which a water-main must be 

 slung up, the work on the sewer is done at an additional cost 

 to the contractor, who is likely to claim an " extra " for it, and 

 with the chance of damage to both pipes. If the sewers are 

 laid out regardless of the position of other pipe-lines, it still 

 remains possible to move either line when they are found to lie 

 in the same trench, but the cost of this re-trenching, once or 

 twice repeated, more than covers the cost of a preliminary 

 investigation. 



Information concerning the location of the water- and gas- 

 pipes can often be obtained from the companies' offices, but 

 it is rarely accurate and is often only to be had through the 

 good will of a foreman who has grown old on the works. The 

 position of gas-drips and water-gates should always be located 

 in the field and plotted as a check. The profiles showing the 

 depth of the cross-pipes are of value in determining the depth 

 of the sewer-pipes, and it is desirable to dig enough test-pits 



