Comp Plan 1974-1977 FILE #1 - Laserfiche WebLink

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4. Effective soil treatment area of a seepage pit shall be calculated as the sidewall area below the inlet, exclusive of any hardpan, rock or clay formations. The sidewall area shall be based on the outer diameter of the pit lining plus 12 inches of rock in the annular space. 5. Required treatment area shall be determined by the percolation test described in Section 4.01 and from using the column for seepage beds in Table 4-1. In no case shall a seepage pit be installed in soils where the percolation rate of any stratum is faster than one-half minute per inch (coarse sand). A percolation test shall be made in each vertical stratum penetrated by the seepage pit, and the weighted average of the results, exclusive of results from soil strata in which the percolation rate is slower than 30 minutes per inch, shall be computed and applied to the seepage bed column of Table 4-I as indicated. (a) A minimum of four feet composite depth of porous formation for each installation shall be provided in one or more pits. (b) All pits shall have an inside diameter of at least five feet. 6. Construction of all seepage pits shall conform to the following requirements. (a) To prevent cave-in, the pit shall be precast concrete or lined with brick, stone or block at least four inches thick, laid in a radial arch to support the pit walls. (b) The brick, stone or block shall be laid watertight above the inlet and with open joints below the inlet to provide adequate passage of liquids. (c) A minimum annular space of 12 inches between the pit lining and excavation wall shall be filled with crushed rock or gravel. (d) The seepage pit shall be so constructed at the top as to be capable of supporting the overburden of earth and any reasonable load to which it is subjected. Access to the pit shall be provided by means of a manhole or inspection hole equipped with a watertight cover. The seepage pit may terminate in a conventional manhole top, frame and cover, but if a manhole is used, it shall extend through the earth cover to a point within 12 inches, but no closer than six inches below finished grade. The manhole cover shall be covered v~ith at least six inches of earth. The top of the seepage pit shall be not less than 12 inches below the ground surface. The top shall be provided with an inspection pipe of not less than four-inch diameter extending to a point flush with finished ground level. The top of the inspection pipe shall be provided with a readily removable watertight cap. 24