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0 <br />D. Filter material is defined as clean rock, crushed igneous <br />rock or similar insoluble, durable and decay -resistant <br />material free from dust, sand, silt, or clay. The size <br />shall range from 3/4 inch diameter to 2-1/2 inch diameter. <br />E. Effluent shall be distributed over the filter material by <br />1-1/4 inch diameter perforated pipe under pressure. Per- <br />foration holes shall be 3/16 inch in diameter drilled in a <br />straight line along the length of the pipe. Hole spacing <br />shall be 36 inches. Holes shall be drilled straight into <br />the pipe and not at an angle. A sharp drill shall be used <br />and any burrs in the inside of the pipe shall be removed. <br />The perforated pipe laterals shall be installed level with <br />the perforations downward. <br />F. The perforated pipe laterals shall be connected to a 2-inch <br />diameter manifold pipe and shell have their ends capped. <br />The laterals shall be spaced no further than 40 inches on <br />center and no further than 20 inches from the edge of the <br />filter material. Laterals shall be no longer than 50 feet. <br />G. The manifold pipe shall be connected to the supply pipe <br />from the pump. The manifold shall be sloped toward the <br />supply pipe fx)m the pump. <br />H. At least 2 inches of filter material shall be placed over <br />the lateral pipes. <br />I. Straw or marsh hay to an uncompacted depth of 3 to 4 inches <br />or untreated building paper shall be placed over the filter <br />material. <br />J. Construction vehicles shall not be allowed on the filter <br />material until backfill is placed. <br />K. Sandy loam soil shall be placed on the filter material to a <br />depth of one foot in the center of the mound and to a depth <br />of six inches at the sides. <br />L. Six inches of topsoil shall be placed on the fill material <br />over the entire area of the mound. A grass cover shall be <br />established over the entire area of the mound. <br />M. No shrubs shall be planted on the top of the mound. Shrubs <br />may be placed at the foot and side slopes of the mound. <br />N. Side slopes of 4 feet horizontal to 1 foot vertical (4:1) <br />are suggested for the dikes of the mound. This gentle slope <br />will allow easy mowing of the grass cover. If area is lim- <br />ited, steeper side slopes of 3:1 can be used. But in no <br />case shall the dike slope be steeper than 3:1. The soil <br />material at the toe of the dike should be slightly 1 ;s <br />- 10 - <br />