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Mr. James Brownlee <br />September 23, 1987 <br />Page Two <br />The City of Orono requires at least three feet elevation difference <br />between to bottom of the filter rock of a septic system and ground <br />water or indication of periodic soil saturation such as soil <br />mottling. In order to maintain the required separation, a mound <br />system is the recommended replacement septic system for this site. <br />The mound is designed to serve a four bedroom house. Design sewage <br />flow is 600 gallons per day. With a design infiltration rate of <br />1.2 gallons effluent per square foot per day for the medium sand <br />fill material of the mound, the required rock bed area of the <br />mound is 500 square feet. <br />600 gal/day t 1.2 gal/ft^/day = 500 ft' <br />A rock bed 10.0 feet wide by 50.0 feet long provides the needed <br />area. A minimum of one foot (1.0*) of medium sand should be con­ <br />structed below the rock bed. <br />The pressure distribution system of the mound consists of Schedule <br />40 PVC plastic pipe. The supply pipe should slope back towards the <br />pumping chamber so that it drains after the mound is dosed. The <br />laterals are 1.5 inch inside diameter pipes. The laterals should <br />have 1/4 inch diameter holes drilled at a spacing of 3.0 feet. The <br />laterals should be assembled to the manifold so that the holes <br />point downwards into the rock bed. The distal ends of the laterals <br />should be drilled horizontally in the end cap near the crown of the <br />pipe to facilitate air venting. <br />A submersible effluent pump capable of delivering at least 37.5 <br />gallons per minute against a total dynamic head of at least 13.6 <br />feet should be selected. Headlosses are calculated as follows: <br />1. Vertical headless of 7.7 feet between pump discharge (approx, <br />elev. 90.0) and manifold (approx, elev. 97.7) <br />2. Friction loss of 0.7 feet in 30 feet of supply pipe (2.3 feet <br />per 100 feet 2.0 inch inch I.D. plastic pipe at 37.5 gpro flow). <br />3. Friction loss of 0.2 feet in pipe fittings equal to 25 percent <br />of friction loss in supply pipe. <br />4. Five feet (5.0*) to account for losses in distribution network. <br />If as-built elevations are differnet from those above, headless <br />should be recalculated to ensure proper pump selection.