1978-02-13 Septic System Design Report

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78-08B Mr. David Nitz -4- February 13, 1978 design for a system in this area, subject to change, based on percolation tests run next spring. However, it would be based on a rate of on the orda rof 80 mpi, which is above the normal minimum acceptable standards. Although standards have not been set up for developing a system based on an 80 mpi rate, a larger than normal system consisting of seven 30-inch wide trenches, 75 feet in length, with 7 foot center -to -center spacing may be adequate for this system. This rate was interpolated from the standard curve system which indicates requirement rates per bedroom based on the minutes per inch reading. Based on this system, a typical 4-bedroom home would then require approximately 325 lineal feet of absorptive trench per bedroom. Although a system of this stature appears feasible, there is some risk of future failure. A sewage treatment mound would be the second alternative for the site. With this system, sand and rock fill can be placed directly on the natural clayey soils in the proposed drainfield area. It should be noted that general topography in this area should be relatively flat, with less than 3t grade slope. This system would be developed based on 125 square feet per bedroom or .83 square feet per gallon of waste per day. For a proposed 4-bedroom home, the mound'bed would require 500 square feet of total area. This can be accomplished with a bed length of 50 feet and a maximum width of 10 feet. The system then consists of approximately 12 inches of sand fill overlying the natural soils. A 9- inch layer of 3/4 to 2�-inch clean rock is then placed directly over the sand and used as a bedding for the pipe. A sandy soil should then be placed over the pipe, the thick- ness of which should be between 6 and 12 inches. A 6-inch layer of topsoil would then be placed immediately over the sand. The sideslopes of the dike should not be steeper than 3 feet horizontally to 1 foot vertically. If either of the two above systems are not feasible for the lot, a third alternative would be a sewage osmosis system. The sewage osmosis system can be useful in areas of heavy clay soils and in areas where the seasonal water table is high. This patented system, using a set of cathodes and anodes, together with the special drainfield trenches, should be designed, constructed, and maintained by a licensed dealer. This system, as well as those mentioned above, are, of course, all subject to City of Orono approval. s�un EN(i1NEERINQ TESTING