1983-05-11 Septic System Design Report

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Jann b Renee Olsten May 18, 1983 Page 2 PERCOLATION TESTS The percolation test data is given on the attached sheets, which are copies of the actual field test sheets. A sheet describing the general test procedures followed is also included. The percolation rates are somewhat faster than normally expected for a sandy clay (clayloam) type soil, especially when considering the wet, spring time conditions found at the site. SEWAGE TREATMENT SYSTEM It is our understanding that it is planned to construct a three bedroom house with a total floor area approaching 3200 sq. ft. It is planned to puce the first floor at about elevation 984, indicating the ground floor slab will be placed at about 977' or slightly thereunder. Existing conditions are not suitable for constructing a normal drain field treatment system; however, a workable system can be constructed, as described below. The percolation test results show a range of about 40-160 min/in. We suggest that the size of the treatment area be based on a percolation rate of about 80 min/in. We suggest that the perforated, lateral lines be placed near the surface and that the trench area be long and narrow. For a type I, three bedroom home, the estimated daily sewage flow is about 450 gal/day. W%- suggest that the trench bottom area be based on 2.45 sq. ft./'4al/day, for a total trench bottom area of 1100 sq. ft. We suggest that two long trenches be constructed. The trenches should be 2' wide and excavated to 24" below the exi-ling surface. About 6" of relatively clean sand with less than 10% material finer . n the #200 sieve should be placed in the bottom and tapered up the sides. About 12" of clean gravel, consisting of 3/4" to 22" diameter material, should be provided for below the perforated tile lines and should extend a minimum of 2" over the lines. By placing the 6" of sandy soil and 12" of gravel, the total trench bottom area can be reduced by about 30%, to 770 sq. ft., re- sulti.ng.in two long trenches of about 190' in length. This will require about 45 cubic yards of clean gravel and about 20 cubic yards of sand. A drop bo should be located at the center of the first trench with 95' long lipeg-- — 1 extending in both directions. The upper line can be placed at about elevatigr' 875'_� The lower line should be plat about 10' or more from the upper line and co teci with drop boxes located at each end of the upper line. About 4" of hay or straw should be placed over the gravel and should be covered with red rosen paper. About 4"-6" of silty sand (sandy loam) type soil should be placed over the rosen paper followed with about 4" of topsoil dressing and a thick grass cover. The final grade in the drainfield area will be about 8" higher than the present grade. Ideally, the sewage treatment system should be constructed in the late summer or fall at which time the water content of the sandy clay soil is normally at the lower end of the moisture cycle. This would tend to minimize smearing and tightening of