1986-03-06 Septic System Design Report

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t Mr. Chuck VanEeckhout Page 2 March 6, 1986 Percolation test results are as follows: Depth Soil Texture at Percolation Rate Hole Elevation (inches) Bottom of Hole (min/in) P-1 109.8 24 Silty sand to medium sand 1 P-2 107.8 18 Silty sand to clayey sand 15 P-3 107.9 18 Sandy clay 17 P-4 109.1 24 Silty sand 6 P-5 108.4 24 Silty sand 16 P-` 106.1 18 Sandy clay 23 Measured percolation rates are consistent to somewhat rapid for the texture of the soil materials in which the percolation tests were run. The City of Orono requires at least three (3.0) feet separation between the bottom of the filter rock of a septic system drainfield and groundwater or indication of periodic soil saturation such as soil mottling. In order to provide the required separation, a mound septic system design is recommended for both the primary and alternate septic system sites on this lot. The proposed mound system is designed to serve a four bedroom house. Design sewage flow is 600 gallons per day. With a design infiltration rate of 1.2 gallons effluent per square foot per day for the medium sand fill material of the mound, the required rock bed area of the mound is 500 square feet. 600 gal/day = 1.2 gal/ft2/day - 500 ft2 A rock bed 10.0 feet wide by 50. a lon ovides the needed area. A minimum of one and one-half f et (1.5') of m dium sand should be constructed below the rock bed. The basal area calculation of the mound is based on a loading rate of 0.45 gallons per square foot per day for silty clay to sandy clay loam soils. The mound should have at least 1,333 square feet of basal area. 600 gal/day _ 0.45 gal/ft2/day - 1,333 ft2 The basal width of the mound (basal width - distance between upslope edge of rock bed and toe of medium sand fill) is 27 feet. (See cross section of mound on enclosed sketch.)