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J. H. KI.EINFELDEK & ASSOCIATFS File No. 5-2314-1 <br /> — August 15 , 1978 <br /> PAGE ELEVEN <br /> Discussion of Percolation Test Results <br /> As noted on Plate XVIII the results of the Percolation <br /> i Tests varied from 2 to almost 400 min./in. : Except for Test <br /> .� <br /> No. 5 , a trend of greater percolation with increased depth- <br /> was generally observed. We conclude therefore, that the 1, 1 <br /> underlying soils at this site are much more permeable than <br /> the surface silty clay soils. For this reason we recommend <br /> '^ that leach lines be placed beneath the dark-brown to black <br /> silty clay soils which were encountered during our field <br /> — explorations to depths of 1 to 3 feet below the existing <br /> ground surface. A reasonable approach to calculate a design <br /> percolation rate in our opinion, would be to average the <br /> percolation rates shown on Plate XVIII below the 2-foot depth <br /> and apply a relatively conservative factor of safety. Since <br /> clear water was used during the tests , the percolation rates <br /> :n <br /> reported do not necessarily directly relate to domestic waste <br /> water. This is one of the reasons why a relatively conservative <br /> factor of safety is suggested. <br /> The soils encountered in our test borings are stratified <br /> V■ which results in horizontal permability several times greater <br /> than the vertical permability. Because of this , the majority <br /> of seepage generally occurs horizontally. This is not only <br /> important for leach field design but also for the storm water <br /> percolation basins . <br /> There are many factors which influence domestic and storm <br /> water disposal. we recommend that our firm be consulted to <br /> evaluate the percolation design plans and be given the opportunity <br /> to respond in writing to the manner in which our data has been <br /> interpreted. <br />