1983-05-11 Septic System Design Report

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PERCOLATION TEST PROCEDURES Percolation tests are set up in 6" diameter holes put down with either a power auger or a hand auger. The tests are normally set up adjacent (within 5' - 6') to the deeper exploratory boring. They are extended to varying depths, most often about 2' . 4' below the surface. The number and spacing of tests depend on the soil conditions and the expected volume of effluent The bottom of the hole and the lower portion of the wall are scratched with a sharp instrument to provide an open natural soil into which the water can pert,_ te. All loose material is removed. A 2" layer of fine gravel (pea gravel) is placed in the bottom of the hole to : iize scouring. Water is then placed 6 the hole through a pipe or tube, to a depth of at least 12" over the gravel. A reference board is then placed across the hole and is firmly held in place, either with stakes or by moulding soil over each end of the board at a sufficient distance from the hole. Alternatively, a "Perfect Perker" with a built-in float type m-suring system is used. Several measurements are made during the initial portion of the soaking period to determine the approximate seepage rate. In clean, sandy soils where all the water seeps away in less than 10 minutes, the test can be carried out immediate. ly. The water level is adjusted to 6" over the gravel and the drop in water level is then recorded every 10 minutes until three consecutive measurements .ary by less than 10%. Alternatively, the time when all the water seeps away in less than 10 minutes is recorded. The level is adjusted to the 6" depth after each recording. For all other soils, water should be maintained at the 12" depth for a minimum J four hours. The hole is then nearly filled with water just prior to leaving the site and the soil is then allowed to soak and swell overnight. If water remains in the hole after the overnight soaking period, it is adjusted to a depth of 6" over the gravel and a minimum of two measurements are taken at 30 minute intervals. If a slurry or sloughing -in is noted , the bottom of the hole is completely cleaned out and a fresh layer of; ^a gravel is again placed in the bottom of the hole. The water level is then adjusted to the 6" depth and the drop in water level is then recorded every 30 minutes until three consecutive readings are within 10%. The test is terminated if two consecutive measurements indicate a rate slower than 120 minutes per inch. In sandy soils where the first 6" of water seeps away in less than 30 minutes after the overnight soaking, measurements taken at 10 minute intervals. The drop in water level in sandy soil is measured to the nearest 1/8" and in clayey soil to the nearest 1/16". The given percolation rates are taken from the final measurement at each location, unless otherwise noted. SOIL eXPLORBbon SE-2600A)