1985-04-30 Soil Report - Laserfiche WebLink

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t li i V i PERCOLATION TEST PROClDURlS Perculaiion tests are set up In 6" diameter holes put down with eithei a power auger or a harxl auger. The tests are normally set up adjacent (within 5' - 6') to the deeper exploratory boring. They are extervled to varying depths, most often about 2' - 4' below the surface. The number and spacing ot tests deperxl on the soil conditions and the expected volume of effluent. The bottom of the hole and and the lower portion of the wall are scratched with a sharp instrument to provide an open natural soil into which the water can percolate. All loose material is removed. A 2" layer of fine gravel (pea gravel) is placed in the bottom of the hole to minimize scouring. Water is then placed in 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 states or by mounding soil over each end of the board at a sufficient distance from the hole. Alternatively, a "Perfect Pertef" with a built-in float type measuring system is used. Several measurements are made during the initial portion of the soaking period to determine the ipproxi- mate seepage rate. In clean, sandy soils where all the water seeps away in less than 10 minutes, the lest can be carried out immediately. 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 vary by less than 10%. Alternatively, the tin* 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 of 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. The water level can also be maintained with an automatic syphon. If water remains In the hole after the overnight soaking period, it is adtusted to a depth of b" over the gravel and a mirUmum of two measurements are taken at 10 minute intervals. If a slurry or sbugh in Is noted, the bottom of the hole is completely cleaned out and a fresh layer of pea gravel is again placed in the bottom of the hole. The water level is then ad|usted to the 6" depth and the drop in water level is then recorded every 10 minutes until three consecutive readings are within about 10%. The lest is terminated if two consecutive measurements indicale a rate slower than 120 minutes per irKh. Alter natively, the time it takes the w^ef level to drop 1" from an g" reference poirg. after mamtainirsg a constan; water depth of at least 8" fef 4 hours, can he taken as the percolation rale. In saixty soils where the first h" of water seeps away In less than K) minutes after the overnight soaking, measurements are taken at 10 minute imervah. The drop in wafer level m sandy soil is measured to the nearest 1**8" and in clayey soil to the neareH l/lb". The percolation rates are taken from the latter measurements at each (cicalton. unless uChet^ wise noteri ■•JiiiHb