1985-08-21 Soil Report - Laserfiche WebLink

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■ PERCOLATION TEST PROCEDURES Percolation tests are set up in 6" diameter holes put down with either a pa ver auger or a hand auger. The testi are normally set up adjacent (within S' - 61 to the deeper exploratory boring. They are extended to varying depths, most often about 2' - 4' below the surtrre. The number and spacing of tests depend on the soil conditions and the expected volume of effluent. The bottom of the hole and and the lower portion of the v -all are scratched with a sharp Instrument to provide an olien natural soil into* hit h the water can percolate. All loose material is removed A 2 ' layer of fine gravel (jxea 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 rs then placed across the hole and is firmly held in place. ember with stakes cr by mounding soil over each end of the board at a sufficient distance from the hole. Ahernaiively, a ' Perfect Perker" with a built-in float type measuring system is used. Several measurements are made during the initial portion of the %raking penrxl to determine the approxi- mate seepage rate In clean, sandy sods where all the water seeps away in less than 10 minutes, the test 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 time when all the water seeps away in '?ss 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 lust prior to leavicg the site and the sod is then allowed to soak and swell overnight. The water level can also be muntained with an auto^tatic syphon. If water remains in the hole after the overnight soaking period. it is adiusted to a depth of 6" wet the gravel and.: minimum of two measurements are taken at 30 minute intervals. If a slurry or slough -in is noted the'"om 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 adjusted to the 6" depth and the drop in water level is then recorded every 30 minutes until three consecutive readings are within about 10%. The test is terminated of two consecutive measurements indicate a rate slower than 120 minutes per inch. Alternatively, the time it takes the water level to drop I" from an 8" reference point. after maintaining a constant water depth of at least 8" for 4 hours, can be talen as the percolation rale. In sandy soils where the first 6" of water seeps away in less than 30 minute, atter the overnight soaking, measurements are taken at 10 minute intervals. The drop in water Iesel in sandy soil is measured to the nearest 118' and in clayey soil to the nearest 1116" The giv en per( alar ion rates are taken from the !atter measurements at each location, unless other- wise noted. SE -26 IU B� MOIL eXPLORat1On mrroorw