City of Deer River Municipal Ordinances
Standard Percolation Test Procedure
The following percolation test is considered a fundamental and objective procedure:
1. Number and location of tests. Six or more tests shall be made in separate test holes spaced uniformly over the proposed absorption field site.
2. Type of test hole. Dig or bore a hole with horizontal dimensions of from 4 to 12 inches and vertical sides to the depth of the proposed absorption trench. In order to save time, labor, and volume of water required per test, the holes can be bored with a 6-inch auger.
3. Preparation of test hole. Carefully scratch the bottom and sides of the hole with a knife blade or sharp pointed instrument, in order to remove any smeared oil surface and to provide a natural soil interface into which water may percolate. Remove all loose material from the hole. Add 2 inches of coarse sand or fine gravel to protect the bottom from scouring and sediment.
4. Saturation and swelling of the soil. Carefully fill the hole with clear water to a minimum depth of 12 inches over the gravel. By refilling, if necessary, or by supplying a surplus reservoir of water such as in an automatic siphon, keep water in the hole for at least four hours and preferably overnight. Allow the soil to swell overnight. This saturation procedure insures that the soil is given the opportunity to swell and approach the condition that it will be in during the wettest season of the year. Thus, the test will give comparable results in the same soil whether made in a dry or a wet season.
In sandy soils containing little or no clay, the swelling procedure is not essential and the test may be made as described under item 5, c after the water from one filling of the hole has completely seeped away.
5. Percolation rate measurement. With the exception of sandy soils, percolation rate measurements shall be made on the day following the procedure described under item 4, above.
a. If water remains in the test hole after the overnight swelling period, adjust the depth to approximately 6 inches