Percolation Test - Soil Properties: Testing, Measurement, and Evaluation - page 243

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CHAPTER SEVENTEEN

Percolation Test

Percolation refers to movement of water through soil. Percolation tests
are performed to determine the rate at which percolation occurs (i.e., the
rate at which water moves through soil). Percolation rates are needed to
determine whether or not given job sites will be suitable for certain
engineering projects, such as reservoirs, sewage lagoons, sanitary
landfills, and septic tank drain fields. In the first three of these, bottom
soil should not have a high percolation rate. If it did, considerable water
could be lost through the bottom of a reservoir, lagoon, or landfill. Such
water loss would, of course, be undesirable for reservoirs; and in the case
of lagoons and landfills, water loss could carry waste material with it
and thereby contaminate groundwater in the area. On the other hand,
relatively high percolation rates are needed for soils to be used for septic
tank drain fields, so that the liquid part of sewage will percolate readily
through the soil and thereby be removed from the septic tank and
drainage pipes.
Percolation tests are performed in the field, in place, at locations
where seepage is a matter of concern. They are performed, essentially,
by digging a hole and measuring how long it takes a given depth of
water to drain (seep) out of the bottom of the hole. For septic tank drain
fields, the depth of the test hole should generally be about the same as
the depth at which the drain pipe is to be placed. To ensure adequate

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