Percolation, colloquially called a ‘perc’ test, is a test to determine the absorption rate of soil for a septic drain field or ‘leach field.’ The results of a percolation test are required to properly design a septic system.
In general, sandy soil will absorb more water than soil with a high concentration of clay or where the water table is close to the surface.
A percolation test consists of digging one or more holes in the soil of the proposed leach field to a specified depth, presoaking the holes by maintaining a high water level in the holes, then running the test by filling the holes to a specific level and timing the drop of the water level as the water percolates into the surrounding soil. There are various empirical formulae for determining the required size of a leach field based on the size of facility, the percolation test results, and other parameters.
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