A “perc test” is a measure of soil’s ability to allow water to flow through it. Perk is short for “percolation” and is sometimes spelled “perk”. Before installing a septic system, a perc test is performed to determine the rate at which the soil where the drain field will be installed can absorb water. This information is used to determine the minimum size of the leech field or in some circumstances, whether a traditional gravity fed septic system can be installed on the site.
Most jurisdictions require a perc test to be performed before a permit will be issued to install a septic system. The exact procedure for the test varies by jurisdiction, but essentially it consists of digging or drilling one or more holes, filling the holes with water, and timing how long it takes for the water to be absorbed. The type of soil and the local water table both influence the percolation rate.
Local ordinances specify the number and size of the holes and how much water should be poured into them. The ordinance will also specify the minimum rate at which the soil should absorb water for the property to pass the perk test and qualify for a septic system permit to be issued. If the property cannot pass a perc test, an alternative sanitation system will need to be installed instead of a traditional gravity fed system.
The results of the perc test are also be used for planning the drain field installation. A larger drain field would be specified for property with a passing, but relatively low perc rate compared to a property with a much higher perc rate.
