Perc test

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A perc test (from the word percolation, alternatively spelled "perk test") is a test to determine the absorption rate of soil for a septic drain field or "leach field". In order to gain the permits necessary to build a house, the surrounding land must be tested to determine if the land is suitable to be built on. This includes the permit to put a septic system on the property.

In general, sandy soil or soil that has a high concentration of gravel would absorb more water than soil with a high concentration of clay or where the water table is too high.

[edit] Testing methods

There are two methods for determining the absorption rate of a drain field. The traditional method has been abandoned in most areas because of cost. In this method, three holes are dug that are roughly 6-8 inches (15-20 cm) in diameter and 3 feet (1 m) deep. These holes are filled to the top with water and allowed to drain by having the surrounding soil absorb the water. An additional amount of water is poured to fill the bottom 10 inches (25 cm) of the holes. Next, a board is laid across the top of the holes, and the distance between the board and the top of the water is measured. Additional measurements are made every hour for five hours. The test is over when either the surrounding soil has absorbed all the water or at the end of the five hours. If the last hourly absorption was less than 1 inch (2.5 cm) in 60 minutes, the land fails the test. This test is not used much because of the cost of having a county health official, who must oversee the test, spend five hours on a single parcel of land.

The modern or conventional method is conducted by having a backhoe dig three 10-14 foot (3-4 m) deep holes. The county health official then comes out and physically examines the soil. Using his knowledge and experience with different types of soil, the official determines if the soil would "perc" or "not perc". With this method the official need only be on the land long enough to examine the soil. In states with soil science licensing, soil examinations are performed by consulting soil scientists.

[edit] Test failure

If land fails a perc test, it does not mean that a suitable septic system cannot be installed. If the perc test fails, a homeowner would need to consult an engineer who specializes in designing septic systems and septic drain fields. The engineer would be able to design a system whereby the surrounding soil would be made to be able to absorb the necessary amount of waste water.