The Importance of Perc Testing

Most states require percolation(perc) testing. This test is performed before installing a septic system to determine whether the soil is suitable and to design the system properly.

A perc test is conducted by a specialist with the equipment and insight necessary to complete the test. The purpose of this procedure is to measure the ability of the soil to drain a specific amount of liquid over a set time. The test is performed by digging holes 2-3 feet deep in the proposed drain field of the septic system. This is done to simulate the conditions in a working septic system. The technician will prepare the hole, fill it with water, and measure the time it takes for the water to drop by one inch. A rate of 60 minutes per inch(MPI) is the standard cutoff for a gravity-flow septic system.

The location of the test is the proposed drain or leach field. Leach fields consist of an underground system of perforated pipes adjacent to your septic tank. After contaminants and liquid waste are broken down by bacteria in your septic tank, they flow into the leach field through underground pipes. As liquid travels through the leach field pipes, it seeps into the ground below and is naturally filtered by the soil.

Traditional septic systems only work if the soil in the leach field area is sufficiently permeable, meaning it can readily absorb the liquid effluent (waste, sewage) flowing into it. This explains the crucial role of soil permeability in the functionality of a septic system. Otherwise, untreated effluent may back up and pool on the ground surface.

For the site to pass, at least a few feet of good soil must extend from the bottom of the perforated leach pipes to the rock or impervious hardpan below or to the water table. Much of the treatment takes place in this soil layer.

Even if your site fails, all is not lost. In recent years, a wide range of alternative septic systems have been developed for use on almost any type of site.

For more information, see:
https://buildingadvisor.com/buying-land/septic-systems/soil-and-perc-testing/