What is a Percolation Test?

A percolation test is a test which is performed during the course of a site evaluation. Percolation tests are conducted to find out whether or not a septic system can be installed on site, and to gather information which will be used to design the system. People are usually required to submit the results of a percolation test to public health authorities before they will be allowed to get a permit for a septic system, and a permit for a septic system is usually needed to obtain a building permit if a lot cannot be collected to municipal water and sewer. Therefore, percolation tests are critical during the evaluation stages of property development in many areas of the world.

Also known as a “perc test,” a percolation test is designed to see how well the soil can absorb water. This will play a direct role in determining whether or not the soil can support a septic system. The results may also indicate how large the system will be, where it can be installed, and how it should be designed. For example, the results of the test may indicate that a site is only suitable for a single family home, not a duplex or larger development, which can impact how the property will be developed.

To conduct a percolation test, a series of holes are dug, and the sides of the holes are roughened before the holes are presoaked. The presoak takes place the night before the percolation test. On the morning of the test, residue is removed from the holes, and a controlled amount of water is poured in. The reading of the test results is based on how long it takes the soil to absorb the water added to the hole.

This test is often monitored and administered by a health department official. The official confirms that the test was conducted properly, notes down the readings, and issues a formal report after the test is concluded.

Site evaluation includes a number of tests beyond percolation tests. In some cases, a real estate agent will sell a site which has already been evaluated, with test results indicating how the site can be used and providing important information about conditions at the site. A pre-evaluated site can be more appealing to buy, because people will not be going into the purchase without any knowledge of how the site can be used. If the evaluation also includes permits, it can be especially appealing to potential buyers.