What is a Percolation Test?


A percolation test is a soil test designed to evaluate the soil’s capacity to accept a subsurface sewage disposal system (septic system). The test has two parts, the soil evaluation, and the site evaluation.

The soil evaluation determines if the soil on the lot or parcel being tested can do two things:

  1. Function Hydraulically
  2. Provide Treatment

To function hydraulically, the water drop being measured during the percolation test must fall within the time periods specified by the State and County regulations. If the water does not drain within the required timeframe, the system is likely not to function at all or prematurely malfunction. Conversely, the water cannot drain too quickly or the soil will not adequately provide treatment of the sewage effluent. If the soil does not provide adequate treatment, the groundwater or drinking water wells could possibly become contaminated. Another part of the soil evaluation is the soil description. In this part of the percolation test, the Health Department representative makes many observations of the soil’s texture, color, and structure. These descriptions are helpful in determining what type of septic system to install.


The site evaluation consists of many factors. The property is evaluated for the degree of slope, the presence of drainage swales, and many other physical site conditions. The site is also evaluated for the location of neighboring wells and septic systems that may impact the new well or septic system being proposed.

Percolation tests can be conducted for a variety of reasons. They can be conducted on unimproved residential and commercial properties for existing parcels or lots of record. They also can be conducted for new subdivisions for residential and commercial properties. Percolation tests are also required for repairs to existing septic systems that are malfunctioning. Repair percolation tests are required to best assess what repair options are available. If conventional percolation test is unsatisfactory some properties are eligible for Innovative and Alternative percolation testing. Innovative and Alternative percolation testing is conducted with single ring inclinometers. Single ring infiltrometers are large steel rings that weigh about 70 lbs.