Information about Performing a Perc Test
Much of the information here is generic and is designed to give you a basic knowledge of the process.. If you are interested in buying land in one of the neighboring Counties in Maryland, we will help you get information from the other jurisdictions to give you a complete picture of what to expect. This information is only a guide. If you want more information on perc tests, you should contact the Department of Health for the County in Maryland where you plan to build.
What is a Percolation (Perc) Test
and Why is one Performed?
A perc test is a hole dug or bored into the ground. Water is poured into the hole. It is then measured and timed to determine how rapidly is be absorbed into the soil. This is much the same as how water percolates through coffee grounds in a coffee maker. The test is performed to determine if a proposed building lot can support a septic system.
A perc test tells whether the land will absorb the water required for a septic system. It also shows how fast the water will be absorbed. The absorption rate is used along with the size of the proposed house to determine the amount of required septic drain field.
What is a Water Table Test?
The water table test is simply a hole dug at the lowest elevation of the proposed septic area for the purpose of determining the depth to free ground water. The ground water level must be known to ensure that there is adequate separation between the septic system and the water table.
How is a Perc Test Done?
Generally, the water table test is performed first. A hole is dug to the depth of the water table or to the limits of the machinery, whichever comes first. After that, the perc holes are dug at the depth of the most permeable soils. They must be a minimum of four feet above the water table. For example, if the water table is encountered at 15 feet, the perc tests can be performed at anywhere between 2 feet and 11 feet deep, depending on the location of the “best” soils.
What is a Good Perc Location?
When choosing a perc location, you should look for an area that is on higher ground with good natural drainage. Ideally, the area should be close to the proposed house site, but lower in elevation. An area of no less than 100 x 100 feet is required. The area should also be free of steep slopes, creek beds, drainage swales, etc.