What Is Perc Testing?

July 15, 2021 7:21 pm Published by Leave your thoughts

A land survey with percolation testing is an important aspect of property consideration, purchase and preparation for building. This process reveals whether the property is suitable for a septic system, which can influence purchase and construction choices. So, exactly what is perc testing? Here’s what you need to know.

Why it’s necessary

Land survey and percolation testing provide crucial information that affects how you proceed with a property purchase and development. This testing determines whether a standard septic system will work on the property. The system will only be able to function if the property has soil that is sufficiently permeable to water. The perc test reveals the ground’s permeability, effectively determining if a standard septic system will work, if an alternative system is necessary or if the site might be unbuildable.

How it works

To perform a perc test, technicians dig two or more holes between 30 and 40 feet apart in the area of the property where the septic drain field would be located. The holes should be two to three feet deep and six to 12 inches in diameter. In the bottom of each hole, the technician will place two inches of gravel.

Next, the technician will loosen any compacted soil on the sides of the holes and remove it from the holes. The soil is then pre-soaked to attain a natural saturation of the soil. The technician will continue to add water to maintain about a foot of moisture in the hole for a minimum of four hours. This process may take up to 12 hours to complete.

The following day, the technician will clean out any additional loose soil that has fallen into the holes and fill the holes with six inches of water. Over the next 30 minutes, the technician will measure how far the water drops. The rate at which the water drops is referred to as the percolation rate, or perc rate. The perc rate is the time it takes for the water to drop one inch.

How it’s documented

The percolation rate is recorded as minutes per inch drop. For example, a perc rate of 60 MPI (minutes per inch) means that the water dropped one inch in one hour.

Standard requirements

For a standard gravity-flow septic system, the standard is typically 60 MPI or better. If the rate is too fast, the water absorbs too quickly for proper treatment before it reaches the groundwater. Standards vary by location, so it’s important to check with your local municipality to confirm the requirements.

Learn more

For more information on land surveying and percolation testing, contact the experts at Polysurveying. Family owned and operated for over three generations, we specialize in testing and surveying for both commercial and residential projects, including perc testing, land surveys, boundary surveys, elevation and topographical surveys, construction layout and staking surveys. Our mission is to provide fast and reliable service while maintaining the quality of work our clients have come to expect. Call us today with any questions at 251-666-2010. We look forward to partnering with you for your next project.

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