In everyday practice it is generally not practical or necessary to conduct a perc test in the traditional manner because a County Health Official is required to be present for the duration of a percolation test, it would be exceedingly expensive to hire the County for the 5 hours required to complete the traditional test.

Fortunately there is a practical alternative. Rather than digging 3 small holes, a back-hoe is hired to make three digs of 10-14 feet deep. In this way the County Inspector can physically examine the soil and based on his knowledge and experience make a determination as to whether or not the soil will be able to absorb the anticipated discharge.

If the determination is made that the proposed site can efficiently absorb the anticipated effluent discharge from a septic system, it is said that the property "percs;" if not, then the property "doesn't perc."

Roughly speaking if the dig sites are rich in gravel or sandy soil, it will likely perc. If the soil has a lot of clay or if the water table is too high it probably won't perc.


Can I still build on a property that doesn't perc? YES. By all means! One of the most common misconceptions about vacant land is that if it doesn't perc it's the end of the world. That is simply not true.

All it means is that rather that just beginning construction of your septic system you need to have a system designed by an engineer and have that design approved by the County. Hence the term "engineered septic system."

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. This ground water level must be established 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, and 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 that are a minimum of four feet above the water table. For example, if the water table is encountered at 15 feet, the perc tests could be performed at anywhere between 2 feet and 11 feet deep, depending on the location of the "best" percing 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.

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