Terri’s RURAL RUMBLINGS #1 - Perc Tests
WHAT IS A PERC TEST?
A perc test (also spelled perk - both are correct) is short for percolation test. It is a test which measures the absorption rate of the soil where a proposed septic system will be installed.
BACK IN THE OLDEN DAYS...
The traditional method of conducting this test is to dig three holes in the area where the disposal field is to be located (6 to 8 inches in diameter and 3 feet deep, the correct depth for a disposal field). When dug, the holes would be filled to the top with water. When the water has been absorbed into the ground (this simulates the actual working conditions of the soil when the disposal is installed), the test begins.
Water is then poured into the holes to a depth of 10 inches from the bottom of the hole. Lay a board across the top of the hole and measure the distance from the bottom of the board to the top of the water. Record this distance and the time. Do not add any water during the test. After one hour, again measure the distance from the board to the top of the water. The difference between the first measurement and the second is the inches-per hour absorption rate. Continue the test by recording the distance down to the water level until the test has been conducted for five consecutive hours, or until all the water has been absorbed. If the water is absorbed before the end of the five hour test period, the test will be ended.
Generally speaking, the last hourly rate of absorption is less than 1 inch in 60 minutes, a disposal field will probably not work in that area. Areas where clay or hard pan type soils are near ground level are not satisfactory for disposal fields.
HOW A PERC TEST IS CONDUCTED TODAY. . .
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 usually 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.
WHAT IF THE PROPERTY DOESN'T PERC? Can I still build on it?
Absolutely! If it doesn't perc it's not the end of the game. Instead, prior to construction, you'll need to have a different septic designed (such as sand filter, cap & fills, etc) and approved by the county as an alternative.