The Perc Test: The Foundation of Every Mobile Septic System

If you are planning to build a new home or add an addition in the Mobile area, you will undoubtedly hear the term "Perc Test" (Percolation Test). It is the single most important hurdle in the construction process. Without a passing perc test, you cannot get a permit for a septic system, and without a septic system, you cannot build your home. Here is what every landowner in South Alabama needs to know.

What is the Perc Test Measuring?

A perc test measures how quickly the soil on your property can absorb water. Since a septic system eventually discharges treated wastewater into the ground, the soil must be able to "percolate" that water at a specific rate. If the soil drains too fast (pure sand), the water isn’t treated properly before it hits the groundwater. If it drains too slow (heavy clay), the yard will flood and the system will back up.

The Alabama Clay Challenge

In our region, we often deal with "Yazoo Clay" or other dense soil types. These clays can be very tricky for perc tests. Often, a property might "fail" in one spot but "pass" just twenty feet away. This is why it is vital to have an experienced professional perform the test. We know how to read the landscape and identify the areas most likely to have the right soil composition for a successful drainfield.

The Process: What to Expect

The test involves digging several holes (usually 2 to 3 feet deep) across the proposed drainfield area. These holes are filled with water to saturate the soil, and then we measure how much the water level drops over a specific period. The results are measured in "minutes per inch" (MPI). If your MPI is too high, you may be required to install an alternative system, such as an aerobic treatment unit (ATU) or a mound system, which can be significantly more expensive.

Timing Your Test

In Mobile, the best time to do a perc test is during the "normal" season. If you do it in the middle of a drought, you might get a false pass. If you do it during a flood, you will almost certainly fail. We work closely with the Alabama State Department of Health to ensure all tests are performed according to regulation and provided with accurate data for your permit application.