What Is a Perc Test, and Why Does Marshall County Require One?

A percolation test, or perc test, measures how quickly water drains through soil at the proposed drain field site, which is what determines whether a standard gravity drain field will work or whether the property needs a larger field or an engineered alternative system instead. Marshall County requires a passing perc test before it will permit new construction or a full septic system replacement. The test itself involves digging test holes to the depth of the proposed field, filling them with water, and timing the drop rate after the soil is presoaked. Because a lot of the county sits on glacial till that drains unevenly, two lots on the same road can come back with meaningfully different results, so a neighbor's perc test result isn't a reliable stand-in for your own. We coordinate the test directly with the county permitting office and build the timeline into any new installation quote.