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Run percolation tests where your regulator requires them

A percolation test measures how fast water soaks into the soil at the depth of a planned dispersal field. It is used with the soil profile, never alone, to size septic systems.

How

1. Ask your health or environment regulator which method it accepts: some use percolation tests, some use soil profile evaluation only, some use both.
2. Typical procedure (Kansas example): six or more holes 6 to 8 in wide and 24 in deep, presoaked for 24 hours, with the rate reported in minutes per inch. Other jurisdictions use different depths, such as about 36 in or the proposed field depth.
3. Roughen smeared hole sides in clay and add a little gravel at the bottom to prevent scouring.
4. Measure the water drop at equal time intervals until readings stabilise, and report the final reading. Minutes per inch = interval in minutes / drop in inches.
5. Use the slowest or most restrictive result. Very fast results (under about 5 minutes per inch) point to coarse soils that need special designs.
6. Beware dry cracked clays that give falsely fast rates, and test in the season your regulator specifies.
7. Pass results to the sanitation module for system selection and sizing.

Safety: Cover or fence test holes so children and animals cannot fall in.

Do these first

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Sources

1. Site and Soil Evaluation for Onsite Wastewater Systems (MF2645). Kansas State University Research and Extension, accessed 2026-11
2. WTS-25: Soil Surveys. Nevada Division of Environmental Protection, accessed 2026-11
3. Percolation Testing Manual. CNMI Division of Environmental Quality, accessed 2026-11

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