What is a percolation test used to determine?

• A. Absorption rate of the soil for a septic or leach field
• B. Soil pH
• C. Soil temperature
• D. Soil moisture at depth

Answer: (A)

Percolation tests measure how fast water moves through soil, i.e., the soil’s absorption or infiltration rate. This rate is what determines whether the ground can accept effluent from a septic system and how large the leach field must be. In practice, a hole is filled with water and the time it takes for the water to drop by a set amount is recorded, giving a rate (often expressed as minutes per inch). Soils that absorb water quickly allow smaller drain fields, while slow-percolating soils require larger fields or alternative wastewater disposal methods. This isn’t about soil pH, temperature, or moisture at depth, which are different properties.