Soil Percolation Test Guide

The Soil Percolation Test Guide walks you through the process of conducting a perc test and interpreting results for septic system design.

Standard perc test procedure:

Dig test holes 6-12 inches in diameter at drainfield depth (24-30 inches)

Pre-soak by filling holes with water for at least 4 hours (overnight is better)

Refill water to 6 inches above the reference point

Measure water level drop every 30 minutes until stabilized

Calculate rate in minutes per inch (MPI)

Interpreting results:

Under 1 MPI: Too fast — may not filter effluent adequately

1-10 MPI: Excellent — ideal for conventional drainfields

10-30 MPI: Good — standard conventional systems work well

30-60 MPI: Fair — larger drainfield or pressure distribution needed

Over 60 MPI: Poor — alternative system likely required

Important: Official perc tests for permit applications must be conducted by authorized personnel following local procedures.