FullCalculator

Septic Percolation Test Interpreter

Formula

Drain Field Size (sqft) = Daily Flow (gpd) / Application Rate (gpd/sqft) | Daily Flow = Bedrooms x 150 gpd | Application rate varies by soil perc rate

Frequently Asked Questions

What is a percolation (perc) test?
A perc test measures how quickly water drains through soil. A hole is dug, filled with water, and the time for the water level to drop one inch is measured. Results are expressed in minutes per inch (MPI). Most jurisdictions require a perc test before approving a septic system installation.
What perc rate is acceptable for a septic system?
Generally, percolation rates between 1 and 60 minutes per inch are acceptable, though ideal rates are 5-30 MPI. Rates below 1 MPI indicate soil that drains too fast (poor filtration), and rates above 60 MPI indicate soil that drains too slowly for a conventional system.

You may also need