How can I perform a simple septic system percolation test at home to gauge drainage efficiency and assess drain field performance?

Question

Tyler Smith · Accepted Answer

While a professional percolation test is required for new system installations, a simple DIY percolation test can offer a preliminary, non-binding assessment of your existing drain field's drainage efficiency. This can be useful for homeowners who suspect issues but want a general idea before calling a professional. Buyers frequently ask how to get a basic understanding of their soil's absorption.

Important Disclaimer: This is a homeowner's guide and not a substitute for a professional, code-compliant percolation test. Always consult with a licensed septic professional for accurate assessments and repairs.

Steps for a Simple DIY Percolation Test:

1. Locate Your Drain Field: Identify the general area of your septic drain field. Avoid areas directly over the tank or near existing pipes.
2. Dig Test Holes: Dig several test holes, roughly 6-12 inches deep and 4-6 inches in diameter, within the drain field area. Dig at least three holes spaced evenly apart to get a representative sample. Ensure the holes are dug to a depth that reaches the soil where the drain field laterals are typically situated.
3. Presaturate the Soil: Fill each hole with water and allow it to drain completely. This process, called presaturation, mimics the conditions of a saturated drain field and helps provide more accurate results. You may need to refill the holes multiple times until the water drains steadily.
4. Measure the Percolation Rate: Once presaturated, refill each hole with exactly 6 inches of water. Using a ruler, measure the water level immediately after filling, and then measure it again every 15-30 minutes for a few hours. Keep a log of your measurements.
5. Calculate the Rate: For each hole, subtract the final water level from the initial water level to find the total drop. Divide this drop by the total time elapsed (in minutes) to get the percolation rate in inches per minute or minutes per inch.

Interpreting Results: A healthy drain field typically shows a percolation rate where water drains within a reasonable timeframe, often between 1 to 4 inches per hour, or roughly 15-60 minutes per inch. If water stands for many hours or doesn't drain at all, it's a strong indicator of a failing or clogged drain field, necessitating professional inspection. Remember, these are rough estimates, and factors like soil type, moisture content, and recent rainfall can significantly influence results. This test is best used as an early warning system rather than a definitive diagnostic tool.