Percolation Rate Calculator

| Added in Construction

What is Percolation Rate?

Percolation rate measures how fast water passes through soil. This is a critical measurement for septic system design, drainage planning, and construction site assessment.

How to Calculate Percolation Rate

The formula is:

[\text{Percolation Rate} = \frac{\text{Volume of Water}}{\text{Time}}]

Results are typically expressed in mL/min or the time required for water to drop one inch (minutes per inch).

Calculation Example

If 500 mL of water drains through soil in 20 minutes:

[\text{Rate} = \frac{500 \text{ mL}}{20 \text{ min}} = 25 \text{ mL/min}]

Percolation Test Procedure

  1. Dig a test hole to required depth (typically 18-36 inches)
  2. Roughen the sides and add gravel to the bottom
  3. Pre-soak the hole for 24 hours to saturate the soil
  4. Fill with water and measure time for water level to drop
  5. Repeat multiple times and average results

Acceptable Rates by Soil Type

Soil Type Rate (min/inch) Suitability
Sandy 1-10 Excellent drainage
Loam 10-30 Good drainage
Clay loam 30-60 Marginal drainage
Heavy clay Over 60 Poor drainage

Implications for Construction

  • Fast rates (under 1 min/inch): May need engineered septic systems
  • Normal rates (1-60 min/inch): Standard septic systems appropriate
  • Slow rates (over 60 min/inch): Alternative systems or no development

Frequently Asked Questions

Percolation rate measures how quickly water moves through soil. It is expressed as the volume of water that passes through soil per unit of time, typically in minutes per inch or mL per minute.

Percolation rate determines if soil can adequately drain wastewater from septic systems. It is required for building permits in many areas.

For septic systems, acceptable rates are typically between 1 and 60 minutes per inch. Rates under 1 minute drain too fast, while over 60 minutes is too slow.

Dig a hole to the depth required by local codes, saturate the soil, then measure how long it takes for water to drop a set distance. Multiple tests are usually required.