The percolation rate is calculated for each test hole by dividing the time interval used between measurements by the magnitude of the last water level drop. This calculation results in a percolation rate in terms of minutes per inch.

How do you measure water percolation?

Measure the drop in water level at 30-minute intervals over a four-hour period, refilling the hole to a depth of 6 inches as necessary after each 30-minute period. Calculate the percolation rate based on the drop that occurs during the last 30-minute period.

What does a percolation test tell you?

Perc tests determine the right and wrong locations for a septic system, and they’re often required by local jurisdictions before a new one can be built or an old one replaced. That’s because septic tanks work by holding wastewater long enough to naturally separate liquids and solids.