How to calculate percolation and absorption rate.

A percolation test (from percolation, colloquially called a perc test) is a test to determine the absorption rate of soil for a septic drain field or "leach field". The results of a percolation test are required to properly design a septic system. In its broadest terms, percolation testing is simply observing how quickly a known volume of water dissipates into the subsoil of a drilled hole of known surface area. While every jurisdiction will have its own laws regarding the exact calculations for the length of line, depth of pit, etc., the testing procedures are the same.

In general, sandy soil will absorb more water than soil with a high concentration of clay or where the water table is close to the surface.