Fail a perc test? There are properties out there that will not be suitable for septic systems. Due to varying reasons, such as groundwater issues, high water tables, and soil structure, a property may not pass a percolation (or “perc”) test. If the percolation rate of soil on a property is found to be unacceptable, it will fail a perc test. A conventional drainfield or “leach field” requires a certain absorption rate in the soil to handle dispersing the sewage effluent put into it. Different types of soils have different absorption rates. For example, sandy soils have better absorption than clay soils. A property with a lot of clay in the soil may not be able to handle the amount of flow an average septic system puts out.

Soils that fail perc tests do not meet the necessary absorption rates required for septic systems. These soil types will not properly absorb and treat sewage effluent. Without proper percolation and absorption, drainfields will not work properly and will cause backups or overflows.