What is the minimum soil separation required for septic designs concerning impermeable layers?

In septic system design, it is crucial to consider the separation distance between the bottom of the drain field and any impermeable layers, such as rock or hardpan, which can restrict the movement of effluent and impede proper filtration. The minimum soil separation required is typically set at 2 feet. This distance allows sufficient room for the effluent to percolate through the soil, ensuring that contaminants are adequately filtered before reaching groundwater, thus protecting public health and the environment.

Having a separation of 2 feet is a widely accepted standard because it balances the need for effective treatment of wastewater with the practicalities of site conditions. If the soil layer above the impermeable layer is shallow, it could result in poor treatment and potential groundwater contamination, making this minimum separation critical to the proper function of septic systems.