Where should the bottom of a leaching field be placed regarding maximum groundwater when the underlying natural soil has a perc rate faster than one minute per inch?

The placement of the bottom of a leaching field is critical in ensuring proper functioning and environmental protection. When the underlying natural soil has a percolation rate faster than one minute per inch, it indicates that the soil can absorb water quickly. In such cases, it is essential to position the leaching field at a depth that allows for adequate drainage while preventing contaminants from reaching the groundwater too quickly.

A separation of 24 inches from the maximum groundwater level is considered appropriate in this scenario. This depth allows the effluent from the septic system to adequately percolate through the soil, facilitating treatment and reducing the risk of contamination in the groundwater. It also ensures that there is sufficient filter media (i.e., the natural soil) to attenuate contaminants before the effluent enters the groundwater, which is crucial for protecting water quality.

Other depths, such as 12, 18, or 30 inches, either do not provide enough separation for proper treatment in rapidly draining soils or exceed the necessary distance, which could be unnecessary and hinder the functionality of the system. Therefore, 24 inches is the precise recommendation for maintaining effective filtration and protecting groundwater in such soil conditions.