What is the minimum soil depth required below the bottom of a mound for effective drainage?

The minimum soil depth required below the bottom of a mound for effective drainage is 12 inches. This depth is essential because it provides adequate space for effluent to move through the soil layers, allowing for proper treatment and absorption of wastewater. A depth of 12 inches ensures that there is sufficient soil to filter contaminants and provide adequate drainage without interfering with the overall function of the mound system. Having this layer of soil prevents the effluent from reaching any underlying restrictive layers that could impede drainage, thus ensuring the longevity and efficiency of the soil absorption system.