What is the minimum thickness of coarse gravel that must be placed before collection lines in a sand filter?

The minimum thickness of coarse gravel that must be placed before collection lines in a sand filter is 2 inches. This requirement is based on the need to ensure proper drainage and to create an effective filtration layer. The coarse gravel serves multiple purposes: it allows for adequate water flow towards the collection lines, prevents the sand from migrating into the collection system, and helps to distribute the effluent evenly across the sand filter.

Placing at least 2 inches of coarse gravel provides sufficient depth to achieve these goals while minimizing the risk of clogging in the collection lines. Thicker layers may enhance these benefits, but the minimum requirement is set to ensure structural integrity and functionality within the system. Using gravel that is properly sized also contributes to the overall efficiency of the septic system, as it helps to maintain the necessary aeration and facilitates bacterial activity in the filter bed.