After a septic tank is set, it must be appropriately backfilled. All tanks should be backfilled with successive tamped “lifts” or depth increments of uniform gradation.
The installer should verify that the backfill material is free of clods, large rocks, frozen matter and debris that can result in voids in the backfill that may allow settling over time. Crushed rock or pea gravel 1/2-inch in diameter is preferred if native materials are not appropriate.
Each layer should be uniform, no greater than 24 inches thick, and of nearly equal heights around the perimeter of the tank. However, compaction under the
