Earth fill and Compaction under a Septic Leach field

If you are placing fill beneath the future leach field, you may need to use sand for a few feet beneath the field. What do the local laws say?

Local laws do not have specific guidance on the compaction of backfilled soils below the leach field.

Sometimes, you are required to perform the grading, and then conduct your percolation test. Depending on the fill material, you might be able to compact to a lesser amount than structural fill.

It will all be a function of the soil composition, compaction, and depth of fill. If the fill soil has more sand, you will have higher flow rates than in clay. Compaction to 85 percent will have higher flow rate than 95 percent. That kind of thing. You probably don't want to conduct lab testing on the permeability of the fill material at different densities to determine the target compaction, that will get costly.