Question

You are designing a house for a client in the country and you decide to add a sand filter to his septic system. What is the likely reason for doing so, and how does a sand-filter septic system work?

Answer

You probably would use a sand-filter septic system because of poor water percolation in the soil, possibly due to clay-type soils. A typical septic system has a below-grade septic tank where the solid waste is treated through settling and bacteriological activity. The effluent (liquid wastes) is drained off into a drain/ leach field, where it seeps into the ground, oxidizes, and is further decomposed by aerobic bacteria.

In soil types that cannot accept and hold the effluent during this last step, a sand filter is placed between the septic tank and drain field. The sand filter is a large pile of granular material — 24 feet by 24 feet by 3 feet deep (7.3 by 7.3 by 0.9 meters) is not an uncommon size. Effluent is pumped into the sand filter, which then provides an area for the natural oxidation and pretreatment of the effluent before it is piped to the leach field.