What is a mound system and when is it used?

• A. A raised, engineered drainfield built above native soils using imported fill; used when native soils are too poor for infiltration or high groundwater is present.
• B. A standard trench drainfield buried in native soil with no fill.
• C. A sealed tank installed above ground to treat effluent.
• D. An on-farm spray irrigation system.

Answer: (A)

A mound system is an engineered, elevated septic drainfield built above the native soil, using imported fill to create the required absorption area. It relies on a sand-based infiltration zone and a controlled distribution system to move effluent through the sand and into the drainfield below, while keeping infiltration away from shallow groundwater or perched water. This design is chosen when the native soils are too poor for infiltration (very slow percolation) or when the groundwater table is too high for a conventional drainfield, so raising the absorption area and providing a designed infiltration media allows proper treatment and disposal of effluent.

In practical terms, you’d use a mound when standard trench systems wouldn’t work due to soil limitations, which is why this option describes a raised, engineered drainfield built above native soils with imported fill and is used specifically for those soil or water-table conditions. The other scenarios describe different systems or configurations (a standard trench buried in native soil, a sealed above-ground tank, or spray irrigation), none of which match the mound’s purpose and construction.