How does a mound system differ from a conventional drainfield?

• A. It raises the drainfield above grade with engineered soil and enhanced treatment to accommodate less suitable soils or high groundwater.
• B. It uses a sealed concrete tank instead of a drainfield.
• C. It requires no maintenance.
• D. It discharges directly to surface water.

Answer: (A)

A mound system is designed for soils or water tables that won’t support a conventional drainfield, so the drainfield is raised above grade and built with engineered soil. The raised mound uses a sand fill and a controlled, often pressurized distribution to create an elevated, well-aerated infiltration area. This setup improves drainage, provides extra treatment time, and keeps effluent away from saturated native soils or shallow groundwater, which helps prevent system failure in challenging sites.

In contrast, a conventional drainfield sits buried in the native soil and relies on that soil’s natural permeability to absorb and treat effluent. If the soil is too wet, too shallow, or has poor drainage, a conventional system won’t function reliably. The mound’s engineered profile and elevated position address those limitations by providing an optimized treatment environment above problematic soils or groundwater.

The other options don’t fit because a mound system isn’t simply a sealed concrete tank, it does require ongoing maintenance like any septic system, and it doesn’t discharge directly to surface water.