What Is a Mound Septic System?
A mound system is a septic drain field built in a raised bed of fill soil instead of in the natural ground. It is used where the natural soil is too shallow or too wet to treat effluent, and it can show as a small hill in the yard.
Explanation
Florida's septic rule defines a mound system as "a drainfield constructed at a prescribed elevation in a prepared area of fill material." Any drain field with any part of its bottom at or above the level of the undisturbed native soil counts as a mound (Rule 62-6.002(40), F.A.C.). A filled system is a related type: only part of the drain field's sides sit above native soil (Rule 62-6.002(26)).
Florida's site rule explains why a lot may need one. Rule 62-6.006 requires the wet-season water table to be at least 24 inches below the bottom of the drain field, with suitable soil reaching 42 inches or more below it. Where the wet-season water table is at or above the ground surface, the rule allows a system only when enough suitable fill is permitted to raise the site, and the design is then based on the final lot elevation. The rule also notes that other permits may be needed before filling a site.
The EPA describes a typical mound: effluent flows from the septic tank to a pump chamber, and a pump sends it to the mound in measured doses. The effluent is treated as it filters through the sand and then spreads into the native soil. The EPA adds that mounds need a substantial amount of space and periodic maintenance, and that systems with pumps or float switches should be inspected more often, generally once a year.
Published ranges from Fixr and HomeGuide put a new mound system at about $10,000–$50,000 or more.
When to seek help
- The system's alarm goes off, if it has one. Call a septic company.
- Soggy spots, standing water or sewage odors on or around the mound.
- You plan to drive, park, build or plant trees near the mound. The EPA says not to park or drive on a drain field.
- You are buying a home with a raised drain field and want to know how it was permitted.
Learn more in how a septic system works in Florida, new septic system installation costs and why drain fields struggle in the rainy season. If your home is in a flood zone, read flood zones and septic systems, or compare septic installation companies.