If you’ve ever wondered why so many Brainerd Lakes Area properties have a raised, grass-covered berm in the yard instead of a flat, invisible drainfield, the answer comes down to what’s underneath the soil, not a design preference.
The problem: not enough soil above the water table
A standard septic drainfield works by letting wastewater filter slowly downward through several feet of unsaturated soil, which is where the actual treatment happens — soil microorganisms break down contaminants as the water percolates through. That process needs real vertical separation between the drainfield and the water table or bedrock below it. Minnesota’s SSTS code (Chapter 7080) sets minimum separation distances for exactly this reason.
Much of the soil around Crow Wing County’s lakes doesn’t offer that separation naturally. Shallow soil over a high water table, or over bedrock or dense glacial till, is common on lakeshore parcels — the same geology that makes the lakes themselves possible often means the ground right around them can’t support a standard in-ground system.
The solution: build the separation instead of relying on what’s there
A mound system solves this by building an engineered bed of sand, gravel, and pea rock up and out of the ground, essentially manufacturing the vertical separation the natural soil doesn’t provide. Wastewater from the tank is pumped up into this raised bed in metered doses, filters down through the engineered sand fill, and disperses at the base — getting the same treatment process a standard drainfield relies on, just elevated above the limiting layer instead of relying on it.
Why a pump is required
Gravity alone can’t move wastewater uphill into a raised mound, so mounds require a lift pump and a control panel to dose the bed evenly and on a schedule, rather than flooding one section continuously. That’s the single biggest practical difference for an owner: a mound has electrical and mechanical components a standard system doesn’t, which is also why mound-specific problems tend to be pump or control issues rather than drainfield failures. See our lift pump and alarm page for what that maintenance actually involves.
Not unique to Minnesota, but especially common here
Mound systems exist anywhere soil conditions demand them, but the combination of glacial-era soils, a high concentration of lakes, and a state SSTS code that takes separation requirements seriously makes them especially common across Minnesota’s lake country generally, and the Brainerd Lakes Area specifically. If you’re relocating from a part of the country where mound systems are rare, it’s a genuinely different kind of system to own — not more failure-prone, just more mechanical.
What this means for a property owner
Owning a mound system means accepting a maintenance profile that includes electrical and mechanical components, not just periodic pumping. Watching for alarm signals, testing the system periodically, and calling promptly when something seems off protects an investment that cost more to install than a standard system in the first place — see our mound repair page for the specific warning signs worth knowing.
The upside worth remembering
It’s easy to read all of this as a downside, but a properly designed and maintained mound system does exactly what a standard system does — it just does it on soil that couldn’t otherwise support treatment at all. Without mound technology, a meaningful share of the region’s lakeshore simply couldn’t be developed for septic-dependent housing in the first place. The mound in your yard is, in a real sense, the reason your property is buildable.
Why Mound Systems Are Common Here FAQ
Are mound systems more expensive than standard systems?
Yes, generally — the engineering, materials, and pump components involved mean mound systems typically cost more to install than a standard drainfield, reflecting the additional work of manufacturing the separation the site doesn’t provide naturally.
Can a property with a mound system ever switch to a standard system?
Only if a new site and soil evaluation finds the underlying conditions support it — unlikely if the original conditions that required a mound haven’t changed, but worth confirming rather than assuming.
Do all lake properties in the region have mound systems?
No — some sit on soil with enough natural separation for a standard system, and the tightest lots may run holding tanks instead. Mounds are common, not universal.
