Septic Systems

How it works

Homes without a sewer use a private onsite wastewater treatment system (POWTS), usually a septic tank and a drainfield.

In the septic tank, wastewater sits long enough for solids to settle to the bottom as sludge and for oil and grease to float to the top as scum ¹. Bacteria slowly digest some of the solids. The clearer liquid in the middle, the effluent, flows out to the drainfield, a set of trenches or beds, where it seeps into the soil. The soil does the real treatment, filtering out harmful bacteria and viruses before the water reaches groundwater ¹.

Where native soil is too shallow, too wet, or too tight, Wisconsin systems use mounds, sand filters, aerobic units, or other designs that pump effluent through engineered media ^{1 2}. Where nothing will treat on site, a holding tank stores all the wastewater for hauling away ².

Permits and plans

In Wisconsin, installing or modifying a POWTS requires a sanitary permit from the county or other governmental unit, issued only after the plans are approved; a permit expires after 2 years if unused ². Every system has a management plan listing its maintenance and servicing needs ². Well separation still applies: 25 feet from a septic tank to a well, 50 from the drainfield ³.

Maintenance

Wisconsin’s rules ²:

• A septic tank must be serviced (pumped) at least when the combined sludge and scum equal one third of the tank’s volume.
• A holding tank is pumped at least when the wastewater reaches one foot below the inlet.
• An older POWTS (before July 1, 2000) that uses soil for treatment or dispersal must be visually inspected at least every 3 years for effluent ponding on the surface.
• Servicing is done by licensed pumpers.

EPA’s rule of thumb for a household system: inspect at least every three years, and expect pumping every three to five years ¹. Skip it and sludge washes into the drainfield and clogs the soil, which is the expensive part to replace.

Protecting the drainfield

EPA’s care list ¹:

• Don’t drive or park on the drainfield; weight crushes pipes and compacts soil.
• Send roof drains and sump pump discharge elsewhere; extra water floods the soil and slows treatment.
• Plant trees far enough away that roots stay out of the trenches.
• Don’t flush wipes, feminine products, floss, or paper towels; don’t pour grease or harsh chemicals down drains, which harm the bacteria.
• Use water efficiently: spread out laundry, fix running toilets. A typical home uses up to 70 gallons per person per day indoors.

Warning signs of trouble: slow drains throughout the house, sewage odors, soggy or unusually green grass over the drainfield, or wastewater surfacing.

What to take from this

The septic tank separates solids (sludge) and grease (scum), and soil in the drainfield or mound treats the effluent. Wisconsin requires a sanitary permit to install, pumping when sludge and scum fill a third of the tank, 3-year inspections for older soil systems, and licensed pumpers; EPA advises inspection every three years and pumping every three to five. Keep vehicles, roof water, and roots off the drainfield, and keep wipes, grease, and chemicals out of the drains.