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MINNESOTA POLLUTION CONTROL AGENCY viiww.pCa.S#dte.rCln.uS i Septic systems 101 Facts about subsurface' sewage treatment systems Subsurface sewage treatment systems (SSTS), commonly known asseptic systems, are soil -based treatment systems used by homes:and.busihesses that are not cohnectedto municipal sewers. The systems treat and dispose of wastewater generated on -site. More'than 500,000 septic systems are in use in Minnesota, which includes 30%-of the state's households. Septic systems treat approximately 25% of wastewater generate0h the state. Wastewater contains sewage,.which includes bacteria, viruses; parasites, nutrients, and some chemicals: Correctly treating acid disposing of wastewater is critical to protecting public health and the environment. More than two-thirds of Minnesotans get.their-drinking-waterfrom groundwater, and poorly built for ill-Nrictiepi ig septic systems can contaminat.e.grouhdwatersand otheTwater. resources. When*constructed-and maintained. properly, septic systems are highly -effective at trea#ing-sewage and keeping Minnesota's groundwater, lakes, and rivers safe and clean. How septic systems work SSTS treat .sewage with a combination of biological, physical, and chemical processes. A system's design must.. account ftseveral"factors: • The amountof daily wastewater generated on -site • Using. gravityor a pump for distribution • The slte's soil conditions i The need for developing a biological layer (biomat) Atypical SSTS includes a septic tank and a soil -based treatment system where liquid waste can come in contact. WI th soils, The septic tank Sewage is piped from a home or business into a buried; watertight septic tank, Which Is-slzec!16 retain wastewater for 24 to 36 hours. The time allows the wastewaterto separatgAnto three layers,ln the tank: • solids sink to the bottom • Greases, fats, and soaps.fioat:t0 the top • The remaining liquid (effluent) flows out to the drainbeld for final treatment Baffles in the tank at the iolet-and outlet help prevent.the top and bottom layers from moving to the draiinfield, where they can clog distribution plpes.afiid cause. premature drainfield failure, Over time, these layers will accumulate, and must be pumped outof the tank -at regular Intervals. Anaerobic bacteria (bacteria that dbesn'tneed.oxygen) in thetank beglnthe.process of.greaking down organic. matter in the sewage. But microorganisms and pathogens remain. Research shows that effluent leaving.the septic tank contains high counts of bacteria (about 1,000,000 colonies per 100 mi) that must be.furthertreated in the soil. Minnesota Pollution Control Agency I June 2019 1 wq-wwist51=10 651-296-6300 1 800-657-3864 or use your preferred relay service l Info. ocaPstate.mn.us Avaiiabie.ln alternative formats