Sewage Treatment & Septic Systems
Understanding & Maintaining Your Septic System
Septic systems are designed to hold, treat, and dispose of household wastewater. Household wastewater contains bacteria, viruses, household chemicals, and nutrients, all of which can cause health problems and pollute groundwater or surface water. Therefore, treatment is needed to prevent water contamination.
How Your Septic System Works
Most septic systems have two major parts, a septic tank and a drainfield. Wastewater from sinks, toilets, showers and other drains flows to an underground septic tank. In the tank, solids settle to the bottom and a layer of scum or grease floats to the surface on an intermediate liquid layer. As raw sewage is added to the tank, an equal amount of liquid flows out into the drainfield.
The drainfield is where most treatment occurs. It consists of gravel-filled trenches containing plastic chambers or perforated plastic pipe. Effluent moves through the pipes and seeps into the surrounding soil. Soil particles filter out small suspended solids and organic matter, while soil baceteria break down harmful microorganisms and other organic components. Viruses adhere to clay particles in the soil and eventually die. The treated effluent continues its downward flow through the soil layers.
Maintain Your System to Keep it Functioning Properly
Regular maintenance will keep your system functioning properly and extend its life.
- Do not use additives in your system. They provide no benefit and may harm the system. Additives can result in sludge being flushed into the drainfield, plugging the soil pores.
- Pump the tank regularly. Depending on your water use, pump the tank every two to five years.
- Discharge all wastewater from the septic tank. Don't run wastewater from laundry or a sauna directly into the drainfield as the detergent scum will quickly clog soil pores and cause failure.
- Avoid compacting soil over the drainfield. Compacted soil cannot treat wastwater and once compacted, it can't be restored.
Best Management Practices to Keep Your System Working
- Conserve water. Excessive water use is the most common cause of septic failure, so reduce water used for bathing, laundry, and flushing the toilet.
- Repair water leaks. Repair leaking pipes, sticking float valves in toilets, and dripping faucets to reduce wastewater. A dripping faucet can waste 15-20 gallons per day.
- Take shorter showers and choose showers over baths. A full bath uses 50-60 gallons of water, while a shower uses only about 5 gallons per minute.
- Install low-volume toilets and low-flow shower heads. Typical toilets use 5-6 gallons per flush, providing nearly half of the wastewater from a house. Toilets using only 1.5 gallons of water are available.
- Do not use the toilet as a waste basket. Don't flush facial tissue, diapers, tampons or any kind of plastic down the drain.
- Do not use garbage disposals. Ground up garbage does not decompose easily, causes rapid build up of solids in the tank, and may move solids into the drainfield, clogging pipes and soil pores.
- Never put coffee grounds down the drain.
- Dispose of household hazardous waste properly – not down the drain. Contact your county sanitarian to learn about proper hazardous waste disposal.
- Do not flush or pour unused, unwanted or expired medications down the drain. Medications are being found in groundwater and the consequences for human and environmental health are not fully understood. Take your medications to a "take-back" collection event. If that is not possible, add water and then ashes, dirt, kitty litter or coffee grounds and place in an outer container, such as a plastic tub (to prevent discovery) and dispose with household trash.
- Wash only full loads in the dishwasher.
- Wash only full loads of laundry. To avoid overloading your system, spread washing out over the week instead of washing several loads in one day. A single load takes about 40 gallons of water.
- Minimize use of household chemicals and cleaners. Normal amounts of detergents, bleach, drain cleaners and other cleaners won't harm bacterial action in the system.
Signs of a Problem With Your System
- Sewage backup in your drains or toilets. This may be black liquid with a bad odor.
- Slow toilet flushing.
- Wet areas or water seeping near the drainfield. it may or may not have an odor.
- Excessive growth of aquatic weeds or algae in the lake near your home. Incomplete treatment of nutrient-rich wastewater seeping from your system promotes this growth.
- Bacteria or nitrates found in your well water. This indicates a serious contamination problem that may come from your own or a neighbor's failing system.
What to Do if Your System Fails
- Have your tank pumped. This may solve the problem. If the drainfield or household piping is clogged or if high water levels are a problem, this won't help.
- Fence off the area to minimize human, pet or wildlife contact with wastewater.
- Don't use additives – they may harm your system.
- You may need to upgrade or replace the system or drainfield. A permit from the county health department is required for all new construction and replacement.
For more information about septic systems and how to maintain them, please check out the following resources:
- See the Groundwater section under Planning for Clean Water on our website for information about septic system permitting.
- Homeowner Septic System Checklist, PDF (EPA)
- Septic System Impact on Surface Water: A review for the inland northwest, 2005, Tri-State Water Quality Council.
- Septic Tank Inspection and Trouble-shooting, 2006, MSU Extension Service.