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Environmental Health Division

ONSITE SEWAGE TREATMENT SYSTEMS

Onsite sewage treatment systems serve over 30,000 Kalamazoo County properties, where municipal wastewater service is unavailable. Rather than relying on a central wastewater treatment plant, onsite sewage treatment systems use soil at the property to treat small wastewater flows. A properly constructed and maintained sewage system relies on natural soil organisms, such as beneficial bacteria, to digest nutrients and kill pathogens in the wastewater before the liquid reaches groundwater -- Kalamazoo County's only source of drinking water.

The Kalamazoo County Sanitary Code details specific construction and permit requirements. A typical onsite sewage treatment system (STS) includes two components -a septic tank and a soil absorption system. Some systems may also include a pump chamber and pump.

Septic tank
The septic tank is a watertight concrete box that collects all wastewater leaving the house. In the septic tank, solid materials in the wastewater settle and collect at the bottom of the tank. Oils and scum float to the top of the tank. Clarified liquids discharge through a tee to a soil absorption system.

The Environmental Health Division recommends hiring a septic tank pumping service (see "septic" in the YellowPages) to remove accumulated solids in the tank every three years, so solids are not allowed to fill the tank or overflow into the soil absorption system. Since 2008, all new and upgraded sewage systems are required to have a riser(s) to grade to allow access to the septic tank for pumping.

The number of bedrooms and the presence of a garbage disposal determine the size of the tank. A garbage disposal is strongly discouraged because the disposal increases the amount of kitchen scraps and other solids that enter the septic tank and possibly pass into the soil absorption system.

A typical tank also contains a T-shaped outlet (known as a baffle or sanitary tee) in the septic tank to prevent sludge and scum from leaving the tank and moving into an absorption system. Effluent filters (or screens) are recommended (and required in systems using a pump) to keep solids from entering the soil absorption system.

Soil Absorption System
Liquid effluent passes from the septic tank to a soil absorption system. A soil absorption system consists of tile trenches, drainbeds, drywells (see Informational Sheets for more information), or other systems to distribute the effluent to the soil underground where natural microorganisms and oxygen treat the effluent by killing pathogens and digesting or recycling nutrients before reaching the groundwater. The depth of soil covering most new absorption systems is limited to six to 24 inches, so oxygen from the atmosphere can reach soil microbes.

Many newer absorption systems include an alternator valve. The valve divides the absorption system into two parts by directing the flow of effluent. One half of the absorption system works, while the other half rests and recovers, which extends the life span of the system. Each year, a homeowner should turn the alternator valve and maintain access to the valve. Contact us if you are having trouble locating the valve. Alternator valves have been commonly installed in Kalamazoo County since 1997.

Maintaining and Protecting Your Onsite Sewage Disposal System
A key reason to maintain your onsite sewage treatment system is to save money! Failing systems are expensive to repair or replace, and poor maintenance is often the culprit.

  • Have the septic tank pumped every three years by a licensed contractor.
  • Turn the alternator valve annually to allow one part of your absorption system to rejuvenate.
  • Use water efficiently. Leaky sinks and toilets can waste as much as 200 gallons each day. Low-flush toilets, an Energy Star-rated front-loading washing machine, and faucet aerators significantly reduce the amount of water that your sewage system needs to treat.
  • Due to its high salinity, water softener discharge should be kept out of your onsite sewage treatment system.
  • All wastewater from sinks, baths, showers, toilets, washing machines, and dishwashers must be discharged to the sewage treatment system.
  • Plant only grass over and near your sewage treatment system. Do not plant any shallow rooted trees or shrubs, like willows or soft maples, near any portion of the system. Their roots will grow and travel laterally underground. As they seek water, they can grow into pipes causing blockages.
  • Keep roof drains, groundwater sump pump drains, and other rain or surface water drainage systems directed away from the absorption field.
  • Be alert. Unpleasant odors, soggy soil, liquid waste flow, or excessive grass growth over the absorption area can be signs that the system is in need of service.
  • Do not build anything over or within fifteen feet of any part of your onsite sewage treatment system.
  • Do not allow anyone to drive heavy vehicles, like cars or trucks, over any portion of the system. Pipes and tanks may be damaged or crushed.
  • Don't dispose of household hazardous wastes in sinks or toilets. The Kalamazoo County Household Hazardous Waste Center accepts unwanted chemicals from most county households for no charge, including pure used motor oil, antifreeze, brake fluid, oil-based paints and stains, gasoline, cleaners, and other items.
  • Avoid flushing sanitary napkins, tampons, disposable diapers, condoms, or other non-biodegradable products into your sewage system.
  • Avoid flushing prescription and over-the-counter medications into your sewage system. Dispose of unwanted medications in your garbage cart for pickup service.

Click here to watch a short video on Sewage Treatment Systems.

Informational Sheets

Sewage Backup Clean Up Recommendations (pdf)
Septic Tanks -Why Should I Pump My Tank? (pdf)
Can My Water Softener Discharge to My Onsite Sewage Disposal System? (pdf)
Bull Run Alternator Valve (pdf)
Trench (pdf)
Drainbed (pdf)
Mound (pdf)
Drywell (pdf)




The Kalamazoo County Health and Community Services Department programs are open to all without regard to race, sex, color, national origin, religion, height, weight, marital status, political affiliation, sexual orientation, gender identity, or disability.

Links to external sites do not constitute endorsements by Kalamazoo County.

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