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Onsite Wastewater Management

onsite system being dug
Environment, Great Lakes, and Energy

Onsite Wastewater Management

The Onsite Wastewater Management Unit is a required service for local health departments under Michigan’s Public Health Code, Act 368 of 1978. The State of Michigan contracts annually with local health departments and provides contract oversight through the Michigan Local Public Health Accreditation Program.

Program elements for the EGLE Onsite Wastewater Management Unit is to offer assistance and training to local health departments in the review and approval of:

  • Land developments utilizing onsite wastewater systems.
  • Large capacity onsite systems discharging up to 10,000 gallons per day.
onsite wastewater system

What is an Onsite Wastewater System (aka: Septic System)?

All wastewater treatment systems, either municipal or single family onsite wastewater systems include:

  • Collection system
  • Treatment components
  • Dispersion into the environment

In this picture of an example onsite wastewater system:

  • #1 is the building sewer or collection system leading to
  • #2 the septic tank which is the first step in the treatment system followed by
  • #3 and #4 the drainfield where the final treatment and dispersal into the environment happens.
septic tank

What is a Septic Tank?

The septic tank holds wastewater long enough for solids to settle to the bottom and fats, oils, and greases will float to the top.  This collection system is a key and primary component that needs maintenance.  When solids accumulate, they reduce the available clear zone and consequently the residency time for treatment.

septic drainfield

What is a Drainfield?

Conventional Systems, as shown in this picture, is where liquid wastewater from the middle third of the septic tank exits the tank and is spread evenly throughout the drainfield. Once in the drainfield, the wastewater percolates into the soil, which reclaims the water for future reuse by naturally removing harmful bacteria and some nutrients.

A properly sized drainfield is in the upper soil profile which is a friendly environment for the aerobic bacteria that treat our wastewater. Additionally, there is an unsaturated zone of separation from the drainfield to the seasonal high-water table. It has been established that when we percolate wastewater through unsaturated soil, we can discharge the treated wastewater into the groundwater which either recharges our groundwater aquifers or eventually discharges into our streams and lakes after proper treatment.


EPA's SepticSmart Program educates homeowners about proper septic system care and maintenance all year long. In addition, it serves as an online resource for industry practitioners, local governments, and community organizations, providing access to tools to educate clients and residents.

Michigan, Do Your Part and Be SepticSmart!
Flood photo

Septic Systems and Flooding Events Frequently Asked Questions

Flooding can impact all parts of the septic system. This includes the septic tank(s) along with the soil treatment area (aka: drainfield/absorption area).

What can I do before a flood?

  • First, you should mark your system to keep off that area until the floodwaters recede.
  • This area could become hazardous and contaminated if the tank structure becomes impaired.
  • It can also be an electrocution risk if a pump chamber is used that contains a pump serviced by electricity.
  • Make sure that electricity to the pump is turned off to prevent electrocution risks.
  • It is best to restrict wastewater from entering into a flooded septic system to prevent backup into the house.
  • Decrease or eliminate water use that discharges into the septic system.
  • Make sure all sump pumps and water softener discharges are NOT connected into the septic system.
  • All gutter downspouts should be directed away from the septic system to carry water away from the site.

What can I do after a flood?

  • Be patient and allow the system to thoroughly dry and restrict water use from the house.
  • Do not pump the septic tank(s) until the surface and groundwater has receded.
  • If the tanks are pumped during high groundwater, it can cause the concrete tanks to become buoyant and start shifting towards the surface. Plastic tanks can collapse or crush under the pressure. This can cause structural damage to the tanks and piping.
  • Have your septic tank(s) and absorption field professionally inspected for any structural damage or clogging.
  • Contact your local health department for a list of professionals that can inspect your septic system.
  • If the tanks are filled with floodwaters, that can introduce fine particles of silt and mix solids that can plug your drainfield pipes.
  • The tanks must be pumped by a licensed septage hauler AFTER the floodwater and groundwater recedes.
  • If your septic system includes a pump chamber and pump, the electrical system should be inspected by a licensed professional to assure all electrical connections, pumps, and alarms are in proper working order before electricity is turned back on.
  • If your system has any pretreatment components, contact your maintenance provider to inspect the system for damage before the system is put back into use.
  • Always take preventative measures and mark your septic tank and absorption area to assure any clean-up activities do not affect the integrity of the septic system.

What shouldn't I do after a flood?

  • DO NOT attempt to service a septic system. A septic system contains a potential for disease transmission, dangerous gases, electrical shock and substances that can be hazardous to your health and safety.
  • DO NOT park or drive over any part of the system. The soil can become compacted and the basic function of the system can become restricted.
  • DO NOT place heavy machinery, dumpsters, or building material on any part of the septic system. The tank could collapse from the weight and the pipes can become dislodged in the drainfield.
  • DO NOT leave the opening to a septic tank uncovered. Assure that all the hole openings are immediately secured, repaired or replaced if the covers have shifted, broken, or lost in the flood. This is to prevent debris from falling into the septic tank along with maintaining safety from people falling into the tanks during clean-up activities.


If your water well has also been flooded, it could be contaminated. Contact your local health department for questions if your well is safe to drink and how to test the water.

Where can I get more information?

If you are unsure where your Onsite Wastewater Treatment System (aka: Septic System) is, contact your local health department for additional advice and assistance. Local health department information can be found at the Michigan Association for Local Public Health website or by visiting the CDC website. For additional flood safety information, visit the Michigan Department of Health and Human Services Flood Safety Fact Sheet Series.



Local health department staff can submit OWM Requests and Training Requests to the Onsite Wastewater Management (OWM) program using the Michigan Environmental Health and Drinking Water Information System (MiEHDWIS). To learn more about MiEHDWIS and how to create an account, visit

Local Health Department staff who need to submit a request to the Onsite Wastewater Management Program? Check out MiEHDWIS!