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Michigan State University Extension
21885 Dunham Road, Suite 12, Clinton Township, MI 48036
(586) 469-6440

How Your Septic System Works


Wastewater from the bathrooms, kitchen, and washing machine enter the septic system

  1. Heavier solids settle to the bottom of the septic tank and form a sludge layer

    1. Anaerobic bacteria break down most of the solid material, but not all

  2. Lighter wastes such as oil and grease rise to the top and form a scum layer

  3. Liquid wastewater/effluent settles in the center and passes into the drainfield

    1. Perforated pipes allow the liquid to be distributed in the gravel filled disposal field

    2. The soil acts as a final filter for the treatment of wastewater

      1. Physical filter

      2. Biological filter

      3. Soil Type as a Factor

        1. Sand and Clay soils filter differently

Why septic system maintenance is important

  1. The design and function of a septic system requires maintenance

    1. Not all solids break down therefore periodic pumping is necessary

    2. Too much water flowing into a tank can cause solids to enter the drainfield, clog the small holes in the perforated pipes, and lead to a failure of the system

    3. Most septic systems, even with maintenance, will work effectively only for an average of 15 to 25 years

  2. Money

    1. Failing septic systems are expensive to repair or replace

      1. Poor maintenance is a common cause of early system failures

  3. Health of your family, community, and environment

    1. Macomb County isolation distances

      1. Water wells must be at least 50 feet from septic system (residential), 75 feet (all other)

      2. Water supply pressure lines, foundations, property lines, and roadside ditches must be at least 10 feet from septic system

      3. Surface water must be at least 50 feet from a septic system

    2. Untreated wastewater can pose significant health risks and can contaminate nearby water sources

      1. Surface water contamination

        1. Septic systems in certain soil types do not completely remove nutrients such as phosphorus and nitrogen

          If you live on a lake or stream, plant or retain natural vegetation along the water's edge to intercept excess nutrients

        2. Excess algae and weed growth, or eutrophication

      2. Groundwater contamination

        1. Nitrate

        2. Bacteria

        3. Viruses

        4. Protozoans

  4. Economic health of your community

    1. Failed septic systems can cause property values to decline

      1. Building permits and real estate sales can be delayed

      2. Rivers, lakes, and shorelines that the community uses for commercial or recreational activities can become unusable

How to maintain your septic system


  1. Do have your tank pumped out every 2-3 years by a license operator.  Why pump?

    1. Bacteria breaking down solids leaves behind a residue or sludge layer which must be removed periodically to prevent it from entering and clogging the drainfield

    2. It is probably the single most important thing you can do to protect your system

    3. Once pumped, inquire as to where your septage will be disposed of (wastewater treatment plant, land.)

    4. Consider a group pumping program where several neighbors coordinate the same day to pump septic tanks

    5. Costs are reduced

  2. Do have your septic system inspected annually

    1. Locate the system

    2. Keep a map handy once it has been located

    3. Uncover the manhole and inspection ports

      1. If they are buried, try to make access to the ports easier for future inspections

    4. Flush the toilets

      1. This is done to determine if the plumbing going to the system is working correctly

    5. Measure the scum and sludge layers

      1. This helps determine when the tank needs to be pumped

    6. Check the tank and drainfield

      1. This ensures all of the parts of the system are functional and in good condition

  3. Do keep a detailed record of repairs, pumpings, inspections, permits issued, and other maintenance activities

  4. Do learn the location of the septic tank and drainfield and keep a sketch with your maintenance record

  5. Do take leftover hazardous chemicals to the Health Department (586) 469-5236

  6. Do use bleach, disinfectants, and toilet bowl cleaners sparingly because harsh chemicals can kill beneficial bacteria in your septic tank

  7. Do cut the grass over your drainfield to allow for proper evaporation

  8. Do limit water entering your tank

    1. Use water-saving faucets, showers, and toilets

      1. A one-liter bottle filled with water and placed in the toilet tank can conserve water in older tanks

    2. Spread clothes-washing, or other high water use activities, over the entire week and avoid half-loads of laundry

    3. Minimize amount of water used for bathing and dish washing

    4. Fix all faucet and toilet float valve leaks


  1. Don't go down into a septic tank. Toxic gases are produced by the natural treatment processes and can kill in minutes. Extreme care should be taken when inspecting a septic tank.

  2. Don't allow heavy vehicles to drive over or park on the septic system

    1. Compacted soil limits oxygen that bacteria need to treat the effluent

    2. Vehicles can break pipes in the drainfield

  3. Don't allow sources of water: roof drains, house footing drains, sump pumps, etc. to drain onto the lawn above the septic system

  4. Don't plant trees or shrubs on the drainfield because the roots can clog and damage the drain lines

  5. Don't cover the drainfield with a hard surface - only grass cover

    1. Bacteria need oxygen to treat the effluent

  6. Don't fertilize the soil above a drainfield

    1. Nutrients saturate the soil and cause it to stop absorbing nutrients from the wastewater

  7. Don't repair your septic system without checking with the health department to see if you need a permit.

  8. Don't overuse a kitchen garbage disposal unit because the increase in solid material can shorten the life of your drainfield

  9. Don't use harsh drain cleaners

    1. Alternative: plunger, 1 cup baking soda, ½ cup vinegar, boiling water, plunger or ½ cup salt, ½ cup baking soda, boiling water, let sit for several hours

  10. Don't use septic tank additives because they usually do not help and may actually hurt your septic system

  11. Don't allow backwash from water softeners to enter the septic system

  12. Do not flush or wash these items down the drain: coffee, fat, grease or oil, condoms, grinds, kitty litter, paper towels, feminine hygiene supplies, dental floss, disposable diapers, cigarette butts, paints, pesticides, varnishes, gasoline, paint thinners, photographic solutions

How to know if your system is failing

  1. Warning Signs

    1. Slow draining sinks and toilets

    2. Gurgling sounds in the plumbing

    3. Plumbing backups

    4. Sewage odors in the house or yard

    5. Wet or mushy ground over the drainfield

    6. Tests showing the presence of bacteria or nitrates in well water

    7. Grass growing faster and greener over the drainfield

    8. Excessive weed or algae growth along the shoreline

  2. No warning sign is a sure indication of a failing system, but any warning sign should lead to an inspection

  3. Routine inspections should also occur since a system can fail without the presence of a warning sign

What to do if your septic system fails

  1. Immediate actions

    1. Call local health department

    2. Have septic system pumped

    3. Conserve water

    4. Fence off any areas where effluent is reaching the surface

  2. Long-term options

    1. Redesign and replace entire system in a new location

    2. Increase the size of the drainfield

    3. Conserve water

      1. The smaller amount of water flowing through a system, the longer it will last

    4. Install perimeter drains to alleviate consequences of saturated soils

    5. Connect to community sewage if it is available

Evaluating septic systems as part of the home buying and selling process

  1. Why?

    1. For the buyer:

      1. Protects the value of the buyer's investment

      2. Protects the buyer from incurring extra costs

      3. Protects the buyer from the difficult task of reselling a home with a malfunctioning septic

    2. For the seller

      1. Protects the seller from possible lawsuits

      2. A properly functioning system can be a good selling point

  2. What is involved in an evaluation?

    1. The evaluation should be done before the home is sold and with enough time so that repairs can be made, if necessary

    2. It should be evaluated by a professional sanitarian

      1. What should be checked for?

        1. Location, age, size, original design: Are isolation distances met for the septic system?

        2. Soil conditions and drainage: Do neighbors indicate frequent problems with their septic systems?

        3. Septic system maintenance history: Current sludge level in the septic tank if not pumped within the past year

        4. Testing of well water for bacteria

        5. Condition of the drainfield

          • Is the ground soggy or smelly?

          • Is the grass much greener over the drainfield, even when the weather is dry?

          • Are there any areas that appear highly compacted?

        6. Condition of the plumbing fixtures and their layout to determine if structural changes were made

          • Is the water softener connected to the septic system?

          • Have any major additions been made to the house after the present septic system was installed?

          • Do toilets flush slowly?