What is a household sewage treatment system?

Jennifer Michaelson - Contributing Columnist

There are many types of household sewage treatment systems used in Madison County where centralized (public) sewer systems do not exist.

The most common is a system with a septic tank followed by one or more leach fields. Another common system is an aeration system. The main difference between an aeration and a septic tank is how the wastewater is treated. In a septic tank, treatment occurs in the absence of oxygen and in and aeration system, treatment is facilitated with the induction of oxygen.

Most often the tank is followed by a leach field. A leach field is also referred to as a soil absorption field. All the wastewater from your home’s sinks, tubs, toilets, dishwasher and washing machines drains into one main drain out to the septic tank.

The septic tank can be made of concrete, fiberglass or polyethylene and is usually buried in the ground. The tank holds the wastewater long enough to allow solids to settle down to the bottom of the tank and be broken down by naturally occurring microorganisms. The settled solids are referred to as sludge. Grease and oil from cooking, washing dishes or your hands will float to the top and this layer is referred to as scum.

The size of the tank will vary from 500 to 2,500 gallons. The tanks usually have two compartments and have an outlet designed to prevent the sludge and scum from leaving the tank and potentially clogging the leach field. Smaller tanks may only have one compartment. Some systems have multiple septic tanks. The size and number of tanks is based the number of bedrooms in the house. Typically a three-bedroom house has one 1,500 gallon septic tank.

Newer systems are required to have caps and risers over the inlet and outlet of the tank and be above the grade for easy locating when the tank needs to be pumped. In older systems the inlet and outlet often does not have risers and the openings to the tank are buried. The caps range from concrete to plastic and are either round or square in shape. The plastic caps are screwed down and the concrete caps are heavy to prevent small children from removing them. Risers and caps can easily be placed on older systems for access.

The septic tank needs to be pumped routinely. The timing between pumping the tank will vary with the number of people living in the home and the size of the system. Typically it ranges from every three to five years. The tank must be pumped by a registered hauler/pumper. A list of registered haulers is available through your local health district.

We can also assist you in determining the location of your septic tank from system records on file and a property visit. Older systems are harder to locate because there may not be records on the system or the tank is buried deeper than our soil probes can reach. We are willing to meet you and at least narrow down the area for digging when the tank needs to be pumped.

The wastewater leaving the tank is referred to as effluent and will flow or be pumped to the leach field, where it filters into the soil where further treatment occurs. Microorganisms in the soil remove bacteria, viruses and nutrients from the effluent. Eventually the effluent will be absorbed by surrounding vegetation and contribute to the area’s aquifer.

Newer systems will also have a distribution box (D-box) to separate the fields and leach lines. The distribution box will be concrete or plastic with a cap and riser above grade for easy access. This box allows the owner to switch fields and lines as needed. Many systems have two leach fields on the property. Only one field is used at a time to treat the effluent while the other is left unused or resting.

Switching fields and resting fields allows the soil and the soil microorganisms to recover from the daily treatment of the effluent. The home owner or the system provider will switch the fields by closing off the previous used field. This is usually done routinely and the timing will depend on the system layout and the property’s soil characteristics. The size of the leach field is based on the septic tank size and the soil type and drainage.

It is important to also have an area set aside for replacing the leach field, should it ever fail. It is referred to as the replacement area, and is open and hopefully undisturbed location on the property. It is important to avoid building on the area or disturbing it in any way.

Maintenance tips:

1. Obtain a copy of your sewage treatment system installation permit and layout for your home records.

2. Don’t pour grease, oil, paint, pesticides and chemicals down your drains.

3. Maintain a routine of pumping the septic tank and switching the leach fields.

4. Don’t plant trees in the area of the leach field or replacement area. The tree roots can damage the leach field.

5. Don’t drive or park vehicles on the leach field or the replacement area.

6. Plan areas for fenced and penned animals away from the leach field and replacement area.

7. Don’t overload the septic tank with large amounts of water by spreading out multiple clothes washing to one or two loads per day.

8. Make sure the sump pump doesn’t discharge into the septic tank.

9. Direct surface runoff and downspouts away from the septic tank and the leach field area.

Signs of potential system failure include:

1. Wastewater backing up into the household drains.

2. Bright green, spongy grass over the leach field area during dry weather.

3. Pooling water or muddy soil around the caps and risers of the tank, distribution box or leach field.

4. A strong sewage odor around the tank or leach field.

Not sure if you have a septic tank or an aeration sewage treatment system? Is your system showing signs of failure? Contact the Environmental Health Division of the Madison County/London City Health District at 740-852-3065 Monday through Friday between 8:30 a.m. to 4:30 p.m. Our sanitarians can help you to learn more about your system.

Jennifer Michaelson, R.S., is the director of environmental health at the Madison County-London City Health District, 306 Lafayette St., London. She can be reached at 740-852-3065, ext. 1517.


Jennifer Michaelson

Contributing Columnist