Septic tanks with gravity flow drainfields have been used for many years in areas not served by public sewers. Unfortunately, not all soil and site conditions are well-suited for conventional septic systems. To protect public health and water quality, alternative systems are often used in areas where conventional systems cannot guarantee safe sewage treatment. The mound system is one such alternative. It provides:

• Dosing and resting cycles.
• Uniform distribution of effluent.
• Known level of sewage treatment in the sand fill before disposal.
• Greater distance for effluent to travel before reaching groundwater.

The following information will help you understand your mound system and keep it operating safely at the lowest possible cost. A typical mound system has three working parts:

1. The septic tank.

2. The pump chamber with the pump.

3. The mound with is replacement area.

The Septic Tank

The typical septic tank is a large buried container made of concrete, fiberglass or polyethylene. Wastewater from your home flows into the tank. Heavy solids settle to the bottom where bacterial action partially decomposes them. Most of the lighter solids, such as fats and grease, rise to the top and form a scum layer.

The wastewater leaving the septic tank is a liquid called effluent. It has been partially treated but still contains disease-causing bacteria and other pollutants. From the tank, the effluent flows by gravity to the pump chamber.

Proper Care:

1. Inspect your septic tank once a year and pump it when needed. If the tank is not pumped periodically, solids escaping from the septic tank will clog the pump and mound. Using a garbage disposal will increase the amount of solids entering the tank, requiring more frequent pumping.

2. Avoid flushing harmful material into the septic tank. Never put grease, newspapers, paper towels, cigarettes, coffee grounds, sanitary napkins, solvents, oils, paint or pesticides into the tank. For information on the proper disposal of hazardous household waste, call the Recycle Hotline, 1-800-RECYCLE.

3. Avoid using any chemical or biological septic tank additive. Additives do not improve the performance of the tank. They do not reduce the need for routine pumping, and some are even harmful to the system.

The Pump Chamber

The pump chamber is a concrete, flberglass or polyethylene container that collects the septic tank effluent. The chamber contains a pump, pump control floats, and a high-water alarm float. The control floats are adjustable and are set for pumping a specific volume of effluent. When the effluent rises to the level of the ON float, the pump starts delivering effluent to the mound. The pump lowers the effluent level to the OFF float and stops.

The high-water alarm float in the pump chamber starts an alarm to warn you of any pump or system malfunction. The float is set to start when the effluent in the pump chamber rises above the ON float. The alarm should consist of a buzzer and an easily visible light. It should be on an electrical circuit separate from the pump.

The pump discharge pipe should have a union or other quick-disconnect coupler for easy removal of the pump. A piece of nylon rope or other noncorrodible material should be attached to the pump for taking the pump in and out of the chamber.

Proper Care:

1. Check the pump chamber, pump and floats every year and replace or repair worn or broken parts. Pump maintenance should follow the manufacturer's recommendations. Electrical parts and conduits should be checked for corrosion. If the alarm panel has a push-to-test button it should be checked regularly.

2. Install a septic tank effluent filter or pump screen if your system does not have one. Screening or filtering the septic tank effluent effectively prevents solids from clogging the pump and pipes. Inspecting a screen or filler, and cleaning when necessary are quick and easy, and prevent costly damage from solids entering the mound system.

3. Take action to protect the mound after a prolonged power outage or pump failure. Effluent will continue to collect in the chamber until the pump resumes operation. With additional effluent in the pump chamber, the pump may dose a volume greater than the mound can handle. If all of the reserve storage inside the chamber is used, the plumbing in your home can back up. When the pump is off for more than 6 hours, take the following measures to help protect the mound:

a. Reduce your water use to a minimum.
b. Turn off the pump at the control panel.
c. After power is restored or pump service is completed, switch the pump on and let it run for 5 minutes maximum, and turn it off again. Repeat this manual switching every 6 hours until the effluent drops to the OFF float level and the pump turns off automatically. If there is little water use during the problem, the pump may automatically turn off during the first manual switching.

The Mound

Proper Care:

1. Know where your system and replacement area are located and protect them. Before you plant a garden, construct a building, or install a pool, check on the location of your system and replacement area.

2. Practice water conservation and balance your water use throughout the week to keep from overloading the system. The more wastewater you produce, the more the mound must treat and dispose of.

3. Divert water from surfaces such as roofs, driveways, or patios away from the mound and replacement area. The entire mound is graded to provide for runoff. Place structures, ditches, and driveways far enough away so that water movement from the mound is not disrupted.

4. Keep traffic such as vehicles, heavy equipment, or livestock off your mound and replacement area. The pressure can compact the soil or damage pipes.

5. Landscape your mound properly. Do not place impermeable materials over your mound or replacement area. Materials, such as concrete or plastic reduce evaporation and the supply of oxygen to the soil needed for proper effluent treatment. Grass is the best cover for the mound.

6. Inspect the mound and downslope areas periodically for odors, wet spots, or surfacing sewage. Check your system's inspection pipes regularly to see if there is a liquid level continually over 6 inches. This may be an early indication of a problem. Call your local Health Agency for assistance.

What If the Alarm Goes On?

If, for any reason, the effluent level inside the pump chamber reaches the alarm float (due to a faulty pump, floats, circuit, or another problem), the alarm light and buzzer will start. By using water conservatively (avoid baths, showers, and clothes washing), the reserve storage in the pump chamber should allow you enough time to get the problem corrected. To silence the alarm, push the reset light on the alarm panel. Before calling for service or repair, check to see if the problem could be:

1. A tripped circuit breaker or blown fuse. The pump should have a separate circuit with its own breaker or fuse. If it's on a circuit with other equipment, that equipment can cause the breaker to trip.

2. A pump or float switch power cord plug that has come unplugged. If electrical connections are the plug-in type, make sure that switch and pump plugs are making good contact in their outlets.

3. Control floats tangled by other parts in the chamber such as the electric power cord, lifting rope, or pump screen. Make sure that floats operate freely in the chamber.

4. Debris on floats and support cable that is causing the pump to switch off. Lift the floats out of the chamber and clean.

CAUTION! Always turn off the power supply at the circuit breaker, and unplug all power cords before handling the pump or floats.

Do not enter the pump chamber. Gases inside pump chambers are poisonous and the lack of oxygen can be fatal.

If the problem cannot be located with the above steps, call your pump service person or on-site system installer for service or repair. The service of pumps and other electrical equipment must be done by an experienced person.

Additional Information

More information is available from the following Department of Health publications:
Guidelines for Fill or Mound Systems, 1986.
Understanding And Caring For Your Septic Tank System, DOH 334-009.
Water Saving Guideline 1, DSHS 22-643 (x) 5/88.
Septic Tank System For Your Home, DSHS 22-45A 11/83.
On-Site Sewage System Regulations, DOH 334-006A WAC 246-272.

These are available from your county health agency or by writing to:

Washington State Department of Health Office of Community Environmental Health Mail Stop LD-11 Olympia, WA 98504

Other sources of information include your local:
Health Agency
Soil Conservation Service Office
Cooperative Extension Office

Reprinted with permission from the Washington State Department of Health.

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30. 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Trade names have been used to simplify information; no endorsement is intended. Published June 1992. Subject code 376. A