The performance of a septic system under normal conditions depends upon the system design, installation and maintenance. Wastewater flows from the sewer line to the septic tank where heavy and light solids separate forming a sludge layer on the bottom of the tank and a scum layer toward the top of the tank. A liquid layer, called effluent, forms between the sludge and scum. Effluent flows out of the tank to a soil absorption field distribution pipe or chamber where it is spread out over the soil. Final treatment occurs in the soil.
If the area around a septic system is flooded or saturated, the system is not working properly. Soil particles have spaces between them, called pore spaces. Normally, some pore spaces will be filled with water and some with air. Under saturated conditions, all pore spaces are filled with water. Septic systems are not designed to function properly when the soil around the soil absorption field (drainfield) is saturated. These conditions can lead to failure in one of two ways:
- If the soil absorption field is saturated, its ability to accept wastewater effluent is reduced or eliminated. This can result in sewage backing up into the house.
- The ability of saturated soil to treat wastewater is reduced or eliminated and can result in wastewater being returned to groundwater, where it can contaminate your private drinking water supply.
Before the flood
- It may be desirable to pump the tank to remove the sewage, but the tank must be properly anchored in the ground. This is not mandatory, but can help with reducing the amount of sewage that backs up into the home. If pumped, some sewage solids will remain in the tank and could mix with floodwaters that enter the tank, but it will be much less than if the tank isn't pumped. It may be helpful to block any lower level drains in the dwelling to help reduce sewage backup. Only licensed professionals are allowed to pump septic tanks in Nebraska.
- Turn off water softeners to prevent them from regeneration.
- If the septic system has any electrical devices such as pumps or alarms, turn them off.
During the flood
- Do not use the septic system until the soil has adequately dried to allow sewage to be absorbed. This may take several weeks after flood waters receed.
After the flood
- Have tanks checked to see if they contain floodwaters. If so, the tanks should be pumped by a certified professional to keep the silt particles from entering the soil treatment system. If the tanks are not anchored, do not pump until the drainfield is unsaturated. Pumping under saturated conditions could cause some empty tanks to float out of the ground and others to collapse, causing damage to the tank and the inlet and outlet pipes. The professional should be sure the manhole cover to the septic tank is secure and that inspection ports have not been blocked or damaged. Also, have the certified professional pump the distribution box, or other similar device.
- Have septic systems inspected by a certified professional and serviced if damage is found. Signs of damage include settling over the tank or drainfield, or an inability to accept water. Most septic tanks are not damaged by flooding since they are below ground and completely covered. However, flooding of the septic tank may have lifted the floating crust of fats and grease, called scum, in the septic tank. Some of this scum may have floated and/or partially plugged the outlet tee. If the septic system backs up into the house, have a professional check the tank first for outlet blockage.
- When returning the the system to use, conserve water as much as possible while the system restores itself and the groundwater table falls. For example, take laundry to a laundromat if possible. (More water conservation tips)
- The home cleaning process will likely result in the discharge of high amounts of disinfectants and cleaners into the septic tank. It is best to pump the tank a second time (if floodwaters were previously pumped) to allow the system to work properly and avoid discharging these chemicals into the soil treatment portion of the system.
- Do not dump flood waters that have entered the house into a plumbing fixture which discharges into the septic treatment system.
- Do not drive vehicles and equipment over the system during clean-up or restoration activities. Do not set dumpsters or building materials over the system. It is a good idea to fence off the system to protect it while restoration activities take place.
- If the septic system still will not accept wastewater after the floodwater has receded from the drainfield and the surrounding soil has had a chance to dry, the drainfield or soil might be plugged. Consult a certified professional to evaluate options.
- Often flood waters can cause components of septic systems to be partially or completely washed away. Do not attempt to correct problems by adding soil or "fill or installing new components. Contact a certified professional to discuss options that will meet state and local codes.
Septic system information provided by: Wayne Woldt, Associate Professor of Biological Systems Engineering and Environmental Engineer, University of Nebraska - Lincoln Extension