Sewage systems and flooding: safety, sanitation, and clean-up

Flooding of a private sewage system can be dangerous for homeowners. Sewage can back up into the home and may contaminate drinking water.

Remember: A well can become contaminated during a flood. Therefore, do not drink the water until it has been tested.

What should I do during a flood?

  • Limit the use of your sewage system or, even better, not use it at all.  This means minimizing or halting toilet flushing, using the shower, or doing dishes or the laundry.  If the soil is saturated and flooded, the waste water will not be treated and will become a source of pollution.
  • Shut the power off to your sewage lift pump to prevent silt from entering your septic system. When the pump chambers are flooded, silt can settle in the chambers and clog the drain field.
  • Avoid pumping your sewage system tanks.  Empty tanks are buoyant and may “pop” out of the ground during flooding.
  • Plug floor drains, if necessary, to keep sewage from backing up into the basement. Floodwaters may still enter the basement through cracks and seams, however.

What should I do after a flood?

Once flood waters have receded, homeowners should remember:

  • Do not use the sewage system until the water level is below the level of the tank and the tile bed.
  • Do not open the septic tank for pumping while the soil is still saturated or flooded. Mud and silt can enter the tank and enter the drain field.
  • Have your septic tank professionally inspected and serviced if you suspect it is damaged; signs of damage include settling and the system not being able to accept water. As septic tanks may contain dangerous gases, only trained specialists should repair septic tanks. 
  • Examine all electrical connections for damage and ensure they are dry and clean before restoring electricity.
  • Most septic tanks are not damaged by a flood since they are below ground and completely covered. However, sometimes septic tanks or pump chambers become filled with silt and debris. If this happens a new tile bed may need to be installed (in extreme cases). The Building Code requires that a licensed person construct, repair and maintain a septic system.

Have your septic system (and the lift station if applicable) pumped by a professional as soon as possible after the flood, once the soil is no longer saturated or flooded. 

Wait til the soil is no longer saturated before you have it pumped. Pumping out a tank that is in saturated soil can cause it to “pop out” of the ground, which can damage the inlet and outlet pipes. Systems that were installed recently can “pop out” of the ground because the soil has not had enough time to settle and compact.

Do not compact soil over the soil absorption field by driving or operating equipment over the area. Saturated soil is especially susceptible to compaction, which can reduce the soil absorption field’s ability to treat waste water and can lead to system failure.

Ensure the septic tank’s manhole cover is secure and that inspection ports have not been blocked or damaged.

Examine the vegetation over your septic tank and soil absorption field. Repair erosion damage and sod and/or reseed as necessary to provide a vegetative cover.

What should I do in the house?

If the septic system backs up into the house, check the tank first for outlet blockage. Flooding of the septic tank will have lifted the floating crust of fats and grease in the septic tank. Some of this scum could have plugged the outlet tree.

Clean up any floodwater in the house. Avoid dumping water into the sink or toilet until the flood water has receded. Flood waters from the house that are passed through or pumped through the septic tank will cause higher flows through the system. This can cause solids to transfer from the septic tank to the drain field and will cause clogging.

What about my flooded well? 

A well can be contaminated during a flood.  Be sure to test your well water before drinking.  Contact the North Bay Parry Sound District Health Unit for information on testing your water and decontaminating your well after a flood.

Sources and Resources

North Bay Parry Sound District Health Unit

Sudbury and District Health Unit