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Septic Systems and Flooding

diagram of a conventional septic system. for a complete description contact the U.S. Environmental Protection Agency
Image courtesy of the U.S. Environmental Protection Agency

Because they are located belowground, septic systems may not always be a homeowner’s first concern during a flood (out of sight, out of mind). However, as South Dakotans continue to navigate an exceptionally wet spring with record-setting flooding and snowmelt, some consideration to your septic system should be given to prevent damage to your home and protect your family’s health. During a flood or period of severe wet weather, wastewater (and sewage) from your septic system can back up into your house because the water is unable to drain from the septic tank to the drainfield due to saturated soil conditions. Warning signs that a septic system is not functioning properly may include a slow flushing/draining toilet, slow running drains throughout the house, odors, or water beginning to backup into basement floor drains. Below are a number of actions that can be taken before, during, and after a flood that may reduce some of the negative impacts to your septic system and property.

Before The Flood

  • Keep stormwater runoff away from your septic system drainfield as much as possible. Water from roofs and driveways should be diverted if possible.
  • The soil over your septic system/drainfield should be mounded to encourage runoff.
  • Have your septic system inspected and pumped every 3 to 5 years by a professional. A well-maintained septic system can better withstand the stresses of flooding or heavy rains than one that is not.
  • If you live in a flood prone area, have a licensed plumber install a backflow preventer to prevent sewage from backing up into the home.

During The Flood

  • As contradictory as it may sound, do NOT pump your septic system during times of flooding or saturated conditions. Hydrostatic pressure from the saturated soil can cause empty septic tanks to become buoyant and pop out of the ground. This can lead to costly damage of the inlet and outlet pipes and additional risk for you and your family.
  • Because the water in the drainfield has nowhere to go, all additional water that goes down a drain and into the septic system will make a bad problem worse. It is important to have a plan to reduce water use in your home. Some considerations are: check and fix leaky faucets, reduce the number of times a toilet is flushed, wash clothes at a laundromat instead of at home, reduce bath/shower usage. Remember, while it may seem “gross” to skip a day of showering, adding more water to your septic system could cause backflow of sewage into your basement.
  • Do not pump water from your sump pit into your septic system.
  • Do not drink well water as wells can become contaminated during a flood. For more information regarding well contamination, see Checking and Treating Domestic Water Supplies After a Flood.

After The Flood

  • Do not drink well water until it has been tested for bacterial contamination.
  • Have your septic system professionally inspected if you suspect damage due to flooding.
  • If sewage has backed up into your basement, clean and disinfect the area using chlorine bleach. Discard any items that cannot be cleaned and disinfected adequately.

Additional Resources