What To Do With Your Septic System Before & After a Flood

Septic system floating in flood waters

Before the flood...

  • Outfitting your home with a backwater valve, plugging low-level drains during a flood event, and reducing water use in the aftermath are your best bets for keeping things clean and dry.
  • If you know flood conditions are on their way, turn off any pumps operating in the system, as well as any electrical components. If you employ a water softener, it too should be switched off.
  • Be sure that downspouts off rain gutters are not directing water into the septic system's drain field (also called the "leach field").
  • Know the distance down to your tank: if this is not found in any installation documents, probe the ground above to find out.

The aftermath...

  • As soon as possible, contact the local authority having jurisdiction over septic systems, who can offer guidance and advice. They may also refer you to the Health Department should the situation be particularly dire.
  • Limit household water use as much as possible during a flood, and in the days and weeks after - it could take a while for the ground to dry out.
  • When your system is limited or unusable, consider using portable toilets, and paper plates and disposable/recyclable utensils in lieu of your standard dishes. Pay the local laundromat a few visits instead of running your own washing machine, and hit up friends for shower facilities, if possible.
  • Septic tanks can take in floodwaters through leaks in the lid or the inlet/outlet pipes. When this happens, the layer of scum and other grossness that floats upon the effluent can block the inlet and/or outlet, resulting in backups. If drains aren't draining or sewage is going into the home, check these pipes, and if safe, clear them.
  • Backups can also be due to a flooded drain field that can no longer take up the tank's discharge. If this is the case, try to use the system as little as possible until the water recedes.
  • If sewage has backed up into the house, it needs to be dealt with swiftly and carefully. Check out our sewage backup guide for helpful tips on cleanup.
  • If sewage has backed up outside the house, be sure that pets and children cannot get to the contaminated area. Solids and as much wastewater as possible should be removed. Hydrated (or "slaked") lime or a chlorine bleach solution can be applied directly to the ground and left to sit for 24 hours. Enough lime should be used to raise the soil's pH to 12, which kills most microbes.
  • Do not have the tank pumped during a flood, or while the ground is still saturated. Pumping is only safe when the water level falls completely below the tank.
  • If it's safe to pump, have only half of the tank contents removed: any more, and a plastic or fiberglass unit could actually float out of the ground thanks to its newfound buoyancy in the saturated soil. Be especially careful with recently installed plastic or fiberglass tanks, which can more easily pop out.
  • In a mound system, pumping can commence when water is about a foot below ground level. The system should then be safe for limited use.
  • Once the water level is safe, check the tank for floodwater. If present, the tank should be pumped to ensure silt and other debris won't clog the drain field.
  • The water level under the drain field needs to be below the water level around the house before normal system operation can resume.
  • A septic tank can be used as a "holding tank" when the water level surrounding it allows for safe pumping, but the drain field remains saturated. With sufficient conservation measures, an initial pumping will keep the water level inside the tank low enough to prevent discharge to the drain field. Regular pumpings are necessary until the field dries out, and will be based on your household's water usage and the capacity of your tank.
  • Limit foot and vehicle traffic over the drain field. Soggy soil is easily compacted, limiting the effectiveness of the drain field in properly treating wastewater.
  • It's always best to have a professional inspect your system after a flood. Too many things can go wrong that can be missed by the untrained eye. Likewise, there are a number of hazards and complications inherent in compromised septic systems. For any diagnostic or repair work, call in the pros.

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