The United States Environmental Protection Agency (EPA) has published resources for people who have experienced flooding in their home or property.
Flood waters in the home may contain a variety of contaminants and you should limit your contact with it. Wearing proper protection is recommended during any cleanup activity. When cleaning it is advised that you wear the following: An N-95 respirator (available at most hardware stores), eye-protection, gloves, long sleeves pants and shirts, and boots or work shoes.
After flooding, remove standing water and dry indoor areas. Clean and dry hard surfaces and consider throwing away any anything that was wet with flood water and cannot be cleaned or has been wet for more than 48 hours.
Standing water on property also has the potential to allow for mosquitos to breed which can sharply increase in numbers after flooding. Get rid of standing water in rain gutters, old tires, buckets, plastic covers, toys, non-operating pools, or any other containers.
Learn more here: https://www.epa.gov/natural-disasters/flooding
Septic Systems:
High waters in lakes, ponds, and rivers can flood septic systems on shoreland and adjacent properties. This can cause sewage to back-up into the house or to discharge untreated to the surface water.
Guidance for currently flooded septic systems
If the entire septic system (the septic tank and the leach field) are fully inundated, the homeowner should not use the system. Sewage can back-up into the house and cause unsanitary conditions or discharge untreated waste to the surface water. In this situation, the homeowner can:
• Leave the structure vacant, if it is not a primary home.
• Use the sanitary facilities at another house, office, gym, restaurant, etc.
• Arrange for a port-a-potty.
If the leach field is inundated but the septic tank is not under water, the homeowner can continue to use the septic tank as a holding tank. They would have to hire a septic hauler to pump out the tank regularly to prevent discharges to the leach field. For a typical 4-bedroom home, that would mean pumping every 2 days. If the homeowner is able to conserve water, they might be able to go a week between pump outs. Conversely, pump outs might have to occur daily for short-term rentals where many people are staying in one house.
If the system is washed out or otherwise damaged by flood waters, the homeowner should not use the system. If the tank is still in place, the owner can plug the outlet and use it as a holding tank. Homeowners should contact a licensed septic system designer to develop a replacement plan for the damaged system. Flood insurance or homeowner insurance may pay for repairs to damaged systems depending on the terms of the policy.
Guidance for after the flood waters recede
For a septic system that is state-approved, we expect it to work again once it dries out. It could take up to 2 weeks after the flooding for the leach field to dry out, because groundwater recedes slower than surface waters. Homeowners should follow the advice provided above until the groundwater levels return to normal. Owners can ask for an evaluation of their system by a licensed designer if they are concerned about the condition of their system.
For systems that are not state-approved or are old, grandfathered systems, homeowners should have the system evaluated by a licensed designer before using it again. The system may not have enough separation from the groundwater and surface waters to adequately treat the waste. The tanks may be old and unsealed.
To find a licensed septic system designer in your area, please go to NHDES Subsurface One Stop at htps://www4.des.state.nh.us/SSBOneStop/.
Questions about permitting for replacement systems should be directed to NHDES at 603-271-3501, Reviewer of the Day.
Questions about pump outs and port-a-potties should be directed to NHDES at 603-271-2818, Wade Pelham, Sludge and Septage Coordinator.