Wells and Flooding

Flooding seems to be happening more and more often in Minnesota, both in the spring as a result of snow melting and and runoff and after large rain events that cause flash flooding. Over the last few years, some places have been experiencing flooding that have not flooded in the past. Floodwater is not clean – it can contain contaminants such as raw sewage and petroleum or hazardous chemicals. For these reasons, it is important that well owners prepare for the possibility that their wells may flood.

The impact that flooding has on wells and water quality are often not as visible as other types of flood damage. It is important to take preventive action now that may save well users more trouble down the road.

If you think your well might become flooded, store a supply of clean water that will last for at least a few days. Shut off power to the well pump to avoid having floodwater pumped into your plumbing system or home. If you only have a little time before a flood, you can cover the well with a heavy plastic bag or sheeting and secure it with electrical tape. This won’t completely protect your well from contamination but will help reduce the amount of water and debris that could enter your well.

If a well is submerged by floodwater, or floodwater comes within 50 feet for a well, the power for the pumping system should be disconnected, and the well should not be used until flooding is over and floodwaters have receded. 

If floodwater reaches your well, assume your well is contaminated. Water from a contaminated well should not be used for drinking, cooking, or brushing your teeth until the floodwater recedes and the following steps have been completed:

  • Avoid electrical shock. Do not approach a flooded well until it has been completely disconnected from its power source.
  • If floodwater covered your well or may have entered your well directly, have a licensed well contractor inspect the well, clean out sediment or debris, and disinfect it. Using your well pump to remove sediment or debris could ruin the pump.
  • If floodwater reached your well but you are confident that floodwater did not enter the well, have a licensed well contractor disinfect your well or complete the disinfection yourself. Detailed instructions are available on the MDH website here.
  • After you or the licensed well contractor disinfects your well and pumps out the chlorine solution, contact Anoka County Environmental Services or another certified water testing laboratory to get your well tested for coliform bacteria.
    • If you well water test comes back positive for coliform bacteria, repeat the disinfection and testing process. You may need to disinfect your well several times before your well is free of bacterial contamination.
    • Do not use the water from your well until you have been informed that it is safe and free of bacterial contamination.

If floodwater came within 50 feet of your well – but did not reach the well – consider having your well water tested for coliform bacteria as a precaution. You do not need to disinfect your well before having it tested. However, if the test comes back positive for bacteria, the well needs to be disinfected.

Wells that meet the standards of the Minnesota Well Code are the safest wells. The Minnesota Well Code (Minnesota Rules, chapter 4725) has many requirements that can protect wells from flooding, including well location, casing height, and approved well caps. The code requires that wells be located and maintained at a distance of 35 feet or more from the normal high-water mark of a lake, river, or stream. For wells completed in flood areas, the code allows several options:

  • The well casing must extend at least 5 feet above the 100-year flood elevation if the 100-year flood elevation is less than 5 feet above the ground surface at the location of the well; or
  • The well casing must extend at least 10 feet above the ground surface if the 100-year flood elevation is more than 5 feet above the surface at the location of the well and the well must have a watertight cap installed on it; or
  • The well casing must extend at least 2 feet above the ground surface and be surrounded by an outer, cement grouted, protective casing that is installed in compliance with the Minnesota Well Code. Both casing must have approved, waterproof caps installed; or
  • The well casing must extend at least 2 feet about the ground surface and a sealed pitless unit spool or flowing well pitless unit is installed. The casing should be covered with an approved, waterproof, non-vented, compression seal well cap.

See the Minnesota Well Code or consult with a licensed well contractor concerning these options. To determine if a well is, or will be, located in an area prone to flooding, you can check floodplain maps here.

For more information, see the Minnesota Department of Health’s Well Management Program’s website.

Click here for a list of licensed well contractors in and around Anoka County.

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