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Flooded Wells Must be Cleaned

["NDSU Extension water quality experts offer advice on cleaning flooded water wells.", ""]

Surface water can partially or fully submerge private wells during a flood.

When this happens, the well can become contaminated with sewage, petroleum products, sediment, bacteria, viruses and other floating debris, North Dakota State University Extension Service water quality experts warn.

The water’s smell sometimes will change if surface water gets into a well. If you suspect surface water contamination and you must use the water for drinking or food preparation, here are some recommendations from the Environmental Protection Agency for making it safe:

  • Boiling the water will kill most types of disease-causing organisms that may be present. If the water is cloudy, filter it through clean cloths or allow it to settle, and draw off the clear water for boiling. Boil the water for one minute, let it cool and store it in clean containers with covers.
  • If you can’t boil water, disinfect it with household bleach. Bleach will kill some types of disease-causing organisms that may be in the water. Filter cloudy water through clean cloth or allow it to settle and draw off the clear water for disinfection. Add 1/8 teaspoon (or eight drops) of regular, unscented liquid household bleach for each gallon of water, stir it well and let it stand for 30 minutes before using it. Store disinfected water in clean containers with covers.

After floodwaters recede, the well should be disinfected and the water should be tested to make sure it is safe. Obtain a water test kit for bacteria and nitrates from your county health department or a private certified laboratory. A list of certified labs is available in Extension publication WQ-1341, “Drinking Water Quality: Testing and Interpreting Your Results.” The publication is available from county Extension offices or on the Web at http://www.ag.ndsu.edu/pubs/h2oqual/watsys/wq1341.pdf.

The well needs to be inspected before it can be disinfected. First, turn off the electricity to the pump. Look at the area around the well casing. Remove accumulated debris and sediment. If the well cap is missing or the casing is damaged, call a certified well installer because large amounts of sediment and other materials may be in the well and can’t be seen by looking down the well.

If the well cap still is on and not damaged, look inside the well for damage to the pump, piping, wires, casing, etc. You will need a good flashlight to look down the well. If the inside of the well casing is relatively clean, the well can be disinfected using shock chlorination. Shock chlorination also should be done after a well installer has pulled the pump and cleaned the well.

Use the following steps to shock chlorinate a well:

  • Before turning on the well pump after a flood, the only place you want water to come out in the house or barn is at outside faucets and hydrants, bathtubs and sinks. Disconnect all other water appliances. Use the bypass valves on water filters, water softeners and water treatment devices. Shut off the water heater’s supply valve and drain the heater. Shut off power to electric heaters; for a natural gas or propane water heater, shut off the fuel supply and put out the pilot light.
  • With the electricity off to the well pump, clean the well cap and outside of the casing with a solution of 1 ounce of laundry bleach in 2 gallons of clean water. Use a coarse brush.
  • Turn on the electricity and pump the well until the water is clear. Do this at the faucet or hydrant nearest to the well. Collect discharge water in a white bucket to check the color of the water and look for sediment. Next, open each faucet in the home until it runs clear. Close all faucets and turn off the electricity to the pump.
  • Prepare a mixture of household bleach and water to pour down the well. You will need at least one 10-gallon container or two 5-gallon containers for mixing the bleach and water. Be sure to use eye protection and rubber gloves when mixing. You’ll need at least 200 parts per million (ppm) of chlorine throughout the water column in the well. The amount of household bleach you’ll need depends on the diameter and depth of water in the well. If your well is 3 to 4 inches in diameter with about 50 feet of water, mix 2 quarts of bleach in 10 gallons of clean water. For a well 5 to 6 inches in diameter with 50 feet of water, mix 1 gallon of bleach with 10 gallons of clean water. If you are not sure of the amount of water in your well, double the amount of household bleach in the mixture. Because household bleach is about 6 percent chlorine, doubling the amount will not do any harm. Remember, 200 ppm is the minimum chlorine level.
  • Pour the diluted bleach solution into the well against the side of the casing. Avoid pouring directly onto the pump wiring if possible but try to wash down the entire inside of the casing.
  • Mix the chlorine throughout the water column in the well. Turn on the electricity. If possible, connect a garden hose to the nearest hydrant or faucet and place the discharge end in the top of the well. Run the water for 15 minutes. You also can mix the chlorine by starting and stopping the pump quickly several times. Let the chlorine mixture sit in the well for at least an hour.
  • One at a time, open every water outlet on the system. Run the water until you can smell the chlorine, then close the faucet. Flush the toilets, refill the water heater and allow the chlorine solution to remain in the system for at least four hours, although eight hours would be the best.
  • Open all the faucets or hydrants to purge the chlorine from the system. Start with the faucet or hydrant nearest the pressure tank and work your way to the farthest faucet or hydrant. Run each one until you can’t smell chlorine.

Now use your water test kit to obtain a water sample for bacterial safety. Continue to use an alternative water source or boil your water until the laboratory reports that the water is safe. A safe report indicates that E.coli and total coliform bacteria are absent. Have the well tested again in about two weeks to make sure the disinfection has been completely effective.

For more details about cleaning flooded wells or other flood preparations, visit NDSU’s flood information website at http://www.ag.ndsu.edu/flood.


NDSU Agriculture Communication - April 14,2011

Source:Tom Scherer, (701) 231-7239, thomas.scherer@ndsu.edu
Source:Roxanne Johnson, (701) 328-7240, roxanne.m.johnson@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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