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The Frederick County Health Department supplies the following information to citizens whose well water is contaminated. The department recommends the following procedure for chlorinating a contaminated well.

  1. Before treatment, turn off the pump breaker before removing the well cap to eliminate shock hazard.
  2. Remove the wires on the top of the well and move them outside the well casing, making sure water which will be recirculated from an outside hose, does not splash on the wire connections. We suggest protecting the connections with a plastic bag.
  3. Turn well pump on and attach a hose to an outside spigot near the well. For each 150 feet of well depth, add 1 gallon of household bleach containing approximately 5% chlorine, directly into well. Recirculate water through the hose and into the well until an odor of chlorine is detected coming out of the hose. Turn on all household taps (including toilets, sinks and washing machines).  The chlorine must reach all fixtures of your plumbing system for a minimum of three minutes. Once chlorine is detected, turn off pump and place the wires back into well and tighten well cap.  The well should be left undisturbed for a period of 12-24 hours.
  4. After the standing period, run water from the system from an outside hose avoiding septic and well areas, as well as natural streams.  Pump the water for one half hour, let it stand for one hour and pump for another half hour, repeating until you can no longer smell the chlorine.
  5. If your well is a low-yielding well or you are chlorinating during a drought season, you should avoid rushing the chlorine out of the system.
  6. At the completion of the chlorinating process when no chlorine can be detected in the water, the water should be retested.


If water fails after initial chlorination, repeat the process with the following change in step 3:  Add 10 oz. Of Powder shock which contains 65% chlorine.  Powder Shock can be purchased at most area pool retail stores. This powder should be added to one gallon of water, mixed and poured directly into well.



If water fails after second chlorination, repeat the process with the following change in step 3:  Add 3-4 large chlorine tablets, or 6-8 small chlorine tablets directly into well.  These tablets contain approximately 90% chlorine. These tablets can be purchased in most area pool retail stores. Please note that ALL of the chlorine must be out of the system before a valid sample can be taken.