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Well Sanitizing

Joe Mumford Plumbing & Heating Company recommends the following procedures for sanitizing a well properly.

Try and figure out how many gallons of water is stored in your well.
Pour unscented household bleach (Clorox, Purex, etc. 5-¼% solution) directly into the well. Do not use swimming pool chlorine as it is unsuitable for use in drinking water. The chlorine can be added directly to the well casing access. (Do not introduce chlorine into the pump column, drop pipe or electrical conduits.) Use a gallon of household bleach for every 500 gallons of water in the system. For example, you will need about ½ gallon of household bleach to disinfect a well that is 200 feet deep with a static water level of 30 feet.
The chlorinated water can be circulated by pumping it from the well and discharging it back into the well through a hose. This will clean the well above the water line, and mix the chlorine and water solution. You will need to use a pool tester to see that you maintain 3 to 5 ppm chlorine solution. If it is any lower, it will not disinfect the well.
Pump the chlorinated water throughout the entire system but first drain the water heater and refill with chlorinated water from the well. Then open each tap until you can smell the chlorine coming through, shut off the tap and go to the next one. Now you should test with your chlorine tester to make sure you are maintaining the 3 to 5 ppm required for killing bacteria. Leaving a line undisinfected can recontaminate a system, so be sure to flush all toilets and open every tap, including hot water taps.
Allow the chlorinated water to stand in the entire system for as long as possible. Overnight is adequate, but twenty-four hours is better. This gives the chlorine a chance to work on any contamination that may be in the system.
Flush out the entire system until the chlorine is gone. This can take several hours and it can be difficult to determine of all the chlorine has been removed. Be sure to test this with your chlorine tester. If you have a septic system, it would be advisable to discharge the water from an outside faucet. In addition, discharged water should be disposed of in areas where no harm will occur to animals, fish or vegetation.
Once the chlorine has been removed and it has been about 4 days, then the water supply should be tested for bacteria. Only a laboratory can determine if the water is free from contamination. It is also recommended that you do not drink the water or use it for cooking purposes during the disinfection process.
If the contamination is not corrected, repeat the above procedure. Wells must be constructed so as to protect the groundwater from any surface contamination. To disinfect a well or water storage tank that is not protected from surface contamination is wasted effort.
In those instances not resolved by protection of the water source and repeated disinfection efforts, you may have to install an approved automatic chlorinator which continuously disinfects the water, drill a new well or connect to an approved public water supply.