Disinfection of Domestic Wells
To disinfect a drilled well remove the cover or vent pipe from the well cover and add household bleach to the well in the following manner:
Take one gallon of household bleach and add to it four gallons of clean water in a five gallon clean bucket. Although not absolutely necessary, you can rinse down the sides of the well casing with chlorine solution as it is poured down the well.
Open all water taps beginning with the outside taps. Let the water run until the odor of chlorine is detected. After this occurs, open each tap inside the house until you can smell chlorine. Once the odor of chlorine is detected, turn the taps off. By doing this, you have chlorine in all your waterlines.
One note of concern: If the system utilizes a bladder tank that does not have a flow through design, special precautions are needed to insure proper disinfection of the tank. After chlorine is mixed in the well and the well pump is off, open the first tap until chlorine is detected and the well pump starts running again. Turn off the tap and wait until well pump stops. Chlorine solution should then be in the bladder tank. Then proceed with opening and closing the other taps as noted.
Let chlorinated water stand in the system for at least 12 hours if possible, four hours minimum, before purging the chlorine from the system.
To purge the chlorine from the system open all the outside taps first, and let the water run until no chlorine is detected. This is done to protect the septic tank system. Then open the inside taps until the chlorine is gone. Also, do not drain the chlorine water directly into a stream.
To determine whether the water is safe to use, a bacteriological water sample(s) should be collected several days after the chlorine is out of the system.
Disinfection should be repeated if the water sample(s) indicate the presence of coliform organisms. If continued disinfection does not clear up the contamination, contact you local Environmental Health Specialist for additional advice.
If a storage tank (other than a pressure tank) is on the system, it may be advisable to add bleach directly to the storage tank at the same time you are disinfecting the well. Let the storage tank drain into the distribution system. After sitting 24 hours, drain the storage tank through a drain valve or through the system.
Again, be careful that any discharged chlorinated water doesn't eventually run into a stream, canal, storm sewer, or other waterway.