when my pump was replaced last summer they had me pour about 3/4 of a gallon of bleach directly into the well.
If the source of the contamination is within the well casing or the building, sanitizing the well will often clear up the problem. After completing the well disinfection process, be sure to re-test the water after all of the chlorine is purged from the system.
1) Mix 2 quarts of bleach in 10 gallons of water. Pour the solution into the well while it is being pumped. Keep pumping until the chlorine odor appears at all taps. Re-circulate the water back into the well (via a hose) for at least an hour. Then close the tap and stop the pump.
2) Mix 2 more quarts of bleach in 10 gallons of water and pour this chlorine solution into the well. Allow the well to stand idle for at least 8 hours and preferably 12 to 24 hours.
3) Pump the well to waste, away from grass and shrubbery, through the storage tank and taps, such as an outside connection, until the odor of chlorine disappears. The chlorine may persist for 7 to 10 days depending on how much water is used.
4) After all the chlorine is pumped out, a water sample should be collected and tested to determine whether all contamination has been eliminated. A sterile sample bottle obtained from the testing laboratory is needed to collect the sample.
Remember that disinfection is no assurance that the water entering the well is free of chemical pollution. A positive Coliform Bacteria test after sanitizing the well often indicates that the aquifer itself is contaminated and that the installation of a chlorinator or an ultra-violet light system will be required to control these microorganisms.
Good luck, Tom