The following is a state suggested formula for using bleach to disinfect a well:
1. Remove well cover. Pour the required amount of bleach into the well. SEE TABLE BELOW.
2. Run ALL faucets in the house, one at a time, until you smell the chlorine at the faucet.
This ensures that the whole system will be disinfected.
3. Connect a garden hose to an outside tap or an indoor tap with the correct thread fitting. Put the other end of the hose into the well, turn on the faucet, and from time to time move the hose so that the chlorinated water bathes the sidewalls of the well casing. Do this for at least six hours. Turn off tap and remove the hose from the well.
4. Replace the well cover.
5. DON’T USE THE WATER for at least twelve hours. Forty-eight hours in optimal.
6. Run the water to waste but NOT IN THE SEPTIC SYSTEM for several hours, or until the chlorine taste is dilute enough to be unobjectionable. The best way to run the water to waste is to use the garden hose mentioned above (item 3). Direct the hose into an area where the chlorinated water will not cause environmental damage or affect the water supply of others. For a typical well, this may take 3-4 hours.
NOTE: To avoid pump overheating and possible damage, turn off the water when flow is at a trickle and wait at least 15 minutes before turning on the pump again.
7. After a week of use, retest for bacteria.
8. In some cases, one chlorination treatment WILL NOT be sufficient. Repeat disinfection procedures as needed. You can also use calcium hypochlorite granules to provide a continuous release of chlorine in your well.
It is my opinion that you can never entirely disinfect a contaminated well. Think about it. You're using chlorine to attempt to eliminate every single individual bacteria. No. What you're doing is buying some time. The population will slowly rebuild. When you use chlorine you also release dangerous trihalomethanes into your water supply. These are very dangerous but can be removed with the proper filtration.
I recommend using hydrogen peroxide in place of chlorine. Both are oxidants. Hydrogen peroxide does not last as long in the well. It dissipates, converting to water and oxygen. Thus, you may have to repeat the treatment more often, but the byproducts are not hazardous. Apparently though if you have bromides in your well it can convert these to bromates which do have health impacts. As always, it is best to test before proceeding. The following instructions provide a thorough disinfection.
Some people recommend the use of calcium hypochlorite granules to provide slow release of chlorine in a well to control bacteria, iron, or hydrogen sulfide odors. This will also provide a constant source of carcinogens.
I try to stick with all natural non-toxic methods whenever possible.
If you have a problem with bacteria I would recommend that you also install a 5 micron filter, followed by an Ultra Violet light. This will kill the bacteria as they enter your home.
Further thoughts....
Be aware of activities in your community that can put your drinking water at risk. Talk to your neighbors to determine if problems with your drinking water are individual or community-wide. Check out the history of the area in which you live to determine if past activities are having a present impact on your drinking water.
And manage your own septic tank if you have one. Replenish it on occasion with bacteria (I use Roebic K-37, which you can buy at any hardware store) to aid in digestion and limit your use of chemicals in the house, such as bleach, Lysol, and other sanitizers, that will kill the bacteria in the septic. Visit my link on using natural cleaning products to learn more.
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