Well Chlorination Procedure: when and how to shock a drinking water well InspectAPedia® -
How to shock the well - well shocking procedure
When to shock or chlorinate a drinking water well
What is the procedure to shock or chlorinate a well?
How much bleach or hypochlorite do you use to shock a well?
When should well water be re-tested after shocking the well?
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Here we explain how to shock a well, when, why, and exactly how to chlorinate a drinking water well. This is a description of the well shocking procedure using household bleach to sterilize well water and water equipment. The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at
the time of disinfection and is not intended to kill bacteria that might be introduced at a later time. Page top sketch of deep and shallow wells courtesy of Carson Dunlop.
This website explains many common water contamination tests for bacteria and other contaminants in water samples. We describe what to do about contaminated water, listing common corrective measures when water test results are
unsatisfactory. We include water testing and water correction measures warnings for home owners and especially for home buyers when certain conditions are encountered, with advice about what to do when these circumstances are encountered.
Various treatment methods for contaminated water are reviewed and the pros and cons of each are discussed.
Readers concerned with the effects of well shocking on septic systems should see CHLORINE IN SEPTIC WASTEWATER.
When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination in Well Water
This information is from the Dutchess County Health Department's environmental laboratory but you'll find that it is consistent with the well shocking or well chlorination procedures recommended by most health authorities.
The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at
the time of disinfection and is not intended to kill bacteria that might be introduced at a later time.
Our photo shows an owner who has lifted the loose, poorly-sealed well piping and cap right off of the steel well casing. This well needed repairs and it needed to be sterilized using the well chlorination procedure we discuss here.
Therefore it is vital that the well be constructed so that no new contamination may enter the well following completion of the
shock disinfection. In order to achieve a satisfactory disinfection of the system, the bacteria must be brought in contact with a chlorine solution of sufficient strength and remain in contact with that solution for a sufficient time to achieve a complete kill of all bacteria and other microorganisms.
Chlorine in Wells - Safety Warnings
When working with chlorine, people should be in a well-ventilated place. The powder or strong liquid should not come in contact with skin or clothing. Solutions are best handled in wood or crockery containers because metals are corroded by strong chlorine solutions.
Details of the Well Chlorination Procedure - Exactly How to Shock a Well, Where to Put Chlorine, How Much Chlorine to Use to Shock the Well
If drinking water has been tested and has not passed standards for safe drinking, or any time the building water supply system has been opened for repairs (such as replacing a submersible well pump or a jet pump foot valve), the well should be disinfected following these procedures, and should be re-tested as described below.
Our photo shows a standard modern 6" steel well casing - it's easy to spot at a property.
If you don't know where the well is located you'll have to find it before this well chlorination procedure can be best performed. See WELLS CISTERNS & SPRINGS for articles that describe different types of water wells, what they look like, where they're found, and their operating characteristics.
It's possible to get chlorine into the well by sending it through the building piping and pump but that step won't sterilize the interior and sides of the well casing - so the procedure below is a better one.
Pour Clorox™ Bleach (or an equivalent brand of household bleach) or hypochlorite granules down into the well. Some people use swimming pool chlorine tablets which have the advantage that they sink to and sterilize water at the well bottom, and the disadvantage that it takes longer to flush out the chlorine.
How much bleach to use when shocking a well: Health department officials can give more precise guidance about the amount of disinfectant needed based on the depth of the well. Common guidelines:
Well depth 100' - 3 cups Clorox or 2 oz. of granules.
Well depth 200' - 6 cups Clorox or 4 oz. of granules.
Well depth 300' - 9 cups Clorox or 6 oz. of granules.
Well depth 400' - 12 cups Clorox or 9 oz. of granules.
Well depth 500' - 1 gallon Clorox or 12 oz. of granules.
NOTE to be accurate in reaching the necessary concentration of chlorine in your well, treat the "depths" listed above as if they were the height of the actual column of water in your well (assuming a standard casing which is 1.5 gallons per foot of height). So if your well is 400 feet deep, but if 100 feet of it is air, your water depth is actually 300 ft.
Introduce the chlorine solution into the top of the well. Remove the cap at the upper terminal of the well casing and pour the chlorine solution down the inside of the casing. If the well casing terminates through the floor of a pump house, then the casing is required to have a well seal at the upper terminal [i.e. at the top of the casing]. This well seal can be loosened and the chlorine solution introduced into the well at that point. In a large diameter well [such as a public supply company's well], the chlorine solution should be poured or splashed around the wall of the well so that all inside surfaces of the well are brought into contact with the strong chlorine solution.
Using a garden hose, spray water down into the well pipe to wash the chlorine solution down to the bottom of the well. Ten gallons of water should be enough. [More won't hurt nor risk running the well dry since you're recycling the well water through the plumbing and back to the well.]
Turn on all cold water household taps until you can smell the Clorox coming out of the faucet farthest from the well.
Turn off the water and do not use it for 8 to 24 hours. Seal the top of the well. Do not run laundry with this chlorinated water or it may bleach clothing unexpectedly.
At the end of the standing period, operate the well pump (run the water) water until you can no longer smell the Clorox. Do not run Clorox into the septic system - run water outside through an outside faucet or hose. There should be a hose connection at the at the bottom of the water tank. When you no longer smell chlorine at the hose draining the water tank, close off the drain and open all faucets in the house to flush out house piping for fifteen minutes or until you no longer smell or taste chlorine [whichever is longer].
Retest the well water after all the Clorox or chlorine is out of the system and the water has been used for 5-7 days (typical health department guideline) or 7-10 days (my suggestion) after the disinfection.
The longer you wait until the retest the more valid will be the results. We elaborate on this point at "When to re-test your well water" below.
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General water testing and corrective measure advice: contact your local health department.
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