Health officials recommend the following disinfection procedure be used to properly disinfect private wells that have become contaminated by microbiological organisms. Utmost care should be taken in conducting this procedure due to the high concentration of chlorine that is used. If this procedure does not eliminate the microbiological contamination after two attempts, a licensed water well contractor should be contacted for assistance in disinfecting the private well.
Step 1: Prepare the Solution
If you use calcium hypochlorite – (unstabilized) Note: This chemical is routinely used to disinfect swimming pools. Dissolve 2 ounces (approximately 4 heaping tablespoons) of dry chemical in 2 quarts of water. The solution should be mixed vigorously for 10 to 15 minutes and then allowed to stand until all the inert material settles to the bottom. The clear liquid should then be poured into a 5 gallon container and the container filled with water. The inert material should be discarded. This will provide 5 gallons of chlorinated water to be used in the disinfection of the well.
If you use unscented household bleach (sodium hypochlorite) - Place 4 cups (1 quart) of the bleach in a total of 5 gallons of water. This will also provide 5 gallons of chlorinated water to be used in the disinfection of the well.
Step 2: Pour the solution down the well through the vent or cap. The pump should be pulled if possible to prevent any damage to the pump. Also, the solution should be poured through a garden hose that has been run down into the well. This hose should be pulled up and down as the solution drains into the well.
Step 3: This solution should then be followed by an additional 10 gallons of water disinfected with 1/2 tablespoon of calcium hypochlorite or 1/2 cup of unscented household bleach.
Step 4: If the well pump was not pulled, the pump should be started and pumped until there is a definite chlorine odor from the water.
If the pump was pulled, every part of the pump should be disinfected with a mild chlorine solution (at least 100 mg/l) prior to placing the pump back into the well
Step 5: The chlorinated water should then be allowed to stand in the well for at least 8 hours and preferably 24 hours if at all possible.
Step 6: The well should then be pumped until no chlorine is present in the water. A bacteriological sample should be taken and sent to the Mississippi State Department of Health for analysis. It normally takes 24 hours to analyze the sample from the time it reaches the MSDH environmental laboratory. NOTE: To receive the fastest results, these samples should be hand delivered to the laboratory. If the sample is shipped by overnight courier from one of the MSDH county health departments, the analysis of the sample will be delayed 24 hours. These samples should be taken Monday through Thursday.
Step 7: If the bacteriological sample is free of coliform bacteria, the private well can be considered to be properly disinfected and free of microbiological contamination.
If the bacteriological sample is not free of coliform bacteria, the disinfection procedure should be repeated.
For more information on private water well disinfection, visit the MSDH website at www.HealthyMS.com or contact the Mississippi State Department of Health toll-free 24 hours a day, seven days a week at 1-866-HLTHY4U (1-866-458-4948.)