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1 When a laboratory analysis report shows the presence of coliform organisms, use the following procedure for well disinfection:

  1. Locate the wellhead and remove an access plug or bolt so that the area within the well casing is exposed.

 
 

  1. Using a funnel, pour in an appropriate amount of liquid chlorine bleach (Clorox, Purex, etc.).  See chlorine bleach dosage below.



    Well Depth Amount of Bleach
    Less than 100 feet 1 quart
    100 to 200 feet 1/2 gallon
    200 to 300 feet 3 quarts
    300 and greater 1 gallon or more

These dosages are approximate.  Greater amounts are recommended for excessively cloudy water.

 

  1. Using the nearest faucet and a garden hose, allow water to run through the funnel into the well for one hour.  This will circulate the chlorinated well water and improve the germ-killing action allowing all fittings and equipment in the well to be exposed to the chlorine solution.

  2. After the well water has circulated for an hour, the garden hose and funnel may be removed and the access plug replaced.  The disinfection process should be extended throughout the entire plumbing system.

  3. To disinfect the remainder of the plumbing system, turn on the next available faucet and allow it to run until the bleach odor can be detected, then turn it off.  Repeat this step throughout the plumbing system at each faucet.  Then, allow the chlorinated water to remain in the plumbing system overnight, or for 24 hours if possible.  During this time, the water should not be used for drinking or cooking.

  4. After disinfecting the well and plumbing system, flush all faucets until the bleach odor disappears and the water is clear of any debris or color.  Flush outside faucets first - you do not want to flood the septic system.

  5. Submit another bacteriological sample to determine if the disinfection process was successful.

   
Keep in mind that a single disinfection may not be sufficient because certain well systems, particularly shallow wells, hand-dug wells, wells in fissured areas, and old wells are more vulnerable to contamination.  Water from these types of systems should be checked periodically submitting samples for bacteriological analysis.

 

2 Retrace the proper steps for sampling, carefully following guidelines.  Most reasons for an unsuitable sample can be avoided.