Shock
Chlorination of Wells and Springs
A Common Problem
Bacterial
contamination is one of the most common water quality problems among private
water systems.
Surveys
have shown that approximately 40 percent of wells and springs contain coliform
bacteria. These bacteria are a potential problem because they may cause serious
gastrointestinal illnesses.
Homeowners
often assume that a positive test for coliform bacteria in their well or spring
indicates a contamination problem that must be treated continuously with a
disinfection treatment system like ultraviolet light or chlorination.
However,
some positive bacteria tests are the result of a less-serious, one-time
contamination incident. For example, bacteria may be introduced when a new
submersible pump is installed in a well or from surface runoff during an
unusually heavy rainfall.
Shock
chlorination is a simple and inexpensive process that can be used to disinfect
water supplies that have been contaminated as a result of these one-time
contamination incidents. When done
After
following the procedure outlined below, retest your water for coliform bacteria
approximately two weeks after the shock chlorination.
If
no coliform bacteria are present, wait an additional two to three months and
have the water tested again. If the bacteria return in either of these
subsequent tests, a continuous disinfection treatment system will be necessary
to correct the problem.
When to Shock Chlorinate Your Well
or Spring
* After construction of a new well (many well drillers
do this as a standard practice)
*
After working on an existing well or installing a new submersible pump
* After
receiving a positive water test report for coliform bacteria
Disinfection Procedure
- Wells
If
your water is cloudy or contains any suspended particles, the well should be
pumped until the water clears. Cloudy water will greatly reduce the ability of
the chlorine to kill bacteria.
Unscented
household chlorine bleach containing 5.25 percent available chlorine may be
used to shock chlorinate private water supplies; however, only chlorine
products with label information specifying
Use
the table on the next page to determine the amount of bleach you will need.
Note
that the water depth shown in this table refers to the actual depth of water in
the well and not the total depth of the well. In some cases, it may be
difficult to determine the actual depth of water in the well.
In
these cases, use a minimum of ½ gallon of bleach if you estimate the water
depth to be less than 80 feet and the well diameter is 8 inches or less.
For
wells with greater water depth and diameter, use one gallon of bleach. It is
always better to use too much chlorine rather than too little!
Remove
the cap or seal from the top of the well and mix the chlorine with 5 to 10
gallons of water in a non-metallic container. Pour this solution into the well.
Inside
the home, turn on all of the faucets (one at a time) until a strong chlorine
odor is noticeable at each tap. This will ensure that the chlorinated water has
been dispersed throughout the plumbing system.
Allow
the water to sit in the plumbing for a minimum of six hours and preferably 12
hours. Flush all of the indoor faucets by letting them run until the chlorine
smell dissipates to an acceptable level. Note that complete removal of the
chlorine smell may take several days of normal water use.
- Springs
Proper
shock chlorination of a spring is difficult because the water often runs
through the spring box too quickly to provide adequate contact with the
chlorine to kill bacteria.
Shock
chlorination of a spring can be attempted by mixing about ½ cup of household
bleach with five gallons of water and use this solution to scrub the walls of
the spring box.
Estimate
the volume of water in the spring box in gallons (there are 7 ½ gallons of
water in each cubic foot of storage).
For
each 100 gallons of water in the spring box,
Pour
the disinfection solution into the spring box. Use the instructions above to
disinfect each of the faucets in the home and run the water to a disposal site
the next day.
Because
of the prevalence of bacteria in springs and the difficulty in adequately shock
chlorinating the spring source, it is often necessary to install continuous
disinfection treatment equipment for spring sources that test positive for
coliform bacteria.
The
first water used following chlorination will have a chlorine concentration
about the same as used for bleaching laundry. It may be used for cleaning or
run on the ground. Bare ground is best, sprinkling on grass is ok, do not apply
to foliage of ornamental shrubbery or to any water body containing fish.
Related Posts:
Bryan
R. Swistock, Extension Associate
William E. Sharpe, Professor of Forest Hydrology
Paul D. Robillard, Associate Professor of Agricultural
Engineering
http://www.water-research.net/Waterlibrary/privatewell/shockchlorination.pdf
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