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Ohio Department of Health -
Bureau of Environmental Health
Disinfection Fact Sheet for Flooded Drinking Water Wells
Simple Procedures for Homeowners
The following well disinfection procedures may be carried out by
homeowners on an existing well after flooding of the well has
occurred. During
flooding, contaminated water enters the well casing and forces
flood water out into the geologic formations providing the water
supply. This water
will need to be removed from the well and then the well must be
disinfected. A
total coliform bacteria sample is used as an indicator of
unsanitary conditions. If total coliform or e-coli positive
samples persist, then an experienced registered private water
systems contractor should be contacted to professionally
disinfect your well using superchlorination methods.
Step 1. Pump the Well.
Turn on as many faucets in the home as possible, and run the
water for several hours (24 hours if possible) to waste in the
yard or other drainageway.
The well should be heavily pumped to remove as much flood water
as possible from the casing and the geologic formation.
When a well is flooded, the contaminated water enters the well
and can move out into the geologic materials that supply water
to the well.
Overpumping well help remove flood water from the ground water
supply. Do
not discharge this water to the septic system, as it will
cause the system to become overloaded.
Step 2. Determine the total volume of water stored in your well.
The volume of chlorine used for disinfection depends on the
total volume of water stored in the well casing and the
distribution lines (plumbing).
The total volume of water stored in the well casing can be
calculated based on the total depth of the well and the static
water level in the well.
Information on the total depth and static water level (water
level under non-pumping conditions) of the well can be obtained
from the well log.
The well log is a record of the construction, depth and geologic
materials encountered in the well and is filled out by the water
well driller. After
the well is drilled, copies of the well log are filed with the
Ohio Department of Natural Resources, Division of Water, the
local county health department, and a copy is provided to the
well owner. If you
do not have a copy of your well log,
search the ODNR website, or contact ODNR, Division of
Water at (614) 265-6740.
The total depth of the well will be recorded at the right side
of the well log, and the static water level will be recorded
under the well test section of the well log.
Subtract the static water level from the total depth of the well
to determine the total feet of water held in the well casing.
Step 3. Determine the volume of chlorine to use for
disinfection.
Once the total feet of water stored in the casing is known, then
the volume of water stored in the casing can be calculated based
on Table 1. Take
the total feet of water stored in the well, and based on the
well diameter, multiply the total feet times the appropriate
gallons per foot of water.
Example:
Total well depth is 100 feet, static water level is 60 feet,
well casing diameter is 5 inches.
100 feet - 60 feet = 40 feet of water in the well casing
From Table 1, a 5-inch casing has 1 gallon stored per foot.
40 feet of water in the casing x 1 gallon per foot = 40
gallons volume of water in casing.
Table 1. Volume of water in well
Diameter of well |
Gallons per foot of water |
3 |
0.37 |
4 |
0.65 |
5 |
1.0 |
6 |
1.5 |
8 |
2.6 |
The total volume of chlorine to be used for disinfection can be
calculated based on the Table 2.
For the example cited above (40 gallons of water in the well
casing), use approximately one-half of the amount of chlorine
necessary to disinfect 100 gallons.
Table 2. Amount of chlorine added to 100 gallons of water for
disinfection
Chlorine concentration |
Gallons of 5.25% sodium hypochlorite - liquid bleach |
Pounds of dry calcium hypochlorite |
Minimum contact time |
250 ppm |
0.5 gallon |
0.38 pounds |
8 hours |
500 ppm |
1 gallon |
0.75 pounds |
8 hours |
If the total volume of water stored in the well casing is
unknown then add two gallons of fresh 5.25 % unscented laundry
bleach, also called sodium hypochlorite, to five gallons of
water. Mix the solution in a new clean garbage can, or clean a
garbage can and line it with a new plastic garbage bag.
Laundry bleach loses its? effectiveness the longer it sits on
the shelf in the store or in your home. Solid chlorine pellets,
which are 65% to 70% calcium hypochlorite, should be dissolved
in a five gallon bucket of water. Be aware that some solid
chlorine products used for swimming pools may have additional
chemicals, such as algaecides, in them and should not be used
for well disinfection.
Place the can next to the well to pour the solution or siphon
the chlorine solution from the can to the well.
Step 4. Add the chlorine solution.
Remove the cap from the well.
Pour this solution directly into the well.
Step 5. Add vinegar.
Add 1 quart of white vinegar to a five gallon bucket of water
for each 100 gallons of water stored in the well.
If the total amount of water stored in the well is unknown, add
2 quarts of vinegar.
Add this solution to the well.
Step 6. Flush and recirculate.
With a garden hose, re-circulate this solution back into the
well washing down the sides of the casing for about ten minutes.
Debris may begin to slough off the side of the casing, and iron
or manganese in the water may begin to turn solid as the
chlorine reacts with the minerals.
Turn on all faucets
connected from the well throughout the house and outside the
house. Make sure to turn on faucets that rarely or never get
used, especially yard hydrants.
Remember to run water into the washing machine and flush all
toilets. Run the water until the chlorine smell is detected.
Do not by-pass the water softener or the water heater.
The water softener and water heater must be disinfected
also. The resin bed of the water softener can provide a place
for bacteria to grow. Remove and discard any carbon filters or
cartridge filter elements and thoroughly clean the inside of the
filter housing.
Step 7. Maintain sufficient contact time.
Once the odor of chorine is detected in all water lines, shut
off the faucets and let the water sit in the plumbing for at
least 24 hours.
Step 8. Flush the chlorine from the water system.
After 24 hours have elapsed, run the water to waste until the
entire odor of chlorine is gone.
This will take a while depending on the volume of the well and
the plumbing. Do
not run the water into your septic system as this will cause
the system to become overloaded.
Step 9. Retest the well for total coliform.
Wait a minimum of 48 hours, then contact the local health
district to have another sample collected for total coliform
bacteria. Make sure that the water is checked for chlorine
before collecting the water sample. If there is any indication
of chlorine in the water, the sample should not be collected.
This helps avoid getting an indication of a safe sample that may
be due only to the continuing activity of leftover chlorine and
may not reflect the true condition of the water. Do not replace
carbon filters or filter elements until a coliform negative
sample has been achieved.
What if the well tests positive for total coliform after
disinfection?
There are many instances where the previously described
disinfection procedures may not work in making a water well
bacteria free. In some cases the pH of the water may need
further adjustment in order to get the optimum disinfection from
the added chlorine, or superchlorination procedures may be
required. The well casing may also need a thorough scrubbing or
cleaning to remove flood sediment, or non-pathogenic slime
forming or iron bacteria that can build up on the well casing
and borehole walls.
This type of cleaning is best performed by a registered
contractor. If
total coliform or e-coli bacteria persist in water samples then
contact an experienced registered private water systems
contractor to professionally disinfect your well.
Contact your local health district when you experience
any problems with your well or for assistance.
The Ohio Department of Health registers and bonds private water
systems contractors.
Please contact your local health district or check
the
ODH list
( Adobe Acrobat Reader Required -
Download here if needed)
of registered contractors.
Residential Water and Sewage Program
Bureau of Environmental Health
Ohio Department of Health
246 N. High St.
Columbus,
Ohio
43266-0118
(614)466-1390
www.odh.state.oh.us
August 2003
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