BE AWARE THAT
FREE WATER TESTS CANNOT and DO NOT DETECT MOST OF THE TOXIC
SUBSTANCES AND DISEASE CAUSING ORGANISMS THAT MAY HARM YOU!!! OUR ANALYSES DO!!!
Shock Chlorination of Wells and water storage reservoirs
(we have a
and toll free technical support available to help you do this correctly - rather
Bio-films are layers of bacteria and their organic products that attach to the
interior walls of water distribution pipes, appliances, water filters,
purification devices, and to one another. This bacterial community traps
nutrients, other microorganisms, and waterborne pathogens to eventually form an
almost impenetrable material. Almost immediately after attaching itself to
pipeline walls, the organism begins building upon itself, adding layer upon
layer, forming a plaque-like coating similar to the plaque that forms on teeth.
If you’ve had your teeth cleaned, you know how difficult that coating can be to
remove. For shock chlorination to be most effective, as much of this biofouling
layer should be removed as is practical. Small pipe interiors are sometimes
impossible to access, but larger tanks and other areas that can be accessed
should be mechanically scrubbed before proceeding. Because this biofilm protects
microorganisms from the disinfectants that are used to kill them, “infected”
systems that are positive for Iron Reducing Bacteria, Slime Bacteria, or Sulfur
Reducing Bacteria, should be disinfected using the higher dosages and longer
exposure times, and residual testing should be done to assure adequate
any of the following occur, you should have bacterial testing done to determine
the cause, and then treat the system accordingly.
Reduced well yield
Restricted water flow in distribution lines
Staining of plumbing fixtures and laundry
Clogging of water treatment equipment
Rotten egg odor
Slime growth – especially apparent on inside of toilet tanks and other
Proper and effective shock-chlorination procedure requires:
A dose of 50 to 200 ppm of free chlorine evenly distributed through out
the piping and fixtures
Testing of the residual to verify that the levels are present at the
fixtures and hose bib or valve sections.
Contact time with the piping, undisturbed for 12 to 48 hours. The longer
contact time the better the result.
Retesting of the chlorine residual after 12 hours
the chlorine residual is less than 10 ppm after 12 hours, repeat the entire
procedure above. If the beginning dose is 50 to 100 ppm and the remaining
residual after 12 hours is less than 10 ppm, this indicates severe bio-fouling
or large amounts of dirt or slime present.
Shock chlorination is a relatively inexpensive way to control bacterial growth
in a well and its distribution system. However, it will not eliminate the source
of the problem, so it is very important to identify the source and correct any
problems that can lead to recontamination of the well and distribution system
before shock chlorinating.
Proper shock chlorination will disinfect:
The entire well depth
The porous water-yielding geological formation around the bottom of the
The pressure system
Some of the water treatment equipment (CAUTION – some water treatment
equipment will be permanently damaged by chlorine, or will be rendered
ineffective, so be sure to check that each element in your water purification
system can tolerate chlorination. If not, remove it, divert chlorination around
it, or plan to replace it after shock chlorination is completed. This includes
all filters in the system.)
The distribution system
shock chlorination will NOT do.
It will not eliminate a contamination source leaking into your system
It will not kill cryptosporidium or giardia cysts, and some other hardy
It will not remove problems that arise out of the presence of chemicals
in the water. It will not detoxify most chemical contaminants.
Iron or Sulfur or Slime bacteria have been found in the system:
They may not be eliminated in a single shock chlorination. You may need to
repeat the procedure several times. In some cases after a second or third
shocking, the problem is solved, and no further symptoms are encountered.
However, if this is not the case with your system, there are several options
Make chlorine-shocking part of your annual well maintenance program.
Usually shocking once in spring and once in Fall is enough. In some cases, once
a year is enough
Install a continuous chlorination system to chlorinate the well at levels
just high enough to prevent further microbial growth
very severe cases the pump may have to be removed and chemical solutions added
to the well with vigorous agitation carried out with special equipment. This is
to dislodge and remove bacterial slime and biofilm. A drilling contractor should
do this. Thankfully, in White County, this is almost never the case.
Sources of chlorine:
Household bleach from local retail stores. Do NOT use bleaches with
special additives, fragrances, or enzymes etc.
12% Industrial sodium hypochlorite and 70% high test hypochlorite are
water treatment suppliers
swimming pool maintenance suppliers
dairy equipment suppliers
some hardware stores
Before you begin the shock chlorination process, run some fresh water into a
five gallon container. If concentrated chlorine accidentally comes in contact
with your eyes or skin, use this fresh water to flush the affected area for
10-15 minutes. If you get some of the chlorine solution in your eyes, see your
doctor after thoroughly flushing the affected eye.
A second safety practice is to wear appropriate safety clothing and equipment.
Wear goggles to avoid contact with the strong chlorine material and your eyes.
Wear a pair of rubber gloves to protect your hands and rubber boots on your
feet. To prevent discoloration of your clothing, wear a waterproof suit,
coveralls or a full-length apron.
Never mix acids with chlorine – it produces toxic gases.
Do not mix chlorine while standing in a depression or enclosure. The chlorine
gas will build up around you and can quickly kill an unsuspecting individual.
Shock chlorination of the well consists of mixing sufficient chlorine-based
chemical with the well water to create a solution containing 200 milligrams per
liter (mg/l), or parts per million (ppm) of chlorine throughout the entire
system (well, distribution pipeline, water heater, pressure tank and other
Remember that chlorine is very volatile so it is dangerous to work with in
Make sure the work area is well ventilated. Prepare a mixture of one-half gallon
of household bleach per 5 gallons of fresh water. Disinfect the well pit, spring
house or other portions of the distribution equipment that may contribute
bacteria to the water supply (pump, motor, pressure tank and exposed wiring
Drain as much water from the system as possible. For systems with pressure
tanks containing a bladder, the rubber air-water separator inside the tank could
be damaged by the chlorine solution. Check manufacturers' recommendations to
determine if the pressure tank should be bypassed. For pressure tanks without
bladders, release the air so that the tank can be filled with chlorinated water.
Drain water from the water heater so that chlorinated water can be circulated
through the hot water pipelines.
Backwash and clean water softeners, sand filters and iron removal filters with
a strong chlorine solution. Do not chlorinate activated carbon filters
since these filters will remove the chlorine until they become overloaded.
Activated carbon filters should be removed from the distribution system until
after chlorine has been flushed from the system.
Determine the amount of chlorine product required for a 200 ppm solution.
Table I lists the product amounts needed to create a 200 ppm chlorine solution
using typically available sources. If you decide to purchase laundry bleach, you
will need 3 pints of bleach per 100 gallons of water in the well and
distribution system. For our example, you would
need to purchase 14 pints or 1.75 gallons of liquid laundry bleach. You would
determine this by using the
worksheet at the end of this article (477 gallons divided by 100, multiplied
by 3 pints per 100 gallons, and divided by 8 pints per gallon is equal to 1.75
Table I: Amount of Chlorine Product required to create a chlorine concentration
of about 200 ppm
Amount per 100 gallons of water
Household Chlorine Bleach (5.25% NaOCl)
Commercial Strength Bleach (12-17% NaOCl)
Chlorinated Lime (25% CaOCl2)
Calcium Hypochlorite (65-75% Ca(OCl)2)
water containing iron, hydrogen sulfide, or organic substances may require more
chemical to create a 200-ppm solution. Chlorine combines readily with these
materials, making some of the chlorine ineffective as a disinfectant.
How to calculate what you need:
Volume of Water
1. Depth of Well
2. Depth to Water
3. Total depth of Water (#1- #2)
4. Diameter of Well (Measure inside diameter of well in
5. Calculate Volume of Water per Foot using (23.5 X #4/24 X
Ex 23.5 X (30¸24)
23.5 X 1.5 X 1.5 = 52.88
6. Total Volume of Water in Well #3 X #5;
Ex. 10ft X 52.88gal/ft =
7. Volume in Storage Tank, cistern or Reservoir (in gallons)
8. Volume in Distribution System Pipelines (estimate in
9. Water Heater (in gallons)
10. Pressure Tank (in gallons)
11. Entire System Volume = (#6 + #7 + #8 + #9)
Calculate the amount of Chlorine Product to achieve 200ppm for the particular
Chlorine product used
Chlorine Product and Calculation
Amt / 100 gallons
12. Amount of chosen product needed per 100 gallons (ex 4
ounces Calcium Hypochlorite is needed per 100 gal)
13. Entire System Volume
Calculate total product needed:
#12 X #13 =
Ex 4 ounces X 16.38 =
Introduce the chlorine material into the well and distribution system.
The best way to introduce chlorine material into the well or storage tank is to
dissolve the chlorine in a 5-gallon bucket of fresh water. Be sure the bucket is
plastic and has been thoroughly washed. Then pour the chlorine solution into the
well or storage tank. Try to splash the solution on the sidewalls of the well or
storage tank casing as much as possible. Attach a hose to the water hydrant or
faucet nearest the well or storage tank and run water through the hydrant and
back into the well or storage tank. This will thoroughly mix the chlorine
solution and well or storage tank water. A larger container can be used, and the
chlorine solution siphoned into the well, but this is a bit more risky.
After the chlorine has been placed in the well or storage tank, and the casing
has been washed down, move around the water distribution system and open each
faucet (hot and cold), hydrant or other water outlet including dishwasher,
washing machine, water heater, etc.. (Consult your water treatment equipment
supplier to find out if any part of your system should be bypassed to prevent
damage). Allow water to flow until a strong chlorine odor reaches that position
in the system. Then close the valve at that location. Do this with all faucets,
hydrants and other outlets in the system.
a strong chlorine odor is not detected at each site, add more chlorine to the
well or storage tank. This may be an indication that your well or water storage
reservoir contains iron, hydrogen sulfide or organic materials (ex. Biofilm).
This lack of odor is caused by the chemical removal of chlorine when it reacts
with ionic or organic matter in the water or biofilm.
the chlorine disinfect the system.
The most difficult step is to refrain from using water from the well or water
storage reservoir so that the chlorine can disinfect the system. The system
should remain idle for at least 8-48 hours, preferably overnight. Longer is
the system to remove the chlorine.
After the water system chlorination has been completed, the entire system must
be emptied of chlorine and thoroughly flushed with fresh water. Open an outside
tap and allow the water to run until the chlorine odor dissipates. Make sure to
direct this water away from sensitive plants or landscaping. Distribute the
wastewater on gravel roads or other areas without plants or aquatic life, which
it might harm. Do not allow the chlorinated water to enter the septic
system. If possible, attach a hose to outlets inside the house and
distribute the water to a non-grassy area away from the house. The chlorine will
eventually evaporate into the atmosphere. Flush the chlorine from the hot water
heater and household distribution system. The small amount of chlorine remaining
will not harm the septic tank.
Backwash and regenerate any water treatment equipment.
Chlorine compounds are volatile so they will degrade with time. Purchase only
what you'll need and use it all. Always read and follow manufacturers'
recommendations. When using chlorine bleaches, do not purchase bleaches that
have scents or other additives. Do not add other cleaning materials to the
chlorine solution. Some combinations of chlorine and acids or ammonia could
produce dangerous gases.
sure all work areas are well-ventilated.
How To Perform a Shock
Chlorination: Abbreviated Version
Shock chlorination is the addition of chlorine for disinfecting a water
supply system including the well, and all distribution pipelines. Shock
chlorination is recommended when Coliform bacteria are detected, or after system
repairs. Treated water, with a concentration of at least 200 ppm, is pumped
throughout the distribution system and allowed to set for at least 24 hours
before flushing with untreated water
From the Cooperative Extension Service:
Shock chlorination is recommended whenever a well is new, repaired or found to
be contaminated. It is essential following a flood or entrance of surface water
into the well. It is also done to control nuisance problems such as iron
Before shock treatment, warn everyone not to use the water. Children and elderly
persons in the household may require special care. Strongly chlorinated water
(less than 500 ppm chlorine) is not harmful to livestock but they will refuse to
drink unless very thirsty. Make provisions for drinking water before doing a
shock chlorination treatment, particularly if the solution is to be left in the
Be sure you have all the needed materials and equipment before beginning this
- Remove all loose or
foreign debris and thoroughly clean the well house or storage tank. Scrub
accessible interior surface with a strong chlorine solution (1/2 gallon bleach
per 5 gallons water).
- Mix 2 quarts of
household bleach (5.25 percent available chlorine) in 10 gallons water; pour
into well while pumping.
circulate solution until strong chlorine odor observed at all taps
continue circulating one hour
close taps and stop pump
- Mix additional 2
quarts bleach in 10 gallons water; pour into well without pumping.
allow well to stand at least 8 hours (preferably 12-24 hours)
pump water to waste, away from grass and shrubbery, until chlorine odor
chlorine may persist 7-10 days
- After complete
chlorine removal (1-2 weeks after flushing), test water for biological
- Repeat testing in 2-3
If bacteriological problems persist following shock chlorination a definite
health hazard exists, and the problem must be identified and eliminated or a
continuous chlorination system may be required.