Instructions to Shock Chlorinate a Well or Cistern

The following procedures (adapted from several sources including Water Conditioning & Purification, May 99) will successfully decontaminate your entire household plumbing from the well to the various taps and can be used to temporarily eliminate bacteria and/or hydrogen sulfide odor. Most people prefer to have a well service company shock their well but for those who would like to do it themselves, here are some guidelines and procedures for shocking a standard construction well with a submersible pump. Some well contractors may not take as much care as is described below so if the job is hired out, this document will enable the homeowner to ensure that the procedure carried out is thorough and complete.

Preparation

• Since the entire process may take up to 24 hours, you should set aside a supply of fresh water for drinking and cooking, although a limited amount for toilets and hand washing can be used. Because the water will have a high level of chlorine, it would be best not to use the water for laundry, cooking, drinking, or bathing.
• Ordinary household bleach (5.25%) – not scented – should be used. Use the table below to determine the appropriate amount of bleach. The depth of water in the well is the difference between the depth of the well and the static water level. Dilute the suggested amount of bleach – one part bleach to 10 parts water – in a clean 5-gallon bucket.
• If you have a reverse osmosis unit for your drinking water, shut off the supply line before proceeding.
• Be aware that a large dose of chlorine to your septic system can upset the bacterial balance.

Chlorine Required to Dose 100ft of Water at 100ppm Chlorine

Procedures For The Well (if you do not have a cistern)

1. Connect a hose to an outside faucet and run hose to the well. Remove well cap to allow direct access to the well.
2. Prepare bleach mixture in a bucket. You may have to make up several batches to get all the required amount of bleach.
3. Pour bleach mixture into the well casing.
4. Run water through the hose and into the well at full force until the water coming out of the hose smells strongly of chlorine. Depending on the depth of water in the well, you may have to run the hose for 15-30 minutes. If no chlorine odor is noticeable, add more chlorine mixture.
5. After you notice the chlorine smell, continue running the water for 20-30 minutes or until approx. 100-200 gals of water have been run back into the well. This will insure a good mix of the water in the well.
6. Then spray the walls of the well along with the seal, cap, or concrete lid to disinfect the inside of the well. Then reseal the well and spray the outside of the well, being careful of the electrical wiring.
7. Turn off the hose and open one inside cold water faucet and let it run until you smell the chlorine then turn off the faucet.
8. If you have a softener, bypass the softener at this time. You will have run some chlorinated water into the softener by doing step 7 above which will disinfect the resins. If you leave the softener in line after this point (not bypassed) you run the risk of damaging the resins.
9. Then run each cold water faucet in the house shutting it off as soon as you smell the chlorine. Include toilets, ice makers, outside spigots, and any other water using appliance.
10. Use hot water for normal operations like clothes washing (whites), dishwashing, etc (or just drain the hot water tank) and eventually the chlorine will come through the hot water tank. Then run hot water lines one at a time at sinks, tubs, showers, dishwasher, washing machine, etc. to bring the chlorine to the taps. At this point, all of the piping will be in contact with the chlorine.
11. Then let the system "sit" overnight – ideally 12-24 hours. (Contact may need to be longer if attempting to reduce hydrogen sulfide producing bacteria.)
12. Then to remove the chlorine, the well and/or cistern must be emptied of the chlorinated water. Use a hose to run this water into an area you don't care particularly about. In the winter, or when water supply is limited, you may want to have an alternate source of water for drinking, cooking, watering inside plants, etc., to be used until the chlorine has cleared. This water can be very rusty. Run it until it looks clear and has no residual chlorine odor.
13. Run indoor spigots until they are clear of chlorine odor.
14. If applicable, as soon as there is no chlorine residual remaining, which you can check with an inexpensive chlorine test kit, (it may take several days) you can safely turn your RO/softener, etc. units back on.

Procedures for the Cistern

A cistern will need to be chlorinated separately. To do this, be aware that the volume of the cistern (from 500 to 2500 gal) is a factor in the dilution of the chlorine. (Use about 1 gallon of bleach per 500 gallons in the cistern).

1. Direct a hose into the cistern and create a swirl in the entire volume of the tank.
2. Add the chlorine while continuing to hose water into the cistern. Continue this process until the water from the hose smells of chlorine, then wash down the walls and lid of the tank.
3. Then carry out the above process for the well but note that during the hosing down of the well, that only a low cistern level will trigger the well pump. You may have to run enough water out of the cistern to turn the well pump on. Then run the chlorinated cistern water through the hose to the well to wash the well down.
4. After the “sitting” period of time, clearing the cistern of chlorine will require a long time and a lot of water. If the well runs direct to the cistern, for an initial clearing, start draining the cistern and allow the well pump to run for 20-30 minutes, then you can turn off your well pump while you drain the rest of the cistern. If your cistern pump is not protected, be very certain that the cistern pump does not run dry.
5. Then turn on the well pump to refill the cistern. The initial well pump run should have cleared most of the chlorine from the well. You may have to repeat this process to clear the chlorine.

NOTES

• The amount of chlorine you will use in this process is basically determined by the volume of water that needs to be treated. The standard for well drillers and pump installers is putting in 100 parts per million (ppm) to disinfect the well after their work.
• If you can’t get the bleach solution into the well, contact your well contractor.
• If your water has high iron or sulfide levels, more chlorine may be needed than indicated in the table above.
• You may get colored water when you flush the system the next day - this is not abnormal.
• It is possible that iron deposits or other slugs of material may break free and clog the pump inlet. Do not continue to run pump if water does not flow and immediately contact your well contractor.
• Be sure to completely flush the system of chlorine; high chlorine levels can be corrosive to well component metals and pumps.
• Many people have good success controlling odor with chlorination; however, if odors persist, repeating this process within 30 days may give better results and prevent regrowth. If odors return again within several months, you should probably explore other treatment options.

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