Instructions for disinfection of water supply wells

All water supplies should be disinfected upon completion of construction, maintenance, repairs, pump installation, and after a positive water test result.

You will need to know how deep your well is.
Use the following formula to determine the amount of water in the well.

A = Diameter of pipe or well tile in inches
B = Number of feet deep (well)

Formula: (A x A) x B x 0.041 = gallons of water

Example: 6' well and 100' deep

(6 x 6) x 100 x 0.041 = 148 gallons of water

Amount of chlorine to use: 3 ounces of hypochlorite per 100 gallons of water

Chlorination

1. Chlorine should be placed in the well in sufficient quantities to produce a chlorine residual of at least 100 parts per million (ppm) in the well.
2. A chlorine solution may be prepared by dissolving high-test calcium hypochlorite, 70% available chlorine, (HTH, Chlor-Tabs, etc.) in water. Hypochlorite is available where swimming pool chemicals are sold.
3. Avoid using stabilized chlorine tablets or hypochlorite products containing fungicides, algaecides, or other disinfectants.
4. Follow manufacturer directions for storing, transporting, and using calcium hypochlorite products. About three ounces of hypochlorite containing 65 percent to 75 percent available chlorine is needed per 100 gallons of water for at least a 100 ppm chlorine residual.
5. Place the chlorine in the well by one of the following methods:
   1. Chlorine tablets may be dropped in the top of the well and allowed to settle to the bottom. -or-
   2. Unscrew the short vent pipe on top of the well casing. Use a funnel and pour the chlorine solution into the well.
6. Agitate the water in the well to ensure thorough dispersion of the chlorine.
7. The well casing, pump column, and any other equipment above the water level in the well should be thoroughly rinsed with the chlorine solution as part of the disinfecting process.
8. The chlorine should stand in the well for a period of at least 24 hours.
9. After 24 hours the well should be pumped to an outside faucet until the system is clear of the chlorine before the system is placed into use. Do not run water into sinks or bathtubs, as the chlorine can damage the septic system. Another coliform bacteria test is recommended after about 30 days or sooner, if no chlorination odor is detected.

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• North Carolina Environmental Health Website
• North Carolina Environmental Health Administrative Rules
• North Carolina Division of Water Quality
• What's in your Water
• Water Quality & Health Council