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Emergency Water Well Disinfection
By: National Groundwater Association

February 2005

This advisory is designed for the treatment of wells under emergency conditions with limited equipment. Do not over treat wells with excessive chorine. Be sure to leave the chlorine solution in the well for at least 6 hours. Any circulation of the chlorinated water in the well hole will improve disinfection.
1. Disconnect the well from any water distribution system
2. Begin pumping the well to flush the salt water and any debris from the well.
3. While the well is pumping, clean up any debris from around the well. Remove any standing water and taper the soil away from the well head, so that surface water drains away from the well.

The well will have to be pumped from 1 to 3 hours to remove the salt water. This can be checked by a conductivity meter.(Ocean water will average 30,000 to 50,000 micro siemens). If meter is not available dip your figure in and taste the water. A salty taste indicates the need for continued pumping. If is is likely the water is contaiminated treat the glass of water with a hypochlotie solution (5% liquid bleach) and wait several minutes. If the pumped water is not clear continue pumping uniil clear and free of sea water

4. Pump some of the clear water from the well into a drum or tank (50 gallons or 200 liters) Put a spigot near the bottom of the drum so a hose can be attached.
5. Add the amount of liquid bleach or cups (250mls) of powered calcium hypochlorite indicated in the chart below and mix. Pump or siphon the hypochlorite mix into the well. A longer hose allows a deeper placement of the disinfectant solution. After removal of the hose, the pump can be momentarily used to allow the water to rise and fall back into the well. This should be done several times to mix the chlorine solutions throughout the well. Let the well set for 6 hours or overnight, then pump the well and dispose of the pumped water until no chlorine is detected.

Smaller Diameter Well/1 cup = approx 0.25 kilometers

Approximate Dosage per Well Diameter and Water Depth in Liters of Liquid Hypochlorite or Cups of Powdered Hypochlorite.

Consideration for wells which require a large amount of hypochlorite: Wells which require more than 15 liters of liquid hypochlorite should repeat the mixing and addition procedure by preparing a tank of disinfectant for each 15 liters required. Wells which require more than 15 cups of powdered hypochlorite should repeat the procedure for each 15 cups required. This procedure is necessary to properly place the disinfectant in the borehole and provide for disbursement throughout the well and surrounding formation. If you have a well with larger diameters please The National Ground Water Association email: or call 614-898-7791