In light of the recent natural disaster that hit southern Asia, the National Ground Water Association has developed an emergency well disinfection guide. The guide is a very simplified procedure designed for people who have no expertise with wells. Also, it can be applied to drilled wells or shallow dug wells. Understanding the utter devastation and chaos in the affected areas, the association's goal is to provide as easy a disinfection guide as possible.
This advisory is designed for the treatment of wells under emergency conditions with limited equipment. Do not overtreat wells with excessive chlorine. Be sure to leave the chlorine solution in the well for at least six hours. Any circulation of the chlorinated water in the wellbore or 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 wellhead so that surface water drains away from the well. The well will have to be pumped from one to three 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 a meter is not available, dip your finger in and taste the water. A salty taste indicates the need for continued pumping. If it is likely the water is contaminated, treat a glass of clear water with five drops of hypochlorite solution (5% liquid bleach) and wait several minutes. Then dip your finger in the water and taste to check whether all the floodwater has been removed. If the pumped water is not clear, continue pumping until clear and free of salt 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 (250 ml) of powdered 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 solution throughout the well. Let the well set for six hours or overnight, then pump the well and dispose of the pumped water until no chlorine is detected.
Consideration for wells that require a large amount of hypochlorite:
Wells that 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 that 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.
Consideration for wells that require a large amount of hypochlorite:
Wells that 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 that require more than 5 kilograms of powdered hypochlorite should repeat the procedure for each 5 kilograms required or dilute the disinfectant at the same ratio in larger tanks if available. This procedure is necessary to properly place the disinfectant in the borehole and provide for disbursement throughout the well and surrounding formation.
ND
Report Abusive Comment