How to Disinfect Water Wells Affected by Hurricane Helene

Buncombe County -- October 5, 2024: Buncombe County Government News: Environmental Health is working to ensure

flooded wells or wells that were damaged during the storm provide safe water for use at home. A flooded well is a well where water was over the top of the well at any point during the storm. Wells may also receive structural damage. If a well was either flooded or damaged during the storm, it must be disinfected. 

Once the well is disinfected, call 828-250-5016 and some will come out to collect a water sample. 

Water preservation: put a filled 2-liter bottle in the back of your toiler, reuse water by using dishwashing water in the back of the toilet for flushing. At this time, we ask that you do not use water from rivers, streams, or creeks due to contamination from the storm. 

N.C. State Cooperative Extension:  Shock chlorination is a simple procedure for disinfecting wells. Use a solution made of calcium hypochlorite containing 65% to 70% available chlorine such as HTH granules. DO NOT use household bleach as it is too weak. All new wells should be disinfected before use. Existing wells may not be safe sources of water for drinking or cooking if disease-causing bacteria have entered the water. This can happen when the well is opened, such as to replace a pump. It can also happen if the well was surrounded by floodwaters, or if the ground nearby was flooded. Poorly constructed wells can allow contaminated water to enter, and animal waste on the ground near a well can be carried in.

Note: Do not drink untreated water from heavily contaminated wells, or wells in flooded areas, until testing by your local health department determines that the water is safe.

To kill disease-causing organisms in the well, the well must be disinfected. Shock chlorination is a simple procedure for disinfecting a well using a solution made of calcium hypochlorite containing 65% to 70% available chlorine such as HTH granules. The goal is to add enough chlorine to raise the concentration in the well high enough to kill potentially harmful bacteria and viruses.

This procedure does not protect the well from future contamination. It also has no effect on contaminants other than bacteria, such as gasoline or iron in the water.

Before you begin:

1. If water is cloudy or discolored, run an outdoor faucet until the water runs clear.

2. Do not chlorinate activated carbon or charcoal filters. Use the “bypass” valve on the filter if there is one. Otherwise, disconnect the filter temporarily during shock chlorination.

3. Use rubber gloves, goggles and a protective apron when handling chlorine solutions. If chlorine gets on the skin, flush immediately with fresh water.

4. Never mix chlorine solutions with other cleaning agents, especially ammonia, because toxic gases may be formed.

5. Use a solution made of calcium hypochlorite containing 65% to 70% available chlorine such as HTH granules. Do not use scented or color-safe bleach or other special laundry products to disinfect a well.

Shock chlorination procedure:

1. Select a time when well water will not be used for at least 24 hours. You may wish to store enough drinking water for this period or do the procedure before you leave for a short trip.

2. Determine the volume of water in your well. This depends on the diameter of your well and the height of standing water in the well.

First, you need to determine the height of the standing water. The height of standing water is the difference between the depth of your well and the distance from the top of the well down to the water level. For example, if the well depth is 150 feet and the water level is 50 feet down from the top, then subtract to find that the height of standing water is 100 feet.
Then, you need to determine the diameter of your well casing. You can do this with a flexible measuring tape. Wrap the tape around your well casing and measure the circumference. Be sure you measuring your WELL CASING and NOT the well cap or collar on the top. Divide your circumference by 3.14. The result is the outside diameter. To determine your inside diameter, you’ll want to subtract  5/8″ from that. Your result should be close to one of the standard sizes – 2, 4, 4.5, 5, 6, 6.25, 7 or 8 inches.

Further instructions can be found in the attachment below. You can also visit the N.C. State Cooperative Extension website:   ncsu