Well Contamination

An excerpt from the New York State Department of Health website

"If the area around your well gets flooded or if you suspect that your well is contaminated, you need to disinfect the water in the well before using it for washing and at the tap before using it for drinking water or for cooking. You should continue disinfection at the tap until the water is tested and found suitable for drinking. Contact your local health department for information about testing your well. Changes in the water's appearance, taste or odor may indicate possible contamination.

After disinfecting the well, the water should be tested to determine whether all bacterial contamination has been removed. You should wait several days to test the water to be sure that all the chlorine has been flushed from the water system. Contact your local health department for more information about testing your well. Until testing shows that the water is free of contamination, you should continue to use bottled or disinfected water for drinking and food preparation as described in the Disinfecting Water section.

You may wish to consider retesting the well water again after several weeks. If flooding and groundwater contamination is extensive, your well may not be a suitable source of drinking water for some time. Severe flooding that damages the well casing, deposits debris around the well or submerges electrical controls will require a qualified professional for evaluation, servicing and disinfection.

Procedure for Disinfecting a Well:

1. Run water until clear, using an outdoor faucet closest to the well or pressure tank.

2. Mix two quarts household bleach containing about 5% chlorine in 10 gallons of water in a large bucket or pail in the area of the well casing.

3. Turn electrical power off to the well pump. Carefully remove the well cap and well seal if necessary. Set aside.

4. Place hose connected to outdoor faucet inside well casing. Turn electrical power back on to the well pump and turn water on to run the pump.

5. Carefully pour the water and bleach mixture from the bucket or pail down the open well casing. At the same time, continue to run the water from the hose placed inside the well casing.

6. At each indoor and outdoor faucet, run the water until a chlorine odor is present, then shut each faucet off.

7. Continue running water through the hose inside the well casing to recirculate the chlorine- treated water. Use the hose to also wash down the inside of the well casing.

8. After one hour of recirculating the water, shut all faucets off to stop the pump. Disconnect power supply to pump. Remove recirculator hose from well.

9. Mix two more quarts of bleach in 10 gallons of water and pour mixture down the well casing. Disinfect the well cap and seal by rinsing with a chlorine solution. Replace well seal and cap. Allow the well to stand idle for at least eight hours and preferably 12 to 24 hours. Avoid using the water during this time.

10. After the well has idled for the recommended period of time, turn the pump on and run the water using an outdoor faucet and garden hose in an area away from grass and shrubbery until the odor of chlorine disappears. Run all indoor and outdoor faucets until the odor and taste of chlorine disappears."

For further information contact:
New York State Department of Health, Center for Environmental Health
at 1-800-458-1158 ext. 2-7650 or bpwsp@health.state.ny.us

New York State Department of Health.
February 2007.
Don't Be Left in the Dark - Weathering Floods, Storms, and Power Outages.
Retrieved on July 11, 2007 from

Bacteria: A Definition

An excerpt from the New York State Department of Health website

What are Coliforms?
"Coliforms are bacteria that are always present in the digestive tracts of animals, including humans, and are found in their wastes. They are also found in plant and soil material.Total Coliforms, Fecal Coliforms, and E. Coli. The most basic test for bacterial contamination of a water supply is the test for total coliform bacteria. Total coliform counts give a general indication of the sanitary condition of a water supply.

A.   Total coliforms include bacteria that are found in the soil, in water that has been influenced by surface water, and in human or animal waste.

B.   Fecal coliforms are the group of the total coliforms that are considered to be present specifically in the gut and feces of warm-blooded animals. Because the origins of fecal coliforms are more specific than the origins of the more general total coliform group of bacteria, fecal coliforms are considered a more accurate indication of animal or human waste than the total coliforms.

C.   Escherichia coli (E. coli) is the major species in the fecal coliform group. Of the five general groups of bacteria that comprise the total coliforms, only E. coli is generally not found growing and reproducing in the environment. Consequently, E. coli is considered to be the species of coliform bacteria that is the best indicator of fecal pollution and the possible presence of pathogens. Are Coliform Bacteria Harmful?

Most coliform bacteria do not cause disease. However, some rare strains of E. coli, particularly the strain 0157:H7, can cause serious illness. Recent outbreaks of disease caused by E. coli 0157:H7 have generated much public concern about this organism. E. coli 0157:H7 has been found in cattle, chickens, pigs, and sheep. Most of the reported human cases have been due to eating under cooked hamburger. Cases of E. coli 0157:H7 caused by contaminated drinking water supplies are rare. Coliform Testing

Testing for bacteria is the only reliable way to know if your water is safe. You cannot tell by the look, taste, or smell of the water if disease-causing organisms are in it. The New York State Department of Health recommends that well owners test their water for coliform bacteria at least once a year. If you have experienced bacteria problems in the past, it is recommended that you test your well more frequently. When Should I Test?

Late spring or early summer are the best times to test your well, since coliform contamination is most likely to show up during wet weather. Whether your test results are positive or negative, understand that the sample you collected is just a "snapshot" of your well’s water quality. The more samples you have tested, the more confident you can be about the quality of the water you are drinking.What do the Results Mean?

If coliform bacteria are present in your drinking water, your risk of contracting a water-borne illness is increased. Although total coliforms can come from sources other than fecal matter, a positive total coliform sample should be considered an indication of pollution in your well. Positive fecal coliform results, especially positive E. Coli results, should be considered indication of fecal pollution in your well. What Should be done if Coliform Bacteria are Detected in a Well?

When coliforms have been detected, repairs or modifications of the water system may be required. Boiling the water is advised until disinfection and retesting can confirm that contamination has been eliminated. A defective well is often the cause when coliform bacteria are found in well water. What Kinds of Defects can Allow Contamination?a missing or defective well cap - seals around wires, pipes, and where the cap meets the casing may be cracked, letting in contaminants contaminant seepage through the well casing - cracks or holes in the well casing allow water that has not been filtered through the soil to enter the well. This seepage is common in the wells made of concrete, clay tile, or brick contaminant seeping along the outside of the well casing - many older wells were not sealed with grout when they were constructed well flooding - a common problem for wellheads located below the ground in frost pits that frequently flood during wet weather. Long-Term Options for Dealing with Bacterial Contamination of a WellConnecting to the regional public water system, if possible Inspecting wells for defects and repairing them if possible Constructing a new well Installing continuous disinfection equipment Using bottled water for drinking and food preparation."

For further information contact:
New York State Department of Health, Center for Environmental Health
at 1-800-458-1158 ext. 2-7650 or bpwsp@health.state.ny.us.

New York State Department of Health. March 2005.
Coliform Bacteria in Drinking Water Supplies.
Retrieved July 11, 2007 from

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Feb 4, 2017