Thursday, December 31, 2009

There is Coliform in my Well- What to Do?


  1. Retest using proper sampling procedure and verify that E coli is tested for.
  2. If the sample still tests positive for total coliform then treat the system with chlorine
  3. Retest the water after the chlorine has left the system in about 10 days to two weeks (make sure that the water tests negative for chlorine).
  4. If your well water tests positive for total coliform then carefully check the well and water system for points of contamination.
Many instances of total coliform contamination are introduced in the water system and do not originate in the water supply. Washington State is currently investigation the percentage of problems are a result of ground water contamination.

Coliform bacteria are commonly found in soil, on vegetation, and in surface water. They also live in the intestines of warm-blooded animals and humans. Some coliform bacteria strains can survive in soil and water for long periods of time. Coliform bacteria will not likely cause illness. However, because coliform bacteria are most commonly associated with sewage or surface waters, the presence of coliform bacteria in drinking water indicates that other disease-causing organisms (pathogens) may be present in the water system. There are three different groups of coliform bacteria; total coliform, fecal coliform and Escherichia coli (E. coli) each has a different level of risk. Total coliform serves as a proxy for fecal coliform and E. coli bacteria. Coliform bacteria do not occur naturally in most aquifers. Fractured or creviced bedrock aquifers that are close to the surface are the exception and testing for e. coli and fecal coliform and nitrogen will help differentiate the naturally occurring coliform from contamination that might impact your health.

Bacteria washed into the ground by rainfall or snowmelt are usually filtered out as water seeps through the soil, so properly constructed water wells do not typically harbor Coliform bacteria. However, coliform bacteria can persist within slime formed by naturally occurring ground water microorganisms. The slime (or biofilm) clings to the well screen, casing, drop pipe, and pump and may even invade filter systems. Disturbances during pumping or well maintenance can cause the slime to dislodge, releasing the coliform bacteria.

Keep in mind that coliform bacteria do not always show up in every sample. They can be sporadic and sometimes seasonal when they occur in a water supply. Be concerned but do not panic if coliform bacteria are detected. Before treating, repairing, or replacing the well, it is wise to resample immediately if a positive sample is collected making sure to use proper testing procedures. If you receive a second positive sample for total coli forms, or if the initial sample is positive for fecal coliform, do not consume the water. Bring the water to a rolling boil for one to five minutes (the higher the elevation the more time is necessary) to kill the bacteria. You may also want to consider using bottled water as a temporary drinking and cooking water source.

The different bacterial tests are total coliform, fecal coliform, 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. Total coliform includes bacteria that are found in the soil, in water that has been influenced by surface water, and in human or animal waste. Fecal coliform is the group of the total coliform that is considered to be present specifically in the gut and feces of warm-blooded animals. Because the origins of fecal coliform are more specific than the origins of the more general total coliform group of bacteria, fecal coliform are considered a more accurate indication of animal or human waste than the total Coliform. E. coli is the major species in the fecal coliform group. Of the general groups of bacteria that comprise the total Coliform, only E. coli is 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.

Bacteria can be introduced into a new well during construction and can remain if the water system is not thoroughly disinfected and flushed. Well construction defects such as insufficient well casing depth, improper sealing of the space between the well casing and the borehole, corroded or cracked well casings, and poor well seals or caps can allow sewage, surface water, or insects to carry coliform bacteria into the well. These problems are common and the most likely source of the coliform bacteria contamination. Unplugged abandoned wells can also carry coliform bacteria into deeper aquifers. In an existing well system that formerly was bacteria free look for defects. These include: openings at the top of the well; old, rusty, or damaged well casing; unprotected suction line; buried wellhead; and, close proximity of a well to septic tanks, drain fields, sewers, kitchen sinks, drains, privies, barnyards, animal feedlots, abandoned wells, and surface water.

After a confirmed positive total coliform test, check following things to look for as a source of contamination introduction. Any defects in the system should be repaired, the system treated with chlorine and then retested after 10 days to two weeks. Items to look for are:
  1. A missing or defective well cap and check seals around wires, pipes, and where the cap meets the casing may be cracked, letting in contaminants.
  2. 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. This can also happen to a steel pipe well that was hit by a piece of equipment such as a car, snow blower, lawn tractor or mower or that has rusted.
  3. Contaminant seeping along the outside of the well casing - many older wells were not sealed with grout when they were constructed or the grouting has failed. Check the grouting carefully especially if water seems different after severe rains.
  4. Well flooding - a common problem for wellheads located below the ground in frost pits that frequently flood during wet weather.
Since bacterial contamination cannot be detected by taste, smell, or sight, all drinking water wells should be tested at least annually for Coliform bacteria. Most state’s well construction code requires all new, repaired, or reconditioned wells to be disinfected with chlorine to kill bacteria that may have been introduced during construction. Testing is required initially to demonstrate that the water is free of Coliform bacteria before the well is put into service. A Coliform bacteria test is also recommended immediately if:
  1. A sudden change occurs in your water’s taste, appearance, or odor.
    The water turns cloudy after rainfall or the top of the well was flooded.
  2. You suspect a contamination source (e.g., septic system or barnyard) is within 50 feet of your well.
  3. Family members are experiencing unexplained flu-like symptoms.
Before implementing one of the solutions listed below, be sure to inspect the well for defects, check the grouting, casing, and clean the water delivery system and filter of slime and flush the system fully. Then retest. If the system passes let a few weeks go by and retest again. If repairing and cleaning the system does not solve the problem then one of the long-term solutions will have to be implemented.

Long-Term Options for Dealing with Bacterial Contamination of a Well
  1. Connecting to the regional public water system, if possible
  2. Constructing a new well (it is best to determine the source of contamination before a new well is installed)
  3. Installing continuous disinfection equipment
  4. Using bottled water for drinking and food preparation

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