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Coliform Bacteria Contamination -
Frequently Asked Questions
What are coliform?
Coliform bacteria are indicator organisms which are used in
water microbiological analysis. Coliforms are a group of bacteria which are
readily found in soil, decaying vegetation, animal feces, and raw surface
water. They are not normally present in deep groundwater and treated surface
water. These indicator organisms may be accompanied by pathogens (i.e.,
disease-causing organisms), but do not normally cause disease in healthy
individuals. However, individuals with compromised immune systems should be
considered at risk. Coliforms, rather than the actual pathogens, are used to
assess water quality because their detection is more reliable. Pathogens
appear in smaller numbers than coliforms, so are less likely to be isolated.
Drinking water found to contain coliforms is considered biologically
contaminated.
How does the laboratory detect coliforms in a water sample?
Since visual examination of water under the microscope is
unreliable, Laboratories use the Colilert presence/absence method. In brief,
this method combines two separate examinations. First, the 100 milliliter
sample is combined with growth medium, and then incubated for 24 hours at 35.0
degrees Centigrade. After 24 hours, only coliform bacteria will use the growth
medium for food, resulting in a change in the water sample's appearance.
Depending on the lab and the tests requested, a second examination is
performed to determine if the coliform present is from feces. Thus, the test
is completed 24 hours after it has begun.
A TOTAL COLIFORM ABSENT report means that there are no
coliform bacteria present at the time of sampling and the water may be
considered bacteriologically safe to drink.
A TOTAL COLIFORM PRESENT report means that coliform bacteria
is present at the time of sampling and the water may not be considered safe to
drink. You will be advised to super-chlorinate the water system.
How did the water become contaminated?
Surface waters, such as streams, creeks, and lakes, will
almost always contain some degree of contamination. This is due to exposure to
animals, humans, aquatic life, etc. Raw surface waters should always be
treated prior to domestic use, and must include disinfection and filtration to
remove turbidity and parasites that are resistant to simple disinfection.
Wells and springs can become contaminated by faulty construction, poor
protection from surface activity including rain and flooding, a shallow water
table, entrance of unfiltered surface water via rock fractures, close
proximity to a sewage disposal system or leaky sewer pipe, and/or
contamination during repair or reconstruction. A false, positive coliform
count can occur by contaminating the water sample (e.g., putting one's finger
into the water sample bottle) or by using a non-approved water sample bottle.
A well or spring should be super-chlorinated prior to the coliform test,
especially if a repair has been made and the system was not chlorinated at the
time.
How do I cure my contamination problem?
Examine the well, spring, storage tank, etc. to determine
that it is adequately sealed to prevent contamination entry. Most of the time,
assuming that the well/spring is properly constructed, the contamination can
be cured by spot chlorination. This involves pouring chlorine bleach down the
well shaft (or into the spring containment box), and allowing to stand for 30
minutes. Next, each tap is opened, one at a time, to bring the chlorine
solution into contact with all of the plumbing. Make sure every tap is
operated, both inside and outside the house. Once the chlorine odor is
noticeable, shut off the tap and proceed through the remainder of the system.
When done, let sit overnight (at least 12 hours). The next day, the
chlorinated water can be flushed out by opening taps and running water until
chlorine odor is undetectable. Once the chlorine is completely gone (can be
checked with a swimming pool test kit), the water should be retested for
coliform contamination. Normally, the contamination will be eliminated by this
temporary disinfection method.
{To estimate the amount of 5.25% chlorine (household type
bleach) to use: for a 6-inch diameter well, figure the depth of water in the
well and for every 66 feet of water (100 gallons), use 1 quart of chlorine}.
In some cases, if the contamination cannot be eliminated,
the well/spring may require reconstruction or another permanent solution.
What are some other forms of water contamination?
Water contaminants commonly found in this area include
hydrogen sulfide (rotten egg odor); excess iron (reddish brown stains); iron
bacteria (foul taste and odor); manganese (blackish stains, metallic taste);
hardness (white deposits, increase in soap usage); salinity; corrosiveness
(evidenced by the dissolving of copper plumbing leading to blue-green stains
and a bitter taste); turbidity (cloudy and/or dirty water); and sediment.
These are not considered health hazards but there are water treatment systems
available for the removal /reduction of all of the above. Contact a
professional water treatment company for more information.
www.kinetico.com
Man-made chemicals, such as pesticides, herbicides,
solvents, etc., can easily leach into a subsurface water supply through
careless handling and dumping. Fortunately, these forms of water contamination
rare.
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