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BY
DON MEEHAN
FLOODING CONTAMINATION OF PRIVATE WELLS
Having rainfall events such as we've had during November this year makes one think twice about the level of protection our private wells have in such events. The county health department and our office have received numerous calls about wells which had flooding over the top of them. This type of occurrence is not that frequent here and most of us do not know what the consequences are.
There are a number of factors which need to be considered in evaluating whether a well has become contaminated. Some of the key ones are well depth, color changes in the water, age of the well, well construction, and the type of the delivery system.
In general, wells which are deep, have been sealed around the casing to a depth of 20-30 feet at the time of installation, have been properly capped, and have well sealed delivery systems are less likely to be contaminated.
The contamination which is of most concern is that from sewage and manure wastes. Wells are always tested for this type of contamination (coliform bacterial count) since it could mean disease-causing organisms have entered the water. If your well has been flooded, this is one test that is vital to have performed.
Contaminated wells which have no treatment system for adding disinfectants can be shock treated. Water used prior to the treatment and confirmation of no bacterial contamination based on tests can be boiled for at least 10 minutes to make safe. It should not be consumed, used for teeth cleaning, or for cooking or washing dishes until it is known to be safe. There is also a way to treat using ordinary household bleach that does not require heating.
For treating wells it is important to thoroughly clean the well site and all areas of the well which may have been contaminated. Pump the well to remove as much sediment as possible, then disinfect it. Chlorine bleach will work well for this cleaning. For treating the water in the well, calculate (estimate) the number of gallons of water that are in the well casing. Multiply that number by 7.5 gallons to get the total estimated quantity.
Add one gallon of 5 1/2% chlorine bleach to 1000 gallons of water in the well. Hence, if your estimate is that there are only 500 gallons in the well then a half gallon of bleach would need to be poured down the well. Once done the well pump should be turned on with the output going into a hose that is directed back into the well. Use this water to hose down all parts of the well casing. It also helps to mix the water in the well so there is good contact with the chlorine. When recirculating the water it should have a strong odor of chlorine. If not, you have under-estimated the volume of water in the well. Add more chlorine.
The treatment should be left in the system for a minimum of two hours, but longer is better. The health department recommends 12 hours. Contact time is very important for the chlorine to do an adequate job. Once this is finished, pump the well until the chlorine smell is gone. Test the water!
There are lots of little ins and outs of this process. If you are facing it, give our office a call or speak to the county health department.
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