There are many ways that well water can become contaminated by coliform bacteria without any change in taste or odor to the water. It is important to periodically monitor private water wells to see if contamination is present. The United States Environmental Protection Agency recommends that private water supplies be tested annually for coliform bacteria to detect contamination problems early. This post will focus on contamination of well water through recent work done on the well, and how correct it through shock chlorination using liquid chlorine bleach.
Coliform bacteria tests are used as an indicator of the possible presence of disease-causing bacteria. Other bacteria such as iron and sulfur bacteria, while not a health threat, can produce obnoxious odors, tastes, and color, and can cause plugging problems in pump and water systems. Shock chlorination can eliminate the disease-causing bacteria, and other nuisance organisms that cause tastes, odors and slime.
Wells which have recently been worked on can be contaminated by the work which had been done by the well driller or contractor. Introduction of coliform bacteria can occur from the tools that are used, drilling pipe, fluids used in the drilling and any number of other items used in drilling and servicing wells. Tools or dirt falling down into the well while it is being worked on or even airborne particles being carried down into the well can also cause contamination.
There are two basic ways coliform bacteria can get into a well by a well driller or contractor. One is by the original drilling and installation of the pump. The other is when the well or pump is being repaired. Original drilling processes include the activities related to the original construction of the well, including the original pump installation. This represents the first and usually most severe exposure of the well to bacterial contamination. Because there are so many different ways to introduce bacteria into the system, the original well construction can often be the cause of an ongoing bacteria problem that can go on for many years.
It is important that all water used in the drilling process be chlorinated treated water or, at the very least, free from any bacteria or viruses. Thorough chlorination of the water should be done for all water used during drilling and before it is introduced into the well. It is important not to trust that the water used for drilling obtained from a neighboring well is free from bacteria. Chlorine of not less than 50 PPM (mg/L) should be added to any water entering the well, no matter where the water came from. Equipment and tools lying on the ground or the bed of a service truck also represent excellent paths for bacteria or viral contamination. This equipment should be kept as dry and clean as possible, covered until needed, and washed down with a chlorinated solution before placing into the well.
Shock Chlorination Using Liquid Chlorine Bleach
1. Clean the well house, springhouse or storage tank or reservoir. Remove debris and scrub or hose off any dirt or other deposits or interior surfaces. Pump to remove any suspended solids or foreign matter in the water if possible. Scrub interior surfaces with a strong chlorine solution containing ½ gallon household bleach to each 5 gallons of water.
2. Determine how much chlorine to use to disinfect your well by consulting Table 1 (below). If you don’t know your well depth, contact your well driller as they often keep records that will show the depth of the well. Table 1 Wells: Amount of 5% bleach (sodium hypochlorite) needed for disinfection to obtain approximately a 50 ppm chlorine solution in the well. If using pool chlorine (10% to 12% sodium hypochlorite) you can use half as much chlorine bleach.EXAMPLE: The well is 4″ in diameter, with a depth of 400 feet. The water level is 100 feet below the surface. 400 – 100 = 300 feet.
From Table 1, a 4 inch well with 300 feet of water requires 3 quarts or 3/4 of a gallon of bleach. NOTE: In applications where it is inconvenient to determine water depth, at least ½ gallon of household bleach, or ¼ gallon of pool chlorine, may be used for wells up to 8″ in diameter with water estimated to be less than 80 feet deep; one gallon should be used for similar sized wells with water greater than 80 feet.