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How Work Done on Your Well Might Contaminate Your Drinking Water

Well Drilling - Rotory Drill Rig

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.

Contamination Through Recent Well Work

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.chlorine diagramEXAMPLE: 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.

3. Mix the chlorine solution above with 10 times as much water before pouring down well. Avoid pouring strong bleach down the well.

4. Open the well cap, or if your well has a well top seal, remove the ½” plug or air vent and use a large funnel to pour chlorine down well. CAUTION: well caps and seals are integral to the safety and integrity of your well. They are often regulated by the state and local codes. Be certain to comply with all applicable codes and licensing laws, whenever opening a well. If you are unsure of any of the following steps, seek the assistance of a qualified or licensed well driller or pump installer or contractor.

5. Do not attempt to remove the sanitary well seal without the assistance of a qualified well driller or pump contractor. Do not loosen the bolts that compress the seal.

6. Wells equipped with a packer jet pump can be thoroughly disinfected only though the removal of the pipe, pump and jet unit from the well.

7. As you are adding the chlorine solution, take precautions to protect yourself from splashing chlorine and fumes. Protect your eyes with safety goggles, and wear protective gloves and clothing.

8. Pour the chlorine solution down the well. Avoid pouring the chlorine solution on the pump wire connectors. If in doubt, use dry chlorine pellets.

9. If the well is relatively deep, the disinfectant may be dispersed to the bottom by alternatively starting and stopping the pump several times (although dry pellets work better for this reason). If possible, place a garden hose in the top of the well, and turn on the faucet and circulate the chlorine solution for 15 minutes until a strong 50 ppm chlorine residual is detected, by using a chlorine test kit.

10. Add more bleach as needed to bring up the chlorine solution residual in the well to 50 to 100 ppm.

11. If possible, circulate the water from the well by connecting a garden hose to a nearby hose bib or sill cock, and feed the water back down into the well. This will also wash down the sides of the well and insure proper mixing. After approximately 15 minutes a strong chlorine odor should develop. To be more precise use a chlorine test kit to make sure the chlorine is over 50 ppm.

12. Water should be pumped from the well into the pressure tank and plumbing system.

13. All water faucets should be turned on in the house and all outside fixtures and hose bibs including fire hydrants, watering troughs, and other supply lines to other buildings, until a 50 ppm chlorine residual is detected.

14. At this point, turn off the fixtures and let remain in the pipes a minimum of 2 hours, up to 12 hours or overnight.

15. After the chlorine has been left in the well and the plumbing system if applicable for a minimum of two hours, the chlorinated water can be discharged. Large amounts of chlorinated water should not be discharged into the septic tank, or onto lawns or gardens. If possible, discharge as much of the water as possible through an outside faucet with hose attachment. Do not discharge the chlorinated water into streams or rivers. The small amount of chlorinated water, which remains in the household plumbing, can be discharge into the septic system.

16. Backwash water softeners; flush the water heater; and replace all filters if present.

17. For wells and piping systems that have bacterial contamination or have been flooded, resample the water and retest for coliform, after all the chlorine residual is gone.

18. If bacteria are detected again, repeat procedures above. Until a safe test result is obtained, use an alternate known safe water source, or boil all water, or use bottled water. In case of large diameter wells, a greater quantity of chlorine solution is needed. As a general rule, it takes 1 gallon of 5% laundry bleach to treat 1000 gallons of water with 50 ppm of chlorine. NOTE: For heavily iron-fouled wells, severe contamination with bio-films or slime, or excessive levels of hydrogen sulfide gas, apply a 100 ppm or 200 ppm residual by multiplying the chlorine bleach used by 2 or 4 times in Table 1 or the pounds of chlorine pellets being used in Table 2.

Wells with submersible pumps have pipes that either enter in through the top or through the side. Many wells are underground or in vaults in areas with freezing temperatures:well_submersible_pump2For more help on removing bacteria from your water, visit our Bacteria page on our Water Problems tab. If you still have questions, don’t hesitate to e-mail us at, leave us a message on Facebook, or use our online contact form for prompt, personalized assistance from our trained professionals.  Thanks for reading!

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