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Technical Resources >> How-To-Guides >> Sanitizing Wells, Storage Tanks, and Pump Systems by Shock Chlorination (Page 1)
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It is important to periodically monitor private water wells to see if contamination is present. The United States Environmental Protection Agency recommends: “… test private water supplies annually for nitrate and coliform bacteria to detect contamination problems early. Test them more frequently if you suspect a problem”. http://www.epa.gov/safewater/pwells1.html
Coliform bacteria in a well or home piping system indicate that disease-causing bacteria and viruses are likely to be present. 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 these disease-causing bacteria, and other nuisance organisms that cause tastes, odors and slime.
When wells are first drilled and put on line, or when submersible well pumps are serviced (right), the well, pump, pressure tank and piping system should be thoroughly sanitized with chlorine to prevent or retard bacterial and bio-film growth.
How To Test Your Water
Most water testing for chlorination purposes is done to detect the presence of colifom bacteria. Coliform bacteria tests are used as an indicator of the possible presence of disease-causing bacteria.
You can use our mail order Bacteria Check test kit, or for a certified test, take the sample to a licensed laboratory in your area. Use a sterile bottle obtained from the laboratory.
Consider Shock Chlorination for Routine Well Maintenance
Shock chlorination of the well and/or pumping, distribution or home piping system is usually recommended after:
A new well has been constructed
Any time a well is opened for repairs
Floodwater has entered a well
A new holding tank, pump or pressure tank has been installed
A new pipeline or other piping or plumbing work has been done
Tests indicate the presence of coliform bacteria
Odors or slime caused by iron or sulfur bacteria are present
CAUTION: It is important to remember, while shock chlorination corrects immediate bacteria and/or odor problems in wells and piping systems, it does not correct the source of the bacteria. If bacteria are entering the well from a septic tank or other source, one should correct the problem, otherwise bacteria will redevelop.
How Shock Chlorination Works
Shock chlorination involves introducing a strong chlorine solution into the water source and plumbing system, and letting it disinfect the system for 12 to 24 hours. You can use regular household bleach (non-perfumed type) that contains 5.25 percent sodium hypochlorite, which kills bacteria and certain viruses. You can also use pool chlorine, which is 10% to 12% sodium hypochlorite and twice as strong as household bleach, and/or calcium hypochlorite pellets. For best results don’t use pool dry pellets, unless it is pure calcium hypochlorite.
Odors Caused by Bacteria
Often well waters contain odor. Sources of the odor may be from the action of bacteria and sulfates, iron or manganese. Some waters contain an excessive amount of sulfates with various strains of sulfate bacteria. These bacteria, harmless to health, will react in stagnant water that has been depleted of oxygen, and can produce hydrogen sulfide gas. These bacteria cannot grow in the presence of atmospheric oxygen, which may account for their not being noticed in cold water lines, and their presence in water heaters and hot water lines. Other types of bacteria, such as iron or manganese bacteria, utilize these elements for their cell wall production, and produce slime in wells and piping in addition to odors.
Iron and Manganese Odors
It is important to note that odors from iron and manganese (such as rusty odors, or oily odors) will not be eliminated by shock chlorination. Iron and manganese are usually found in a dissolved or clear state in well waters, and after exposure to oxygen or other oxidants such as chlorine, will color the water. In some cases, shock chlorination of waters high in iron or manganese will turn clear water into rusty, orange, red, pink, or black water depending on the water chemistry and levels of iron or manganese present.
Note of Caution:
Shock chlorination of wells or piping systems may loosen up scale, iron deposits and other materials, which can clog fixtures, appliances and valves in the piping system. Care should be taken when flushing the piping, and all aerators removed to prevent clogging. In some extreme cases of corroded piping, the piping may fail and start to leak after this procedure. Chlorination will not remove nitrate or other contaminants.
Shock Chlorination Methods:
1. Liquid chlorination using household bleach (sodium hypochlorite)
2. Dry pellet chlorination using 70% available (calcium hypochlorite)
Shock Chlorination by Liquid 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, or ¼ gallon of pool chlorine to each 5 gallons of water.
2. Determine how much chlorine to use to disinfect your well by consulting Table 1. 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 5.25% bleach (sodium hypochlorite) needed for disinfection to obtain approximately a 50 ppm chlorine solution in the well.
If using pool chlorine (12% sodium hypochlorite) double amounts below.
Well Casing Diameter Distance From Water Level to Bottom of Well (Water Depth)
0’ – 50’ 50’ – 100’ 100 – 200’ 200’ - 300’ 300’ – 400’ 400’ – 500’
4” 8 oz. ½ qt. 1 qt. 2 qt. ¾ gal. ¾ gal.
6” ½ qt. 1 qt. ¾ gal. 1 gal. 1 ¼ gal. 1 ½ gal.
8”– 12” ½ gal. ¾ gal. 1 ¼ gal. 1 ¾ gal. 2 ½ gal. 3 gal.
12” – 16” ½ gal. 1 gal. 2 gal. 3 gal. 4 gal. 5 gal.
20” - 24” 1 gal. 3 gal. 5 gal. 7 gal. 9 gal. 11 gal.
30” – 36” 3 gal. 5 gal. 10 gal. 15 gal. 20 gal. 25 gal.
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 takes 1 quart 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 (see Method II).
9. If the well is relatively deep, the disinfectant may be dispersed to the bottom by alternatively starting and stopping the pump several times. 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.
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