Shock Chlorination for Iron Bacteria Control

by Bill Andresen, Sask Water, Outlook, Saskatchewan

Water systems are often infested with iron bacteria. For example, Crenothrix lives on dissolved iron in water and reduces mineral content. Identifiable as a reddish slime, these bacteria do not cause disease in humans but can damage or destroy a water system.

Iron bacteria in a water system causes:

• rapid deterioration of metal fittings
• stained laundry
• corroding or clogging of water pumps, pipes, pressure tanks, filters, screens, and valves
• reddish-brown slime on household fixtures and toilet tanks
• zeolite water softeners to lose their softening capacity due to slime coating
• reduces water flow capacities and pressure in pipes and fittings due to slime hardening
• an unpleasant taste and odour to water

The standard laboratory test for iron bacteria is a microscopic examination of sludge deposits. In the rural home, check the inside of the toilet flush tank for a red slime deposit which indicates the presence of iron bacteria.

Iron bacteria cannot be eradicated but can usually be controlled by regular shock chlorination, a process which flushes strong dosages of chlorine into the water system. This procedure is usually required at least twice a year to control the bacteria.

It is difficult to determine the exact quantity of chlorine required to shock chlorinate a water system. After chlorination, when pumping the chlorine solution to waste, the following will help determine if the correct amount of chlorine was used:

• If there is a very faint or no chlorine odour, the chlorine strength was too weak.
• A distinct foul or "slough" odour indicates insufficient chlorine was used. The chlorination procedure should be repeated and strength increased.
• A strong chlorine odour and difficulty in removing the chlorine from the well indicates too much chlorine was applied.
• When the correct quantity of chlorine is used, the waste water will have a chlorine odour, but all odours will disappear after the well has been pumped continuously for at least 2 hours.

The following procedure is suitable for most rural water systems, but not for flowing wells:

1. Thoroughly clean the well removing all floating debris. Scrub or hose foreign material from the well casing.
2. Pump the well until the water is clear.
3. Make provisions for storing enough water to meet household and farm needs for 12 hours.
4. Pump 300 gal. (approx. 1,200 L) of water into a clean storage container close to the well head.
5. Allow water to return to a nonpumping level in the well.
6. To the clean storage container, add one of the following: approximately 6 gal. (23 L) of household laundry bleach which contains 5.25% sodium hypochlorite, or 3 gal. (14 L) of 12% sodium hypochlorite, or 5 lbs. (2.25 kg) by weight of 65% powder (granular) calcium hypochlorite.
7. Pour 1 gal. (4.5 L) of household bleach directly down the well, covering as much of the inside well casing as possible.
8. Lower a clean valved hose down the well as far as possible and allow the solution in the storage container to siphon into the well.

   It is very important that the solution added to the well is added at a rate slower than the yield rate of the well. This will ensure that the well development is not disturbed.

   
   
9. Allow the well to return to its non-pumping or static water level. This procedure forces the 300 gal. (approx. 1,200 L) of chlorine solution into the well and surrounding aquifer, treating a volume of water much larger than the storage capacity of the well.
10. Open all hydrants and faucets on the distribution system and allow them to run until the water at the outlets has a chlorine odour, then close all outlets. It may be advisable to bypass any water treatment equipment, because loosened debris may plug the mechanical operation of any equipment.
11. Leave the chlorinated water in the distribution system and well for approximately12 hours. Plan to do this overnight.
12. After the chlorine solution has been in the system for approximately 12 hours, open an outside tap and let it run on the ground surface until all chlorine odours have disappeared. Waste water is not harmful to hardy plant growth (woody plants and grass) but should not be used for water flowers or other tender species.
13. If the chlorine solution was run through any filters or softener, they should be backwashed and the hot water tank flushed.

For information on shock chlorination of flowing wells and sandpoints, contact your regional office of Sask Water, Alberta Agriculture or Manitoba Water Services Board.