Why Shock Chlorinate Your Well?

By Bob Buchanan, Alberta Agriculture, Food and Rural Development, Barrhead

If it's not broke, don't fix it, right? Well, not always. Even if you're not experiencing any problems with your well, a regular shock chlorination treatment can provide life insurance for your well and water system. The treatment helps control problems caused by bacteria accumulation in a well. Typical problems can include:

• A slow to immediate deterioration in water quality (e.g. foul taste, odour and staining)
• Plugging of pump and well screens, as well as water pipes and water treatment filters, causing reduced well yield and restricted water flow
• A slimy film of bacteria which coats the inside of tanks and piping throughout the water system
• Corrosion of well casing and pumping equipment
• Human health concerns

To effectively control bacterial problems, shock chlorination must disinfect a portion of the groundwater formation, the entire well depth and water piping system. To accomplish this, a large volume of superchlorinated water (usually two to three hundred gallons) is poured down the well to displace all the water in the well and some of the water in the formation around the well. The chlorine solution is left in the well and water system for 8 to 48 hours and then pumped completely out. This procedure is called shock chlorination.

Regular shock chlorination treatments once or twice per year will generally control nuisance types of bacteria, such as iron and sulphate-reducing varieties. These bacteria are commonly found in water wells.

Shock chlorination can also be effective for harmful types of bacteria which can affect human health. Bacteria tests should be done following the treatment to gauge its effectiveness. In some situations, it may be necessary to provide a continuous method of disinfection for household water.

Shock chlorination can also prevent bacteria problems before they develop. Wells often become contaminated with bacteria when submersible pumps are removed and replaced with a new pump. The problem originates with the bacteria in the surface soils where the pipe and pump are laid. As a result, the treatment should be done immediately after any work is done to a well. New wells should also be treated immediately after completion.

Shock chlorination is an effective and low-cost method of improving water quality problems caused by bacteria accumulation in wells. It will also help to extend the life of your water well.

For more information on shock chlorination of wells, water quality and treatment, contact your local district or regional agriculture office, or public health inspector.