Treating Your Well With Chlorine

Anna Aldridge Technical Topics

A little chlorine applied regularly is the best bet

Questions about water well disinfection are among the most common questions water specialists hear from producers. It is acceptable to use chlorine, but regular application is the safest and most efficient solution, says Bob Buchanan, a water specialist with Alberta Agriculture and Food (AF).

“By doing regular disinfection every six to 12 months, you may be able to save yourself from the more costly and technically difficult shock chlorination treatment that is best done by an experienced water well driller,” says Buchanan.

How chlorine works

Chlorine bleach is the most common chemical method for disinfecting water wells. It becomes a significant disinfecting agent when it combines with nitrogen compounds such as ammonia to form chloramines.

However, chloramines are slow acting disinfectants that require long contact times for effective disinfection. A faster acting solution is created when higher levels of chlorine are added to the water. The excess chlorine then forms hypochlorous acid (HOCL), a fast acting, more powerful disinfecting agent.

Although adding more chlorine may be beneficial, Buchanan says there is a point where excessive chlorine concentrations can create more damage than benefit. “High dosages of 1,000 parts per million (ppm) of chlorine are less effective due to a change in water pH,” he says.

“Liquid and granular chlorine are both extremely alkaline. This results in an increase in pH when mixed with water. As the pH of the solution rises, the effectiveness of chlorine to kill bacteria is dramatically reduced. This higher concentration of chlorine is quite corrosive to the metal well casing and can be a concern for some older wells.”

Well disinfection vs shock chlorination

The terms “well disinfection” and “shock chlorination” are often used interchangeably, says Buchanan. However, well disinfection involves routine control of bacteria with small chlorine dosages of 50 to 200 ppm while shock chlorination is recommended to remediate bio-fouled wells and control problems created by high levels of nuisance bacteria.

Shock chlorination requires a much higher chlorine dosage of 200 to 1,000 ppm and the addition of an acid to lower the pH of the treatment solution in order to be effective. Buchanan recommends regular well disinfection as a way to help avoid the costly shock chlorination process that generally requires a water well driller to do properly and safely.

Further information on disinfecting wells is available in Water Wells That Last, a publication available on-line at the AF Ropin’ the Web site at www.ropintheweb.com.

Information and assistance on disinfecting wells and a number of other on-farm environmental practices is available through a strong network of technical assistants (TAs) throughout the province.

This article may be reprinted with the credit:  Alberta Environmental Farm Plan
For more how-to fact sheets or other information, visit www.albertaEFP.com.

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