What is Shock Chlorination?

Shock chlorination is simply the process of adding a sanitizer to the well in high concentrations to destroy any bacterial growth.  It can be effective in reducing an iron bacteria, hydrogen sulfur, or coliform bacteria problem.  However, in severe cases, it may be only a temporary solution and must be repeated periodically.

There are a number of reasons to shock treat a well:

  1. Your well has tested positive for coliform bacteria.
  2. Iron bacteria has plugged pumps, pipes, etc.
  3. Flooding or other natural events have contaminated the well.
  4. Smelly water caused by hydrogen sulfide.
  5. General well maintenance.  Many states recommend annual well sanitation.

Household bleach (sodium hypochlorite) is often used as a well sanitizer, but it has limitations that may cause your shock chlorination project to fail.  The bleach you purchase at the store has only 5.25% available chlorine, and it may be less depending on how long it has been sitting on the shelf.  Also, dumping liquid down the well may only sanitize the upper part of the well and may not get down to the bottom.

Calcium hypochlorite (dry chlorine) is the most practical product for sanitizing a well because:

  1. Highly concentrated (65-73% chlorine, compare to household bleach at 5.25%)
  2. Available in pellet and granular form. Pellets will sink to      the bottom of the well.
  3. More effective in the presence of organic matter.
  4. Longer shelf life than bleach.

Instructions for Shock Chlorination

  • Consult your local or state health department before sanitizing your well to determine specific requirements.
  • Determine if there are any obstructions in your well i.e. pitless adapter, wiring, that may stop pellets from reaching the water.
  • Use a combination of granular and pelleted chlorine. Pellets will sink to the bottom of the well.  Combine granular portion with 3-5 gallons of water and mix thoroughly.
  1. Check the pH of the well water.  A pH of 7 or below is ideal. If pH is 7.5 or higher, adding white vinegar or another high acid product will lower pH.
  2. Refer to the chart below to determine how much chlorine you will need.
  3. Drop pellets into well, making sure you can hear them hit the water.
  4. Pour liquid chlorine solution in well.
  5. Run water from a faucet or hydrant (plumbed to the well) back down in the well for approx. 15 minutes. After a short period of time there will be a strong chlorine odor.
  6. Run water through all taps, spigots, etc., until the smell of chlorine is present. Allow treated water to stand 12-24 hours.  After this time, flush all taps.
  7. After the system has become completely flushed with clean water, a bacteria check should be done.