Certainty of the rehabilitation effort, site restrictions, customer demand and cost all must be evaluated carefully.

You've come across a well that is suffering a loss in specific capacity or is experiencing degradation of water quality. Or perhaps it's pumping excess sand, any gravel or air. If the well is encountering any of these problems, it may be time for you to take on a well rehabilitation project.

What exactly causes the well to need rehabilitation? Among other things, clogging of perforations, biofouling, sand sealing or cementation in the near-well zone (e.g. filter pack) certainly may be to blame. Corrosion that causes enlargement of perforations or holes in the casing or screen also may be the culprit.

Experience in the industry has shown that approximately 10 percent of all large-capacity municipal water supply wells will be relined at some time during their lives. The rehabilitation percentage is much higher - 70 percent - making it rare for a well to go without some rehabilitation during its life.

Deciding if you should redrill or rehabilitate a well is a tough question to answer. Certainty of the rehabilitation effort, site restrictions and customer demand all must be evaluated carefully. And, as always, cost is a paramount concern - both jobs can end up being quite expensive, so you want to make sure you're doing the right thing. To help you compare the costs for well construction against those for rehabilitation costs, we've included two charts that list the typical costs for each project. We also have included a "Decision Tree for Rehabilitation," which is a handy tool for determining which option may best solve your problem. Ultimately, though, it's up to you to evaluate the well and provide a professional diagnosis for each unique situation.

If you do choose to rehabilitate the well, there are a variety of tools available for this project. See the accompanying sidebar for some of the more common options.

This article is excerpted from Dennis E. Williams' presentation - "Well Rehabilitation: Is It Time? Is It Worth It?"at the "Water Well Maintenance and Rehabilitation Seminar," sponsored by the California-Nevada Section of the American Water Works Association. Williams is the founder and president of GEOSCIENCE Support Services Inc., Upland, Calif.

Sidebar: Common Rehabilitation Methods

You've decided to rehab, but which way you are going to go about it? There are plenty of options from which you may choose, and in her presentation, "Well Rehabilitation ¿Does It Work?" Karla Tebben, an environmental engineer at the City of Ames, Iowa, Water and Pollution Control Department, lists some of the more common well rehabilitation methods.

Chemical

• Acids
  
• Muriatic, Sulfamic, Hydroxyacetic, Oxalic, Citric
  
• Caustics
  
• Caustic soda
  
• Polyphosphates
  
• Chlorine
  
• Hydrogen peroxide
  
• Quaternary ammonium and organically available chlorine

Physical

Jetting

Surge block

Surge pumping and backwashing

Swabbing

Compressed air surging

Ultrasonic jetting

Explosives

Liquid and gaseous carbon dioxide agitation

In conclusion, Tebben reminds that in many cases, well rehabilitation seems to help for a while, but rehabilitation methods don't work for every situation. She recommends that well maintenance be emphasized more and that we continue to study to find the optimum rehabilitation methods for various causes of decreased well production.