Rehabilitation vs. Redrill -- A Difficult Question
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.
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.
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 MethodsYou'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.
- Muriatic, Sulfamic, Hydroxyacetic, Oxalic, Citric
- Caustic soda
- Hydrogen peroxide
- Quaternary ammonium and organically available chlorine
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.