WorldWide Drilling Resource

Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Common Causes of Well Failure - Premature Aging In a time when we are asking our wells to perform far past their design life spans, well design and con- struction decisions, as well as maintenance issues, can impact the life and health of the well. Poor decisions in these areas can certainly result in wells aging much faster than expected, and all kinds of unexpected prob- lems. Well design and maintenance issues can have a huge impact on the life span and operating costs of the well over time. Not properly rehabilitating a well, for instance, can result in microbiological issues such as sulfur-reducing bacteria, which can produce hydrogen sulfide gas, resulting in corrosion of the casing and screens, and potential premature failure. We often see, as a cost-saving measure in new wells, construction which incorporates a lower grade steel casing and a stain- less steel screen. While this may initially seem like a good practice to reduce the construction costs of a new well, in actuality, the presence of dissimilar metals in contact with each other produces an electrochemical galvanic corrosion circuit resulting in acceler- ated corrosion of the lower grade steel which manifests itself as pitting and eventual holing of the casing, requiring expensive repairs and, eventually, well failure. At a minimum, where dissimilar metals are used in a well, a dielectric coupling should be used to join them together to reduce corrosion. The best approach is to use all the same metals, preferably stainless steel in a corrosive envi- ronment. How do you know if you have a corrosive environment? The most scientific way is to run a Langelier Saturation Index (LSI) on the well water. The LSI can distinguish between corrosive water and those likely to produce mineral incrustations, so it should really be standard practice in new well construction to help guide design and construction. An easier and more practical method is the nail test, where a common steel nail is submerged in a sample of the groundwater from the well and observations are made on how long the nail takes to rust to determine how corrosive the well water is. A nail that starts to rust within hours shows the groundwater is very corrosive, while a nail that goes a week and barely shows a pinkish tint in the water is in a much less corrosive environment. Of course, the LSI is the more quantitative approach, where the nail test is a bit more subjective. Still, they can both point you in the right direction on terms of well design considerations. Tom Tom Ballard may be contacted via e-mail to michele@worldwidedrillingresource.com 23 WorldWide Drilling Resource ® DECEMBER 2019 WTR