By Christopher S. Johnson, PG, CHg
Work or pleasure, when we travel we almost always want to know where we are going, but even more importantly, how to get home.
Home is safety, comfort, where we are most at ease. Wells can’t (or shouldn’t) move, so “home” for a well is a state of highest efficient operation, free of impediment or restriction. That said, there are several actions that can be taken for either a new well or an existing well. The value and meaning of the data generated needs to be accounted for with respect to new or existing, but in either case we can use the information to make comparisons in well status going forward in time and judge what additional steps might be warranted based on what “home” looks like.
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The status of a well can be described in terms of operational capacity and performance. Operational capacity relates to the structural integrity of the well and the maintenance of the well. The capacity of a well to provide water will be decreased by structural failures or by the presence of entrained sand or clogging of the well perforations. Performance relates to the measured amount of water pumped from the well, along with the unit rate of production (i.e. so many gallons per minute per foot of drawdown) and lastly the water quality. It is important to note both the operational capacity and performance of the well will change over time, not if, but when. As such, determining the baseline conditions of the well, i.e. what “home” looks like, is vital to assessing the status of a well.
Begin by conducting a pumping test. A valuable pumping test will generate data on flow rate, pumping water level, and power input—all compared to the amount of time the well was pumped. This information can be used to describe both the performance of the well and the aquifer in which it is completed. Furthermore, routinely conducting such tests will provide an invaluable means of identifying performance decreases, which may allow a well owner to intercede in a well maintenance issue sooner, when it is less expensive, rather than later which is almost always more costly. Traditional step-drawdown tests are useful if the permanent pumping equipment will safely accommodate different flow rates, and partial constant rate tests are often possible. Another good general test is a constant drawdown test, particularly if you are trying to keep the pumping water level above the pump by a fixed distance and want to know what kind of sustainable flow rates are possible if groundwater elevations decline in response to drought or over-pumping of an aquifer.
Next collect water samples. This is best done at the completion of a pumping test or a period of protracted pumping, just prior to shutting the pump motor off. The samples should be collected according to standard protocols using appropriate equipment (e.g. clean glass containers from the laboratory, nitrile gloves, etc.) and keep iced until they get to the laboratory. The samples can be analyzed for their chemical composition, e.g. calcium, sodium, bicarbonate, etc., which will give indications of water quality, suitability for consumption, or irrigation. Additionally, it is recommended the biology of the well and aquifer be tested to the extent differences in the bacteria present in the well versus the aquifer are readily apparent. Changes in water chemistry or quality may occur seasonally or under the influence of recharge, so plan accordingly and evaluate water chemistry more than once, depending on the changes that are occurring in the area around the well. These changes may be important and indicate when maintenance of the well is needed sooner rather than later.
Lastly, video log the well. Don’t settle for a micro-camera/pump-left-in the well options, this just costs money for a highly frustrating visual record of less-than-acceptable quality in most cases. Rather, remove the motor and pull the pump. You could do this during regularly scheduled maintenance but in general that does not occur often enough to make it worthwhile waiting. Select a reputable contractor who has a history of well video logging, and if at all possible work with someone who has experience in interpreting the video log.
Hopefully the well has been video logged before and that proper indexing of salient internal features occurred, such that follow on comparisons are possible. If not, then plan the logging effort so clear objectives are provided to the logging company, such that this first visual record not only provides a good understanding of the readily apparent condition of the inner workings of the well, but also will act as a home condition, i.e. a baseline reference point for subsequent assessments.
The pumping test and water quality data, along with a good video log (and log interpretation) provide a benchmark, or home, against which changes in the operational capacity and performance can be judged. This baseline data will facilitate timelier and most likely less costly maintenance as it is used to compare the data to subsequent tests and video logs.
Christopher S. Johnson, PG, CHg, is the president and principal hydrogeologist at Aegis Groundwater Consulting LLC in Fresno, California. Johnson works with well owners and operators on a variety groundwater-related projects, including locating new water resources, well design and construction management, aquifer testing, and well rehabilitation. He can be reached at firstname.lastname@example.org.