Published in October 2019 Focus on the Environment Newsletter
Thanks to the hydrologic cycle, the water on earth is being continuously recycled as it moves from one storage place to another. The quantity of water at any particular place or time fluctuates depending on seasonal cycles in temperature, rainfall, evaporation, plant uptake, and recharge. This cycle is evident in the seasonal fluctuation of groundwater levels that typically rise during the winter and spring (periods of lower demand and greater recharge) and decline during the summer and fall (higher demand and less recharge). Although the magnitude can vary from year to year, seasonal groundwater level fluctuations in shallow unconfined aquifers in Ohio can be on the order of several feet or more.
Seasonal declines in the water table often translate to a loss in well capacity. As groundwater levels decline, the saturated thickness of the aquifer becomes thinner, reducing the volume of water moving through the formation. Under these conditions, the well must work harder (i.e. create more drawdown) to maintain the pumping rate. This additional drawdown is compounded on top of any extra drawdown resulting from factors such as well loss (i.e. the physical, chemical and/or biological plugging of the well screen) and/or well interference. In shallow aquifers, where available drawdown is a limiting factor, pumping rates are often throttled back to prevent pumping levels from dropping below critical levels.
The prelude to understanding the individual factors affecting well performance begins with the regular collection and review of information pertaining to the past and present performance of the well field. Although periodic inspection and testing establish current performance characteristics, record-keeping procedures are more useful for identifying normal operating trends and their relationship to overall performance. The regular collection of static groundwater levels, pumping levels, pumping rates and duration, and related data provides the information necessary to document well interference effects, track individual well performance trends with time and determine the range of seasonal groundwater level fluctuations. Collectively, the data provides the water well operator with ability to identify which factor(s) has the greatest influence on a given production well. Well performance losses attributed to physical, chemical and/or biological plugging of the well screen and/or mechanical deterioration of the pump and/or motor can be forecast in advance and addressed prior to the seasonal low groundwater period. Similarly, well pumping schedules can be managed, to the degree possible, to minimize the adverse effects of well interference on individual well capacities.
Finally, if the limiting factor turns out to be the seasonal low groundwater level, then about all you can do is ride it out until the recharge cycle kicks in and provides relief. You can’t fight Mother Nature, but with a little bit of data and planning, you can give yourself a fighting chance to ensure a dependable supply to your customers.
Doug is a licensed professional geologist in Indiana and North Carolina. As a consulting hydrogeologist, Doug specializes in aquifer characterization and yield determinations, well and wellfield performance evaluations, and the design and testing of both vertical well and horizontal collector well systems. Additional areas of expertise include environmental assessment and remedial system evaluation and design. He has worked throughout the United States on a wide variety of groundwater supply and environmental contamination related projects. Doug’s wide-ranging expertise and extensive experience in the groundwater supply industry add another dimension to Cox-Colvin’s technical staff and provide additional opportunity to support our clients in meeting their needs and reaching their business goals.