In 2015, DGS became aware of a situation east of Dover where there is potential for overpumping of the Columbia aquifer by the City of Dover’s Long Point Road wellfield (LPRW) and numerous large-capacity irrigation wells in the surrounding area (Figure 1). Overpumping is a cause for concern for two primary reasons: 1) the risk for saltwater intrusion from saline tidal creeks and marshes on the east, north, and south, and other saline tidal creeks that bisect the area; and, 2) drawdown could reduce the transmissivity of the aquifer and decrease well yields. The potential for overpumping will become more significant when a electric generating station served by the LPRW becomes fully operational in the next few years and requires more water.
To investigate the potential for overpumping, a digital groundwater flow model was constructed and run in steady state and transient modes. As is the case with most models, many assumptions and simplifications had to be applied because of data limitations. The model was calibrated to a spatially limited set of data. Much of groundwater pumping for irrigation is not reported and has been estimated from irrigation demand estimates. Consequently, model outputs are meant to inform how the aquifers behave given the assumptions and simplifications and will not represent precise predictions of water pressures in the area represented by the model. Additional data are now being collected in the model domain to refine the accuracy and precision of model results.
One of the results of the work is a three-dimensional solids model (Figure 2 from work by McLaughlin et al, 2014) that depicts the position and thickness of the Columbia (top), Frederica, Federalsburg, and Cheswold (bottom) aquifers and confining beds in the model domain. This solids model along with hydraulic properties of aquifers and confining beds, and climatic data are the bases for groundwater flow model simulations.
Click on this link to show a short video of monthly water-table fluctuations between January 1995 and December 2015. It illustrates how the water table rises and falls in response to monthly and seasonal changes in weather and pumping. In the video, time has been compressed to show 20 years of simulation time in about 30 seconds of real time. https://youtu.be/fa0L5Qs8_38