The Delaware Geological Survey released a new Open File Report titled “Results of Groundwater Flow Simulations in the East Dover Area, Delaware,” which was prepared by Changming He and A. Scott Andres of the Survey. DGS Open File Report No. 52 documents monitoring and modeling work that were conducted in the east Dover area to investigate the impacts of current and potential future groundwater withdrawals on the local groundwater system.

In 2015, staff of the Water Supply Section of the Delaware Department of Natural Resources and Environmental Control (DNREC) informed the DGS of their concerns about overpumping of the unconfined Columbia aquifer in an area east of Dover. In this area, the City of Dover’s Long Point Road Wellfield and numerous irrigation systems pump water from the shallow Columbia aquifer. Overpumping is a cause for concern because it may 1) increase the risk for saltwater intrusion into the aquifer from saline tidal creeks and marshes and, 2) induce extra drawdown that could reduce the transmissivity of the aquifer and decrease well yields.

To evaluate the impacts of overpumping in the east Dover area, groundwater levels and specific conductance data were collected in selected wells and a three-dimensional numerical model was constructed to simulate the groundwater flow in the unconfined Columbia aquifer and several underlying confined aquifers.

Model results indicate that pumping by the City of Dover and irrigation systems have a significant impact on groundwater elevations and flow directions in the Columbia aquifer within the study area. The magnitude of the impact varies with pumping rates, with larger pumping rates causing greater drawdown of groundwater elevations and in larger areas where flow directions change more than 90 degrees.

There is increased risk for intrusion of saline water into wells and irrigation water sources in areas associated with water-table elevations near or below sea level and located in proximity to saline tidal creeks and marshes. Areas where pumping significantly reduces the thickness of saturated the aquifer are at risk for reduced well yields due to decreased aquifer transmissivity, and, increased pumping costs due to lower dynamic heads in the wells. For both concerns, the risks are greatest during the irrigation season when pumping rates are greatest.
This information in this report will be useful for water supply planning and for management of water-dependent environmental resources.

The report fulfills part of the DGS’s mission to understand hydrologic systems and to advise, inform, and educate Delawareans about the results of such investigations so they can serve as a resource for scientists, engineers, planners, emergency managers, and the public.

Open File Report No. 52 is available in pdf format from the DGS web site at http://www.dgs.udel.edu/publications. For additional information, contact the Survey at (302) 831-2833 or via email at delgeosurvey@udel.edu.