Maryland Department of Natural Resources

Reports

Hydrogeology of the Coastal Plain aquifer system in Queen Anne's and Talbot Counties, Maryland, with emphasis on water-supply potential and brackish-water intrusion in the Aquia aquifer


2001, Drummond, D.D.

Report of Investigations 72


Purpose and Scope

The purpose of this report is to present the results of a 3-year study of the hydrogeology of Queen Anne's and Talbot Counties. The study focused on the hydrogeology, water-supply potential, and brackishwater intrusion in the Aquia aquifer, but also examined the hydrogeology of the other aquifers used in the study area, including the Piney Point, Matawan, Magothy, and Upper Patapsco aquifers. The Columbia and Chesapeake aquifers, which are shallower than the Piney Point aquifer, were included in the ground-water flow model, but were not examined in detail. Existing wells were inventoried during the study to document data on water levels, water quality, and pumpage amounts. Geophysical logs were obtained on four new wells, and compiled with 22 existing logs to create gamma-log cross sections. Ground-water samples were obtained from 30 wells for chemical analysis, in order to fill in data gaps in the Aquia and Piney Point aquifers, and to document water quality in the Cretaceous aquifers. A synoptic water-level measurement was conducted in the fall of 1997 to develop potentiometric surfaces for the Aquia and Piney Point aquifers, and to provide scattered head measurements in the Cretaceous aquifers. Monthly water-level measurements were taken in a network of wells screened in each of the major aquifers to document head changes caused by seasonal variations in recharge, evapotranspiration, and pumpage. Shortterm water-level variations were documented by installing continuous water-level recorders on two wells in the Aquia aquifer. Field measurements were taken for chloride concentration and specific conductance on water from 18 wells, mostly in Talbot County, to determine if brackish-water intrusion was a problem south of Kent Island. A ground-water flow model was developed to simulate water levels and flow rates in each of the major aquifers in the study area. The flow model was calibrated to historic water levels, and used to estimate future changes in ground-water levels as a result of various projected-pumpage scenarios. The model was also used to estimate changes in ground-water flow at the brackish-water interface on Kent Island, which provides an indication of the potential for brackish water intrusion for each of the pumpage scenarios. A particle-tracking routine was also used to estimate the potential for brackish-water intrusion.