Evaluation of the water-supply potential of aquifers in the Potomac Group of Anne Arundel County, Maryland
1986, Mack, F.K. and Achmad, G.
Report of Investigations 46
A multi-layer aquifer model was developed to simulate the effects of pumping stresses on aquifers in the Potomac Group in northern Anne Arundel County, Maryland. The model represents a hydrologic system including four Coastal Plain aquifers known locally as the Patuxent, the lower Patapsco, the upper Patapsco, and the overlying Magothy aquifer. These aquifers are layers composed mainly of sands that dip gently to the southeast from band-shaped outcrops in the northwestern part of the modeled area, and are separated from one another in downdip areas by relatively impermeable confining beds.
The model was developed by using measured values for the hydrologic properties of the aquifers and confining beds where they were available and by using estimated values where measured values were not available. The model was calibrated by using monthly pumpage of more than 250 production wells and water levels measured in 39 observation wells over the 12-year period from December 1965 through December 1977. The calibration was accomplished by comparing the computed potentiometric levels with the corresponding water levels measured in the field for both steady-state and transient-state conditions. The maximum difference between the computed and observed water levels of the 39 observation wells was about 30 feet, but the difference was generally less than 10 feet. Trends of 30 of 39 hydrographs compared well; eight were fair, and one was poor.
Pumpage by the Anne Arundel County Department of Utilities, other governmental agencies, and industry is expected to total 118 million gallons per day by the year 2000 in the model area, which includes all of Anne Arundel County and portions of the adjacent counties. The calibrated model was used to predict the effect of that pumpage on water levels in each aquifer. The results indicated that deep cones of depression would be developed in some aquifers, but that the well fields could provide the quantities needed.