Hydrogeology & Hydrology Program
Anne Arundel County Aquifers	contact: David Andreasen (dandreasen@dnr.state.md.us)

Water-Supply Potential of the Magothy, Upper Patapsco, Lower Patapsco, and Patuxent Aquifers in Anne Arundel County, Maryland

Project Objectives

     The Maryland Geological Survey in cooperation with Anne Arundel County Department of Public Works has initiated a 2 1/2-year study to determine the effect of projected (2040) withdrawals from the Magothy, Upper Patapsco, Lower Patapsco, and Patuxent aquifers on ground-water levels and recharge rates. The study will also determine optimum pumping rates for production wells operated by the Anne Arundel County Department of Public Works and as well as the selection future well sites that minimize drawdown in the aquifers.

Background

     Anne Arundel County relies primarily on ground water pumped from the Aquia, Magothy, Upper Patapsco, Lower Patapsco, and Patuxent aquifers. Average daily withdrawals totaled approximately 46 million gallons per day (Mgal/d) in 2000. Of that amount, a total of 23 Mgal/d was pumped on an average daily basis from the Upper and Lower Patapsco aquifers and Patuxent aquifer by public-supply wells operated by the Anne Arundel County Department of Public Works. Wells completed in these aquifers are typically more than 500 feet deep. The Anne Arundel County Department of Public Works does not withdraw water from either the Aquia or Magothy aquifers; however, the Magothy aquifer is hydraulically connected to the Upper Patapsco aquifer on Broadneck Peninsula (Mack and Andreasen, 1991). The county operates five major well fields in the central and northern part of the county at Arnold (Upper and Lower Patapsco aquifers), Broadcreek ( Upper and Lower Patapsco aquifers), Crofton Meadows (Lower Patapsco and Patuxent aquifers), Glen Burnie (Patuxent aquifer), and Severndale (Lower Patapsco and Patuxent aquifers). The county also maintains several relatively low capacity community well systems. Pumpage from the well fields have caused cones-of-depression to develop at Arnold, Broadcreek, Crofton Meadows, and Severndale (Curtin and others, 2000a and 2000b). Water-level trends over the last five years are either flat or decline at rates up to 1.5 feet per year (Fewster and Andreasen, 2002). Water levels measured in observation wells generally do not exceed 75 feet below sea level in any of the aquifers; however, pumping levels in production wells may be significantly deeper. The combination of relatively deep aquifers and shallow water levels result in a substantial amount of available drawdown, especially in the Lower Patapsco and Patuxent aquifers, which could be utilized for additional withdrawals. Average daily withdrawals from all county-operated well fields may increase by as much as 44 Mgal/d by 2040. An increase of that magnitude may potentially cause water levels to exceed management levels or exceed the aquifer’s recharge capacity. The water-supply potential of the major aquifers underlying Anne Arundel County were evaluated previously using ground-water-flow models (Mack and Achmad, 1986; Achmad, 1991). Those models were developed based on the hydrogeologic data and water-use projections available at the time. Revised water-use projections and refinements in the hydrogeology of the aquifer system, however, necessitate developing a new ground-water-flow model to reassess water-supply potential and effects on water levels from increased pumpage. In addition, an updated model can be used to develop optimum well withdrawal rates and to select future well sites that reduce drawdown in the aquifers. Changes in the water budget can also be evaluated as recharge from outcrop increases to supply greater pumpage demands.

References

Achmad, G., 1991, Simulated hydrogeologic effects of the development of the Patapsco aquifer system in Glen Burnie, Anne Arundel County, Maryland: Maryland Geological Survey Report of Investigations No. 54, 90 p.

Curtin, S.E., Andreasen, D.C., and Wheeler, J.C., 2000a, Potentiometric surface of the upper Patapsco aquifer in Southern Maryland, September 2000: U.S. Geological Survey Open-File Report 02-246, 1 p.

________ 2000b, Potentiometric surface of the Lower Patapsco aquifer in Southern Maryland, September 2000: U.S. Geological Survey Open-File Report 02-247, 1 p.

Fewster, T.B., and Andreasen, D.C., 2001, Hydrographs and tables showing ground-water level records for selected observation wells in Anne Arundel County and hydrograph showing surface-water flow in Sawmill Creek, 2002: Maryland Geological Survey, unpublished report, 47 p.

Mack, F.K., and Achmad, G., 1986, Evaluation of the water-supply potential of the aquifers in the Potomac Group of Anne Arundel County, Maryland: Maryland Geological Survey Report of Investigations No. 46, 111 p.

Mack, F.K., and Andreasen, D.C., 1991, Geohydrologic data for the Coastal Plain sediments underlying Broadneck Peninsula, Anne Arundel County, Maryland: Maryland Geological Survey Open-File Report No. 92-02-6, 70 p.