Reports
Simulated changes in water levels of the Aquia Aquifer using revised water-use projections to 2025 for Calvert and St. Mary's Counties, Maryland
2001, Achmad, G. and Hansen, H.J.
Supplemental Report S1 / Report of Investigations 64
Summary of Key Results
Forty-six wells and three springs in the Piedmont region of Baltimore County that had been sampled in 1994-96 were resampled in 2000-01 to document what changes, if any, had occurred in the ground-water quality. Samples were analyzed for major ions and nutrients, iron, manganese, lead, five volatile organic compounds, 47 pesticides, radon, gross alpha-particle activity and gross beta-particle activity. Data analysis has resulted in these key results:
The ground-water flow model simulations discussed in this report supplement related information contained in Maryland Geological Survey Report of Investigations No. 64 (Achmad and Hansen ,1997) and are based on revised population projections submitted by the Calvert County Deparlment of Planning and Zoning, the St. Mary's County Metropolitan Commission, and the Maryland Office of Planning. The Aquia aquifer is the focus of the analysis because it is the chief source of supply for major ground-water appropriators (greater than 10,000 gallons per day) in Calvert and St. Mary's Counties.
Three new pumping scenarios are presented that simulate water-level drawdowns in the Aquia aquifer for the period 1999 to 2025 . The simulated water levels are related to management water levels at key sites; the management level is used as an indicator of available drawdown in an aquifer and functions as a regulatory constraint on groundwater appropriations.
Scenario 1 assumes that 2025 pumpage from both the Aquia and Piney Point-Nanjemoy aquifers increases from 6.7 million gallons per day in 1999 to about 9.1 million gallons per day in Calvert County and from 10.5 million gallons per day in 1999 to 19.5 millions gallons per day in St. Mary's County. Simulation of these conditions results in deep, Aquia water levels in 2025 in St. Mary's County; for example, near pumping wells at Country Lakes (253 feet below sea level), Leonardtown (279 feet below sea level), and Wildewood (343 feet below sea levelj where local management levels are exceeded. Elsewhere in St. Mary's County deep water levels are simulated at Lexington park (273 to 308 feet below sea level) and Patuxent Naval Air Test Center (284 feet below sea level), although local management levels are not exceeded because the Aquia aquifer is deeper at these sites. In Calvert County none of the sites evaluated exceed the management level, although comparatively deep Aquia water levels are simulated at Chesapeake Ranch Estates (303 feet below sea level) and Solomons (285 feet below sea level) in 2015.
Scenario 2 assumes a moderate additional increase in Aquia and Piney Point-Nanjemoy usage in St. Mary's County (to 19.9 million gallons per day in 2025) compared with scenario 1, but increases pumpage in Calvert County by 34 percent(to 12.2 million gallons per day in 2025). In St. Mary's County 2025 Aquia water levels are from 10 to 26 feet deeper than the comparable water levels simulated in scenario 1. In Calvert County, however, 2025 water levels are appreciably deeper than in scenario 1, reflecting an increase of 3.1 million gallons per day in Aquia pumpage. For example, at Solomons (344 feet below sea level) and Chesapeake Ranch Estates (372 feet below sea level) simulated water levels in the vicinity of pumping wells are, respectively, 2 feet below and 3 feet above the local management water level.
Scenario 3 assumes that in the future, aquifers deeper than the Aquia will be increasingly used. In this modification of scenario 2 about 20 percent of the pumpage is gradually reallocated, so that by 2025 Aquia and Piney Point-Nanjemoy pumpage is reduced to 15.5 million gallons per day in St. Mary's County and 9.7 million gallons per day in Calvert County. This is accomplished by holding all withdrawals by major appropriators at 1999 levels, while permitting domestic pumpage to increase at scenario 2 levels. Under these conditions, 2025 Aquia water levels near pumping wells are substantially higher than the levels simulated in scenario 2; for example, 2l6 feet below sea level at Wildewood and 225 feet below sea level at Chesapeake Ranch Estates. In scenario 3, 2025 water levels near major Aquia pumping centers remain above local management levels.
