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

1. Define the hydrogeologic framework and natural water quality of the Aquia and Magothy aquifers in southern Anne Arundel County.
2. Establish an observation-well network in southern Anne Arundel County.
3. Estimate — utilizing a three-dimensional, ground-water-flow model — the water-supply potential of the Aquia aquifer and predict the effects of current and estimated future withdrawals on water levels.
4. Estimate the water-supply potential of the Magothy aquifer using a semi-analytical model.

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Water for domestic supply in southern Anne Arundel County is pumped almost entirely from individual wells screened in the Aquia aquifer. Large, individual supplies (public or commercial) account for a relatively small part of the total water pumped. The Aquia aquifer is the most desirable source of ground water in the area, given its relatively shallow depth and generally acceptable water quality. The Aquia aquifer is both confined (artesian aquifer) and unconfined (water-table aquifer) in southern Anne Arundel County. The deeper Magothy aquifer--capable of supplying large quantities of water to wells--is an additional, easily obtained source of ground water in southern Anne Arundel County. However, the presence of elevated iron concentrations may make it less appealing for individual, residential use. Currently, the Magothy aquifer is used primarily for irrigation and minor public supply. Approximately 0.3 million gallons per day (Mgal/d) was pumped from the Magothy aquifer in southern Anne Arundel County in 1998. In comparison, the Aquia aquifer was pumped at a rate of approximately 2 Mgal/d in 1998. Increased demand on the Aquia aquifer in southern Anne Arundel County and in areas south have caused water levels to decline. The current rate of water-level decline is approximately 1-2 feet per year in the confined part of the aquifer. The declining water levels have resulted in moderate reductions in the available drawdown. Increased production of the Aquia aquifer caused by the growing population will result in additional drawdown. Effective water-supply management to insure long-term productivity of the Aquia aquifer requires an evaluation of the impact of both current and estimated future pumpage on water levels. Previous water-supply studies of the Aquia aquifer (Chapelle and Drummond, 1983; Achmad and Hansen, 1997) included southern Anne Arundel County, but were focused primarily on Calvert and St. Mary's Counties where withdrawals are greatest. The purpose of this study is to (1) determine the hydraulic characteristics of the Aquia and Magothy aquifers and quantify their water-supply potential in southern Anne Arundel County, and (2) determine the cumulative impact of increasing ground-water pumpage in Anne Arundel, Calvert, and St. Mary's Counties on future Aquia water levels in southern Anne Arundel County.

An additional purpose of the study is to quantify the natural water quality of the Aquia and Magothy aquifers and determine any spatial trends in water quality. Water quality of the Aquia aquifer is generally good; however, at some locations, elevated iron, hydrogen sulfide, and calcium concentrations result in poor water quality. These constituents do not pose health risks but are aesthetically undesirable--collectively causing iron stains on clothing and plumbing fixtures, "rotton-egg" smell, reduced ability to form soap lather, and formation of white scale on the heating of water. Residential water-treatment systems are widely used to correct these water-quality problems at varying levels of effectiveness and cost. The Aquia aquifer may also be locally susceptible to brackish-water intrusion on the northern end of the Shady Side peninsula where the aquifer is overlain by less confining material. Water from the Magothy aquifer in central Anne Arundel County and from the few wells tested in southern Anne Arundel County have elevated iron concentrations. There is, however, an insufficient number of water analyses from the Magothy aquifer in southern Anne Arundel County to characterize its water quality adequately.

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1. Compile existing hydrogeologic data for the Aquia and Magothy aquifers in southern Anne Arundel County and vicinity and prepare maps, cross-sections, graphs, and tables.
2. Field inventory high-capacity wells and selected domestic wells. Make synoptic water-level measurements and prepare potentiometric maps.
3. At up to three sites, drill one test hole to the base of the Magothy Formation and convert to a 4-inch well screened in the Magothy aquifer. Adjacent to each Magothy well, construct one 4-inch well screened in the Aquia aquifer. Collect drill cuttings and geophysical logs. Complete an 8-hour aquifer test on each well. Collect water samples and analyze for major inorganic constituents and indicators of radium (gross alpha- and gross beta-particle activity). Equip each well with a continuous-reading, water-level recorder.
4. Collect water samples from 20 to 25 residential wells screened in the Aquia aquifer and the several existing wells screened in the Magothy aquifer. Analyze samples for major inorganic constituents and indicators of radium.
5. Obtain from county and state planning agencies population and water-use forecasts (2001 to 2025) for southern Anne Arundel County and vicinity.
6. Develop a three-dimensional, finite-difference, ground-water-flow model using the U.S. Geological Survey's code MODFLOW. Simulate ground-water flow and water levels in the Aquia aquifer based on: 1) steady-state, prepumping conditions, 2) transient conditions (1900-2000), and 3) future conditions (2001-2025) using various pumpage scenarios representative of a range of estimated population growth. Relate drawdown to the 80-percent management level.
7. Develop a semi-analytical model (multiple-well Theis analysis) of the Magothy aquifer. Simulate water-level drawdowns associated with future (2001-2025) pumping conditions associated with various growth scenarios. Relate drawdown to the 80-percent management level.
8. Write a Report of Investigations discussing the results of the study.

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Achmad, G., and Hansen, H. J., 1997, Hydrogeology, model simulation, and water-supply potential of the Aquia and Piney Point-Nanjemoy aquifers in Calvert and St. Mary's Counties, Maryland: Maryland Geological Survey Report of Investigations No.64, 197 p.

Chapelle, F. H., and Drummond, D. D., 1983, Hydrogeology, digital simulation, and geochemistry of the Aquia and Piney Point-Nanjemoy aquifer system in southern Maryland: Maryland Geological Survey Report of Investigations No. 38, 100 p.

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