[Final Report in PDF format (13,000 kb)]

Water-Supply Potential of the Coastal Plain Aquifers in Calvert, Charles, and St. Mary’s Counties, Maryland, with Emphasis on the Upper Patapsco and Lower Patapsco Aquifers

by
David D. Drummond

Executive Summary

A study was conducted of the water-supply potential of the aquifer system in Calvert, Charles, and St. Mary’s Counties. A ground-water flow model was developed that simulates water levels in the five major aquifers in Southern Maryland. The flow model was calibrated using historical pumpage and water levels, and was then used to estimate future water levels through 2030 based on future pumpage scenarios compiled in conjunction with county planning departments.

Projected water demand in Calvert and St. Mary’s Counties through 2030 could be met by increased pumpage in the Aquia aquifer (without shifting withdrawals to deeper aquifers) without reducing water levels below the 80-percent management level. Shifting a portion of public-supply withdrawals from the Aquia aquifer to the Upper Patapsco aquifer would result in an increase in available drawdown in the Aquia aquifer in many areas of the counties, with minimal effects on drawdowns in the outcrop area in Charles County.

In Charles County, the proximity of the major pumping centers to the outcrop/recharge areas of the Patapsco aquifers, and the relatively shallow depth of the aquifers limit their productive capabilities. Withdrawals from the Magothy aquifer in the Waldorf area cannot be increased significantly above 2002 amounts without lowering heads below the 80-percent management level by 2030. Simulated future drawdowns indicate the potential for river-water intrusion into the Upper Patapsco and Lower Patapsco aquifers from the Potomac River in the Indian Head area. Simulated drawdowns also indicate the potential in shallow portions of the Patapsco aquifers for reduced base flow to streams and a lowered water table, which could reduce the amount of water available in some types of wetlands. These issues could not be specifically addressed in the context of a large regional study, but require additional examination. Alternative water-supply options should be evaluated in Charles County, such as utilizing the Patuxent aquifer, or replacing current production well fields with new wells in the Patapsco aquifers farther southeast.

updated 10/4/05

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