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

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.

[Summary provided by David D. Drummond, Maryland Geological Survey.]