MGS geologists presented talks at the 2015 Maryland Groundwater Symposium, September 20, 2015

An Overview of Groundwater in Maryland

Andrew Staley

ABSTRACT

More than one-quarter of Marylanders depend on groundwater as their primary water source. Yet to many people, groundwater is somewhat mysterious, largely because we cannot observe it directly. This talk will introduce the fundamental concepts of groundwater, with emphasis on groundwater settings that exist in Maryland. Topics for discussion will include the hydrologic cycle, porosity, permeability, recharge, water table versus confined aquifers, and cones of depression. Methods of investigation including water-level measurement, geophysical well logs, pump tests, and groundwater flow models also will be covered. In addition, challenges to our groundwater quality and availability, including drought, drawdown, and saltwater intrusion will be discussed.

The occurrence of groundwater in Maryland is largely dependent on the subsurface geology in which it is found. The aquifers consisting of unconsolidated sediments of the Coastal Plain, for example, will store and transmit groundwater very differently from the fractured crystalline bedrock of the Piedmont. As a result, aquifers in the varied regions of the State will respond differently to drought and excessive pumping, and will be susceptible to contamination in different ways.

Studying the Effects of Dredge Material Placement at Masonville and Cox Creek

Johanna Gemperline

ABSTRACT

The Port of Baltimore shipping channels require periodic maintenance dredging to maintain adequate depths. Due to possible contamination, dredge material must be confined. Recent proposals from the Maryland Port Administration to increase future storage capacity include a confined aquatic disposal (CAD) system in the Masonville area and the raising of dikes and expansion of the existing Cox Creek Dredged Material Containment Facility (DMCF).

The potential effects of dredge material placement on groundwater, especially the Lower Patapsco and Patuxent aquifer systems, are of concern to both the Masonville and Cox Creek studies. At the Masonville site, located in the outcrop area of the Lower Patapsco aquifer system and overlying the Patuxent aquifer system, the concern is that contaminants could migrate from the dredge material either horizontally into the Lower Patapsco aquifer system or vertically into the Patuxent aquifer system. At Cox Creek, overlying both aquifer systems, the potential effects include not only the vertical migration of contaminants but also a change in local groundwater flow direction.

In order to determine the potential effects of dredge material on groundwater, the Maryland Geological Survey completed a pair of studies in 2014 and 2015 at the Masonville and Cox Creek sites respectively. Both studies used geophysical and lithologic logs to establish the hydrogeologic framework at the sites, and groundwater levels in monitoring wells to determine the local and regional potentiometric surfaces. At Masonville, the direction of groundwater flow prevents the landward migration of contaminants into the Lower Patapsco aquifer system, while the Arundel Clay confining unit forms a hydraulic barrier to the vertical migration of contaminants into the Patuxent aquifer system. At Cox Creek, the Patapsco confining unit effectively prevents the migration of contaminants into the Lower Patapsco aquifer system, and the Arundel Clay confining unit further prevents contamination of the Patuxent aquifer system.