Patuxent Naval Air Station Hydrogeology

WRD PROJECT #: MD124
PROJECT CHIEF: Klohe, Cheryl A.
BEGIN DATE: 17-December-1997
END DATE: 30-September-2002

Customers currently supporting the project:

U.S. Navy, Patuxent Naval Air Station

Problem

The Southern Maryland Counties of Calvert and St. Marys are experiencing rapid growth. The Piney Point/Nanjemoy aquifer and Aquia aquifer are the main sources of potable (drinkable) ground water in the two-county area, including Patuxent Naval Air Station. Aquia aquifer water levels have declined substantially forming a large cone of depression that is 131 feet below sea level at its deepest point. Because of substantial population growth, there is concern among water managers (State, County, Naval Air Station) that the management level (80 percent available drawdown) will be exceeded in both aquifers. Once this level is exceeded, no additional pumping for water supply will be allowed in these aquifers. In addition, this large cone of depression has reversed the natural ground-water flow direction and has the potential to cause saltwater intrusion problems in large production wells.

Objectives

Complete a hydrogeologic assessment of water supply, water quality, and the potential for saltwater intrusion in Piney Point/Nanjemoy and Aquia aquifers near the Patuxent Naval Air Station.

Approach

1. Inventory existing data from USGS data bases; Water-Quality Data base (QWDATA), Ground-Water Site Inventory Data base (GWSI), State Water-Use Database (Surface WaterUD) and Navy data bases to establish a framework of known hydrogeologic data near the Station.
2. Design a long-term water-level monitoring network in the Piney Point/Nanjemoy and Aquia aquifers. Instrument several wells (either newly constructed or existing) with continuous recorders to monitor water level changes over time. Make synoptic water-level measurements during April and October of each year.
3. Investigate water-quality trends and determine the potential for saltwater intrusion in the Piney Point/Nanjemoy and Aquia aquifers. Trends in water quality will be examined from existing water-quality data and newly sampled wells. Saltwater intrusion will be analyzed using Piper diagrams and sodium, chloride, ratios of bromide/chloride, etc., and isochrons to determine the extent of saltwater intrusion (if any).
4. Determine the hydrogeologic framework of the confined aquifers from existing and new data. This includes the preparation of geologic cross sections, existing and new well-lithology logs, fence diagrams, contour maps of aquifer surfaces, thickness, potentiometric surfaces, etc.
5. Develop detailed ground-water-flow model and optimization algorithms for the Piney Point/Nanjemoy and Aquia aquifers at the Patuxent Naval Air Station.
6. Design a visualization of geologic data, ground-water flow, and optimization of management scenarios using three-dimensional visualization computer tools.