Virginia Chloride Monitoring Network

Problem

Demands for freshwater in the Coastal Plain of Virginia continue to increase. More pumping wells are being added each year to supply present and future needs; however, supplies of freshwater in some of the most productive aquifers--the Cretaceous and early Tertiary aquifers--are limited by the presence of saltwater which tends to increase with depth and to the east toward the Chesapeake Bay and Atlantic Ocean. In fact, some production wells are designed to pump slightly saline (brackish) water which is then desalinated and mixed with water from other sources. Information about the distribution of saline water in these aquifers and an evaluation of the potential for intrusion or upcoming of saline water will contribute to the wise management of the groundwater resources of the Coastal Plain.

Objective

Objectives of the program are to (1) evaluate the spatial and temporal distribution of chloride concentrations in the aquifers, (2) evaluate the factors that affect the spatial and temporal distributions of chloride, and (3) assess the potential for upcoming or lateral intrusion of saline water in the aquifers.

Relevance and Benefits

Information about the distribution of saline water in these regional aquifers will aid in evaluating the potential for intrusion or upconing of saline water. Information about the general chemistry of the aquifers could provide further insights about the origin of saltwater, which has impaired the availability of groundwater in the Coastal Plain of Virginia. Information gained through this project will contribute to the wise long-term planning and management of the groundwater resources of the Hampton Roads area.

Approach

A multi-phase and multi-year systematic approach was proposed and initiated in 1995 by the Virginia District of the USGS. Major study components include (1) compilation and preliminary analysis of existing chloride data, (2) compilation of additional geologic, geophysical, hydraulic, and water-use information for aquifers and confining units with an emphasis on areas with limited data and areas where concentrations of chloride are of greatest concern, (3) evaluation of alternatives for obtaining additional data in areas of insufficient data, (4) expansion and refinement of a long-term monitoring program for salty groundwater, and (5) analysis of the potential for upcoming and lateral movement of salty water.