CHARACTERIZATION OF PIEDMONT AND BLUE RIDGE FRACTURED BEDROCK GROUND-WATER SYSTEMS IN NORTH CAROLINA -- A FEDERAL AND STATE COOPERATIVE STUDY

The U.S. Geological Survey has begun a multiyear cooperative study with the North Carolina Division of Water Quality, Groundwater Section, to characterize ground-water flow systems at selected locations in the Piedmont and Blue Ridge Provinces of North Carolina. The study is focused on identifying hydrogeologic conditions that influence water quality at specific sites that, conceptually, are representative of regional hydrogeologic terranes.

The goal of the study is to provide a better understanding of the hydraulics of ground-water flow systems, and thereby controls on water quality within the hydrogeologic terranes. During the first phase, eight sites are planned. The site may be as small as a few ten's of acres or as large as a ten square mile watershed, depending on site research objectives. Soil and rock cores collected at each site are being examined for factors that affect ground-water quality and movement. Borehole geophysical logs are being used to describe the subsurface hydrogeologic setting, including lithology, fabric orientation, fracture occurrence and orientation, and flow characteristics.

Wells are being installed in clusters along transects to characterize flowpaths, hydraulic gradients, and water-level fluctuations. Aquifer tests and water-quality geochemistry in these wells will provide information on the hydrologic characteristics of the various geologic units. Tracer tests and age-dating techniques will be used to provide estimates of time-of-travel and to delineate flowpaths in the fractured rock ground-water system. Analyses of major ions will be used to examine rock-water interactions and geochemical processes within each hydrogeologic terrane. Surface-water samples from sites having nearby lakes and/or streams will be analyzed to evaluate ground-water/surface-water interactions.

Data produced by this study will provide a baseline for measuring the effects of changes in watersheds that affect water quality and flow characteristics. This information will be useful as a management tool for identifying ambient ground-water quality, delineating areas of high vulnerability to ground-water contamination, and abundant or limited ground-water supplies for meeting potable water needs.