National Ground-Water Association, 2005 ground-water summit, San Antonio, Tx.
Session S18 Comprehensive Regional Water-quality Monitoring Programs and Data Interpretation Issues

Abstract

The Piedmont aquifer system (PAS) is one of the principal regional aquifers being studied by the U.S. Geological Survey (USGS) in Cycle II of the National Water-Quality Assessment (NAWQA) Program. The PAS underlies an area of about 78,000 square miles in the Piedmont Physiographic Province. The Piedmont is bounded on the south and east by the Fall Line and the Atlantic Coastal Plain and on the north and west by either the Blue Ridge, the Ridge and Valley or the New England Physiographic Provinces. Nine NAWQA study units include parts of the PAS.
Ground water in the Piedmont moves along relatively short, localized flow paths rather than long, regional flow paths; therefore, the regional approach for water-quality assessment is to evaluate and summarize the study unit surveys of ground-water quality in areas with similar rock types and land uses. There have been a total of 11 individual surveys of ground-water quality conducted by the nine study units since 1993. The occurrence and distribution of contaminants in water from wells sampled in these surveys are analyzed to determine whether or not these studies provide information to 1) adequately characterize water-quality conditions, and 2) indicate patterns that can assist water managers in understanding the susceptibility of the PAS to ground-water contamination. Three rock types (crystalline, siliciclastic, and carbonate) are used to subdivide the Piedmont into the aquifers that have unique characteristics of ground-water flow.
Synthesis results indicate that the uneven spatial distribution of sampling and small number of samples limit the conclusions that can be drawn from the study and prohibit rigorous spatial analysis of ground-water quality. However, patterns of contaminants in the areas that were sampled can provide significant insight into the susceptibility of the aquifers to natural and anthropogenic contaminants.
Concentrations of nitrate are higher in the areas underlain by carbonate bedrock, as are detections of pesticides and volatile organic compounds (VOCs). Nitrate concentrations and pesticide detections are related to the intensity of agricultural activity. VOCs are related to the population density. Radon concentrations are higher in areas underlain by igneous and metamorphic rock. Arsenic concentrations are highest in the area underlain by siliciclastic bedrock. Sampling density and changes in analytical methods limit the ability to make conclusive statements about some of these issues, but these findings may help direct future studies of water quality in the aquifers of the Piedmont.