GROUND-WATER QUALITY IN THE PIEDMONT AQUIFERS, EASTERN UNITED STATES – A SUMMARY OF STUDIES BY THE U.S. GEOLOGICAL SURVEY NATIONAL WATER-QUALITY ASSESSMENT PROGRAM, 1993-2003

The U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program is conducting a systematic study of the nation's water quality in 50 of the largest river basins and aquifers, known as study units, across the United States. These studies assess the chemical quality of ground water and surface water, as well as ecological health of streams. The collection and analysis of water-quality data have been conducted at the study-unit scale; some major topics have been synthesized at the national scale. To link together ground-water findings at the study-unit and national scales, the current focus of the NAWQA Program is at a regional scale based on principal aquifer.

The NAWQA study of the Piedmont Aquifers was based on data from 270 wells from 6 NAWQA study units in 7 states. The data were classified according to lithology into categories of igneous and metamorphic, carbonate, and siliciclastic aquifers. Land use also was considered during analysis. Ground-water samples were analyzed for nutrients, pesticides, volatile organic compounds (VOCs), radon, and in some cases, trace elements and bacteria.

Major findings of the study indicate few contaminants exceeded drinking-water standards. The constituents that exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) were nitrate, radon, arsenic, and bacteria. Nitrate concentrations exceeded the USEPA MCL of 10 milligrams per liter in 11 percent of the wells sampled. Most nitrate detections were in carbonate aquifers with agricultural land use. Radon exceeded the proposed USEPA MCL of 300 picocuries per liter in nearly 90 percent of the wells sampled. Wells completed in aquifers with igneous and metamorphic rocks with a predominantly felsic mineralogy had the highest concentrations of radon. Arsenic exceeded the MCL of 10 micrograms per liter in 3 percent of the wells sampled. Wells in siliciclastic aquifers had the highest arsenic concentrations. Total coliform bacteria were detected in 61 percent of the wells sampled and fecal coliform in 14 percent of the wells sampled. Higher bacteria concentrations were related to higher percentages of agricultural land use. Herbicides were related to agricultural land use. Insecticides and VOCs were related to urban land use.