The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009

The aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions underlie an area with a population of more than 40 million people in 10 states. The suburban and rural population is large, growing rapidly, and increasingly dependent on groundwater as a source of supply, with more than 550 million gallons per day withdrawn from domestic wells for household use. Water from some of these aquifers does not meet human-health benchmarks for drinking water for contaminants with geologic or human sources. Water from samples in crystalline- and siliciclastic-rock aquifers frequently exceeded standards for contaminants with geologic sources, and samples in carbonate-rock aquifers frequently exceeded standards for contaminants with human sources, most often nitrate and bacteria.

Major Findings

• Many contaminants in groundwater have geologic sources, but geochemical conditions control whether or not those contaminants dissolve and move through groundwater
• Concentrations of nitrate and bacteria—the main drinking-water contaminants with human sources—were high in carbonate-rock aquifers and frequently exceeded human-health benchmarks
• Large contributions of nitrate and phosphorus from groundwater to streams have a negative effect on ecological health of estuaries, such as the Chesapeake Bay and Albemarle-Pamlico Sound