Tammy M. Zimmerman Melinda J. Chapman Charles A. Cravotta III, Zoltan Szabo Bruce D. Lindsey 2015 <p>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rapidly, and increasingly dependent on groundwater as a source of supply, with more than 550 million gallons per day withdrawn from domestic wells for household use.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.</p> <h4><strong>Major Findings</strong></h4> <ul type="disc"> <li>Many contaminants in groundwater have geologic sources, but geochemical conditions control whether or not those contaminants dissolve and move through groundwater</li> <li>Concentrations of nitrate and bacteria&mdash;the main drinking-water contaminants with human sources&mdash;were high in carbonate-rock aquifers and frequently exceeded human-health benchmarks</li> <li>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</li> </ul> application/pdf 10.3133/cir1354 en U.S. Geological Survey 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 reports