"The nutrient nitrate was the only constituent from manmade sources that exceeded the human-health benchmark. These findings were in the Valley and Ridge carbonate-rock aquifers and the Piedmont and Blue Ridge carbonate-rock aquifers at a low percentage (2 percent)."
Technical announcements for five aquifers studied:
Basin and Range basin-fill aquifers (western U.S.)
Valley and Ridge carbonate-rock aquifers and the Piedmont and Blue Ridge carbonate-rock aquifers (eastern U.S.)
Northern Atlantic Coastal Plain aquifer system (east coast of U.S.)
Southeastern Coastal Plain aquifer system (southeastern U.S.)
Coastal Lowlands aquifer system (south central U.S.)