The SANT NAWQA has assessed the water quality of major aquifer systems used for water supply in the Santee River and Coastal Drainages study unit. Thirty existing wells have been sampled in each of the Sandhills (Summer, 1997), Floridan (Spring, 1998), and Piedmont (Summer, 1998) studies. Water samples were analyzed for field parameters (pH, water temperature, specific conductance, and dissolved oxygen), organic carbon, major-ions, nutrients, radon, pesticides (including insecticides and herbicides), and volatile organic compounds (VOCs).