Radium-228 and radium-226 in ground water of the Chickies Formation, Southeastern Pennsylvania

Routine sampling of public water supplies by the Pennsylvania Department of Environmental Resources (PaDER) and the U.S. Environmental Protection Agency (USEPA) revealed three supplies in the Chickies Formation that exceeded the USEPA drinking-water maximum contaminant level (MCL) of 5 pCi/L (picoCuries per liter) dissolved radium. The ground waters are slightly reducing and contain detectable Fe and Mn concentrations. Data from PaDER suggest that the radium anomalies are limited to the Chickies Formation. In these acidic waters, Ra2+ is probably mobilized and remains in solution rather than being adsorbed as in most ground-water systems. A study being conducted by the U.S. Geological Survey, in cooperation with the Pennsylvania Topographic and Geologic Survey (PaT and GS), which includes the sampling of 180 wells completed in or near the Chickies Formation, is expected to characterize the hydrogeology and geochemical environment associated with elevated radium concentrations. An understanding of the mechanisms controlling the occurrence of radium in solution could facilitate the location of alternative water supplies and help to anticipate radium concentrations in similar lithologies. Radium-228 concentrations for 48 wells ranged from less than 0.5 to 50 pCi/L, and radium-226 concentrations ranged from less than 0.1 to 9.5 pCi/L. Forty-three of the 48 analyses had radium-228 concentrations in excess of those for radium-226 suggesting that gross alpha screening should be used with caution because radium-228 is not an alpha emitter