MGS presented a talk at the 2016 National Water Monitoring Council Annual Conference, Tampa, FL, May 2-6, 2015

Dave Bolton presented MGS research at the 2016 National Water Monitoring Council Annual Conference in Tampa, Florida. The conference focuses on information and technology related to all water resources, including rivers and streams, lakes, wetlands, coastal waters and estuaries, groundwater, and processed water. Conference themes attract professional papers and posters addressing a variety of topics ranging from monitoring and assessment to protection and restoration, as well as cutting-edge technologies and methods.

Elevated Radioactivity in Groundwater in Charles County, Maryland

David Bolton and David Andreasen

ABSTRACT

Charles County, Maryland, located about ten miles south of Washington, District of Columbia, is a rapidly growing county that is dependent upon groundwater for its water supply. Gross alpha-particle activity (GAPA) in untreated wellwater samples from five public-water supply systems in the county have exceeded the US Environmental Protection Agency’s Maximum Contaminant Level (MCL) of 15 picocuries per liter (pCi/L). Polonium-210 was detected in two of the water systems in concentrations up to 46 pCi/L. Radium-226 plus radium-228 values were all less than the MCL of 5 pCi/L. GAPA in eleven other water systems was between 10 and 15 pCi/L. These water systems obtain water from the (confined) Upper and Lower Patapsco aquifer systems, which consist of interbedded, laterally and vertically discontinuous sands, silts, and clays that collectively are up to 900 feet thick. To identify the specific stratigraphic interval(s) within these aquifers that are associated with elevated radionuclide levels, existing water quality data from the Maryland Department of the Environment’s Public Drinking Water Information System (PDWIS) and well-construction data from well completion reports were compiled. Public-supply wells that are completed in the Upper and Lower Patapsco aquifer systems have multiple screened intervals that draw water from discrete sand layers, making it difficult to assess whether the radioactivity is localized within specific stratigraphic intervals. Inconsistencies and variability in data reporting, combined with a lack of information on where and how the samples were collected, provided additional challenges in interpreting the data. As a result, the existing data did not indicate whether specific stratigraphic interval(s) within the aquifers are the sources of radioactivity. Additional sampling is planned for domestic water-supply wells that are located within one mile of the affected public water systems. Because domestic water-supply wells typically have screened-interval lengths of ten feet or less, testing for radionuclides in samples from these wells will help determine whether the source of radioactivity is restricted to discrete stratigraphic intervals or is dispersed throughout the Upper and Lower Patapsco aquifer systems.