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Gross alpha-particle activity and high 226Ra concentrations do not correspond with high 210Po in the Atlantic and Gulf Coastal Plain aquifers of the United States
210Po, which is of human-health concern based on lifetime ingestion cancer risk, is indirectly regulated in drinking water through the U.S. Environmental Protection Agency’s gross alpha-particle activity (GAPA) maximum contaminant level of 15 pCi/L (picocuries per liter). This regulation requires independent measurement of 226Ra for samples exceeding the GAPA screening level of 5 pCi/L. There is n