The importance of uranium isotope composition for gross alpha activity regulation. Issue 2 (19th April 2023)

• Record Type: Journal Article
• Authors: Scott, Sean R.; Wiersma, Amy K.; Krinke, Gary
• Is Part Of: AWWA water science. Volume 5:Issue 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-19
• Subjects: alpha spectrometry -- gross alpha activity -- groundwater -- uranium isotope ratios; Water -- Analysis -- Periodicals; Water-supply engineering -- Periodicals; Water -- Social aspects -- Periodicals; Water -- Purification -- Periodicals; Water-supply engineering; Water -- Social aspects; Water -- Analysis; Electronic journals; Periodicals; 628.162
• DOI: 10.1002/aws2.1329
• Languages: English
• ISSNs: 2577-8161

Abstract

Abstract: Uranium is a regulated contaminant (maximum contaminant level [MCL] 30 μg/L) that contributes to the gross alpha activity of groundwater. The adjusted gross alpha activity (MCL 15 pCi/L) is determined by subtracting the total uranium activity from the measured gross alpha activity. U.S. water utilities can use mass‐based and radiochemical analysis methods for compliance monitoring of uranium. Mass‐based measurements use a conversion factor of 0.67 pCi/μg of uranium to calculate the adjusted gross alpha activity. This conversion factor assumes that the activity of 234 U equals 238 U. Here, we present two decades of uranium isotope data measured by alpha spectrometry that shows 234 U activity typically exceeds 238 U. Using mass‐based measurements, the total uranium activity is biased low causing artificial exceedances of the adjusted gross alpha activity. Therefore, water utilities with gross alpha activities >15 pCi/L should utilize radiochemical analyses for uranium for the most accurate calculation of adjusted gross alpha activity.