T130 Global Drinking Water and Public Health: Conditions, Contaminants, Concerns, and Strategies

Monday, 5 November 2018
1:30 PM - 5:30 PM
Room 238-239

OCCURRENCE AND GEOCHEMISTRY OF LEAD-210 AND POLONIUM-210 IN PUBLIC-DRINKING-WATER SUPPLIES FROM PRINCIPAL AQUIFERS OF THE UNITED STATES

Paper number: T130-5
Program: Technical Sessions
Time: 2:25 PM – 2:40 PM

Authors

Abstract

Concentrations of lead-210 (210Pb) and polonium-210 (210Po) in over 1,100 samples of untreated water from public-supply wells located across 18 principal aquifers (PAs) were determined since 2012 as part of the U.S. Geological Survey’s National Water Quality Assessment project. These 18 PAs account for a majority of the groundwater withdrawn for public-supply purposes in the United States. The U.S. Environmental Protection Agency has estimated maximum contaminant levels (MCLs) of 1.0 and 0.7 picocuries per liter (pCi/L) for 210Pb and 210Po, respectively, based on lifetime cancer risks. These estimated MCLs, however, have not been promulgated due in part to a lack of monitoring data.

210Pb concentrations greater than 1.0 pCi/L occurred most frequently in samples from the Piedmont (23%), North Atlantic Coastal Plain (NACP) (10%), Colorado Plateaus (8%) and Coastal Lowlands (7%) PAs. Among these PAs, concentrations of 210Pb were most strongly correlated with radon-222 (222Rn) concentrations in the Piedmont, indicating 210Pb occurrence in this aquifer system is controlled primarily by the aqueous concentration of 222Rn. 222Rn has a half-life of 3.8 days and decays through three short-lived progenies to form polonium-214 (214Po) and then 210Pb in about 49.5 minutes. In the Piedmont, which had the greatest 222Rn concentrations of all PAs, elevated 210Pb concentrations commonly occurred in young (post 1950), oxic, calcium-magnesium – bicarbonate water types with pH values near 7.0 (neutral) – geochemical conditions that otherwise favor sequestration of lead. However, alpha-recoil from the decay of 214Po adsorbed on aquifer solid surfaces mobilizes 210Pb into solution accounting for the high frequency of concentrations greater than 1.0 pCi/L.

210Po concentrations greater than 0.7 pCi/L occurred most frequently in samples from select Coastal Plain aquifers in the NACP (27%), Southeast Coastal Plain (6%) and Coastal Lowlands (3%) PAs. Elevated concentrations of 210Po in these aquifers were associated with old (pre 1950), reducing, sodium – bicarbonate water types with pH greater than 8. Under these geochemical conditions, sorption capacity is diminished and 210Po forms neutral species that are inefficiently sorbed, which allows an increasing fraction of 210Po to accumulate in groundwater.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322088

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