Strontium and radium occurrence at the boundary of a confined aquifer system

Plechacek, Amy; Scott, Sean; Gotkowitz, Madeline B.; Ginder‐Vogel, Matthew

doi:10.1016/j.apgeochem.2022.105332

Cited by 6 publications

(8 citation statements)

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“…Mathews et al (2022) analyzed groundwaters from discrete intervals within a single well in southern Wisconsin and found ( 234 U/ 238 U) from 4.76 to 11.11. Plechacek et al (Plechacek et al, 2022) measured ( 234 U/ 238 U) from 1.9 to 18.0 from groundwater wells in Fond du Lac County, Wisconsin that included public water systems, individual household wells, and irrigation wells. In addition, the alpha project at WSLH that preceded the SDWA analyses found similar ranges in total uranium activity and ( 234 U/ 238 U) in samples representative of the range of groundwater compositions occurring in Wisconsin (Arndt & West, 2004).…”

Section: Resultsmentioning

confidence: 99%

“…Highly oxidized waters tend to mobilize all water‐available uranium (including 238 U) which dilutes the excess concentration of recoil‐released 234 U and decreases the ( 234 U/ 238 U) as the increasing amount of total uranium in the water comes closer to the isotopic ratio of the uranium sourced in the bedrock. These dynamics are especially significant in Wisconsin, where both regionally confined and regionally unconfined portions of the aquifer, dictated by the presence or absence of the Maquoketa Shale, control variations in oxidation state and overall geochemistry of the aquifer system (Grundl & Cape, 2006; Plechacek et al, 2022; Stackelberg et al, 2018).…”

Section: Resultsmentioning

confidence: 99%

“…One aliquot was diluted for uranium concentration analysis by sector field inductively coupled plasma mass spectrometry. A second aliquot was used for uranium isotopic analysis by multi‐collector inductively coupled plasma mass spectrometry using methods adapted from (Sims et al, 2008) and provided in (Mathews et al, 2022; Plechacek et al, 2022). Prior to isotopic analysis the uranium was purified by anion exchange chromatography.…”

Section: Methodsmentioning

confidence: 99%

“…However, the MCOAS, the drinking water source for many Wisconsin municipalities, has been known to possess large variations in the ( 234 U/ 238 U), ranging from 2.0 to 40.7 in Illinois (Gilkeson et al, 1984). More recent work that focused on the Wisconsin MCOAS has shown similar variations, though not to the extreme levels found in Illinois (Mathews et al, 2022;Plechacek et al, 2022). Although the radiological risks associated with uranium concentrations measured in Wisconsin are generally low, large variations in the ( 234 U/ 238 U) ratio may lead to outsized impacts on the gross alpha activity.…”

Section: Distribution Of Uranium In Wisconsin Groundwatermentioning

confidence: 99%

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The importance of uranium isotope composition for gross alpha activity regulation

Scott¹,

Plechacek

Krinke³

2023

AWWA Water Science

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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.alpha spectrometry, gross alpha activity, groundwater, uranium isotope ratios | INTRODUCTIONUranium is regulated by the United States Environmental Protection Agency (EPA) due to its toxicological properties (Dinocourt et al., 2015;Selden et al., 2009;Zamora et al., 1998). The radionuclides rule was updated in 2000 to include a uranium maximum contaminant level (MCL) of 30 μg/L (US EPA, 2015). The radionuclides rule also addresses gross alpha activity. When the gross alpha activity is measured above 15 pCi/L, analysis of uranium is required to determine the adjusted gross alpha activity (gross alpha minus the uranium and radon activities). Establishing compliance with the MCL requires four consecutive quarterly samples, and initial compliance is based on the running average of these four initial samples. Any exceedance of the MCL during this period or in subsequent sampling efforts triggers additional quarterly monitoring. Ultimately, any entry point in a drinking water distribution system must demonstrate four consecutive quarterly samples below the MCL to comply with the radionuclides rule for adjusted gross alpha activity. Because total uranium activity is subtracted from the gross alpha activity for compliance monitoring, quantification of the total uranium activity is a critical factor for adhering to this regulation.Both radiochemical and mass-based measurements are approved for compliance monitoring of uranium under federal rule when this analysis is triggered by a

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Distribution Of Uranium In Wisconsin Groundwatermentioning

confidence: 99%

See 2 more Smart Citations

The importance of uranium isotope composition for gross alpha activity regulation

Scott¹,

Plechacek

Krinke³

2023

AWWA Water Science

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“…Aqueous 87 Sr/ 86 Sr is dependent on Sr inputs from weatherable Sr-bearing solid phases present in aquifer systems and is not fractionated by chemical or mechanical processes. − 87 Sr is produced from the decay of 87 Rb ( t 1/2 = 49 Ga); therefore, minerals with higher Rb/Sr ratios (e.g., silicates) will have more radiogenic (higher) 87 Sr/ 86 Sr − (Table S3) and are positively correlated with the Sr/Ca ratio ( R s = 0.79, p = 0.05; Figure S7A), indicating carbonate mineral influence on 87 Sr/ 86 Sr . Within the dissolved phase plume, aqueous 226 Ra activities are negatively correlated with aqueous 87 Sr/ 86 Sr ( R s = −0.68, p = 0.1), indicating that aqueous 226 Ra activity is higher where the prevalence of low Rb/Sr minerals (e.g., carbonates) dominates aqueous 87 Sr/ 86 Sr (Figure S7B).…”

Section: Resultsmentioning

confidence: 99%

Elevated Radium Activity in a Hydrocarbon-Contaminated Aquifer

Plechacek

Mathews

et al. 2023

Environ. Sci. Technol.

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Hydrocarbon spills that reach the subsurface can modify aquifer geochemical conditions. Biogeochemical zones typically form proximal to the source zone that include iron (Fe(III)) and manganese (Mn(III/IV)) (hydr)oxide reduction, with potential to release associated geogenic contaminants to groundwater. Here, multi-level monitoring systems are used to investigate radium (226Ra, 228Ra) activities in an aquifer contaminated with a mixture of chlorinated solvents, ketones, and aromatics occurring as a dense non-aqueous phase liquid in the source zone. 226Ra activities are up to 10 times higher than background 60 m downgradient from the source zone, where pH is lower, total dissolved solid concentrations are higher, and conditions are methanogenic. Correlations indicate that Fe and Mn (hydr)oxide reduction and sorption site competition are likely responsible for elevated Ra activities within the dissolved phase plume. 226Ra activities return to background within the Fe(III)/SO4 2–-reducing zone 600 m downgradient from the source, near the middle of the dissolved phase plume. Geochemical models indicate that sorption to secondary phases (e.g., clays) is important in sequestering Ra within the plume. Although maximum Ra activities within the plume are well below the U.S. drinking water standard, elevated activities compared to background emphasize the importance of investigating Ra and other trace elements at hydrocarbon-impacted sites.

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