Graduate Thesis Or Dissertation
 

Forensic Hydrogeography : Assessing Groundwater Arsenic Concentrations and Testing Methods within the Harney Basin, Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hh63sz81j

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  • Harney County contains defining characteristics of regions containing arsenic within the groundwater such as its location in the western United States, unique closed basin geography, complex geology, and seasonal groundwater level fluctuations. Confirmation of arsenic concentrations above the Maximum Contaminant Level Drinking Water Standard of 10 μg/L has been observed on a recurring basis. Private land owners within the Harney Basin solely depend on private wells for domestic, agricultural, and livestock water supply and are not required to test for or meet the 10 μg/L MCL water quality standards for public water systems, as established by the United States Environmental Protection Agency. The purpose of this study was to expand on previous arsenic investigations to determine if a relationship exists between arsenic occurrence and the geography, hydrology, and geology within the Harney Basin. The effects of well depth, latitude/longitude, and hydrogeologic units were analyzed to create a regional depiction of arsenic occurrence through a conceptual model. For each sample, total arsenic, pH, and conductivity was measured. A total of 140 samples were evaluated, 91 were integrated from previous studies and 49 were collected throughout the Harney Basin as part of this study. For each of the 49 samples collected in this study, total arsenic was quantified by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and semi-quantitative arsenic field screening tests were also performed for comparison. These data were used to determine if a link exists between groundwater arsenic occurrence, geology, and the source aquifer. The secondary purpose of this study was to assess the accuracy and precision of the field tests to inform the community if a more available and less-expensive option than ICP-MS could be used for routine monitoring. Data acquisition was challenging due to citizen concerns about anonymity, difficulty contacting land owners, and their perceived effects on land values. The analysis identified that arsenic contamination is widespread throughout the valley. While one hydrogeologic unit provided statistically higher concentrations of arsenic, there is no single clear geogenic source of arsenic. The results from the field test produced questionable results, with both overestimates and underestimates of concentrations compared with the ICP-MS analysis. The results of this research will be informative to groundwater users and public health officials and the results will be confidentially shared with stakeholders. Communities reliant on private well water with similar geologic characteristics may utilize this report to understand the importance of arsenic testing.
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