Multivariate statistical analysis of arsenic and selenium concentrations in groundwaters from south-central Nevada and Death Valley, California

Abstract

Arsenic and selenium concentrations along with the major solutes were measured in ground-waters sampled from springs in Pahranagat Valley and Ash Meadows, Nevada, Death Valley, California, and from wells from the Nevada Test Site and Yucca Mountain, Nevada. The multivariate statistical technique correspondence analysis was applied to the data to determine relationships between the groundwaters from these areas, the aquifer materials and the As and Se concentrations, and to examine the relationships between As and Se and the other chemical parameters included in the statistical analysis.The correspondence analysis indicates that a strong relationship exists between chloride and Se in the groundwaters and that As is not associated with chloride. The strong association between chloride and Se suggests that Se behaves more conservatively than As in these oxygenated, circumneutral pH groundwaters. No strong association was observed between the As and/or Se concentrations of the groundwaters and the aquifer material with which these waters interact (i.e. regional Paleozoic carbonate aquifer, Tertiary tuffaceous volcanic rocks, and/or basin-fill deposits). However, it is likely that sampling of groundwaters from the various aquifers was insufficient to determine relationships between the aquifer materials and groundwater chemistry. Associations were observed between the groundwaters of the Nevada Test Site and Yucca Mountain regions and the groundwaters of the regional carbonate aquifer that discharge at Ash Meadows and Death Valley, suggesting mixing of these waters. Ground-water from the regional carbonate aquifer in Pahranagat Valley, which is upgradient from the Nevada Test Site, Yucca Mountain, Ash Meadows, and Death Valley, exhibited no association with groundwaters from these regions.