MULTIVARIATE STATISTICAL-ANALYSIS OF ARSENIC AND SELENIUM CONCENTRATIONS IN GROUNDWATERS FROM SOUTH-CENTRAL NEVADA AND DEATH-VALLEY, CALIFORNIA

Arsenic and selenium concentrations along with the major solutes were measured in groundwaters sampled from springs in Pahranagat Valley and Ash Meadows, Nevada, Death Valley, California, and from wells from th e Nevada Test Site and Yucca Mountain, Nevada. The multivariate statis tical technique correspondence analysis was applied to the data to det ermine relationships between the groundwaters from these areas, the aq uifer materials and the As and Se concentrations, and to examine the r elationships between As and Se and the other chemical parameters inclu ded in the statistical analysis. The correspondence analysis indicates that a strong relationship exists between chloride and Se in the grou ndwaters and that As is not associated with chloride. The strong assoc iation between chloride and Se suggests that Se behaves more conservat ively than As in these oxygenated, circumneutral pH groundwaters. No s trong 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 tuffaceo us volcanic rocks, and/or basin-fill deposits). However, it is likely that sampling of groundwaters from the various aquifers was insufficie nt to determine relationships between the aquifer materials and ground water chemistry. Associations were observed between the groundwaters o f the Nevada Test Site and Yucca Mountain regions and the groundwaters of the regional carbonate aquifer that discharge at Ash Meadows and D eath Valley, suggesting mixing of these waters. Groundwater from the r egional carbonate aquifer in Pahranagat Valley, which is upgradient fr om the Nevada Test Site, Yucca Mountain, Ash Meadows, and Death Valley , exhibited no association with groundwaters from these regions.