David K. Kreamer

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.

Sorption of benzene and trichloroethylene (TCE) on a desert soil: Effects of moisture and organic matter

Sorption of Trichlorethylene (TCE) and Benzene onto a desert soil has been investigated, at two different temperatures and various moisture contents, using a gas chromatographic method. Sorption of these two VOCs to the unmodified soil was compared to sorption onto the same soil that was alternately treated with hydrogen peroxide (to remove organic carbon) or with humic acids (to add organic carbon) in order to examine the role of soil organic matter in vapor phase sorption. Results from this study indicate that organic carbon plays only a minor role in sorption at low moisture contents.

Slow vapor‐phase desorption of toluene from several ion‐exchanged montmorillonites

Abstract The sorption and desorption of volatile compounds from soils and clays exhibit a wide range of kinetics. While much of the sorptive interaction is very rapid, a certain fraction of volatile compounds that enter soil and clays are only slowly desorbed. It is generally believed that the formation of this recalcitrant or slowly desorbing fraction of volatile organic compounds (VOCs) in soils is due to the diffusion of compounds to poorly accessible sorption sites. However, the exact nature of these sites is in doubt. In montmorillonite, there are two likely possibilities for formation of the recalcitrant fraction: sites between the clay lamella and sites within clay particle aggregates. Because montmorillonite may be an important fraction of many soils, we have explored the formation of slowly desorbing toluene on a montmorillonite clay that was ion exchanged with five different ions (K+, Na+, Ca2+, Mg2+, and Fe3+) to form mineralogically similar clays with varying interlamellar spacing. The recalci...

Identifying local and regional groundwater in basins: chemical and stable isotopic attributes of multivariate classification of hydrochemical data, the Lower Virgin River Basin, Nevada, Arizona and Utah, U.S.A

ABSTRACT In the Basin and Range Province of the Southwestern U.S.A., deep carbonate groundwater has been suggested as a significant source to many overlying basin-fill alluvial aquifer systems. Notwithstanding, testing this hypothesis is limited by obtaining data from such considerable depths and complex geology. This study uses δ2H and δ18O data from springs, rivers, and wells tapping shallow basin-fill groundwater to test the hydrochemical interpretation of deep regional carbonate groundwater flow into the basin-fill aquifers. Stable isotopic and major ion attributes of hydrochemical facies suggest basin-fill alluvial groundwater of the Lower Virgin River Basin is a mixture of precipitation recharge within the Lower Virgin River Basin or the Clover and Escalante Desert Basin northwards, and the deep carbonate flow. The data support the conclusions that in the Lower Virgin River Basin, deep carbonate groundwater is an important source to the alluvial aquifer system and likely accounts for approximately 50% of the alluvial aquifer groundwater. Na+, K+, and SO42– increase in the basin-fill alluvial groundwaters outside the Virgin River floodplain appears to be related with upwelling of deep regional groundwater, and indicating that the chemical character of the basin-fill alluvial groundwaters are related to the deeper flow systems.

Water Circulation in Karst Systems: Comparing Physicochemical and Environmental Isotopic Data Interpretation

Many studies have used physicochemical response observed at karst springs during storm events to investigate the concept of diffuse flow in karst systems, but the complete description of the karst systems including the interactions of all components is not fully understood. Studies have shown that physicochemical response measured at karst springs can decrease or increase in response to storm events. It is clear from these studies that the use of only physicochemical response in interpreting water circulation in karst systems can be ambiguous. In this study, both physicochemical and isotope (stable and radiogenic) responses at City Spring, Cookeville, Tennessee, during snowmelt were used to interpret the hydrological cycle of a karst system. At the beginning of snow melting, all physicochemical parameters dropped, and thereafter, temperature, Ca, Mg, and HCO3 increased steadily with increased discharge and total dissolved solids. In contrast, generally Na, Cl, and SO4 remained constant after dropping; however, very high values were observed in the spring water mixed with stormwater runoff. δ2H, δ18O, and 87Sr/86Sr of spring water were stable and contrastingly different from the snow, rain, and spring water mixed with stormwater runoff samples. CO2 pressure was higher than atmospheric and appeared to be degassing. The data suggest that spring discharge is a mix of pre-event water stored in the soil, epikarst zone, and underlying bedrock. The circulation depth is unknown, but is likely controlled by the amount of storm event recharge that occurs through the piston effect. There is little evidence to support dilution by snowmelt. This study shows that combining the techniques and data can provide greater insight into water circulation and monitoring of karst aquifer systems than applying the techniques and data individually.