Controls on species distribution and biogeochemical cycling in nitrate-contaminated groundwater and surface water, southeastern Australia.

A detailed study of groundwater and surface water nitrate over four seasons across an area of varied landuse provided insights into the mechanisms that underlie accumulation and transport of nitrate. High nitrate concentrations found in a significant percentage of surface water and shallow groundwater samples are due to anthropogenic contamination. Statistics (PCA, ANOVA, parsimonious model and general linear regression) were used to explore the relationship between NO and land use, and confirmed that areas of high NO concentration are associated with dairy pasture and horticulture.

Review: Technical and policy challenges in deep vadose zone remediation of metals and radionuclides.

Contamination in deep vadose zone environments is isolated from exposure so direct contact is not a factor in its risk to human health and the environment. Instead, movement of contamination to the groundwater creates the potential for exposure and risk to receptors. Limiting flux from contaminated vadose zone is key for protection of groundwater resources, thus the deep vadose zone is not necessarily considered a resource requiring restoration.

Isotopic tracking of Hanford 300 area derived uranium in the Columbia River.

Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area and to follow that U downriver to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates.

Pathways of aqueous Cr(VI) attenuation in a slightly alkaline oxic subsurface.

Column experiments combined with geochemical modeling, microscopic inspections, spectroscopic interrogations, and wet chemical extractions were used to study sediment-dependent Cr(VI) desorption, physical location, mineral association, and attenuation mechanism(s) in four freshly or naturally aged contaminated sediments exposed to concentrated Cr(VI) waste fluids. Results showed that majority of Cr(VI) mass was easily removed from the sediments (equilibrium site K(d) varied from 0 to 0.33 mL g(-1) and equilibrium site fraction was greater than 95%).

Measurement of helium isotopes in soil gas as an indicator of tritium groundwater contamination.

The focus of this study was to define the shape and extent of tritium groundwater contamination emanating from a legacy burial ground and to identify vadose zone sources of tritium using helium isotopes (3He and 4He) in soil gas. Helium isotopes were measured in soil-gas samples collected from 70 sampling points around the perimeter and downgradient of a burial ground that contains buried radioactive solid waste. The soil-gas samples were analyzed for helium isotopes using rare gas mass spectrometry.