Applying the Quadrant Method for Pumping-Trace Metal Correlations in Variable Time, Low-Data Systems.

Due to increasing global demand for fresh water, it is increasingly necessary to understand how aquifer pumping affects groundwater chemistry. However, comprehensive predictive relationships between pumping and groundwater quality have yet to be developed, as the available data, which are often collected over inconsistent time intervals, are poorly suited for long-term historical correlation studies. For example, we needed an adequate statistical method to better understand relationships between pumping rate and water quality in the City of Norman (OK, USA).

Dissolution of Mn-bearing dolomite drives elevated Cr(VI) occurrence in a Permian redbed aquifer.

Municipalities in central Oklahoma, U.S.A.

Transformation of mackinawite to greigite by trichloroethylene and tetrachloroethylene.

Trichloroethylene (TCE) and tetrachloroethylene (PCE) are common ground water contaminants susceptible to reductive dechlorination by FeS (mackinawite) in anaerobic environments. The objective of this study was to characterize the mineral-associated products that form when mackinawite reacts with TCE and PCE. The dissolved products of the reaction included Cl and Fe, and trace amounts of cis 1,2-dichloroethylene (for TCE) and TCE (for PCE).

Biological versus mineralogical chromium reduction: potential for reoxidation by manganese oxide.

Hexavalent chromium (Cr(vi), present predominantly as CrO4(2-) in water at neutral pH) is a common ground water pollutant, and reductive immobilization is a frequent remediation alternative. The Cr(iii) that forms upon microbial or abiotic reduction often co-precipitates with naturally present or added iron (Fe), and the stability of the resulting Fe-Cr precipitate is a function of its mineral properties. In this study, Fe-Cr solids were formed by microbial Cr(vi) reduction using Desulfovibrio vulgaris strain RCH1 in the presence of the Fe-bearing minerals hematite, aluminum substituted goethite (Al-goethite), and nontronite (NAu-2, Clay Minerals Society), or by abiotic Cr(vi) reduction by dithionite reduced NAu-2 or iron sulfide (FeS).

Using chromate to investigate the impact of natural organics on the surface reactivity of nanoparticulate magnetite.

Chromate was used as a chemical probe to investigate the size-dependent influence of organics on nanoparticle surface reactivity. Magnetite-chromate sorption experiments were conducted with ∼ 90 and ∼ 6 nm magnetite nanoparticles in the presence and absence of fulvic acid (FA), natural organic matter (NOM), and isolated landfill leachate (LL). Results indicated that low concentrations (1 mg/L) of organics had no noticeable impact on chromate sorption, whereas concentrations of 50 mg/L or more resulted in decreased amounts of chromate sorption.

Size-dependent reactivity of magnetite nanoparticles: a field-laboratory comparison.

Logistic challenges make direct comparisons between laboratory- and field-based investigations into the size-dependent reactivity of nanomaterials difficult. This investigation sought to compare the size-dependent reactivity of nanoparticles in a field setting to a laboratory analog using the specific example of magnetite dissolution. Synthetic magnetite nanoparticles of three size intervals, ∼ 6 nm, ∼ 44 nm, and ∼ 90 nm were emplaced in the subsurface of the USGS research site at the Norman Landfill for up to 30 days using custom-made subsurface nanoparticle holders.