Determination of hexavalent chromium concentrations in matrix porewater from a contaminated aquifer in fractured sedimentary bedrock

Zhao, Jiujiang; Al, Tom A.; Chapman, S.; Parker, Beth L.; Mishkin, Katherine; Cutt, Diana; Wilkin, Richard T.

doi:10.1016/j.chemgeo.2015.10.034

Cited by 7 publications

(14 citation statements)

References 18 publications

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“…The reaction between H 2 O 2 and different mineralogical forms of Cr in soil was investigated by Rock et al (2001), who found that it was successful in extracting recently precipitated Cr(III) solids in electroplating waste, but was not effective in extracting Cr from serpentine-rich soil at a former Cr mine site. An additional benefit of the H 2 O 2 approach is that aqueous Cr(VI) in porewater is extracted along with labile Cr(III), allowing for calculation of labile Cr(III) as the difference between total extractable Cr (H 2 O 2 extraction) and Cr(VI) from the previous method (Zhao et al, 2015) (NaOH extraction).…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Bedrock core samples were collected within the plume using the Discrete Fracture Network (DFN) approach (Parker et al, 2012). Additional details on sampling and sample handling are provided by Zhao et al (2015) who presented a detailed vertical distribution of Cr(VI) concentrations in the bedrock porewater. The present study utilizes 145 discrete depth bedrock core samples from the same borehole, positioned mid-plume between the source area and river, and collected over a depth interval from about 21 to 108 mbgs (meters below ground surface), where the ground surface elevation at the study site is 5.0 m ASL.…”

Section: Study Site and Materialsmentioning

confidence: 99%

“…The NaOH extraction procedure targets Cr(VI) using approximately 1 g of rock material and 0.01 mol/L NaOH as reported by Zhao et al (2015). The labile Cr(III) is operationally defined as the difference between the H 2 O 2 and NaOH extractions, both of which are corrected for the background from rock matrix.…”

Section: Extractionmentioning

confidence: 99%

“…A laboratory reference material with low Cr(VI) concentration (LRS) was prepared from rock core collected at the study site from > 80 m depth, well below the Cr(VI) plume (Zhao et al, 2015). Crushed samples (< 2 mm) were pulverized, blended and sieved (< 180 μm).…”

Section: Quality Control (Qc) Materials and Analytical Proceduresmentioning

confidence: 99%

“…In a previous study, a method was developed for determining the concentration of aqueous Cr(VI) in the porewater of core samples from contaminated fractured bedrock aquifers (Zhao et al, 2015). In an effort to investigate the reduction of Cr(VI) to Cr(III) in the natural environment, the objective of the present study was to develop a complementary method to quantify Cr(III)-hydroxides formed in-situ by reduction of Cr(VI) in the bedrock matrix.…”

Section: Introductionmentioning

confidence: 99%

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Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI)

Zhao

Chapman

et al. 2017

Chemical Geology

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Hexavalent chromium Cr(VI) is toxic and can be highly mobile in many aquifer systems. Redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to Cr(III), forming labile Cr(III) oxyhydroxide precipitates, which is a natural attenuation process. In fractured bedrock aquifers, reduction of Cr(VI) in the rock matrix can enhance attenuation beyond that from matrix diffusion only, and potentially reduce back diffusion if concentrations in fractures decline following source reduction via natural processes or engineered remediation. In this study, we develop an extraction method for labile Cr(III) precipitates from Cr(VI) reduction using 5% hydrogen peroxide (H 2 O 2 ). Combining Cr(III) extractions with an established sodium hydroxide (NaOH) method for determination of Cr(VI) concentrations in rock porewater, a measure of the labile Cr(III) and Cr(VI) fractions in geologic samples is achieved. The methods were applied to cores from a contaminated groundwater system in fractured porous bedrock in order to assess the effectiveness of natural attenuation and whether Cr(VI) mass that diffused into the bedrock matrix was undergoing reduction. Detailed vertical distributions display two depth intervals with corresponding elevated concentrations of Cr(VI) in the porewater and extractable total Cr. The correspondence of Cr(VI) and labile Cr(III) provides evidence for reduction of Cr(VI) contamination in the bedrock matrix. Mineralogical analysis suggests that Fe(II)-bearing minerals, chlorite and biotite are the most likely candidates for natural reductants. This study provides evidence for the natural attenuation of anthropogenic Cr(VI) contamination in the porewater of a fractured bedrock aquifer, and it outlines a quantitative method for evaluating the effectiveness of natural attenuation in groundwater systems.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Study Site and Materialsmentioning

confidence: 99%

Section: Extractionmentioning

confidence: 99%

Section: Quality Control (Qc) Materials and Analytical Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI)

Zhao

Chapman

et al. 2017

Chemical Geology

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Occurrence and fractionation of Cr along the Loushan River affected by a chromium slag heap in East China

Chen

Dong

Xin

2017

Environ Sci Pollut Res

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This study investigated the chromium (Cr) occurrence and distribution along the Loushan River adjacent to a chromium slag heap. The speciation and chemical fractionation of Cr in different environmental media were determined. The potential ecological risks for the surrounding environment were assessed on the basis of both potential ecological risk index (RI) and risk assessment code (RAC). The results show that the surface soil experienced severe Cr contamination with Cr(T) and Cr(VI) values of 3220 ± 6266 and 64 ± 94 mg/kg, respectively, even though the chromium slag heap had already been removed. The chromium slag enhanced the Cr concentration level in the surface soil, water, and sediment samples more than the background level to different extents, which indicates that Cr released from the chromium slag actually affects the surrounding environment. The spatial distribution variety of Cr implies that their transport might have been affected by soil leaking, atmospheric transport, and fluvial hydraulics. The chemical fractionation results demonstrate that the residual fraction was the dominant form, accounting for 54.6 and 66.1% Cr(T) in surface soil and sediment samples, respectively. The content of bioavailable exchangeable Cr fraction correlated with the organic matter (OM), cation exchange capacity (CEC), and pH value. The ecological risk assessment suggests no considerable ecological risk toward the biota despite a relatively high Cr(T) level. Nevertheless, attention should be paid to the potential long-term risks owing to the slow release of oxidizable and residual fractions.

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Highly sensitive detection of Cr(vi) in groundwater by bimetallic NiFe nanoparticles

Liu

Ding

et al. 2017

Anal. Methods

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Determination of hexavalent chromium concentrations in matrix porewater from a contaminated aquifer in fractured sedimentary bedrock

Cited by 7 publications

References 18 publications

Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI)

Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI)

Occurrence and fractionation of Cr along the Loushan River affected by a chromium slag heap in East China

Highly sensitive detection of Cr(vi) in groundwater by bimetallic NiFe nanoparticles

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