Deducing the Distribution of Terminal Electron‐Accepting Processes in Hydrologically Diverse Groundwater Systems

Chapelle, Francis H.; McMahon, Peter B.; Dubrovsky, Neil M.; Fujii, Roger; Oaksford, Edward T.; Vroblesky, Don A.

doi:10.1029/94wr02525

Cited by 279 publications

(206 citation statements)

References 31 publications

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“…At G202, hydrogen concentrations were in the range of 2.5 -5 nM, characteristic of a sulphate-reducing environment [Chapelle et al, 1995]. Further downgradient, at G212, the hydrogen levels declined to 0.5 -1.5 nM, suggesting iron-to sulphate-reducing conditions prevailed, consistent with the elevated iron concentrations and the relatively unchanging sulfate levels that were found.…”

Section: Redox Conditionssupporting

confidence: 60%

Hydrogeologic assessment of in situ natural attenuation in a controlled field experiment

Devlin

McMaster²,

Barker

2002

Water Resources Research

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[1] An experiment to investigate the natural attenuation of three volatile organic compounds, toluene, carbon tetrachloride, and tetrachloroethene ($1-10 mg L À1 ) was performed in a 3 m deep, sandy aquifer isolated within a 24 m long, 2 m wide, three-sided sheet pile alleyway (hereafter referred to as the gate). A constant flow was maintained in the test volume by pumping a well at the closed end of the gate at 130 mL min À1 . The test compounds were introduced to the aquifer using diffusive emitters installed inside 25 cm diameter wells located at the open end of the gate. Monitoring was performed by sampling along six multilevel fences (consisting of 12 sampling points each) ranging in distance from 1 to 22 m from the source wells. A bromide tracer experiment established that there were no significant hydraulic leaks, nor was there any continuous channeling through the gate. Degradation of the test compounds was assessed by mass balance calculations between fences located 1 and 7 m from the source, and the results were compared with degradation rate estimates from snapshot analyses and the analysis of fluxes. There was reasonably good agreement between rates estimated by these different methods. Toluene degraded with a half-life of 58-62 days, carbon tetrachloride degraded with a half-life of $11 -13 days, and tetrachloroethene degraded too slowly for a reliable estimate of rate to be made. Transformation products identified in the gate included acetate, possibly from toluene degradation, chloroform, trichloroethene, and cis-1,2, dichloroethene. The latter two compounds only appeared in trace quantities and could not be assessed for continuing degradation. However, chloroform degradation was assessed with the snapshot data and using the flux estimates and was found to degrade with a half-life in the range of 10-34 days. No additional chlorinated methanes were detected in the gate, suggesting that the carbon tetrachloride was completely dechlorinated by natural processes within 10 m of the source wells. This experiment demonstrated that degradation of chlorinated solvents occurs naturally at the Borden site but that the ethenes are more resistant to biodegradation than the methanes. In addition, the flux calculations were found to be the most robust in terms of estimating degradation rates.

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Section: Redox Conditionssupporting

confidence: 60%

Hydrogeologic assessment of in situ natural attenuation in a controlled field experiment

Devlin

McMaster²,

Barker

2002

Water Resources Research

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“…Evaluating the redox processes is an essential tool for understanding geochemical evolution in groundwater systems according to Chapelle et al (1995). Usually the ORP value is used to evaluate the redox potential (Lindberg and Runnells 1984).…”

Section: Major Ionsmentioning

confidence: 99%

Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

et al. 2017

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In the Bandung basin, Indonesia, excessive groundwater pumping caused by rapid increases in industrialization and population growth has caused subsurface environmental problems, such as excessive groundwater drawdown and land subsidence. In this study, multiple hydrogeochemical techniques and numerical modeling have been applied to evaluate the recharge processes and groundwater age (rejuvenation). Although all the groundwater in the Bandung basin is recharged at the same elevation at the periphery of the basin, the water type and residence time of the shallow and deep groundwater could be clearly differentiated. However, there was significant groundwater drawdown in all the depression areas and there is evidence of groundwater mixing between the shallow and deep groundwater. The groundwater mixing was traced from the high dichlorodifluoromethane (CFC-12) concentrations in some deep groundwater samples and by estimating the rejuvenation ratio (R) in some representative observation wells. The magnitude of CFC-12 concentration, as an indicator of young groundwater, showed a good correlation with R, determined using 14 C activity in samples taken between 2008 and 2012. These correlations were confirmed with the estimation of vertical downward flux from shallower to deeper aquifers using numerical modeling. Furthermore, the change in vertical flux is affected by the change in groundwater pumping. Since the 1970s, the vertical flux increased significantly and reached approximately 15% of the total pumping amount during the 2000s, as it compensated the groundwater pumping. This study clearly revealed the processes of groundwater impact caused by excessive groundwater pumping using a combination of hydrogeochemical methods and modeling.

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“…Redox dynamics are well studied in flooded environments, where patterns in water movement and the distribution of electron donors and acceptors create strong spatial gradients in redox (Chapelle et al 1995). Redox is less well studied in upland systems, but evidence suggests that it varies at multiple spatial scales.…”

Section: Introductionmentioning

confidence: 99%

Spatial patterns in oxygen and redox sensitive biogeochemistry in tropical forest soils

Liptzin

Silver

2015

Ecosphere

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Abstract. Humid tropical forest soils are characterized by warm temperatures, abundant rainfall, and high rates of biological activity that vary considerably in both space and time. These conditions, together with finely textured soils typical of humid tropical forests lead to periodic low redox conditions, even in well-drained upland environments. The relationship between redox and biogeochemical processes has been studied for decades in saturated environments like wetlands and sediments, but much less is known about redox dynamics in upland soils. The goal of this study was to understand the spatial variability of redox sensitive biogeochemistry within and across two forest types at the ends of a high rainfall gradient (3500 to 5000 mm y À1 ) in the Luquillo Experimental Forest, Puerto Rico. The two sites differed significantly in average soil chemical and physical properties, but the scale of variability was similar across sites, with greater variability in soil gas concentrations than extractable Fe and P. Soil P and Fe pools and trace gas concentrations were more strongly correlated with each other and exhibited more spatial structure at the wetter site. While the within-site relationships among these redox sensitive variables were typically weak, the relationships across sites were much stronger. We provide a conceptual model that elucidates how the strength of the relationships between indicators of redox-sensitive biogeochemical processes depends on the spatial scale of analysis.

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Deducing the Distribution of Terminal Electron‐Accepting Processes in Hydrologically Diverse Groundwater Systems

Cited by 279 publications

References 31 publications

Hydrogeologic assessment of in situ natural attenuation in a controlled field experiment

Hydrogeologic assessment of in situ natural attenuation in a controlled field experiment

Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

Spatial patterns in oxygen and redox sensitive biogeochemistry in tropical forest soils

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