Release of contaminants from a heterogeneously fractured low permeability unit underlying a DNAPL source zone

Dearden, Rachel; Noy, D.J.; Lelliott, M.; Wilson, Ryan D.; Wealthall, Gary

doi:10.1016/j.jconhyd.2011.05.006

Cited by 18 publications

(11 citation statements)

References 34 publications

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“…Regional groundwater quality management models must upscale the transport equation sufficiently to represent the effects of heterogeneity, including preferential flow in well‐connected high‐conductivity networks and mass transfer between the high‐ and low‐conductivity media. The early arrivals of contaminants caused by the preferential flow and the asymptotical tails resulting from transport through low permeability materials have been frequently observed, which significantly challenges long‐term management (e.g., Bianchi et al, ; Brusseau & Guo, ; Brusseau et al, , ; Dearden et al, ; Fogg et al, ; Fogg & LaBolle, ; Fogg & Zhang, ; Guo & Brusseau, ; LaBolle & Fogg, ; Matthieu et al, ; Seyedabbasi et al, ). Although the effects of heterogeneity can be simulated by explicitly including the spatial variability of hydraulic properties in the model, this approach is not feasible for most plume‐scale contamination sites and is definitely not feasible for regional‐scale models covering 10s to 100s of kilometer.…”

Section: Introductionmentioning

confidence: 99%

Upscaling of Regional Scale Transport Under Transient Conditions: Evaluation of the Multirate Mass Transfer Model

Guo

Fogg

Henri

2019

Water Resources Research

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Regional scale transport models are needed to support the long‐term evaluation of groundwater quality and to develop management strategies aiming to prevent serious groundwater degradation. The purpose of this study is to evaluate the capacity of a previously developed upscaling approach to adequately describe the main solute transport processes, including the capture of late‐time tails under changing boundary conditions. Potential factors that impact the performance of upscaling methods, including temporal variations in mass transfer rates and mass distributions, were investigated. Advective‐dispersive contaminant transport in a 3‐D heterogeneous domain was simulated and used as a reference solution. The equivalent transport under homogeneous flow conditions was then evaluated by applying the multirate mass transfer (MRMT) model. The random walk particle tracking method was used to solve the solute transport for heterogeneous and homogeneous MRMT scenarios under steady state and transient conditions. The results indicate that the MRMT model can capture the tails satisfactorily for plumes transported with ambient steady state flow fields at all studied scales using the same parameters. However, when the boundary conditions change in either local, plume, or regional scale, the mass transfer model calibrated for transport under steady state conditions cannot accurately reproduce the tailings observed for the heterogeneous scenario. The deteriorating impacts of transient boundary conditions on the upscaled model are more significant for regions where the flow fields are dramatically affected, which highlights the poor applicability of the MRMT approach for complex field settings. This finding also has implications for the suitability of other potential upscaling approaches.

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Section: Introductionmentioning

confidence: 99%

Upscaling of Regional Scale Transport Under Transient Conditions: Evaluation of the Multirate Mass Transfer Model

Guo

Fogg

Henri

2019

Water Resources Research

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“…When the concentration level in the fractures is lower than in the matrix slow counter diffusion will start (Parker et al, 2004). Thus, the contaminants are likely to stay in the matrix for several decades and can serve as a long-term secondary source to groundwater contamination of an underlying aquifer (Dearden et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

Damgaard

Bjerg

Bælum

et al. 2013

Journal of Contaminant Hydrology

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a b s t r a c tThe degradation of chlorinated ethenes and ethanes in clay till was investigated at a contaminated site (Vadsby, Denmark) by high resolution sampling of intact cores combined with groundwater sampling. Over decades of contamination, bioactive zones with degradation of trichloroethene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) to 1,2-cis-dichloroethene (cis-DCE) and 1,1-dichloroethane, respectively, had developed in most of the clay till matrix. Dehalobacter dominated over Dehalococcoides (Dhc) in the clay till matrix corresponding with stagnation of sequential dechlorination at cis-DCE. Sporadically distributed bioactive zones with partial degradation to ethene were identified in the clay till matrix (thickness from 0.10 to 0.22 m). In one sub-section profile the presence of Dhc with the vcrA gene supported the occurrence of degradation of cis-DCE and VC, and in another enriched δ 13 C for TCE, cis-DCE and VC documented degradation. Highly enriched δ 13 C for 1,1,1-TCA (25‰) and cis-DCE (−4‰) suggested the occurrence of abiotic degradation in a third sub-section profile. Due to fine scale heterogeneity the identification of active degradation zones in the clay till matrix depended on high resolution subsampling of the clay till cores. The study demonstrates that an integrated approach combining chemical analysis, molecular microbial tools and compound specific isotope analysis (CSIA) was required in order to document biotic and abiotic degradations in the clay till system.

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“…The shallow aquifer underlying the site consists of c. 1 m of made ground overlying c. 5 m of superficial Quaternary alluvium and river terrace gravels (Chambers et al, 2010;Dearden et al, 2013). Below this lies c. 50 m of relatively impermeable Triassic mudstone (Mercia Mudstone Group) which may be weathered in the top 0.5 to 1.25 m (Chambers et al, 2010).…”

Section: Field Site and Historical Field Data Overviewmentioning

confidence: 99%

“…The river terrace deposits comprise coarser sands and gravels formed from river channel deposition. The water table is typically 1-2 m bgl (below ground level) with hydraulic gradients of 0.001-0.002 towards a local river (Chambers et al, 2010;Dearden et al, 2013).…”

Section: Field Site and Historical Field Data Overviewmentioning

confidence: 99%

Monitoring well utility in a heterogeneous DNAPL source zone area: Insights from proximal multilevel sampler wells and sampling capture-zone modelling

McMillan

Rivett

Wealthall³

et al. 2018

Journal of Contaminant Hydrology

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This version is available at https://strathprints.strath.ac.uk/63641/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. ABSTRACTGroundwater-quality assessment at contaminated sites often involves the use of short-screen (1.5 to 3 m) monitoring wells. However, even over these intervals considerable variation may occur in contaminant concentrations in groundwater adjacent to the well screen. This is especially true in heterogeneous dense nonaqueous phase liquid (DNAPL) source zones, where cm-scale contamination variability may call into question the effectiveness of monitoring wells to deliver representative data. The utility of monitoring wells in such settings is evaluated by reference to high-resolution multilevel sampler (MLS) wells located proximally to shortscreen wells, together with sampling capture-zone modelling to explore controls upon well sample provenance and sensitivity to monitoring protocols. Field data are analysed from the highly instrumented SABRE research site that contained an old trichloroethene source zone within a shallow alluvial aquifer at a UK industrial facility. With increased purging, monitoring-well samples tend to a flow-weighted average concentration but may exhibit sensitivity to the implemented protocol and degree of purging. Formation heterogeneity adjacent to the wellscreen particularly, alongside pump-intake position and water level, influence this sensitivity. Purging of low volumes is vulnerable to poor reproducibility arising from concentration variability predicted over the initial 1 to 2 screen volumes purged. Marked heterogeneity may also result in limited long-term sample concentration stabilization. Development of bespoke monitoring protocols, that consider screen volumes purged, alongside water-quality indicator parameter stabilization, is recommended to validate and reduce uncertainty when interpreting monitoring-well data within source zone areas. Generalised recommendations on monit...

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Release of contaminants from a heterogeneously fractured low permeability unit underlying a DNAPL source zone

Cited by 18 publications

References 34 publications

Upscaling of Regional Scale Transport Under Transient Conditions: Evaluation of the Multirate Mass Transfer Model

Upscaling of Regional Scale Transport Under Transient Conditions: Evaluation of the Multirate Mass Transfer Model

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

Monitoring well utility in a heterogeneous DNAPL source zone area: Insights from proximal multilevel sampler wells and sampling capture-zone modelling

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