Heterogeneous hyporheic zone dechlorination of a TCE groundwater plume discharging to an urban river reach

Juliana G. Freitas, Michael O. Rivett, Rachel S. Roche, Megan Durrant (neé Cleverly), Caroline Walker, John H. Tellam

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

The typically elevated natural attenuation capacity of riverbed-hyporheic zones is expected to decrease chlorinated hydrocarbon (CHC) groundwater plume discharges to river receptors through dechlorination reactions. The aim of this study was to assess physico-chemical processes controlling field-scale variation in riverbed-hyporheic zone dechlorination of a TCE groundwater plume discharge to an urban river reach. The 50-m long pool-riffle-glide reach of the River Tame in Birmingham (UK) studied is a heterogeneous high energy river environment. The shallow riverbed was instrumented with a detailed network of multilevel samplers. Freeze coring revealed a geologically heterogeneous and poorly sorted riverbed. A chlorine number reduction approach provided a quantitative indicator of CHC dechlorination. Three sub-reaches of contrasting behaviour were identified. Greatest dechlorination occurred in the riffle sub-reach that was characterised by hyporheic zone flows, moderate sulphate concentrations and pH, anaerobic conditions, low iron, but elevated manganese concentrations with evidence of sulphate reduction. Transient hyporheic zone flows allowing input to varying riverbed depths of organic matter are anticipated to be a key control. The glide sub-reach displayed negligible dechlorination attributed to the predominant groundwater baseflow discharge condition, absence of hyporheic zone, transition to more oxic conditions and elevated sulphate concentrations expected to locally inhibit dechlorination. The tail-of-pool-riffle sub-reach exhibited patchy dechlorination that was attributed to sub-reach complexities including significant flow bypass of a low permeability, high organic matter, silty unit of high dechlorination potential. A process-based conceptual model of reach-scale dechlorination variability was developed. Key findings of practitioner relevance were: riverbed-hyporheic zone CHC dechlorination may provide only a partial, somewhat patchy barrier to CHC groundwater plume discharges to a surface water recept or and, monitoring requirements to assess the variability in CHC attenuation within a reach are expected to be onerous. Further research on transient hyporheic zone dechlorination is recommended.
LanguageEnglish
Pages236-252
Number of pages17
JournalScience of the Total Environment
Volume505
Early online date16 Oct 2014
DOIs
Publication statusPublished - 1 Feb 2015

Fingerprint

hyporheic zone
Dechlorination
dechlorination
trichloroethylene
Groundwater
plume
Rivers
Chlorinated Hydrocarbons
groundwater
chlorinated hydrocarbon
river
riffle
Sulfates
sulfate
Discharge (fluid mechanics)
Biological materials
Natural attenuation
organic matter
natural attenuation
Chlorine

Keywords

  • chlorinated hydrocarbon (CHC)
  • dechlorination
  • groundwater-surface water interaction
  • hyporheic zone
  • natural attenuation
  • trichloroethene (TCE)
  • urban river
  • water contamination

Cite this

Freitas, Juliana G. ; Rivett, Michael O. ; Roche, Rachel S. ; Durrant (neé Cleverly), Megan ; Walker, Caroline ; Tellam, John H. / Heterogeneous hyporheic zone dechlorination of a TCE groundwater plume discharging to an urban river reach. In: Science of the Total Environment. 2015 ; Vol. 505. pp. 236-252.
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Heterogeneous hyporheic zone dechlorination of a TCE groundwater plume discharging to an urban river reach. / Freitas, Juliana G.; Rivett, Michael O.; Roche, Rachel S.; Durrant (neé Cleverly), Megan; Walker, Caroline; Tellam, John H.

In: Science of the Total Environment, Vol. 505, 01.02.2015, p. 236-252.

Research output: Contribution to journalArticle

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T1 - Heterogeneous hyporheic zone dechlorination of a TCE groundwater plume discharging to an urban river reach

AU - Freitas, Juliana G.

AU - Rivett, Michael O.

AU - Roche, Rachel S.

AU - Durrant (neé Cleverly), Megan

AU - Walker, Caroline

AU - Tellam, John H.

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N2 - The typically elevated natural attenuation capacity of riverbed-hyporheic zones is expected to decrease chlorinated hydrocarbon (CHC) groundwater plume discharges to river receptors through dechlorination reactions. The aim of this study was to assess physico-chemical processes controlling field-scale variation in riverbed-hyporheic zone dechlorination of a TCE groundwater plume discharge to an urban river reach. The 50-m long pool-riffle-glide reach of the River Tame in Birmingham (UK) studied is a heterogeneous high energy river environment. The shallow riverbed was instrumented with a detailed network of multilevel samplers. Freeze coring revealed a geologically heterogeneous and poorly sorted riverbed. A chlorine number reduction approach provided a quantitative indicator of CHC dechlorination. Three sub-reaches of contrasting behaviour were identified. Greatest dechlorination occurred in the riffle sub-reach that was characterised by hyporheic zone flows, moderate sulphate concentrations and pH, anaerobic conditions, low iron, but elevated manganese concentrations with evidence of sulphate reduction. Transient hyporheic zone flows allowing input to varying riverbed depths of organic matter are anticipated to be a key control. The glide sub-reach displayed negligible dechlorination attributed to the predominant groundwater baseflow discharge condition, absence of hyporheic zone, transition to more oxic conditions and elevated sulphate concentrations expected to locally inhibit dechlorination. The tail-of-pool-riffle sub-reach exhibited patchy dechlorination that was attributed to sub-reach complexities including significant flow bypass of a low permeability, high organic matter, silty unit of high dechlorination potential. A process-based conceptual model of reach-scale dechlorination variability was developed. Key findings of practitioner relevance were: riverbed-hyporheic zone CHC dechlorination may provide only a partial, somewhat patchy barrier to CHC groundwater plume discharges to a surface water recept or and, monitoring requirements to assess the variability in CHC attenuation within a reach are expected to be onerous. Further research on transient hyporheic zone dechlorination is recommended.

AB - The typically elevated natural attenuation capacity of riverbed-hyporheic zones is expected to decrease chlorinated hydrocarbon (CHC) groundwater plume discharges to river receptors through dechlorination reactions. The aim of this study was to assess physico-chemical processes controlling field-scale variation in riverbed-hyporheic zone dechlorination of a TCE groundwater plume discharge to an urban river reach. The 50-m long pool-riffle-glide reach of the River Tame in Birmingham (UK) studied is a heterogeneous high energy river environment. The shallow riverbed was instrumented with a detailed network of multilevel samplers. Freeze coring revealed a geologically heterogeneous and poorly sorted riverbed. A chlorine number reduction approach provided a quantitative indicator of CHC dechlorination. Three sub-reaches of contrasting behaviour were identified. Greatest dechlorination occurred in the riffle sub-reach that was characterised by hyporheic zone flows, moderate sulphate concentrations and pH, anaerobic conditions, low iron, but elevated manganese concentrations with evidence of sulphate reduction. Transient hyporheic zone flows allowing input to varying riverbed depths of organic matter are anticipated to be a key control. The glide sub-reach displayed negligible dechlorination attributed to the predominant groundwater baseflow discharge condition, absence of hyporheic zone, transition to more oxic conditions and elevated sulphate concentrations expected to locally inhibit dechlorination. The tail-of-pool-riffle sub-reach exhibited patchy dechlorination that was attributed to sub-reach complexities including significant flow bypass of a low permeability, high organic matter, silty unit of high dechlorination potential. A process-based conceptual model of reach-scale dechlorination variability was developed. Key findings of practitioner relevance were: riverbed-hyporheic zone CHC dechlorination may provide only a partial, somewhat patchy barrier to CHC groundwater plume discharges to a surface water recept or and, monitoring requirements to assess the variability in CHC attenuation within a reach are expected to be onerous. Further research on transient hyporheic zone dechlorination is recommended.

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KW - dechlorination

KW - groundwater-surface water interaction

KW - hyporheic zone

KW - natural attenuation

KW - trichloroethene (TCE)

KW - urban river

KW - water contamination

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