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Comparison of E(h) and H2 measurements for delineating redox processes in a contaminated aquifer

Environmental Science and Technology

By:
, , , , and
DOI: 10.1021/es960249+

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Abstract

Measurements of oxidation-reduction potential (E(h)) and concentrations of dissolved hydrogen (H2) were made in a shallow groundwater system contaminated with solvents and jet fuel to delineate the zonation of redox processes. E(h) measurements ranged from +69 to -158 mV in a cross section of the contaminated plume and accurately delineated oxic from anoxic groundwater. Plotting measured E(h) and pH values on an equilibrium stability diagram indicated that Fe-(III) reduction was the predominant redox process in the anoxic zone and did not indicate the presence of methanogenesis and sulfate reduction. In contrast, measurements of H2 concentrations indicated that methanogenesis predominated in heavily contaminated sediments near the water table surface (H2 ~ 7.0 nM) and that the methanogenic zone was surrounded by distinct sulfate-reducing (H2 ~ 1-4 nM) and Fe-(III)-reducing (H2 ~ 0.1-0.8 nM) zones. The presence of methanogenesis, sulfate reduction, and Fe(III) reduction was confirmed by the distribution of dissolved oxygen, sulfate, Fe(II), and methane in groundwater. These results show that H2 concentrations were more useful for identifying anoxic redex processes than E(h) measurements in this groundwater system. However, H2-based redox zone delineations are more reliable when H2 concentrations are interpreted in the context of electron-acceptor (oxygen, nitrate, sulfate) availability and the presence of final products [Fe(II), sulfide, methane] of microbial metabolism.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Comparison of E(h) and H2 measurements for delineating redox processes in a contaminated aquifer
Series title:
Environmental Science and Technology
DOI:
10.1021/es960249+
Volume
30
Issue:
12
Year Published:
1996
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Science and Technology
First page:
3565
Last page:
3569
Number of Pages:
5