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Factors Controlling In Situ Biogeochemical Transformation of Trichloroethene: Field Survey
Author(s) -
Whiting Kent,
Evans Patrick J.,
Lebrón Carmen,
Henry Bruce,
Wilson John T.,
Becvar Erica
Publication year - 2014
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/gwmr.12068
Subject(s) - mackinawite , pyrite , biogeochemical cycle , greigite , environmental chemistry , iron sulfide , chemistry , iron oxide , sulfide minerals , sulfide , sulfur , mineralogy , organic chemistry
We have previously defined in situ biogeochemical transformation as the biogenic formation of reactive minerals that are capable of abiotically degrading chlorinated solvents such as trichloroethene without accumulation of degradation products such as vinyl chloride (AFCEE et al. [, 2008]). This process has been implemented in biowalls used to intercept contaminated groundwater. Abiotic patterns of contaminant degradation were observed at Altus Air Force Base ( AFB ) and in an associated column study, but not at other sites including Dover AFB . These abiotic patterns were associated with biogenic formation of reactive iron sulfide minerals. Iron sulfides in the form of small individual grains, coatings on magnetite, and sulfur‐deficient pyrite framboids were observed in samples collected from the Altus AFB biowalls and one of the EPA columns. Larger iron sulfide grains coated with oxide layers were observed in samples collected from Dover AFB . Altus AFB and the EPA column differed from Dover AFB in that groundwater flow at Dover AFB was relatively slow and potentially reversing. High volumetric sulfate consumption rates, an abiotic pattern of trichloroethene ( TCE ) degradation, and the formation of small, high surface area iron sulfide particles were associated with relatively high rates of TCE removal via an abiotic pattern. Geochemical modeling demonstrated that iron monosulfides such as mackinawite were near saturation, and iron disulfides such as pyrite were supersaturated at all sites. This environmental condition can be supportive of nucleation of small particles rather than crystal growth leading to larger particles. When nucleation is dominant, small, high surface area, and reactive particles result. When crystal growth dominates the crystals are larger and have lower specific surface area and reactivity. These results taken together suggest that creation of a dynamic environment can promote biogeochemical transformation based on generation of reactive iron sulfides.