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Carbon Isotope Analysis to Evaluate Nanoscale Fe(O) Treatment at a Chlorohydrocarbon Contaminated Site
Author(s) -
Elsner Martin,
Couloume Georges Lacrampe,
Mancini Silvia,
Burns Leanne,
Lollar Barbara Sherwood
Publication year - 2010
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/j.1745-6592.2010.01294.x
Subject(s) - environmental chemistry , biodegradation , trichloroethylene , environmental remediation , chemistry , zerovalent iron , isotope analysis , contamination , groundwater , isotopes of carbon , reductive dechlorination , abiotic component , degradation (telecommunications) , total organic carbon , organic chemistry , adsorption , geology , ecology , paleontology , oceanography , telecommunications , geotechnical engineering , computer science , biology
Remediation of groundwater contaminated by chlorinated hydrocarbons via in situ technologies such as direct injection of nanoscale zero valent iron (ZVI, Fe(O)) particles is increasingly common. However, assessing target compound degradation by abiotic processes is difficult because (1) the injection may displace the contaminant plume so that concentration measurements alone are often inconclusive and (2) biodegradation may also occur, making it challenging to identify and evaluate the abiotic degradation component. In this study, trichloroethylene (TCE) and 1,1,1‐trichloroethane (1,1,1‐TCA) were treated in a highly heterogeneous hydrogeologic setting. The purpose of this study was to evaluate the potential for compound‐specific stable isotope analysis (CSIA) to monitor the effectiveness of ZVI injection by assessing TCE and 1,1,1‐TCA degradation. Prior to ZVI injection, carbon isotope measurements demonstrated biodegradation of TCE by native microorganisms. This in situ biodegradation was quantified by measuring the enrichment of 13 C in TCE samples downstream of the suspected source. When ZVI was injected through only two injection wells, no changes in TCE and 1,1,1‐TCA isotope signatures were detected compared to preinjection values. In contrast, when ZVI was injected through 11 wells covering a greater portion of the contaminated area, 5 out of 10 monitoring wells showed further enrichment of 13 C in either TCE or 1,1,1‐TCA, indicating additional target compound transformation. The abiotic nature of this TCE transformation was confirmed through temporal trends in carbon isotope values of the putative transformation products cis ‐dichloroethylene ( cis ‐DCE), ethene and ethane. This demonstrates the usefulness of CSIA in distinguishing abiotic vs. biotic transformation in the field.