| Title: | Unintentional contaminant transfer from groundwater to the vadose zone during source zone remediation of volatile organic compounds |
| Address: | "Department of Earth, Ocean and Atmospheric Sciences, Faculty of Science, 2020 - 2207 Main Mall, University of British Columbia, Vancouver V6T 1Z4, BC, Canada; BGC Engineering Inc., 980 Howe St, Vancouver V6Z 0C8, BC, Canada. Electronic address: achong@eos.ubc.ca. Department of Earth, Ocean and Atmospheric Sciences, Faculty of Science, 2020 - 2207 Main Mall, University of British Columbia, Vancouver V6T 1Z4, BC, Canada" |
| DOI: | 10.1016/j.jconhyd.2017.08.004 |
| ISSN/ISBN: | 1873-6009 (Electronic) 0169-7722 (Linking) |
| Abstract: | "Historical heavy use of chlorinated solvents in conjunction with improper disposal practices and accidental releases has resulted in widespread contamination of soils and groundwater in North America and worldwide. As a result, remediation of chlorinated solvents is required at many sites. For source zone treatment, common remediation strategies include in-situ chemical oxidation (ISCO) using potassium or sodium permanganate, and the enhancement of biodegradation by primary substrate addition. It is well known that these remediation methods tend to generate gas (carbon dioxide (CO(2)) in the case of ISCO using permanganate, CO(2) and methane (CH(4)) in the case of bioremediation). Vigorous gas generation in the presence of chlorinated solvents, which are categorized as volatile organic contaminants (VOCs), may cause gas exsolution, ebullition and stripping of the contaminants from the treatment zone. This process may lead to unintentional 'compartment transfer', whereby VOCs are transported away from the contaminated zone into overlying clean sediments and into the vadose zone. To this extent, benchtop column experiments were conducted to quantify the effect of gas generation during remediation of the common chlorinated solvent trichloroethylene (TCE/C(2)Cl(3)H). Both ISCO and enhanced bioremediation were considered as treatment methods. Results show that gas exsolution and ebullition occurs for both remediation technologies. Facilitated by ebullition, TCE was transported from the source zone into overlying clean groundwater and was subsequently released into the column headspace. For the case of enhanced bioremediation, the intermediate degradation product vinyl chloride (VC) was also stripped from the treatment zone. The concentrations measured in the headspace of the columns (TCE approximately 300ppm in the ISCO column, TCE approximately 500ppm and VC approximately 1380ppm in the bioremediation column) indicate that substantial transfer of VOCs to the vadose zone is possible. These findings provide direct evidence for the unintended spreading of contaminants as a result of remediation efforts, which can, under some circumstances, result in enhanced risks for soil vapour intrusion" |
| Keywords: | "Biodegradation, Environmental Groundwater/*chemistry Manganese Compounds/*chemistry Models, Theoretical Oxidation-Reduction Oxides/*chemistry Soil/chemistry Solvents/chemistry Trichloroethylene/*chemistry Vinyl Chloride/chemistry Volatile Organic Compound;" |
| Notes: | "MedlineChong, Andrea D Mayer, K Ulrich eng Netherlands 2017/08/24 J Contam Hydrol. 2017 Sep; 204:1-10. doi: 10.1016/j.jconhyd.2017.08.004. Epub 2017 Aug 7" |
