The Remediation Technology Summit

March 7 - 9, 2017

Colorado Convention Center
Denver, CO

wilson amyAmy Wilson, PhD, PE
Principal Engineer
TRC

Amy Wilson is a civil engineer and hydrogeologist with 20 years of environmental consulting experience. Her technical expertise includes: groundwater and soil vapor fate and transport; conceptual site/hydrogeologic modeling; numerical modeling; water quality; and feasibility analyses, with an emphasis on developing solutions for large-scale, complex sites. Ms. Wilson earned a PhD in Civil Engineering from the University of California at Berkeley and is a registered engineer in the State of California.


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A Multi-Year Evaluation of Natural Attenuation of Chlorinated Ethenes and Methanes using CSIA

Background/Objectives.
Historical disposal practices at a former hazardous waste landfill have resulted in groundwater impacts comprising multiple VOCs, primarily chlorinated ethenes (PCE, TCE, and their daughter products), chlorinated methanes (carbon tetrachloride, chloroform, and their daughter products), 1,2-DCP, and benzene, and acetone. Groundwater at the site is deep (approximately 100 feet on average) and the geology is heterogeneous, with migration controlled by discontinuous preferential high-permeability pathways. The plumes are large and diffuse. A remedy consisting of containment and monitored natural attenuation (MNA) is being implemented at the landfill,

Approach/Activities.
In order to evaluate MNA, compound-specific isotope analysis (CSIA) is being performed for tetrachloroethene (PCE), trichloroethene (TCE), vinyl chloride (VC), carbon tetrachloride (CT), and chloroform. 1,2-Dichloropropane is also being evaluated. The wells used in the CSIA study are generally located along the centerlines of the VOC plumes, which enables data analysis with distance and travel time, while also generally representing the highest COC concentrations on site. Degradation trends and fractionation factors in individual wells over time are evaluated. CSIA data have been collected for seven VOC compounds in nine wells on a semiannual to annual basis since 2011. Microbial studies, and the ongoing collection of geochemical data, support the CSIA analyses.

Results/Lessons Learned.
The data over space and time reveal a complex degradation system that is likely confounded by multiple landfill sources and releases, and by groundwater geochemistry that varies significantly throughout the plumes. Although spatial trends can be used to evaluate natural attenuation in a single “snapshot” monitoring event, temporal trends, along with other lines of evidence such as geochemical and microbial conditions, have allowed for a rigorous level of MNA demonstration at this site.

CO-AUTHOR: Elizabeth Schwartz, PG, CHG (TRC, Concord, CA, USA)