2016 NGWA Groundwater Summit

An Integrated Approach for Deducing Degradation Pathways at Sites Contaminated with Chlorinated Ethylenes

Monday, April 25, 2016: 3:20 p.m.
Confluence Ballroom A (The Westin Denver Downtown)
Todd H. Wiedemeier , T H Wiedemeier & Associates, Inc., Sedalia, CO
John Wilson, Ph.D , Scissortail Environmental Solutions, Ada, OK

Bioremediation, both natural and engineered, has emerged as the preferred remediation approach at many sites contaminated with chlorinated ethylenes. A number of prognostic and diagnostic tools are available, yet guidance documents to assist site owners in selecting the most efficacious bioremediation approach are limited. Although the value of substrate additions (i.e., biostimulation) to enhance contaminant degradation has been demonstrated, this approach may not be needed at sites where monitored natural attenuation (MNA) is sufficient to meet remedial goals. Both remediation costs and associated environmental impacts will increase as more invasive and aggressive treatment options are implemented. Therefore, selection of the most appropriate bioremediation approach can result in substantial savings of capital investment and operation and maintenance (O&M) costs. Furthermore, avoiding unnecessary aquifer amendments, such as substrates and inocula, minimizes undesirable secondary impacts such as pH changes, formation of greenhouse gases, and reduced aquifer permeability. On the other hand, aggressive bioremediation can significantly shorten remedial timeframes, thereby reducing O&M costs as well as long-term environmental impacts.

There is no clear guidance on how to choose between MNA, biostimulation, and bioaugmentation, a shortcoming that causes unnecessary expenses and potentially detrimental environmental impacts. A systematic framework was developed under a project sponsored by ESTCP. This framework represents an extension of the 1998 USEPA Technical Protocol for Evaluating the Natural Attenuation of Chlorinated Solvents and (i) incorporates quantitative information of Dehalococcoides mccartyi biomarker genes, (ii) uses Compound-Specific Isotope Analysis (CSIA) results, (iii) considers the contribution of abiotic transformation of contaminants, and (iv) recognizes that natural attenuation is an important component of integrated remediation strategies. This approach allows identification of existing degradation mechanisms and integrates groundwater geochemical and contaminant data with quantitative real-time PCR and CSIA information, along with the current understanding of biological and abiotic degradation mechanisms, to deduce degradation pathways.

Todd H. Wiedemeier, T H Wiedemeier & Associates, Inc., Sedalia, CO
Todd Wiedemeier has more than 14 years of experience in remediation and has conducted natural attenuation and bioremediation feasibility studies at more than 100 sites contaminated with fuel hydrocarbons, MTBE, and chlorinated solvents. Wiedemeier is the author of more than 100 publications on remediation.

John Wilson, Ph.D, Scissortail Environmental Solutions, Ada, OK
John Wilson recently retired from the position Research Microbiologist for EPA’s Ground Water and Ecosystems Restoration Research (GWERD) Subsurface Remediation Branch. He holds a B.S. in Biology from Baylor University, an M.A. in Microbiology from the University of California at Berkeley, and a Ph.D. in Microbiology from Cornell University. Wilson led research dealing with biological and non-biological processes that destroy contaminants in groundwater and provided training and technical assistance to EPA’s regions and to state agencies on natural attenuation of hydrocarbon components in groundwater.