Using Stable Isotope Probing to Confirm Biodegradation of 1,4-Dioxane During In-Situ Remediation

Tuesday, August 8, 2017: 9:30 a.m.
Caitlin Bell, PE , Arcadis, San Francisco, CA
Kathleen Gerber , Vandenberg Air Force Base, Vandenberg AFB, CA

1,4-Dixoane is a common co-contaminant with chlorinated solvents and treatment of 1,4-dioxane via natural or enhanced biodegradation processes provides a viable remedial strategy. 1,4-Dioxane can be co-metabolically biodegraded in the presence of alkane gases and oxygen. At Vandenberg Air Force Base in California, historical use of chlorinated solvents resulted in 1,4-dioxane in groundwater. Previously, in-situ propane biosparging was implemented and resulted in 1,4-dioxane concentration reductions (as published by others). This work builds on the prior field demonstration to confirm biodegradation as the mechanism for 1,4-dioxane concentration decreases via stable isotope probing (SIP). SIP includes addition of a 13C-enriched compound into the test system to act as a carbon-atom tracer to track the biotransformation of 1,4-dioxane.

This second propane biosparge field demonstration was initiated in December 2015. Operation of the system included sparging a mixture of air and propane (20 percent of the LEL) at up to 5 standard cubic feet per minute into one sparge point, for 30 minutes every four hours. Bioaugmentation with a propanotrophic culture was conducted, alongside nutrient addition of diammonium phosphate. SIP included use of Bio-Trap®samplers “baited” with isotopically enriched 1,4-dioxane.

After two months of operation, 1,4-dioxane concentrations decreased approximately 45 to 83 percent at monitoring locations in the test area. The SIP results confirmed the biodegradation mechanism associated with 1,4-dioxane groundwater concentration decreases. The co-metabolic biotransformation of 13C-enriched 1,4-dioxane is expected to result in generation of carbon dioxide which was measured as 13C-enriched dissolved inorganic carbon. Additionally, evaluation of microbial biomass indicated incorporation of 13C into the cellular phospholipids. Because significant carbon uptake into microbial biomass is not commonly associated with co-metabolism, the 13C-enriched biomass values observed here may be attributed to uptake of the mineralization intermediates or the carbon dioxide end product, rather than the 1,4-dioxane directly.

Caitlin Bell, PE, Arcadis, San Francisco, CA
Caitlin H. Bell, PE, a principal engineer and the lead expert on 1,4-Dioxane for Arcadis, with nearly 10 years of consulting experience. A remediation engineer who focuses on subsurface treatment of soil and groundwater using in situ techniques, she specifically focuses on in situ bioremediation applications for a variety of chemicals of concern, including emerging contaminants. Ms. Bell serves as a technical resource to clients on topics such as molecular biology tools, bioaugmentation, compound-specific isotope analysis, and challenging bioremediation approaches for compounds like 1,4-dioxane. She was a member of the team who authored the Interstate Technology & Regulatory Council’s Environmental Molecular Diagnostics technical guidance document and has presented routinely on remediation topics at industry conferences. Ms. Bell is also a coauthor of the upcoming book, Handbook of Emerging Contaminants. She holds a B.S. in chemical engineering and an M.S. in environmental engineering.

Kathleen Gerber, Vandenberg Air Force Base, Vandenberg AFB, CA
Kathleen Gerber, PG, has over 25 years of government and consulting environmental restoration experience with a focus on investigation and remediation of large-scale solvent and fuel plumes. Kathleen is currently the restoration project manager (RPM) at Vandenberg Air Force Base (VAFB) and has supported the base for over 14 years as an environmental remediation design specialist, hydrogeologist, project manager, contracting officer representative, and supervisor. As the designated RPM for the base, she is responsible for the success of the negotiations with the state stakeholders. She is a strong advocate for intergovernmental and interagency partnering to achieve mutually beneficial outcomes for VAFB’s Restoration Program. She is the Air Force project manager for Site 24 and technical lead for the environmental cleanup program at VAFB.