Nationally recognized experts met at the California NanoSystems Institute on March 22-23, 2016 to discuss progress and potential collaboration on SERDP and ESTCP funded efforts investigating remedial strategies for 1,4-dioxane-contaminated soils and groundwater. The meeting, hosted by Dr. Shaily Mahendra at the University of California in Los Angeles, attracted more than twenty scientists in this field. Results from a total of eleven projects were presented and included the following projects:

• Effects of metals and chlorinated solvent co-contaminants on 1,4-dioxane biodegradation led by Dr. Shaily Mahendra under SERDP project ER-2300. Among other results, initial studies demonstrate that chlorinated solvents inhibit biodegradation of 1,4-dioxane.
• Evaluation of branched hydrocarbons as stimulants for in situ cometabolic biodegradation of 1,4-dioxane led by Dr. Michael Hyman at North Carolina State University under SERDP Project ER-2303. Interim results show that isobutane-metabolizing bacteria can consistently degrade low (<100 ppb) concentrations of 1,4-dioxane, often to concentrations <1 ppb. These organisms also can degrade many chlorinated co-contaminants such as 1,1,1-trichlorethane (1,1,1-TCA) and 1,1-dichoroethene (1,1-DCE).
• Development and validation of gene probes to quantify 1,4-dioxane biodegradation capacity in order to support decisions to select or reject MNA and assess bioremediation performance led by Dr. Pedro Alvarez at Rice University under SERDP Project ER-2301. Interim results show that the targeted dxmA biomarker reliably indicates 1,4-dioxane degradation capacity more accurately than conventional 16S probes.
• Identification of the scale of 1,4-dioxane contamination at groundwater sites led by Dr. David Adamson at GSI Environmental, Inc. under SERDP project ER-2307. Results to date have shown that 1,4-dioxane plumes are fairly similar in size to co-occurring TCE and 1,1-DCE plumes (Adamson et al., 2016).
• Development of advanced-oxidation ISCO for 1,4-dioxane degradation by enhancing the solubility, stability, and transportability of strong oxidants, which will enable the in situ treatment of groundwater plumes. This project is led by Dr. K.C. Carroll from New Mexico State University under SERDP project ER-2302.
• Development of a passive flux meter approach to quantifying 1-4 dioxane mass flux led by Dr. Mike Annable from the University of Florida under SERDP project ER-2304. Results to date show that the passive flux meter is capable of quantifying low absorbing compounds such as 1,4-dioxane.
• Investigation of a microbially-driven Fenton reaction for in situ remediation of groundwater contaminated with 1,4-dioxane, tetrachloroethene (PCE) and trichloroethene (TCE) led by Dr. Thomas DiChristina at Georgia Institute of Technology under SERDP project ER-2305. These contaminant mixtures have been successfully degraded with the microbially-driven Fenton reaction; future studies will scale up the process.
• In situ bioremediation of 1,4-dioxane by methane oxidizing bacteria in coupled anaerobic-aerobic zones led by Dr. Charles Schaefer from CDM Smith under SERDP project ER-2306. Results to date show that ethane effectively serves as a cometabolite for facilitating the biodegradation of 1,4-dioxane at relevant field concentrations.
• In situ treatment and management strategies for 1,4-dioxane-contaminated groundwater led by Dr. David Adamson at GSI Environmental, Inc. under SERDP project ER-2307. Laboratory studies to date indicate that in situ chemical oxidation can be successfully combined with bioaugmentation for managing dioxane contamination.
• Development of a reliable method for performing compound-specific isotope analysis (CSIA) on low levels of 1,4-dioxane in groundwater and to assess whether CSIA can be used to document the co-metabolic degradation of 1,4-dioxane led by Dr. Peter Bennett at Haley & Aldrich, Inc. under SERDP project ER-2535. The method currently developed is applicable to 1 μg/L.
• Interim results from a demonstration using slow release chemical oxidant cylinders were presented, led by Dr. Patrick Evans at CDM Smith under ESTCP project ER-201324. Column studies are promising; future efforts are focused on field implementation.
• Final results on a completed demonstration using extreme soil vapor extraction to remediate vadose zone contamination also were presented by Dr. Rob Hinchee at IST under ESTCP project ER-201326. 1,4-Dioxane was reduce by >90% in the treatment zone with no apparent downward migration of 1,4-dioxane.

Several of these projects are anticipated to be completed within the next year. More information on these projects is available at www.serdp-estcp.org.