Use of Bioremediation Natural Attenuation Processes for Cleanup of a TCE Groundwater Plume

Cronk, Gary

Use of Bioremediation Natural Attenuation Processes for Cleanup of a TCE Groundwater Plume

Presented on Thursday, December 17, 2015

Gary Cronk, PE, JAG Consulting Group Inc., Santa Ana, CA

Following active remediation of an extensive TCE and 1,1-DCE plume in La Mirada (Los Angeles County), CA using pump and treat for 10 years, then followed by several chemical oxidation injection events, a final remedial strategy was sought to complete the remaining groundwater cleanup process. In pursuit of this final remedial strategy, evaluation of monitored natural attenuation (MNA) was implemented by collection and analysis of microbial populations and physical water quality parameters at the site.

The site groundwater exhibits a wide microbial diversity, with many types of aerobic and anaerobic bacteria, including the presence of low numbers of Dehalococcoides bacteria, which indicates the potential for complete reductive dechlorination of TCE and 1,1-DCE to occur at the site. In addition, key functional genes (such as TCE reductase and VC reductase) were identified at the site.

An unexpected discovery was the confirmation of a robust population of methane oxidizing bacteria (methanotrophs) which are causing the co-metabolism of TCE. Under aerobic conditions, methane oxidizing bacteria can co-metabolize or co-oxidize TCE, DCE and vinyl chloride. The presence of moderate amounts of soluble methane mono-oxygenase enzymes indicates that an increased rate of co-metabolism can be supported at this site. Based on the relative populations of methane oxidizing bacteria in comparison to DHC bacteria (up to 600 times greater), it is estimated that the co-oxidation degradation rates at the site are far greater than the reductive dechlorination rates.

Over the last four years (since 2010) of groundwater monitoring, the TCE and 1,1-DCE levels (up to 150 µg/ml) in 11 key monitoring wells have attenuated by 50% or more due to natural attenuation processes. Currently, we are in negotiation with the Los Angeles Water Quality Control Board to use natural attenuation as a 3-year strategy to obtain groundwater cleanup goals and obtain final site closure.

MP3 Presentation Slides

Gary Cronk, PE

JAG Consulting Group Inc., Santa Ana, CA

Mr. Gary Cronk is the President of JAG Consulting Group, Inc., a consulting and remediation firm based in Santa Ana, CA that specializes in providing services for the design and implementation of in-situ chemical oxidation, enhanced bioremediation, chemical reduction, and other in-situ technologies. Mr. Cronk has experience in the design and implementation of over 75 injection projects in California and the Western U.S. To date, Mr. Cronk has been successful in attaining No Further Action requirements from regulatory agencies for 12 sites using in-situ injection technology. Mr. Cronk is a California Registered Professional Engineer, a California Certified Hazardous Substances Removal and Remedial Actions Contractor (A-HAZ), a Class A General Engineering Contractor, and a Certified Hazardous Materials Manager (CHMM). He is a frequent speaker at conferences and seminars on in-situ injection technologies.

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