Topic Area: 3b. Bioremediation Case Studies

Formatted Title:

Large-Scale Remedy Design and Implementation Coupling Zero-Valent Iron with In Situ Bioremediation for Variable Site Conditions

Background/Objectives:

Historical releases of a wide variety of volatile organic compounds (VOCs) to groundwater associated with a nineteenth century 87-acre former chemical manufacturing plant has been the subject of a decades-long remediation program under the California Regional Water Quality Control Board and Department of Toxic Substances Control. Challenges included varying compositions of chlorinated VOCs in 13 geochemically unique areas of the site which persisted in a shallow low-permeability overburden aquifer adjacent to the San Francisco Bay. Over the last 3 years, a full-scale remedy was developed and implemented to remediate the property via combined chemical reduction with micro-scale zero-valent iron (mZVI) and in situ bioremediation.

Approach/Activities:

The design approach was developed from numerous pilot studies performed between 2007 and 2012 as well as a laboratory biotreatability study conducted in 2021 to evaluate degradation of chlorinated ethenes, ethanes, and methanes under the varying geochemical conditions of the site. The studies indicated complete degradation of site VOCs could be achieved by tailoring bioaugmentation cultures specific to each treatment area. Interestingly, the benefits of mZVI addition were varied in the different areas tested. The results of the study were used as the design basis for area-specific biostimulation, mZVI dosing, and bioaugmentation consortia selection. The final design employed a novel application of combined in situ bioremediation using seven different bioaugmentation cultures and in situ chemical reduction.

Implementation took place over a period of 6 months and included hydraulic emplacement of more than 700 tons of mZVI and 250,000 gallons of EVO solution with bioaugmentation cultures at over 1,000 injection point locations. The work was conducted in two stages—first creating subsurface fractures within the low permeability aquifer comprised of mZVI, electron donor, and bioaugmentation culture, followed by emulsified vegetable oil and additional culture delivery via injection wells that were engineered to access the mZVI fracture network.

Petra Eberspacher

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(Group 2, Poster Board #71) Large-Scale Remedy Design and Implementation Coupling Zero-Valent Iron with In Situ Bioremediation for Variable Site Conditions