Theme: 04. Addressing Challenging Site Conditions

Topic Area: 4f. Low-Permeability Zone Treatment Approaches, Permeability Enhancements, and Case Studies

Formatted Title:

Large-Scale Design and Implementation of Zero-Valent Iron Coupled with In Situ Bioremediation for VOC Treatment

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 have been the subject of a decades-long remediation program under the California Regional Water Quality Control Board and Department of Toxic Substances Control. The site VOCs include 1,1,2-trichloroethane, benzene, chlorobenzene, chloroform, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, tetrachloroethene, trichloroethane, cis-1,2-dichlorothene, trans-1,2-dichloroethene, and vinyl chloride, which occur in a shallow low-permeability overburden aquifer adjacent to the San Francisco Bay. Over the last 2 years, a plan to remediate the property via a combined chemical reduction with micro-scale zero-valent iron (mZVI) and in situ bioremediation was developed and implemented

Approach/Activities:

The design approach employed a laboratory biotreatability study in 2021 to evaluate degradation of chlorinated ethenes, ethanes, and methanes. The study indicated bioaugmentation is necessary to promote complete dechlorination of site VOCs to their respective end products. 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 implemented in 2023 employed a novel application of combined in situ bioremediation using six different bioaugmentation cultures and in situ chemical reduction with hydraulic emplacement of mZVI at over 1,000 injection locations. The implementation was performed in two stages—first creating subsurface fractures comprised of mZVI, electron donor, and bioaugmentation culture, followed by emulsified vegetable oil and additional bioaugmentation delivery via injection wells that were interconnected with the mZVI fracture network.

Results/Lessons Learned:

The detailed biotreatability study yielded data necessary to select the correct bioaugmentation cultures for each treatment area and evaluated the effects from high sulfate (greater than 1,000 milligrams per liter) associated with saline groundwater in some areas of the site. The implementation presented logistical challenges related to scale and work sequence that necessitated close coordination between the design firm, biotreatability laboratory, bioaugmentation and material vendors, subcontractors, regulators, and local stakeholders. This presentation will discuss the challenges and lessons learned with this large-scale design and implementation project and present performance data collected to date.

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Andrew Romolo