Theme: 01. Remediation Technology Innovations

Topic Area: 01f. Emerging Remediation Technologies

Formatted Title:

Field-Scale Pilot Study Using In Situ Electrobiochemical Reactors to Address Soil and Groundwater Benzene Impacts

Background/Objectives:

A historical benzene release in low permeability soils, along a former transmission line, has been undergoing remediation since the early 2000s. Several remedial approaches including in situ chemical oxidation, soil vapor extraction, and multi-phase extraction (with and without fracturing) have historically been attempted. Presently, multi-phase extraction (MPE), which is energy- and time-intensive, is being implemented in a phased approach. Following the completion of the initial phase of the MPE remedy implementation, soil concentrations reached asymptotic levels above the established cleanup criteria. Therefore, alternative remedial approaches, using innovative in situ methods, were evaluated to potentially replace the existing MPE remedial approach. The use of an innovative in situ electrobiochemical reactor to generate a continuous zone of in situ oxidation was identified and selected for further field-scale pilot testing. This technology is expected to be more effective at reducing soil and groundwater benzene impacts and be more cost effective and sustainable when compared to the current MPE remedial technology.

Approach/Activities:

The electrobiochemical reactor (EBR) field-scale pilot study was implemented for a total time of 6 months and was conducted in an area where there are two distinct subsurface conditions. The field-scale pilot study was completed from June through December 2023. The first 3 months of the field-scale pilot study was completed in native soils (weathered silts and clays) that were historically impacted with benzene; the last 3 months of the field-scale pilot study was completed in native soils that were previously subjected to in situ hydraulic fracturing. Four (4) EBR reactors were utilized in each of the two areas to generate a continuous zone of in situ reactive oxidant species (ROS – including hydroxyl, super-oxide, and ferrate radicals) along with enhanced geochemical conditions that are conducive to follow-on enhanced biological processes (i.e., natural attenuation). The EBR reactor configurations were varied from a square pattern in the unfractured area to a linear pattern in the fractured area. Real-time monitoring of subsurface conditions was also completed using a series of downhole sondes which transmitted real-time data to the cloud so that the system performance could be continuously observed / monitored to provide details related to the effective radius of influence, interconnectivity between individual EBR reactor wells, and subsurface geochemical conditions. Microbial data (pre- and post- testing) were collected to provide for the evaluation of the potential for enhanced biodegradation. In order to generate benzene concentration data during the field-scale pilot testing, a portable field GC was incorporated into the pilot study to provide rapid turnaround of groundwater concentrations. Following the completion of pilot testing in each of the test areas, follow-up soil and groundwater sampling was completed to verify the field results along with the efficacy of benzene removal. Further, operational data (i.e., power consumption, system uptime and O&M) was collected as part of the real-time monitoring so that an operational cost comparison and feasibility evaluation of the EBR technology compared to existing MPE remedial alternative could be completed.

Results/Lessons Learned:

A summary of site conditions, baseline soil and groundwater conditions, an overview of the EBR technology, summary pilot study results, along with a sustainability and operating cost comparison to the existing MPE remedy will be presented. Additionally, lessons learned during the completion of the pilot study such as required EBR system maintenance intervals, real-time parameter monitoring, and the use of field-based GC monitoring will be presented. To date, the pilot study results in the unfractured area indicated ~90% reduction of benzene in groundwater in 90 days of operation, and soil concentration results are pending. Results from the fractured zone pilot study area will also be presented to compare the EBR system performance in the two areas.

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Betsy Witt