Theme: 01. Remediation Technology Innovations

Topic Area: 01c. Permeable Reactive Barriers: Best Practices and Lessons Learned

Formatted Title:

Combined Remedy PRB Approach Arrests 1500-ft CVOC Plume Protecting Surface Water Body while Saving Client $380K

Background/Objectives:

Background/Objectives. Operations at a former manufacturing and warehouse facility outside of downtown Indianapolis released high concentrations of chlorinated solvents into the groundwater. This led to the formation of a substantial groundwater plume extending to the White River. Upon site assessment, it was determined that a significant trichloroethene (TCE) groundwater plume had migrated across several major thoroughfares toward the river. The overall plume’s length exceeded 1,500 linear feet, with TCE concentrations typically ranging from 10 to 200 parts per billion. The plume traversed shallow and deep aquifer zones as the sand unit carrying the contaminants thickened west to east across the site and offsite. The plume was underlain by a clay aquitard, preventing further vertical migration of the TCE while also serving as a source for contaminant back-diffusion.

Approach/Activities:

Approach/Activities. The treatment objectives aimed to eliminate off-site migration and prevent contaminants from entering the river. As part of Design Verification Testing (DVT) to ensure accurate remedial placement and dosing, flux mapping tools were installed in monitoring wells to delineate the contaminant flux zones. Information gained from these tools guided the precise application of remedial amendments to the highly transmissive zones driving the plume's development. By concentrating on treatment of these high flux zones, the project achieved a cost savings of approximately $380,000 for full-scale implementation. Immediately downgradient of the source area, an enhanced reductive dechlorination (ERD)/dual valent iron (DVI) approach was implemented consisting of 2,400 lbs. of an engineered three-stage electron donor, 3,600 lbs. ferrous gluconate solution, 18L anaerobic dechlorinating microbes, which were injected via 32 direct push technology (DPT) injection points. Further downgradient, a series of four permeable reactive barriers (PRBs) consisting of 63,200 lbs. of colloidal activated carbon 23,300 lbs. of sulfidated zero valent iron, and 71L of dechlorinating microbes were injected to capture and degrade TCE and prevent downgradient migration.

Results/Lessons Learned:

Results/Lessons Learned. Balancing the need for cost-effectiveness and efficiency, the team designed a multi-faceted remedy to halt plume migration immediately and eliminate potential impacts on the river. This presentation will cover the pre-site investigation which includes delineation of contaminant flux zones, soil core collection to confirm lithology changes, and groundwater sampling to assess baseline biogeochemistry. Remedial amendment injectant and implementation logistics will be discussed followed by a summary of the results which demonstrated a reduction of over 75% reduction in TCE and daughters near the source and over 90% downgradient of the barriers.

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Scott Connors