Background

A railroad tanker spill on an active rail yard resulted in a 2.5-mile-long groundwater plume of trichloroethylene (TCE). The plume was located under low-income residential property, a Department of Homeland Security (DHS) and National Guard facility, public schools, and city-owned property.

Approach

Foth proposed a series of interim measures to reduce long-term risks. We provided remedial investigation planning and implementation, QAPP, a sampling and analysis plan, and baseline risk assessment. We also provided interim remedial action work plans, interim remedial action construction completion reports, a feasibility study, supplemental investigation work plans and plan implementation, quarterly reporting, and agency negotiations.

Source remediation consisted of soil removal using negotiated Tier 3 cleanup levels. In the source area’s saturated zone, two in situ remedial technologies were implemented sequentially. The first technology consisted of in-well air stripping and groundwater recirculation. The second, employed to treat recalcitrant zones, was in situ chemical oxidation using Fenton’s chemistry. In situ chemical oxidation injections were performed both within the active rail yard and immediately downgradient on sensitive properties.

The recommended remedy for the central portion of the groundwater plume was enhanced reductive dechlorination using a permeable reactive barrier configuration. A pilot study was performed to demonstrate the feasibility of the technology, including the use of an oil substrate and microbial inoculation, resulting in a bioreactive zone that achieved up to a 96% reduction in TCE concentrations.

Down-gradient plume control was achieved through the installation of a hydraulic control system with six extraction wells. The wells discharge to a Foth-designed treatment building where the extracted groundwater is treated using activated carbon before discharge to a NPDES outfall.

Results

The interim measures we employed removed over 700 tons of contaminated source soils and over 400 pounds of TCE through in situ air-stripping. Our measures also destroyed more than 40% of the remaining TCE in the source area and more than 90% of the dissolved contaminants underlying DHS property. They also demonstrated the applicability of enhanced reductive dechlorination and controlled the further migration of the plume.  Our groundwater modeling and optimization supported a fixed-price remediation strategy, and our client is proceeding to full-scale plume treatment and long-term measures based on the results.