Vapor Intrusion Mitigation and Soil and Groundwater Remediation, United States Naval Base
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Project Objective

Historical United States Navy operations resulted in trichloroethylene (TCE) impacts to soil and groundwater beneath a large military manufacturing building. The Navy turned to Geosyntec to quickly evaluate the vapor intrusion (VI) pathway in the occupied 23-acre building without interfering with mission-critical military manufacturing. Geosyntec later designed and installed systems to inhibit VI and to remove or destroy TCE contamination in soil and groundwater below the building. This project faced unique challenges associated with construction inside hallways, offices, and manufacturing spaces and navigated requirements of the unionized workforce.

Geosyntec’s Scope of Services

Geosyntec used high-volume sampling (HVS) to investigate subsurface sources of TCE in soil and at the water table. The results showed significant TCE impacts below a small portion of the building, and they showed that TCE was not present in the shallow subsurface under most of the building. Geosyntec was awarded the follow-on task order to design, construct, and operate four remedial systems, including a vapor intrusion mitigation system (VIMS), soil vapor extraction (SVE) system, in situ chemical oxidation (ISCO) injection system, and bioremediation injection system. Geosyntec developed the designs, oversaw construction, and implemented the operation, maintenance, and monitoring (OM&M) of the four systems.

The VIMS, SVE, ISCO injection, and bioremediation injection systems were installed beneath occupied rooms. The configuration of SVE wells was changed periodically to optimize mass recovery. In its first seven months, the SVE system removed nearly 500 kilograms of TCE. Performance monitoring showed complete destruction of dissolved contaminants in groundwater in the ISCO pilot area and strong reductive dechlorination in the downgradient bioremediation area.

Notable Accomplishments

Geosyntec’s HVS investigation strategy replaced an impractical approach that would have used traditional methods, cost significantly more, taken longer to execute, and risked operational disruption. Later, Geosyntec used thoughtful design to minimize piping runs, reduce operational noise, and minimize disturbance. The team worked nights and weekends to avoid interfering with mission-critical military operations. The SVE system alone extracted nearly 700 kilograms of TCE during the contract period. This project demonstrated that SVE, bioremediation, and in situ chemical oxidation can effectively treat large and complex chlorinated solvent plumes beneath active military operations without interruptions.