The brownfield site is a former industrial facility where chlorinated solvents were spilled during industrial manufacturing processes occurring from 1941 to 1970. The site redevelopment plan includes an apartment complex and commercial buildings. Before redevelopment could proceed remediation was needed to address the groundwater contamination. PES Environmental, Inc. of Novato, California, was selected by the developer as their environmental consultant for this project. PES teamed with REGENESIS to develop and implement the in-situ remediation program.
Investigations to define the nature, extent, and general structure of the groundwater plume had been ongoing at the site since the 1980s and these identified an approximate 1.5-acre plume area requiring remediation. This historical information was supplemented by further characterization using passive flux meters (PFMs) to delineate the prominent flux zones and magnitudes of groundwater and contaminant flux. The PFMs indicated that the average groundwater velocity was about 300 feet per year, roughly four times less than the earliest estimates using traditional hydraulic characterization methods. Using this information, REGENESIS prepared an optimized remediation approach to achieve the two-year remediation goal with the greatest economic efficiency, leading to the submittal of a Response Plan to the Regional Water Quality Control Board (RWQCB).
The Response Plan included source area excavation and disposal of contaminated soils, in situ source area remediation, and a series of five permeable reactive barriers within the downgradient plume. To monitor performance, paired wells were installed downgradient of each transect beyond the injection radius of influence.
After approximately one-year post-injection, the remediation program has met the predicted performance expectations. In the source area, the combined excavation and in situ injections have reduced CVOC concentrations by 98 percent, and greater than 90 percent CVOC reductions have been achieved in the plume area. Significant concentrations of ethane, an abiotic degradation byproduct, have been observed indicating complete degradation of the CVOCs is occurring with minimal daughter product formation.
In summary, the use of DVT and predictive modeling tools allowed the REGENESIS and PES team to maximize the injected remediation technologies’ functionality to achieve the greatest benefit and attain the remedial objectives well within proposed the two-year timeframe. Based on the observed performance after one year, PES has successfully petitioned the RWQCB to end plume monitoring and remove the performance monitoring wells so that the property redevelopment can proceed.
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