Bioremediation, Environment, Federal Government, North America, United States
Combined Remedies Restore Complex Site for Reuse
Innovative combined remedies treat contaminated soil and groundwater in aggressive timeframe for reuse by city
At the complex CERCLA site at Hunters Point Naval Shipyard (HPNS) in San Francisco, California, soil and groundwater were contaminated with chlorinated solvents, including dense non-aqueous phase liquid (DNAPL). A timely and economical treatment solution was required to reduce contamination below compliance goals and prevent contaminant migration from the site.
CDM Smith conducted a full-scale treatability study and designed a multicomponent remediation system that combined in situ bioremediation (ISB) and in situ thermal remediation (ISTR) to reduce ISTR’s footprint and cost, improve ISB mass removal rates and polish remaining contaminants. DNAPL, soil and groundwater contaminant data and hydrogeologic properties were integrated into a 3D visualization tool that optimized ISTR treatment volumes and evaluated technology performance.
ISB was initiated in the low-permeability aquifer by emplacing long-lived (estimate 5+ years) iron and cellulose compound, EHC™, throughout the contaminated area using soil fracturing. The physical, chemical and biological degradation mechanisms accelerated DNAPL removal in contaminated soils, vapor and groundwater. ISTR volatilized contaminants, including DNAPL, which were treated both through soil vapor extraction with ex situ and in situ treatment as they migrated through the permeable fracture network containing EHC.
The synergy of these two innovative technologies overcame site challenges for unprecedented results. Remedial objectives were achieved with DNAPL removal, a 90 percent reduction in soil contaminant mass and 80 percent reduction in groundwater concentrations within 18 months. Within 3 years, thermally enhanced ISB resulted in 90-99.99 percent reductions in contaminants and will achieve part-per-billion-level groundwater cleanup criteria.
The solution saved the Navy $5 million in capital costs because of the significant reduction of injection points required with hydraulic fracturing and the longevity of EHC™. This successful cleanup was accomplished within an aggressive timeframe, facilitating the Navy’s transfer of a valuable adjacent property to the city of San Francisco for redevelopment.