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USACE Final Source Area Excavation and Remediation

US Army Corps of Engineers
Location: Building 258, Fort Hunter Liggett, California
Contract Value: $5,003,133

Ahtna excavated 6,700 cubic yards of gasoline-contaminated soil at Fort Hunter Liggett (FHL) Building 258, a former fuel depot, using a 36-inch diameter continuous flight auger (CFA) and completed soil remediation by land farming and bioremediation. In late 1989, an environmental response was identified at FHL to address a gasoline spill from a leaking underground storage tank (UST) at the former fuel depot located at Building 258. After decades of in-situ cleanup activities, the ultimate response action required the removal of an additional 6,700 cubic yards of contaminated soil.

However, today, this area is an active vehicle maintenance facility, which complicated the possibility of performing a removal action. Traditional excavation would have required the demolition of two vehicle maintenance buildings critical to the mission, associated equipment and utilities, and a main roadway. It would have also displaced 30 onsite vehicle mechanics.

Ahtna had been providing environmental services at FHL since 2009 under multiple contracts, including groundwater monitoring, well maintenance, installation/O&M of a Soil Vapor Extraction Well and System, and advanced profiling assessments, which included use of MIP and UVOST technologies, to further delineate extent of dissolved phase and residual phase hydrocarbons across a 2,500-foot long by 750-foot wide plume. Our in-depth site knowledge and technical expertise were essential to the successful design and execution of this excavation project. Based on our expertise, we recommended Continuous Flight Auger (CFA) drilling to “surgically” excavate the source area, which was otherwise inaccessible or cost prohibitive using standard sloped dig-and-haul excavation techniques. CFA drilling also allowed us to perform the work within a limited area, avoiding disturbances to ongoing vehicle maintenance activities at the site.

To comply with FHL’s Net Zero Goal Ahtna recommended the use of land farming and bioremediation to treat contaminated soils onsite and make all remediated soils available for construction reuse. Ahtna completed the project within budget, and 11 months ahead of schedule, achieving all performance goals. The project is now moving forward to low-threat regulatory case closure. Ahtna performs ongoing quarterly groundwater monitoring to provide data to establish continuing hydrocarbon trends.



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Services Provided:

  • Advanced profiling assessments
  • Groundwater monitoring
  • Installation and O&M of Soil Vapor Extraction Well and System
  • Remediation
  • Removal action
  • Waste management in support of Net Zero
  • Well maintenance