The Williamsburg Works MGP site is located in a 6-acre commercial/industrial area. A predecessor gas company to National Grid operated the former Williamsburg MGP from the 1850s to the 1930s. Gas production produced coal tar, which escaped from subsurface structures and pipes and contaminated the site’s surrounding subsurface soils and several adjoining properties. Primary COCs included coal tar.
As the prime contractor, Sevenson’s remediation activities included the in-situ stabilization of 4,681 CY and excavation, handling, and disposal of 44,000 tons of MGP-impacted waste utilizing three Sevenson-constructed temporary containment buildings, ranging from 0–23 ft. BGS. Deep excavation required extensive support, protection, and monitoring of active subsurface utilities. Crews designed and constructed an excavation support system consisting of a steel sheet pile wall placed within a cement-bentonite slurry wall (installation of 620 LF of steel sheet piling at 46 ft. BGS). Sevenson also designed, constructed, operated, and maintained an on-site 200-GPM WWTP which treated and discharged >2.8M gallons of water.