Project:
Former Electronics Manufacturing Facility
Bottom Line: Developed and implemented a remediation program to remove saturated soils impacted by VOCs and a continuing source of contamination to groundwater by excavating down to a depth of 55 feet inside a building with a relatively low ceiling height of 12 feet.
Summary of Project
Located in an industrial area, the site contained a one-story building in which microwave and semiconductor components were assembled and tested from 1968 to 1993. Waste solvents from the manufacturing process, primarily TCE, were stored in a UST from 1970 to 1982. The UST was removed in 1983. Environmental investigations found VOC-impacted soil in the vicinity of the UST, and impacted soil up to the building foundation was excavated and disposed of off site in 1984. The excavation was backfilled with pea gravel and a 6-inch-diameter perforated pipe (“eductor”) was installed for groundwater extraction purposes.
The building was remodeled from 2001 to 2003, with part of the building replaced with a two-story section overlying the excavation area. The site was unoccupied until 2015, when interior remodeling commenced for a new tenant, requiring another phase of investigation and remediation. The objectives of the remediation activities were to remove source area soil with elevated VOC concentrations and reduce the potential for future impact to groundwater and/or vapor intrusion into the building.
- Conducted a soil investigation of the upper two saturated soil zones (shallow zone down to 20 bgs and the next zone 20 feet and below) in the source area (depth to groundwater at 8 feet bgs). Installed and collected soil samples from an initial 5 borings down to 25 feet below; installed and collected soil samples from an additional 34 borings from 25 to 40 bgs to evaluate the lateral and vertical extent of VOC-impacted soil.
- Collected groundwater grab samples to correlate the saturated soil VOC concentrations with groundwater samples.
- Collected and analyzed confirmation soil samples, including angle-drilling under the existing building footing to reach otherwise inaccessible areas.
- Managed and disposed of VOC-impacted soil as a hazardous waste, including preparing hazardous waste manifests for disposal at the proper facilities.
- Designed excavation of VOC-impacted vadose zone and saturated zone soils to a depth of 55 feet inside a building with a ceiling height of 12 feet. Provided oversight during excavation of VOC-impacted soil in the source area, including the scopes of work of two subcontractors that: (1) stabilized the proposed excavation area, reportedly backfilled with pea gravel, and prevented the collapse of the gravel sidewalls during the remediation by injecting ultrafine cement slurry into the former excavation area; and (2) removed the concrete slab over excavation area and drilled 86 borings from 20 to 55 feet below grade, using a large-diameter bucket-auger rig capable of drilling inside the building, to excavate approximately 400 cubic yards of VOC-impacted soil.
- Oversaw the backfilling of the excavation and, during concrete slab restoration, installation of vapor collection piping tied into a passive sub-slab vapor collection system previously installed throughout the building.
- Provided design for and oversaw a subcontractor to seal concrete slab control joints, cracks, and saw cuts; seal concrete slab penetrations; seal gap space between walls; and inspect elevator shaft slab for cracks.