Contaminated Soil Remediation

Forgen has extensive experience performing the safe excavation and transport of contaminated soils and other source materials. Our project management teams prepare job-specific safety protocols and traffic control plans that prevent exposure to workers, as well as the surrounding community and environment. When required, air monitoring is utilized to further ensure that fugitive dust and emissions do not leave the project boundaries. All vehicles utilized for transport of impacted media are securely tarped, thoroughly inspected, and properly decontaminated prior to leaving the project site to prevent the accidental spread of contamination. Traffic routes are carefully planned to maximize safety and limit potential community exposure. Forgen’s experience with contaminated source removal has included soil and other media contaminated with heavy metals, volatile organic compounds, solvents, pesticides, PCBs, dioxins, and asbestos.

Vallejo, California

  • Excavation of 15,000 cy of TPH and metal impacted soils
  • On-site screening of soils
  • Off-site disposal of 8,000 tons of RCRA hazardous soil
  • Construction of low permeability clay cap
  • Installation of new electrical utility duct bank
  • Site restoration with hydroseeding and asphalt paving

Forgen completed remedial construction activities at the Crane Test Area on the former Mare Island Naval Base in the summer of 2010. The project involved remediation of a 4 acre site known as the crane test area on at the former Mare Island Naval Station in Vallejo, CA. The scope of work included clearing and grubbing, removal of site debris, construction of a lined stockpile/screening area, excavation, screening and off-site disposal of waste soil, removal and replacement of existing site utilities, backfilling with on-site and imported soil fill, placement of a clay cap, and site restoration.

The site was subdivided into three soil excavation areas identified as the Soil Gas Area, Existing Utility Corridor, and New Utility Corridor respectively. The Soil Gas Area was divided into 4 subareas requiring a total of approximately 11,000 cy of excavation. During excavation, each bucket of soil was checked for TPH using a Flame Ionization Detector (FID). A one acre stockpile area was constructed over a 60 mil HDPE liner to facilitate screening and temporary stockpiling of excavated soils and debris. All soil containing less than 50 ppm TPH was screened to remove debris and stockpiled for reuse as backfill in the soil excavation areas. All soil containing greater than 50 ppm TPH or gross debris contamination was stockpiled separately for waste characterization and off-site disposal.

The Existing Utility Corridor was excavated to remove an abandoned electrical duct bank, miscellaneous pipelines, and surrounding soils containing elevated levels of lead. This excavation area contained 10,000 cy of soil requiring off-site disposal as California hazardous waste, RCRA hazardous waste suitable for direct disposal, and RCRA hazardous waste requiring stabilization prior to disposal. The New Utility Corridor was excavated to create a clean corridor for future utility installation. All utility excavations have been backfilled with clean, imported soil fill material.

Following completion of the excavation activities, the site was graded and capped with a minimum 3 foot layer of imported low permeability clay fill. The cap was compacted to 95 percent with final maximum permeability of 1×10-5 cm/sec. Other work included the excavation of a new joint utility trench and installation of a new electrical duct bank. The new joint utility trench and electrical duct bank was approximately 600 feet long and ran along the outside perimeter of the site under an adjacent roadway. Site restoration work included re-paving the adjacent roadway surface and hydroseeding the clay cap.

The Dalles, Oregon

  • Excavation and disposal of 55,000 tons of PAH contaminated soil at a former aluminum smelter
  • Demolition and removal of 4,000 lf of railroad track
  • Recovery and salvage of recyclable metals
  • Placement and grading of 40,000 tons of clean fill
  • Diversion, excavation, and restoration of contaminated drainage ditch

This project involved the removal of PAH and heavy metals contaminated soil from a former aluminum smelter in order to achieve an Oregon Department of Environmental Quality (DEQ) No Further Action (NFA) decision for the site. Forgen excavated and loaded 55,000 tons of polycyclic aromatic hydrocarbon (PAH) contaminated soil for disposal at a local landfill. Excavation areas and depths varied across the site. After removal, Forgen back filled disturbed areas with 40,000 tons of clean fill and graded the site to ensure positive drainage.

Another aspect of the project was recovery and salvage of remaining recyclable metals from the site. This included demolition and removal of 4,000 lf of railroad track, hand sorting to recover aluminum and other non-ferrous metals from former metal processing areas, and sweeping areas with magnets to recover ferrous metals from the site. Remedial action on the site included excavation of a drainage ditch to remove potentially contaminated materials. This effort required diversion of water, wetland excavation, lining the ditch with 60-mil HDPE liner, and back fill with wetland approved soils.

Performed as an RCRA corrective action under the regulatory authority of Utah’s Department of Environmental Quality, the barrier wall was constructed around a series of evaporation ponds to prevent process residuals and waste byproducts stored in the ponds from migrating off-site. Since the project was situated in the former dry lake bed of the Great Salt Lake, due to soft underlying soils and groundwater at or near the existing grade, a five-foot working platform had to be constructed in order to provide a stable working surface for barrier wall construction. Working platform construction consisted of placing 1.5 ft of material, produced at the on-site quarry, and stabilizing the lower 3.5 ft of subgrade with In Situ soil stabilization.

The soil stabilization effort required stabilizing 30 percent of the lower 3.5 feet of the working pad to meet the seismic requirements of the design and help strengthen the subgrade below the upper 1.5 feet of the work pad. Chemical constituents in the existing soils and groundwater elevations, relative to the finish grade of the working pad, varied throughout the site. To meet the unconfined compressive strength requirements for In Situ stabilized soils, Forgen had to continually monitor the grout mix to account for variable subsurface soil conditions and the presence of destabilizing constituents such as sodium chloride, ammonium chloride, sodium hypochlorite, and raffinate.

Forgen successfully completed In Situ soil stabilization by making consistent and ongoing adjustments to the amount of grout added and water to cement ratio of the grout mix while monitoring preliminary unconfined compressive strength testing throughout the project. The In Situ soil stabilization was performed during the winter and required additional effort to prevent the grout from freezing in the batch plant, hoses, and mixing equipment. This was accomplished by working 24 hr per day and utilizing specialized heating units. Upon completion of the In Situ soil stabilization, the site was shut down for the remainder of the winter.

Construction of the composite HDPE/soil-sepiolite slurry wall commenced in May of 2013. In total, 11,000 lf of slurry wall was constructed around the ponds to a maximum depth of 38 feet. Construction progress was accelerated utilizing a two shift per day schedule and the wall was completed in less than one month. The performance specification for the slurry wall backfill permeability was 1 x 10-7 cm/sec. Actual permeability measured post installation was 5 x 10-8 cm/sec. A total of 275,000 sf of HDPE sheeting were installed in the center of the soil-sepiolite slurry wall using a custom-made mandrel to ensure the structural integrity of each panel. A hydraulic sealant was applied to each joint of the HDPE sheet pile prior to installation in the trench. Forgen also utilized an in-house, custom designed and fabricated slurry batch plant for mixing the soil stabilization grout and slurry trench backfill.

Additional work included grading to improve site drainage, installation of various drainage pipelines and outfalls, construction of a perimeter site access road, and placement of rip-rap for dike slope armoring around the outer perimeter of the new dike construction.