Vanadium Site Operable Unit #3 Remediation

Significant Project Features

• Utilized a unique fixed price no change order contract
• Excavation, loading, transportation and consolidation of 152,350 CY of slag contaminated soil beneath and around high voltage transmission lines and towers
• Excavation, loading, transportation and consolidation of 11,250 CY of sediment from existing wetland areas and the creation of three habitat islands
• Installation of 134,150 CY of common borrow in two 9-inch lifts
• Installation of 467,250 SF geosynthetic clay liner (GCL) in various swales on low lying areas
• Installation of 49,700 CY of topsoil placed in one 6-inch lift
• Installation of 215,000 SF of permanent access roads, pull pads and cranes pads
• Installation of 4,700 lf of permanent chain link fence with barb wire and two 20 feet wide access gates

Project Gallery

History & Location Details

Project Description

After mobilization to the site, a survey was performed to document the existing conditions and establish control points for site layout. Access roads and work zones were established, and erosion and sediment controls measures were installed.

Once the required erosion and sediment controls were in place and the perimeter air monitoring units were set up, Sevenson began to strip and stockpile existing topsoil within the site contract limits using bulldozers and excavators. In the majority of the areas that required excavation and cover, Sevenson was require to utilize low ground clearance equipment in order to stay within the specified guidelines of the high voltage proximity act, due to the limited overhead clearance from the high voltage transmission lines. This mainly consisted of large bulldozers pushing topsoil and slag from beneath the confines of the overhead transmission lines where an excavator could load off-road haulers for transportation to specified areas for consolidation.

Sevenson excavated material from two wetland areas and created three habitat islands immediately south of OU1. The area was difficult to access from within the contract limits. In an effort to reduce the disturbance to existing wetlands, Sevenson established access agreements with neighboring property owners which allowed access to perform the wetland work from the northern and southern properties.

As the slag was excavated to the design grades, Sevenson obtained survey verification shots and initiated the placement of common borrow that was both salvaged from an onsite source and imported from an off-site source. The common borrow was placed in two 9-inch lifts and each lift was compacted to a minimum 90% standard proctor verified by a third party compaction technician using a nuclear density gauge.

As drainage swales were excavated and low-lying areas were created, a geosynthetic clay liner (GCL) was installed over a 6-inch bedding layer material. GCL collars were heat seamed around transmission tower bases to create a seal. Drainage geocomposite was placed above the GCL beneath the soil cover on the upland permanent access road.

Site restoration included the installation of a 6-inch topsoil cover placed over the 18-inches of common borrow as well as a 6-foot chain link fence and barb wire properly grounding in accordance with National Grid’s transmission standards.