Significant Project Features
- Remediation of hexavalent chromium contaminated soil at a 25-acre commercial property
- Excavation, transportation and disposal of 7,000 CY of contaminated soils from two excavation areas ranging in depths of 0-ft. to 20-ft. BGS. Soils <20ppm chromium were reused onsite and soils >20 ppm chromium were removed from the site during T+D operations
- Installed 281 LF of permanent steel sheet piling to depths of 49-ft. to 64-ft. BGS to reinforce the wester hydraulic barrier wall and installed 128 LF to provide temporary excavation support during remedial activities to depths of 45-ft. BGS
- Designed, constructed, operated and maintained stormwater controls, dewatering system (depressurization wells) and 150 gpm temporary WWTP onsite; treated 1,100,000 gallons of wastewater (as of October 26, 2020)
- Sevenson utilized Calciment to dewater and stabilize 750 CY problematic soils
- Completed site rehabilitation activities and placed backfill material in all remediated areas
- Sevenson completed over 14,000 safe workhours without a lost time incident
History & Location Details
Study Area 6 (SA-6), located in Jersey City, New Jersey, encompasses a 25-acre commercial property. The site was used for commercial property. The site was used for commercial and industrial activities for much of the past 100 years. Historically, the area was contaminated by hexavalent chromium from Chromium Ore Processing Residue (COPR), which was stored and utilized as fill material. As part of proposed redevelopment of the site by New Jersey City University and in compliance with an Administrative Consent Order (ACO) from the PRP and the New Jersey Department of Environmental Protection (NJDEP), remedial action was implemented on the site.
Prior to site excavation activities, Sevenson obtained the approval of applicable pre-construction submittals, designs and permits. Site mobilization operations included the installation of temporary facilities; BMPs; local notifications; the installation of signs and barriers to control site access; and coordinating with Facility Operations and local maritime operations. Crews installed upland stormwater controls and staging pads, a decontamination pad, temporary WWTP and the associated conveyance piping. Sevenson constructed temporary access roadways to access remediation areas.
Sevenson excavated soils in the Open Space Area (OSA) to reduce surcharge loading on the existing bulkhead in areas west of the hydraulic barrier wall (HBW). Clean cover soils were excavated from the liner system and transported to the SA-7 staging area for future reuse. The liner was subsequently removed and disposed of as debris. Crews removed 800 CY of materials from depths ranging from O-ft. to 10-ft. BGS from designated areas in the OSA and staged the materials in SA-7 for reuse on-site during backfill operations.
Sevenson utilized a PC300 excavator to remove materials to desired depths in a phased orderly fashion. Crews removed 6,200 CY of materials from four areas in the Deferred Are (west to the HBW) from depths ranging from 0-ft. to 20-ft. Crews sloped or benched materials to create higher elevations towards the loadout area and lower elevations away from the loadout area to promote gravitational drainage of soils. Materials were excavated and handled based on chromium category. Excavated materials sampled to be <20 ppm chromium were segregated from materials >20ppm chromium and transported to the SA-7 staging area to be reused onsite during backfilling operations. Excavated materials sampled to be >20 ppm were subsequently transported to the material staging area and removed from site during T+D operations. Crews removed 2,000 CY of materials ranging <20 ppm chromium and 5,000 CY of materials ranging >20 ppm chromium.
Sevenson installed a temporary Wastewater Treatment Plant (WWTP) onsite to efficiently manage all water recovered from the dewatering system and excavate in dry conditions. Deep watering wells and necessary sumps were installed within each excavation area to accomplish dry conditions. Dewatering was completed utilizing the deep well system and/or sumps to maintain groundwater levels at a minimum of 2-ft. below excavations. Captured groundwater was pumped into two adjacent frac tanks with a capacity of 21,000-gal. each, and subsequently pumped to the WWTP. The dewatering system extracted up to 150 gpm, however, flowrates varied after the initial drawdown and upon reach equilibrium. Wells were installed at depths up to 20-ft. BGS and electric pumps were placed in each sump to transport groundwaters to the WWTP. The WWTP is designed to be operational for 24/7/365—however, for this project, the WWTP was run for 10 hours a day 5 days a week. Analytical testing was performed on effluent water prior to discharge to meet permit requirements.
Steel Sheet Piling
Prior to excavation operations, pre-trenched the existing western HBW and removed any debris and obstructions prior to the installation of permanent steel sheet piling. Crews placed 281 LF of low permeability sheet piling at depths randing from 49-ft. to 64-ft. BGS to reinforce the water side timber bulkhead and the HBW. To provide excavation support around deep excavation areas in the Deferred Area, crews installed 128 LF of temporary steel sheet piling at depths to 45-ft. BGS and created a coffer dam in the excavation areas.
Backfilling operations commenced upon the completion of excavations, survey and concurrence from the Engineer. Sevenson backfilled the individual excavation areas using materials <20 ppm chromium deemed suitable for reuse onsite, staged in SA-7 and pre-approved offsite borrow material trucked into the site. All offsite backfill materials were from a virgin source and certified clean by the supplier to the most stringent NJDEP Impact to Groundwater Soil Screening Level Soil Remediation Standards. Sevenson placed approximately 9,480 tons of trucked-in backfill in excavation areas. Backfill materials were placed in 12-inch loose lifts prior to compaction. Sevenson utilized low ground pressure equipment to compact the backfilled materials in accordance with compaction guidelines and provided oversight of compaction testing performed by a licensed NJDOT-approved geotechnical field technician. Crews placed class A non-woven geotextile with 1-ft. overlapped edges on remediated backfilled areas and placed lightweight fill on top of the geotextile fabric. Subsequently, crews placed common fill on top of the lightweight fill to bring the area to 6-in. within grade. A 6-inch topsoil layer was placed on top to bring the remediated areas to grade. Newly remediated areas were blocked off from traffic to minimize disturbance and promote vegetation restoration.
Crews removed the temporary sheet piling used in deep excavation areas prior to backfilling operations. Sevenson decontaminated all materials and equipment onsite prior to site demobilization.