DuPont Chambers Works
FUSRAP Site

Significant Project Features

• Excavation of over 37,000 CY of radiologically and chemically contaminated soil to depths up to 16 ft bgs
• Operations on a 130-year-old active chemical manufacturing facility under CISA security controls
• Contaminates include uranium, thorium, radium, chlorinated and fluorinated compounds (PFAS/PFOAs), dioxan/furans, BTEX, TEL, naphthalene and assorted aromatic hydrocarbons, and a range of herbicides and pesticides
• Installation of 1444 LF of steel sheeting to depths of 50-ft BGS for excavation support as well as to control ground water from entering the excavation areas
• Retrofit, operate, and maintain the existing on-site 80 GPM WWTP. To date over 12.1M gallons of water have been treated
• Operate and maintain an on-site radiological laboratory with over 13,500 samples processed and analyzed to date
• Characterized, packaged, and shipped >420 gondola rail cars of excavated soils for off-site treatment and disposal; treatment methods include pozzolanic stabilization, chemical oxidation, and thermal
• Sevenson has worked >199,000 hours and 930 consecutive days without loss-time

Project Gallery

History & Location Details

From 1942 to 1947, E.I. du Pont de Nemours and Company (DuPont) contracted with the Manhattan Engineer District, and later the Atomic Energy Commission, to produce, refine and process uranium. Operations resulted in residual radioactive contamination in surface and subsurface soil at portions of the Site. COCs include U-234; U-235; U-238; Th-230; Ra-226 (more than 10,000 pCi/g); tetraethyl lead; BTEX; VOCs; and other heavy metals (cadmium and arsenic).

Project Description

USACE 2021 Project of the Year

In July 2021, the DuPont Chambers Works FUSRAP site was named the United States Army Corps Project Delivery Team of the Year Award for Excellence. “The DuPont Chambers Works FUSRAP Project … is truly a testament to the outstanding support and collaborative efforts of Sevenson Environmental Services,” Ramon Brigantti, LTC, Commanding Officer of the USACE Philadelphia District said. “The co-operative work of the Sevenson team has resulted in great progress towards achieving the overall USACE project goals for remediating the radiological contamination at the site and creating new and better processes for the FUSRAP Program. This is especially evident with the rapid integration of on-site test results with the GIS capabilities, allowing for streamlined identification of new areas of contamination. These assets with the most important item, which is accomplishing the mission while maintaining an outstanding project safety record on a site with truly complex challenges. It is a great foundation for continued project success. Nearly 1000 days without a lost time accident at this site is a great success by itself.”

Scope of Work

Sevenson’s SOW includes planning, site preparation, WWTP O&M, onsite laboratory setup/operations, deep/supported excavation, waste management and offsite treatment/disposal, final status sampling and survey, site restoration and closeout.

Site Preparation

Sevenson developed all USACE-approved work plans, obtained all required permits and mobilized company-owned equipment to the site.

WWTP

Due to the high-water table, reliability of the existing 80-gpm WWTP to treat all water generated during remediation was critical, as the Delaware River is 500 ft. from the site. Before excavation, field crews identified and retrofitted deficiencies in the existing WWTP. This included replacement of broken piping, spent vessel media, and coatings on rusted vessels; installation of heat tracing/insulation to protect components during winter season operations; replacement of pumps, flow meters, and chemical metering pumps; and updating PLC logic and software. To date, the WWTP, staffed by an N-4-licensed plant operator, has treated over 11M gallons of water thus far.

Dewatering

Based on site boring data, Sevenson was prepared to encounter groundwater infiltration during excavation operations. Field crews jack-pumped groundwater using 3-in. electric pumps, conveying water to Frac tanks for treatment. A sump was installed at one end of the excavation to facilitate dewatering. When the excavation areas were dewatered, they were further separated into smaller units to improve water management. Continuous dewatering was key to supporting Surface Gamma Scans (SGS) and Final Status Survey activities. Without adequate dewatering, water would deflect the gamma rays associated with the COCs which could affect data. Additionally, Sevenson installed and operated a dual by-pass system of an onsite surface and subsurface drainage system.

Soil Excavation

Using a PC300 excavator, Sevenson has excavated >37,000 CY of radiologically and chemically contaminated soil to depths up to 16 ft bgs to achieve ROD cleanup goal of 65 pCi/g total uranium. MARSSIM remedial support and final status surveys were performed in completed excavation areas to verify waste profiles and to determine whether further excavation was required. Soils were directly loaded into haulers and transported to a transfer area where soil was characterized and further dewatered prior to conditioning and load out.  At the waste transfer area, soils were allowed to dewater by gravity and conditioned with Portland cement as a stabilization reagent, as needed. Dust and odor control measures were employed for stockpile management.

Sheet pile Installation

Sevenson installed a hydraulic containment area of 1,444 LF of NZ26 sheet piles, up to 51.5 ft below ground surface (bgs), with deep excavation cells requiring additional bracing systems. Sheet piling was necessary for excavation stability, to control inflow of groundwater into the excavation area, and to limit the excavation volumes. Without sheet piling, Sevenson would have had to slope/ bench the excavation, resulting in a much larger excavation area and subsequent waste volumes. Within the sheeted excavation areas, over 12K CY of contaminated soils have been excavated between 8-16 ft bgs. Sevenson performed vibration monitoring to ensure that sheet-driving operations did not disturb nearby structures and monitored sheet deflections daily. All open excavations that did not require sheeting were adequately sloped/benched to allow safe access and work inside the excavation areas.

Transportation & Disposal

After soil was adequately dewatered and stabilized, field crews used loaders and/or off-road haulers to transport material to the Waste Transfer Facility, where Sevenson crews loaded material into individual 110-ton gondola railcars. After each railcar reached holding capacity, waste loading personnel sealed the railcar liners to ensure safe transportation to the off-site Subtitle C disposal facilities based in Utah and Michigan. To date, Sevenson has loaded and shipped >480 rail cars for off-site disposal. More than 37K CY has been disposed of off-site – >27KCY was low-level rad and >10K CY was RCRA hazardous and low-level rad requiring treatment for heavy metal, VOCs, SVOCs, and herbicides/pesticides.

Radiological Laboratory

Sevenson setup, operates, and maintains a USACE approved on-site radiological laboratory to perform sample analyses and waste screening activities in support of remediation activities. Operations include sample control, processing, analysis, data management, and archiving. To date, Sevenson has collected and analyzed >13,500 gamma spectroscopy samples and >5,000 gas-flow proportional counter samples.

Health and Safety

Sevenson’s SSHO implements and enforces the site-specific, USACE-approved H&S Plan for all Sevenson on-site personnel as well as all subcontractor personnel.  Work is performed in Levels B, C, and modified D PPE. Sevenson also manages an air monitoring program which includes the calibration, implementation, and maintenance of upwind/downwind air monitors – samplers include: RADECO 809, RAE PGM-6228, Dustrak 8530, PPB RAE, PPM RAE, Ultra Multi RAE, and GilAir 5, to monitor airborne contaminants. Sevenson’s H&S staff also manage the exposure program for all on-site personnel. All personnel are monitored for potential exposure to U, Th, Ra, benzene, TEL, BTEX, coal tar, arsenic, and lead. To date, Sevenson has completed >199,000 safe workhours, including almost 1,000 consecutive days without a lost-time incident.