Welsbach/General Gas Mantle Superfund Site

Significant Project Features

• Work performed under the direction of the U.S. Army Corps of Engineers, Philadelphia District
• Performing highly complex excavation operations involving radiologically contaminated materials from 47 residential and 16 commercial properties
• Excavation, characterization, segregation, and disposal of 327,000 tons of radiologically contaminated soil and 61,000 tons of other contaminated media
• Designing, constructing, operating, and maintaining Waste Water Treatment Plants that effectively treated 42M gallons of contact and groundwater
• Successfully coordinating Transportation & Disposal (T&D) operations to safely convey 388,000 tons of radiological waste and other material to a USACE-approved landfill facility
• Completing all contracts and task orders on schedule and within budget
• Achieving over 1.2M safe workhours without a lost-time incident

Project Gallery

History & Location Details

Welsbach/GGM in Gloucester City and Camden, New Jersey, used radioactive thorium to manufacture gas lamp mantles from the late 1800s to 1941. Thorium tailings were used to fill low-lying areas and provided sub-base and common fill for construction throughout the towns. Welsbach/GGM consists of multiple commercial and residential properties impacted with radiological contamination. Primary contaminants of concern at Welsbach included Ra226, Ra228, Th230, and Th232. Sevenson met radiation cleanup standard of 5 pCi/g above background on all properties in the scope and restored sites to pre-existing conditions.

Project Description

For each of the following contracts and respective task orders, Sevenson performed all remedial action and construction operations, using primarily company-owned equipment, as the self-performing prime contractor. Over the lifespan of the company’s involvement at the Welsbach Superfund Site, spanning over 12 years.

W912DQ-04-D-0023 – TASK ORDER 0002

This $45.3M CPFF task order, Sevenson’s scope of work included excavating, characterizing, segregating, and shipping approximately 103,000 tons of radiologically contaminated soil and material, from active residential and community properties, to an off-site disposal facility. Over the course of this task order, Sevenson treated 8M gallons of contact and groundwater; achieved cleanup objectives for all impacted properties; and completed 278,000 workhours without a lost-time incident. Major properties remediated under this task order included, but were not limited to:

• RESIDENTIAL PROPERTIES: Sevenson excavated radiologically contaminated soils from 23 residential properties. Work included relocation of residents and belongings; pre-work structure assessments (photographs and videos); demolition of contaminated structures; precision excavation of contaminated soil (primary and secondary excavation); MARSSIM surveys; reconstruction and restoration of affected work areas. Unique aspects of residential remediation included underpinning and temporary supports put in place as part of remediating interior radiological contamination. In several cases, temporary support systems were installed to allow partial removal of foundation walls and basement floors to access and remove contaminated soils.
• COMMUNITY PROPERTIES – SWIM CLUB:Sevenson demolished a series of tennis courts on the Swim Club property, a major community recreation facility impacted by contamination. During removal, the SSHO performed continuous air monitoring for dust, LEL, VOCs, CO, and H2S, and all asphalt materials were surveyed for radiological contamination. During demolition, Sevenson encountered and worked carefully in proximity to fragile utility infrastructure. A water service line, traversing the intersection of Collings Avenue and Essex Street to the Swim Club’s northern boundary, was bypassed to conduct remedial activities.

W(12DQ-04-D-0023 – TASK ORDER CF02

Under this $66.2M CPFF contract, Sevenson excavated contaminated soils and debris from residential properties within an active neighborhood. Major scope of work operations included performing excavations of up to 15 ft. below ground surface (BGS) of 124,000 tons of radiologically contaminated soil and 18,000 tons of other rad-impacted material; achieving cleanup targets for all contaminated properties; treating 16M gallons of impacted contact/groundwater; and, completing approximately 464,000 safe workhours without a lost-time incident. Sevenson’s scope of work addressed contamination at some of the following sites:

• RESIDENTIAL PROPERTIES: Sevenson excavated radiologically contaminated soil and debris from 17 residential properties. Field crews implemented a range of effective excavation support techniques to protect the structural integrity of property foundations and utility infrastructure. These techniques and tools included utilizing steel sheet pile retaining walls, shoring, trench boxes, and benched excavation for deep excavation along active roadways and adjacent to buildings; concrete underpinning for foundation walls and joist supports to remove and replace foundations, as necessary, during residential remediation; vibration monitoring on homes adjacent to sheet pile wall installation; and, groundwater controls to eliminate the potential of undermining structures.
• COMMERCIAL PROPERTY & PUBLIC UTILITIES – GGM/4^TH ST.: This site required remediation of soils underlying the footprint of the original General Gas Mantle Facility (GGM), as well as excavation of contaminated soils formerly used to backfill adjacent properties and underlying 4th Street in Camden, New Jersey. The remedial approach was complex, both due to existing buried utilities infrastructure; the depth of the excavations (up to 15 ft. below grade); and the local groundwater conditions. Successful completion of this work relied on a variety of utility location technologies; an engineered H-Pile support rack to support a high-pressured Transco Gas Main traversing 4th Street; a well point dewatering system to adequately dewater an excavation adjacent to a brick sewer, located 15 ft. below grade, which also involved a sanitary sewer bypass; and, multiple on-site frac tanks and an on-site water treatment plant to adequately manage, treat, and discharge water. The most challenging aspect of work at this site was implementing an H-Pile pipe support structure which supported the 8-inch, high-pressure Transco Gas Main, a utility serving a large number of residential and commercial properties. The challenge was primarily due to the safety risks that needed to be managed and mitigated to complete the work. Daily oversight by representatives was provided through Sevenson’s health and safety manager, who also coordinated this work with local emergency response officials. Removal of soil underlying the Transco Gas line was safely and successfully executed without incident.
• RESIDENTIAL ROADWAYS – TEMPLE AVE: Sevenson excavated up to 14,800 CY of radiologically contaminated soils from this site in Gloucester City, New Jersey (owned by the City), which would eventually become the location of an on-site WWTP. Remediation involved excavation within tidal areas; installation of 5-ft.-diameter water barrier (Geotube) in conjunction with berms and cut-off trenches; dewatering utilizing sumps and pumps; and, designing, constructing, operating, and maintaining a 100-GPM WWTP.

W912DQ-10-D-3006 – TASK ORDER CF02

Major remedial action operations executed under this $74.5M CPFF contract included excavation, up to 17 ft. BGS, of >100,000 tons of radiologically contaminated soil and 43,000 tons of other rad-impacted materials from residential and commercial properties; segregating and transporting waste offsite by rail for disposal; and, completing over 458,000 safe workhours without a lost-time incident. Major contaminated properties addressed under this task order included, but were not limited to:

• RESIDENTIAL PROPERTIES: Sevenson excavated radiologically contaminated soils and debris from 7 residential properties. To protect the structural integrity of private homes, Sevenson implemented excavation techniques to ensure operations did not adversely impact foundations and walls, which included installing concrete underpinning for foundation walls and joist supports to remove and replace foundations, as necessary, during residential remediation; vibration monitoring on homes adjacent to sheet pile wall installation; and, groundwater controls to eliminate undermining structures.
• COMMUNITY PROPERTIES & UTILITIES – BALL FIELDS SOUTH AND 4^TH & JEFFERSON AVE:Sevenson excavated 50,000 CY of radiologically contaminated soils, with excavation depths of up to 15 ft., from the Ball Fields South Site, an active community facility. Excavation support systems included sheet pile walls, slide rails, and trench boxes. The eastern site boundary abutted the Newton Creek, which strongly influenced the local groundwater conditions at the Ball Fields South Site. Dewatering was accomplished using a combination of pumps, channels/gravity outlets, and sump pits. Water was pumped to on-site frac tanks and then through a force water main to an on-site treatment facility. Site restoration included backfilling the site with clean fill, followed by complete restoration of a ballfield complex with a new concession stand and bathroom/storage building.During the original remediation at the General Gas Mantle (GGM) site, Sevenson observed that the secondary excavation would extend into the intersection of 4th Street and Jefferson Avenue. This intersection is underlain by a dense infrastructure of buried utilities, including cast-iron gas lines/mains, cast-iron water lines/mains, and old brick sewer lines. For this reason, remediation of the intersection was postponed until the complexity of the site could be understood and adequately evaluated. Sevenson ultimately completed the remediation by installing a strategically designed soldier pile and lagging excavation support system, and by manually digging to remove soil. Through close coordination with the terminal, well-planned safety protocols, and efficient coordination with the City of Camden Officials and County Police, Sevenson executed remediation without disrupting local traffic.
• COMMERCIAL PROPERTY – ARMSTRONG BUILDING & COURTYARD: Sevenson decontaminated the active, three-story 200,000-SF Armstrong Building, one of the largest food terminals in the northeast. Scope of work included removing 70,000 SF of radiologically contaminated concrete, and decontaminating approximately 60,000 SF of concrete floor slabs and 10,000 SF of brick surfaces throughout 12 rooms of the building. Operations required Sevenson to implement higher PPE protocols, which necessitated on-site personnel to wear respiratory protection in all areas of the buildings until floors were vacuumed.