East 173rd Street Works Site

Bronx, New York

Date of Execution: November 2006

Significant Project Features:

• Excavation, transportation, and disposal of MGP-impacted soils, former MGP structures, and debris.

• On-site segregation of urban fill overburden from MGP-impacted soils and analysis to identify those soils that could be processed, screened, and used for backfilling and those requiring disposal off site.

• Installation of sheet piling for excavation support and groundwater exclusion.

• Installation of deep dewatering wells to prevent groundwater intrusion into excavation.

• Design, installation, operation, and maintenance of a temporary wastewater treatment system sized at 200 gpm to treat water encountered during remediation activities.

• Construction of an environmental soil cover cap system.

History and Location of Project:

The East 173rd Street Works Site is an approximately 3-acre former manufactured gas plant (MGP) site. Situated within Starlight Park, a municipal park currently owned by the City of New York, the East 173rd Street Works Site was once owned and operated by the Northern Union Gas Company, a predecessor to Consolidated Edison (Con Ed). The plant operated continuously from at least 1893 through 1912. Records suggest that between 1912 and 1923, the site was used primarily for gas storage and as a standby plant. Sometime prior to 1943, the three gas holders and some associated structures were razed. Other remaining structures were demolished during the 1940s. Con Ed used the site as a storage facility and vehicle garage from the time it purchased the site in 1936 until it was sold to the City of New York in 1945. All remaining buildings were demolished in the late 1950s, although foundations and subsurface MGP structural remnants remained. Starlight Park was reportedly constructed on and around the site by the City of New York in the late 1950s, at approximately the same time that the Bronx River channel was realigned approximately 300 feet south of its original channel and the Sheridan Expressway was built. Fill was placed on top of the MGP-era fill to raise the ground surface for construction of Starlight Park.

A Focused Remedial Investigation (FRI) and a Supplemental Remedial Investigation (SRI) were conducted to characterize the former MGP at the East 173rd Street Works Site. The FRI included investigations within Starlight Park and adjacent areas of the Bronx River. Based on the results of this FRI, Con Edison and the New York State Department of Environmental Conservation (NYSDEC) agreed to administratively separate the site. The 3-acre former MGP site has been designated as Operable Unit 1 (OU-1) of the East 173rd Street Works Site, and the adjoining Bronx River, which is currently undergoing additional investigation activities to determine any MGP-related impacts from the East 173rd Street Works Site, has been designated as OU-2 of the site.

The central and eastern portions of the East 173rd Street Works Site are currently in use as a park, and the western portion of the site abuts the Sheridan Expressway. Since 2000, the New York State Department of Transportation (NYSDOT) has been conducting a rehabilitation project on the Sheridan Expressway that included using the site as a construction staging area and the installation of storm sewers through the park to the Bronx River. While excavating within the park, NYSDOT encountered potential MGP-impacted soils.

Description of Work:

Remedial action at the East 173rd Street Works Site began with site preparation work. Remediation was then conducted, followed by off-site disposal and site restoration. Sevenson’s work at the site included:

• Excavating and stockpiling urban fill for reuse as backfill material. Sevenson removed pre-existing urban fill material to a depth of approximately 5 feet BGS, to access the MGP-era contaminated soils. These overburden soils were stockpiled and processed to meet geotechnical properties required for reuse as backfill material after the removal of the underlying MGP-impacted soils. Soil staging areas were constructed outside the MGP excavation footprint to ensure no cross-contamination between the urban fill and the MGP-impacted soils. Approximately 19,000 tons of urban fill material was excavated and processed for reuse on site.

• Excavation Support System/Dewatering. Extensive perimeter sheet-piling walls, consisting of cantilevered, anchored-tieback, anchored-deadman, and internally braced, were installed for excavation support and perimeter groundwater exclusion. Deep-well dewatering wells were installed to lower groundwater below the lowest excavation depth. Potentially contaminated water was pumped to an on-site temporary water treatment plant that Sevenson designed, operated, and maintained. The plant processes include oil/water separation, sand filtration, carbon absorption, metals removal, and Ph adjustment at treatment rates of up to 200 gpm. Sevenson treated approximately 5 million gallons of water to meet state discharge requirements.

• Excavation of MGP-impacted soils and former MGP structures and piping. MGP-impacted soils and structures were excavated to depths ranging from 5 to 15 feet deeper than the urban fill overburden and stockpiled separately from the urban fill material. Visibly MGP-impacted site soils were stockpiled and sampled for waste classification before being sent for off-site treatment and disposal. Sevenson also performed in-situ sampling for waste classification to allow for direct loading of MGP-impacted site soils for off-site disposal. Approximately 45,000 tons of MGP-impacted site soil was excavated and transported off site for disposal and thermal treatment.

• Backfilling the remedial excavation. Sevenson backfilled and compacted the remedial excavation area with the previously processed and stockpiled urban fill overburden. Additional clean backfill was brought on site to restore the excavation area to final design grade and to construct a cover cap.

• Installation of a cover cap and final grading. Sevenson excavated beyond the perimeter of the original remedial excavation for the installation of a 3- to 6-foot-thick clean-fill cover layer. A demarcation barrier was placed between the clean-fill cover layer and the underlying fill material. Finally, the site was rough graded and hydroseeded to restore it for reuse as a future park.

Health and Safety Overview:

• Unique Characteristics: Personal protective equipment was required for employees on the East 173rd Street Works Site because of the presence of MGP-impacted site soils.

• Health and Safety Measures: Workers utilized Modified Level D protection during hazardous waste removal operations. Modified Level C protection was utilized during confined-space work.

• Health and Safety Staff: Paul J. Hitcho, PhD, CIH, was responsible for the development and oversight of the East 173rd Street Works Site health and safety plan. Sevenson’s on-site Health and Safety Officer was responsible for the day-to-day implementation and enforcement of the plan.

• How 40-Hour Training Was Implemented: Sevenson performs both 40-hour and 8-hour Occupational Safety and Health Administration (OSHA) training in house for all company employees

<- Back to: Project Listings