Project Description

Following are the steps most often required by the New York State Department of Environmental Conservation in the investigation and remediation of a former MGP site.

Remedial Investigation/Feasibility Study
Interim Remedial Measures
Record of Decision (or Decision Document)
Design and Construction

Operable Unit 1 of the Clifton project, the former holder parcel, is now in the Operations, Maintenance & Monitoring phase, remedial construction having been completed. Operable Unit 2, the former Main Site, is in the construction phase. Interim Remedial Measures have been completed both in areas of the two Operable Units and in off-site areas.

On-site construction of
Operable Unit 1 remedy

Remedial Investigation Findings:

KeySpan Corporation (now National Grid) entered into an Order on Consent in 1998 with the New York State Department of Environmental Conservation (NYSDEC) to conduct a remedial investigation of the former Clifton manufactured gas plant (MGP) site. As required by the Order on Consent, a field investigation for the Remedial Investigation was completed in the 1999-2000. Based on the findings of the completed field program, additional sampling activities were recommended. Additionally, a qualitative human exposure assessment and an evaluation of environmental risks were performed.

The findings of the Final Remedial Investigation Report for OU-1 include:

  • The on-site OU-1 soils contain various chemical constituents related to the gas manufacturing processes that occurred previously at the Site.
  • The overall extent of tar, staining, sheen, odors, and chemical constituents detected in soils was located primarily within, beneath, and immediately adjacent to the former Relief Holder No. 2 on the 40 Willow Avenue Parcel.
  • The vertical extent of tar ceased prior to encountering the saprolite (weathered bedrock). The saprolite is located at a depth of approximately 125 feet below grade surface (bgs).
  • Tar-related observations were noted at discrete soil intervals south of the former holder area underneath properties along Lynhurst Avenue at depths greater than 24 feet bgs. These deeper tar-related observations are not associated with a potential exposure pathway based on samples of the shallow groundwater in this area that do not exhibit impacts from the deeper tar-related materials.
  • Benzene, toluene, ethylbenzene and xylene (BTEX) compounds were the principal volatile organic compounds (VOCs) detected at OU-1 and are the common VOCs associated with tar. Semi-volatile organic compounds (SVOCs) were also detected at the Site, with polyaromatic hydrocarbons (PAHs) being the common subset of SVOCs in tar. In general, elevated levels of total polyaromatic hydrocarbons (TPAHs), carcinogenic PAHs (CPAHs), and BTEX correlated with the occurrence of observable tar, odor and/or sheen.
  • Analytical data from surface soil samples obtained from the Lynhurst Avenue properties noted the presence of lead at elevated concentrations. These soils were addressed during the Interim Remedial Measure (IRM) conducted at the site (discussed below).
  • Free product migration at OU-1 is predominately vertical, although there is a horizontal flow component which results in the migration of free product towards the OU-1 boundaries.

Installation of concrete cap in OU-1

The findings of the Final Remedial Investigation Report for OU-2 include

  • The materials encountered within soils and groundwater at OU-2 are consistent with the chemical constituents expected at former MGP sites. These include BTEX and PAHs. Other site operations, including former petroleum storage, have also contributed to the contaminants encountered in on-site soils and groundwater.
  • Constituents of MGP wastes from OU-2 have not impacted potable water supplies in the area. Potable water is supplied by the New York City water system.
  • There is no indication that the constituents of MGP wastes detected on the site adversely impact fish and wildlife in the area.
  • There is no indication that persons working on or visiting the portions of OU-2 not situated at the 25 Willow Avenue parcel are being exposed to site-related contaminants associated with MGP wastes, although they have been detected at off-site locations.
  • A qualitative assessment of potentially complete exposure pathways indicates that workers and/or visitors to the building at 25 Willow Avenue may be exposed to indoor air vapors containing chemicals common to former MGP operations and former site uses, including automobile servicing by third party owners.

Interim Remedial Measure in OU-1 (Lead contaminated soils):

Interim Remedial Measure in OU-1 (Lead contaminated soils):
An Interim Remedial Measure was conducted in 2002 and into 2003 to remediate lead contaminated soils, mostly in the backyards of residential properties abutting KeySpan’s 40 Willow property. The IRM was designed to address the lead found in the soil, regardless of the source. The IRM consisted of the removal of soil from the backyards (at #67, 59, 55, 53 and 49 Lynhurst) down to a level at which lead levels are reduced to below the 400 parts per million (ppm.) level set by the United States Environmental Protection Agency (in the range of 1 – 3 feet), and removal of soil to similar depths at those locations on front yards (at #67 and #59) at which “hot spots” of lead concentrations were found. The removed soil was replaced with clean fill under standards established by the NYSDEC and re-grassed. KeySpan also repaired or replaced structures on some properties which had to be moved to ensure a complete remediation, or to ensure property owners would provide access. Completion of the IRM successfully eliminated direct contact exposure pathways and mitigated the risks presented by the impacted soils.

Interim Remedial Measure at 89 Willow Avenue (removal of purifier waste):

While preparing the property for redevelopment, the owner of 89 Willow Avenue noticed the presence of material associated with the former MGP operations. On investigation, this material was identified as purifier waste, wood chips impregnated with contaminants removed in purifying gas produced in the plant. National Grid conducted an Interim Remedial Measure in 2007 to remove the purifier wastes and surrounding soils and replace them with clean fill.

Remedial Action Plan for Operable Unit 1 (40 Willow Holder Site):

The major elements of the Remedial Action Plan for Operable Unit 1 selected by the New York State Department of Environmental Conservation included:

  • Construction of a containment barrier completely surrounding the former holder area to a depth of approximately 125 feet to be anchored in bedrock.
  • Construction of a low permeability cap across the entire surface of OU-1 and of a drain system to prevent run-off from the cap reaching neighboring properties.
  • Institutional controls including an environmental easement, limitations preventing using the holder area for residential purposes, a soil management plan and long-term monitoring.

The Remedial Action Plan for this Operable Unit has been completed. The OU is now in the Operations, Maintenance and Monitoring phase. The institutional controls have been implemented.   

Construction of Temporary Fabric Structure.JPG

Remedial Action Plan for Operable Unit 2:

The major elements of the Remedial Action Plan for Operable Unit 2 selected by the New York State Department of Environmental Conservation include:

  • demolition of the existing building
  • excavation of contaminated soils and removal (where feasible) of contaminated underground structures
  • installation of a 44 foot deep perimeter barrier wall to contain remaining contamination
  • replacement of contaminated soils and materials with clean backfill.

The construction activities are extensive, reflecting the depth of excavation required, the known complex of underground facilities and structures that may have to be removed, the proximity of nearby businesses and the nature and extent of contaminants in the soil and structures. There is the potential for impacts to the community during implementation (noise, odors, vibration, additional traffic and necessary re-routing of pedestrian walkways). National Grid and its consultants have developed and the NYSDEC has approved a construction plan for this aspect of the project that addresses these issues.

Mobilization of personnel and equipment to the parcel to begin the remediation began in February 2012. The project is expected to require approximately 15 months to complete. Information related to the construction plan can be found in the Key Documents/Major Reports section of this website.