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/Remedial Action Plan
Interim Remedial Measures
Record of Decision
Design and Construction

The Glen Cove project is now in the phase of developing remedial alternatives, as is done in a Remedial Action Plan.

Final Remedial Investigation (RI) Summary:

The following presents the Key Findings obtained during the Remedial Investigations at the site regarding existing surface and subsurface conditions, the nature and extent of the MGP related residuals and residual constituents, and potential exposure pathways for human and environment receptors:

  1. The Final RI results define the existing site conditions, nature and extent of chemical constituents at the site and in the surrounding environmental media and potential human health and environmental risk, sufficient to fulfill the remedial investigation requirements of DER-10 and in the determination of a significant threat under 6 NYCRR Part 375.
  2. The shallow geology beneath the site consists of heterogeneous fill soil underlain by glacial outwash deposits. The fill soils extend from the surface to depths of 10 feet beneath the site proper, and to depths of 30 feet under the elevated area north of the site. The fill soils consist of sand and gravel with varying percentages of silt, clay and coal fragments. The underlying glacial outwash extends to the greatest depth investigated (82 feet). The outwash soils consist of highly permeable sands and gravelly sands interbedded with lower permeability silty sands. Groundwater occurring under water table conditions was generally first encountered near the base of the fill soils at a depth of 8 feet below the site surface and is part of the regional Upper Glacial Aquifer. The groundwater flows generally from east to west across the site toward Glen Cove Creek.
  3. MGP-related residuals have been visually observed in the subsurface soils in the form of solid tar, dense non-aqueous phase liquid (DNAPL), blebs (individual droplets), or as coatings, sheens; and stains on the soil particles which are residuals expectable of a former MGP. MGP-related residuals contain chemical constituents of concern including benzene, toluene, ethylbenzene and xylenes (BTEX) and polycyclic aromatic hydrocarbons (PAHs) several of which are carcinogenic. DNAPL residual impacts occur over a relatively compact area beneath and just downgradient of the former MGP operations and extend just beyond the northern site limits. The DNAPL impacts generally begin at or just above the water table and decrease with depth to approximately 45 feet below the site. The absence of DNAPL impacts in the surface fill suggests the fill was placed after the removal of the former MGP.
  4. Measurable DNAPL occurred in only one site well, in the area of the former gas holder. No measurable DNAPL was observed in the other site monitoring wells or piezometers.
  5. The limited extent of DNAPL visual impacts is a key factor in understanding the distribution of the dissolved BTEX and PAH constituents in soils and groundwater. Elevated BTEX and PAH constituents generally coincide with or are downgradient of the MGP residuals and DNAPL observed in the subsurface soil. In groundwater the estimated extent of the dissolved phase contaminant plume (BTEX and PAH at 10 parts per billion (ppb)) occupies a relatively compact area and appears limited to the same areas/depths of soil exhibiting MGP-related DNAPL. The dissolved phase BTEX and PAH concentrations in groundwater decrease in both the horizontal and vertical direction from levels in the range of 1,000 parts per billion (ppb) beneath the former MGP operations area to negligible and non-detectable concentrations immediately downgradient of the former MGP operations, the site perimeter at Glen Cove Creek and just beyond the site limits to the north.
  6. As a result of the relative absence of MGP-related DNAPL visual impacts in soil above the water table, BTEX constituents are not constituents of concern in the upper 10 feet of site soil. Comparison of the background surface soil study results to PAHs detected onsite in surface soils suggest a potential contribution of PAH constituents from activities conducted on the former MGP site after or as part of placement of the surface fill soils. The background surface soil study indicated certain metals detected on-site are consistent with local conditions surrounding the site and are not likely attributable to the activities on the former MGP site.
  7. The RI and Qualitative Human Health Exposure Assessment (QHHEA) indicate that there are potential pathways through which individuals (receptors) on and near the site could be exposed to potentially hazardous materials related to former MGP activities. The existing institutional and engineering controls, including the existing gravel or other surface cover restrict direct contact with surface soils; the fencing and gating restrict public access; and continued employee awareness training of the site soil and groundwater conditions mitigate these pathways and should be maintained. The greatest risk of potential exposure is associated with subsurface construction activities in near surface soils and groundwater, if undertaken without appropriate precautions. Another potential pathway is through public supply/domestic wells. A domestic and/or an expanded public supply well search will be conducted upon guidance from the NYSDEC. However, domestic or public supply wells located within the potential search radius are not anticipated to be impacted, due to their significant distance (greater than ½ mile) from the former Glen Cove MGP site and the horizontal and vertical limits of the estimated extent of the dissolved phase plume. Overall, there are no significant imminent threats to human health that warrant an interim remedial action.
  8. Fish and wildlife potential impacted media were identified as Glen Cove Creek surface water and sediments since groundwater flowing beneath the site discharges to the creek. However, no surface water impacts were observed in samples from Glen Cove Creek. Supplemental sediment samples collected from Glen Cove Creek, recommended by the initial Fish and Wildlife Resources Impact Analysis (FWRIA), indicate that concentrations of PAHs, are representative of generally background PAH sources and are not related to the site. Overall, there are minimal potential risks of wildlife exposure, given the industrial use of the property and highly transient nature of the wildlife.

Interim Remedial Measures:

Prior to its acquisition by National Grid, KeySpan undertook an Interim Remedial Measure (IRM) to minimize any current impact of the environmental conditions related to the historic use of the site. In 1999, KeySpan undertook a “cut-and-plug,” capping underground pipes that could act as conduits for the migration of contaminated groundwater or source material. In addition to the IRM, National Grid has worked with LIPA, the owner of the site, to ensure that the investigation and remedial activities do not disrupt the operation of the electric system substation in any way.

Phase I Remedial Action Plan and Remedial Construction

Because of the importance of maintaining the LIPA electric system on the site in full operational condition, and reflecting LIPA’s need to expand the substation on the 2011 – 2012 timeframe, the NYSDEC approved remediation of the Site in phases.

The first remedial action was the excavation and removal of contaminated soils in several areas of the site. Before starting the excavation, National Grid removed trees located on the hillsides north and east of the site. This was a necessary precaution to protect workers and to protect site infrastructure. Related to the excavation, National Grid then stabilized the hillside and planted fast-growing trees to replace the ones being removed.

Contaminated soil was excavated from varying depths up to 15 feet below the surface. Trucks followed a Department of Transportation and City of Glen Cove approved route to an authorized disposal facility in another state. The trucks were lined and had both a plastic cover and solid tarp cover to contain the removed soils and reduce odors and dust while in transit. Specialized foams, mists, and/or other technologies were used as necessary to minimize odors. Excavated soil was replaced with clean fill from NYSDEC approved sources. Photographs made during the project can be found in the weekly reports for 2011 in the archive section of the Key Documents tab on this website.

Plans and procedures approved by the NYSDEC and NYSDOH were put in place to assure minimal impact on the community during this work. A Community Air Monitoring Program was in place throughout invasive activities during the project. While a parking ban near the Site entrance was required during the excavation, the community was given advance notice and no significant problems were reported. The parking ban for the remediation project has been lifted since August 2011 when the excavation and soil removal was completed.

Phase 2 Remedial Action

Phase 2 of the Remedial Action Plan for the Glen Cove former MGP Site will include the installation of an oxygen injection system to accelerate the bioremediation of groundwater contaminants and the installation of recovery wells to collect and withdraw DNAPL from underground soils. Work plans for these activities are being developed and the installations should begin in 2012.