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

Design and Construction

The Sag Harbor Site project is now in the Design and Construction Phase.

Remedial Investigation Summary:

• Contaminants detected in soil and groundwater are consistent with those expected for a former MGP site (primarily the BTEX complex – Benzene, Toluene, Ethylbenzene and Xylene; PAH’s – polycyclic aromatic hydrocarbons).


• The contaminants associated with the site were observed to be migrating off-site in a north-northwesterly direction, under an adjacent public roadway and privately owned properties, in the direction of Sag Harbor Cove. However, sampling of sediments and surface water in the Cove did not show the presence of contaminants associated with the former MGP operations


• There are no data to suggest that the public is being exposed to the chemicals present in surface soil or groundwater either on the site or in the community, although the potential for exposure – in both current and potential uses – exists absent remedial measures. There are also no data to suggest that the contaminants are having an adverse impact on fish or the transient wildlife in the community.

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.

• Early in the project, 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 completed the demolition of the Hortonsphere and its related structures on the property, and the relocation of utilities in the areas where excavation or construction will take place.

Record of Decision:

The Record of Decision, issued by the NYSDEC in March 2006, describes the remedial goals and specific remedial requirements for the site to achieve those goals. For the Sag Harbor site the goals, and summarized in the NYSDEC’s Fact Sheet announcing the Record of Decision, are:
 

• to eliminate or reduce to the extent practicable exposures of persons at or around the site to PAHs and BTEX in soil, groundwater and soil gas vapors;


• environmental exposures of flora or fauna to PAHs and BTEX in soil, groundwater, soil gas vapors and sediment;


• the release of contaminants from soil into groundwater that may create exceedances of groundwater quality standards; and the release of contaminants from surface soil, subsurface soil, soil gas vapors, groundwater, and sediment into surface water, indoor air, ambient air, sediment, and soil gas vapors through storm water erosion, vaporization, wind borne dust, and groundwater discharge.

Further, the remediation goals for the site include attaining to the extent practicable:

• ambient groundwater quality standards and
• recommended soils cleanup values for surface soils

The remedial requirements for the Sag Harbor site, as listed in the NYSDEC Fact Sheet, are:

• Excavation of visibly tar-contaminated soil to approximately 10 feet below ground surface (bgs).
• Installation of passive tar collection wells to remove deeper tar that cannot be removed by excavation.
• Evaluation and, if necessary, installation of vapor mitigation systems under existing or new structures constructed on or adjacent to the site to control potential migration of contaminated soil gas into these structures.
• Covering all vegetated areas with clean soil and all non-vegetated areas with either concrete or a paving system.
• Development of a site management plan to address residual contamination and any use restrictions.
• Provide certification of the institutional and engineering controls

Remedial Action Work Plan:

Description of Work:

The remediation work will consist of excavation of contaminated soil in the top 10 to 15 feet of the site and on several surrounding properties.  Constructing and completing the remedy consists of several activities:

• Prior to excavation, a soil mix wall will be installed around the perimeter of the excavated area.  The purpose of the wall is to provide stability during the excavation and to assist in dewatering the hole.  A soil wall was chosen instead of sheet piling to reduce the impacts of noise and vibration on the community. The wall will extend approximately 1000 feet around the perimeter and be 10 to 15 feet wide. 
• Once the wall is installed, a temporary fabric structure (tent) will be erected on the site over the area being excavated.  This structure helps control the release of vapors and dust during the excavation activities.  The tent is operated under negative pressure, air from within the tent will be continually evacuated and treated using carbon filtration prior to release.  The tent will be moved from one area to another through the course of the excavation activities.  Between 15,000 and 20,000 cubic yards of material will be excavated from the site. Excavation and backfilling will generate between 2500 and 3000 trucking trips over a several month period, or 30-40 trucks per day. A trucking plan to minimize traffic impacts has been developed with the Village Police Department and no trucking will occur on weekends.
• During excavation activities a dewatering system will be used to lower the groundwater levels at the site, allowing more efficient and complete removal of impacted soils.  Water will be removed from the subsurface using a series of pumps and wellpoints.  The water will be treated to remove site related contaminants to meet state permit limits prior to discharge.  Estimates of the rates of pumping range from 750,000 to 1,000,000 gallons per day. The treated water will be discharged through a pipe to an area of Sag Harbor Cove specifically chosen because minimal impact to water salinity will occur there. The pipe will be located and clearly marked so as not to interfere with marine navigation.
• Soil will be excavated and stockpiled under the tent prior to loading into trucks for transport and disposal.  The truck beds used to transport the soils are lined with a plastic liner and the tops of the trucks covered to prevent leaks or spills in transit. 
• Soils excavated from the site will be sent offsite for thermal treatment at a permitted disposal facility.  There are several such facilities located in New Jersey, Pennsylvania and New York.  The specific facility used will be selected based on available capacity to accept the soil.
• The hole will be backfilled using certified clean soil from a local source.  Backfilling will occur as the excavation of other areas of the site goes forward. Following the completion of activities, the site will be returned to current grade and all of the equipment used during the remediation will be demobilized.

Other Key Elements:

• All work related to construction of the remedy will be undertaken between September 2008 and May 2009. No work will be conducted during the “summer season” to minimize disruption to community activities.
• Bridge Street will be closed at Long Island Avenue during the entire project. Portions of Long Island Avenue will be closed during the construction of the perimeter wall at the start of the project.  Portions of the Village Parking Lot behind the Post Office will be used to support the project. KeySpan is working with the Village to identify alternative parking capacity. Road closures will be coordinated with the Department of Public Works, identified with signs noting detours and advertised on local radio.
• A Community Air Monitoring Plan will be in place throughout the project as well as continued testing of the water influent and effluent from the dewatering system. The excavation will be continually monitored to ensure that all accessible source material is removed.