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Sag Harbor Former Manufactured Gas Plant Site

Record of Decision Issued:

The New York State Department of Environmental Conservation (NYSDEC) and the New York State Department of Health (NYSDOH) are pleased to announce the selection of a remedy for the Sag Harbor Former Manufactured Gas Plant Site. The Record of Decision (PDF) (52 Page, 907KB) was signed by NYSDEC on March 31, 2006.

Background:

From 1859 to 1930 the site was operated as a manufactured gas plant. The plant originally produced gas from coal or wood rosin and was switched to a water gas process in 1892. The by-products of gas production that either spilled, leaked, or were disposed on the site are responsible for the contamination.

Remedial Investigation:

From 2000 through 2004, field work was performed to define the nature and extent of the contamination at the Sag Harbor MGP site. This work included the collection of surface and subsurface soil, groundwater, soil vapor, and ambient air samples for analysis. The samples were taken from locations over the entire site as well as beyond the perimeter of the site. Off-site samples were located along Long Island Avenue, Bridge Street, and on the private properties adjacent to the site itself. Sediment, pore water, and surface water samples were also collected from Sag Harbor Cove.

The chemicals of concern at this site are residues of the former MGP process and include volatile organic compounds, semi-volatile organic compounds, and cyanide. The volatile organic compounds of concern are benzene, toluene, ethylbenzene, and xylene. Together they are known as BTEX. The semi-volatile organics of concern are polycyclic aromatic hydrocarbons (PAHs). BTEX and PAHs are the primary constituents of coal tar which was the main byproduct of gas production.

The principle waste material at this site is coal tar, a thick, black, oily liquid which was a byproduct of the gas production process. The coal tar typically appears as a Dense Non-aqueous Phase Liquid (DNAPL) which is a flowable product which does not readily mix with water and is denser than water. Coal tar is a subsurface soil contaminant and is a source of groundwater contamination.

Coal tar has been found underneath most of the site and extends about 60 feet to the north and about 20 feet to the south under the adjacent properties. Most of the tar is shallow, in the upper twelve feet. However, in the center of the site, there is a location where the tar was found as deep at 90 feet below grade. The groundwater is contaminated by contact with the coal tar and moves to the north, almost as far as Sag Harbor Cove.

The detailed results of the analytical work are in two Remedial Investigation Reports which are available at the document repositories listed below.

Health Exposure Assessment:

There are currently no ongoing exposures to contamination from this site. The site is fenced to restrict access, and a layer of stone at the surface further reduces the likelihood of direct contact with contaminated soil. Exposure to contaminated groundwater is not occurring, as there are no supply wells located in the contaminated area. The area surrounding the site is served by a public water supply, which is regularly tested to ensure that it meets state and federal drinking water standards for a number of contaminants, including those associated with the site. Indoor air samples from buildings surrounding the site have not shown evidence of site-related contamination. There is a potential for people to be exposed to soil, groundwater, and vapor contamination in the future; the selected remedy would minimize or eliminate these potential exposure pathways.

Feasibility Study (FS):

A Feasibility Study was performed. The report, titled "Feasibility Study Sag Harbor Former MGP Site," and dated September 2005, describes and compares the remedial alternatives.

Remedy:

Based on the evaluation of various alternatives, the Department has decided to use a combination of remedial techniques to address the contaminated materials found at this site. The remedy includes:

  • Excavation of visibly tar-contaminated soil to roughly ten feet below ground surface (bgs).
  • Installation of passive tar collection wells to remove deeper tar which can not be reached by excavation.
  • Evaluation and, if necessary, installation of vapor mitigation systems under existing or new structures constructed on and 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 landuse restrictions.
  • Periodic certification of the institutional and engineering controls.

A more detailed description of the site history, existing conditions, and the remedy can be found in the Record of Decision (ROD).


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