The Site Investigation Report (SIR) includes both the January 2011 site Investigation Data Report and the July 2011 Remedial Alternative Evaluation Report. The key findings of the Site Investigation Data Report are as follows. The complete report can be found in the Documents tab of this website.
- Soils and groundwater at the site contain various chemical constituents related to the MGP and electric generation processes that occurred previously at the site.
- The main contaminants at the site are DNAPL, LNAPL, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), certain metals, and inorganics. DNAPL is generally associated with coal tar, a dark viscous material that is denser than water and persistent in the environment. LNAPL is generally associated with petroleum hydrocarbons (fuel oil), a lighter phase material which is typically less dense than water. Benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds were the principal volatile organic compounds (VOCs) detected at the Site and are the common VOCs associated with coal tar and fuel oil. These constituents tend to dissolve more in water and are found in most petroleum-based products (e.g., gasoline, diesel fuel, solvents, and adhesives). Semi-volatile organic compounds (SVOCs) were also detected at the site, with PAHs being the common subset of SVOCs in coal tar. These semi-volatile compounds are less soluble in water when compared to the VOCs. In general, elevated levels of total petroleum hydrocarbons (TPH), PAHs, and BTEX correlated with the occurrence of observable coal tar, petroleum hydrocarbons, and/or sheen. The primary inorganic compounds detected on the site included arsenic, lead, and cyanide. These compounds are typically associated with former MGP sites.
- MGP residuals and petroleum hydrocarbon related impacts were detected in both surface and subsurface soils at the site. In general, subsurface soils located at/or below the water table exhibited more significant impact when compared to surface soils. Surface soils (within approximately 2 feet of the ground surface) at the site exhibit elevated concentrations of PAHs and certain inorganics (most notably arsenic and lead). The vertical extent of soil impacts generally ceased prior to encountering the glacial till, which is located at a depth below the ground surface of approximately 15 to 50 feet. The exception was the area along the river adjacent to the former MGP structures and the area east of former gas holders where impacts in these areas were noted within the till layer/top of bedrock. Groundwater impacts were generally observed in the eastern portion of the site along the Seekonk River in areas where LNAPL and/or DNAPL impacts were also noted. Observations of NAPL in groundwater monitoring wells have been limited to approximately 20 of 66 locations. Typical of former MGP and power plant sites, the most prevalent compounds detected in groundwater were benzene and naphthalene.
- The site investigation developed sufficient information to identify and delineate impacts to surface soils, subsurface soils, groundwater, and sediments. Elevated contaminant concentrations appear to be coincident with areas where historical features, operations, and evidence of filling were located and also coincident with the depths of staining and other observations of impacts.
- The site is secured with a perimeter fence and locked gates which significantly limit potential exposures to people near the site. The planned site remediation will be designed to mitigate potential exposure pathways and risks to human health and the environment.
