Between 2006 and 2011, National Grid conducted a Phase II study of the types of compounds present at the Site and their extent. As part of this study, National Grid collected more than 140 soil samples and 175 groundwater samples from borings and wells drilled in the upland areas, and nearly 300 sediment samples from the harbor. National Grid took other types of samples, too, such as samples of harbor water; air contained in the soil (“soil gas”) beneath commercial buildings; and porewater (water in the pore spaces of the sediments beneath the mudline in the harbor). National Grid presented the results to the Massachusetts Department of Environmental Protection in its July 2011 Phase II Report. The key findings:
The Site extends over multiple properties and across portions of the navigation channel in the harbor. National Grid found chemical compounds related to operations of the former Manufactured Gas Plant (MGP) in the soil and groundwater (beneath the surface) at these properties, and in the sediments and porewater in the harbor.
The main compounds at the Site are dense non-aqueous phase liquid (DNAPL), heavy petroleum hydrocarbons, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and inorganic compounds. Each of these compounds is described further below:
- DNAPL is a term for coal tar that is not dissolved in water. It is a dark viscous material that is denser than water, which causes it to sink to the bottom of a column of water. It is present 40 to 60 feet below the ground surface in the upland area of the Site and within harbor sediments near the former MGP.
- Heavy petroleum hydrocarbons from coal tar, specifically compounds called C11 to C22 aromatic hydrocarbons, were detected at elevated concentrations in the soil at the former MGP. These compounds do not dissolve easily in water, and do not migrate far from their original location.
- Benzene and naphthalene were the principal VOCs detected at the Site. Benzene is found in most petroleum-based products (e.g., gasoline, diesel fuel, solvents, and adhesives), whereas naphthalene is typically associated with coal tar or other products like mothballs. These compounds tend to dissolve in water, and National Grid detected them in groundwater samples from the upland properties and porewater samples from the harbor.
- PAHs are a type of semi-volatile organic compounds. They are formed by the burning of organic matter like coal and wood, and are found in asphalts and tars. They are less soluble in water than the VOCs, and National Grid detected them in soil samples from the upland properties and sediment samples from the harbor.
- The primary inorganic compounds detected at the Site are metals, which are prevalent throughout this area of Gloucester but especially on those properties where boat maintenance and painting occurred. Other inorganic compounds included relatively low levels of cyanide, a by-product of MGP purifying operations, that is not harmful at the levels detected.