MGPs and Power Plants in Rhode Island
Before the introduction of electricity, communities used manufactured gas for lighting, which became known as gaslight. Gaslight was produced in manufactured gas plants (MGPs), or “gasworks.” The first MGP in the United States opened in the early-19th century. By the mid-19th century, gaslight had become so popular that many American communities larger than a village had their own gasworks. The industrialized states of the Northeast had the highest concentration of MGPs.
Power generation facilities operated in Rhode Island during roughly the same time period as MGPs. During this timeframe, the facilities used coal and petroleum-based products to generate electricity. Oftentimes, the facilities also used by-product tar from the MGP for electricity generation. Likely by-products of a coal-fired plant would include coke, ash, and clinker. These facilities required the storage of large amounts of coal and petroleum products. The primary source of potential environmental impacts associated with the former power plants is the storage, handling, transfer, and use of fuels (petroleum products).
Two major types of waste materials are present at many MGP sites: coal tars and purifier waste. Coal tars are reddish brown, oily liquids which do not readily dissolve in water. Materials like these are commonly referred to as a non-aqueous phase liquid, or NAPL. Although most tars are slightly denser than water, the difference in density is slight. Consequently, they can either float or sink when in contact with water. Near the ground surface, some of the tars may weather and partially solidify. Elsewhere, the tars retain their original, oily fluid properties and may still be capable of moving slowly through the subsurface. Purifier waste is a mixture of wood chips and iron filings which was used to remove sulfur and other compounds from the manufactured gas before the gas was distributed to the public. Purifier waste which was no longer capable of removing the impurities was often disposed on site.
The main categories of contaminants associated with MGP operations are volatile organic compounds (VOCs) and semi-volatile organic compounds. The main VOC of concern in soil and groundwater is typically benzene. Specific semi-volatile organic compounds of concern in soil and groundwater are polycyclic aromatic hydrocarbons, referred to as PAHs. This class of compounds includes naphthalene. These are the compounds that make up tars and asphalt. The main categories of contaminants associated with power generation facilities are VOCs.
MGPs were sometimes referred to as “gasworks” or “town gas.” From each plant, a network of underground pipes brought the gas into local homes and businesses where it was used for lighting, cooking, and heating – the same purposes that natural gas is used for today. Most Rhode Island MGPs ceased operating in the 1950’s and 1960’s. Approximately 20 former MGPs have been identified in the state.