Manufactured gas plant sites: 18th century technology with modern impact
Manufactured gas plants (MGPs) are rooted in late 18th century England where it was found that baking coal produced a gas that could be used for illumination. The technology eventually spread to the U.S. where the first MGP began operating in Baltimore, Maryland in 1816.
MGPs were often referred to as “gasworks” or “town gas.” From each MGP a network of pipes carried manufactured gas to homes and businesses where it was used for lighting, heating and cooking – just as natural gas is used today. Most MGPs in NYSEG’s service area were constructed in the last half of the 1800s and many operated well into the first half of the 1900s.
MGPs became obsolete with the widespread availability of natural gas. Natural gas was more efficient than manufactured gas, it burned cleaner and it was cheaper to “harvest” than manufactured gas was to produce.
Two categories of waste materials are often found at the sites of former MGPs:
- MGP tars are reddish-brown to black oily liquids that do not mix with or dissolve in water. Most MGP tars are more dense – or heavier – than water, but densities differ so that some MGP tars may sink while others float.
MGP tar can migrate away from the location where it was released; sometimes it is
carried along with the flow of groundwater, while other times it moves simply because
of gravity. Near the ground surface, MGP tar is often observed to be solidified to various
degrees due to exposure to natural elements such as wind, rain and sunlight.
- Purifier waste is a mixture of wood chips and iron fillings that was used to remove sulfur and other impurities before the manufactured gas was delivered to the end users.
The main classes of chemical byproducts in MGP tar are volatile organic compounds and semi-volatile organic compounds.
The group of volatile organic compounds of most concern at MGP sites are BTEX – benzene, toluene, ethyl-benzene and xylenes; the group of semi-volatile organic compounds of most concern are polycyclic aromatic hydrocarbons (PAHs). This latter group of chemicals is formed from the incomplete combustion of anything containing carbon, and while present at all MGP sites they are prominent in the environment from many non-MGP sources.