Manufactured gas (also historically called “town gas”) is a form of natural gas produced from coal or oil. It can be used as a substitute for natural gas and is suitable for transportation in natural gas pipelines and consumption by natural gas consumers. Before natural gas was available by production from underground reservoirs, manufactured gas was delivered by the original natural gas utilities that developed in the mid-1800s through the early 1900s. As natural gas became available from pipelines during the 1940s and 1950s in the United States and during the late 1960s and 1970s in the United Kingdom and Australia, manufactured gas no longer was used. However, it is still used in a few countries around the world.
Manufactured gas was produced in manufactured gas plants (MGP), in most cases using coal as fuel. The coal was heated in a closed furnace resulting in release of useful fuels including hydrogen, methane, and ethylene. The process also produced a variety of byproducts, some of which were useful and marketable, such as coal tar and lampblack. But it also created waste byproducts that were buried on site during the 1800s and 1900s.
As natural gas became available via pipelines from gas production basins, most MGPs were closed down and the byproducts were left buried on site. In the 1980s, the United States Environmental Protection Agency (EPA) conducted research that identified more than 1,500 former manufactured gas plants around the country. Many of these still contain significant concentrations of toxic chemicals. Significant mitigation efforts by gas utilities and communities have been required to clean up these sites.