About Manufactured Gas Plants (MGPs)

Yesterday’s Energy Source

Supplies of natural gas, which many of us take for granted today, were not always available in Illinois. In fact, beginning in the mid-1800’s, it was necessary to manufacture gas from coal or oil using processes developed in England. Manufactured gas plants (MGPs) provided gas for cooking, heating, lighting and, later, industrial applications. Cleaner and safer than wood or oil, manufactured gas dramatically improved people’s lives. Eventually, as demand for manufactured gas grew, an estimated several thousand plants operated throughout the United States. Towns that had an MGP were considered to be progressive and forward thinking.

Typical Manufactured Gas Plant

Manufactured gas was produced when some combination of coal, coke and/or oil was heated to generate gas. The gas was cleaned of impurities and stored on site before it was delivered to the surrounding community.

In the 1920s and 1930s, the construction of natural gas pipelines across the country made cheaper and more efficient natural gas available. Manufactured gas ceased to be a major energy source in Illinois during the 1930s and the manufactured gas plants began to shut down.

Today’s Environmental Challenge

As with most manufacturing processes, gas production created byproducts such as ashes, cinders and tar. Tar was typically stored in underground structures at plant sites and sold for use in road paving, roofing materials and other commercial products. These byproducts were commonly left in place when the plants closed. The environmental effects of tar and other plant residuals were not a concern at the time. Today, we know more about tar and other residuals and how they can affect the environment and are taking steps to make sure that byproducts from past operations are managed in accordance with today’s standards.

MGP-related residuals can be found in both the soil and groundwater at MGP sites. They can contain polycyclic aromatic hydrocarbons (PAHs), such as naphthalene; volatile organic compounds (VOCs), such as benzene and toluene; and metals and other inorganic materials. PAHs are commonly found in the environment, because they form as a result of combustion, such as from vehicle exhaust. VOCs are often found in fuels and solvents. Some of the residuals can have odors similar to roofing tar or mothballs. Those odors occur at levels well below those that would present a health risk.

What Are We Doing About These Sites?

Nicor Gas and ComEd are proactively addressing environmental issues related to MGP sites to bring these sites in line with current environmental standards. The Utilities are in the process of investigating and remediating them, including the former Aurora MGP. The project is being conducted in cooperation with, and with oversight by, the Illinois EPA through its voluntary Site Remediation Program (SRP). The SRP establishes investigation and cleanup guidelines for sites based on risk-based, site-specific cleanup objectives designed to be protective of people and the environment. Through the SRP, the Illinois EPA reviews and approves the cleanup work.

Successful participation in the SRP results in regulatory closure at the MGP site, primarily through the issuance of a No Further Remediation Letter by the Illinois EPA. The letter is filed with the county office that maintains property transfer records so that future landowners and others are aware that the site was previously cleaned up.