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Environmental Health: Cleaning Up Former Manufactured Gas Plants

In the 1800s, towns and cities across the United States made their own fuel for electricity. The fuel—produced at a manufactured gas plant (MGP)—was used to light homes, businesses, and streetlamps.

To manufacture the fuel, MGP workers heated coal and other ingredients in large brick ovens. This heating process produced a gas, which was filtered from the ovens and stored in tanks. The fuel provided electricity for the whole community.

During the 1950s, MGPs began to decline and a nationwide network of natural gas pipelines took their place. Natural gas was cheaper to use than MGP-produced fuel, and once it became widely available, many MGPs closed.

Although many were abandoned and eventually demolished, MGPs are still discussed today because of their lingering environmental and public health concerns. Wisconsin has about 60 former MGP sites throughout the state.

MGPs produced a lot of waste when they manufactured gas from coal. Typically, the plants dumped the coal waste in nearby ravines or ditches, or used it as fill for construction projects. Today, we know that much of the coal waste is hazardous, containing:

  • Cyanides
  • Metals
  • Oily tars
  • Solvents

The oily tars are made up of organic chemicals called polycyclic aromatic hydrocarbons. These chemicals are commonly found at MGP waste sites and have been linked to cancer.

MGP waste can be found in soil, surface water, and groundwater. Depending on the site, the contamination can vary from minimal to extensive. Most contamination is buried under the soil and doesn’t pose a direct health risk, but if coal tar residue comes in contact with the skin, it can cause redness and a rash. In some people, coal tar can also cause a sunburn effect on the skin. If it gets into the eyes, it can cause eye irritation.

Although it’s rare, when contamination has spread into groundwater, it can pollute drinking water. There are tests that can determine if this has occurred.

The Wisconsin Department of Natural Resources and the Wisconsin Department of Health Services (DHS) are working with local governments to address and clean up former MGP sites.

There are a few ways to clean up a site. One uses a method that heats up contaminated soil so contaminants can quickly be removed. This technology reduces the need for transportation and disposal of contaminated soil offsite, making the cleanup more efficient and cost-effective.

Other methods use a series of extraction wells that pump the coal tars from the ground into holding tanks. The coal tars are then transported offsite and either burned as fuel or dumped at an approved landfill.

Cleanup can include odors, noise, and the presence of heavy machinery. The most reported complaint is about odors, which can have a gasoline or mothball-like smell. People with breathing conditions, like asthma, may be affected if the odors reach hazardous levels.

Contractors who clean up former MGP sites are trained to do it safely. They also monitor and control chemical vapors from reaching levels that could affect the health of nearby residents. Because workers are frequently close to the contamination, they sometimes wear special protective clothing and use protective equipment, like supplied air, during cleanup work.

DHS works with the cleanup team to make sure communities are minimally affected by odors and other nuisances.

Report concerns, such as noise or odor complaints, directly to the site cleanup contractors or DNR staff.

You can also attend public meetings related to the MGP site to get more information and ask questions.

If you live near a former MGP site and have a well, consider testing the water to look for volatile organic chemicals and chlorinated solvents that cause vapor intrusion.

In Wisconsin, some former MGPs still have their original buildings. Others have been converted to different uses but still have waste below them. Coal tars, light oils, and inorganic wastes typically found in soil, sediment, and groundwater near former MGPs can cause environmental and public health concerns.

The Division of Public Health (DPH) developed guidance for regulatory agencies, environmental consultants, and contractors, for cleaning up old MGP sites, P-45077 (PDF). This should complement information already available to people in the energy and environmental industries. It provides a public health perspective on emerging technical and regulatory issues related to air quality and air management around MGP sites, with an emphasis on community outreach and risk communication.

Also, the DNR’s Remediation and Redevelopment Program consolidates state and federal cleanups into one program. The program oversees the investigation and cleanup of environmental contamination and the redevelopment of contaminated properties.

If you have more questions, email

Last revised June 21, 2023