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small brand Manufactured Gas Plant Impacts


From the early 1800s until the 1950s, prior to the availability of natural gas, communities relied on manufactured gas – or town gas – to produce fuel for street lamps, cooking, heat and lights. During this time, at least 1,500 manufactured gas plants (MGP) operated within the U.S., including several
in our service territory.

In the 1930s, utilities began installing natural gas pipelines gradually eliminating the need for MGPs. A by-product of the gas manufacturing process was coal tar, a black substance that has a viscosity and appearance similar to driveway sealer. Typically, operators burned the coal tar in a generator, used it at the plant sites, or sold it for use in manufacturing preservatives, coatings, resins and other products. Unfortunately, MGP sites released coal tar into the environment at many sites. Today, we are working diligently to address the environmental impacts associated with our predecessor companies’ operation of former MGPs at three sites in Nebraska, two in Montana and one in South Dakota.

Helena manufactured gas plant site

The Helena MGP site was elevated to a high priority status by the Montana Department of Environmental Quality in 2016. Since that time, NorthWestern has been working with DEQ to develop a Remedial Investigation Work Plan (RIWP) that will fully characterize the nature and extent MPG impacts.

TarGOST® technology is being used as a tool for providing a more extensive and detailed characterization of the Helena MGP site. The identification of specific locations where TarGOST® will be deployed were refined using data obtained during an underground utilities identification investigation that used a technology known as ground-penetrating radar (GPR). The GPR investigation was able to identify the presence of several historical underground features that were constructed during MGP operations (as documented in historic Sanborn Fire Insurance Maps).
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