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Minnesota utility regulators on Thursday will likely decide whether two planned carbon dioxide pipelines should be classified as "hazardous," and thus regulated.

The multistate pipelines would transport carbon dioxide captured at ethanol plants, including eight in Minnesota. CO2 is considered a hazardous pipeline material under federal law and in some states, but not Minnesota.

In December, the Minnesota Public Utilities Commission (PUC) opened an inquiry into the two multibillion-dollar pipelines, which also cross neighboring states, particularly Iowa. If the PUC opts to regulate the pipelines, both would require the commission's approval.

Currently, individual counties would have to approve both pipelines.

Several state agencies have submitted comments to the PUC favoring regulation, including the departments of public safety, commerce and transportation.

"All of Minnesota, including state agencies, rely on the robust regulatory process that the commission provides, and carbon capture projects that fall within the correct size category should be no exception," the Transportation Department said in PUC filing.

The Midwest Carbon Express, proposed by Ames, Iowa-based Summit Carbon Solutions, would run for 150 miles in Minnesota, connecting to seven ethanol plants. The Heartland Greenway, proposed by Texas-based Navigator CO2 Ventures, would jog 12 miles into Minnesota, linking to one ethanol plant.

The companies would store carbon dioxide deep underground — below drinking water aquifers — in North Dakota for Summit, and in Illinois for Navigator.

Environmental groups, Indian bands and several citizens have also weighed in on the side of PUC oversight.

The Upper Sioux Community, which is nearby one proposed pipeline, said in a PUC filing that it "believes that further review is necessary by the state to ensure the preservation of human, animal and plant health for this generation and future generations."

In a filing, Navigator CO2 said the state's current regulatory scheme is adequate and PUC intervention now would delay and possibly jeopardize its project. Summit questioned whether the PUC has the authority to modify its own rules, saying that's the Legislature's responsibility.

"The current statutory definitions of [a] pipeline do not suggest the Legislature considered CO2 a hazardous liquid for the purposes of pipeline regulation," Summit said in a PUC filing.

There are only about 5,000 miles of U.S. carbon dioxide pipelines — a fraction of the nation's 2.6 million miles of natural gas, oil and petroleum products pipelines. CO2 pipelines mostly ship natural forming underground CO2 to oil fields, where it's used to extract hard-to-get crude.

CO2 is heavier than air, so if a pipeline ruptures, it can collect in low-lying areas and displace oxygen. It's a potential asphyxiant and can cause breathing difficulties, rapid heartbeat, vomiting, headaches and impaired thinking.

The worst U.S. accident on a CO2 line appears to have occurred in 2020 near Satartia, Miss. A 24-inch pipeline owned by an oil and gas company ruptured, leading to the evacuation of more than 300 people. Forty-six were treated for injuries at local hospitals.

Still, the Great Plains Institute, a Minneapolis-based nonprofit energy research group, said in a PUC filing that there's never been a fatality from a CO2 pipeline accident — and that risks can be avoided if a pipeline is properly sited.

The Great Plains Institute argued against deeming CO2 as hazardous, saying such a classification could hinder the development of carbon capture projects — which are vital to address climate-change goals.

Some other clean energy and environmental groups, however, are skeptical of carbon capture, saying it prolongs the lifespan of CO2-emitting power and fuel production.

Ethanol plants produce copious amounts of CO2, but it is particularly pure. That makes it easier and more cost efficient to sequester than CO2 emissions from coal-fired power plant emissions.

Still, numerous federal tax credits are needed to make the two CO2 pipeline projects feasible.