Detroit residents, business owners and a local congressman spoke out Tuesday about the growing piles of pet coke along the Detroit River, Sarah Cwiek reports on Michigan Public Radio. 

That byproduct of the oil-refining process is being dumped in massive piles—now several blocks long and building stories high--along the river. It’s stored in the open, and wasn’t approved through any permitting process.

This pet coke is the result of processing Alberta tar sands oil at Detroit’s Marathon oil refinery. That facility recently expanded to process more of the Canadian oil.

U.S. Rep. Gary Peters calls the situation “unacceptable.” He plans to introduce federal legislation to conduct “a complete health study” of pet coke—and how it could play into the larger debate over tar sands oil and the Keystone XL pipeline.

“We 'd better understand the health impacts of it,” Peters says. “We'd better understand how we store this properly, and understand the damage this can do to the environment…not just in the storage, but when you burn this pet coke.”

Read more: Michigan Radio