DETROIT, MI -- The company responsible for storing petroleum coke along the Detroit River released photos Thursday night showing sealed drains in response to concerns raised over potential watershed contamination.

Large piles of petroleum coke in Southwest Detroit have raised fears among residents and lawmakers who say not enough is known about potential health and environmental effects of the substance for it to be kept near water and in open air.

But Detroit Bulk Storage has maintained that it is being stored safely and legally.

The oil refining byproduct comes from tar sands processing at the Marathon Petroleum refinery in Southwest Detroit. The substance is being sold to Koch Carbon and stored along the river for shipment.

U.S. Rep. Gary Peters (D-Bloomfield Twp.) on Thursday after introducing a bill calling for a study into potential risks of petroleum coke exposure released a Michigan Department of Environmental Quality photo from the site that appears to show an open drain beside one of the piles.

Spokesman for Detroit Bulk Storage Daniel Cherrin later released more photos showing that drains have been sealed and said the company is working with the MDEQ and the city to take precautions.

"We welcome any inquiry by the government and the community about the precautions we are taking in the storage and loading of dry bulk products," Cherrin said. "We continue to work with the DEQ and the city of Detroit as we work through the process to ensure the necessary safeguards are in place. For example, asphalt was installed before any petroleum coke was stored and the loading area slopes away from the waters edge. The drains also have been capped and sealed."

State Rep. Rashida Tlaib (D-Detroit), meanwhile, introduced a bill in the state legislature that would require companies to store petroleum coke in enclosed containers and obtain storm water discharge permits.

"Such a potentially harmful substance should never be stored so close to residents and our waterways, but given that we do have to live with stored pet coke, then we must have strong storage requirements in place that protects the environment and the health of people who live in neighborhoods near these piles,” said Tlaib in a news release.