In a document sent to the state, U.S. Steel Corp. said a chain of events kicked off by a missed acid delivery to its Midwest Plant in Portage led to a large discharge of iron into a nearby waterway in late September.
The company sent a letter to the Indiana Department of Environmental Management Sept. 30, several days after a reddish-orange discharge was seen in the Burns Waterway and Lake Michigan.
U.S. Steel said preliminary samples indicated the discharge was due to excess levels of iron that were discharged. IDEM later verified the company’s assessment, saying preliminary sampling results showed the discharge did not indicate any health risks and was below the limit of levels allowed by the company’s discharge permit.
Both the company and IDEM said they were investigating the discharge, but the company’s preliminary investigation found that an acid delivery not completed by its chemical vendor two days before the discharge may have worsened a situation developing at its wastewater treatment plant.
The company said the Final Treatment Plant operator determined sulfuric acid would need to be added to the treatment system in order to adjust the pH levels at the equalization basin the morning of Sept. 26.
When the operator went to add acid to the treatment system, the operator found a low supply of sulfuric acid due to a missed delivery by the chemical vendor on Sept. 24.
The operator borrowed acid from the part of the steel plant used to remove impurities and contaminants from steel, known as the pickle line, for the treatment. During the treatment, the operator realized the acid feed from the pickle line overfed the system and shut off the acid after 14,000 gallons were fed at a rate faster than the plant usually handles.
The iron discharged sometime after the acid overfeed.
U.S. Steel said it found out about the discharge after management received calls from IDEM and the National Park Service and launched its investigation soon after.
The company idled the plant until it could stabilize its operations.
The unnamed chemical vendor delivered sulfuric acid Monday morning, and the treatment plant was able to improve water quality. The plant began starting up operations and returned to full operation Sept. 29.
The discharge led to the Indiana Dunes National Park closing its beaches and Indiana American Water shutting down its treatment facility at the Ogden Dunes. Both have since reopened.
The company said it has since improved coordination for sulfuric acid deliveries and developed a process for using acid from alternative sources.
IDEM and the U.S. Environmental Protection Agency continue to investigate the discharge.