PORTAGE, Ind. — Water samples from Lake Michigan and one of its tributaries show no significant discharge of a potentially carcinogenic chemical from a U.S. Steel Corp. wastewater spill in northern Indiana, the Environmental Protection Agency said Friday.

Results from about 200 water samples showed no significant trace of the chemical hexavalent chromium in the lake or the tributary called Burns Waterway after the Tuesday spill at U.S. Steel’s Midwest Plant in Portage, about 30 miles east of Chicago, the agency said.

U.S. Steel said it expected “a controlled, phased and highly monitored restart” would begin Friday at the plant while the EPA and other government agencies conduct water and soil sampling. The restart would occur while a water company’s nearby intake remained closed and access to parks and beaches in the area remained restricted, U.S. Steel said.

The plant has sat idle since Tuesday, when the company said an expansion joint failed in a pipe, allowing wastewater to flow into the wrong treatment plant at the Portage complex. That wastewater eventually flowed into Burns Waterway at a point about 100 yards from Lake Michigan.

“Preliminary results of water samples collected by EPA from Burns Waterway and Lake Michigan, including Indiana American Water’s intake, on April 12, do not indicate hexavalent chromium impacts in either water body. All results were below EPA’s method detection limit of 1 part per billion,” the EPA said.

However, the Chicago Department of Water Management said Thursday that its own water sample from Lake Michigan about a mile north of the spill contained 2 parts per billion of hexavalent chromium. That’s “a level higher than would be expected to be found in raw lake water,” the department said, but just a fraction of the EPA’s drinking water standard of 100 parts per billion for all forms of chromium.

U. S. Steel said the restart would begin with operations that do not use chromium and would include water sampling every two hours.

“If elevated levels of chromium are detected, all operations will be immediately shutdown,” the company said. “If all non-chromium-involved lines restart successfully and sampling is acceptable, the lines that involve chromium would be restarted in the same controlled, phased, and highly monitored manner.”

U.S. Steel issued a statement Thursday evening saying it had identified the source of the spill and “has made the necessary repairs.”

The EPA said it recommended that U.S. Steel delay the restart until the agency had sufficient data to show there were no lingering effects to the tributary or Lake Michigan. The agency said it reviewed the restart plan, as did the National Park Service, which closed three beaches at nearby Indiana Dunes National Lakeshore.

The EPA has said hexavalent chromium — a toxic byproduct of industrial processes — might be carcinogenic if ingested. The toxic heavy metal is used in a variety of industrial processes, including steelmaking and corrosion prevention, and as a pigment in dyes, paints and inks. It’s also found in ash from coal-fired power plants.

A case involving the chemical was made famous by the 2000 film “Erin Brockovich,” which was based on a utility’s disposal of water laced with hexavalent chromium in unlined ponds near Hinkley, California. That disposal method polluted drinking water wells and resulted in a $333 million settlement.