NIAGARA FALLS, N.Y. (From news reports) -- A Niagara Falls paper mill subject to multiple complaints of foul odors was punished Thursday with a $375,000 fine and state-mandated plant improvements that will cost the plant's owners an estimated $2 million.

Quebec-based Cascades Containerboard Packaging Inc. has signed a consent order agreeing to the monetary penalty and the plant upgrades, the Department of Environmental Conservation announced Thursday.

The 19-point consent order committed Cascades to conducting "comprehensive air sampling to evaluate additional potential sources of odorous emissions," the DEC announcement said.

The odors derive from hydrogen sulfide, commonly called a "rotten egg" smell.

It comes from the sludge generated in the plant's process of recycling paper to produce new cardboard, Cascades spokesman Hugo D'Amours said in late August.

"It is so hard to describe. It is a mix of rotten eggs and chemicals," nearby resident Duane Walsdorff said at that time.

DEC Commissioner Basil Seggos said the agency's action holds the company accountable for "intolerable odors" that impacted the neighborhood.

"We are very sorry about that situation," D'Amours said. "We've done everything in our power, including investing in equipment, to mitigate the odors and repair the reactor."

He was referring to a malfunction in the anaerobic reactor the mill uses to process the sludge, containing mostly paper fiber, which results from processing recyclable paper into cardboard.

The reactor, which uses microorganisms that are supposed to destroy the organic material in the effluent, was the main source of the smell.

In May, the DEC ordered Cascades to stop storing sludge outdoors and to take other odor control actions. The DEC issued a notice of violation on June 4.

D'Amours said the company repaired the reactor and restarted it in early July, but in early August it broke down again. That led to another enforcement visit from the DEC on Aug. 19.

The reactor has been repaired again, D'Amours said Thursday.

Other requirements in the DEC order announced Thursday include continued monitoring of hydrogen sulfide emission levels at the plant's property line, and immediate mitigation when state thresholds are exceeded.

Cascades also must submit plans to replace temporary covers with permanent ones on sludge reactors, tanks and other emission sources, as well as to manage secondary sludge to mitigate potential odors.

The company must evaluate its operations to find and report any emission sources not covered by its state air quality permit, and amend the permit application to include those sources.

Wastewater treatment also must be evaluated, with improvements identified to ensure the system's stability.

Cascades also must submit weekly progress reports to the DEC summarizing complaints and plans to correct them. Those complaints can be phoned to a hotline at (833) 461-8898 or emailed to niagara@cascades.com.