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The mining company Asarco LLC has agreed to spend up to $880,000 to clean up a century-old, contaminated mining site southeast of Tucson, state officials said.

The agreement to clean up the Helvetia mine site is one of several that Asarco and Arizona Department of Environmental Quality officials are negotiating as part of Asarco's bankruptcy settlement overseen by U.S. Bankruptcy Court in Texas, officials said.

"This agreement will help ensure that contamination from this old mining site will be cleaned up at last," said Steve Owens, ADEQ's director.

Asarco officials and attorneys couldn't be reached for comment on the state's announcement, which came late Friday.

The cleanup will entail removing contamination by acids and heavy metals used at the Helvetia site. The area is about 28 miles southeast of Tucson near the Santa Rita Mountains.

The 6-acre site has about 50 piles of mining wastes, said Mark Shaffer, an ADEQ spokesman.

"This is an old, old site, from the late 1890s and 1900s," Owens said. "There's been a lot of long-standing contamination out there that's been exacerbated over the years."

He said the contamination resulted in part from drainage of acidic materials and soil erosion. An investigation in coming months will determine the extent of contamination, Owens said.

"More likely than not there are some waste piles out there that have been there for a long time," Owens said.

"For example, you have a waste pile that has soils contaminated with acid residues and heavy metals. The pile gets wet and water seeps down through the pile, which causes acids and metals to leach out of the waste pile and get into the soil below the waste pile."

State officials don't believe that the wastes have contaminated groundwater, but they want to prevent any further erosion and runoff of contaminants from the site, he said.

Most likely, a cleanup would involve capping the site and using erosion control such as planting vegetation, he said.

"Unless we find something that is unexpected, this contribution from Asarco should be adequate to cover the cost, based on our experience around the state with sites similar to this one," Owens said.

Asarco owned the site in the past and assumed liability for the cleanup, Owens said. The company didn't own the site at the time it was contaminated, he said.

"Way back, there was a variety of entities who owned the site over the years," he said.

State officials are in the midst of negotiations for cleanups at several other Asarco sites statewide, but Owens said he couldn't say which ones because these are confidential discussions, "just like in any legal proceedings."

He also couldn't say if Asarco's Silver Bell and Mission Mine sites are covered by the negotiations.

In June, the bankruptcy court approved an agreement between the two parties for the company to spend $13.5 million to clean up Asarco sites in Hayden and Winkelman northeast of Tucson.