Lacey developer, MC Construction, is ready to buy the site. However, it's expected to assume responsibility for only half of the estimated $45 million in cleanup work that remains, including as many as 500 contaminated residential yards, adjacent industrial properties and nearby aquatic lands.

Asarco was once a Fortune 500 company that in 2005 filed for Chapter 11 bankruptcy. If allowed to walk away from some of the nation's most expensive environmental cleanups, it would leave taxpayers with more than $1 billion in obligations - a low estimate, some regulators say.

Ruston and Tacoma represent just a fraction of Asarco's cleanup nationwide. As part of its bankruptcy filing, the company disclosed that state and federal officials hold it responsible for contamination at 94 sites in 21 states.

Asarco set up an environmental trust fund three years ago as part of a settlement with federal regulators. Over the next five years, it is expected to provide $62 million, plus interest. In contrast, individual smelter cleanups typically cost about $200 million.

Distribution of the trust fund is prioritized based on human health risks, making the Pacific Northwest sites less pressing.

Areas at the top of the list:

-Omaha, Neb., site of largest residential lead cleanup in the United States.

-El Paso, Texas, contamination from a mothballed smelter and its 800-foot smokestack extends into Mexico and New Mexico.

-Hayden, Ariz., a still- operating Asarco copper smelter has polluted its surroundings.

The Asarco bankruptcy was among the 10 largest filed in the nation in 2005 and its list of creditors is long.

Officials with the Environmental Protection Agency had yet to confront a polluter that sought to unload its cleanup responsibility midway through the process - until Asarco.

"We're in uncharted waters," said Kevin Rochlin, the EPA manager overseeing the $180 million Tacoma cleanup. "There has never been anything of this magnitude and this complexity."

Cleanup remains at dozens of sites in the West and Midwest, where Asarco maintained mining and metal extraction operations for more than a century. Those places, in some cases entire towns, are now some of the nation's largest Superfund sites.

In Idaho, for example, Asarco is among the mining companies blamed for contamination spread across the 1,500-square-mile Coeur d'Alene River basin. Cleanup is likely to last for generations, and the EPA has estimated the cost of the first 30 years at $359 million.

In Omaha, Asarco ran a lead smelter and refinery on 23 acres along the west bank of the Missouri River for more than 120 years. It shut down in 1997, and in 2003 was designated a Superfund site after blood tests detected dangerously high levels of lead in hundreds of children.

The Omaha site encompasses 20 square miles, but could expand because the boundaries of the lead contamination haven't been mapped. The budget for the first five years of cleanup work is $77.4 million. The EPA also has ordered the Union Pacific Railroad to pay.

"By the time we're done, total site costs could be more than $200 million," said Bob Feild, an EPA manager for Omaha.

Other places sullied by Asarco's mining and smelting operations include East Helena, Mont., and Everett, where state Ecology officials estimate 550 residential properties are contaminated with arsenic.

In Ruston, the EPA added a smelter site there to its national Superfund priorities list in 1983. Asarco has denied state regulators' allegations that its smokestack spread arsenic and lead contamination over 1,000 square miles. Damages could be included in the state's bankruptcy court claim.

In the Tacoma area, cleanup estimates have topped $33 million for residential soil removal, cleaning the slag peninsula where the Tacoma Yacht Club stands and dredging the yacht basin and capping other contaminated sediments in Commencement Bay.

After Asarco's bankruptcy filing, the EPA tapped Asarco's $100 million nationwide trust fund to continue the residential cleanups in Tacoma, which in the first three years of distributions received $16.6 million.

It remains questionable whether what's left of the trust will be enough to satisfy Asarco's creditors and the needs of unfinished cleanup.