Updated

Decades-old coal ash hurled from the grounds of a Wisconsin power plant into Lake Michigan during a landslide this week probably doesn't pose a significant environmental risk, experts said Wednesday.

Officials rushed samples of tainted water and spilled ash to laboratories to analyze the debris that plummeted onto the shore and into the water Monday, seeking to assess the extent of any possible harm to the lake. The ash slid into the lake when a section of cliff about the size of a football field gave way near a We Energies plant outside Milwaukee. Company officials said the cause hadn't been determined.

It will take several days to complete the analysis, said Phillippa Cannon, a spokeswoman for the U.S. Environmental Protection Agency. Of particular concern were heavy metals such as arsenic, lead and mercury found in the ash from coal incineration

About 2,500 cubic yards of ash, or enough to fill about 200 dump trucks, may have reached the water, utility spokesman Brian Manthey said.

The material has the potential to smother fish habitat and pollute sediments near the lakeshore, said Val Klump, director of the Great Lakes WATER Institute in Milwaukee. But even if a large volume got into the water, the ecological fallout probably won't reach far beyond the immediate spill area, he said.

"It's a big lake. It gets diluted pretty fast," Klump said.

A vessel from the research institute also took samples in the area and was analyzing them, he said. Crew members spotted a debris plume and an oily sheen in the water.

"Obviously this spill is not a good thing," Klump said. "It's too early to know for sure. But I would think the stuff that comes off our city streets and farm fields during a major rainstorm and washes into the lake probably has as big an impact as this."

Ann Coakley, spokeswoman for the Wisconsin Department of Natural Resources, also said she didn't anticipate widespread damage from the ash.

"Most will stay where it is and they'll scoop it out," Coakley said. "That's not to say none of it will migrate but it's likely not going to cause a great deal of environmental harm."

The spilled ash was generated in the 1950s, state and federal officials said.

Coakley said the heavy metals concentration could be different from that of present-day ash because the coal burned a half-century ago might have had different characteristics. Also, the plant would have lacked modern emission control equipment.

She said local officials weren't concerned about drinking water contamination because the spill wasn't close to Lake Michigan intake pipes.

Environmentalists said the spill illustrated the need for strong regulation of coal ash, which is not classified as hazardous under waste laws. They have pushed for new rules since an ash disposal pond failure in Kingston, Tenn., flooded hundreds of acres and killed fish in nearby rivers.

"We know coal ash contains toxic substances," said Joel Brammeier, president of the Chicago-based Alliance for the Great Lakes. "The Great Lakes region is still digging out from a legacy of contamination that's 100 years long. We shouldn't tie the hands of agencies that are working to protect the lakes."

The Republican-controlled House voted last month to put states in charge of regulating coal ash, which would pre-empt EPA standards that could be tougher.

Workers built earthen berms Wednesday to keep rainfall from the debris and to prevent more of the ash from washing into the lake, Manthey said. Two skimmers were cleaning the water's surface.

The company and its contractors will stabilize the shoreline and bluff over the next several days, Cannon said. After the area is declared safe, additional cleanup will be done.

No one was hurt in the landslide. A pickup truck and other equipment tumbled into the lake.

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Flesher reported from Traverse City, Mich.