"We wanted to move out as soon as we heard about it," said Jenny Collier, whose children are 8 months and 3 years old. "It was good we found out."
Previous tenants are not known, and there is no plan to track them down, said Jim Matsuyama, environmental health director for the Tri-County Health District.
Exposure to lead can cause learning disabilities and mental retardation in children. Swallowing water or soil that contains arsenic can cause cancer in children or adults.
EPA tests of soil near the swing set showed lead levels of 8,500 and 12,000 parts per million, Liverman said.
By comparison, the EPA is cleaning up yards contaminated with 1,000 parts per million lead in Idaho's Silver Valley. The agency calls for immediate cleanup of Silver Valley yards that register 2,000 parts per million, if those houses are occupied by children or pregnant women.
The Washington state standard for residential land is even tougher, at 250 parts per million.
Arsenic levels on the Bonanza property registered as high as 443 parts per million. The state standard is 20 parts per million.
The EPA discovered the contamination in recent months, while looking for sources of metals pollution in Lake Roosevelt. The Cominco smelter in British Columbia is considered the biggest source. But investigators also sampled the soil at old mines and mills in Stevens and Pend Oreille counties, in Washington.
The Bonanza mill was about two miles northwest of Colville. It processed ore from the Bonanza mine, about 15 miles northwest of town. The mill and mine were most productive between 1944 and 1950, when the late Earle Gibbs processed about $2 million worth of lead.
The mill shut down in 1950, but was briefly reopened three years later. "Production now is 100 tons daily," with the ore running about 22 percent lead, The Spokesman-Review reported in 1953.
Leftovers from the milling process -- tailings that are still high in lead -- apparently were spread over the mill site, a formerly marshy area along the Colville River.
Workers built a berm to keep the river off the land, except during high water. They dug a ditch leading through the tailings to the river to keep the land drained.
"There's anecdotal evidence that at some point, the levy was breached and (tailings) were pushed into the river" to make room for more, Liverman said.
Soil tests in the Colville River did not show high lead and arsenic levels, Liverman said. But, "it's reasonable to conclude that during high flood events, the materials would be washed into the river and carried downstream" to Lake Roosevelt, he said.
Cleanup will include capping the ground around the houses with fresh soil and sod, and capping other areas with gravel. Crews will line the ditch and strengthen the berms to prevent contaminated tailings from reaching the river, Liverman said.
Brothers Duane and Darrel Webley bought the land in 1999. They paid less than $100,000 for the land and the two houses, where renters already were living, Darrel Webley said.
The brothers spent about $35,000 fixing up the houses, which were "eyesores," Darrel Webley said. The remodeling included siding that makes the houses look like new log cabins.
Mostly, though, the Webleys used the land for the seasonal storage of logs and lumber for the nearby sawmill they've operated for 35 years.
Liverman said the Webleys were cooperative and concerned about their tenants when told about the test results. "They were immediately responsive to the potential health issues," he said.
The contamination "was very much of a surprise," Darrel Webley said Tuesday. "Nothing was disclosed to us when we bought the property and, naturally, we didn't run any (soil) tests or anything."
But, Webley said, he did have the well tested twice before being contacted by the EPA, and twice since. None of those tests showed any water contamination.
Liverman said it's possible, but unlikely, that the EPA may demand that the Webleys cover part of the costs. Darrel Webley said the brothers won't agree to pay much without a court battle.
Once cleanup is completed, the EPA may give the OK for tenants to move into the houses.
"I'll be real leery of doing that," Darrel Webley said. "I'd want to make sure they (the tenants) knew" about the cleanup.