SILVERTON, Wash. -- The Environmental Protection Agency announced Wednesday it is clearing the way for volunteer groups to clean abandoned mine sites.

That announcement comes at a time when state and Snohomish County health agents are investigating mercury contamination on private property in Silverton, Wash. on the south fork of the Stillagaumish River.

There they've found parts of an old mercury concentrator left by miners long ago.

Samples were taken from the soil surrounding the structures – and found to be contaminated - but heavy rains and spring runoff are whisking the soil away.

"He came up with some mercury, some arsenic and some cadmium that exceeded our clean-up standards," said Brian Sato, of the Dept. of Ecology.

Shifting stream currents are eroding away the soil supporting one of the structures, raising concerns it could collapse.

"The structure would be lost, destroyed in the creek, and if, there is contamination in it, it would be released in the creek but we don't know at this time," Sato said.

Investigators say just because the soil is contaminated doesn't mean the century old structures are.

They will do more sampling and develop a plan.

In some cases it may be best to just leave gated sites like this alone.

But remnants of the region's mining legacy are surround the site: There are hundreds of other mine-related sites that may be laced with the same chemicals.

Health officials warn everyone to use caution if they stumble upon abandoned mines while hiking in the wilderness.

Investigators will gather more samples to determine just how contaminated the old structures are.

They may also decide to divert the stream bed that threatens it.