Imagine a pile of contaminated dirt three stories high that stretches from Pike Place Market nearly to Pioneer Square.

That’s the size of a heap of polluted soil the mining company Glacier Northwest wants to build near drinking-water wells on Maury Island, the waste product of the company’s proposal to massively expand a sand and gravel mine.

But would the big pile of dirt encapsulated in plastic liners be a “landfill,” which local laws would prohibit there? Or is it a “containment facility,” as Glacier calls it? If it’s a landfill, Glacier could face the much more expensive alternative of barging that soil off the island for disposal in a special landfill for toxic waste.

Said King County Councilman Dow Constantine, a leading opponent, “It is, in every way, a landfill, based on a plain reading of the law.”

Pete Stoltz, Glacier’s permitting coordinator, said it’s more appropriately considered a “containment facility” because it will store soil, not garbage.

“What we’re proposing is the standard method that’s used to contain material like this across the country,” Stoltz said. “It’s not a new technology. It’s very well-known and well-defined.”

Critics worry about contamination of wells less than half a mile from the dirt mound. But Glacier says there’s no danger because, at the spot where the dirt will be dumped, underground water flows in the opposite direction of the wells.

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This latest flash point comes in a long-standing feud over whether Glacier Northwest should expand the little-used mine, which would involve building a dock on Puget Sound to load sand onto barges as long as a football field. The dispute has come into sharper focus recently as government officials and others launched a renewed effort to resuscitate the ecologically ailing Sound.

Critics ask: How can the state permit a major new industrial activity at a relatively untouched piece of the Sound’s biologically crucial shoreline — while at the same time talking about restoring the Sound?

But Glacier says it would take extraordinary measures to protect the environment at the shore and elsewhere — including near the top of the hill, where the dirt would be piled.

The dirt in question was contaminated by arsenic, cadmium and lead because Maury Island is directly downwind from a Tacoma metal smelter that operated for most of the past century, spewing the pollutants out its smokestack.

To get to the sand and gravel it wants below, Glacier would chop down the madrone trees covering the hillsides and scrape off the top few feet of soil, the part that contains the contaminants.

That 271,000 cubic yards of dirt would be piled 2,100 feet long and up to 30 feet high. That would be immediately south of Southwest 260th Street and less than half a mile from where the Dockton Water Association draws drinking-water supplies for more than 1,100 residents. At least one more well is nearby.

Opponents emphasize that the dirt would sit as little as 15 feet above the underground layer that produces drinking water — and atop a geological fault that could shift in an earthquake, which they fear could spill toxic dirt.

They also have dug up nine-year-old lab work showing that soil at the site, when tested to simulate what would happen if it were rained on, generated runoff containing arsenic at a level 20 times federal standards for drinking water. And groundwater at the site already violates government standards for arsenic.

“It makes my blood boil,” said Amy Carey, president of Preserve Our Islands, a group of environmentalists and residents spearheading opposition.

“Our concerns regarding Glacier’s proposal to landfill this enormous amount of highly contaminated soil is not based on assumptions or guesswork,” Carey said. “We have Glacier’s own studies showing the arsenic in the soils is mobile and presents a significant risk to both public and environmental health.”

Preserve Our Islands and allied environmental groups want county officials to reject Glacier’s plans, citing a 2004 county ordinance that prohibits landfills atop areas where water drawn from the ground is the only drinking-water source available.

They point out that, like a landfill, the dirt would have a liner at the bottom designed to collect any water that manages to seep through.

Carey points to a 1999 environmental study prepared for county officials that says the dirt would be governed under regulations covering “solid waste,” and that the report, when discussing the facility to hold the dirt, speaks about exemptions for certain “landfills.”

The Dockton Water Association, with its wells close by, “is concerned” about the contamination, said Doug Dolstad, manager of the water system. But there’s more. Glacier’s towering hills of sand help shape the underground water supplies.

“When they take away that mountain of soil, they’re going to change the water table … which may affect our springs,” Dolstad said.

King County agencies have taken differing viewpoints on whether what Glacier proposes would be a landfill, records show.

“Public Health considers contaminated soils … to be solid waste,” Yolanda Pon wrote in a March 4 e-mail to another county official. “Therefore, it appears they plan to landfill on-site and would need to obtain a landfill permit.”

But later that month, Stephanie Warden, of the County Department of Development and Environmental Services, wrote to Carey, “The Public Health Department has concluded that the on-site containment cell does not meet the definition of a landfill.”

The opponents met with King County Executive Ron Sims. Assistant County Executive Rod Brandon, asked by the Seattle P-I about the apparent conflict in the departments’ interpretations, said he would check into it and answer the question. He never called back. The P-I sought an answer from the executive’s office in several phone calls over a period of more than two weeks.

Opponents also have been lobbying the state Ecology Department to take a harder look at the mine. The agency issued its approval, saying it believes the project will comply with water-quality standards and other environmental protection measures.

And it was the Ecology Department that originally proposed the idea of stockpiling the contaminated soils right on Glacier’s land.

Nevertheless, the department will re-examine the soil-disposal idea in a formal process required under the state’s toxics-cleanup law, including a new opportunity for public comment, said Norm Peck, the agency’s manager for the Glacier site.

But Peck said he is confident the precautions envisioned would keep water from leaching into the contaminants and spreading the pollutants underground.

It’s true that the groundwater violates state standards, Peck said, but there is naturally occurring arsenic in many places around Western Washington, and the arsenic measured in the groundwater at the mine site appears to be natural.

Ecology says it is actually being more careful about the Glacier dirt than it would be about garbage. Owners of a garbage landfill are required to check for contamination leaking for 20 years after they stop accepting waste. Glacier would have to make provisions for the pollution checks to go on forever.

Peck said that what Glacier is proposing has been used to handle contaminated soils in a number of locations around Western Washington.

“You won’t have water running through it to leach (contaminants) out,” Peck said. “It puts the contamination in a place where people can’t get to it, so there won’t be exposures. It protects human health and the environment.”

P-I reporter Robert McClure can be reached at 206-448-8092 or robertmcclure@seattlepi.com. Read his blog on the environment at datelineearth.com.