Arsenic has been detected in two residential wells below East Helena.

The level of arsenic is below federal drinking water standards, but the fact that measurable amounts are in the wells is prompting Asarco to step up monitoring efforts.

"We need to accelerate our monitoring program ... from a bi-monthly to a monthly program," Asarco's Environmental Manager, Jon Nickel, told a crowd of about 30 people at Asarco's annual meeting Wednesday night.

Arsenic was found at a concentration of 3 parts per billion (ppb) in one of the residential drinking wells along Gail Street, and at 6 ppb in a residential well used for irrigation purposes. The federal drinking water standard is 10 ppb.

Arsenic, a known carcinogen, occurs naturally in some soil and rock. It's also a byproduct of lead smelting, and a century of operations at Asarco's East Helena plant has led to arsenic concentrations of up to 100,000 ppb on portions of the plant site.

That arsenic has leached into the water underneath the plant and has moved off-site in a narrow plume -- something Scott Brown of the Environmental Protection Agency calls "the sleeping giant."

The 600-foot-wide plume is anywhere from 30 to 80 feet below the surface, and stretches north from the plant site under Highway 12, cutting through the northwest side of town toward Wylie Drive. Asarco samples around 100 monitoring wells on a semi-annual basis to keep track of the plume, which is estimated to be moving anywhere from as fast as 300 feet per year to as slow as 265 feet in 50 years.

Arsenic has been detected in at least one monitoring well at about 1,200 times federal drinking water standard; that test well was only two blocks south of the residential wells. Still, until recently arsenic hadn't been found not in any of the 15 residential wells that are along Gale Street even though they tap into the same aquifer.

Five years ago, at least six of the 15 residential wells were the main drinking water supply for the homes; two were for irrigation purposes only and the others weren't in use. Asarco has urged all of the homeowners to hook onto city water, which isn't affected by the arsenic plume.

"If you want us to come and sample your water, we will do that free of charge at any convenient time," Nickel said. "That is something we've offered at all of our public meetings and continue to offer today."

Arsenic also is being detected at the northwest edge of the plume in increasing amounts, and in low concentrations in monitoring wells recently installed in a field on the northwest side of Wylie Drive, which was thought to be beyond the plume's reach.

Asarco is taking steps to try to contain the plume on-site, or at least lessen the amount of arsenic moving off-site, which was another topic of discussion at Wednesday's meeting. One effort involves an experimental program in which iron filings were placed in a trench on the boundary of the idled lead smelter's property. The theory is that the arsenic will bond with the iron and halt the plume's migration.

Asarco also has dug a trench in a trapezoidal shape, about one acre in size, and is filling the trench with a benzonite/clay mixture, then will cap it. The hope is that this will contain the arsenic in the former acid plant drying area, where some of the highest arsenic concentrations n the 100,000 ppb -- were found. The plan calls for a similar project near the speiss/dross plant, where concentrations of around 70,000 ppb have been located.

"What we are looking at is what are the things we can do quickly to make a big difference," said Bob Miller, a hydrologist with Asarco.

However, he added that they've noticed "a kick" in arsenic concentrations in recent months. He attributes that to the deterioration of structures at the site, as well as the ongoing dismantling of numerous buildings.

That dismantling prompted members of Wednesday's audience to question Asarco's continuing assertion that the East Helena plant is "temporarily" closed. Lewis and Clark County Commissioner Mike Murray asked whether this was just a ruse in order to avoid additional cleanup requirements, and another man noted that if this was a permanent closure, retirees' monthly checks would increase by about $225.

"We're growing a little impatient with this 'temporary closure.' Now you're removing structures from the smelter and that gives me real heartburn," Murray said.

Linda Jacobson with the EPA's Denver office said the East Helena plant's operational status isn't affecting the cleanup effort, and her office can't tell a company whether it's permanently shut down or not.

"A shut down facility gives us more cleanup options anyway," she said. "We have more flexibility now for testing surface soils."

Nickel added that the East Helena facility still retains many, if not all of its operating permits. Still, he acknowledged that the plant's future is uncertain.

"We are not going to operate under past operating scenarios," Nickel said. "However, the company continues to be receptive to other possibilities. We've had interested entities come in and look at the plant's other metal type operations; we have a responsibility to look at those."