Arsenic that showed up recently in tests of residential wells in the Seaver Park subdivision between Helena and East Helena probably leached out of the soils, and doesn’t seem to be related to the underground arsenic and selenium plumes emigrating from the nearby Asarco lead smelter, officials told a crowd of about 50 people Tuesday night.

Bob Anderson, a senior hydrologist for Hydrometrics, said that volcanic tertiary soils like those in the area historically contain arsenic, and after sampling residential and irrigation wells in and around the Seaver Park subdivision he’s concluded that’s the probable source.

“It kind of looks like there’s two different sources of arsenic,” Anderson said to those gathered for Asarco’s 14th annual meeting at the East Helena volunteer fire hall. “One is coming from the plant site and a secondary one is out of the foothills near (Highway 12).”

Jon Nickel, environmental manager for Asarco, added that of the 50 wells sampled in Seaver Park, the average was about 9.6 parts per billion (ppb) arsenic, compared to the federal municipal drinking water standard of 10 ppb. A map he displayed showed that 10 wells were about the standard, with the highest at 24 ppb, and seven were at the standard.

Nickel said they’ll try to validate their suspicion that the arsenic is naturally occurring, and told residents they can solve any concerns by putting a simple reverse osmosis water filter on their faucets.

He and Anderson noted that Asarco, which shuttered the East Helena smelter in 2001 and has torn down most of the structures, is still trying to figure out the extent of the selenium and arsenic plumes that have moved via groundwater from under the plant site into East Helena and extend toward Prickly Pear Creek and the Helena valley.

Groundwater in the plume under the plant site has had as much as 22,900 times the federal drinking water standard for arsenic; federal officials say consuming less than two 8-ounce glasses of water with arsenic at this amount would kill an adult. It’s less dangerous off site, but one test well at Second and Main shows up to 1,000 times the federal drinking water standard.

Humans need low levels of selenium for muscle and enzyme functions. But according to the Agency for Toxic Substance and Disease Registry, if the amount of selenium found below East Helena were consumed during a period of a few months, a person might experience symptoms like deformed fingernails or toenails, and brittle hair or hair loss. Those most at risk are infants, elementary and preschool-age children, since they would get a higher dose due to their lower body weights.

Most of the East Helena residences are hooked up to city water, so they’re not tapping into the wells. But concerns over the plume’s ongoing progression prompted the installation of 15 new monitoring wells this year and a hazard rating of “moderate to high” susceptibility for the contaminants to get into multiple public and private drinking water supplies.

Anderson said the company has a total of 133 monitoring wells in place, and they’ll continue to watch the plumes as Asarco works with federal, state and local officials to come up with a plan on how to deal with the plumes.

He noted that arsenic plume doesn’t appear to have expanded much in recent years, and as work winds down on the plant site contamination levels in the groundwater also seem to be dropping.

“On site, the groundwater concentrations, although still high, aren’t as bad as they were previously,” Anderson said.

However, he’s not sure whether they’ve found the leading edge of the selenium plume.

Iver Johnson, who is heading the onsite cleanup effort for the state Department of Environmental Quality, said they’ve removed 29,000 tons of hazardous waste this year, putting it into a nearby high-tech landfill, and recycled 1.3 million pounds of scrap metal.

Now that most of the buildings, as well as the historic smoke stacks are gone from the Asarco property, additional soil and water sampling is taking place, and officials are continuing to assess health risks to humans and animals in an effort to better determine what kind of additional cleanup needs to take place and what future uses the site might support.

“The final remedy is likely to be a combination of engineered structures and controls, institutional controls and land management practices,” said Linda Jacobson, who is heading the EPA’s cleanup work on the plant site.

Reporter Eve Byron: 447-4076 or eve.byron@helenair.com