The arsenic and selenium plumes underneath East Helena aren’t showing many fluctuations, according to the most recent samples from the dozens of test wells that dot the landscape.

However, two of four new wells drilled earlier this summer to ascertain the leading edge of the plumes did come back with elevated selenium levels, meaning Asarco may have to drill addition sampling wells to be able to truly delineate the extent of the groundwater contamination.

“We’re seeing some bouncing around of analytical results (in the older wells), but that’s within an envelope that we expected. There are no red flags,” said Randall Breeden, a geo-hydrologist for the Environmental Protection Agency in Denver.

“But wherever there are sentinel wells installed that come back with readings above the MCL (the federal Maximum Contaminant Level for drinking water), Asarco will be required to step out and further define the plume. That hasn’t been finalized with the EPA, but is something we need to talk to them about.”

The groundwater plumes, along with above-ground cleanup activities relating to the former Asarco lead smelter in East Helena, will be discussed at the annual meeting slated for 7 p.m. Wednesday at the East Helena Volunteer Firehall at 4 East Pacific St.

Arsenic occurs naturally in low levels in water in the Helena area, and selenium is present naturally in some environments. However, both are byproducts of the lead-smelting process, and the five underground plumes — one containing arsenic and two with selenium in the “shallow” aquifer between 6 and 30 feet underground and two similar plumes about 30 to 60 feet below ground under East Helena — have elevated levels that could be dangerous to humans or animals if consumed.

For example, a monitoring well in the intermediate aquifer below Second and Main streets contains arsenic at 10 parts per million (ppm), which is about 1,000 times the MCL of .01 ppm in municipal drinking water, according to the most recent round of tests done in May 2008. Yet that’s actually down 3 ppm from a test last fall.

The intermediate arsenic plume is fingerlike, stretching from the plant site to Wylie and Gail, and is about a block wide with concentrations highest in the middle section of the finger and diffusing toward the edges.

One block over, selenium was detected in a similar-depth test well last spring at 0.28 ppm, which is five times above the MCL. That’s up slightly more than previous amounts, but not significantly, noted both Breeden and Bob Miller, a hydrologist for Asarco. That selenium plume in the intermediate aquifer plume is wishbone shaped, and reaches from the Asarco plant into Lamping Fields on the west side of Wylie Drive.

The arsenic plume in the shallow aquifer is called “the mitten” plume due to its shape. It starts near the south side of the Asarco plant site, with the thumb around Riggs and Second, and the fingers stretching from Cleveland to Helena streets, north beyond the city limits. This plume contains some of the highest arsenic levels, concentrated on the plant site — around 174 ppm, or 17,400 times the MCL in the most recent tests. The amounts drop dramatically as the plume moves offsite, but are still above the MCL; a monitoring well near Thurman and Main is .418 ppm, which is about 40 times the MCL.

Selenium has two parallel plumes in the shallow aquifer, one about two blocks wide, that generally follows Prickly Pear Creek and stretches past Gail Street. The other shallow selenium plume almost reaches Riggs near Second Street.

Jon Nickel, environmental manager for Asarco in East Helena, is quick to add that no one is tapped into these plumes, and the 15 residential wells in East Helena don’t have either arsenic or selenium at levels greater than the MCL. None of those wells is used for drinking water.

Almost all East Helena homes are hooked into the city water system.

Along with the dozens of monitoring wells that are checked regularly, Asarco also has sampled public water supplies for the Twilight Mobile Home Park north of East Helena, the city’s municipal wells and for subdivisions east of town.

“Again, there wasn’t anything remarkable,” Nickel said. “They’re all below detection levels.”

Asarco “idled” the East Helena smelter in April 2001 and is in the process of dismantling it.

The company readily admits it is the source of the arsenic in the groundwater, but is still trying to discover where the selenium is originating.

“We have elevated numbers in the slag pile wells, and also on the west side of the plant relative to the ore storage facility,” Miller said. “But we haven’t found the smoking gun per se.”

The selenium came as a surprise to Asarco and the EPA when it was detected in test samples two years ago. Asarco expanded the list of elements it tests for to 19 elements, including aluminum, barium, chromium, mercury, nickel, silver and copper, but didn’t find anything significant, Miller said.

“In my review of the data, nothing stood out,” he said.

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.

In comparison, the amount of arsenic present under the city would cause nausea and vomiting if a person were to drink it. After a few weeks, that amount of arsenic could destroy a person’s digestive tract and cause organ failure.

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