By EVE BYRON

Independent Record

Deep in the heart of the East Helena Asarco plant, under and around the buildings where a century of smelting took place, lies toxic, arsenic-laden soil that's marrying with groundwater to flow into the Helena valley.

In places, the arsenic in the groundwater under the former lead smelter is 22,900 times the federal drinking water standard -- so toxic that drinking two 8-ounce glasses would be fatal to an adult. It would take less than one glass of water with arsenic at this level to kill a child, according to information from the federal Agency for Toxic Substance and Disease Registry.

"Don't drink it or even taste it," said Selena Chou, an environmental health specialist with the Registry. "That amount is very, very, very high."

It's cost prohibitive -- and almost impossible -- to remove the arsenic from the groundwater. So the Environmental Protection Agency is trying to slow, or even halt, the plume's movement off-site.

The derived-upon solution is surprisingly simple. Dig four ditches, generally 35 to 45 feet deep, 3 feet wide and 200-plus-feet long, making a 1,350-foot-long roughly rectangular shape. At the bottom is a layer of volcanic ash and clay.

Fill those ditches with a mixture of soil and bentonite, then put a clay or asphalt cap on top of it.

Voila.

The arsenic is contained by this "slurry wall" -- or so the theory goes.

"It's like installing a bathtub around it," said Linda Jacobsen, the on-site project manager for the EPA. "We're isolating the source area so the groundwater goes around the contaminated materials rather than through and carry it down-gradient" into East Helena and the Helena Valley.

The slurry wall won't remove the contamination. Bob Miller, a hydrologist for Asarco, said that's not an option at this point.

"The bottom line is it isn't very practical" to remove arsenic from groundwater, Miller said. He adds that it's also not practical to excavate all of the contaminated soils from which the arsenic is leaching because "there's just not enough money in the world" to remove that amount of cubic yards of material.

"The slurry wall is an interim measure," Miller said. "Those can be permanent -- they may not be standing alone -- but it is an interim measure."

Jacobsen said that by isolating the high source of arsenic, they'll stop feeding the plume into East Helena and eventually that plume will become diluted with clean groundwater.

"They told me and convinced me you have to do source control first," Jacobsen said. "So we identified the major source areas -- the former acid drying area, and the speiss/dross area. Doing source control there will allow the aquifer to stabilize."

Those areas generally are in the middle of the East Helena plant.

The underground arsenic plume stretches northwest from the Asarco lead smelter to monitoring wells west of Wylie Drive, which were installed in 2005 in an effort to locate the leading edge of the plume. The amount of arsenic in water at the farthest well is detectable, but still below the federal drinking water standard.

However, that's not the case elsewhere. A well at Wylie and Groschell is 200 times the federal standard. Two blocks closer to the plant -- at Second and Main -- the plume is 1,100 times the standard.

Groundwater depth in the monitoring wells ranges from 8 feet to 35 feet below the surface.

Residential wells are in the plume's path, but EPA officials say those wells are used only for nonconsumptive uses and the amount of arsenic in them, if any, is below the drinking water standard.

Although not as widely reported, elevated levels of arsenic also are present in monitoring wells on either side of Prickly Pear Creek, which runs through the center of East Helena. A well between Cleveland and Morton, just south of West Main Street, is six times greater than the standard. On the other side of the creek, in a test well near the intersection of East Main and Thurman, arsenic is 39 times the standard.

One well has a depth to groundwater of 8 feet; the other is 16 feet. Jacobsen said the contaminated water in that aquifer doesn't flow into Prickly Pear Creek because it's lower than the creek.

"It appears that Prickly Pear Creek isn't in connection with the groundwater that's lower than the creek," Jacobsen said.

A new wrinkle was added to the underground plume dilemma last year, when selenium was discovered in test wells under the city. Now, it's even showing up in wells without elevated levels of arsenic, and appears to be more widespread than the arsenic, although it's at much lower levels.

It's unclear if the two issues are related, or where the selenium originated. Arsenic occurs naturally in low levels in water in the Helena area, and selenium can be present naturally in some environments. In fact, a certain amount of selenium is needed for muscle and enzyme functions.

But both arsenic and selenium are known byproducts of the smelting process.

It's clear the arsenic is coming from the lead smelting plant in finger-like flows. But recent tests didn't show elevated levels of selenium in the groundwater there and the selenium plume lies horizontal to the plant. The elevated levels don't show any patterns.

"Almost all of the samples we pulled from the plant site are lower than what we are seeing in the city of East Helena," Miller said. "One thing that we'll do is sample everything for selenium and try to get a better pattern. ... It really isn't a major element relative to the smelting process, but in smelting you get a little bit of everything."

The selenium is present at elevated levels in 20 of the 31 monitoring wells under East Helena, generally between double and six times the federal drinking water standard.

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.

Afew years ago, the EPA installed a test barrier, known as a PRB -- or permeable reactive barrier -- generally consisting of a ditch filled with iron filings. Water could flow through the PRB but the arsenic bonded with the iron, lessening the off-site migration.

Jacobsen said the EPA has a contractor testing different combinations of reactive media to see what might be able to contain both selenium and arsenic.

"We'll continue to look at boundary systems, before you get across Highway 12," Jacobsen said. "The PRB will work better if we cut the source of the arsenic off and if the selenium isn't there."

They're also considering installing a PRB near the head of the arsenic plume to keep it from moving farther into the Helena Valley.

But both Jacobsen and Miller stress that these are possibly only temporary measures. Even if they are permanent, the final cap for the slurry wall would have to be replaced because it would be contaminated during the ongoing demolition effort of plant buildings.

In addition, at this point, no one knows what will become of the East Helena plant site.

"Any kind of permanent measure would have to look at future reuse of the facility," Jacobsen said. "Asarco and I realize that as more of the demolition is done, we'll do a risk assessment, looking at ecological and public health and we'll do a corrective measure study. We'll see what kind of other uses there may be for the site, then determine the final remedy. If these measures are working -- and we have 13 monitoring wells around it, both in and about the site -- it will probably be left in place.

"Our goal is to get to the (drinking water) standard, but whether that's ultimately achievable, that's the question."

To browse through the IR's archive of ASARCO coverage and to explore an interactive map of the plant, check out www.helenair.com

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