Residents of Dewey-Humboldt at an open house Saturday learned about the Environmental Protection Agency's (EPA) remediation efforts for the area's Iron King Mine/Humboldt Smelter Superfund Site - a location declared a Superfund in 2008.
EPA Remedial Project Manager Jeff Dhont presented an overview of the area's historical mining and smelter activities that created large amounts of tailings and slag. Tailings are wastes left over after saleable metals are removed from mined ore. Around 1964, part of the mine's tailings pile collapsed, causing contaminants to flow into the Chaparral Gulch, pass downstream, cross Highway 69 and mix with tailings from the Humboldt Smelter.
Now, Dhont said, investigators will take a closer look at the Area of Potential Site Impact that includes the former Iron King Mine property, the former Humboldt Smelter operation across Highway 69 and the areas north of Prescott Street, east past the Agua Fria River and south of the smelter property, to name a few.
"We can't make it all go away, but looking at the health impacts, we need to select a remedial action to clean up the site," Dhont said, referring to the contaminants. He further explained that the investigative team must determine just how toxic the site is by looking at the health and exposure risks, and pick a remediation option with the public's input. The team is still in the remedial investigation stage, he said.
In the coming months, residents will notice plenty of digging activity along the site's landscape, specifically sonic bore rigs designed to dig deep into bedrock. Several areas are slated for digs, including where 3rd Street in Humboldt crosses the Chaparral Gulch where visible mine tailings exist. Workers will also dig the Middle Chaparral Gulch, west of the Humboldt smelter and a large tailings depression south of Prescott Street. The team will drill and sample the borings in addition to adding11 groundwater monitoring wells at depths from 6 to 125 feet.
In addition, the team will collect soil samples in the residential site areas that either did not allow access or were not available in the 2009 study. Dhont said investigators will calculate the sample results using statistics. If a sample tests unusually high for arsenic, for example 500mg/kg, "then we know that something else is going on, but we don't expect to see something that high," Dhont said. The EPA's Low Risk Range for arsenic levels in soil, specific to the Superfund site, is 0 to 145mg/kg.
As to how the contaminated soils may be affecting residents on or near the site, Dhont explained arsenic bioavailability - the percentage of arsenic that remains in the body after ingestion. The area's residential bioavailability has been analyzed at 20 percent, but is not locked in. Investigators will study exposure and risk for each location within the site.
"We're going to make sure we're right about that. The highest we think is 60 percent," Dhont said.
The team then will conduct a feasibility study and make the proposed remediation plan public.
"The 2009 Remedial Investigation report did not answer all of the questions we needed. We are amending it," Dhont said. "The new report should be available this summer."
Clean-up will be similar to past efforts and already the EPA has removed nearly two feet of topsoil from a dozen yards on Sweet Pea Lane and East Main Street, where higher levels of arsenic and lead existed. Workers moved more than 7,000 tons of soil to the old Iron King Mine site, planted native seeds to stabilize the tailings, and applied soil fixative to ash piles at the defunct Humboldt Smelter site to reduce dust.
"Most of the Superfund work we are looking at is much lower than acute toxic levels that would immediately make you sick," he said.
Representatives from the Arizona Department of Health Services and the University of Arizona Superfund Research Program spoke about exposure at the site, for example skin contact with soils; ingestion, such as when children don't wash their hands or home-grown vegetables are washed improperly or by inhaling dust; and drinking water that tests high in arsenic or lead.
In the recent Metals Exposure Study in Homes (MESH) several nearby residences were tested and volunteers submitted blood, urine and toenail samples. Researchers also tested soil and tap water samples. Researchers found a wide variation in levels, said Miranda Loh, a representative of UA Superfund Research. Physical sample results were low - only 1 household in the MESH study tested over 15ppb in lead and the well water tested for arsenic was either at or above safe drinking levels, she said.
Representatives urged private well users to test their water once every three years to determine chemical levels, and once a year for bacteria.
For residents on the Humboldt Water System, the next lead compliance monitoring study is due Sept. 2014, to check chemical levels in the drinking water.
Important contact information:
Environmental Protection Agency
Remedial Project Manager - Jeff Dhont 415-972-3020
Community Involvement Coordinator - Amanda Pease 415-972-3068, toll free 800-231-3075
Arizona Department of Environmental Quality Community Involvement Lead
Remedial Projects Section - Wendy Flood 602-771-4410, toll free 800-234-5677.
For help understanding well water test results, call Jennifer Botsford with the Arizona Department of Health Services at 602-364-3128.
For information on groundwater wells and water treatment systems call the ADEQ at 602-771-4641. Call the Humboldt Water System at 602-771-4641.
For property access permission from the EPA research team (Consent for Access to Real Property), call the EPA toll-free line at 800-231-3075 or Amanda Pease at 800-231-3075.