Polluted Argonaut Mine in Jackson on shortlist of EPA Superfund sites

An old hard rock mine near downtown Jackson is so polluted that the U.S. Environmental Protection Agency has put it on a list of eight places nationwide that may be tagged as federal Superfund sites.

The 65-acre Argonaut Mine is currently an abandoned hard rock gold mine just west of downtown Jackson. The mine processed ore and disposed of tailings – the mined rock left over after gold is removed – at the site from the mid-1800s to 1942. That activity introduced what the EPA has characterized as extremely high levels of arsenic, lead and mercury to the site.

The site is now regarded by the EPA as a special-case scenario because the mine is near Jackson Junior High School, homes and an aging dam whose collapse would pose serious environmental risks, according to Jared Blumenfeld, regional director of the EPA.

The EPA estimates that the 100-year-old Eastwood Multiple Arch dam holds back 1 million cubic yards of contaminated material. The dam has been deemed structurally unstable.

Blumenfeld said the EPA has already taken action on the highest contamination at the site. That work included a $3 million cleanup of 11 residential yards and a vacant lot. It also involved installing a protective cover on steep soil slopes at Jackson Junior High last year.

The Superfund program, created in 1980, investigates and cleans up complex, uncontrolled or abandoned hazardous waste sites that pose health risks to humans and the environment. Inclusion into the Superfund program adds a site to a federal National Priorities List, making it eligible for federal funding for long-term, permanent cleanup.

The funding is crucial for sites where no owner can be established to pay for cleanup, as is the case at the Argonaut Mine. The state would contribute 10 percent of the cleanup costs for a Superfund site, Blumenfeld said.

The California Department of Toxic Substances Control, the lead state agency in the cleanup plan at the site, is evaluating options for the expansion of cleanup at the site.

Toxic chemicals have been an ongoing concern at the site with state investigations in 1987, 1992 and 1993 showing high levels. A 2008 state study found that barren soil in a 5-acre area at the property had arsenic concentrations of 39,000 parts per million. That level is far above the naturally occurring background level for arsenic, which is 20 ppm.

The state is also seeking to address the dam issue. Last November, the DTSC installed a $1 million stormwater diversion at the dam in anticipation of heavier winter rains due to El Niño conditions, said DTSC spokesman Jorge Moreno.

A weather station installed at the site shows a total of 24 inches of rain since the station was installed, Moreno said.

Currently, the canyon behind the dam is filled to within 3 feet of the top of the dam. “The pumps installed in November were turned on and are working,” said Moreno.

The Argonaut mine became one of the more notorious mine sites in California when 47 miners perished in a mine fire 4,650 feet below ground in 1922. It remains one of the worst gold-mining disasters in the state’s history.

Edward Ortiz: 916-321-1071, @edwardortiz