A 99-year-old “dilapidated” Eastwood Multiple Arch Dam above the city of Jackson, east of Sacramento, potentially holds back more than 165,000 cubic yards of mine tailings and soil contaminated with high levels of arsenic, lead and mercury from gold mining operations that ceased in 1942.

The U.S. Army Corps of Engineers released a report in June that said the dam was unsafe and could fail if rain ever returned to the area. They estimated it could take two years to make the needed repairs.

But winter is upon us, and El Nino looms, with the potential to bring record precipitation and cause unprecedented damage. So, California’s Department of Toxic Substance Control (DTSC) began work on a quicker fix and announced what it was doing and why (pdf) this week.

Charlie Ridenour, supervising hazardous substance engineer for DTSC, said, “There is a very serious danger to the City of Jackson if this dam collapses. We are working swiftly to help reduce the chances of a possible catastrophe.” The June report estimated economic harm to Jackson could top $100 million.

The state is constructing a diversion system by creating an embankment 60 feet above the damn to capture storm warm. Pumps will then redirect the water through pipes around both sides of the dam to a new culvert where it will be captured. They hope to complete it by November 23 and that it doesn’t rain before November 24.

The U.S. Environmental Protection Agency (EPA) began an evaluation of the Argonaut site in September 2014, and in March began cleaning up contaminated mine filings in nearby residential areas, including Jackson Junior High School. The June report recommended it be put on the national Superfund list, a special designation for our nation’s finest blighted areas.

The EPA capped an embankment below the school athletic field with concrete to “limit potential exposure by direct contact or inhalation pathways.” Pioneer Elementary is also close by.

ABC10 described the damn as “cracked and crumbling.” But Jackson Mayor Patrick Crew told the station that no one knew how bad it was. “You get scientists and engineers and you look at the problem and go, oh, ooh. ‘This is not what we thought it was,’ ” he said.

One homeowner told ABC10 it didn’t matter what it was. “I think it's a waste of time and effort. I think they should just build on it and get it over with,” Charlie Hetzler said, noting that the old courthouse was built on the filings.   

The dam lays below the 90-acre historic Argonaut Mine, which began producing gold in 1850. It was the site of the state’s worst mining disaster in 1922, when 47 miners, mostly immigrants from Italy, Spain and Serbia, died from fire and toxic fumes under suspicious circumstances.

Jackson is the county seat of Amador County.

–Ken Broder

To Learn More:

State Warns Foothills Dam Could Collapse This Winter (by David Bienick, KCRA)

Dam Below Historic Argonaut Mine Threatens City of Jackson (by Dave Marquis, ABC10 News)

Community Meeting and Upcoming EPA Activities (U.S. Environmental Protection Agency) (pdf)

DTSC to Build a Storm Water Diversion System at a 99-Year-Old Dam Site to Protect Jackson (California Department of Toxic Substances Control) (pdf)