The Biden administration announced Wednesday the addition of a historic Northern California mine to the Superfund National Priorities List — a federal index that ranks hazardous waste site risk and helps in prioritizing cleanup operations.
The Afterthought Mine, located in Shasta County about 200 miles north of Sacramento, produced gold, silver, copper, lead and zinc from 1862 to 1952, according to the Environmental Protection Agency (EPA).
Despite its name — denoting the site’s attachment to a much larger initial claim — Afterthought became one of Shasta County's biggest copper mines. But the property, which changed hands multiple times over the years, also went on to cause environmental contamination for decades beyond its mid-20th-century closure.
Both the mine and the Afterthought Smelter, about a mile downstream, were "in direct contact with surface water" in the adjacent Little Cow Creek, according to the EPA's Hazard Ranking System documentation record.
"The surface water and sediments in Little Cow Creek are contaminated with cadmium, copper and zinc at levels approximately 100 times, 1200 times, and 1000 times, respectively, above the California Toxics Rule Water Quality Criteria for acute risk," an accompanying EPA document stated.
Little Cow Creek, which is frequented by fishing enthusiasts, also hosts a variety of wetland wildlife and has been designated as a critical habitat for steelhead trout, per the document.
Other fish found in the waterway include largemouth bass, smallmouth bass, Chinook salmon, brown trout, brook trout and rainbow trout, according to the EPA.
The agency attributed the widespread metal contamination to waste rock, acid mine drainage and tailings produced via historic mining and smelting operations.
"Remnants of the mine are still present on the mine property, including waste rock piles, adits/portals and the ruins of the mine plant," the hazard ranking document determined.
Since the late 1970s, the report added, multiple sample investigations have been conducted both on the property and downstream by federal and state bodies. And in 2022, the EPA performed an inspection to decide whether the site could qualify for placement on the National Priorities List.
"Other federal and state cleanup programs were evaluated, but no other program has the appropriate authorities or resources to address the site at this time," the agency found.
U.S. West officials have long been pushing for federal action in cleaning up the Afterthought and other abandoned mines across the region.
"Abandoned or inactive mines are responsible for many of the greatest threats and impairments to water quality across the Western United States," Joan Card, a representative of the Western Governors' Association, told members of a House subcommittee in 2006 testimony.
Emphasizing the difficulties associated with "identifying legally responsible and financially viable parties for particular impacted sites," Card noted that "mine operators responsible for conditions at a site may be long gone."
Card named the Afterthought among such abandoned sites, calling for actions such as sealing the site's portals, removing and covering the tailings pond and remediating the access road.
With the Afterthought mine's inclusion on the National Priority List, the EPA has now recognized the site as one of "the nation’s most serious uncontrolled or abandoned releases of contamination."
That list, the agency explained, serves as a basis for prioritizing EPA cleanup funds and relevant enforcement actions.
"EPA is helping protect vulnerable communities from uncontrolled hazardous waste releases,” Michael Regan, the agency's administrator, said in a statement. “We are also contributing to the affected communities’ economic and overall wellbeing by restoring land currently blighted by contamination.”
