EPA Superfund Site

AFTERTHOUGHT MINE

CA | EPA ID CAN000908808

About this site’s exposure pathways: As of May 2025, the Afterthought Mine Superfund site is considered “Insufficient Data to make a Human Exposure evaluation” (HEID). The Afterthought Mine was recently finalized on the NPL on 09/05/2024, and there has not yet been an evaluation of the human health exposure risks.

EPA uses this Human Exposure status when there is insufficient data/evidence to determine whether actual or reasonably anticipated human exposures are occurring, and/or whether those exposures are above acceptable risk-based levels. The planned activities to collect sufficient information to make a human exposure evaluation includes development of a Remedial Investigation/Feasibility Study to assess the extent of acid mine drainage and mine tailings discharging into Little Cow Creek, and developing remedial alternatives as part of a Feasibility Study. EPA currently anticipates that there will be sufficient data to make a Human Exposure determination by December 31, 2028. By this date, a Remedial Investigation will have yielded sufficient data to adequately characterize potential risks to human health and the environment.

Currently, EPA suspects that only trespassers are at risk of direct contact with contaminated waste at the site. This does not necessarily mean that unacceptable exposures are occurring, however. If you live near this site or are trespassing, please avoid all acidic drainage coming from mine tunnels and non-vegetated areas because those areas typically have high concentrations of metal contamination. Adhere to all posted signage and access restrictions to minimize risk of exposure to contamination.