Abandoned and covered entrance to mine site

Abandoned Mines Preliminary Assessments and Removal Investigations


California, USA

There are hundreds of abandoned mines on Bureau of Land Management property in California. SLR was retained as the subject matter expert to assess potential impacts on human health and environment posed by tailings and mine waste at three of these abandoned mines. These mines were abandoned at least 70 years ago.

Issues at these abandoned mines vary. One southern California location has thousands of tons of tailings from a Merrill-Crowe cyanide leach process that were released to the local watershed. A second Southern California location with former onsite crushing has residual waste rock and significant exposures of mineralised rocks. A Northern California site has a caved-in mine adit that is continuously draining arsenic affected mine water and may be accumulating hydraulic pressure behind the caved materials, creating risk of a hydraulic blowout.

Our Role

  • Subject matter experts in remediation of mining legacy issues and California regulations.
  • Develop and execute sampling and analytical workplans.
  • Develop remediation approaches for residual tailings and mine waste. 
  • Develop engineering solutions for mitigation of potential hydraulic blowouts from caved in adits.
  • Prepare human health and ecologic risk assessments.


  • Identified mine waste vs. tailings or native materials.
  • Conducted research into the previous operations, facilities, and pollutant sources of each location.
  • Provided engineering solutions for avoidance of potential hydraulic blowout of caved in mine adit.
  • SLR expertise in the California regulatory programmes is key to efficient scoping and performance of the project.

Additional Information

SLR has and continues to support Ahtna Environmental as mining subject matter experts and knowledge of California mine-related regulations. 

Want to know more?

If you have any questions, or would like to discuss a project, our team would be happy to hear from you. Find out more