Emergency Response to Gold King Mine Release Incident (2015)

U.S. Environmental Protection Agency, Region 6, under subcontract to Weston Solutions, Inc.


  • Surface water, groundwater, and sediment sample collection for total and dissolved metals.
  • Use of multi-parameter water quality instruments
  • Multiple sampling areas and potential exposure areas
  • Involvement with local, state, and federal emergency response agencies

The  U.S. Environmental Protection Agency (EPA) was conducting an  investigation of the Gold King Mine near Silverton, Colorado in August  2015 to assess the on-going water releases and treatment options for the  inactive mine. During excavation conducted as part of the investigation  on August 5, 2015, pressurized water began leaking above the mine  tunnel. Approximately three million gallons of heavy metal-laden  wastewater spilled into Cement Creek, a tributary to the Animas River.  Colorado and New Mexico state officials declared a state of emergency  and upheld restrictions on residential well water use and recreational  river use. Farmers refrained from using irrigation ditches for livestock  and agricultural.  In August 2016 John Cassels mobilized to the  disaster area as a part-time employee of Avatar Environmental,a  subcontractor to WESTON under their Region 6 START (Superfund Technical  Assessment and Response Team) contract. Once onsite, Cassels joined  teams of technicians which collected surface water and sediment samples,  assessed river water quality.

River monitoring efforts  included the daily collection and analysis of surface water and sediment  samples at nine locations along the Animas and San Juan Rivers. These  nine locations were strategically located upstream of water intakes  which support the towns of Aztec, Farmington, the Lower Valley Water  Users Association, Morning Star Water Supply System and the North Star  Water Users Association. Surface water samples collected were analyzed  for total dissolved and suspended solids, total metals, pH, alkalinity,  and anions. In addition, in-situ measurements were recorded and include  pH, ORB, conductivity, turbidity, and dissolved oxygen. Sample site  photographs looking upstream and downstream were taken daily to document  river conditions for each sample.