USE OF A CONCEPTUAL SITE MODEL AND INNOVATIVE TECHNOLOGIES TO DELINEATE ACID MINE DRAINAGE SOURCES, LITTLE JAMES CREEK WATERSHED, COLORADO

Delineation of surface and ground water acid mine drainage (AMD) sources is essential for effective remediation at mine sites. Traditional methods for identifying source contributions can be costly and inefficient. In support of the U.S. Environmental Protection Agency (EPA) Office of Superfund Remediation and Technology Integration Brownfields Technology Support Center and EPA Region VIII, Tetra Tech EM, Inc., has designed a conceptual site model (CSM) which consists of dynamic work strategies and innovative technologies for delineation of AMD sources at the Argo and Evening Star Mines located in the Little James Creek watershed, Boulder County, Colorado. At these sites, surface water and bedrock sourced groundwater are contaminated by AMD from mine shafts, adits, tailings, and waste piles within the Little James Creek watershed. To develop an accurate CSM, data from previous investigations in the watershed have been compiled and reviewed. Data gaps influencing CSM accuracy were identified and data collection strategies proposed to refine the model. The CSM includes an assessment of potential remediation strategies and identifies data collection efforts required to evaluate the feasibility of each remedial option. Technologies selected for use include radon, intrinsic tracers, trace metals, and XRF whole rock analysis, reaction pathway modeling, petrography, and real-time well and stream monitoring. The effectiveness of proposed remedies is contingent on understanding relative contributions from surface and groundwater AMD sources in this fractured flow system. Current proposed remedies for the Argo and Evening Star Mines focus on surface water improvements, including adit and mine shaft plugs, tailings piles and waste rock consolidation, trenching and capping, and use of flow cells for water neutralization prior to discharge. However, remediation of solely surface water AMD sources may be inadequate when primary AMD sources are associated with groundwater discharge to surface water. Therefore, additional remedies to constrain groundwater contamination may be necessary.