Geophysical Identification of Potential Groundwater – Surface Water Interactions in the Bonita Peak Mining District, San Juan County, Colorado
This report includes the results and interpretation of geophysical investigations to aid in the location, identification, and conceptual site model (CSM) development of the near surface groundwater and surface water hydrology of the Upper Cement Creek and California Gulch of the Animas Rivers within the Bonita Peak Mining Districts (BPMD). Mine influenced water (MIW) from numerous mine adits within the BPMD has altered the geochemistry and ecology of these ground and surface waters. Many studies of varying scales have investigated the geology, hydrogeology, geochemistry, and aqueous chemistry of these adits and impacted areas. Field investigations using non-invasive geophysical methods were conducted in the summer of 2019 to aid in identifying potential groundwater inputs to these streams and further the CSM of the near surface within and along these streams.
Two field deployments were completed in August and September of 2019. In August 2019, Phase 1 was completed using multifrequency electromagnetic induction (EMI) and thermal infrared imaging (TIR) to measure the bulk electrical conductivity, magnetic susceptibility, and the temperature response at known and suspected groundwater seeps into the Upper Cement Creek and California Gulch stretches of these alpine streams. Results and interpretation from Phase 1 identified stretches of these streams for detailed fiber optic distributed temperature system (FODTS) monitoring of the temperature dynamics for sub-meter identification of potential groundwater – surface water interactions during Phase 2. Phase 2 included additional EMI measurements, FODTS measurements, and repeating some Phase 1 measurements for improved data quality.
The results from both Phase 1 and Phase 2 interpreted in concert with the synoptic geochemical sampling (USGS data release: https://www.sciencebase.gov/catalog/item/5f18a30082cef313ed84879b ) event during Phase 2 provided detailed near surface electrical conductivity and magnetic susceptibility mapping, discrete TIR imaging, and several kilometers of FODTS data. These data were georeferenced and used to identify potential groundwater seeps into these streams. The results reveal a very complex near surface geology and hydrogeology regime. Seeps are classified and spatially correlated to the EMI, TIR, and geochemical sampling results.
This report is a thorough compilation of the geophysical field efforts in the summer of 2019, the data processing, and interpretations of these data. These data alone should not be used for final interpretations of the complex hydrogeology within these alpine systems. Rather, these data should be combined with other known data from various investigations to further refine the CSM and guide decisions for future investigations, watershed protective measures, and other site decisions. Geographical information system (GIS) layers of these results are available to project managers for such integration and combined interpretations.
Impact/Purpose
This report details geophysical identification and mapping of groundwater inputs to Upper Cement Creek and the California Gulch section of the Animas River in Silverton, CO. These are within the Bonita Peak Mining District (BPMD) where active and legacy hardrock mining activities release mine influenced water (MIW) as groundwater that travel to surface water bodies. This MIW is often of low pH and alters the biogeochemistry of these waters, alters the surface water ecosystem, and sometimes renders the surface water contaminated with elevated metals. Identifying the zones where this MIW groundwater enters these high alpine streams will be used by remedial project managers, stakeholders, and site investigators to guide the remediation and protection of the River. The report serves the BPMD community and demonstrates the unique application of geophysical methods for understanding groundwater – surface water interactions in an alpine environment impacted by MIW.Citation
Werkema, D., N. Terry, M. Briggs, E. Rutila, AND S. Dyment. Geophysical Identification of Potential Groundwater – Surface Water Interactions in the Bonita Peak Mining District, San Juan County, Colorado. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-24/007, 2025.Download(s)
- WERKEMA_BPMD_EXTERNAL REPORT_FEB_2025_FINAL_508 COMPLIANT.PDF (PDF) (NA pp, 16.7 MB, about PDF)