Geochemical and geotechnical evaluation of the Bulldog Mine tailings impoundment

The Bulldog Mine was operated as an underground silver mine and mill in southwestern Colorado. As part of reclamation planning, the source characteristics of the tailings were evaluated for their potential to impact groundwater resources. This investigation included (a) sampling and geotechnical laboratory testing to assess the consolidation and flow characteristics, (b) geochemical testing to assess acid generation potential, including field testing to measure oxygen content and diffusion characteristics, and (c) pore water analyses and determination of leaching characteristics of the tailings. Results of the investigation showed that after tailings disposal ceased, infiltration of precipitation combined with low tailings hydraulic conductivity has maintained the tailings in a saturated, reduced condition. These conditions have influenced the geochemical and consolidation behavior of the tailings. Seepage from the tailings is at a low rate and of relatively good quality compared to groundwater standards, and is likely to remain so under the planned reclamation scenario.