WHAT THE HECK IS HAPPENING TO MINE POOL WATER AT LEADVILLE?

The hydrogeology of the Leadville Mining District is complex and presents a serious challenge when the goal is to describe what and what may not be “mine pool water” in the presence of shallow and deep ground water and seasonal recharge. This catchment is at an altitude of more than 3,000 - 4300 m asl and thus contains a significant portion of snow and ice that, until this summer, was essentially perennial. A CERCLA investigation involves California Gulch, an essentially perennial surface stream, that prior to construction of the Leadville Mine Drainage Tunnel (LMDT) also involved ground water that was part of the mine pool. Mine Pool Water currently discharges through the LMDT to a treatment plant operated by the U.S. Bureau of Reclamation, but unfortunately the state of repair of this tunnel is questionable at best. Data from the mine pool from the past decade show ominous rising ground-water levels and suggest that the efficiency of the drainage tunnel is declining. Unfortunately the rising ground water levels are not accompanied by a great amount of data and although it seems that mine pool waters may actually be rising, it is not clear why, since snow pack (and recharge?) has been declining for years. Using tracing and tritium data it appears that the LMDT waters are being mixed with surface waters, however, even though the largest amount of snow melt occurs in the spring, hydrographs seem to peak in September. Stable isotope data suggest that for the entire summer, frozen precipitation is the source of the recharge - possibly explained by the nature of recharge from the high altitude catchment area. Isotopic data collected at different times of the year show shifts in fractionation that sometimes suggest rapid recharge of mine workings in the “vadose zone,” significant components of high-altitude surface water, and possibly transfer of other water from a catchment area that discharges through the adjacent Yak Drainage Tunnel. Possible methods of measuring the relative contributions of these waters may seem laborious but this may have to be done to even partially understand what is what.