243 Hydrogeology (Posters) II

TOMMYKNOCKER HEAVEN: ATTEMPTING QUANTITATIVE HYDROGEOCHEMISTRY IN THE LEADVILLE MINING DISTRICT AND ITS HINTERLAND

Paper number: 243-17
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The Leadville Mining District contains many hundreds of kilometers of mine workings as deep as nearly 300 m below ground as well as three major drainage tunnels many kilometers in length. The district is part of a U.S.EPA CERCLA investigation. Operable Unit 6 (OU6), which is within the California Gulch SUPERFUND site, includes mine-related sources of heavy metals that occur within and below Evans Gulch, an east –west trending, intermittent stream valley in the northern portion of the district. Waste-rock piles occur within upper Evans Gulch contain low grade ore, which is easily oxidized when snowmelt and rainfall infiltrates resulting in low pH and subsequent transport of metals such as zinc and cadmium. During each years snowmelt this water discharges into workings that connect with the Leadville Mine Drainage Tunnel (LMDT). Discharge from the LMDT portal is at the US BOR treatment plant.

Three large mine pools exist beneath OU6 and were created when the workings associated with Fryer Hill, Carbonate Hill and Downtown sub-districts filled after mining declined in the 1930’s. The mine pools are connected by workings and hold a total of approximately 4 million cubic meters of water. Prior to 1953 these mine pools were drained primarily by Canterbury Tunnel to to the north of Evans Gulch and intermittently through shafts in lower California Gulch to the south of Evans Gulch. Since 1953 the mine pools have been drained primarily through the LMDT. In recent years there has been a growing concern that collapses within the LMDT have significantly reduced its efficiency as a drain tunnel. Source-control techniques (including plugging and /or backfilling tunnels and shafts, grouting water inflows to tunnels and shafts, and segregation of “clean” inflows) are being considered to: isolate contaminated mine pool waters, divert clean inflows around mine workings, reduce the volume of discharge from tunnel portals and reduce the risk of large unregulated discharges into surface streams.

Wells have been constructed along the LMDT and in the bedrock nearby. Multiple tracers, including stable isotopes, tritium, cation and anions have been used and quantitative tracing with fluorescent dyes in the mine workings and in the LMDT. Additional evaluation will be done using end member mixing analysis and cluster analysis.