CASE STUDY: UTILIZING PASTE TECHNOLOGY FOR RECLAMATION OF THE UTE ULAY UPPER TAILINGS IMPOUNDMENTS, LAKE CITY, COLORADO 1

The Ute Ulay Mining complex, located approximately five miles west of Lake City, CO is an inactive Ag, Au, and Zn mining/milling operation that operated from the 1880's until the 1970's, and sporadically into the mid 1990's. During operation, milled tailings were pumped upstream from the mine/mill site in a sluice box and deposited into five tailings impoundments. The tailings impoundments comprised 13,000 yd 3 , on 6 acres of public lands managed by the Bureau of Land Management (BLM). Prior to reclamation, windblown tailings from the impoundments exposed the public to potentially harmful dust, the tailings from the lowest pond washed into Henson Creek during high flow, and Zn, Pb and Cd leached into groundwater through the unlined tailings ponds. The objective of the reclamation was to mitigate the risk of human exposure to air- borne dust, and to protect surface and groundwater sources from further contamination from the tailings impoundments. Reclamation of the mine and mill waste materials was completed using cementatious paste technology. All waste materials were screened and separated on-site, and the fine-grained waste materials were mixed with cement and water to form the paste. The repository was constructed using a layered design, with paste forming the base and cap, and coarse waste materials placed as a middle layer within the enclosing paste. Following repository completion, the site was graded, drainage channels were constructed, groundwater-monitoring wells were installed, and six acres were revegetated. Reclamation was completed in October, 2009, with maintenance in 2011. Following three growing seasons, the vegetation community is healthy, with minimal weedy species, and no noxious weeds. The surface water quality in Henson Creek indicates a slight reduction in Zn and Cd levels, and other metal concentrations in the groundwater have declined by over an order of magnitude.