2011-09-27_REVISION - M1990057 (10)

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Geologic Setting UMC concurs with CTL that the TSF is in an area of a temporary perched water condition, prevalent during spring melts and wet years. As discussed in CTL Thompson's April 1990 Report, Permeability Study Tailing Pond Area Leadville Mining and Milling Corporation Mill near Leadville, Colorado, the tailings disposal area soils are colluvial. There appear to be two colluvial types, clays with lower permeabilities and gravel lenses with higher permeabilities. Most of the tailings disposal area is over the lower permeability clays (k =2ft/yr to 7ftlyr). The northern TSF area appears to be over a 1.5ft thick gravel lens with a permeable of 5000ft/yr at 8 feet of depth. Other gravel lenses have permeabilities of 230ft/yr. A monitoring well and several permeability test holes from 20yrs ago still exist within the existing TSF area. UMC samples /observes the monitoring well quarterly. Additionally, UMC has sporadically observed permeability test wells over the last several years. All but one of the permeability test wells will become part of the TSF impoundment. Monitoring well MW -1 (OH -1 in CTL Thompson reports) shows minor water levels in the spring, and then is dry, or at best damp following precipitation events. MW -1 is completed to a depth of 9685 (9ft below the bottom of the impoundment) and is completed in a layer described as "sand, dense, very clayey, gravelly, moist, red -brown (SC) ". UMC monitors this well quarterly and reports the results in the annual report. All but one sample period has reported no water. Permeability test holes PT -2, located just south of the existing TSF disturbance and in the northern portion of the proposed TSF disturbance, has shown water levels during spring melts with the water dissipating over time. PT -2 is completed to a depth of 9693 feet (lft below the bottom of the impoundment) and is completed in a layer described as "gravel, dense, very clayey, very sandy, moist, red -brown (GC) ". PT -2 averages a permeability of 2ftlyr. Based on random observations over 3 years, UMC's concludes water infiltrates this hole in the spring and dries out in the summer. PT -3, located east of MW -1 and to the southeast of the proposed TSF disturbance, has not shown water levels during spring melts. PT -3 is completed to a depth of 9701 feet (7ft above the bottom of the impoundment) and is completed in a layer described as "gravel, dense, very clayey, very sandy, moist, red -brown (GC) ". PT -3 averages a permeability of 7ft/yr. Recently drilled TH -2, located on the existing TSF disturbance embankment, ended in water during the spring melt. TH -2 is drilled to a depth of 30 feet from the top of the existing embankment (12ft below the bottom of the impoundment) and ends in a layer described as "sandy clay overlaying clayey sand and gravel ". TH -2 permeability tests were not conducted. TH -2 encountered water at 25 feet, and subsequent measurements have shown water at 28 feet of depth. UMC believes the above test holes all confirm colluvium/alluvium within the TSF area, yielding unsorted sediment of varying particle sizes ranging from boulders to clay and areas of high and low permeability. Snowmelt and storm runoff water saturates the hillside and colluvium in wet periods and migrates through the colluvium/alluvium, creating the observed temporary perched M1990 -057 September 27, 2011