2009-09-25_PERMIT FILE - M2009076 (22)

Home Browse Search

• 6.3.3(1)(i) Impacts to groundwater will be controlled by the recycling of leachate to the process stream, the sealing of joints and fractures in bedrock by the clay content of the hydraulically classified waste stream, and the chemical control of the process water quality as enumerated in 6.3.3(1)(m). A stormwater management plan is created as follows for the construction and operations of the disposal site: 1. Construct sedimentation basin. 2. Construct earthen lined diversion ditches and connect natural diversion channels to sedimentation basin. 3. Construct leachate collection barrier. 4. Rip-rap and/or vegetate tailings dam face using appropriate controls, i.e. jute netting and/or hydra mulch using high-altitude roadside seed mix. Temporary storm water management controls using silt fences and/or straw bales will be used during all phases of excavation. Hydrologic Data Clear Creek is the significant surface water feature within 2 miles of the proposed facility; located 2 ,800' to the south and 1,000' in elevation below the Tailings Impoundment affected area. There are no perched zones or traditionally defined aquifers in this mountainous area. The site is completely composed of crystalline Precambrian rocks, i.e. gneisses and schists, and tertiary intrusive rocks such as quartz monzonites overlain by 0-24" of unconsolidated material. Ground water wells within one mile of site boundary are detailed in a map attached at the end of this Exhibit C, sourced from the Colorado Division of Water Resources. It shall also be noted that the groundwater in this area is is unclassified per the Colorado Division of Water Resources. Unconsolidated materials, soils, of between 0 and 18"-24" overlay the crystalline rocks. The rocks themselves have essentially no porosity or permeability. Random, in-identifiable fractures due to jointing and faulting provide the only groundwater transmissivity and relative porosity. The site is underlain by numerous mine openings, the most important of which is the workings of the Shaffer Mine. The vein of the Shafter Mine outcrops within 100 yards of the proposed disposal area, strikes N 40-600 W and dips 78-80° NW. The Shafter vein (along with the Great American and Edgar) is cut by the Big Five Tunnel at 4,250 feet from the portal, and at a depth of 893 feet on the dip of the vein. The mine workings effectively drain the area underneath the site. Refer to USGS Bulletin 1208, Plate 3, Geologic Section Along the Big Five Tunnel Idaho Springs District. Colorado at the end of this Exhibit C. Another example supporting this is the Colorado School of Mines Edgar Mine Facility (approx. 350' south of the proposed Tailings Impoundment). After a meeting with than on August 31, 2009, it was learned that their mine is "dry". So "dry" in fact that they are working on permitting a well on premises to supply a marginal water supply for drilling operations to keep the dust down. The starting elevation of their well is 7,793' and the borehole was drilled to-254'. Water was determined at -172'. This elevation, 7,621', just so happens to match the Big 5 Tunnel elevation. Safe to say another example of the drainage in this area. A copy of this well log is attached in the appendix of this Exhibit C. Hydraulic conductivity for the undisturbed rock types present at the site, in-situ before mining, ranges from 10"2 - 10?2 gallons per day per square foot (as reported by Freeze and Cherry (1979)) due to joints and fractures in the rock. These joints and fractures will be sealed with hydraulically applied clay that is part of the waste stream. The existence of the underground mine workings provide a direct hydraulic conduit for groundwater beneath the site. The Big Five tunnel, the major drainage for the area, lies 1,000 feet directly below the site. The Big Five Tunnel drainage is monitored, collected, and pumped to the Argo Tunnel Treatment Facility located in Idaho Springs. It produces on average, 35 gallons per minute. According to the most current FEMA Flood Plain Map (reference FEMA Map #08019C0093D effective March 19, • 2007) the proposed disposal site is in Zone X. Zone X is defined as follows: