2016-06-01_REVISION - M1980244 - Laserfiche WebLink

Home Browse Search

Cresson Project – AM-11 Adequacy Review Page 4 May 03, 2016 (Revised May 31, 2016) to the diatreme beneath. However, it appears that the till permeability is too low to allow at least this high infiltration rate water to pass vertically to the diatreme, causing the toe seepage.” Plate 17 – Impact Potential of ECOSA on Grassy Valley shows the northern portion of ECOSA to be located outside of the diatreme. Considering that the ECOSA underdrain system is not functioning properly to drain ECOSA infiltrated water east into the diatreme, the potential for impact to Grassy Valley appears to be high. How will you work to minimize seepage and potentially impacted groundwater flow from ECOSA into Grassy Valley? At the end of Item #1, the text states “Seeps from the toe of ECOSA, if any, will be sampled, characterized, and treated if necessary.” Please provide more detail. What is the current estimated volume of seepage from ECOSA to outside of the diatreme? Where and how often will sampling occur? What parameters will be measured? How will the seeped water be treated if necessary? Will the seeped water be captured and/or diverted in any way? As the ECOSA is loaded to the AM-11 proposed 10,960 ft amsl height, will this increased load intensify seepage from the ECOSA toe? It appears that the underdrain system may not be a long-term (or short-term) solution to preventing impacted groundwater from leaving the diatreme infiltration zone. Are you working on an alternative long-term solution to this problem? 3.6.7 Formation of Pit Lakes in Worked Out Surface Mines  Page 19: The text states that the lowest planned mine floor elevation is 9,200 ft amsl (North Cresson [Globe Hill]), which is 1,000 feet above the water table in this location in CPC14-3 (8,285 ft amsl). Accordingly, no pit lake can form, no impact will occur, and no mitigation will be required.” Although the North Cresson Mine is located mostly within the northern eruptive center of the diatreme, its southern portion (Schist Island) is located in the low-permeability Precambrian rock curtain that separates the north eruptive center from the western and eastern eruptive centers. Is it possible that the Precambrian rock curtain could work to trap water infiltrated into the northern eruptive center area at least temporarily, resulting in some pit inflow? 3.7 Conclusion  Page 19: Under Item #2(b), the text states “while it is not expected that there will be any environmentally significant impacts (from temporary flow from toe of ECOSA during periods of high infiltration), it is proposed that toe seepage be diverted to runoff control ponds or collected for use in the mining process.” Please provide more detail on the surface water structures to be constructed for this purpose, including their design and location(s). The locations of these structures should be shown on a map of the ECOSA area with sufficient detail.  Page 19: Under Item #2(c), the text states “upon reclamation of the project, the valley leach facilities will be punctured and any seepage through the spent ore will be directed to the diatreme. This will result in an increase of the flow to the diatreme of 119 gpm over the pre-mining flow.” Is the pre-mining flow considered to be 7,000 gpm (as listed under 3.4 Ground Water, Item #3 on Page 7), or an average of 1,691 gpm (as listed for the time period of 1992-2002 in the small table shown on