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-2- 4. The original application and the study indicates that no leachate will be generated on an average annual basis. However, a shorter term analysis would be expected to produce leachate. To predict the short term leachate potential, the study presents an analysts on pages 5 through 8. Several concerns were noted with the analysis: A. The study assumed a 1.7 inch rainfall event as the leaching source. It would be appropriate to indicate what rainfall return event this is representative of and how this compares to an average snowmelt. B. The volume of infiltrating runoff 1s calculated as 2,065 cubic feet. However, this assumes that the rainfall is uniformly distributed over a 24-hour period which is rarely the case. Also, in order for the 0.023 dilution factor to occur as listed on pages 5 through 9, it is assumed that the peak runoff discharge coincides with the peak leachate discharge which may not occur. 5. The ore piles are built on three feet of clay with a six inch cap. Even with close controls, the cap may rupture due to settling or construction procedures. If water enters the pile, it may be contained internally until it reaches a static pressure level that causes seepage from the base of the pile. This could happen during a dry time of year and would result in the release of leachate with a long retention time. The application should discuss the potential of this scenario occurring and suggest mitigation measures. Would a pile drain and/or deeper clay cap be feasible and appropriate for the pile? 6. No hydrologic monitoring was proposed in the study. I would recommend one or two wells be placed in the piles. The wells would be useful for verifying leachate quality, identifying water levels in the pile (if any), and serve as access to dewater the pile if necessary. The applicant should propose a hydrologic monitoring plan for the site that would verify hydrologic predictions and identify any impacts. 7. The operator proposes to retain the water treatment pond and a pit that could form a lake. Both structures will impound a considerable amount of water. The State Engineer's Office may need to be contacted to assess water rights related impacts. If the operator has looked into this item, any response would be useful. Reclamation The reclamation plan calls for leaving the south pit as a lake. However, according to the text, there is some doubt as to whether the pit will contain water year around. The applicant should indicate whether any actual pumping rates or even rough field observations exist that could substantiate the contention that a lake could form. Has water quality analysis been done on water contained in the pit? Both quantity and quality data would be very useful in assessing the need for pit revegetation, the usefulness of the pit for wildlife, and hydrologic impacts.