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May Day /Idaho Mine — Comments to Selected Work Plans from the August 2011 Submittal, <br />Exhibit D <br />Page 3 <br />August 22, 2011 <br />b. The plan view indicates two 24 -inch CMPs are required. Is it one or two? <br />c. The typical ditch section A -A shows a 2 -foot bottom width. The FlowMaster® <br />ouput after Table U -6 (Attachment U -3) uses a 4 -foot bottom width. Which is it? <br />d. The placement of the rock check dam immediately downstream of the culvert(s) <br />should be placed far enough downstream such that it does not create a tailwater <br />condition for which the culvert(s) are not designed leading to overtopping flows. <br />Attachment D -4, Chief Drainage and Portal Work Plan and Lamb Affected Area Little <br />Deadwood Gulch <br />11. The approach to the drainage reclamation in the vicinity of the Chief Portal is <br />unacceptable. On June 2, 2011 DRMS met with George Robinson on site and <br />specifically discussed the approach Wildcat should implement in the reclamation of Little <br />Deadwood Gulch in the vicinity of the Chief Portal. We agreed that all mine waste needs <br />to be removed from the drainage. There are many reasons for this approach. The <br />primary reason is to ensure the invert of the reclaimed channel is at an elevation <br />sufficiently low enough to pass the peak flow from the 100 -year, 24 -hour design storm <br />without allowing any flows into the chief portal. The proposed design in the work plan <br />uses a narrow berm to segregate gulch drainage from the portal. This is not a long term <br />solution. The berm will eventually fail or erode away, subjecting the portal to flows from <br />the drainage. DRMS understands that CDPHE has also required all mine rock be <br />removed from the drainage in this area. The applicant is required to resubmit the entire <br />work plan for the Little Deadwood Gulch in the vicinity of the Chief Portal to <br />demonstrate how all the mine waste will be removed. <br />Attachment D -6, Augmentation Pond Work Plan <br />12. Page 3, Construction. The first bullet references Attachment D -6, Figure D -1 for <br />stormwater management controls. Neither Figure D -1 nor D -2 show any BMPs, nor can <br />the augmentation pond be considered a stormwater management control. Please provide <br />stormwater management control locations and type on Figure D -2. <br />13. Page 3, Construction. Item 3 discusses a two -foot (minimum) keyway and a liner for the <br />pond. Neither of these is shown in Figure D -1 or D -2. Please provide enough detail to <br />demonstrate how the liner is installed and at least a conceptual detail of the keyway. <br />14. Page 3, Construction. Item 5 states cut and fill slopes will not exceed 2:1. This is <br />apparently inconsistent with section A on Figure D -2. If the pond slopes are 2:1 as stated <br />on page 2 (Background), the cut slope above elevation 8760 as shown on Figure D -2, is <br />clearly steeper than 2:1. Furthermore, the second to last paragraph on page 8 of Exhibit <br />6.5 discusses slopes not being steeper than 1:1 without DRMS approval, which is not <br />only incorrect, but inconsistent with Exhibit D, Attachment 6. DRMS will require slope <br />stability analyses addressing a) empty /dry conditions, b) full capacity conditions, and c) <br />rapid draw down conditions for any embankment design to impound water with slopes <br />greater than 3H:1 V. <br />15. Page 3, Construction. Item 7 states "the suitability of onsite materials will be evaluated <br />as part of the geotechnical stability evaluations... ". DRMS requires this new information <br />c:\documents and settings\sssUocal settings \temporary internet files \content.outlook \a5ghsruj \exhd - <br />selectworkplancomments mem22aug11.docx <br />