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Engineering Analytics,Inc. 1600 Specht Point Ad. Suite 209 - Fort Collins,CO 80525 .. 970.488.3111 www.EngAnalytics.com ATTACHMENT D October 26, 2016 Project No: 110385 Mr. Robert Noren, P.E. Cotter Corporation (N.S.L.) P.O. BOX 1750 Canon City, CO 81212 Subject: Responses to CDRMS Comments Schwartzwalder Mine DRMS File No. M-1977-300; Technical Revision (TR-23) Jefferson County, Colorado Dear Mr.Noren: Engineering Analytics was tasked to provide responses to comments 6 and 18 in the Colorado Division of Reclamation, Mining and Safety (CDRMS) letter dated July 20, 2016 (Adequacy Review #1) and comment 6 from CDRMS' August 2, 2016 letter (Adequacy Review #2). This work is being provided as a follow up to Engineering Analytics' (EA) submittal for Technical Revision 23 to Mining Permit M-1977-300 dated December 28, 2015. We offer the following comments. 1. Adequacy Review #1, Comment # 6: "Please describe how the Operator will place and compact 4— 6 inches of topsoil on the tops and sides of the WRPs. In addition, clam if the 4,300 cubic yard estimate of required topsoil accounts for compaction." Response: The 4,300 cubic yard estimate was determined assuming 9 inches of topsoil would be placed and track walked to lightly compact it to a final thickness of about 6 inches. In addition to what was presented in TR-23 (EA, 2015), we recommend the following with regard to topsoil placement and revegetation procedures. Topsoil Placement: The topsoil should be end-dumped on the crest of the slope and graded by dozers. Slopes should be graded to avoid concentrated water flow and subsequent erosion. The "Best Practices in Abandoned Mines Land Reclamation" by the Colorado Division of Minerals and Geology (CDMG, 2002) states that for covers "...that the surface of the final slope should be moderately roughened to help in establishing vegetation, but not so rough as to promote pooling of water.... The potential for erosion can be reduced by creating grooves across the slope (or perpendicular to the slope direction). This can be done easily on the last pass of the heavy equipment using a track vehicle running up and down the slope. " They further state that "Ideally, the surface to be vegetated should consist of good uncontaminated soil, moderately roughened to allow the seeds to hold and some moisture to collect. Roughening can simply be the caterpillar tracks of heavy equipment that has been used at the site for regrading." Thus, we recommend track-walking the cover to provide a "dimpled" surface that allows for water infiltration and promotes root growth. Response to CDRMS Comments.docx I Engineering Analytics, Inc.