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Mr. Tom Ka/denbach <br />© Environmental Protection Specialist <br />Colorado Division of Mineralsmul Geology <br />March ?6, 1998 <br />Page 2 <br />As presented in the Slump Investigation and Mitigation Report (MWA, 1998) included in <br />Attachment A, HGCC proposes to stabilize and monitor the slump by installing the following <br />additional mitigative measures and monitoring devices: <br />• An upper French drain to intercept subsurface water from the south and west, <br />near the upslope portion of the slump; <br />• A middle French drain to intercept subsurface water that may drain from the <br />upslope portions of the slump and/or collect in [he middle portion of the slump; <br />• Two surface ditches, above and below the slump to divert surface water away from <br />the slump; <br />• Two slot drains across the toe of the slump to allow drainage of trapped water; and <br />• Permanent movement markers to monitor potential movement of the slump. <br />Additionally, HGCC proposes to regrade portions of the surface of the slump to minimize <br />infiltration of water and provide positive drainage away from the area, particularly from the <br />depression adjacent to the head scarp. HGCC also plans to revegetate any new disturbances <br />created during the mitigation work, which will help to directly stabilize the slope and remove <br />water from the slump mass. The locations of these proposed mitigative measures are shown in <br />the attached Drawing I-I. This drawing will he inserted into the permit application (HGCC, <br />August 1980), as described in Table 1, Summary of Additions to the Permit Application. <br />Although HGCC believes that the slump area is insignificant in both size and in terms of <br />preserving an environmental or safety hazard, it intends to take these precautionary measures <br />now so that the area will be eligible for bond release at the same time as the shrub <br />augmentation parcels. <br />Please call if you have any questions. <br />Sincerely, <br />Montgomery Watson Americas, Inc. <br />Toby Leeson, RG <br />Professional Hydrogeologist <br />Michael Neumann <br />Senior Project Manager <br />cr. David Berry, CDMG <br />R.J. Medler, W.R. Grace <br />