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January 9, 2013 <br />Mr. Oswald <br />Greg Lewicki And Associates, PLLC <br />11541 Warrington Court Phone: (303) 346 -5196 Fax (303)- 346 -6934 <br />Parker, (;0 USA 80138 C -Mail: info ri.levs icki.bir <br />Bob Oswald <br />Colorado Division of Reclamation, Mining, and Safety <br />1313 Sherman Street, Rm 215 <br />Denver, CO 80203 <br />RE: Permit No. M- 2012 -032, Revenue Mine Surface Water Systems Designs — <br />Stormwater Comments — Review of November 29, 2012 Adequacy Response <br />— Soil Unit 112 Details <br />GLA has received and evaluated the comments regarding the surface water systems at the <br />Revenue Mine that Star Mine received from Bob Oswald at DRMS. Since the runoff calculations <br />of stormwater basins SWB -1 through SWB -4 are all affected by the first comment of the review <br />(along with related designs), please evaluate this response separately. <br />DRMS Comment <br />Map G -1: <br />1. The Soil Map Unit 112 (Cryorthents -Rock outcrop) is categorized as being hydrologic <br />soil group (HSG) C. The Soil Resource Report for Ouray Area, Colorado, Parts of <br />Gunnison, Hinsdale, Ouray, San Juan, and San Miguel Counties categorizes 112 as HSG <br />D. Please provide rationale for the use of lower runoff potential HSG for Soil Map Unit <br />112. <br />Applicant Response <br />The Soil Group 112 (Cryothents -Rock outcrop) identified in the Custom Soil Survey generated <br />using the USDA Web Soil Survey covers an area on the south side of Yankee Boy basin uphill <br />from the Revenue Mine. A copy of this soil's description can be found attached to this memo. <br />For the purpose of curve number selection for runoff, the hydrologic soil group (HSG) of C was <br />selected based on the SCS Hydrologic Soil Group definitions. The definitions of HSG C & D <br />are provided below. <br />Group C soils have a low infiltration rates when thoroughly wetted and consist chiefly of soils <br />with a layer that impedes downward movement of water and soils with moderately fine to fine <br />texture. These soils have a low rate of water transmission (0.06 -0.15 in. /hr.) <br />Table 3.15 from Design Hydrology and Sedimentology for Small Catchments. Haan, Barfield, Hayes. 1994. <br />