Laserfiche WebLink
A& Ecological Resource Consultants, Inc. <br /> 35715 US Hwy.40,Suite D204—Evergreen,CO—80439—(303)679-4820 <br /> Technical Memorandum <br /> Date: December 19, 2016 <br /> To: Clara Steward, Newmont <br /> Cc: Ben Larson, Newmont <br /> Jay Janney-Moore, NewFields <br /> From: Troy Thompson/Ryan Hummel, ERC <br /> Re: Poverty Gulch Diversion Channel Sizing <br /> Permit No. M-1980-244; Technical Revision 86 <br /> Introduction <br /> Ecological Resource Consultants, Inc.(ERC)was tasked with sizing a diversion channel at Newmont Mining <br /> Corporation's(Newmont)Cripple Creek&Victor(CC&V)gold mine.The purpose of the diversion channel <br /> is to prevent surface runoff from entering the mine's Globe Hill Pit.The channel will be capable of diverting <br /> all runoff from the 100-year, 24-hour event away from the pit and releasing it to Poverty Gulch <br /> downstream of the pit. <br /> Hydrology <br /> Newmont provided ERC with a 100-year, 24-hour storm depth of 3.5 inches at this site (Newmont 2016). <br /> ERC utilized the U.S.Army Corps of Engineers'(USACE)hydrologic modeling program HEC-HMS(v.4.1)and <br /> the Natural Resources Conservation Service's(NRCS) method to determine the peak runoff rate expected <br /> to enter the channel during the 100-year event. ERC measured the watershed of the proposed diversion <br /> channel to be approximately 74 acres (shown in Figure 1, which was obtained from Newmont 2016). As <br /> the figure indicates the area tributary to the diversion channel is bound by Teller County Road 821 to the <br /> north. Runoff from areas upgradient of Teller County Road 821 is captured in the roadside ditch and <br /> conveyed out of the basin that contributes flows to the diversion ditch. The watershed was divided by <br /> land type as approximately 51 acres of mixed brush and grassland (curve number of 71), 19 acres of <br /> wooded forest area (curve number of 66),and 4 acres of roadways(curve number of 90),for a composite <br /> curve number of 70.8. Curve numbers for each land type were obtained from Steffens and Associates, <br /> Inc.'s Storm Water Management Plan for the site (January 2012). Using topography data obtained from <br /> Newmont,the NRCS lag time method,and an NRCS Type 11 storm event, ERC calculated to the peak runoff <br />