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Attachment Nl}IC <br /> Page No. MHC-3 <br /> Permit No. CO-0044768 <br /> Site Loading Estimate <br /> The site loading estimate for this project was based on visual observations and weighing potential <br /> impact based on assumptions and observations using data extrapolations from tests on similar <br /> material. and monitoring data for Sunnyside's MLR permit. <br /> —Obscn-ations and Assumptions <br /> • Three drainages were found to be [lowing on surface above Tailings Pond No. 1 and the <br /> Mayflower Mill area but not reaching the surface diversion strictures in place to intercept <br /> and divert surface water around these facilities. <br /> • Seeps and springs have been observed at the base and below these facilities during high <br /> groundx\ater season (ie. snowmelt conditions) These seeps and springs appear to occur <br /> along projections of pre-facility drainages that would match the disappearing surface flows <br /> found above the facilities <br /> • It is assumed that if oxygenated surface water percolates and contacts tailings material, <br /> dissolved metals will be picked up by the migrating water. <br /> —Methodology for Estimation of Potential Loading <br /> • The contributing watershed area for these drainages was measured to be approximately 150 <br /> acres. It was assumed that the average annual precipitation on this area would be the <br /> average of Red Mountain and Silverton weather stations due to topography. It was assumed <br /> 60 percent of this precipitation reported as n►n-off to these drainages with 10 percent having <br /> potential for contact with mill tailings and mine waste. <br /> • Loading was calculated based on 1:l leach test results from similar material (ie. tailings and <br /> mine waste from the same source). These results were divided by 20 to account for <br /> groundwater type c\posure. This dilution (20:1) is consistent with dilutions used for TCLP <br /> testing <br /> —Estimation of Dissolved Zinc Loading Potential <br /> • Based on the aboN e methodology for estimation, it is estimated that the potential exists for <br /> an annualized daily loading of 10 pounds of dissolved zinc. This potential loading occurs <br /> primaril\ during snow-melt season over a three month period. Therefore, the potential exists <br /> for a seasonal loading of 30 pounds of dissolved zinc per day <br /> SG IS under no obligation to defend these estimates and they should only be used as an <br /> estimate using many assumptions to obtain. SGC does not represent that its mitigation <br /> project at this site will remove any specific percentage of metals loading from this site: the <br /> loading estimate contained herein does not form the basis for an enforceable permit <br /> obligation <br />