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Poudre Pits SWSP December 3, 2019 <br /> Plan IDs 3218 l* 4585 Page 4 of 9 <br /> through July 2014 was returned directly to the river through an unnamed slough located above the <br /> Whitney Ditch. <br /> In the past, lagged depletions resulting from dewatering at the sites were calculated using <br /> AWAS with the infinite aquifer boundary condition. The following parameters were used in the <br /> model: the distance (X) from the centroid of the exposed groundwater surface to the river; the <br /> transmissivity (T); and the specific yield (S). The Glover parameters used for each pit are shown in <br /> Table D below. <br /> Table D - Glover Parameters Dewaterin <br /> Site Name X (ft) T (gpd/ft) S <br /> La Poudre 1,500 50,000 0.20 <br /> North La Poudre 2,500 50,000 0.20 <br /> Beginning with the 2019 plan year, you began to lag dewatering depletions using the alluvial <br /> aquifer boundary condition, consistent with the methodology and aquifer width parameter for <br /> lagging operational depletions, which is believed to be more appropriate given the close proximity of <br /> the pits to the Cache la Poudre River. In order to ensure that this change in methodology does not <br /> result in unreplaced depletions to the river, you have proposed to continue lagging dewatering <br /> depletions resulting from dewatering that occurred in 2018 and earlier using the infinite aquifer <br /> boundary condition, and to lag depletions resulting from dewatering that occurred in 2019 and later <br /> using the alluvial aquifer boundary condition. Because the remaining depletions resulting from <br /> dewatering prior to 2019 as calculated using the infinite aquifer method lag out for a long time <br /> period in relatively small quantities, you have proposed to "wrap" the lagged depletions remaining <br /> after 2028, which represent less than 10% of the total volume pumped for dewatering purposes, and <br /> redistribute and replace these depletions during the time period of 2019 through 2028. Depletions <br /> resulting from post-2019 dewatering are not proposed to be wrapped at this time. <br /> Based on discussions with the mine operator, dewatering during 2020 is projected to occur at <br /> the Lee Parcel portion of the La Poudre site at a rate of 294 gpm, with 197 gpm delivered directly to <br /> the river and 97 gpm delivered to recharge in the Wildlife Pond. Actual monthly meter readings <br /> must be used to determine the true dewatering rate, and to determine how much water was <br /> delivered to recharge versus being directly returned to the river. <br /> Table E below summarizes the impacts past and projected dewatering operations at each pit <br /> will have on the stream system during this SWSP period of January 1, 2020 through December 31, <br /> 2020, as calculated using the methodologies and assumptions described above. <br />