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Poudre Pits SWSP January 29, 2019 <br /> Plan IDs 3218 Et 4585 Page 3 of 8 <br /> weight. Water for dust control and concrete batching purposes will be pumped from the West Lake <br /> in the La Poudre site. Depletions from the La Poudre and North La Poudre Pits will impact the Cache <br /> la Poudre River upstream of the Whitney Irrigation Ditch (WDID 0300930). <br /> The Alluvial Water Accounting System (AWAS), which uses the Glover method, was used to <br /> determine the lagged depletions to the Cache La Poudre River from past (since 1990) and projected <br /> evaporation and operational losses at each site. The following parameters were used in the model <br /> with the alluvial aquifer boundary condition: the distance (X) from the centroid of the exposed <br /> ground water surface to the river; the width (W) of the aquifer on the side of the river where the pit <br /> is located; the transmissivity (T); and the specific yield (S). The Glover parameters used for each pit <br /> site are shown in the table below. <br /> Table C - Glover Parameters (Evaporative/Operational Losses <br /> Site Name X (ft) W (ft) T (gpd/ft) S <br /> West 512 4,800 50,000 0.20 <br /> La Poudre Middle 399 4,800 50,000 0.20 <br /> East 626 4,800 50,000 0.20 <br /> North La Poudre 2,500 4,800 50,000 0.20 <br /> The lagged evaporative and operational depletions for 2019 will total 124.78 acre-feet for the <br /> La Poudre and North La Poudre sites. <br /> Dewa ELWg <br /> Dewatering has occurred at each pit over varying intervals from 1995 through 2018. The Lee Parcel <br /> is the only portion of either site that is proposed to be actively dewatered during this SWSP period. <br /> In the past, it was assumed that the pits were dewatered at a rate of 500 gpm with all water <br /> released directly to the river. These assumptions have been revised to reflect the historic average <br /> dewatering rate of 100 gpm where the majority (75%) of the water was recharged in the adjacent <br /> pits with only 25% discharged directly to the river. This is based on a reevaluation of historic <br /> operations by the operator's consultant and a December 20, 2012 letter from Mark Johnson, <br /> Compliance Manager with Bestway Concrete and Aggregates as well as submitted pump specifications <br /> and data showing the 100 gpm is a more accurate estimate than the previously accepted 500 gpm. <br /> Mark Johnson described the recharge operation as occurring simultaneously with dewatering in that <br /> the operator would discharge the water into an adjacent, previously mined, cell. Once the cell being <br /> recharged exceeded its hydraulic capacity the water would then be diverted directly to the river. <br /> Dewatering operations at the La Poudre Pit occurred from January 1995 through December <br /> 2002, and during October and November of 2014. As stated above, 75% of the water was recharged <br /> in the adjacent pits with 25% discharged directly to the river. The Lee Parcel began being dewatered <br /> in April 2018 at an average rate of 280 gallons per minute with one-third (33%) of the dewatering <br /> water delivered to recharge in the West Lake and two-thirds (66%) delivered directly to the river. <br /> At the North La Poudre site, dewatering operations occurred from September 2002 through <br /> March 2003 and recommenced from April 2012 through July 2014. The 2012 dewatering was not <br /> metered therefore no recharge credit was given. Instead, all 2012 dewatering was assumed to be <br />