2015-12-30_HYDROLOGY - M1983090 - Laserfiche WebLink

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Poudre Pits Combined SWSP December 28, 2015 Page 3 of 10 ground water surface to the river; the width (W) of the aquifer on the side of the river where the pit is located; the transmissivity (T); and the specific yield (S). The Glover parameters used for each pit site are shown in the table below. Table C - Glover Parameters (Evaporative/Operational Losses Site Name X (ft) W (ft) T (gpd/ft) S Firestein/Tigges 1,112 8,000 120,000 0.20 La Poudre West Lake 512 4,800 50,000 0.20 Middle Lake 399 4,800 50,000 0.20 East Lake 626 4,800 50,000 0.20 North La Poudre 2,500 4,800 50,000 0.20 Dewaterinq Dewatering has occurred at each pit over varying intervals from 1996 through 2015. The West Lake of the La Poudre site is the only site that will be actively dewatered during this SWSP period. In the past, it was assumed that the pits were dewatered at a rate of 500 gpm with all water released directly to the river. These assumptions have been revised to reflect the historic average dewatering rate of 100 gpm where the majority (75%) of the water was recharged in the adjacent pits with only 25% discharged directly to the river. This is based on a reevaluation of historic operations by the operator's consultant and a December 20, 2012 letter from Mark Johnson, Compliance Manager with Bestway Concrete and Aggregates as well as submitted pump specifications and data showing the 100 gpm is a more accurate estimate than the previously accepted 500 gpm. Mark Johnson described the recharge operation as occurring simultaneously with dewatering in that the operator would discharge the water into an adjacent, previously mined, cell. Once the cell being recharged exceeded its hydraulic capacity the water would then be diverted directly to the river. Dewatering operations at the Firestein Pit occurred from January 1996 through June 2001. With the stated recharge that occurred, the lagged depletions to be replaced in 2016 equal 0.16 acre-feet. Dewatering operations at the Tigges Pit occurred from June 2005 through March 2012. With the stated recharge that occurred, the lagged depletions to be replaced in 2016 equal 5.37 acre-feet. Dewatering operations at the Roberts Pit occurred from July 2001 until June 2006. With the stated recharge that occurred, the lagged depletions to be replaced in 2016 equal 0.83 acre- feet. Combined, the dewatering operations at the Firestein/Tigges/Roberts Pit have resulted in a lagged depletion of 6.36 acre-feet that must be replaced in 2016. Dewatering operations at the La Poudre Pit occurred from January 1995 through December 2002, and during October and November of 2014. The site is projected to be dewatered at an average rate of 74 gpm during this plan period, with dewatering water delivered to recharge in the 6.42 -acre pond located in the western portion of the North La Poudre site. Combining the lagged depletions and net accretions from the stated recharge with projected dewatering depletions and accretions, dewatering activities at the La Poudre Pit site will create a net depletion of 81.34 acre- feet during 2016. At the North La Poudre site, dewatering operations occurred from September 2002 through March 2003 and recommenced from April 2012 through July 2014. The 2012 dewatering was not metered therefore no recharge credit was given. Instead, all 2012 dewatering was assumed to be discharged directly to the river creating no lagged accretions. The operator installed meters at this site by January 2013 and starting January 2013 the actual meter readings are used in the