Laserfiche WebLink
Poudre Pits Combined SW S P Page 3 of 9 <br /> June 18, 2014 <br /> Water for dust control and concrete batching purposes will be pumped from the West Lake in the La <br /> Poudre site. Depletions from the La Poudre and North La Poudre Pits will impact the Cache la Poudre <br /> Poudre River upstream of the Whitney Irrigation Ditch (WDI D 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 with <br /> the alluvial aquifer boundary condition: the distance (X) from the centroid of the exposed ground water <br /> surface to the river; the width (W) of the aquifer on the side of the river where the pit is located; the <br /> transmissivity (T); and the specific yield (S). The Glover parameters used for each pit site are shown in <br /> the table below. <br /> Table C - Glover Parameters (Evaporative/Operational Losses) <br /> Site Name X (ft) W (ft) T (gpd/ft) S <br /> Firestein/Tigges 1,112 8,000 120,000 0.20 <br /> West Lake 512 4,800 50,000 0.20 <br /> La Poudre Middle Lake 399 4,800 50,000 0.20 <br /> East Lake 626 4,800 50,000 0.20 <br /> North La Poudre 2,500 4,800 50,000 0.20 <br /> Dewatering <br /> Dewatering has occurred at each pit over varying intervals from 1996 through 2013. The North <br /> La Poudre site is the only site that witl be actively dewatered during this S W S P period. In the past, it <br /> was assumed that the pits were dewatered at a rate of 500 gpm with all water released directly to the <br /> river. These assumptions have been revised to reflect the historic average dewatering rate of 100 gpm <br /> where the majority (75%) of the water was recharged in the adjacent pits with only 25% discharged <br /> directly to the river. This is based on a reevaluation of historic operations by the operator's consultant <br /> and a December 20, 2012 letter from Mark Johnson, Compliance Manager with Bestway Concrete and <br /> Aggregates as well as submitted pump specifications and data showing the 100 gpm is a more <br /> accurate estimate than the previously accepted 500 gpm. Mark Johnson described the recharge <br /> operation as occurring simultaneously with dewatering in that the operator would discharge the water <br /> into an adjacent, previously mined, cell. Once the cell being recharged exceeded its hydraulic capacity <br /> the water would then be diverted directly to the river. <br /> Dewatering operations at the Firestein Pit occurred from January 1996 through June 2001. <br /> With the stated recharge that occurred, the lagged depletions to be replaced in 2014 equal 0.19 acre- <br /> feet. Dewatering operations at the Tigges Pit occurred from June 2005 through March 2012. With the <br /> stated recharge that occurred, the lagged depletions to be replaced in 2014 equal 16.9 acre-feet. <br /> Dewatering operations at the Roberts Pit occurred from July 2001 until June 2006, when the reservoir <br /> was lined. With the stated recharge that occurred, the lagged depletions to be replaced in 2014 equal <br /> 1.09 acre-feet. Combined, the dewatering operations at the Firestein/Tigges/Roberts Pit have resulted <br /> in a lagged depletion of 18.18 acre-feet that must be replaced in 2014. <br /> At the North La Poudre site, dewatering operations occurred from September 2002 through <br /> March 2003 and recommenced from April 2012 through present time. The 2012 dewatering was not <br /> metered therefore no recharge credit was given. Instead, all 2012 dewatering was assumed to be <br />