2012-01-23_HYDROLOGY - M1977439 - Laserfiche WebLink

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Site Name T X W S Home Office Pit 160,000 1,000 6,500 0.2 Overland Ponds Pit 160,000 2,000 3,000 0.2 North Taft Hill Expansion Site Pit 160,000 1,600 2,900 0.2 R Mr. Jared Dains Lafarge Upper Poudre Combined SWSP January 11, 2012 Page 3 Home Office Pit as being a Pre -81 exposure. Of the 100, 22.1 acres are within the Partners Lamb A pond as reflected in the Partner's SWSP for their portion of the Home Office Pit. Therefore, for Lafarge's SWSP 77.9 acres are recognized as Pre -81. The Pre -81 exposure locations have previously been set and are not allowed to be relocated to other areas of ground water exposure within the gravel pit boundary. A stream depletion model using the Glover method was used to calculate the lagged depletions to the Cache La Poudre River. The alluvial aquifer model uses four aquifer input parameters for each site as follows: 1) X- distance from well to river, 2) W- distance from the aquifer boundary through the well to the river channel, 3) T- transmissivity of the alluvial aquifer (in gallons per foot /day) between the well and the river, and 4) S- specific yield - 0.2 was used for all wells. The following parameters for each site listed in the table below were used in the model: As of January 1, 2011 the Partners are augmenting their portion (125.5 acres in Treiber A & B, and Lamb B & C lakes) assuming a steady state condition, thereby accounting for lagged depletions from past evaporation. Therefore, these areas were not included in the determination of lagged depletions to be replaced through this SWSP. The estimated monthly consumptive use and lagged stream depletions due to evaporation and operational losses are 77.34 acre -feet as shown on the attached Table 1. The three sites are assumed to have been continuously dewatered and to be in a steady state condition where dewatering accretions equal the lagged depletions. Lafarge estimates that the Home Office Pit and Overland Ponds are dewatered at a rate of 800 to 1,000 gpm for approximately 12 hours per day. Dewatering at the North Taft Hill Expansion site is accomplished by gravity draining pooled water through a pipe and into an excavated area to the south within the Home Office Pit. This water is then dewatered through the Home Office Pit dewatering operations. Lafarge plans to maintain these operations throughout this SWSP approval period. Once dewatering ceases or is reduced in its flow, lagged depletions will immediately hit the river. At least three years prior to a modification in dewatering operations, the Applicant must provide a plan showing how lagged post - pumping depletions will be replaced in the proper time and amount. All volumes pumped for dewatering must be metered by a Totalizing Flow Meter and be reported on the accounting submitted monthly. Future SWSPs for these pits will not be approved until volumes pumped for dewatering are properly metered. Replacement Replacements for this combined plan will come from accretion credits from recharge of 5.75 Taylor and Gill Ditch shares, and leased water from the Lake Canal and Reservoir Company. The 5.75 Taylor and Gill Ditch shares will be diverted into a recharge pit located on the Home Office site. The evaporation losses from the recharge pond during this approval period are estimated at 2.57 acre -feet (see attached Table 5). Since 2006, 5.75 Taylor and Gill Ditch shares have been diverted into the recharge pond to produce accretions to the stream for replacement purposes. The 5.75 shares will be diverted in the recharge pond again in 2012 to provide replacement water for this combined plan. The 5.75 shares were historically used to irrigate 104.5 acres of pasture grass, all of which have been taken out of production. The historical consumptive