2011-05-20_HYDROLOGY - M2004013 - Laserfiche WebLink

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Jacob Bauer, Martin and Wood May 20, 2011 Page 2 Under Scenario B, there will be no mining on this site during the approval period and no operational losses to account for. Evaporation will occur from exposure of a total of 7.46 acres of water in four settling and wash ponds and in the mined cell for the entirety of the approval period. Your attached Table 1 B shows the site net evaporation calculations (26.19 acre-feet) and water consumed by site operations (0 acre-feet). Effective precipitation credit was applied to this plan. DEPLETIONS You have provided a monthly breakdown of lagged depletions at this site for each of the aforementioned scenarios in your attached Table 2. The stream depletion model was developed based on the following assumptions: the exposed surface area is 2,030 feet from an active stream, the transmissivity is 100,000 gal/day/ft, the specific yield is 0.2, and the location of the impermeable boundary is 7,875 feet from the live stream. Table 2 shows that under Scenario A, the lagged stream depletions during the period January 2011 - December 2011 are estimated to be 25.57 acre-feet and the lagged stream depletions during the period January 2012 - December 2012 are estimated to be 26.29 acre- feet. These estimates are based upon evaporative losses from the settling and washing ponds, mined cell, and dewatering trench, water removed in the mined product, and water used for dust suppression (see attached Table 1A). As requested in the previous approval letter dated July 2, 2009, depletions associated with refilling the dewatered mined cell were accounted for in this request as shown in Table 2 under Scenario A. It was estimated that the mined cell would return to its October 2010 level (approximately 2 feet deep) within one month in August following mining. The volume of water refilled in the cell (2.75 acre-feet) was added to the total evaporation and operational losses in August 2011 and August 2012, and lagged to the stream. An instantaneous credit of 2.75 acre-feet from dewatering the cell prior to mining was removed from stream depletions in June 2011 and June 2012. Table 2 shows that under Scenario B, the lagged stream depletions during the period January 2011 - December 2011 are estimated to be 26.12 acre-feet and the lagged stream depletions during 'the period January 2012 - December 2012 are estimated to be 26.19 acre- feet. These estimates are based upon evaporative losses from the settling and washing ponds, and mined cell (see attached Table 1 B). REPLACEMENTS The proposed sources of replacement water for this pit are a ten year lease to deliver 27 acre-feet annually of fully consumable water from the Board of Water Works of Pueblo (PBWW). The lease water will be provided from the Board's stored water at Clear Creek Reservoir, Turquoise Reservoir, Twin Lakes Reservoir, Pueblo Reservoir, from direct flow transmountain water, reusable return flows from transmountain water, or from any other reservoir or place from which the Board may legally deliver water, and will be delivered to the Arkansas River Near Avondale USGS stream gage. The monthly depletions and replacement requirements are provided on the attached Table 2. A transit loss of one percent was applied to the required monthly replacement amounts, as shown in Table 2. Under Scenario A, estimated replacements are 25.83 acre-feet for the period January 2011 - December 2011, and 26.57 acre-feet for the period January 2012 - December 2012. Under Scenario B, estimated replacements are 26.40