2012-02-06_HYDROLOGY - M2005059 - Laserfiche WebLink

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Peter Wayland Nelson Mining Resource SWSP February 1, 2012 Page 2 In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $186,814 through the Division of Reclamation, Mining, and Safety ( "DRMS "). This bond is for reclamation requirements under the current permit but may not be sufficient for lining or backfilling the pit to ensure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. Future SWSPs for this site will not authorize any additional use of ground water until the Applicant provides documentation that a bond sufficient to cover lining or backfilling of the pit has been obtained. In addition according to the information provided you indicated that the land owner Mr. Howard Nelson has entered into a lease agreement with the applicant, which states that Lessor will grant to Lessee the water rights associated with the property for processing and augmentation during the term of the lease. The term of the lease is for a period of 20 years from the date entered into the agreement, which was April 18, 2001. Depletions Consumptive use of water at the property consists of 30.75 acre -feet of evaporation from up to 12.6 acres of exposed surface area. No groundwater was exposed at this site prior to January 1, 1981. Depletions from evaporation at the mine site will accrue to Saint Vrain Creek. You have provided a monthly breakdown of the annual depletions at this site in your attached Table AI1.1. The IDS AWAS stream depletion model was used to determine the lagged depletions from evaporation to Saint Vrain Creek. The aquifer characteristics used in the model are: transmissivity (T) = 157,000 gallons per day per foot and specific yield (SY) = 0.2, the distance of the exposed ground water to the stream = 2,013 feet, and the location of the parallel impermeable boundary was estimated to be 2,126 feet from the stream. For purposes of this SWSP, the distance of the exposed ground water to the river X is accepted; however, should the Applicant seek to renew this SWSP, the Applicant must calculate the depletions with the X value measured from the centroid of the pond. Replacements The proposed source of replacement for this pit is the historical consumptive use from the dried -up of 30 acres of land historically irrigated with 0.434 shares of Last Chance Ditch diverted from Saint Wain Creek used for irrigation of the mined property lrriga - has ceased on the Nelson Pit site due to the mining operation and groundwater lakes. The Applicant owns 1.5 shares of the outstanding 20 shares of the Last Chance Ditch. The 1.5 shares of the Last Chance Ditch were historically used for irrigation on the Nelson Pit mining site. The historical use of the irrigation supply was quantified using the average monthly diversion from 1950 through 2005. The total irrigated crop acreage varied from 101 acres (1950 to 1965) to 121 acres (1966- 1990) to 72 acres (1991- 2005). The ditch loss used the consumptive use analysis was 10 percent based on the ditch location, its length and previous experience and the irrigation efficiency was taken as 50 %. Water in excess of the irrigation requirement was added to the soil moisture bank, which was assumed to have a water holding capacity of 1.95 " /ft. The consumptive use analysis for the 1.5 shares averaged 160.6 acre -feet per year with a non - irrigation season return flow obligation of 14.6 acre -feet (Table AI.7). The pro -rata historical consumptive use credit for the 0.434 shares is 48.18 acre -feet with a non - irrigation season return flow obligation of 4.34 acre - feet. After applying the 0.434 shares of Last Chance Ditch water, there will be 16.87 acre -feet of uncompensated depletions.