2009-04-03_HYDROLOGY - M2003091 - Laserfiche WebLink

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Richard Raines and Sira Sartori April 2, 2009 Page 2 This plan seeks to replace depletions to Boulder Creek that will result from mining at the Duckworth Pit. Mining activities that will produce depletions are evaporation, water lost in mined product, and dust suppression. The site will be dry mined and continuously dewatered through a trench system around the perimeter of the mining area. The trenches will convey ground water to collection areas where sediment will settle out before the water is pumped into Idaho Creek, which now flows through the mining site in a generally northerly direction. Idaho Creek will carry the water removed by the dewatering system approximately % mile east and north to a point of diversion into the east end of Lighthouse Cove Lake ("Lake"), located in Lighthouse Cove Subdivision in the North Y2 of the Northeast % of Section 16, Township 2 North, Range 68 West, 6th P.M. The Lake was created due to mining by Western Paving Construction Company. The dewatered ground water will be measured at both the discharge point into Idaho Creek and the diversion from the creek into the Lake. The addition of the dewatering water will not increase the exposed surface area of the lake or the resulting stream depletions. These depletions are replaced by the Water Users of District 6 according to an augmentation agreement entered into prior to January 15, 1989. The Applicant proposes to replace depletions to Boulder Creek with releases of water from Heaton Reservoir, a lined storage reservoir the Applicant owns. Water for releases will come,4rom the Applicant's 2.0 shares of Rural Ditch, which is approved for storage in the reservoir and release for augmentation and industrial use, under the LaFarge Heaton Property Batch Plant SWSP approved pursuant to C.R.S.37-92-308(4). That SWSP is currently valid through January 31, 2010. Depletions Ground water exposure will occur when the Duckworth Pit is dry mined in two cells, each bounded by a dewatering trench that runs to a collection point, from which the collected water will be pumped into Idaho Creek. The total exposed water surface area will be 1.1 acres, and the resulting annual evaporative consumptive use will be 2.8 acre-feet. Operational losses will include loss of moisture in mined product and water use for dust control. With an annual mining rate of 1.6 million tons of raw material, the consumptive use associated with water loss in product will be 47.1 acre-feet. Another 2.0 acre-feet of water will be used for dust control each year, making the annual operational loss 49.1 acre-feet and the total consumptive use 51.9 acre-feet per year (see Table 2 attached). Over the entire proposed plan period, the consumptive use will total 107.4 acre-feet. Since Duckworth Pit is not adjacent to an active stream, the lagged effect of the mining depletions was computed with the AWAS stream depletion model. The monthly schedule of lagged depletions that will accrue to Boulder Creek during the proposed plan period is presented in the attached Table 3. The depletions begin with 0.06 acre-feet in October 2008; depletions then total 19.8 acre-feet from November 2008 through October 2009 and 36.8 acre-feet from November 2009 through October 2010. Replacements The Applicant will make replacements for stream depletions from water stored in and released from Heaton Reservoir. The Applicant owns 2.0 Rural Ditch shares that provide 86.8 acre-feet per year of historic use credit, of which 10.8 acre-feet are consumed by a concrete batch plant. Based on the accounting provided by the Applicant, there is adequate water in the