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trenches will be 5 feet wide, the eastern cell will expose an area of approximately 0.4 acre, and the <br />western cell will expose an area ofapproximately 0.5 acre. Approximately 0. ] acre ofwater will be <br />exposed in each of the collection areas at the two cells for a total of 0.2 acres. Total exposed surface <br />area at the Duckworth Pit during mining will be approximately 1.1 acres (Table No. 1). The total <br />evaporative consumptive use for the Duckworth Pit was calculated to be 2.8 acre-feet (Table No. 1). <br />Operational Losses <br />The material mined at the Duckworth Pit will be conveyed to the adjacent Cottonwood Pit. M-88- <br />042 for processing. The Cottonwood Pit is also operated by Lafar~ze and is au~nented by the ] 989 <br />District 6 Augmentation Plan. However, the losses for moisture in the mined material at the <br />Duckworth Pit will be replaced by this substitute supply plan. <br />The moisture content of the material removed from the site was assumed to be 4 percent by weight <br />per the SEO's Guidelines. The annual yield for the pit was estimated at an assumed mining rate of <br />750.000 tons of raw material for the first two years. This results in an annual consumptive use of <br />22.1 acre-feet for water retained in product (Table No. 2). <br />'dater will also be applied to haul roads and stockpiles for dust control. The total annual <br />consumptive use for dust control was estimated at 2.0 acre-feet and was distributed throughout the <br />year based on the same percentages as the production of the aggregate mined per the SEO's <br />Guidelines (Table No. 2). The total annual operational losses due to the mining operation during the <br />first two years at the Duckworth Pit are projected to be 26.9 acre-feet (Table No. 2). <br />MINING STREAM DEPLETIONS <br />Due to the fact that the site is set back from the river, the mining depletions ~~~ere assumed not to be <br />instantaneous. A stream depletion model was completed for the Duckworth Pit to displa} the lagged <br />effect of the mining depletions. The model was developed under the following assumptions: <br />• The pumping well was placed 2700 feet from an active stream. This represents the distance <br />between the down-gradient extent of the mining operation and nearby Boulder Creek. <br />• There was no transmissivity data available for the area. A value of 50,000 gpd/ft was chosen <br />based on an average transmissivity for St Vrain Creek and Boulder Creek. <br />• The specific yield was assumed to be 0?, which is typical for an alluvial aquifer. <br />• The distance from the adjacent reach of Boulder Creek to the parallel impermeable boundary <br />was assumed to he 6800 feet. Source: USGS Depth to y'~'ater Table. Sheet ~ of ~ from <br />Geohydrology of the Shallow Aquifers in the Boulder-Longmont Area. CO. 2000. <br />The copy of the stream depletion model is included in Appendix A. The lacgcd mining depletions <br />that will accrue to the stream during Water fears 2004 and 200 during the first t~~'o years of <br />operations at the Duckworth Pit are shown in Table No. 3. <br />Page 3 <br />