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cell in 2004 and complete a 25-acre westem cell in 2005. The Duckworth Pit will be dry mined and <br />continuously dewatered during the minine operation. Prior to mining, a dewaterin_ trench ~~ ill be <br />excavated around the perimeter of the mining area. Groundwater will flow alone the trench by <br />gravity toward a collection area where it will be allowed to settle out prior to pumping into either the <br />Smith and Emmons Ditch or Idaho Creek as described in the mining plan filed with the Division of <br />Minerals and Geology (DMG). <br />Replacements will be made from the storage and release of water from a lined resen oir owned by <br />Lafarge known as Heaton Reservoir (Figure No. 1). Lafarge owns 2.0 Rural Ditch shares, which <br />have been approved by the SEO in a H.B. 1414 substitute water supply plan (S~'~'SP) for stora_e and <br />release from Heaton Reservoir for auk nentation and industrial use. An existing concrete batch plant <br />at the Heaton Reservoirpmnps a portion of the Rural Ditch water stored in the resen~oir. There will <br />be sufficient excess historic consumptive use credit remaining in the resen oirto makereplacements <br />for the mining depletions associated with the Duckworth Pit throughout the year. <br />The mining is scheduled to begin in July 2004 and be completed b} the end of 200d. Afrer <br />reclamation, the Duckworth Pit will have hvo unlined lakes with a total area of approximate'}~ 37 <br />acres. Lafarge plans to file a permanent plan for augmentation in Water Court for this site in Y~OS. <br />PROJECTED CONSU>\IPTIVE USE <br />Water use at the Duckworth Pit will include evaporation from exposed groundwater. dust control of <br />haul roads and stockpiles, and water retained in material removed from the site. <br />Evaporative Losses <br />The NOAA Technical Report NV1'S 33. Evaporation Atlas for the Conticuous 48 United States t l .S. <br />Department of Commerce) was used to determine gross evaporation. For this location, the annual <br />evaporation is 40.0 inches. Monthly evaporation percentages as suggested by the Office ofthe State <br />Engineer for elevations below 6500 feet were used to calculate monthly evaporation. <br />Precipitation was estimated using Colorado Climate Summaries data from the `,','estem Regional <br />Climate Center Website. Annual precipitation at this site was assumed to be equal to that at the <br />nearest station, which is the Longmont y'r'eather Station. The averaged mean precipitation is 13.37 <br />inches for the years ] 948 to 2003. Effective precipitation was calculated as 70°~o of total <br />precipitation. Net evaporation was then computed as the difference between gross evaporation and <br />effective precipitation. Net evaporation at the site was calculated to be 2.fi feet. <br />The evaporative losses at the site will consist of the exposed water within the dewatering trench and <br />the collection area. Again, the Duckworth Pit will be continuously de~aatered during mining. In <br />order to facilitate dry mining at the site. a dewatering trench will be exca~ ated around the perimeter <br />of each of the two mining cells. <br />The total length of the dewatering trench around eastern mining cell is approximately 3200 feet, <br />while the length of the trench encircling the western cell is approximately 400 feet. Assuming the <br />Paee 2 <br />