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weather is the driest, and traffic the greatest, more water for dust control will be used. In the analysis <br />dust control water was distributed between the months of May and September to meet the <br />-- - convergence of dry weather and high pit traffic: Estimated dust control measures require applying <br />approximately a tf;nth of an inch of water to the approximately 6500 lineal feet of haul road per <br />average day. Such an application rate results in an estimated use of 3.0 AF annually for dust control. <br />Water used for du:>t control is considered to be 100% consumed per Paragraph 7 of the Guidelines. <br />Gravel wa:~hing operations involve pumping exposed ground water from the pit for use in <br />processing clean dust-free gravel. Processing of gravel will take place over the entire operational <br />season of the pit. Water used for gravel washing operations is not 100% consumed, most of the <br />water drains back into the pit where suspended silt and sand are settled out. Most of the losses <br />associated with gravel washing operations are due to evaporation from the pit; however, in this <br />analysis 10% of tYte water pumped for gravel washing operations will be considered consumed. <br />While the production of gravel to be processed will occur over the entire year, pit operations <br />generally favor washing gravel during the spring and summer months to avoid complications from <br />freezing weather. Consequently, the water consumed by gravel washing operations is distributed <br />over the summer rrtonths. The rate .of water pumped. for washing operations is estimated to be 400 <br />gallons per minute, 8 hours per day, once a week during early and late summer and twice a week <br />during-peak season. The resulting volume ofwater is 14.3 AF annually, of which 10%, or 1.4 AF; is <br />lost. <br />Water pum~~ed from the pit is used in daily maintenance to wash concrete mixers and related <br />equipment. The water used for these operations is estimated to be 10 AF annually. The annual <br />estimate was distributed evenly over the peak season of operation. <br />4.2 Stream Depletion Analysis <br />In order to determine the lagged depletions occurring in•the Cache La Poudre River due to <br />ground water usage in the Timnath Pit (average annual ground water usage is 67.6 AF) the average <br />monthly evaporative and operational depletions were applied to the 30-year-study period and run <br />through a stream dlepletion analysis. The monthly depletion values were used to calculate a <br />synthesized depletion record spanning the study period. The depletion record was used as input to <br />the SDFView stream depletion software produced by the Colorado State University Integrated <br />Decision Support Group. The hydrogeologic characteristics of the alluvial aquifer in the Boxelder <br />service area were o~~btained from published reports and other available data. These data are also <br />required as input to the stream depletion model. The model was developed based on the following <br />assumptions: <br />C:\Projects\CODKCOI\Admin\DKC 2006 SWSP Application.doc 1 1 Scott Water Engineers, l_LC <br />