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the crops was estimated to consume approximately two feet of water per year as presented in Table 4 resulting in a net <br />excess of approximately one foot of water. <br />Table 4 <br />Area Crop Consumptive Use <br />(values in inches) <br /> <br />Cro <br />Alfalfa Sweet <br />Com <br />Su ar Beets <br />Potatoes <br />Avera e <br />Consumptive Use 31.6 22.8 29.3 28.1 27.9 <br />Notes: <br />Gross consumptive use based on TR-21, Modifed Blaney-Griddle Method, Colorado Inigation Guide Dec. <br />1988. <br />The flatter areas surrounding the site where irrigation waterhas more time to percolate into the ground were assigned a <br />50% surface runoff and a 50% deep percolation of irrigation excess. In the areas east of the Site, where the steeper <br />slopes are underiain by eolian deposits, approximately 70% of the water not consumed by the crops was attributed to <br />surface runoff and 30% to deep percolation recharging the aquifer. <br />Recharge rates of 3.6 inches per year were modeled on the steeper slopes and 6 Inches per year on flatter slopes. The <br />recharge over the Piney Creek Alluvium was modeled with a rate of 2.2 inches per year, approximately 17 percent of the <br />rain recharge. This rate is higher because the Piney Creek Alluvium is a coarser grained geological unit resulting in <br />more precipitation percolating into the aquifer, as presented in Table 5. The areas surrounding the river are underlain by <br />the Piney Creek Alluvium and are on the average not irrigated so only rain recharge was applied. See Figure 5 for the <br />distribution of irrigation recharge. <br />Table 5 <br />Recharge by Geological Unit <br />Area b Geolo ical Unit Rechar er (inchesryear) Notes <br />Ran a 0.65 - 2.6 Brendle, 2002 <br />Eolian 3.6 Irri ated Area, Stee er Slo es <br />Valle Fill 6 Irri ated Area, Flatter Slo es <br />Pine Creekz 2.2 Non-Irri aced Area <br />Notes: <br />1. Values for irrigated areas from agricultural p2c6ces and disassions with irrigators. <br />2. Piney Creek recharge approximately 17 ~ of annual precipitation due to the higher hydraulic conductivity of the Piney Cn;ek <br />geologipl Unit <br />3.9 Boundary Conditions <br />Boundary conditions in a groundwater model are one tool used to approximate existing conditions. The boundary <br />conditions are set sufficiently far away from the area of interest as to allow the aquifer to respond to local stresses and <br />are based Gn hydraulic, hydrogeologic, hydrologic, geological and geographical assumptions. <br />This model extends 2.5 miles north and south of the Site where constant head nodes were placed at water surface <br />elevations ten to 25 feet below the ground. The upgradient area or southem boundary was modeled with constant head <br />nodes to represent assumed groundwater elevations at the southem margin of the model. <br />Groundwater Model Report - SW TKO Water Storage Project - 5 - February 2005 <br />