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