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th A time -line of the model's development is provided below: <br />1. A transient model (Tam001 a) was created to simulate recharge operations for the <br />entire water year from November 1, 2000 to October 31, 2001. During this transient <br />model run seven production wells were periodically pumped, two recharge ponds <br />were operated, the artificial stream was activated along with the three semi -lined <br />storage ponds, and two wetland areas were periodically recharged. Water level <br />measurements from 24 to 31 wells at 10 different time periods, for a total of 267 <br />calibration points, were used in calibrating the model. <br />2. Tam001a was used to analyze the timing and amount of return of ground water to the <br />South Platte River pumped as part of the Tamarack Recharge Project. Evaluation of <br />the model results showed approximately 7% of the Project accretions was lost to <br />additional evapotranspiration (ET) in the model. This occurs because the <br />MODFLOW ET package is set up to vary the ET based on the depth to ground water. <br />When accretions are occurring, the depth to groundwater near the river is slightly <br />elevated resulting in higher ET calculations. To eliminate the MODFLOW <br />calculation of additional ET associated with changes in groundwater level elevation, <br />the model was modified so as to maintain a constant ET rate with respect to the depth <br />to groundwater (Tam001c). <br />3. The Tamarack Recharge model (Tam001) was expanded in area and time. The model <br />grid for Tamarack001 was expanded 5000 meters (over 3 miles) to the west of the <br />Crook bridge and 8,500 meters (over 5 miles) to the east of the Red Lion bridge. <br />This expansion covers the entire Tamarack Recharge Project site and also includes <br />the Condon and Overland Trail Ranch operations adjacent to the Tamarack property. <br />These neighboring operations conduct extensive well pumping for irrigation and <br />some groundwater recharge. The time span included in the updated model is from <br />February 1, 1997 to October 31, 2002. This re- calibrated model is called Tam002. <br />4. Using the pumping and recharge data from the East Recharge Pond, the Stream <br />Depletion Factor (SDF) Method was used to compare Project accretions and <br />depletions to the Tamarack Recharge Model. At the Tamarack SWA, the southern <br />boundary of the aquifer is located within a moderate distance of the recharge ponds. <br />MODFLOW simulates this boundary effect without modification. However, the SDF <br />method, without image wells, does not account for boundary impacts. Therefore, <br />image -well theory was used to adjust the SDF accretions. <br />• <br />Page 5 of 8 <br />