Tamarack Ranch Recharge Project Water Rights

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• 4.2.1 CDOW Analysis CDOW's analysis of the APTs was documented in a Draft Technical Memorandum (CDOW, October 14, 2005). The results of which are summarized herein. Summarized below are the results of the Stieb APT, located upstream of the Tamarack Ranch SWA: • The stream flow gains /losses measured during the pumping and recovery period correlated well with depletions calculated using a method similar to the AWAS(IDSG, 2004). AWAS was the commonly used method for calculating stream depletions from well pumping in the Lower South Platte River. The AWAS method assumes that streambed conductance is large enough so as not to significantly limit flow between the stream and the aquifer. • The drawdowns observed in the monitor wells near the Stieb pumping well indicate that streambed conductance is not a significant factor in stream and aquifer interactions. • After 1 to 2 days of recovery, the measured drawdown in the monitor wells correlate well with those calculated using the AWAS -Type method. The recovery data verifies that the basic AWAS assumption that the streambed conductance does not significantly limit stream/aquifer interactions is reasonable for this site. The results of the second APT, located at the Dinsdale site, are less definitive than the Stieb APT. The following site conditions limited interpretation of the Dinsdale APT results: • The higher stream flow rate, lower pumping rate, and larger distance between the pumping well and the river, resulted in correspondingly smaller changes in stream flow that could not be accurately measured. • The Dinsdale pumping well is partially penetrating. Thereby, it was difficult to identify river or streambed impacts from the drawdown curves for the two monitor wells next to the pump. • The stream stage elevations significantly declined during the testing period due to a large drop in river flow rate. The stream flow rate at the beginning of pumping was approximately 150 cubic feet per second (cfs) which dropped to approximately 50 cfs by the end of the test. This necessitated adjusting monitor well drawdowns thereby imparting additional speculation on data interpretation. Despite these limitations, the drawdowns observed in the monitor well closest to the river (MW3) indicated that streambed conductance does not significantly influence well pumping response at the site. As in the Stieb APT, after 1 to 2 days of recovery, the measured drawdowns in 2 of the 3 monitor wells correlate reasonably well with those calculated using the AWAS- Type method. Measured drawdowns from the third monitor well (MW3) matched the AWAS- Type method calculated drawdown from the start of the recovery period. In summary, both the Stieb and Dindale results support the assumption that streambed conductance does not significantly limit stream/aquifer interactions along the Lower South Platte River. • 11 'Page