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<br />I <br /> <br />. <br /> <br />assumptions and data used to calibrate the model are the most important factors. <br />Factors such as historical pumping, recharge to the aquifer from precipitation, and <br />the movement of water from stream and alluvial material to the aquifer outcrop <br />areas (river conductance) are especially important to the model development. <br />Depending upon which value is used, this model's sensitivity to river conductance <br />significantly impacts the model's computed depletions to the surface drainages. <br />Surface drainages include both the river and the river alluvium. This, in tum, has a <br />direct bearing on the replacement and relinquishment requirements. <br /> <br />The model achieved the best calibration with river conductance at 1x10-4 per day <br />rather than 1 x1 0-5 per day as used in previous models. This calibration resulted in a <br />depletion to drainages of 20.7 percent for pumping "not non-tributary" non- <br />designated areas versus 2.9 percent if the smaller river conductance is used (1 x1 0-5 <br />per day). <br /> <br />An important issue to understand is that pumping from Denver Basin wells <br />permitted prior to SB-85-5 and wells already permitted pursuant to SB-85-5 will <br />most likely deplete the net discharge from the Denver Basin aquifers. Additional <br />pumping from future wells would just hasten the time when total depletion occurs. <br /> <br />Chaoter 10 - Nontributary Groundwater Use and Long-term Impact on Water <br />. Rights <br /> <br />This chapter analyzes the use of non-tributary ground water and its long-term <br />impacts on water rights. For the purposes of this analysis, we addressed impacts <br />that result from either non-tributary or "not non-tributary". pumping of the Denver <br />Basins Aquifers. <br />We also looked at the impacts on surface water rights and tributary ground water <br />rights in the South Platte and Arkansas River drainages as well as the impacts to <br />designated ground water rights, both during Denver Basin Aquifer pumping and <br />after such pumping ceases. <br /> <br />. <br /> <br />It is difficult to determine whether the current replacement requirements will be <br />sufficient for making up stream depletions associated with new pumping. Any ability. <br />to make such a determination will depend upon obtaining accurate groundwater <br />diversion records for both existing and new well owners. The State Engineer <br />currently has limited resources with which to obtain these records. Although well <br />owners are required to maintain ownership and address information in the State <br />Engineer's records, few do. Even when the State Engineer can identify these users, <br />not all measure their diversions or maintain records of past diversions. Without the <br />ability to obtain diversion records by mail or other efficient method, the staff of the <br />State Engineer would have to resort to visiting each well on a regular basis to read <br />meters (assuming they were installed and operating) or to issuing orders to install <br />and provide annual records from totalizing flow meters. The State Engineer would <br />require additional staff to obtain- this data. <br /> <br />- 11 - <br />