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I I I I I I I I I I I I I I I I I I I movement of water from stream and alluvial material to the aquifer outcrop areas (river conductance) are especially important to the model development. Depending upon which value is used, this model's sensitivity to river conductance significantly impacts the model's computed depletions to the surface drainages, Surface drainages include both the river and the river alluvium, This, in turn, has a direct bearing on the replacement and relinquishment requirements, The model achieved the best calibration with river conductance at 1 x1 0'" per day rather than 1x10-5 per day as used in previous models, This calibration resulted in a depletion to drainages of 20,7 percent for pumping "not non-tributary" non-designated areas versus 2.9 percent if the smaller river conductance is used (1x1 0-5 per day), An important issue to understand is that pumping from Denver Basin wells permitted prior to SB-85-5 and wells already permitted pursuani to SB-85-5 will most likely deplete the net discharge from the Denver Basin aquifers, Additional pumping from future wells would just hasten the time when total depletion occurs, Chapter 10 - Nontributary Groundwater Use and Long-term Impact on Water Rights This chapter analyzes the use of non-tributary ground water and its long-term impacts on water rights. For the purposes of this analysis, we addressed impacts that result from either non-tributary or "not non-tributary" pumping of the Denver Basins Aquifers. We also looked at the impacts on surface water rights and tributary ground water rights in the South Platte and Arkansas River drainages as well as the impacts to designated ground water rights, both during Denver Basin Aquifer pumping and after such pumping ceases, It is difficult to determine whether the current replacement requirements will be sufficient for making up stream depletions associated with new pumping. Any ability to make such a determination will depend upon obtaining accurate groundwater diversion records for both existing and new well owners, The State Engineer currently has limited resources with which to obtain these records, Although well owners are required to maintain ownership and address information in the State Engineer's records, few do. Even when the State Engineer can identify these users, not all measure their diversions or maintain records of past diversions, Without the ability to obtain diversion records by mail or other efficient method, the staff of the State Engineer would have to resort to visiting each well on a regular basis to read meters (assuming they were installed and operating) or to issuing orders to install and provide annual records from totalizing flow meters, The State Engineer would require additional staff to obtain this data. It may be necessary to conduct additional modeling using better data that may have to be collected through additional fieldwork. In particular, data on the amount of historical pumping may have to be improved through field investigations and user - 11 -