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Metropolitan Water Supply Investigation Executive Summary While each water supply category evaluated in the MWSI appears to present significant, technically feasible cooperative opportunities, each also raises several issues that present serious obstacles to implementation without considerable additional work. The table below summarizes the MWSI's findings. Cooperative Supply Cateaorv Suoolv or Yield Potential Actions Items/Unresolved Issues Conjunctive Use up to 60,000 acre-feet of South Plalte and Blue River stream depletions surface water yield under Water right constraints example project analyzed F easibilily of long-term, large scale recharge IGA's among participants Balancing groundwater depletions with increased use of surface waters Effluent up to 120,000 acre-feet Relatively high costs of excess reusable retum Public acceptance of potable reuse flows; specific project yields Effects of exchanges on water quality were not investiaated Effects on In stream flows Interruptible Supply up to 190,000 acre-feet Would require major institutional changes of interruptible supply; Impacts to agricultural colTUTlunities specific project yields Geographic/cost considerations were not investioated Other System up to 20,000 acre-feet Water right constraints Integration of yield under example IGA's among participants Oooortunities oroiects analvzed Federal action (Chatfield storaoe reallocation\ COOPERATIVE WATER SUPPLY OPPORTUNITIES Conjunctive Use would involve the linkage of groundwater systems currently serving communities in parts of Douglas and Arapahoe counties with the Denver Water system. Water available from the Denver system in average and wet years could be used to meet demands and for recharge of Denver Basin aquifers. Groundwater sources would be used to meet demands not fully satisfied by surface water sources and during periods of drought. For the example project analyzed, conjunctive use arrangements could yield up to 60,000 acre-feet per year to meet new demands or reduce existing groundwater pumping from the Denver Basin aquifers. Conjunctive use presents a promising solution to continued dependence upon non- renewable groundwater resources by the growing communities in the South metro sub- region. Conjunctive use also raises several unresolved questions. To the extent that a conjunctive use project would rely on additional transmountain diversions from existing facilities and water rights, this would raise objections from West Slope interests. However, the operational flexibility inherent in a conjunctive use project could allow for mitigation of some impacts while still generating significant yield. Other issues and uncertainties associated with conjunctive use include changes in water rights, the feasibility of large-scale recharge over the long term, and the challenges associated with securing required intergovernmental cooperation among potential conjunctive use participants. Pre:pared for the Colorado Water Conservation Board. Colorado Department ofNltural Resources by Hydrosphere Resource Consultants, 1002 Walnut StJee~ Suite 200, Boulder. CO 80302 vii I I I I I I I I I I I I I I I I I I I