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Executive Summary <br />Some further groundwater development is still possible in <br />unincorporated EI Paso County and in the South Metro <br />Denver area. Although many water providers in the <br />South Metro Denver region are working diligently to <br />secure additional surface water supplies, the non- <br />renewable bedrock aquifer supplies continue to be mined <br />at an increasing rate. The increased reliance on <br />nonrenewable, non-tributary groundwater for permanent <br />water supply in many portions of the Denver Basin region <br />brings with it serious reliability and sustainability <br />concerns. <br />Legal Constraints on Groundwater Use <br />Some of the most productive aquifers in the state include <br />the alluvial aquifers along the South Platte and Arkansas <br />Rivers. These aquifers are in direct hydraulic <br />communication with their adjacent rivers. The river water <br />helps sustain groundwater levels in these alluvial <br />aquifers as does seepage from irrigation canals and from <br />surface water used for irrigation that percolates into and <br />recharges the aquifers. An exception to this, where <br />groundwater levels are declining, is in regions such as <br />along the South Platte River in Morgan County where <br />sprinkler (center pivot) systems have been installed that <br />minimize percolation and return flows. <br />Today there generally has not been a limit to the physical <br />supplies of these alluvial aquifers, but there is very <br />clearly a limit to their legal availability. In both the <br />Arkansas and South Platte Basins, most of the well <br />pumping is junior in water right priority to the older <br />surface water rights. Pumping effects on the surface <br />water flows must be replaced and detailed plans for <br />replacement or substitute supplies have been worked out <br />over the years for most wells. As a result of the litigation <br />between Kansas and Colorado over the interstate <br />Compact with Kansas on the Arkansas River, well users <br />in Colorado are having to restrict their historic uses. On <br />the South Platte River, over 4,000 alluvial well users are <br />having to adhere to new rules that may restrict their <br />future use of this abundant supply so as to not affect the <br />rights of senior surface water users. <br />The ongoing issues of water rights, either in-state or <br />across state boundaries, have made the issue of legal <br />availability of water a significant one for many <br />groundwater users and have also called into question the <br />reliability of the alluvial aquifer supplies. The physical <br />and legal availability of alluvial aquifer supplies also need <br />to consider the value of those aquifers in providing <br />baseflow to streams that help maintain riparian wildlife <br />habitat and preserve aquifer supplies so that they are <br />available for use during times of drought. These factors <br />should be considered as components in both the <br />sustainability and reliability of the state's groundwater <br />resources. <br />Conclusion <br />Groundwater as a source of water supply finds itself at a <br />juncture of legal and physical constraints. As an <br />economic and practical source of water for both <br />agriculture and domestic use, the further development of <br />groundwater is highly probable. Concerns about <br />reliability and sustainability are appropriate within the <br />context of drought and the administration of our water <br />resources under the Prior Appropriation Doctrine. <br />6. In-basin Solutions Can Help Resolve Gaps <br />Between M&I Supply and Demand, but There Will <br />Be Tradeoffs and Impacts on Other Uses <br />The Identified Projects and Processes developed by the <br />Basin Roundtables and Options for Future Alternatives <br />formulated as part of the SWSI process generally fall <br />under one of six families of options: <br />^ Conservation Options, including: <br />- Active Municipal & Industrial Conservation <br />Measures <br />~~ <br />..F ti~q , ,M~ . ~; <br />!` n\$ ~~.~ ~ <br />3 : y ' e <br />~~' ,~' a r+, we 1 i;`. . ~`. v. m ., . ~, r.<';S ~~. <br />~ <br />$~ole'ri~ice Wo~e' $upplY Initia~ive <br />- Agricultural Efficiency Measures <br />^ Agricultural Transfers, including: <br />- Permanent Agricultural Transfer <br />- Interruptible Agricultural Transfer <br />- Rotating Agricultural Transfer (Fallowing) with <br />Firming for Agricultural Use <br />- Water Banks <br />~~ <br />S:\REPORT\WORD PROCESSING\REPORT\EXEC SUMMARY 11-10-04.DOC ES-29 <br />