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SOUTH PLATTE RIVER BASIN TASK FORCE COMMENTS BY LARRY DIRKS, P.E., DE1\TVER WATER My comments focus briefly on Denver Water's use of effluent, its future water supply plans and the effects of these plans on flows in the South Platte River below Denver. . Denver Water began importing water into the South Platte Basin in 1936, Imported water is not considered tributary to the South Platte River, and as a result, may be removed from the river and reused to extinction. . Denver \Vater first began reusing water by exchanging reusable effluent to its upstream storage facilities in the 1970s, The remainder of reusable return flows from Denver's imported water have increased flows in the South Platte below Denver and have masked the effects of unreplaced depletions from the pumping of wells. . Denver Water, like most other bITowing water suppliers, still needs additional water to serve the City of Denver and its contract distributors. To accomplish that goal, Denver Water is taking steps to enhance its ability to reuse the remainder of its previously unreused return flows through several projects. o Denver \Vater has constructed a water recycling plant at the outfall of the Meh'o WWTP to reuse 17,000 af. o Denver Water is in the process of constructing 30,000 af of gravel pit storage reservoirs that will allow Denver to capture and regulate previously unreused return flows, o Denver Water has initiated the process of quantifying several thousand acre-feet ofreusable lawn irrigation return flows from its service area. . Denver Water has contemplated that as these reusable supplies are developed, the call on the South Platte will become more senior and the lower river will have less water available for appropriation by junior water rights. Denver Water has also increased its need for gravel pit storage to address a more senior call. . As reusable effluent in the South Platte River is reused, the effect of unreplaced well depletions will increase in maf,rnitude for the following reasons: o Depletions from wells accrue to the river over many years. Well depletions that go unreplaced during periods of call by downstream senior vested and conditional water rights will extend the calling period for those senior vested and conditional rights, This longer call will decrease the yield of Denver's junior rights, o In the past Denver could rely on its unreused transmountain diversions to reduce the adverse impact of unreplaced well depletions, Due to an increasing customer base, more difficult pennitting conditions, and more stringent river administration, Denver must protect the yield of its South Platte water rights. Consequently, Denver can no longer afford to overlook unreplaced well depletions, . The priority system must be maintained and should not be violated for the purpose of relieving water users from bad decisions. Exceptions from the priority system for wells will lead down a slippery slope which will undermine the certainty of the priority system. . Denver Water commends the well users who have already obtained valid plans for augmentation to protect the use of their wells. Like\vise, Denver Water will support future plans for augmentation that are based on reliable, long-term replacement sources.