Final Environmental Impact Statement Volume II Appendix K, Part 2

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COMMENTS OF U.S. ENVIRONMENTAL PROTECTION AGENCY EPA -14 program, and not be limited to a requirement to develop a plan, as currently proposed in the Staff - recommended mitigation and Cont.) enhancement measures presented in Table 5 -3, page 5 -42, of the RDEIS. FERC proposes that the districts collect data and plan for overall water -use efficiency and then develop a water conservation action plan within 4 years of license issuance. FERC does not specify any appropriate conservation efficiency goal or specify whether such saved water be used instream for species recovery purposes. Further, FERC's definition of "economically feasible" seems to be quite conservative. We believe that recent analysis and recent events indicate that FERC should specify water conservation savings to be achieved and require the districts to dedicate such water savings to instream flow for the purposes of water quality maintenance and endangered species recovery. FERC acknowledges that the districts have improved efficiency of their delivery systems in places without substantial adverse effect to the ground water mound beneath the project area. But FERC also indicated that any additional ,7111 improvement in efficiency in canal delivery could decrease the ground water level. FERC appears to believe that only "isolated N areas" exist where efficiency improvements would not affect the ground water mound or river return flow (page 4 -30, RDEIS). EPA -151 FERC appears hesitant about the benefits of water conservation, suggesting a significant portion of the agricultural water saved could be offset by reduced Platte River flows. This assumption is not validated by the geologic evidence. It is most likely that significant seepage in the Platte River basin exits as underflow to the Ogallala aquifer which then discharges southeast to the Big Blue River system. If this is correct, then water savings from improvements in irrigation efficiency could be stored for instream purposes without causing the predicted adverse effect of depleting Platte River flow. In order to investigate this underflow issue, EPA reviewed the following geologic reports: (1) United States Geological Survey (USGS) WRI 87 -4176, Hydrogeology of the Tri -Basin and Parts of the Lower Republican And Central Platte Natural Resources Districts, Nebraska, 1987, (2) Platte River Water Balance And Ground Water Investigation, Lidstone & Anderson, Inc., September, 1993, and (3) Report on the South Central Area Ground -Water Planning Study, 1990. The modeling basis used in these reports assumes the Platte River is a boundary condition and therefore the model does not allow flow to move underneath the River. For example, the USGS analysis uses the assumption that "[u]nderflow does not exist in nodes where the streams are connected to the aquifer" (USGS, 87 -4176, page 88). As a result 11 RESPONSES TO U.S. ENVIRONMENTAL PROTECTION AGENCY EPA -15 We agree with EPA's interpretation of the limitations inherent with the existing regional groundwater flow model. However, that does not have much impact on our approach to water conservation and implementation of a monitoring program. It should be remembered that, in general, the ratio of vertical to horizontal permeability in alluvial material similar to that overlying the Ogallala aquifer is on the order of at least 1:25. Thus, the horizontal permeability of the alluvial material beneath the Platte River is at least 25 times greater than the vertical permeability between the alluvium and the Ogallala aquifer. In addition, the permeability of the Ogallala aquifer is considerably less than the overlying alluvium (Harza, 1993, page III -11). It should also be remembered that the groundwater flow model is simply one tool used to monitor the impacts of changes in groundwater infiltration rates. The implementation of a more sophisticated and comprehensive monitoring program will provide hard data, not computer model predictions, to measure and document the impact that water conservation measures have on regional groundwater levels. We believe that the staff - developed water conservation program spending requirement can achieve 10 to 20 percent gross water savings, but for purposes of analysis we have adopted the Bureau's more conservative estimate of 8 percent. We recommend that the Commission endorse the regional water conservation goals represented by the Cooperative Agreement.