Final Environmental Assessment for the Tamarack Managed Groundwater Recharge Project

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IV 7 low evaporation amounts. The evaporation computed for existing the lower South Platte River Basin in Colorado is recharge Projects in gross flows. typically less than one percent of ' By selecting the correct location of recharge bas' the river, the return flows occurring ms with respect to their distance Depletion Factor ( "SDF" g m the s tare from a standardized Factor )method developed b mthe can Geologic optimized. The Stream accretions used for analyzing the timing ("USGS") is to the river. USGS SDF maps g °f well depletions and recharge canal reaches along the South Platte River gin Col for for recharge basins and Of days and represent the la These SDF factors have units mathematical solution of the SDF emethod, the rg S ° return to the river. From the when 28 percent of the amount recharged SDF factor in days represents the time 72 Percent of the recharge returns to the rive in the ed to the river. The remaining Period- Figure 1 is a USGS time folloWin g River in Colorado. map of SDF factors for the lowest reach o the South plane South Platte River Basin inDColorado ran eel s stems Y and recharge basins in wells will be located g from 60 days to 1,500 the lower between the recharge basins and days. Observation gradients and return flows to the river from the recharge the s �t groundwater monitored. Estimates of return flows to the river from the operation can be Plan may be reviewed b peration of the T Cooperative Agreement. Y the Governance Committee during the term of the Tamarack II• HISTORICAL ANALYSIS Colorado has analyzed how the T _ • 1943 -1994. For the Tamarack Plan would have operated during flows for diversion bP r oof 'this historic Anal s f period Y Tamarack Plan to rec Psis; periods and amounts of excess assumed to occur when the followin age facilities in Colorado were River Compact requirements were satisfied conditions were satisfied: Wildlife Service ( "FWS� and (2) flows ex (1) South Platte Platte ) Year round target flows at the G � the Fish and River in Nebraska. Existing target flows for eve rand Island gage on the analysis and the monthly target values varied with h every month�were used in this average, and dry. hydrologic conditions of wet, This analysis assumed that to recharge basins could cur d - of new groundwater wells located °�� dig the winter next to the river freezing periods due to warmer because wells can operate during Pumping to recharge basins that reflects pore temperatures. This Colorado Division of Wildlife ,s Tamarack operations at the 10,000 also assumed to install approximately Ranch State Wil �� acre pproximately twenty new large capacity lise Area. Colorado plans construct necessary recharge basins tY wells and associated i Of the new recharge and related monitoren Pipelines and barge basins which the wells g features. The SDF values Pmnp into will vary from 60 days to 3