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5.0 CALCULATION OF WELL DEPLETIONS AND POND ACCRETIONS <br /> Two separate methods were used to calculate well depletions and pond accretions depending on structure <br /> location: <br /> Wells Within 900 feet of the River: For wells close to the river, the Revised Tamarack <br /> Recharge Model was used to calculate depletions and accretions. Stream depletions were <br /> calculated for each of the close in wells using a stream leakance of 20 days " Unit <br /> Response Functions (URFs) were than developed from the modeling output for each of <br /> the wells. <br /> Ponds and Wells Greater Than 900 feet from the River: For structures further from the river, <br /> the Original Tamarack Recharge Model was used to calculate well depletions and pond <br /> accretions. URFs were than developed from the modeling output for each of the wells. <br /> To provide depletion data for calculation of URFs, the following procedure was followed: <br /> • A modified version of the appropriate Tamarack Recharge Model was used as the base <br /> model. This modified version does not include neighboring operations and maintains a <br /> constant ET rate regardless of depth to groundwater. <br /> • All pre- existing recharge, pumping and calibration data were deleted. Average yearly ET <br /> and precipitation were used for each zone. This model version is a "clean- slate" version <br /> of the model used to estimate aquifer response under specified conditions. <br /> • Zone Budget, a program written by the USGS (Harbaugh, 1990) was used to identify the <br /> flows into and out of the stream boundary. <br /> For wells, the appropriate model was run twice: 1) run with recharge well pumping for 30 days at <br /> 2500 gallons per minute; and 2) run without any recharge well pumping. The change in flows to <br /> the river boundary between the two runs was calculated. This change represents the impact of <br /> recharge well operations on the river boundary. For ponds the same procedure was used except <br /> the recharge rate was 1500 gpm for 30 days. <br /> The stream depletions were summarized for 30 day intervals and percentages of depletions <br /> occurring during these 30 day intervals were calculated. Tables 6 and 7 provide the URFs for <br /> all the well and pond structures, respectively. URF values in Tables 6 and 7 are displayed to <br /> four decimal places. The modeling results indicate that the depletions go out for several months <br /> with very small URFs until the total depletion reaches 100 %. For months where the URF was <br /> less than 1/2 of 1% (0.0050) the depletion was estimated at 0.0000. To make sure that the URF's <br /> for all months total 1.0000 any difference was added to the previous months URF. <br /> • <br /> 14'Page <br />