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1 <br />' S.4 The Water Budget Spreadsheet <br />The water budget spreadsheet was set up using Excel. Input data included the azea of alluvium to <br />' be removed by the mining operation and the azea of alluvium replaced by unlined ponds, In addition, <br />an aquifer specific yield value was entered for the alluvial material and the unlined ponds. An <br />' specific yield of 0.15 was used for the alluvial material. This value is consistent with this type of <br />aquifer. A specific yield of 1.0 was used for the unlined ponds. This means that for every foot of <br />' alluvial material, 0.15 feet of water is stored; for every foot of unlined pond, one foot of water is <br />stored. The final input into the water budget spreadsheet was the water level fluctuation. The <br />' spreadsheet was set up on a monthly basis. When water levels increased during a given month, [he <br />flow from the stream to the aquifer was calculated. If water levels decreased during a given month, <br />' the flow was calculated to be from the aquifer to the stream. The flow was calculated t~y taking the <br />area of the aquifer, multiplied by the change in water level in the aquifer, and further multiplied by <br />the specific yield. Values were calculated for historic (pre-mining) and future U~ost-mining) <br />' conditions. <br />An example of the wd3er budget spreadsheet calculation is as follows. If 100 acres of alluvium were <br />removed daring the mining process, and the water level in the aquifer historically incr~:ased by one <br />' foot in a month, a lustoric flow from the stream to the aquifer equal to I S ac-fr would lie calculated <br />(100 acres * 1 fr * 0.15). If in the future, the removal of the alluvium was offset by 15 acres of <br />' unlined pond still hydraulically connected to the stream system, and the water level increased by one <br />foot in a given month, the future flow from the stream to the aquifer and the unlined pond would be <br />' calculated to be 15 ac-fr (15 acres * 1 ft * 1.0). In this example, there would be no change in the <br />alluvial aquifer-stream system relationship, and no change in streamflows. <br />L~ <br /> <br />' -27- <br /> <br />