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<br />""'-'.,~ <br />.? <br />.....- i <br /> <br />Data Input for Aquifer Parameters <br /> <br />For each cell in the models, the elevation of the starting water level <br />(head) and the elevation of the bottom of the aquifer must be specified. <br />Cells therefore have vertical dimensions equivalent to the aquifer <br />thicknesses. The heads for the start of a simulation were initialized at a <br />uniform value. Using the appropriate data from the master arrays, the <br />aquifer thickness of each cell was computed and the bottom was set at a <br />distance below the starting head equivalent to the aquifer thickness. <br /> <br />The specific yields of the water yielding materials given in Rule 6 <br />were used to compute the average specific yields, At each model cell the <br />specific yield for the water yielding materials was first multiplied by the <br />thickness of the water yielding materials and then divided by the aquifer <br />thickness. Similarly at each model cell, the hydraulic conductivity of the <br />water yielding material was multiplied by the thickness of the water <br />yielding material and then divided by the aquifer thickness to arrive at <br />average hydraulic conductivity. <br /> <br />If model cells have vertical dimensions equivalent to the total aquifer <br />thickness, the hydraulic conductivities and the specific yields input to the <br />model must represent average values for the aquifer within each cell. To do <br />otherwise would cause drawdowns and gradients to be computed which would not <br />represent drawdowns and gradients in the rea 1 aquifer. The volume of a <br />model cell multiplied by the modeled specific yield must equal the drainable <br />water in storage in that cell. <br /> <br />Recharge and Discharge <br /> <br />Ground water moves vertically between aquifers. Senate Bill 5 provides <br />all aquifers be reduced at least to water table conditions thereby limiting <br />movement of ground water between aquifers to a downward direction. <br /> <br />When an aquifer is pumped the water level is lowered below the top of <br />the aquifer and a fully saturated connection with the overlying aquifer <br />would no longer exist. Movement of water from an overlying aquifer into an <br />aquifer would be independent of water levels in the lower aquifer. Leakage <br />from an overlying aquifer was not simulated in any of the models. <br /> <br />Pumping an aquifer would change the flow from that aquifer into an <br />underlying aquifer in proportion to the change in water level. Changes in <br />leakage from an aquifer into an underlying aquifer were simulated for all <br />aquifers except the laramie-Fox Hills and the Lower Arapahoe. The <br />relatively impermeable clays and shales of the Pierre and Laramie formations <br /> <br />-18- <br /> <br />). <br />.:,~ ..;~ <br />