2018-11-21_REVISION - M2004044 (21)

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r , Table 1: Aquifer Tests Conducted Near Tucson South Mine(Wilson,1965) Well Depth Pumping Rate Hydraulic Well Location Geologic Unit �) (gpm) Conductivity d ) T1S,R67W,Sec.35 Valley Fill 39 360 307 4 miles SW of site Deposits T1S,R66W,Sec.30 Valley Fill 35 140 334 3 miles SE of site' De osits TIN,R66W,Sec.8 Valley Fill 36 540 561 6 miles NE of site Deposits TIN,R66W,Sec. 18 Valley Fill 50 1020 602 5 miles NE of site Deposits TIN,R66W,Sec. 19 Valley Fill 23 450 668 4 miles NE of site Deposits Qp TIN,R66W,Sec.30 Valley Fill 40 610 695 3 miles NE of site Deposits(Qp TIN,ROW,Sec. 13 Valley Fill 38 575 762 5 miles N of site Deposits(Qp) F A pump test was conducted at the east end of the site,near the South Platte River,in 2004 by Bishop- Brogden Associates. Reportedly,the hydraulic conductivity in the clean sand and gravel was 1700 feet per day at a pumping rate of 565 gpm. The well was approximately 30 feet deep. Note that the hydraulic conductivity was quite high because was tested only in the sand and gravel zone. The hydraulic conductivity used in the model reflects an average value for the entire alluvial,cross section (overburden,mud lens,sand and gravel)at every location. No information was available in Wilson(1965)for the hydraulic conductivity of terrace deposits(Qb) and the wind-blown deposits(Qes)west of the site. However,other literature sources report that hydraulic conductivity values of alluvium in northeastern Colorado may range from 20 to 750 feet per day(Hershey and Schneider, 1972). Therefore,the range of hydraulic conductivities for the three geologic units in the area of the reservoir are expected to be from 20 to 1700 feet per day. The hydraulic conductivity of the terrace deposits is expected to be similar to the valley fill deposits,as the-percentage of gravel, sand and silt are similar. The wind-blown deposits are expected to have a lower hydraulic conductivity because they consist primarily of fine to medium sand. In the western part of the model,the bedrock rises,reducing the saturated thickness of the alluvium. To simulate this,the hydraulic conductivity was adjusted based on the ratio of alluvium thickness to the height of the cell. For example,a cell that was vertically half alluvium and half bedrock would have a hydraulic conductivity of 200 feet per day instead of the 400 feet per day used in the cells that consisted entirely of alluvium. Based on experience and literature values,the Specific Yield of the alluvial aquifer was assumed to be 0.2 throughout the domain. 2.4 Recharse Recharge was applied in the model to account for rainfall and snow melt that infiltrates into the ground and reaches the water table. Precipitation recharge in north-central Colorado has been reported to be about five percent of the total precipitation(RMC, 1991). This translates into an annual recharge rate of -4- August 2004 M3919 0t91TS GW ModeATS Repon\Tucson Soud Rpt I &doe