2015-01-12_REVISION - M1985112 (9)

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Mr. J.C. York July 13, 2015 Page 2 Table 1 —Wells within area of Influence of Proposed Slurry Wall Well Data from Wells Within Area of Influence Model Results Well Reported Saturated Max.Change Future Depth Future %Change Name Pemit Rate(gpm) Depth to Thickness in Water Saturated in Sat. Depth Water(ft) (ft) Levels(ft) to Water(ft) Thickness(ft) Thick(ft) DOWNGRADIENT WELLS VARRA 75865 F ND ND ND ND ND ND ND ND DAVIS FARMS 14960 R 101 1150 31 70 -1 32 69 -1% BAAB A C 620 W 45 800 9 36 -1 10 35 -3% TAYLOR JAMES 223885 44 10 11 33 -1 ND ND ND UPGRADIENT WELLS TRUJILLO 23312 25 10 5 20 1 4 21 5% ORONA 28174 _ 19 20 8 11 1 7 12 9% PALMA 297435 ND ND ND ND 1 Uncertain Uncertain Uncertain HARRELL ELDON 226878 50 15 16 34 2 14 36 6% ROTHE 259513 27 20 2 25 1 1 26 4% TRUYELLO 2947 F _ 21 400 6 15 1 5 16 7% HARRELL BRIAN 287278 30 50 ND ND 2 Uncertain Uncertain Uncertain DILKA 44539 34 25 3 31 1 2 32 3% VANBEBER 25941 _ 25 50 2 23 1 1 24 4% WADSWORTH 19472 F _ ND 105 ND ND 1 Uncertain Uncertain Uncertain VANBEBER 16038 25 24 4 21 1 3 22 5% Three down gradient wells can be expected to experience a decline in water levels of approximately 1 foot. Since well yield is proportional to the saturated thickness, we would expect less than a 5% decrease in the maximum theoretical pumping rate of those wells. We do not believe this is a significant impact. Based on our modeling, eleven up gradient wells can be expected to have 0.5 to 2 foot increases in water levels. Only one of those wells (Harrell Eldon) has a reported pre-mining water level depth exceeding 10 feet. The rest of the wells either have reported depths to water of less than 10 feet or no recorded level so the depth remains "uncertain." If the recorded well locations and depth to water are correct relative to the pit and if the wells are located near vulnerable structures (homes with basements or excavations), those structures could be vulnerable to rising groundwater resulting from the slurry wall. Uncertainty Whether future flooding or water logging will occur depend on numerous factors including: 1) well location relative to the pit and slurry wall; 2)the location and depth of vulnerable structures such as homes with basements; 3) the location, magnitude and timing of well pumping and recharge from precipitation, agriculture, and canal seepage that could also affect water levels; and 4) the location of existing drainage or canals that may intercept rising groundwater. Therefore, there is considerable uncertainty whether there is a real and quantifiable risk of significant impact. Mitigation Potential mitigation includes: 1) installing a drain around the slurry wall to minimize any mounding or shadow effect to keep the aquifer at equilibrium 2) or moving or abandoning