2017-01-09_REVISION - M1973007SG

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Memo to Brandon Heser, Grant Smith, Bruce Humphries Page 2 January 5,2017 Mine Plan and Ground Water The Daniels Pit mine does not intercept ground water.There is no dewatering pumping at this site. Alluvial water supply wells, located as shown in Figure 1, are pumped for dust suppression and mine product washing water supply. The waste water from the washing process is mostly returned to the settling pond where it infiltrates into the alluvial aquifer.A portion of the pumped water is reused for washing. The total pumping amounts from the alluvial wells are summarized in Table 1. Pumping rates from the two water supply wells used for washing purposes averaged 315 gpm in 2016 and 272 in 2015.These average rates represent conservatively high estimates of the amounts delivered to the existing settling pond. In addition,water from the Fountain Mutual Ditch is diverted into an augmentation pond,located as shown in Figure 1.The water delivered to the augmentation pond infiltrates into the ground,recharging the alluvial aquifer. The purpose of this augmentation pond is to deliver water to the aquifer to fulfill water rights obligations under the augmentation plan decree for the mine,Division 2 Case No. 79CW68.This practice has occurred for decades and we are not aware of any concerns related to the augmentation plan operations and the PCE ground water plume. These collective activities result in water level drawdowns at the locations of the alluvial water supply wells and ground water mounds at the locations of the settling ponds and the augmentation pond.The amount of water level drawdown and mounding have not been historically quantified.For the purposes of this analysis, we have prepared the following estimates of historical and future water level changes expected to occur in the alluvial aquifer,and we have reviewed water level monitoring data from the Schlage monitoring wells to examine water level changes from the existing settling pond. Water level changes at the existing pond should be similar to water level changes associated with the proposed pond. The proposed pond will overlie a relatively fine grained portion of the upper sand layer, which is mostly unsaturated at this location. Based on borehole data presented in the Brierley Report, referenced below, there ranges between 7 to 20 feet of unsaturated material beneath the current floor of the pit at the location of the proposed pond. The northernmost borehole, BA-1, shows that there may be as little as 7 feet of unsaturated material beneath the northern portion of the proposed pond location. Thickness of unsaturated material increases to the south where it is about 20 feet based on the borehole data. The present water level at the proposed pond location is slightly above the top of the fine-grained clay layer on the north side of the proposed pond location and it is about 5 feet below the clay layer on the south side of the proposed pond location. Embankment Construction and Borrow Material We understand based on information provided by Brierley Associates, the design engineers for the pond embankment,that borrow material may be taken from the existing mine floor at the proposed pond location for the construction of the embankment. We have discussed with Brierley that it is possible that the excavation of borrow material could increase the communication of water between the upper and lower sand layers if the fine-grained material was penetrated. If the excavation was deep enough, there is the potential that the pond could intercept ground water. Brierley indicated that this concern can be mitigated and minimized by limiting the depth of borrow material excavation. Based on our communications, it should be feasible to limit excavation to three feet and still achieve the quantity of borrow material needed. We believe that this amount of excavation should not be a concern as it relates to ground water issues.Care