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Memo to Brandon Heser,Grant Smith,Bruce Humphries <br /> Page 5 <br /> January 5,2017 <br /> We understand that Schlage continues to monitor both water chemistry and water levels in various local <br /> monitoring wells and that this monitoring program will continue moving forward.The monitoring program <br /> includes wells ideally situated to detect any problematic changes associated with ground water gradients <br /> and chemistry.We recommend that Schlage and Transit Mix work together to share information to confirm <br /> these findings so that should any problematic changes associated with the new settling pond occur,the issue <br /> can be addressed. <br /> Opinion of Probable Impacts <br /> The proposed settling pond,by design,will cause some level of ground water mounding because the water <br /> slung is intended to infiltrate into the ground.Water level changes are projected to range from 7 to 16 feet. <br /> Based on historical monitoring data from near the existing pond,water level changes are expected to be <br /> closer to the lower range of these estimates. <br /> The ground water mound will alter the ground water gradient such that the flow of the PCE plume towards <br /> the extraction wells will be accelerated. Pumping rates from the extraction wells will likely increase as a <br /> result of the increased ground water gradient. We have no reason to believe that the acceleration of the <br /> ground water flow towards the extraction wells will cause any adverse impacts to the PCE plume or the <br /> treatment system. <br /> Because of the relative locations of the PCE plume and the proposed pond,we do not see potential for the <br /> ground water mound to cause the PCE plume to migrate away from the extraction wells or to any less <br /> desirable location. <br /> The life cycle of the proposed settling pond and the corresponding ground water mound is expected to range <br /> from 5 to 10 years,depending on market and mining production rates. Ground water mounding will be a <br /> temporary condition. <br /> Care should be taken to minimize the depth of borrow material excavation during construction of the new <br /> pond embankment. The excavation should not intercept ground water and should not penetrate the fine- <br /> grained clay layer.These concerns should be clarified in the construction contractor's specifications. <br /> An existing monitoring program including chemistry and water levels is already in place and is ideally <br /> suited to detect any problematic changes that may result from ground water infiltration from the proposed <br /> settling pond. The monitoring program should continue and Transit Mix and Schage and its consultants <br /> should continue to communicate and share information related to ground water data and mine plan <br /> operations.Based on our communications with Schlage and Geosyntec,consultant to Schlage,both parties <br /> are open to sharing information and monitoring ground water issues at the location of the proposed settling <br /> pond. <br /> Geosyntec, consultants for Schlage, have reviewed a previous draft of this technical memorandum and <br /> generally agree with our findings based on the current understanding of the mine plan and new settling <br /> pond design. Geosyntec and Schlage also agree that it is important to share information and monitor the <br /> aquifer response to the proposed pond and adjust pond operations accordingly if problems should occur. <br /> I� <br />