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Mr. Daniel Hernandez <br />May 31, 2012 <br />Page 2 <br />HISTORICAL MINE FACILITY STRUCTURE MITIGATION STRATEGY <br />In order to prevent the possibilty of surface expression and potential slope instability in <br />the event the structure were to collapse under the load of the waste rock, the structure should be <br />demolished to eliminate the infilling of the cavern -type void. The structure can be broken into <br />pieces utilizing a hammer chisel mounted on a track hoe. The broken concrete fragments can be <br />arranged and compacted in place. The length of the structure to be demolished will only need to <br />include what underlies the footprint of the DWDA embankment, which totals approximately <br />150 ft. Excess concrete fragments, if present, can be pushed into the inby portion of the structure <br />that is not demolished on the east end. Once the broken concrete has been positioned and <br />compacted with several passes of a track dozer (D8 or equivalent), devlopment waste rock can be <br />placed in this area to fill in any voids that may remain. The initial waste rock should be <br />compacted as previously recommended, i.e., 2 -ft lifts compacted to 90% of the maximaum dry <br />density at a moisture content to within ± 2% optimum moisture content as determined by <br />standard proctor (ASTM D698). Following the initial waste rock placement in this area, the <br />overall site can be prepared for the development of the final DWDA. <br />Since the West Portal ventilation fan that is located approximately 200 ft to the southeast <br />of the structure is actively creating negative pressure in the active portion of the mine as <br />designed and intended, it is evident that the collapsed portion of the slope inby of the structure is <br />providing an adequate plug/seal. Because the cave portion of the slope is allowing negative <br />pressure to be created, additional measures to plug/seal the historical opening are unwarranted. <br />This report contains professional opinions based on site visits, laboratory testing, <br />experience and information provided by NECC. AAI makes no warranties, either expressed or <br />implied, as to the accuracy or completeness of the information provided. Opinions are based on <br />subjective interpretations of geotechnical data; other equally valid interpretations may exist. It is <br />acknowledged that these recommendations have been made based on limited data and, thus, <br />there are inherent uncertainties. <br />The signature below certifies that this report was prepared by me. <br />Jonathan Friedman, PE <br />Associate <br />Agapito Associates, Inc <br />JF/hiw <br />Agapito Associates, Inc. <br />