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February 7, 2007 <br />3.0 EVALUATION AND RECOMMENDATIONS <br />3.1 Summary of Findings <br />3.2.1 General <br />The majority of the historical mining features observed were small test pits or small, conical surface <br />workings. Over 430 of these features were mapped. Due to their small size and limited potential to <br />cause geotechnical problems for the proposed VLF, few, if any, of these features will need to be <br />investigated further in the Phase II investigation. However, a large number of shafts, adits, <br />depressions, and stopes were identified, and many of these features will require some type of <br />remediation prior to construction of the proposed VLF. In order to develop a successful remediation <br />plan, further information is required regarding the characteristics and extent of these features. <br />3.2 Recommendations for Future Work <br />-6- 063 -2140 <br />Recommendations for future work include the remainder of the Phase II site investigation <br />recommendations presented in Golder, 2006. Specifically, we recommend the following: <br />• Conduct a preliminary drilling program to locate excavations beneath the ground <br />surface that might adversely impact the stability of the VLF foundation; <br />• Conduct and interpret the results from Electrical Imaging (EI) surveys in the <br />Squaw Gulch area to identify resistive anomalies; and <br />• Develop and conduct a confirmatory drilling program to further evaluate the <br />extent and nature of underground workings and anomalous EI areas with the <br />potential to adversely impact the VLF liner system. <br />3.2.2 Phase Va Preliminary Drilling Program <br />Drawing 2 shows the locations of the drillholes proposed for the Phase Va preliminary drilling <br />program. It is expected that between 109 and 176 percussion borings will be needed to complete the <br />program. The objectives of this program are to conduct a "first pass" assessment to locate open voids <br />underground that might become unstable in the future and to obtain an approximate estimate of the <br />vertical height of the surface crown pillar in areas where voids are identified. Some features which <br />are already known to be major features will not be drilled in this phase, but they will be targeted by <br />later confirmatory drilling programs. Similarly, very minor features (e.g., small test pits) will not be <br />drilled because they represent little risk to the future VLF foundation. In this phase, intermediate or <br />016,2110n100WHI STNIO ucrvosmcmFEemsw- xrsrowc.uwonKINcs- FNLOWEB47 DOC Golder Associates <br />