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February 7, 2007 <br />3.2.3 EI Survey Program <br />-8- 063 -2140 <br />remediation that are located within 50 to 60 feet of the ground surface, except where the overburden <br />is more than 15 feet in depth or where topsoil stockpiles or waste rock piles exist, in which case the <br />target depth should be correspondingly deeper. The target depth may also be deeper where historic <br />records indicate very wide stopes (> 12 feet wide), which have a higher potential to cave and create <br />voids near the surface. It should be noted that many of the drill sites that are recommended for the <br />Phase II investigation will require access support, e.g., road support, clearing, etc. <br />The purpose of EI surveys is to identify subsurface resistive anomalies that may indicate the presence <br />of underground voids. EI surveys consist of making multiple measurements of electrical resistivity <br />along the ground surface. These resistivity measurements are then combined and processed to <br />develop two- dimensional sections of the subsurface showing the distribution of resistivity with depth <br />and distance. Areas of consistently high resistivity indicate the potential for underground voids. The <br />scope of the current EI program is similar to the program conducted in support of the Cresson <br />Phase IV design. EI survey lines should be placed 50 feet on center over the proposed Squaw Gulch <br />VLF Extension footprint. Along each survey line, electrodes should be placed 10 feet on center <br />(typical). EI surveys are most critical in those sectors of the proposed VLF where historic workings <br />are thought to exist, based on the field reconnaissance program and/or the review of historical mining <br />records. Significant resistive features that do not correlate with any known mine void should be <br />targeted for subsequent confirmatory drilling <br />3.2.4 Confirmatory Drilling Program <br />The purpose of the confirmatory drilling program is to define the extent and depth of key <br />underground mine workings identified within the proposed VLF footprint area. The primary focus of <br />this program is to provide definitive delineation of workings that have the potential to significantly <br />impact the stability of the VLF foundation. The confirmatory drilling program generally consists of <br />drilling holes around key shafts with known workings and/or areas with EI anomalies. If an <br />underground working is encountered during the drilling program, the working is "chased" by drilling <br />additional holes perpendicular to the strike of the working until the working is bounded, or until the <br />depth of the working increases such that it will no longer adversely impact the VLF liner (generally <br />depth > 50 feet). <br />1106 o S FNL 07FEBOTPM ORICALWMUCILON FN O,FEB0, DOC Golder Associates <br />