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Memo to Erica Crosby <br />Yoast Mine, TR-04 <br />page 2 <br />appear thorough, comprehensive, and in keeping with standard and prudent <br />practices of the discipline of geotechnology. <br />Less than optimal subgrade conditions were encountered. A keyway was <br />excavated and granular materials placed within it. The granular rock blanket <br />toe drain was enlarged in comparison to the original approved design, rapped in <br />Mirafi fabric, and provided with an enlarged and stronger outfall pipe. The <br />embankment compaction control determined all materials to be placed in excess <br />of the required 95% relative density, normally at moistures slightly dry of <br />optimum. This is the desired normal target for embankment construction. <br />The post-construction stability analysis used the industry recognized SB-SLOPE <br />analytical software. The material properties assigned to the soils and <br />claystone bedrock appear appropriate and conservative for the materials <br />encountered. The low strength of many of the clay soil materials (CL) <br />encountered is compensated for by the relatively low gradient (3.75h:1 v) facial <br />slopes of the 20 foot high embankment. The minimum projected factor of safety <br />under pseudo-static seismic loading conditions was 1.84. The minimum <br />projected static factor of safety for the embankment was 2.26. Both analyses <br />modeled the reservoir full conditions. The analysis is acceptably performed and <br />the results demonstrate the embankment to satisfy our regulatory <br />requirements, as-built. <br />The application also states that Seneca Coal Company will comply with our <br />quarterly inspection requirements. My only recommendation regarding the <br />application relates to inspection of the embankment. Because of the low <br />strength clays encountered and utilized in construction of the embankment I <br />believe it would be appropriate to install several survey monuments on the <br />embankment. I recommend three grouted pins be installed in concrete hubs, <br />centerline atop the embankment, located so as to divide the embankment into <br />four equal segments. The elevation and separation of these monuments should <br />be surveyed immediately after installation. They should be resurveyed <br />quarterly for the first year. If no significant movement is observed, Seneca <br />may then discontinue surveying. In the event that any settlement or <br />