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3.2.4 Piezometers <br />Piezometers were inspected for any signs of damage and or possible collection of water that <br />could affect readings. Measurement procedures were examined and monthly reported results <br />have been reviewed as discussed previously. <br />3.3 RESULTS OF NEW EVALUATIONS PERFORMED AS PART OF DETAILED <br />INSPECTION ANALYSIS <br />In general, the stability analyses performed previously used reasonable and possibly conservative <br />material property and other assumptions in analyses. There is no basis for analyzing stability <br />using different material properties, except for post - earthquake strength reduction of tailing as <br />described below. The following subsections describe an assessment of the previous stability <br />analyses, and the results of additional seepage and slope stability analyses that were performed to <br />evaluate loading conditions on the dam that had not previously been analyzed, including <br />• steady seepage analyses for infiltration from the existing free -water pond to evaluate <br />effects of potential clogging of the underdrain pipes, and <br />• steady seepage and stability analyses for a sustained flood pool condition. <br />3.3.1 Steady Seepage Analyses <br />Seepage analyses were performed to examine steady -state seepage under existing conditions, <br />with a 16 to 17 -acre free -water pond at its current location 600 feet upstream from the dam, <br />sustained by periodic addition of water transferred from the mine site and water pumped back <br />from the collection pond. Two conditions were modeled: 1) present conditions assuming the <br />sub - drainage pipes are fully functional, and 2) a theoretical condition where pipes are clogged, <br />but the granular (sand and gravel) sub -drain blanket layer remains functional. The results are <br />presented in Figure 10. The results indicate that in either case, only a small portion of the tailing <br />directly below the free -water pool are saturated. In the latter case, a small groundwater mound <br />would be expected to form on the liner. In either case tailing near the embankment that could <br />affect stability are anticipated to remain unsaturated. No further analyses are deemed necessary <br />to evaluate the effectiveness of the sub -drain system relative to stability and performance of the <br />dam. Recommendations are provided in Section 6.2 for cleaning and regularly inspecting the <br />sub -drain pipes, along with continued diligence in monitoring of the drain outflows and <br />piezometers in the dam for any signs of significant changes in performance of the sub -drain <br />system. <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 16 February 2014 <br />