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Boreholes were drilled to depths of approximately 35 to 45 below the surface until bedrock was <br /> encountered. After the completion of each borehole,temporary piezometers were installed to measure <br /> groundwater levels.Additionally, split-barrel sampling was also conducted on site to estimate the relative <br /> density and consistency of the subsurface soils.From these exploration and field testing, samples were <br /> taken and further analyzed within EEC's lab for moisture content,strength parameters and classifications. <br /> The site subgrades were then broken down into three designations in the ECC slope stability analysis as <br /> Overburden, Sand with Gravel, and Bedrock. These measurements and test results for each designation <br /> were then incorporated into the slope stability model. <br /> As discussed earlier,a total of two critical slopes were evaluated in the EEC report. Each slope is based <br /> on the determination of critical or non-critical structures from Section 30 of the MLRB Policies. For non- <br /> critical structures,a slope of 2.25h:1v was used and for critical structures,a slope of 3h:ly was used. <br /> Additionally,the slope stability analysis for a critical structure included a distributed load of 2000 psf set <br /> back 50 feet from the slope crest for a length of 130 feet. This is to account for additional loading that <br /> may occur or exist above the mined slope. <br /> For each critical slope,two scenarios were analyzed. The first being under static conditions and the <br /> second under seismic conditions.Based on the provided information in the EEC report and the <br /> requirements of Section 30 of the MLRB Policies,the Division will be evaluating EEC's Factors of <br /> Safety(FOS)to the minimum requirements for FOS of strength measurements resulting from multiple <br /> tests.The resultant FOS from EEC's stability analysis and the Division's requirements are summarized in <br /> the table below. <br /> Factors of Safety-Stiles Mining Resource <br /> Section ECC Division <br /> Requirements <br /> Non-Critical 1.471 1.25 <br /> Non-Critical* 1.154 1.1 <br /> Critical 1.789 1.3 <br /> Critical* 1.315 1.15 <br /> *Under seismic conditions <br /> As shown by the above table, EEC's resulting FOS exceed the minimum requirements of the Division. <br /> Based on the above discussion,ASC has provided all information to satisify the general requirements of <br /> Rule 6.5(1), 6.5(3) and 6.5(4). Stated earlier in the memo,ASC is proposing to backfill,compact and <br /> grade the Mine back to its approximate topographic elevations that existed prior to mining operations <br /> commencing as shown on Map F1.Based on this proposed reclamation plan,no major slope, <br /> embankment, and/or highwall will exists post-mining. Due to this,a geotechnical evaluation as <br /> potentially required under Rule 6.5(2)is not necessary and thus not applicable for this review. <br /> While the information provided under the ECC meets the minimum requirements of Rule 6.5,the <br /> Division has additional comments and questions for additional clarification in regards to the ECC slope <br /> stability report. Please include the following questions and comments for ASC's review: <br /> • In the ECC report,there is limited discussion regarding the bedrock foundation of the <br /> Mine's pit floor.It is noted that bedrock consists of claystone which has the potential to be <br /> expansive and could have an impact on the mined slopes.Please provide additional <br /> discussion regarding if the potential of swelling from the claystone at the Mine exists and <br /> whether it could have an impact to the stability of the mined slopes. <br /> • When reviewing the ECC report,it is unclear to the Division on what strength parameters <br /> Stiles Mining Resource Review Memo January 24,2022 <br />