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INING & ENVIRONMENTAL SERA <br />• <br /> <br />2.2 Rock Strenath <br />The rock strength of the adit ribs and roof in the bulkhead areas was tested to <br />determine whether the rock strength would be a constraint on bulkhead design. <br />The results are included at Tab #4. In all cases, for 3 samples each of the Steve <br />and Pierce, the rock compressive strength exceeded the design concrete <br />strength of 3000 psi used in the preliminary calculations, which means that the <br />concrete strength was the governing constraint with respect to shear at the <br />bulkhead perimeter. <br />2.3 Mine Water <br />Mine water quality data was provided to MES by Whetstone Associates, and is <br />summarized at Tab 15. The mine shaft water quality data were judged to be <br />representative of the expected water quality in a scenario where water was being <br />impounded by the bulkheads. <br />Two parameters which are typically of concern in the design of mine bulkheads <br />are acidity and sulfates, both of which can attack concrete. <br />• A review of this data indicates that the mine shaft water is alkaline, approximately <br />a pH of 7.5 and has a sulfate concentration of about 2000 mg/I. Acidity is thus <br />not an issue. While the sulfate concentration is not high compared to many <br />Figure 4: Borehole in Pierce adit roof <br />