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SECTIONONE Purpose and Scope of Study <br />Interceptor Canal <br />The tailing impoundment is surrounded by an unlined clean water interceptor channel. The <br />channel collects and diverts surface water runoff around the perimeter of the impoundment, <br />discharging it downstream of the facilities. <br />1.2 PURPOSE AND SCOPE OF SERVICES <br />Based on the studies performed by W.W. Wheeler & Associates, we understand that Climax may <br />store the precipitation from extreme storm events (PMP) within the impoundment. We have <br />assumed that Climax will release the decant water through the spillway at a reduced rate. During <br />the PMP event, the decant pond elevation was assumed to rise to near the dam crest reducing the <br />beach width from 1,000 feet for the normal operating pond conditions to 100 feet following the <br />PMP event. The purpose of this study is to evaluate the impact of the elevated decant pond and <br />phreatic surface conditions on the overall dam stability. <br />URS Greiner Woodward -Clyde (Woodward- Clyde) was contracted by W.W. Wheeler & <br />Associates to conduct the necessary geotechnical analysis and prepare this report. Our work <br />consisted of three tasks, which include: <br />Task 1 Dam Seepage Analyses <br />Dam seepage analyses were performed to evaluate the changes in the embankment seepage <br />conditions and estimate the phreatic surfaces that result from storage of the PMP event. <br />Analyses were performed for both the current dam elevation and ultimate design dam elevation <br />of 8900 feet. Seepage analyses were also performed to estimate the post - closure seepage <br />conditions for the ultimate height geometry following the PMP event. The estimated phreatic <br />surfaces were used later to estimate embankment stability. <br />Task 2 Dam Stability Analyses <br />Dam stability analyses were performed to evaluate the embankment stability for the current <br />height, ultimate height, and post closure conditions with the raised phreatic surfaces resulting <br />from the PMP event. Both static and post- seismic loading conditions were evaluated. <br />Task 3 — Report Preparation <br />Results from the dam seepage and stability analyses were compiled, discussed and presented in <br />this geotechnical report. This report also contains our conclusions and recommendations based <br />on the results of the above mentioned analyses. <br />N:IPROJECTS6844618 HENDERSON_MILL BARGISUB0018.0 PROJ_DELMH- MILLR3.DOC124JUL -0111 1 -2 <br />