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OCT-09-96 02:15PM FROM-McCULLEYFRIC~ILMAN 3034471836 ~ T-018 P.04/15 F-154 A proposal was made to leave the cxis[ing railings in place, and to enhance the foundation condmons for the new liner sysum over these tailings by extending the geognd across the full surface area of the tailings and placing a nominal layer of gtanulaz soil over the geogrid prior [o msralhng the liner system. This proposal was rejected by the Colorado Division of Minerals and Geology. The Division uknowlcdged the vahdiry of the concern regarding the stalnhry of the embankment, but cited concerns regarding the long-term integrity of the liner system on a fotmdabon of tmconsohdated tailings in support of their rejection of the proposal. accordingly, a compronuse proposal was developed as follows. • S»rfictal organic materials are to be removed. • The majority of the existing tailings aze to be lcfr in place. • The geogrid reinforcement layer is to be extended across the balance of the surface of the existing tailings, secured to the previously placed geogrid mat near [he upstream toe of the embartlattent -^- raise, but left unsecured at the other edge of the maT cxunsion neaz the toe of the interim berm. • Settlement gauges are to be installed at represrntative locations on [op of the geoid mat exuns,on. • Siuchazge fill (waste rock or other available material) is to be placed on the geoid mat to preload the tailings (At ITEC's discretion, excess fill material may be placed in order to expediu consolidation). • Consolidation of the ttnde[lying tailings is to be monitored via the settlement gauges. • When the tau of settlement is observed to decrease significantly, induating achicrement of primary consolidation of the tathngs, the majority of the surcharge fill material tnay be removed, at ITEC's dislTetiOn, and a cushion ]ayer of finer grained material placed over the fill, as necessary. • The second phase of the bentonite geocompostte liner (GCL) and HDPE primary liner rs to be installed to complete the liner sysum. Based on the observation that there has barn no dtst[ess of the embankmrnt and underlying tailings foundation following completion of the embankmen[ construction, the values for material properties and intertace friction used in the previous stabrltry analyses were reviewed. The block fatlttre analyses were rerun to back calculate appropriate realized values fur the various parameters, given that the apparent factor of safety is at least unity under eturrnt conditions. Figures la and lb present graphical representations of the existing post-construction scenario (static and pseudo static, respecrively), which are considered to be conservative. Table 1 presents the apparent mtnunum realized values for the various parameters. r.Sio1~TECH-Berl WPU ? October 9, 1998