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Discussion <br />The quarry will be developed to the maximum volume recoverable within the footprint of the <br />limits of mining. The maximum recoverable volume is dependent on the final cut slope angles <br />within the mine, which are dependent on the structure and behavior of the rock mass during <br />excavation. The mining plan outlined above is the most aggressive maximum build-out <br />configuration which can likely to be achieved if the rock mass properties are sufficient to support <br />the benches and highwalls as shown. These anticipated maximum build-out conditions are based <br />on information gathered during a visit to the proposed quarry site and from a geotechnical <br />investigation performed by J.A. Cesaze and Associates, Inc. Phase IA will be used as a trial or <br />demonstration phase in which bench and highwall performance wifl be evaluated in various <br />orientations. Observations of Phase IA will lead to recommendations for bench and highwall <br />configurations in Phase ID with continued observations of bench and highwall performance as <br />the quarry is developed. <br />Observational Method <br />Based on presently available information, it is not practical to model the rock mass in sufficient <br />detail to predetermine absolute final slope configurations. Therefore, the "observational <br />method" approach to deternuning stability of final cut slopes will be employed. The <br />observational method is a rigorous series of interactive steps of excavating rock, observing the <br />condition of the rock mass and behavior of rock slopes, and refining the design based upon <br />observed conditions. Based on the observations and evaluations at a given stage, the next stage <br />of the operation is designed and implemented. This approach will give more certainty that stable <br />slopes for reclamation purposes can be achieved. <br />Using this method, Phase IA of the excavation process will involve an "experimental" <br />excavation which will consist of slopes of 50 ft wide benches and 40 ft tall highwalls in various <br />orientations well within the mining limits. Phase IB benches and highwalls will be developed <br />based on the performance of Phase IA. Evaluations will consist of observing rock mass <br />behavior, mapping rock mass features, reviewing stability analyses in light of updated <br />information, and/or kinematic analysis. Periodic review will be done in order to compare current <br />rock mass conditions and slope behavior to those observed in the initial phase. <br />Bench and Highwall Configuration <br />Typical bench and highwall configurations are presented in Figure C-2, Mining Plan Map. There <br />aze two planned designs for benches and highwalls. Above elevation 5800, benches will be 50 ft <br />wide and highwalis will be 40 ft tall. Below elevation 5800, benches will be 40 ft wide and <br />highwaIls will be 50 ft tall. All mining highwalls are proposed with vertical slopes. <br />Highwalls wi21 generally be developed in 40 ft high lifts where practical which corresponds to <br />the typical drill length for blasting holes. For highwalls greater than 40 feet tall, which are <br />possible for the lower portion of the quarry, blasting will be either in multiple lifts of 40 ft or <br />less, or drilled full length with longer drill rod strings. Rock will be loosened and fragmented by <br />conventional blasting, then loaded into an in-pit mobile primary crusher(s), with conveyor <br />transport to the main process azea. <br />Front Range Aggregates, LLC- Parkdale Quarry <br />DMG l l2 Permit Amendment <br />Poge !7 <br />