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The excavation has been divided into four phases. Benches and highwalls above elevation 5800 <br />ft will be developed by leaving intentional short breaks in the highwalls and leaving diagonal <br />haul roads in place in an attempt to break up the horizontal lines created during standard <br />highwall and bench mining (see Figure D-1). These benches will be reclaimed by backfilling. <br />Front Range Aggregates intends to use the quarry for water storage after mining is complete. <br />The approximate water surface elevation will be 5790 ft. Benches and highwalls below <br />elevation 5800 ft will not need to be backfilled as they will be underwater once mining is <br />complete and the pit is used as a water storage reservoir. If necessary, some point-plugging of <br />any leakage will be performed through grouting, although no major grouting is anticipated. <br />Observational Method <br />This permit amendment describes in detail an "Observational Method" to mine slope <br />development which will be implemented at the quarry. The highwall and bench configuration <br />shown represents the most aggressive scenario. The observational method will be used to <br />develop actual highwall and bench configurations based on observations of actual rock mass <br />behavior as described below. Maximum build-out benches and highwalls will consist of 50 ft <br />wide benches and 40 ft highwalls from the highest elevation in the northeast comer of the mining <br />limits down to elevation 5800 feet above sea level. Below elevation 5800, the benches and <br />highwalls will be 40 ft wide by 50 ft high. Actual build-out will vary based on observed highwall <br />performance. <br />The Observational Method is a step-wise approach to slope design by which new information is <br />regularly used to upgrade previous analyses. This method will be utilized as a practical approach <br />to designing slopes in a rock mass with variable conditions. Front Range Aggregates will <br />perform an experimentaUMal initial excavation well within the mining limits in order to observe <br />the actual performance of the benches and highwalls in multiple orientations. This trial <br />excavation will be used to establish the basic design for the benches and highwalls. Evaluations <br />and changes to the highwalls and benches will be made as necessary over time based on <br />continuous observations of bench and highwall performance. <br />Front Range Aggregates will submit a report to the DRMS after the initial trial excavation is <br />complete. This report will detail actual observed bench and highwall performance and present <br />recommendations for the future development of slopes, benches, and highwalls in the mine. It is <br />anticipated that subsequent annual reports will not be necessary. However, the DRMS will be <br />notified by Front Range Aggregates of any significant changes to the mine plan. <br />Phase IA and IB <br />Phase I will consist of two sub-phases, IA and IB, which will develop Area 1 (the northwest <br />corner of the quarry east to drainage 2). Phase IA is an "experimental" initial excavation which <br />will be done well within the mining limits in order to observe actual performance of the benches <br />and highwalls in various orientations. Once this has been done, Phase IB will be implemented <br />for production by beginning mining at the outer edge of the mining limits in the northwest <br />comer. Benches and highwalls will be developed from the northwest comer east to drainage 2 <br />and south towards the process azea, beginning at the northern and western mining limits and <br />Frans Range Aggregates, LLC- Parkdale Quarry <br />DMG 112 Permit Amendment <br />Page l4 <br />