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Hitch Rack Ranch Quarry Waste Stockpile Stability Analyses/591-6 <br /> NORWEST March 13,2018 <br /> 3 3 <br /> COR PORAT ION <br /> 50-year event, equivalent to a 1 in 2,475-year recurrence. The stability models utilize the peak ground <br /> acceleration (PGA)value and the Sl represent approximately 2.0 times to the PGA. <br /> 4. SOIL PROPERTIES <br /> Site specific geotechnical information on the overburden is limited to the visual inspection done in the <br /> drilling programs. Regional database and public accessible information were used to supplement the <br /> geotechnical parameters needed to evaluate the overburden. The overburden within the region is <br /> generally a colluvium material and part of the Coldcreek-Tolman complex as reported by Natural Resource <br /> Conservation Service (NRCS) Soil Survey of El Paso County (NRCS 2015). The detailed parameters from <br /> NRCS are included in Appendix A. The parameters used for the stability analyses and their references are <br /> listed in Table 4.1. Lower-bound values of published ranges for strength parameters for the soil types <br /> present were used in this analysis to be conservative. <br /> The topsoil and the fines stockpiles are assumed to be constructed in lifts between five (5) to 10 ft (1.5 <br /> to 3 m) through dump and spread type operation. Some degree of compaction can be achieved by truck <br /> traffic and loading but for the purpose of the model, the topsoil and fines materials placement are <br /> considered loose and not compacted. <br />