2018-10-24_PERMIT FILE - M2018055 (6)

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WJE , ,, SLOPE STABILITY ANALYSIS Vail Valley Ranch Gypsum, Colorado 1.0 INTRODUCTION The following report describes a slope stability analysis performed by Wiss, Janney, Elstner Associates, Inc. (WJE)for Vail Valley Ranch,a proposed gravel quarry site in Gypsum,Colorado.The site is bounded by US Highway 6 to the north and by the Eagle Valley Airport to the south(Figure A.1).This analysis was performed on a topographic profile derived from the Overlot Grading Plan produced by Alpine Engineer- ing, Inc.(AEI)on November 28,2017.The analysis solely considers the proposed gravel quarry site topog- raphy as presented in the grading plan and is not intended to analyze the stability of the existing slopes. 2.0 OBJECTIVE AND SCOPE OF ANALYSIS The objective of our analysis was to evaluate the stability of the excavated slopes of the proposed Vail Valley Ranch gravel quarry site. As part of that assessment, WJE performed the following tasks: ■ Review existing relevant geotechnical information including geological maps of the site,the report for drilling/gravel exploration by D.A. Smith Drilling Company (DA), the Summary Log of Ex- ploratory Borings by Deere & Ault Consultants, Inc. (D&A), and the Overlot Grading Plan by AEI. ■ Implement both a test pit investigation and drilling program at the site to identify subsurface ma- terials and conditions relevant to slope stability analyses. ■ Use topographic data presented in the Overlot Grading Plan by AEI to derive a representative topographic profile for slope stability analysis. ■ Create a computerized slope stability model intended to define potential slope failure surfaces and related factors of safety using SLIDE 7.0,a commercially available computer program specifically designed for slope stability analysis. ■ Prepare a slope stability analysis report summarizing our findings of slope stability at the Vail Valley Ranch site. 3.0 SITE CONDITIONS The subject site is located directly north of the Eagle Valley Airport. It is irregularly shaped and encom- passes approximately 41 acres (GoogleEarth, 2018). Various east-west-oriented dirt access roads run through the site, and at the eastern end of the site,there is an approximate-five acre parking lot and equip- ment storage area. A north-south-oriented utility corridor crosses the center of the site. Beyond this, there is no existing infrastructure. In the southern portion of the site, the terrain is fairly flat with random, subtle undulations. The ground abruptly steepens to grades of approximately-40%to-50%in the northern portion of the site until the slope abuts the southern shoulder of US Highway 6. Some small, yet distinguishable, drainages are present throughout the site. There are two relatively large depressions, both in the western half of the site, where