2013-09-18_PERMIT FILE - M2013064 (10)

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Introduction The following report presents the results of a slope stability analysis for a proposed open cut gravel extraction operations at the Varra Coulson pit operations near Greeley, Colorado. This analysis was performed at the request of Varra Companies, Inc., ( Varra). It is our understanding the Colorado Division of Reclamation and Mine Safety (DRMS) requires this analysis as part of Varra's mine permit submittal. Background Information The proposed Coulson gravel quarry is located in the NE1 /4, S10, TSN, R65W of the 6th Principal Meridian. The surrounding land use consists of agricultural, rural residential, commercial and open -cut gravel quarry operations. The proposed mine area occupies an estimated 62 acres. The water table at the site is located in unconsolidated alluvial deposits associated with the Poudre River with the depth to water between 5 and 10 feet below grade. Soil conditions generally consist of varying thicknesses of top soil underlain by sand and gravel deposits, which in turn are underlain by Pierre Shale. Over the entire area the average saturated thickness of the sand and gravel deposits (prior to mining) is estimated at 45 feet. It is our understanding that the sand and gravel will be dewatered during aggregate extraction. The site location is presented on Figure 1. Previous Investigations In August 2000, 17 soil borings were drilled from ground surface to bedrock to determine the potential aggregate mass within the proposed mine boundary. The depth to bedrock over the site varied between 29 and 65 feet below ground surface. In general the site consists of three to five feet of top soil underlain by 24 to 60 feet of sand and gravel with occasional clay and sand lenses. Geotechnical studies conducted by Terracon 2011, and CTL Thompson, 2006 document soil strength properties at two adjacent mines (Great Western & Durham). The results of these investigations are presented in Attachment A. Conservative soil strength properties presented by DRMS are presented in Attachment B.