2012-01-20_HYDROLOGY - M1985112 (2)

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INTRODUCTION This opinion of probable cost is intended to address general questions regarding the comparative costs associated with zoned clay liner option and a slurry wall option for the Loloff Pit (M -1985- 112). The Loloff Pit is located east of Greeley, Colorado in the Southeast 1 /4 of the Northwest 1 /4 of Section 4, Township 5 North, Range 65 West in Weld County. The permitted site is approximately 50 acres. ASSUMPTIONS The final reclamation configuration has yet to be determined. For the purpose of quantifying the costs associated with each option, the following assumptions may be applied to both the zoned clay liner and slurry wall options: • All material necessary for reclamation are on site and no additional material will be imported • Final reservoir configuration will generally be parallel to the permit boundary • Bedrock is assumed to be an average of 51 feet below grade throughout the site • Perimeter of the reservoir is assumed to be approximately 5,983 feet • Reservoir embankment slopes will be 3:1 • Engineering costs are estimated to add an additional 10% to the reclamation costs • Mobilization costs are estimated to add an additional 5% to the reclamation costs • Construction observation are estimated to add an additional 10% to the reclamation costs • Testing is estimated to add an additional 2% to the reclamation costs • Construction staking is estimated to add an additional 1% to the reclamation costs • A 30% contingency is estimated to cover variations in unit costs associated with specific economic and market factors. • Costs are based on 2009 dollar values • Both the slurry wall and zoned clay liner options are assumed to provide a comparable barrier to groundwater seepage into the reservoir • Dewatering costs based on operator opinion • Reservoir perimeter assumes a 25 foot setback from the property boundary OPTION 1: SLURRY WALL The slurry wall option is based in part on the use of standard installation methods. A typical slurry wall configuration was used to calculate cost and is included at the end of this report. The cost estimate is based on a vertical slurry wall that is installed seven (7) feet into the bedrock. This means that a slurry wall would need to be installed to approximately 58 feet below grade. Backfilling the embankment to a 3:1 slope was calculated based on the assumption that the top of the embankment would be approximately 25 feet in width around the entire perimeter of the Loloff Pit Engineer's Opinion of Probable Cost I Introduction 1