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Geotechnical Engineering Report Terracon Rollin Consulting Terracon Project No. 21025057 optimum moisture content. A water head of 30 feet (equivalent pressure of 13 pounds per square inch (psi) or 1,872 pounds per square foot (psf)) was used in determining the confining pressure of the permeability test. The remolded permeability test was performed in accordance with ASTM D5084 -Back Pressure Saturated -Flow Pump Method. The results of the remolded permeability test indicated a value of 3.7x10$ cm/sec. Groundwater Conditions: Groundwater was observed in test boring at depths ranging from about 3 to 5 feet at the time of field exploration. These observations represent groundwater conditions at the time of the field exploration, and may not be indicative of other times or at other locations. Groundwater conditions can change with varying seasonal and weather conditions, and other factors. Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. The location and amount of perched water is dependent upon several factors, including hydrologic conditions, type of site development, irrigation demands on or adjacent to the site, fluctuations in water features, seasonal and weather conditions. ' ENGINEERING ANALYSIS AND CONCLUSIONS This analysis is based upon review of field and laboratory testing of the claystone bedrock ' materials and the criteria outlined by the Colorado Department of Natural Resources - Division of Minerals and Geology ('Guide, 2000). As outlined by the Division of Minerals and Geology, the liner fill materials should contain at least a minimum of 20 percent fines, with PI's of at least 10 (although some materials with lower PI's may be considered acceptable), gravel not exceeding 10 percent, and no stones ' or rocks greater than 2 inches. Additionally, the liner fill, when compacted according to specifications, should have a permeability of less than 1 x10 cm/sec. Based on the physical properties of the claystone bedrock materials encountered in the borings, results of the remolded permeability test, and the minimum requirement outlined by ' the Division of Minerals and Geology, it is our opinion that these materials could be considered as potential fiA liner materials far the proposed water storage pond. However, the use of the sandy siltstone bedrock materials encountered in Boring No. 5 should to be ' re-evaluated when the bedrock materials are exposed to confirm the suitability of these materials. ' 'September 2000, Guide to Specification Preparation for Slurry Walls and Clay Liners as a Component of a ^ Co/orado Mined Land Reclamation Permit, Colorado Department of Natural Resources -Division of Minerals and Geology. 4