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ARCADIS <br />Infrastructure, environment, facilities <br />Mr. Steve O'Brien <br />Environment Inc. <br />7985 Vance Dr. #205A <br />Arvada, CO 80003 <br />Subject E/ <br />Priola Pit Potential Stability Issues <br />ARCADIS-US. Inc, <br />830 Place Drive <br />Suite 200 <br />Highlands Ranch <br />Colorado 80129 <br />Tel 720 344 3500 <br />Fax 720 344 3535 <br />www.arcadle-us.com <br />ENVIRONMENTAL <br />Dear Mr. O'Brien: Date: <br />14 May, 2008 <br />Slope stability of the proposed Priola Pit by Albert Frei and Son's Inc was evaluated <br />using a simple analysis to determine the factors of safety associated with the adjacent contact: <br />concrete ditclr.and slurry wall located on City of Thorton property to the north and Gast6n Leone <br />west of the site. The slopes were evaluated using an infinite slope analysis and <br />saturated conditions since the pit will not be dewatered (e.g. the existing water table Pte: <br />30371-3471 <br />will not create an adverse phreatic surface condition). The material in the pit wall <br />will be in-place gravel and is assumed to be cohesionless and have a friction angle Email: <br />(0 of 34 degrees. For an infinite slope the factor of safety is: Qaston.leone®arcadis-! <br />us.com <br />FS = Tan fO) , where 9 is the slope angle. Calculated values are shown below: <br />Tan (0) our rat. G0001898.0000 <br />Slope Evaluated Calculated <br />Slope Angle Factor of Safety for <br />Infinite Slope, 0 = 340 <br />Proposed Slope (2:1) 26.60 1.35 <br />S1opeToe to Conc. Ditch 150(1) 2.58 <br />Slope Toe to Slurry Wall 7.1250(2) 5.49 <br />(')150 angle is calculated from 15 feet slope height and 55 feet horizontal measurement from <br />toe to ditch edge <br />(2)7.1250 angle is calculated from 15 feet slope height and 120 feet horizontal measurement <br />from toe to slurry wall <br />Imagine the result <br />z?D7-©97