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~~ Banks and Gesso, LLC ~~ May 8, 2002 Mr. Tony Waldron Division of Minerals and Geology 1313 Sherman St., Room 215 Denver, CO 80203 720 Kipling St.,Suite117 Lakewood, Colorado 80215 (303) 274-4277 Fax (303) 274-8329 www_banksandgesso.com Re: File No. M-2001-046; Nix Sand and Gravel Mine; Owens Brothers Concrete Company; Slope Stability Analysis for Existing Structures Dear Mr. Waldron, Enclosed are the analysis and relevant material that support mining within the 200 foot setback, per Division of Minerals and Geology (DMG) Rule 6.4.19(b), for the above referenced site. The evaluation establishes mining setback limits in the vicinity of the west and south property lines that will protect existing structures from damage during mining activities. This submittal is in response to DMG's comments at a meeting at the Division's office on April 24, 2002 and in a letter to Banks and Gesso,l_L_C Dated April 29, 2002. A slope stability analysis was submitted to DMG's office on February 28, 2002. The conditions assumed in the previous submittal regarding the peizometric surface, surface water, and mining slopes are no longer valid. The stability analysis is resubmitted herein with more realistic field conditions. In the previous modeling the piezometric surface was assumed to be 3 feet below grade and there was assumed to be no water in the pit during mining. Actually, the pit will be wet mined and there will be ponded water in the pit up to the same elevation as the piezometric surface where this surface daylights along the working face. Also, the slope was previously assumed to be a constant 2:1(H:V) slope. However, because of potential problems with backfilling under weUsaturated conditions, we propose to mine the slope to the reclamation slope of 3:1(H:V) to ten feet below the expected water level and 2:1(H:V) thereafter. Therefore, this slope was used in two of the scenarios analyzed.