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DEERE & AULT <br /> June 22,2015 <br /> i <br /> I <br /> Ms. Ioana Comaniciu,P.E. <br /> Department of Natural Resources <br /> 1313 Sherman Street, Room 818 I <br /> Denver, Colorado 80203 <br /> i <br /> Re: Stagecoach Slurry Wall 30 Day Leak Test Verification Plan,Water Division 1, <br /> Water District 2; D&A Job No. CG-0247.011.00 <br /> Dear Ms. Comaniciu: <br /> This letter was prepared to outline the proposed procedure for conducting a 30-day leak test in <br /> accordance with the"State Engineer Guidelines for Lining Criteria for Gravel Pits,"August <br /> 1999 for the Stagecoach Slurry Wall Project located in Adams County. The proposed below <br /> grade water storage vessel is a slurry wall lined active gravel pit. Construction of the slurry wall <br /> was completed on December 20,2005. The slurry wall was subjected to a 90-day leak test in <br /> 2012. At the end of the test the liner was provisionally approved to the design standard as <br /> described in the approval letter dated August 7,2012. A condition of the provisional approval <br /> was the requirement that a 30-day leak test is performed before the liner is approved to store <br /> water. A copy of this letter is attached for reference. t <br /> I <br /> The proposed 30-day leak test procedure outlined in this letter is schedule to start in June 2015 i <br /> and expected to be completed in July 2015. Based on field observation since the original leak <br /> test in 2012, the slurry wall appears to continue to be effective in cutting off the majority of <br /> inflow of groundwater into the reservoir basin. <br /> BACKGROUND <br /> A vicinity map of the Stagecoach Slurry Wall site is shown on Figure 1. The mine is located <br /> approximately four miles southwest of Brighton in Adams County, Colorado. The pit is bounded <br /> on the west by the South Platte River,Brighton Road on the east, 124 Avenue on the south and <br /> private property and the mine on the north. More specifically, the site is located in the <br /> Northwest Quarter of Section 35 and the Southwest Quarter of Section 26,Township 1 South, <br /> Range 67 West of the 6th Principal Meridian. <br /> The mine is currently owned and operated by Albert Frei and Sons and the area within the slurry <br /> wall consists of two mining permits: one permit for the Stagecoach Pit and one for the Worthing <br /> Pit. The mine is planned to be sold as a lined water storage vessel once mining is complete. <br /> Construction of the soil-bentonite slurry wall was performed by Hall-Irwin Construction. Slurry <br /> wall design and construction observation/quality control testing was performed by Deere&Ault <br /> Consultants, Inc. (D&A). Records of all slurry wall construction tests are available upon request. <br /> i <br /> 600 S.Airport Road,Building A,Suite 205 <br /> Longmont.CO 80503 <br /> Phone: 303-651-1468• Fax: 303-651-1469 <br />