2004-02-24_REVISION - M1977153 (4)

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Geotechnical Data Technical Memorandum Hazeltine -Road Runners Rest II Gravel Pit Lining Project December 2000 1.5 Background and Project Description Three gravel pits are located between Old Brighton Road and the South Platte River from about 112th Avenue to 120`h Avenue. These gravel pits are located in the west half of Section 3 and the east half of Section 4, Township 2 South, Range 67 West of the 6th Principal Meridian. The three gravel pits from south to north are: Western Mobile's (also known as LaFazge) Howe- Haller Pit, Albert Frei and Sons' Hazeltine Pit, and Suburban Sand and Gravel's Road Runners Rest II Pit. The general locations of the pits are shown on Figure 1.1. Denver Water plans to convert all three of these pits into lined water storage facilities. The Howe-Haller Pit will be lined by the current pit operator. The Hazeltine and Road Runners Rest II Pits will be lined by Denver Water and South Adams County Water and Sanitation District. The Hazeltine Pit might be combined with the Road Runners Rest II Pit to create one lined water storage facility, and for purposes of this evaluation it was assumed that these pits would be combined. A perimeter lining system consisting of asoil-bentonite cutoff wall, a compacted clay embankment, or a combination of asoil-bentonite cutoff wall and compacted clay embankment will be constructed around the west, north and east sides of the combined Hazeltine and Road Runners Rest II Pits. This perimeter liner will be connected to the existing compacted clay liner at the north end of the Howe-Haller Pit. The berm between the Hazeltine and Howe-Hailer Pits will not be required to prevent seepage between the two pits, and as a result will be the only segment ofthe perimeter of the Hazeltine and Road Runners Rest II Pits that will not be designed to control seepage into and out of the reservoir. The Hazeltine Gravel Pit site is currently being mined by Albert Frei and Sons, under Mining Permit Number M-77-153 issued by the Colorado Division of Minerals and Geology. The Hazeltine Pit site is about 111 acres. About 11 acres in the northwest corner of the Hazeltine Pit site is used to store mine spoils. This 11-acre area may function as a wetlands area after mining operations are complete and if it is inside of the perimeter liner. Currently, it is anticipated that a soil-bentonite cutoff wall lining system would be placed west of the tailings pond, which will result in containing the tailings pond/wetland area within the liner system. If a compacted clay lining system alternative is used, it would probably be placed east of the tailings pond, which will place the tailings pond/wetland area outside the liner system. The Road Runners Rest II Pit is currently being mined by Suburban Sand and Gravel under Mining Permit Number #M-79-195. The Road Runners Rest II Pit site is about 175 acres. The Howe-Haller Pit is being mined by LaFarge Corporation, the successor to Western Mobile, under Mining Permit Number #M-78-52. The Howe-Haller Pit site includes about 390 acres. 9e+_isg~o ~m,.pa 1 _3 ~ GEl Consultants, Inc.