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• 2.7.7.3 Mine Plan Area Drainages <br />Drainages in and adjacent to the proposed mine plan area have been evaluated for their potential as <br />alluvial valley floors (AVF's). The drainages south of the Williams Fork Mountains have not been <br />evaluated. Generally, ground water leaving the area to be altected flow north away from these <br />drainages from the Williams Fork Mountain drainage divide. Ground water flows down-dip (north} in <br />the proposetl permit area toward the Yampa River. Surface disturt~ance draining south of the <br />Williams Fork Mountains is very limited, and would have no Impact to potential alluvial valley floors <br />(Holtman-verbal communication). Map M51 shows the permit area with drainage divides. <br />The potential to effect these areas was addressed more thoroughly during pre-application confer- <br />antes with the Colorado Mined Land Rectamation Division (CMLRD) and the Office of Surface <br />Mining, Region V (OSM). Appendix H contains a report, "A Review of Potential Alluvial Valley Floors <br />• Associated with Ulah International Int.'s Trapper Mine in Northwest Colorado and Probable Impacts" <br />(McBride et al, 1980). This report was presented in ApRI, 1980 to the CMLRD and the OSM. Con- <br />sensus was reached that Trapper Mine would likery have negligible impact on alluvial systems of the <br />Williams Fork and Yampa rivers. Further investigations of upland dreinages-assoGated with the mine <br />plan area were determined to be necessary. <br />Geologic Setting <br />The sufidal geology of the Trapper Mine area is given in Figure 2.7-2. Two cross-sections have <br />been developed to show the subsurface geology in the area of the potential AVF's. Map M32 gives a <br />north-south cross-section along line 1,426,000 E, while awest-east cross-section is given in Map <br />M33 along line 414,000 N. Maps M34 and M35A shown the location of these two <br />u <br />2-534 (~i2- ~ - - <br />.~i _ <br />,._-_-MAY 1.3 1998. ~- <br />