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2. Groundwater <br />The site will mine a sand and gravel deposit which is an alluvial from the recent period of <br />Quaternary age formed on a bend of the Gunnison River. The alluvium is relatively shallow <br />(averaging 30 feet thick) and is underlain by Mancos Shale. The River itself is actually cutting in <br />the Morrison Formation, which is also known for its purple and green shales. Rising immediately <br />from the west bank of the River and also located 1000 feet further to the east are the resistant <br />reddish sandstones of the Dakota Sandstone Formation. These sandstones form many of the red <br />sandstone canyon rims located throughout the area. The Dakota Sandstone is of Lower Cretaceous <br />age. Figure 1 below shows an example cross section of the regional geology. <br />W <br />2 <br />N E <br />E aa) > lava flows <br />:D 0- green river <br />o o � &Wasatch <br />arias c mesaverde <br />;"� zt•- _Sid and M ¢ <br />mancos shale <br />precembriandakota <br />Figure 1— Cross Section of Regional Geology <br />This geology causes the groundwater level to be very close to the surface. Water is expected to be <br />encountered 18" to 4' below the surface. While the pit is being pumped down the water table will <br />drop, but after reclamation this level is expected to return. The quality of the water is similar to the <br />Gunnison River at this point. A substitute water supply plan is in place to cover out of priority <br />depletions. <br />Ground water quality is protected by dewatering below the operational floor in all of the pits, in <br />addition to gravel filter berms around the pumps. The use of Pit 1 as a sediment sump for <br />dewatering of Pits 2 and 3 will enhance the water quality of these pits discharge. <br />3. Water Consumption for the Operation and Water Rights <br />A Gravel Well Permit and Substitute Water Supply Plan (SWSP) are in place for Tri County. <br />Tri County Pit Sept 2016 G-2 <br />