2002-02-07_REVISION - M1976020 (7)

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5. Lake Mining 2002 Amendment General Plan Since mining operations have been suspended in the River for 2002, Four Comers Materials pro- poses to mine a portion of the first terrace above the river at the south end of the property. The mining would be located in the area that the existing sediment pond and three abandoned treat- ment ponds currently exist, as shown on Map C-2. The total area of lake mining is 4.7 acres. The sideslopes are designed at 3H:1V and the overall top of bank varies from 6664 feet elevation to 6669 feet. The elevation of the bottom of the lake is 6628 feet, therefore the depth from the lowest point along the existing top bank to the bottom is 36 feet. As shown by the cross-sections in Map C-4, most of the lake will be underwater since the typical water elevation in the area is 6656 feet. This leaves an embankment that will have 6 to 12 feet height above water during typical flow conditions in the river. The amount of gravel material expected to be extracted from the lake is 122,000 cubic yards. This will be done in the spring of 2002. None of this material will be processed on site. The raw gravel will be taken to Four Corners Trimble Lane processing site located 4 miles south on Highway 550. No more mining will take place in the lake after the spring of 2002. In order to mine the gravel in a lake near the river embankment, a number of hydrologic controls have been designed, such as a rock jetty and a protected embankment consisting of part riprap and part vegetated slope. These are discussed in detail in the hydrologic discussion of this section. The area to form the lake currently contains the mine sediment pond and three abandoned treatment ponds. Two of the three treatment ponds have been lined with a flexible black impermeable liner, which will be removed prior to gravel excavation. Water does exist in the two lined northernmost ponds. The water quality in these 2 treatment ponds has been shown to be clean and will present no problems in mining or potential contamination downstream. 6. Topsoil Handling for Lake Minine Prior to any mining, topsoil will be stripped from those portions of the lake which have soil. See Map I/J in Appendix B for [he outlines of all soil areas based on the SCS survey conducted years ago. Part of the lake area is currently in the same location as the existing mine sediment pond and the Thomas Pi[ 2/02 12