2002-04-01_REVISION - M1976020 (3)

Home Browse Search

5. Lake Mining 2002 Amendment General Plan ~~`4 G~ j 2~t72 ~iy~8~ ~n9b ~re~ O~ Since mining operations have been suspended in the River for 2002, Four Comers Materia~s ~leary~ & ~rcg poses to mine a portion of the first terrace above the river at the south end of the property. Q9Y 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. Although no sewage material is evident in these ponds, any sewage material encountered will be taken to a landfill. The pond liners will also be prop- erly disposed of. 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 fee[, therefore the depth from the lowest point along the existing top bank to the bot- tom 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 Comers 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 [his 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 the outlines of all soil areas based on the SCS survey conducted years ago. Par[ of the lake area is currently in the same location as the existing mine sediment pond and the Thomas Pit 2/02 12