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~ • Mr. Martin Azcarraga June 19, 2000 Page 3 of 4 However, slope failures large enough to damage the catch basin structure could occur if the mined sand and gravel undercuts the overburden highwall. This condition should not be allowed at the site under any scenario. Not only is there a risk to damage offsite structures, but also a risk to all personnel mining in the immediate area. Therefore, to minimize this potential, all sand and gravel mining, below the water table and within 100-fr of the North, South, and West Permit boundary shall be performed at a 3: I max slope. Groundwater Im pacts: Impacts from pumping out groundwater from the sand and gravel dewatering operations are not expected to impact any structure. Because of the high salinity levels in the groundwater, the water is not suitable for drinking or irrigation purposes. A search conducted the Office of the State Engineer, Colorado Division of Water Resources indicates there are no wells within 600 feet ofthe proposed site (reference permit # 053886-F). Groundwater removed during the mining operations will be pumped into a settlement pond, and into the Canning Factory Drain ditch owned by the Grand Junction Drainage District (GJDD). The GJDD has approved the dischazge of the water into their drainage facilities (Reference Exhibit G of 1 12 Permit #: M-2000-032). Drainaee Impacts: Drainage from the sand and gravel mine are not expected to impact offsite man-made structures. Prior to sand and gravel mining, a drainage Swale will be constructed around the permit boundary that will collect and divert all surface runoff generated by the site, to a new retention pond constructed at the western edge of the site. The retention pond has been designed to accommodate the 100-yr storm event. in accordance with the Stormwater ~Llanagement ~Lfanuo! for the City of Grand Junction. Comuactioo /Vibration Impacts: Backfilled overburden and imported fill material used to fill the mining area will require compaction. Fill materials are anticipated to be placed at 80% to 85% of the maximum soil density. Large, vibrating compactors will not be required to achieve this level of compaction. However, if this equipment is utilized on the site, in the vibrating compaction mode, the operator should maintain a minimum 50-fr buffer between the equipment and aboveground buildings. Motor Vehicle Impacts: M. A. Concrete Construction, Inc., has been using the proposed sand and gravel mine site for the roadbase material storage and processing for the past two years. This type of operation requires equipment similar to that required for sand and gravel mining operations. There have been no motor vehicle related impacts as a result of the current use of the site and this trend is expected to continue.