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Less Than Significant After No River Reduced Depth Alternate Quarry Potentially Significant Impacts Suggested Mitigation Measures Mitigation? No Project Crossing of Excavation Site Geology and Soils Excavation would reduce the surface elevation See'Hydrology and Water Quality' Yes No Impact Similar Impact Reduced Impact Similar Impact of the quarry area,potentially impacting runoff and percolation. Excavation would expose soils to wind and Temporary rcvcgetation in areas where Yes No Impact Similar Impact Similar Impact Similar Impact water erosion. aggregate extraction is complete. Project development could generate potential for Maximum cut slopes for excavation and Yes No Impact Similar Impact Similar Impact Similar Impact slope failure which could endanger worker reclamation areas shall be established by a soils safety and impact adjacent terrace slopes. engineer or certified engineering geologist. Minimum setbacks from terrace slopes for excavation shall be established by a soils engineer or certified engineering geologist. Mixing of subsoil materials with topsoil during Surface soils shall be separated from subsoils Yes No Impact Similar Impact Similar Impact Similar Impact removal and replacement of overburden could and stockpiled separately. Resoiling shall be reduce soil productivity. conducted to restore original soil stratigraphy. Hydrology and Water Ouality Potential river channel bank and levee damage The potential for change in channel alignment Yes No Impact No Impact Similar Impact Similar Impact and increased risk of flooding if bridge should be reduced in case of a levee failure structural elements or fill are placed in the during peak streamflow events.The gravel active river channel. extraction pits shall be left open for as brief a time as possible,particularly during the rainfall season,and the pits should be aligned perpendicular to the streamflow. The new bridge site shall be constructed to minimize constriction of the channel and prevent a decrease in flood carrying capacity of the Mokelumne River that may increase erosion and flood potential. The San Joaquin County Public Works Department and the State Reclamation Board should require the cross sectional area of the channel at the new bridge site to be surveyed to determine that the present channel capacity has not changed since the USGS report. A permit must be obtained from the State Reclamation Board,and bridge relocation must comply with Federal Management Agency and County Flood Prevention Ordinance requirements.