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shall be performed according to the guidelines so as to prevent siltation to the river. Construction shall take place during dry weather and at low streamflow. 4. A retention/percolation basin shall be created which will provide sufficient water storage capacity to allow percolation of surface water to the aquifer in the area of the proposed quarry excavation. Calculations for sizing retention basins (San Joaquin County Department Of Public Works, 1973) indicate a 10-acre, 2-foot deep pond, will provide sufficient water storage capacity for a 10-year storm event. The pond shall be adequately sized to prevent overfilling the pond and flooding of the site, or discharge of water to the Mokelumne River. The reclamation plan shall include detailed grading measures to provide drainage to the retention basin and to prevent ponding of water on the remainder of the site. Installation of a desilting pond may be necessary. Grading shall be performed to prevent direct runoff to the Mokelumne River. The San Joaquin County Department of Public Works shall approve the applicants design for the retention basin, site drainage, and drainage from the town of Clements prior to project construction. 5. The San Joaquin County Department of Public Works shall determine an adequate setback from their drainage pond to prevent inundation of the gravel extraction area in the event of rainfall greater than the 10 year storm. This setback shall be reviewed by a soils engineer or certified engineering geologist to ensure that it is adequate to prevent pond slope failure due to quarry excavation. 6. If the water table is intersected by the extraction pits, the applicant has indicated that the pits would be dewatered prior to continued excavation. If groundwater is encountered, the California Regional Water Quality Control Board (RWQCB) shall be notified to evaluate the proposed disposal of groundwater. A Waste Discharge Permit may be required from the RWQCB. If water from the pit is discharged to the Mokelumne River, a National Pollution Discharge Elimination System (NPDES) permit will be required. 7. If it becomes necessary to extract groundwater from the excavation, a qualified groundwater hydrologist or hydrogeologist shall conduct an evaluation of the potential impact on existing local groundwater wells. The selection of the individual or firm to conduct the evaluation shall be subject to approval by the County and the California Department or Water Resources. The evaluation shall determine the potential drawdown and area of influence of the groundwater extraction. If it is determined that the groundwater extraction could significantly impact local wells, these wells shall be monitored for project related drawdown or groundwater extraction from the excavation shall be limited so that no impact will occur. If significant adverse impacts to local wells is identified, mitigation shall be provided such as deepening or replacement of affected wells. 8. Depending upon the actual groundwater levels encountered at the gravel extraction site, topsoil or other material (as approved by the USDA SCS) shall be added to raise the elevation so that the root zone of crops will not be subjected to saturation conditions under the reclamation plan. The USDA SCS shall approve the required amounts and location of additional material to be added. 9. A reclamation plan for the project shall be submitted to and approved by the County and the California Division of Mines and Geology prior to project operation as required under the Surface Mining and Reclamation Act of 1975 (SMARA). On the north side of the Mokelumne River, the reclamation plan 37