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4- t Impact DW-3: Temporary Increases in Construction-Related Soil Erosion Construction activities would occur over the life of the property development phase that could cause discharges of eroded soil, petroleum products, concrete, and other construction wastes into local drainage channels. Soil and associated contaminants that enter stream channels can increase turbidity, stimulate the growth of algae, increase sedimentation of aquatic habitat, and introduce compounds that are toxic to aquatic organisms. Work that is conducted within an existing drainage channel would pose the most immediate threat of discharges of soil and contaminants. An erosion control plan would be required by SJCPW and because construction of the proposed facilities would exceed 5 acres of land disturbance, an NPDES stormwater permit for general construction activity from the Central Valley RWQCB would be required. In general, construction contractors would be required to implement erosion control and spill prevention BMPs as identified in the NPDES permit, the SWPPP, and the county grading permit. Although regulatory policies exist for implementation of erosion control measures at the local and state level, there is a level of uncertainty associated with the degree of implementation of measures that occur over a long planning timeframe, occupy an extensive area of land, and potentially involve numerous construction contractors. Because of the above uncertainties associated with construction extending over several years, the potential water quality impacts from construction are considered significant. Implementation of the following mitigation measure would reduce this impact to a less-than- significant level. Mitigation Measure DW-3: Obtain and Implement NPDES Permits for General Construction Activity and Implement the Erosion Control Plan Specified in the County Grading Permit The SJCPW in coordination with the Department of Airports should require all construction I contractors to obtain and implement NPDES permits for general construction activity and to implement the erosion control plan specified in the County grading permit. Construction contractors shall be monitored to ensure the proper implementation, operation, and maintenance of erosion control measures. BMPs shall be used that prevent soil erosion, drainage channel scour, and discharges of construction-related pollutants, such as petroleum-based fuels and oils, solvents, paints, cement, and other materials that could contaminate nearby water resources and could contribute to the exceedance of the established RWQCB water quality objectives. 1 . Stockton Metropolitan Airport Project Chapter S. Drainage and Water Quality Draft Environmental Impact Report 5-9 March 20, 1998