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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Surface Hydrology,Stormwater,and Water Quality ■ substantially alter the existing drainage pauem of the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner that would result in _ flooding on or off site; ■ create or contribute runoff water that would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional — sources of polluted runoff; ■ otherwise substantially degrade water quality; ■ place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map; ■ place within a 100-year flood hazard area structures that would impede or redirect floodflows; or ■ expose people or structures to a significant risk of loss,injury,or death — involving flooding, including flooding as a result of the failure of a levee or dam or inundation by seiche,tsunami,or mudflow. Impacts and Mitigation Measures Impact WQ-1: Construction-Related Water Quality Degradation (Less than Significant) As described in Chapter 2, "Project Description,"the Operator proposes to either dry mine the site(referred to as Dry Pit Operations)and dewater the pit as described below,or the Operator may elect to wet mine the site(referred to as Wet Pit Operations),based on the actual amount of groundwater encountered. Construction activities at the site would involve construction of an internal haul road(s), a rock processing plant,asphalt and concrete batch plants, and a — recycling plant,regardless of which type of mining method is chosen. Therefore the potential construction-related water quality impacts on surface waters would be similar for each type of operation. — Grading and excavation associated with construction of the on-site facilities would expose bare soil to erosive forces. Bare soils are much more likely to erode than vegetated areas because of the lack of dispersion, infiltration,and retention properties created by vegetation. The topography of the project area is such that runoff from these areas would likely remain on-site. In addition, no _ drainages or culverts divert runoff in the project area to areas off-site. However, it is possible that runoff during larger storm events could flow off-site from the northeastern portion of the project area and potentially enter stormwater drainages and ultimately surface waters. Construction activities would involve the use of potentially hazardous materials, such as fuels, lubricants, and solvents, the accidental uncontrolled release of which could have adverse effects on nearby surface waters. DeSilva Gates Quarry Project Draft Environmental Impact Report 3.G-8 J5s 05105.05