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Chapter 4 Environmental Setting, Impacts, and Mitigation Measures H. Hydrology, Drainage, and Water Quality than 31 feet bgs. In the vicinity of the southern detention basin, the boring logs indicate that groundwater occurs at a depth of greater than 30 feet bgs.29 3. Key Project Characteristics, Impacts, and Mitigation Measures a. Key Project Characteristics The features of development under the Specific Plan are expected to include the following: . Land uses that provide extensive permeable surfaces in the form of public park land and open space; and . Management of storm drainage through provision of onsite stormwater detention facilities incorporated into the landscape, including detention basins constructed in the Phase II Specific Plan area pursuant to the Phase I Specific Plan that are capable of detaining the increase in runoff from the site under developed conditions for the 100- year storm event; . Compliance of development within the Plan area with Provision C.3 requirements of the National Pollutant Discharge Elimination System (NPDES) Countywide permit (including requirements regarding hydromodification). b. Significance Criteria Significance criteria for the proposed project's impacts on hydrology and water quality are drawn from CEQA Guidelines Appendix G (Items VII (a) through (h)) supplemented by environmental considerations drawn from the revised County N PDES permit (C.3.m) and from guidance provided by the Regional Water Quality Control Board (RWQCB). Summarizing criteria intended to reflect the intent of all three sources, impacts on drainage and water quality would be significant: (1) [If the project would] contribute significantly to downstream flooding or would not adequately protect onsite development from flooding. (2) [If the project would] fail to provide adequate protection of water quality. (3) [If the project would] substantially reduce or degrade local groundwater resources. c. Impacts Consistent with the discussion of impact criteria in the preceding section, this impact analysis focuses on potential degradation of water quality, exposure of people to flooding hazards, and potential impact on groundwater resources (1) Flooding and Hydromodification Development of the Plan area would result in more surface area covered by impervious surfaces (buildings, paved roadways, sidewalks) relative to existing conditions. Undevel- 29 Bhatt, Kaushik, Assistant Engineer II, City of Pleasanton, written communication to Bruce AbelJi-Amen of BASELINE, October 27,2005. 87