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Ponderosa Homes at 6900 Valley Trails Drive Initial Study and Negative Declaration implementation of the project. Therefore, this would be categorized as a less-than-significant impact. c) There is no existing stream, river, lake, drainage channel, or other water body/course on the subject property. Site development would alter the existing drainage pattern compared with existing conditions, given the increase in impervious surface area, but would not result in substantial erosion or siltation. Therefore, this would be categorized as less than significant. d) Although the project would not substantially alter an existing drainage pattern, it would increase the amount of impervious area. This reduction would be mitigated through the required implementation of stormwater retention areas that would manage, slow down, and treat runoff before it enters the storm drain system. As a condition of project approval, the bioretention areas would need to be designed to allow infiltration without compromising impacts on flatwork and pavement due to potential expansive soils, settlement, and/or lateral movement.13 As a result, the project would not substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site. Therefore, the potential impact would be less than significant. g,h) Housing will not be placed within a 100-year flood hazard area. The development will not expose people or structures to a significant risk of loss, injury or death involving flooding. Therefore, this would be categorized as no impact. i) As with most of Pleasanton, the project site is located within the dam failure inundation hazard area for Lake Del Valle Dam. This 235-foot dam impounds a reservoir with a total capacity of 77,100 acre-feet. To provide a flood protection reserve, the dam normally stores from 25,000 to 40,000 acre-feet of water. In 2002, the City adopted an evacuation plan as an addendum to its Comprehensive Emergency Management Plan, to mitigate potential impacts if a dam failure were to occur. Catastrophic dam failure is considered highly unlikely, as the dam is regularly maintained and inspected. Flood retention facilities, including levees, throughout the City are undergoing updates under the Stream Management Master PIan.14 Therefore, this impact would be categorized as less than significant. j) The City of Pleasanton is not at risk from seiche, tsunami, or mudflow. Therefore, this would be categorized as no impact. 13 Cornerstone Earth Group, 2014. 14 City of Pleasanton. Pleasanton General Plan 2005-2025, Public Safety Element. Adopted July 21, 2009, Amended January 6, 2015: 5-19. 30