17 ATTACHMENTS - Laserfiche WebLink

The DEIR evaluated the development's impacts on siesmicity and geology including erosion hazards, liquefaction, shrink-swell potential, and slope stability and defined the mitigation measures for the project-related impacts to these areas. During the scoping of the DEIR, the following comments regarding the proposed project's impact on geology, soils, and seismicity were stated: ^ The location of building sites on steep grades or unstable slopes; ^ The amount and impacts of grading, specifically, the effect of grading on soil instability, susceptibility to erosion, and slides, the reshaping of previously graded landscape, if any, the ecological impact of grading, street and sewer construction on existing watersheds and mountainsides; ^ Construction on fill, specifically the amount of fill to be used and the construction of homes on fill; ^ Slides, specifically the evidence of slides onsite from previous grading, if any, the impact to land stability due to removing existing growth and from future homeowners' watering; and, ^ Requests to include a soils report and an assessment of land movement on the site in the environmental impact report. The site was analyzed by the applicants' consultant, Berlogar Geotechnical Consultants, with their findings peer-reviewed by Cotton, Shires and Associates under supervision by the City Engineer. The analyses were then incorporated into the DEIR. A summary of the DEIR's analysis follows: The project site is located within the San Andreas Fault System of the San Francisco Bay Region. The two most prominent fault zones potentially affecting development on this property include the Calaveras and the Verona faults, which are capable of generating moderate to large earthquakes. The Verona fault is located approximately one mile southwest of the southern boundary of the project site, and is capable of generating a magnitude 6.3 earthquake. The Calaveras fault parallels the west side of Foothill Road and is capable of generating a magnitude 6.8 earthquake. ^ The Pleasanton General Plan characterizes the site's upland areas as moderately susceptible to landsliding and highly susceptible to erosion. The site's unstable areas correspond to the existing landslides and landslide deposits that were identified in the Berlogar geotechnical analysis for the applicant. Unstable slope conditions within the boundaries of building lots are acceptable as long as the building pads are stable. The DEIR notes that it is impractical to remove the remaining unstable deposits underlying the natural slopes that are downslope of the building pads and/or the subdivision improvements. These PUD-33 Page 35 of 59 June 13, 2007