RES 06035 - Laserfiche WebLink

Chapter 4 Environmental Setting, Impacts, and Mitigation Measures F, Geology, Soils, and Seismicity in the southern part of the Amador Valley in the Diablo Range, part of the Coast Ranges Geomorphic Province of California, Major faults, including the Calaveras and Greenville, and minor faults including the Amador, Las Positas, and the Livermore Valley faults have influenced the development of valleys in the region, The Plan area would be subject to very violent seismic shaking during a major earthquake on the Calaveras Fault (and less intense, but potentially still damaging, levels of seismic shaking during earthquakes on other regional faults), Seismic shaking is not the only geologic hazard that could occur at the Plan area during an earthquake, The area could also experience differential settlement, lateral spreading, and liquefaction, The site is relatively level and therefore not generally susceptible to slope instability. In the project area vicinity, surficial and near-surface unconsolidated sediments consist of Holocene age (11,000 years or younger) fine sand, silt, and silty clay, These sediments were deposited by the principal stream, Arroyo de la Laguna, which traverses the western boundary of the project area, Most of the soils within the Plan area are considered to be prime agricultural soils, Some of these soils have high to moderate shrink-swell potential, meaning these soils change in volume when wetted and dried, 3. Key Project Characteristics, Impacts, and Mitigation Measures a. Key Project Characteristics The proposed project includes the following components/characteristics that relate to geology, soils, and seismicity conditions that could result from project implementation, (1) Geology Projects under the Specific Plan would include limited grading, The most substantial grading is expected to occur as part of the expansion of the stormwater detention basins, potential construction of below-grade parking facilities, construction of the cultural arts center, and creation of gently-sloping mounds in the park areas for natural and aesthetic enhancement. Development grading projects would segregate and save productive topsoil during grading operations and place this material in areas designated for revegetation, (2) Soils Those projects that include structures and placement of utilities would carefully manage soils with moderate to high shrink-swell potential. These soils would either be removed from areas where improvements would be placed or the improvements (e,g, foundations, utilities) would be designed to accommodate the expected soil movements, 73