AgdaPkt 2016-04-25 Closed and Joint SA PFA

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7.B. - Page 68 2 Environmental Analysis • If the NAHC-appointed MLD, Caltrans,and the City cannot reach an agreement within 48 hours, the landowner or his or her representative shall rebury the Native American remains on a site where no further subsurface disturbance would occur; • Ground-disturbing activities may resume after the County Coroner and the appropriate law enforcement authority have released the area for construction. With the implementation of this mitigation measure, the potential impacts to human remains would be less than significant. (Less than Significant Impact with Mitigation Incorporation) 2.6 GEOLOGY AND SOILS The Geotechnical Design Report prepared by Cal Engineering&Geology, Inc. (CE&G) describes the existing geologic setting of the project area, evaluates project impacts,and contains site-level design recommendations for mitigating potential impacts associated with geologic hazards (see Appendix F). The City is located within the San Francisco Bay Area,a seismically active region at the boundary of North American and Pacific plates that is susceptible to geologic hazards such as earthquake ruptures, seismic ground shaking,and ground-failure and contains areas subject to liquefaction and landslides. Redwood Creek,bordering project area to the east,was known as "Redwood Slough" until the 1950's. During the 1950's-1960's, levee banks were constructed to raise the creek bank elevation above the tidal waters within Redwood Creek. Additional fill using stiff-clay and gravel materials was added in the project area as development continued. Bay Mud,which is thick and highly compressible silty clay,underlies the fill materials used in the project area. The proposed project area consists of Urban-land Orthents,reclaimed complex soils with 0 to 2 percent slopes (CE&G, 2013 and USGS,2009). CE&G conducted five geotechnical borings within the proposed project area at depths of 10-20 feet using a 4.5 inch solid stem drill with continuous augers. Representative soil samples were collected from the borings and bagged for analysis. The soils that were encountered during drilling of the borings consisted of artificial fill,alluvium,Young Bay Mud,and Old Bay Mud. Artificial fill was encountered in all five of the borings and consisted of firm to hard lean clay in four of the samples and low to medium plasticity of sandy silt in one. Alluvium was encountered in two of the five borings and consisted of poorly graded sand and silty elastic sand. Young Bay Mud was encountered in all five of the borings at various depths 6.0-14.5 feet and consisted of loose, soft to very soft wet clay and elastic silt. Old Bay Mud was encountered in three of the five borings at depths of 13-20 feet and consisted of firm to hard lean clay (CE&G,2013). 2-28 US 101 Pedestrian Undercrossing and Bair Island Road Storm Drain Pump Station Project