2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis GEOLOGY AND SOILS construction of excavations, foundations, building frames, retaining walls, and other building elements to mitigate the effects of seismic shaking and adverse soil conditions. The procedures and limitations for the design of structures are based on site characteristics, occupancy type, configuration, structural system height, and the strength of ground motion with specified probability of occurring at the site. Requirements for GeotecbnicalInnestigations Requirements for geotechnical investigations are included in CBC Appendix J, Section J104 (Engineered Grading Requirements). As outlined in Section J104, applications for a grading permit are required to be accompanied by plans, specifications, and supporting data consisting of a soils engineering report and engineering geology report. Additional requirements for subdivisions requiring tentative and final maps and for other specified types of structures are contained in California Health and Safety Code Sections 17953 to 17955 and in Section 1802 of the 2010 CBC. Testing of samples from subsurface investigations is required, such as from borings or test pits. Studies must be done as needed to evaluate slope stability, soil strength, position and adequacy of load hearing soils, the effect of moisture variation on load hearing capacity, compressibility, liquefaction, differential settlement, and expansiveness. City of Santa Ana The City of Santa Ana adopted the most recent CBC by reference, with certain amendments, into Chapter 8 (Buildings and Structures), Article 2 (Building Code), of the City's Municipal Code. Geologic Setting Regional Setting The project area is in the Los Angeles Basin, a coastal plain consisting of thick layers of sediment deposited by local rivers and with a slight south -to- southwest slope. The Los Angeles Basin, in turn, is in the northwestern end of the Peninsular Ranges geomorphic province, a region of northwest trending mountains and valleys in southwestern California and extending south into Mexico. Project Area The project area is underlain by young alluvial fm deposits, designated Qyfa and Qyfsa on Figure 5.4 -1, Geologic Map. These materials are unconsolidated to moderately consolidated silt, sand, pebbly cobbly sand, and bouldery alluvial -fan deposits having slightly to moderately dissected surfaces, and are of Holocene and late Pleistocene age (USGS 2006). The Holocene Epoch extends from the present to approximately 11,500 years before present (ybp); the Pleistocene Epoch extends from about 11,500 ybp to approximately 1.8 million ybp. Elevations in the project area range from approximately 90 feet above mean sea level (amsl) along the northeastern boundary to approximately 60 feet amsl along the southwestern boundary. The project area has a southwest slope of approximately 0.3 percent. Groundwater The project area is above the Main Orange County Groundwater Basin. Groundwater contours under the project area in June 2011 were approximately at mean sea level near the northern end and approximately 10 Page 5.4 -2 PlaceWorkr