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r Stockton Unified School District Geological and Environmental Hazards Assessment CSU-Stanislaus,Stockton Campus School Site Page 25 The Great Valley Fault Zone, the active fault system nearest the site, is classified as a "Type B" seismic .,. source by the 1997 Uniforn Building Code criteria (Table 16-U; ICBG, 1997) based on its potential to generate a Maximum Credible Earthquake of M6.7 and its estimated long-term slip rate of 1.5 millimeters per year (Petersen and others, 1996). The site is within the Uniform Building Code (UBC) Seismic Zone 3. 7.2.4 Liquefaction Subsidence Potential i. Liquefaction is a phenomenon whereby loose, cohesionless soils (sandy soils) in a saturated state (below the groundwater table) lose shear strength during the cyclic loading accompanying an earthquake. The ' consequences of liquefaction of the soils underlying a site can include: bearing capacity failure of structure foundations; lateral spreading of the liquefied deposits and overlying soils; and localized settlement of the ground surface. Subsurface data for the area suggest that potentially liquefiable sands are present at the site; however, groundwater depths are approximately 30 to 44 feet in the site vicinity. Therefore, the potential for soil liquefaction is considered low. We recommend a Geotechnical Engineering Study be performed for site- specific liquefaction calculations. Mitigation of such settlements typically consists of strengthening foundations and slabs. 7.2.5 Dam or Flood Inundation and. Street Flooding The site is contained within a Non-Flood Zone of the Federal Emergency Management Agency (FEMA) insurance map dated May 1996 (Figure 5). Although the danger of flooding is relatively low, drainage control on local streets should be maintained in accordance with San Joaquin County drainage standards as applicable. 7.2.6 Slope Stability The site is not located on or near a slope. The potential for slope instability or landslides does not exist. L. 7.2.7 Expansive and Compressible Soils Expansive clays are prone to volume changes accompanying changes in soil water content. The Soil Survey of San Joaquin County, California, 1992, classifies the site surface soils as Jacktone—Urban Land Complex. The Jacktone — Urban Land Complex is comprised of clays and clay loams that have a high shrink — swell potential, slow permeability rate, and low strength. The site soils are characterized as having a moderate to high expansion potential. V 8.0 FINDINGS The general site area is the location of institutional, residential, and commercial properties. The parcel has +� historically been used for institutional purposes. The site consists of an approximately 18-acre portion of APN 139-214-04 that currently includes several abandoned buildings, a park area, a track and field, a historical building, a sewer screening station, a drug abuse-recovery house, an electrical distribution �.. station, and storage buildings. Several paved roads are located on the site. The terrain of the site is flat with a general topographic gradient to the south-southwest. The review of ASTM-specified databases revealed more than eighty locations within the specified radii; eightteen of these were submitted to EHD. Condor's review of the E14D files indicated the following: a current subsurface investigation associated with a former-UST; groundwater flow direction varied to the east and northeast; and the past use of PBCs Ntiio� iJCONDOR