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4. ENVIRONMENTAL ANALYSIS 4.7 GEOLOGY,SOILS,AND SEISMICITY historical worldwide earthquakes to determine the characteristics,geologic environments, and — hazards of landslides caused by seismic events. Intensity data from several hundred U.S. earthquakes,used to determine the relationship between landslide distribution and seismic parameters,supplemented the data provided by the 40 historical earthquakes(Keefer, 1984). The — study determined that the number of reported landslides increases with increased magnitude,and those earthquakes with magnitudes smaller than a Richter magnitude 4 caused few landslides. Correlation between earthquake magnitude and landslide distribution reveals that the maximum area likely affected by landslides during an earthquake increases from approximately 0 square mile at magnitude 4.0 to 200,000 square miles at magnitude 9.2(Keefer, 1984). A magnitude 4 earthquake is relatively common in California,with light to moderate perceived shaking that — causes either no or very light damage. The Tracy-Vernalis area,therefore,could be affected by earthquakes occurring in the Bay Area and the San Joaquin Valley and be subjected earthquake magnitudes capable of causing failure in non engineered,unsupported slopes or permanent reclamation slopes. SLOPE STABILITY ANALYSIS FOR PROPOSED PROJECT SITE Geomatrix Consultants(Geomatrix)conducted a preliminary analysis to determine the stability of T the temporary(3/a:t H:V)and permanent(2:1 H:V)quarry slopes expected at the proposed project site. The stability analysis addressed slope stability under static and earthquake-induced conditions(Geomatrix,2002). Geomatrix developed information and subsurface data and conducted the slope stability analysis with an approach consisting of the following items: • Review and application of pertinent RMC Lonestar reports of the Traina-Barnes Property and A&L Ranch aggregate resource assessment studies which contained Becker Hammer data of subsurface materials, • Review of the EIR prepared for the DSS Quarry Site, • Review of the Slope Stability Analysis of the Brown Sand Quarry located 2 miles west of the proposed quarry site, • Conducted a field reconnaissance to observe the site and other active nearby quarries and to obtain basic information for estimating appropriate soil strength parameters for analyses, • Conducted a parameter"sensitivity analysis"that performed a parameter for the active quarry slopes observed during observation to estimate lower bound soil strength parameters. — • Performed a static and dynamic slope stability analysis of the proposed quarry slope configurations based on applicable, available subsurface information,laboratory analysis of _ a clay sample from the DSS Quarry site, and postulated seismic loadings. Geomatrix performed site slope analysis using the available information and observation at nearby quarries with similar slopes to anticipate performance of excavation slopes at the proposed site. However,the Geomatrix study did not include actual soil sampling and geotechnical testing to determine site-specific engineering soil properties of the subsurface materials. Consequently, RMC Pack Vernalis Quarry Mining and Reclamation Project 4.7-18 PSA/203015 Administrative Draft©R March 2OD4