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suitability of available on-site material for use as cover and in construction of <br />containment structures. The permeability of the soils classified as ML (silt) and <br />CL (clay) was determined to range from 10-6 to 10-8 cm/sec when remolded at <br />95 percent relative compaction (ASTM Test Designation D1557 -78A). A sum- <br />mary of laboratory test results are included in Appendix A. <br />Additionally, a seismic refraction survey was conducted by Portola Geophysics to <br />evaluate the rippability of subsurface materials. The locations of seismic lines <br />S-1 through S-6 are included with survey results in Appendix A. Data from the <br />survey indicate that the sediments (to approximately 100 feet) are characterized <br />by low velocity (1,250 to 1,560 ft/sec) materials to medium velocity (2,920 to <br />3,850 ft/sec) materials that will be readily rippable with heavy equipment. <br />4.3.4 Seismicity <br />No known Holocene faults underlie the site. The nearest known faults to the site <br />are the Bear Mountains fault zone (28 km east) and the Melones fault zone <br />(38 km east). Both of these faults are considered part of the Sierran Foothills <br />fault system. All other significant faults are located at least 57 km from the site. <br />These include the Midway, Antioch, and Greenville faults, located 57, 61, and <br />66 km west of the site, respectively (see Appendix A). <br />The site lies in an area of historically low seismic activity. Between 1800 and <br />1986, 19 significant historic earthquakes occurred within 100 km of the site. <br />Maximum historic earthquakes for previously identified faults are summarized in <br />Appendix A. The maximum historic earthquake associated with the Greenville <br />fault (magnitude 5.9) occurred in 1980, approximately 63 km west of the site. <br />The maximum historic earthquake associated with the Antioch fault <br />(magnitude 6.0) occurred in 1889, approximately 70 km from the site. The <br />maximum historic earthquake associated with the Melones fault zone <br />(magnitude 4.0) occurred in 1937, approximately 116 km southeast of the site. <br />Prior to 1975, the Sierran Foothills fault system (i.e., the Bear Mountains and <br />Melones fault zones) was considered inactive. The 1975 Oroville earthquake <br />(magnitude 5.7) occurred along a northern segment of the Sierran Foothill fault <br />system and prompted a re-evaluation of the earthquake potential of this fault <br />PJ9 9390218A.00W 23 Rev. 0 July 20, 1989 <br />