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MainPlace Mall Transformation Project 12126.001 <br />2 FIELD AND LABORATORY EXPLORATION <br />2.1 Subsurface Soil Conditions <br />According to our geotechnical explorations and review of previous geotechnical <br />exploration by Irvine Soils Engineering, Inc. (ISE 1985a, 1985b, 1986, and 1987), <br />the geologic materials observed at the site include undocumented artificial fill <br />overlying young alluvial fan deposits (Qyf) see Figure 3, Regional Geology Map. <br />It should be noted that the boring location maps of the ISE's report could not be <br />located for review. <br />Descriptions of the respective geologic units are as follows: <br />Artificial Fill - Fill materials encountered by Irvine Soils Engineering Inc. (ISE, <br />1985a) throughout the site ranged in thickness up to a maximum of <br />approximately 8 feet bgs. The fill soils encountered by ISE generally consisted of <br />a medium dense to dense silty sand. However, the test boring location map <br />(Plate 1 referenced in the ISE's report) could not be located for review. <br />Artificial fill soils were encountered in all eight of our exploratory borings (LB-1 <br />through LB-8) to depths between 5 and 10.5 feet below ground surface (bgs). <br />The fill materials encountered generally consist of brown to dark brown, loose or <br />soft silty sand, clayey sand, sandy clay, and sandy silt with trace amounts of <br />construction debris. All Leighton's borings were located in the existing parking lot <br />areas and no subsurface exploration was performed inside existing building <br />footprint. Locations of the exploration borings and boring logs are presented in <br />Figure 2 and Appendix B, respectively. The artificial fill materials encountered at <br />the site are likely associated with the existing improvements and initial <br />development of the site. However, the records for fill placement were not <br />available for review. Therefore, the existing fill at the site is considered <br />undocumented. Localized thicker accumulations of fill materials should be <br />anticipated elsewhere at the site. <br />Quaternary Young Alluvial Fan Deposits - Quaternary age (Holocene) young <br />alluvial fan deposits generally consist of brown to dark brown and gray, loose to <br />very dense or soft to stiff sand, clayey sand, silty sand, clay, silt, and gravel with <br />isolated layers of sandy clay were encountered during our subsurface exploration <br />of the site beneath the artificial fill materials to the maximum explored depth of <br />51 Y2 feet bgs. The alluvial soils encountered by others (ISE, 1985a) throughout <br />4 9 <br />Leighton <br />