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625 Cypress Avenue <br />Geotechnical Investigation <br /> <br />Project No. W1895-88-01 - 3 - April 23, 2024 <br />4. SOIL AND GEOLOGIC CONDITIONS <br />Based on published geologic maps of the area, the site is underlain by artificial fill and Holocene age <br />young alluvial fan deposits that consist of clay, silt, and sand (California Geological Survey, 2012). <br />Detailed stratigraphic profiles of the materials encountered at the site are provided on the boring and <br />test pit logs in Appendix A. <br />4.1 Artificial Fill <br />Artificial fill was encountered in our explorations to a maximum depth of 5 feet below existing ground <br />surface. The artificial fill generally consists of dark brown clay with some fine to medium-grained sand <br />and can be characterized as slightly moist to moist and soft to firm. The fill is likely the result of past <br />grading or construction activities at the site. Deeper fill may exist between excavations and in other <br />portions of the site that were not directly explored. <br />4.2 Younger Alluvium <br />Holocene age young alluvial fan deposits were encountered beneath the fill to the maximum depth <br />explored of 61 feet below existing ground surface. The alluvium consisted of dark brown clay to sandy <br />clay, and poorly-graded sand from 3 to 13½ feet below ground surface. These soils can be characterized <br />as slightly moist to moist and soft to stiff, or loose. Below 13½ feet, the soils were predominantly dark <br />yellowish brown silt and clay with various amounts of sand. These soils can be characterized as soft to <br />stiff and dry to wet. <br />5. GROUNDWATER <br />Review of the Seismic Hazard Zone Report for the Tustin Quadrangle (California Division of Mines and <br />Geology [CDMG], 2001) indicates that the historically highest groundwater level in the area is <br />approximately 35 feet beneath the existing ground surface. Groundwater information presented in this <br />document is generated from data collected in the early 1900’s to the late 1990s. <br />Groundwater was encountered in boring B1 at a depth of 49½ feet below the existing ground surface. <br />Based on the depth of groundwater in our borings, the reported historic high groundwater levels in the <br />immediate area (CDMG, 2001), and the depth of proposed construction, static groundwater is neither <br />expected to be encountered during construction, nor have a detrimental effect on the project. <br />However, it is not uncommon for groundwater levels to vary seasonally or for groundwater seepage <br />conditions to develop where none previously existed (especially in impermeable fine-grained soils <br />which are heavily irrigated or after seasonal rainfall), groundwater seepage levels encountered during