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City of Pleasanton—Hidden Canyon Residences and Preserve Project <br />CEQA Findings of Fact and Statement of Overriding Considerations <br /> <br /> <br />FirstCarbon Solutions 37 <br />Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480016/FOF/21480016 Pleasanton Hidden Canyon Residences and Preserve Project FOF.docx <br />Resources Code Section 21081(a)(1) and CEQA Guidelines Section 15091(a)(1), changes or <br />alterations have been required in, or incorporated into, the proposed project that mitigate or avoid <br />the potentially significant impacts as identified in the EIR. Therefore, impacts associated with on-site <br />landslides and collapse would be less than significant with mitigation incorporated. <br />1.6.11 - Impact GEO-4: Expansive Soil <br />Impact GEO-4: The proposed project would not be located on expansive soil, as defined in Table 18- <br />1-B of the Uniform Building Code (1994), creating substantial direct or indirect risks to life or <br />property. <br />Findings: Less than significant impact with mitigation incorporated. (Draft EIR, p. 3.6-32). <br />Changes or alterations have been required in, or incorporated into, the project <br />which avoid or substantially lessen the significant environmental effects as identified <br />in the EIR. (CEQA Guidelines § 15091(a)(1)). <br />Mitigation Measures <br />Implement MM GEO-1. <br />Facts in Support of Findings: The main development areas located in the central and eastern <br />portions of the project site consist of soil of the Diablo clay series, which has expansive capabilities <br />that undergo changes in moisture content as a result of seasonal fluctuations in California’s <br />Mediterranean climate from hot dry summers to cool moist winters. (Draft EIR, p. 3.6-31). Although <br />colluvial and residual soils comprised of stiff clays on the project site range from an approximate <br />depth between 2-11 feet below the surface, this depth varies throughout the project site. In <br />addition, previous plasticity index tests performed on surficial clays one to three feet in depth <br />indicated moderate to high plasticity. Therefore, the proposed project would have a potentially <br />significant impact related to expansive soils. (Draft EIR, p. 3.6-31). <br />Implementation of recommendations from the Updated Geotechnical and Geological Report <br />includes: (1) Burying all expansive colluvial soil located in deeper fills at least two feet below finished <br />grade and (2) Covering all finished graded fill slopes to promote growth of erosion control materials. <br />(Draft EIR, Appendix E). Although implementation of these recommendations would reduce impacts <br />on expansive soils, out of an abundance of caution, the proposed project would implement MM <br />GEO-1 to further reduce these impacts. (Draft EIR, p. 3.6-31). Implementation of MM GEO-1 would <br />require the qualified Geotechnical Engineer to perform a variety of tests evaluating the expansive <br />capabilities of the colluvium on the project site, including an Atterberg Limits Test to investigate the <br />fluctuations in moisture content of on-site colluvium soils. Based on the results of these required <br />tests, the qualified Geotechnical Engineer would provide appropriate recommendations for structure <br />foundations and pavements that would be incorporated into final project grading and building plans <br />in accordance with CBC guidelines. (Draft EIR, p. 3.6-31). Therefore, implementation of MM GEO-1 <br />would ensure that impacts of the proposed project related to expansive soils remain less than <br />significant.