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