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ARROYO LAGO RESIDENTIAL PROJECT ADDENDUM 112 FCS Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480036/Addendum/21480036 Arroyo Lago Residential Project Addendum.docx to control erosion and sedimentation during construction. Compliance with the County’s grading and erosion control ordinance would further reduce potential impacts. Therefore, based on compliance with applicable laws and regulations, the Prior FEIR concluded that impacts would be less than significant. (Draft EIR, p. 3.6-19). Unstable Soils or Geologic Units (Threshold (c)) The Prior FEIR found that the project site includes deep fill materials from past quarry operations, with depths ranging from 22 to 162 feet depending on location. These materials vary in stiffness and density, and some areas contain loose or soft soils. However, the preliminary geotechnical reports concluded that the potential for liquefaction and other ground failures is low. MM GEO-1 would ensure that site-specific engineering recommendations are incorporated into project design and construction to address any instability risk. Therefore, the Prior FEIR concluded that impacts would be less than significant with mitigation incorporated. (Draft EIR, p. 3.6-20). Expansive Soils (Threshold (d)) The Prior FEIR identified that the lean clay fill on the project site has moderate to high expansion potential. Expansive soils can cause damage to foundations and infrastructure due to volume changes with moisture fluctuations. MM GEO-1 would require design-level recommendations to address expansive soils, including foundation design and ground improvement techniques, to be incorporated into the project design and construction. Implementation of this mitigation measure would also ensure that development associated with the County Project would be designed in compliance with the recommendations provided in a Design-level Geotechnical Report, to appropriately address any potentially significant impacts related to expansive soil. Therefore, the Prior FEIR concluded that impacts would be less than significant with mitigation incorporated. (Draft EIR, p. 3.6-21). Proposed Project Analysis and Conclusion The project site location and boundaries of the proposed project would be consistent with the project site and off-site areas evaluated in the Prior FEIR. Therefore, the geologic and soil features in the Prior FEIR for the County Project would be the same for the proposed project. For purposes of potential erosion impacts under Threshold (b), consistent with the analysis in the Prior FEIR, the proposed project would be required to adhere to all applicable laws and regulations, including without limitation, those relating to compliance with NPDES permitting and preparation and implementation of an approved SWPPP, including BMPs to control erosion and sedimentation during construction. Compliance with the County’s grading and erosion control ordinance would further reduce potential impacts. Therefore, based on compliance with applicable laws and regulations, and consistent with the Prior FEIR’s impact conclusions, impacts in this regard would be less than significant. With respect to the items under Thresholds (a), (c), and (d), consistent with the analysis and conclusions set forth in the Prior FEIR for the County Project, the proposed project would be required to implement MM GEO-1, which would ensure that the proposed structures adhere to the implementation of site-specific engineering measures recommended by a Design-level Geotechnical Report, reducing potential impacts to less than significant. The Design-level Geotechnical Report