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ARROYO LAGO RESIDENTIAL PROJECT ADDENDUM FCS 137 Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480036/Addendum/21480036 Arroyo Lago Residential Project Addendum.docx Approximately 20 percent of Zone 7’s water supplies come from groundwater, with the rest coming from surface water sources.37 Groundwater supply is pumped from the Livermore Valley Groundwater Basin. The basin is not adjudicated and is not considered to be critically overdrafted; it is instead considered a medium-priority groundwater basin. As such, the basin is regulated under the Sustainable Groundwater Management Act (SGMA), and the preparation and implementation of a Groundwater Sustainability Plan (GSP) is required. Zone 7 has an approved GSP for the Livermore Valley Groundwater Basin, which identifies projects, practices, and goals related to management of groundwater supplies.38 Adherence to the applicable objectives and sustainability goals provided in the GSP would reduce impacts to groundwater quality within the City. Further, the proposed project would not include any on-site wells that would draw groundwater for proposed project operations. Therefore, impacts related to groundwater recharge and supply would be less than significant, consistent with the analysis and impact conclusions in the Prior FEIR. Therefore, the proposed project would not introduce new significant impacts or create substantially more severe significant impacts than those previously identified in the Prior FEIR. No additional analysis is required. c) Drainage Would the project: Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner which would: i) result in substantial erosion or siltation on- or off-site; ii) substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site; iii) create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff. Prior FEIR Conclusions The Prior FEIR found that construction activities within the project site could result in substantial erosion or siltation, leading to drainage pattern alteration and the increased potential for polluted runoff to enter nearby water bodies. However, the County Project would be required to comply with the regulations of its NPDES permit. Additionally, the County Project would be required to comply with construction-phase BMPs and requirements for erosion and sedimentation control plans. The County Project would be required to design and implement a SWPPP to ensure that erosion, siltation, and operation. The City is actively evaluating future supply alternatives, including potential joint groundwater wells in coordination with Zone 7; however, at present, all water supplies are purchased from Zone 7. 37 Zone 7 Water Agency (Zone 7). 2021. 2020 Urban Water Management Plan. June. 38 Zone 7 Water Agency (Zone 7). 2021. Alternative Groundwater Sustainability Plan for the Livermore Valley Groundwater Basin. December.