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Aubrey Rose November 8, 2024 Page 2 lakes will be interconnected by a series of conduits and used by Zone 7 for local water management functions, thereby enhancing the resiliency and flexibility of Zone 7’s water supply functions. Zone 7 currently owns Lake I and Cope Lake and expects Lake H to be transferred to Zone 7 within the next few years. Maintaining the integrity of the quarry lakes and the quality of the underlying groundwater basin is of utmost priority to Zone 7’s water management mission. Current ly, groundwater recharge occurs through infiltration of both rainfall and releases of imported water made to Arroyo Mocho and Arroyo del Valle. As surface water in these channels reaches the central part of the Livermore-Amador Valley (including the mining areas), it infiltrates into the main groundwater basin and boosts local groundwater supply. These influxes of recharge support salt management in the basin, complementing the agency’s on-going efforts to put both surface water and groundwater to maximum beneficial uses within the County. As further lakes are added to the chain, COL will provide additional capacity and flexibility for flood control and groundwater recharge, including more ability for managing water quality. Lake I, in particular, will pla y a critical role in enhanced groundwater recharge due to its size, location, and recharge face on the western sidewall. Currently Zone 7 is evaluating a Chain of Lakes Conveyance Project to include a multi -use pipeline that will connect the northern COLs area (e.g., Lake I) with Lake A and the South Bay Aqueduct and with Zone 7’s water treatment plant. The concept of the pipeline is to convey excess surface water supply—including imported water and local water from the Arroyo Valle— to the COLs for storage and groundwater recharge. The pipeline will also supply raw water from the COLs to Zone 7’s Del Valle Water Treatment Plant (WTP) for use under emergency and drought situations. A pipeline alignment study has been completed and Zone 7 is further evaluating operational schemes and pertinent details. However, the proposed Project may jeopardize this crucial infrastructure project if sewage or effluent are allowed to directly or indirectly enter the lakes through runoff or infiltration. Groundwater Quality Standards and Groundwater Management in the Livermore Valley Groundwater Basin Zone 7 relies on imported water for approximately 70% of its drinking water supply, and so the groundwater basin is an important backstop to providing water supply in times of drought, or in the event that any portion of the state’s water infrastructure should fail (for example, in the event of natural disaster). Zone 7 strives to maintain the groundwater basin at full capacity whenever possible to ensure that this locally stored water supply is available to meet the needs of County residents. As the exclusive Groundwater Sustainability Agency (GSA) for the Livermore Valley Groundwater Basin, Zone 7 prepared and implements a groundwater sustainability plan (GSP) for the Basin pursuant to the Sustainable Groundwater Management Act (SGMA). Through the GSP, Zone 7 has identified thresholds within which the Basin can be operated without resulting in an impermissible “undesirable result” under SGMA. Significant and unreasonable degradation of water quality is an undesirable result under State law, and Zone 7 is tasked with managing the basin to avoid such an outcome. Consistent with