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2025 URBAN WATER MANAGEMENT PLAN <br /> MAY 2026/FINAL DRAFT/CAROLLO <br /> MWDOC, purchases untreated water from MET for basin recharge, as needed. In addition, OCWD <br /> regulates groundwater levels in the OC Basin by regulating the annual amount of pumping and setting <br /> the BPP for the water year.As defined in the District Act, the BPP is the ratio of water produced from <br /> groundwater supplies within the OCWD service area to all water produced within the area from both <br /> supplemental sources and groundwater within the OCWD (OCWD, 2020a). More information regarding <br /> the BPP is discussed in Section 6.3.1.3. <br /> 6.3.1.1 Basin Characteristics <br /> The OC Basin underlies the northern half of Orange County beneath broad lowlands. The OC Basin, <br /> managed by OCWD, covers an area of approximately 350 square miles, bordered by the Coyote and <br /> Chino Hills to the north, the Santa Ana Mountains to the northeast, and the Pacific Ocean to the <br /> southwest.The OC Basin boundary extends to the Orange County-Los Angeles Line to the northwest, <br /> where groundwater flows across the county line into the Central Groundwater Basin of Los Angeles <br /> County.A map of the OC Basin is shown on Figure 6.4. The total thickness of sedimentary rocks in the <br /> OC Basin is over 20,000 feet, with only the upper 2,000 to 4,000 feet containing fresh water.The <br /> OC Basin's full volume is approximately 66 MAF. <br /> There are three major aquifer systems that have been subdivided by OCWD, the Shallow Aquifer System, <br /> the Principal Aquifer System, and the Deep Aquifer System.These three aquifer systems are hydraulically <br /> connected as groundwater is able to flow between each other through intervening aquitards or <br /> discontinuities in the aquitards. The Shallow Aquifer system occurs from the surface to approximately <br /> 250 feet below ground surface. Most of the groundwater from this aquifer system is pumped by small <br /> water systems for industrial and agricultural use. The Principal Aquifer system occurs at depths between <br /> 200 and 1,300 feet below ground surface. Over 90 percent of groundwater production is from wells that <br /> are screened within the Principal Aquifer system. Only a minor amount of groundwater is pumped from <br /> the Deep Aquifer system, which underlies the Principal Aquifer system and is up to 2,000 feet deep in the <br /> center of the OC Basin. <br /> CITY OF SANTA ANA <br />