Item 27 - Water Supply Assessment for Cabrillo Town Center Project

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Santa Ana 2020 Urban Water Management Plan arcadis.com 6-18 recharge when such supplies are available, especially in relatively wet years. By keeping the basin relatively full during wet years, and for as long as possible in years with near-normal recharge, the maximum amount of groundwater could be maintained in storage to support pumping in future drought conditions. During dry hydrologic years when less water would be available for recharge, the BPP could be lowered to maintain groundwater storage levels. A component of OCWD’s BPP policy is to manage the groundwater basin so that the BPP will not fluctuate more that 5 percent from year to year. Based on most recent modeling of water supplies available for groundwater recharge and water demand forecasts, OCWD anticipates being able to sustain the BPP at 85% starting in 2025. The primary reasons for the higher BPP are the expected completion of the GWRS Final Expansion (GWRSFE) in 2023 and the relatively low water demands of approximately 400,000 AFY. Modeling and forecasts generate estimates based on historical averages. Consequently, forecasts use average hydrologic conditions which smooth the dynamic and unpredictable local hydrology. Variations in local hydrology are the most significant impact to supplies of water available to recharge the groundwater basin.The BPP projection of 85% is provided based upon average annual rainfall weather patterns. If the City were to experience a relatively dry period, the BPP could be reduced to maintain water storage levels, by as much as five percent. Table 6-5: Management Actions Based on Changes in Groundwater Storage Available Storage Space (amount below full basin condition, AF) Considered Basin Management Action Less than 100,000 Raise BPP 100,000 to 300,000 Maintain and / or raise BPP towards 75% goal 300,000 to 350,000 Seek additional supplies to refill basin and / or lower the BPP Greater than 350,000 Seek additional supplies to refill basin and lower the BPP BPP Exemptions In some cases, OCWD encourages pumping and treating groundwater that does not meet drinking water standards in order to protect water quality. This is achieved by using a financial incentive called the BEA Exemption. A BEA Exemption is used to promote beneficial uses of poor-quality groundwater and reduce or prevent the spread of poor-quality groundwater into non-degraded aquifer zones. OCWD uses a partial or total exemption of the BEA to compensate a qualified participating agency or Producer for the costs of treating poor quality groundwater, which typically include capital, interest and operations and maintenance costs for treatment facilities. When OCWD authorizes a BEA exemption for a project, it is obligated to provide the replenishment water for the production above the BPP and forgo the BEA revenue that OCWD would otherwise receive from the producer (City of La Habra et al., 2017). Similarly, for proactive water quality management, OCWD exempts a portion of the BEA for their Coastal Pumping Transfer Program (CPTP). The CPTP encourages inland groundwater producers to increase pumping and coastal producers to decrease pumping in order to reduce the groundwater basin drawdown