operation since 2008 and was expanded in 2015 from 72,000 AF per year to 100,000 AF per year and in 2022 underwent a final expansion to about 134,000 AFY. As previously stated, OCWD manages the basin pumping through its Basin Production Percentage (BPP), which can be adjusted to maintain groundwater storage levels. OCWD operates the Basin to maintain available storage space in order to maximize surface water 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 can be maintained in storage to support pumping in future drought conditions. 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. In 2013, OCWD adopted a policy of maintaining a BPP of at least 75 percent. With completion of the final GWRS expansion and a projected increase in future groundwater demands, OCWD anticipates being able to sustain a BPP of 85 percent (OCWD, 2025). C. Non-Potable Water Management Recycled water has proven to be an effective “drought-proof” reliable supply as a result of the fact that local sewage flows remain virtually unaffected by dry years. As with the potable system, having several sources of supply provides reliability in the recycled water system. Those sources include recycled water from the MWRP and LAWRP, some local groundwater and imported untreated water from Metropolitan to supplement the recycled system. Reliability is further enhanced by IRWD’s recycled water seasonal storage capacity in Rattlesnake Reservoir, Sand Canyon Reservoir, San Joaquin Reservoir, and Syphon Reservoir. By 2030, IRWD expects to increase its recycled water storage capacity by 4,500 AF through the Syphon Reservoir Improvement Project. Only a small portion of IRWD's potable supply, local surface water runoff captured in Irvine Lake, is reduced in single-dry and multiple-dry years. As discussed in Section 6, IRWD’s Baker Water Treatment Plant (Baker), a joint regional project also provides increased water supply reliability. Baker increases local treatment capability from multiple water supply sources, which are imported untreated Colorado River water from Metropolitan and through the local surface water in Irvine Lake. The Baker plant came online in 2016 and is used to treat raw imported Colorado River water from Metropolitan and local surface water runoff from Irvine Lake for potable use. Starting in 2027, the Howiler WTP will be available to IRWD to treat additional untreated Colorado River water from Metropolitan, which will further increase IRWD’s water supply reliability. D. Climate Change Considerations IRWD’s past, current, and future projected customer water use calculations consider climate change effects in several ways. It should be noted that although considered, IRWD does not directly apply adjustments for climate change in the DWR Section 7 Tables. Instead, IRWD relies on Metropolitan and MWDOC’s UWMPs as well as other local documents that indicate retail water supplies will be reliable for all foreseeable hydrologic conditions. These referenced reports include Metropolitan’s Integrated Resources Plan (IRP) which considers climate change conditions and the subsequent effect on imported water supply
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IRWD – 2025 Urban Water Management Plan
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