3) Irvine Desalter Plant (IDP), 5,700 AFY. This is a local groundwater source. 15% of the water pumped is lost due to the treatment process. Salty water is pumped from wells and sent to the IDP facility to make it suitable for drinking purposes. This water is pumped consistently throughout the year with interruptions due to maintenance. 4) Wells 21 & 22 Desalter Treatment plant (Wells 21 &22), 2,400 AFY. This plant recovers and treats local groundwater to remove nitrites and other impurities. 15% of the water pumped is lost due to the treatment process. This water is pumped consistently throughout the year with downtime for maintenance. 5) Baker Water Treatment Plant (Baker), 7,200 AFY. This plant is a joint regional project by five water districts. Baker uses advanced treatment technologies to produce drinking water from local surface water sources and untreated water from Metropolitan. Produced water is shared by the districts and IRWD receives about 24% of the production. 2% of the water is lost due to the treatment process. This water is produced consistently throughout the year. 6) Howiler Water Treatment Plant, 3,000 AFY (3 MGD). This plant produces drinking water from local surface water sources and untreated water from Metropolitan. This water is produced consistently throughout the year. 7) Imported Water via MWDOC and Metropolitan, 15,000 AFY. Imported water supplied from Metropolitan and MWDOC serves to fill any gaps in IRWD local supplies and as such makes up a smaller percentage of the total water used in the IRWD service area. These values are subject to increase in the future if demands grow. Drinking water imported to IRWD comes from Northern California via the Sacramento-San Joaquin Delta (Delta) through the SWP and from the Colorado River via the CRA. IRWD submits imported water demand requests to MWDOC for inclusion in a regional request supplied by Metropolitan. Untreated Water 1) Irvine Lake: A limited number of customers use untreated water directly from Irvine Lake. Irvine Lake water sources include surface water runoff (native water) and imported water from Metropolitan. a) Irvine Lake, native water supply, use is typically ~3,000 AFY. As noted, any native water from runoff is generally delivered to the Baker Water Treatment Plant or Howiler Water Treatment Plant for treatment for potable use 1 . This estimate is based 1 IRWD intends to implement the proposed Santiago Creek Dam Improvement Project that would replace the Santiago Creek Dam outlet tower and spillway facilities and modify the embankment to meet or exceed current seismic, safety, and design requirements. This work is expected to begin in late 2027 or early 2028 and is expected to be completed by 2032. In the interim, use of surface water from Irvine Lake would not be available. IRWD has access to untreated water from Metropolitan that can be bypassed from Irvine Lake to the Baker WTP.
Appendix E - 23
IRWD – 2025 Urban Water Management Plan – WSCP
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