of Southern California (MWD) Lower Feeder or related conveyance facilities that result in disruptions to imported water deliveries from the Colorado River Aqueduct (CRA). The Lower Feeder is a critical component of MWD’s distribution system, conveying CRA supplies to several member agencies, including IRWD, across the region. The Southern San Andreas Fault intersects major water conveyance systems, including the CRA, at the San Gorgonio Pass. Given its proximity to active fault zones, damage to the Lower Feeder would limit CRA deliveries until repairs are completed. • Dyer Road Well Field Reduced Operations: The Dyer Road Well Field (DRWF) relies on blending water from multiple wells to meet regulatory standards at the blending compliance point; if a portion of these wells are contaminated by emerging contaminants, such as trichloroethylene and per- and polyfluoroalkyl substances, the overall supply may no longer comply at the blending compliance point. Regulatory changes, such as stricter maximum contaminant levels, could also cause the blended supply to fall out of compliance. For the purposes of the 2025 Study, IRWD assumed that emerging contaminants could result in a 50 percent reduction in DRWF contractual and physical pumping capacity. For each of these scenarios, water shortages at the 95 th percentile were estimated based on IRPDSM modelling results and mitigation strategies – additional conservation and additional groundwater storage - were evaluated. The DRWF Reduced Operations scenario did not lead to water shortages as imports are sufficient to meet demands under this relatively low-impact scenario. For the Delta Levee Failure and the combined Delta Levee and Lower Feeder scenarios, the 2025 Study recommends that IRWD plan to mitigate for shortages through continued investments in groundwater storage as well as additional schedulable supplies and water banking well recovery capacity. The 2025 Study concluded that IRWD’s proactive investment in a diversified water supply portfolio positions IRWD to reliably meet future demands across a wide range of disruption scenarios. In addition, the 2025 Study reaffirmed that IRWD can manage risks associated with the range of import disruptions and changing regional conditions, as well as risks to local groundwater supplies through implementation of its WSCP, use of its emergency water banking supplies and continued investments in its supply portfolio. 1. 2 Catastrophic Interruption Catastrophic supply interruptions could be the result of regional power outages, earthquakes, floods, water supply interruptions, structural damage from an explosive device, and threat of or possible contamination to the water system. IRWD’s response to a catastrophic interruption of water supply would depend on the cause, severity, and anticipated duration of the emergency. A potential shortage resulting in a reduction of available supplies can be addressed through a combination of alternative supplies and storage, combined with implementation of the WSCP. Since IRWD's major potable water sources include both imported water (including IRWD’s Water
WSCP - 6
IRWD – 2025 Water Shortage Contingency Plan
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