Rialto Wastewater Treatment Plant Expansion/Master Plan

An EIR was prepared for a project that would double the capacity of the City of Rialto Wastewater Treatment Plant (WWTP). The proposed expansion and modernization would accommodate approved projects and the projected population growth of the City. As proposed in the Wastewater Treatment Plant Master Plan, the capacity of Plant 5 would be doubled by duplicating each major piece of equipment. The WWTP currently processes between 9 and 12 million gallons per day (mgd). The proposed expansion would allow for the treatment of up to 16 mgd. Plants 1 through 4 would be decommissioned in place and later removed and new high efficiency filters would be added in addition to an ultraviolet disinfection system which would allow the plant to operate by gravity. This new Plant would make it possible to eliminate the older and less efficient Plants resulting in a higher quality effluent requiring less energy to process than the current Plants 1 through 4. A SWRCB CEQA-Plus checklist was also completed for the project to meet the requirements for State Revolving Fund Loan funding.


The WWTP outfall (also known as the Rialto Drain) is a known reproductive site for the Santa Ana sucker, a federally-listed threatened fish species and a California Species of Concern. This drain also has the potential to support two other sensitive fish species: the arroyo chub and Santa Ana specked dace. The EIR evaluated the potential for the increased outflow to alter the existing spawning habitats for these species and to limit the ability of larval fish to locate and use suitable low-flow habitats. Cumulative impacts to the overall flow in the Santa Ana River were also evaluated. Other resources evaluated included air quality (including climate change), cultural and paleontologic resources, geology and soils, hazards and hazardous materials, hydrology and water quality, noise, and population and housing. This project was completed on an accelerated schedule in order to meet funding deadlines.

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