The City of Santa Cruz has been treating sewage at the WWTF near Neary Lagoon since 1928. The Santa Cruz Regional WWTF, located at 110 California St, Santa Cruz, California, is a critical part of the City’s wastewater system. The facility has been expanded several times to accommodate City growth and flows from the Santa Cruz County Sanitation District. Today, the WWTF serves approximately 145,000 residents, with a rated dry weather design capacity of 17 million gallons per day (MGD), an average daily flow of less than 10 MGD, and a wet weather design capacity of 81 MGD.

The WWTF receives a single 21kV electric power service from Pacific Gas and Electric (PG&E) at the main switchgear and distributes this power via an A/B primary selective system to substations located throughout the plant. Each substation generally consists of an outdoor 21kV selector switch, outdoor 21kV-480V transformer, and an indoor 480V switchgear or switchboard. One substation operates at 21kV-2.4kV with an additional step down from 2.4kV-480V. Each 480V switchgear lineup in turn feeds motor control centers and distribution panels that power process equipment and building loads.

Standby power is provided to critical process loads via diesel standby generators distributed throughout the plant, each connected to a 480V switchgear. The plant also operates two cogeneration engines (820kW and 480kW) which generate electricity using biogas from the WWTF’s treatment process. The cogeneration engines operate in parallel with the PG&E electric service and are not part of the standby power system.

Many key components of the existing electrical distribution system were constructed in the 1980s with some additional equipment installed in the 1990s and beyond. This equipment has been diligently maintained by plant staff, but it has reached the end of its expected useful life and has limitations that can make isolating and maintaining the equipment challenging. Modernization and improvements to the electrical distribution system are needed to provide reliable, safe, and efficient power to support operations, future expansions, and compliance with current standards. Based on prior condition assessment and preliminary design efforts, and with owner advisory support, the City intends to execute this Project collaboratively through a design-build process.

The Project consists of the principal components below. The Project scope of work generally includes the following:

Replace existing PG&E 21kV electric service.

Replace 21kV main switchgear, cables, and substations.

Complete 21kV loop to provide a redundant means of distributing power around the plant.

Replace existing 480V and 2.4kV switchgear (including conversion of the 2.4kV system to 480V).

Convert motors (Interstage Pump 2/3 and Blowers 1/2/3) from 2.4kV to 480V.

Add VFDs for these pumps and blowers and integrate the VFDs with the plant PLC/SCADA system.

Provide new diesel standby generator(s) for plant-wide backup.

Network and integrate new switchgear power meters and protective relays to be monitored from the plant’s SCADA system.

Demolish existing Maintenance Building and construct a new Main Electrical Building.

Demolish existing switchgear, transformers, generators, and associated cabling.

Sequence the work and provide temporary power and controls to maintain continuous operation of the WWTF’s treatment process during all phases of construction.

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