Inland Empire Utilities Agency Regional Plant 1

1. INTRODUCTION

Regional Water Recycling Plant No. 1 (RP-1) serves as the flagship facility and northern solids processing hub for the Inland Empire Utilities Agency (IEUA). Located in Ontario, California, this 44-MGD facility is a critical component of the Chino Basin’s water resource management strategy, producing high-quality Title 22 recycled water for groundwater recharge and landscape irrigation. Commissioned originally in 1948, RP-1 has evolved from a basic sanitation facility into a sophisticated resource recovery center.

RP-1 is distinct within the IEUA network as it handles not only its own influent but also processes the biosolids transferred from Regional Plant No. 4 (RP-4) via an inter-plant pipeline. With an integrated focus on energy neutrality, the facility utilizes advanced cogeneration systems fueled by digester gas. As the region faces persistent drought conditions, RP-1’s role in the optimal management of the Chino Groundwater Basin—one of the largest aquifers in Southern California—makes it a model for arid-region wastewater infrastructure.

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2. FACILITY OVERVIEW

A. Service Area & Coverage

RP-1 serves the heavy commercial and residential zones of the western Inland Empire. The tributary area encompasses the cities of Ontario, Upland, Montclair, and portions of Rancho Cucamonga and Fontana. The collection system feeding RP-1 is gravity-dominated due to the north-to-south slope of the region. The facility operates as part of an interconnected regional system (Regional Sewerage System) allowing flow diversions between RP-1 and RP-4 to optimize hydraulic loading.

B. Operational Capacity

The facility has a permitted liquid treatment capacity of 44 million gallons per day (MGD). Historically, flows have fluctuated based on conservation efforts and economic activity, currently averaging between 26 and 28 MGD. While liquid capacity is sufficient for current needs, the plant’s solids handling capacity is designed to accommodate a regional load equivalent to 70 MGD of liquid flow, processing sludge from both the RP-1 and RP-4 liquid trains.

C. Discharge & Compliance

RP-1 is a zero-discharge-to-ocean facility in practice, though it maintains connectivity to the Santa Ana Regional Interceptor (SARI) line for brine disposal. Treated effluent is discharged into Cucamonga Creek, a concrete-lined channel that feeds the Santa Ana River. However, a significant percentage of effluent is diverted for beneficial reuse. The facility operates under strict requirements set by the Santa Ana Regional Water Quality Control Board, mandating Tertiary Title 22 standards to protect downstream beneficial uses and groundwater quality.

3. TREATMENT PROCESS

RP-1 employs a conventional activated sludge process followed by tertiary filtration and disinfection. The treatment train is designed to meet California Title 22 requirements for unrestricted reuse.

A. PRELIMINARY TREATMENT

Influent wastewater enters the headworks where it passes through mechanically cleaned bar screens to remove large debris, plastics, and rags. Following screening, the flow enters aerated grit chambers where velocity is reduced to allow inorganic sands and gravel to settle. The grit is removed, washed, and dewatered for landfill disposal. Odor control at the headworks is managed via chemical scrubbers to mitigate impacts on neighboring commercial zones.

B. PRIMARY TREATMENT

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Wastewater flows into rectangular primary sedimentation tanks. Here, the hydraulic velocity is minimized to facilitate the settling of settleable solids and the flotation of fats, oils, and grease (FOG). Bottom flights scrape sludge to hoppers for pumping to the thickening facility, while surface skimmers remove FOG. Primary treatment at RP-1 typically removes 50-60% of Total Suspended Solids (TSS) and 30-35% of Biochemical Oxygen Demand (BOD).

C. SECONDARY TREATMENT

The biological treatment utilizes an activated sludge process. The aeration basins are configured to support carbonaceous oxidation and partial nitrification/denitrification. Air is supplied via fine-bubble diffusers powered by centrifugal blowers. The mixed liquor then flows to rectangular secondary clarifiers. The return activated sludge (RAS) is pumped back to the aeration basins to maintain the biomass, while waste activated sludge (WAS) is thickened and sent to the digesters. The secondary effluent meets the standard of 30 mg/L BOD and 30 mg/L TSS before entering tertiary treatment.

D. TERTIARY TREATMENT (Title 22)

To meet recycled water standards, secondary effluent undergoes coagulation and flocculation followed by filtration. RP-1 utilizes deep-bed dual-media gravity filters (anthracite coal and sand). This stage is critical for removing remaining suspended solids and turbidity, ensuring the water is clear enough for effective disinfection. The target turbidity is consistently below 2 NTU.

E. DISINFECTION

Disinfection is achieved through chlorination using sodium hypochlorite in plug-flow contact basins. The contact time is rigorously monitored to ensure adequate pathogen inactivation (virus and bacteria kill). Prior to discharge into Cucamonga Creek, the water undergoes dechlorination using sodium bisulfite to prevent toxicity to aquatic life. Recycled water distributed for irrigation retains a chlorine residual to prevent biological regrowth in the distribution system.

F. SOLIDS HANDLING (Regional Hub)

RP-1 serves as a regional solids processing facility.

• Thickening: Primary sludge and WAS (via Dissolved Air Flotation or Rotary Drum Thickeners) are thickened prior to digestion.
• Digestion: The plant operates a battery of mesophilic anaerobic digesters. These tanks stabilize the volatile solids, reducing pathogen content and generating methane gas. Solids from Regional Plant 4 are pumped to RP-1 for processing here.
• Dewatering: Digested sludge is dewatered using high-speed centrifuges to produce a cake with approximately 20-25% solids.
• Disposal/Reuse: The dewatered cake is transported to the nearby Inland Empire Regional Composting Authority (IERCA) facility, where it is converted into high-quality soil amendments, achieving 100% beneficial reuse of biosolids.

G. PROCESS CONTROL

The facility is managed via a centralized SCADA system, allowing operators to monitor dissolved oxygen levels, turbidity, chlorine residual, and tank levels in real-time. Recent upgrades have integrated automated air flow control valves to optimize blower energy consumption based on ammonia load.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The RP-1 site is situated in a dense mixed-use area of Ontario. The layout reflects decades of expansion, with older abandoned structures adjacent to modern facilities. The site includes extensive maintenance workshops that service the northern IEUA fleet and equipment.

B. Energy Systems & Cogeneration

RP-1 is a leader in energy recovery. The facility utilizes Internal Combustion (IC) engines fueled by biogas produced in the anaerobic digesters. These cogeneration units generate electricity to power plant equipment and heat to maintain digester temperatures. Additionally, IEUA has implemented a battery energy storage system (BESS) at the site to manage peak demand charges and enhance grid resilience. The goal is to maximize self-generation and minimize reliance on the external electrical grid.

C. Odor Control

Given the proximity to the Ontario Convention Center and commercial districts, odor control is paramount. The facility utilizes a combination of chemical scrubbers (wet scrubbers using bleach/caustic) and biotrickling filters to treat foul air extracted from the headworks, primary clarifiers, and solids handling buildings.

5. RECENT UPGRADES & MAJOR PROJECTS

RP-1 Capacity Recovery Project (2018-2022)

• Project Scope: Comprehensive rehabilitation of the liquid treatment train to restore the reliable capacity to 44 MGD. Included replacement of aeration diffusers, rehabilitation of secondary clarifier mechanisms, and upgrades to return activated sludge (RAS) pumps.
• Budget: ~$30 Million
• Drivers: Aging infrastructure had derated the plant’s effective capacity; upgrades were necessary to handle projected growth in Ontario.
• Technical Highlights: Installation of high-efficiency fine bubble diffusers improved oxygen transfer efficiency (OTE), reducing blower energy demand.

RP-1 Headworks Upgrades

• Project Scope: Replacement of mechanical bar screens and washer/compactors. Upgrades to the grit removal systems to improve capture of finer inorganic particles.
• Results: Improved protection of downstream pumps and reduced accumulation of inert solids in the digesters.

Asset Management & Electrical Upgrades (Ongoing)

IEUA maintains a rigorous 10-year Capital Improvement Plan (CIP). Current works at RP-1 focus on 12kV switchgear replacement and the rehabilitation of the digester gas piping network to ensure safety and maximize cogeneration efficiency. Future planning includes the potential retrofitting of aeration basins for enhanced nutrient removal to meet tightening regulatory limits.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

RP-1 operates under NPDES Permit No. CA8000409, administered by the Santa Ana Regional Water Quality Control Board. Key effluent limits include:

• BOD (5-day): 20 mg/L (Monthly Average)
• TSS: 20 mg/L (Monthly Average)
• Total Inorganic Nitrogen (TIN): 8-10 mg/L (depending on discharge point)
• Total Coliform: 2.2 MPN/100mL (7-day median for Title 22)

B. Environmental Stewardship

The facility consistently earns Peak Performance Awards from NACWA (National Association of Clean Water Agencies) for permit compliance. By producing Title 22 recycled water, RP-1 offsets the demand for imported water from the State Water Project, directly contributing to the sustainability of Southern California’s water portfolio.

7. OPERATIONAL EXCELLENCE

RP-1 is staffed by Grade III, IV, and V certified operators (CWEA certification). The operations team utilizes a robust Computerized Maintenance Management System (CMMS) to track asset health. The facility is also a testing ground for innovative technologies, having piloted various membrane technologies and energy recovery devices before wider agency implementation.

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

As the oldest plant in the IEUA system (parts dating to 1948), RP-1 faces significant asset replacement needs. Concrete corrosion in headworks and older channels requires continuous rehabilitation.

B. Salinity Management

Managing Total Dissolved Solids (TDS) is a regional challenge. High salinity in wastewater limits the applicability of recycled water for groundwater recharge. IEUA manages a regional non-reclaimable wastewater system (brine line) to bypass high-salinity industrial dischargers around the biological treatment process.

C. Future Master Planning

The IEUA Facilities Master Plan envisions RP-1 maintaining its 44 MGD liquid capacity but potentially expanding its solids handling role as regional flows increase. Future projects will likely focus on Intensified Nutrient Removal to meet lower nitrogen limits for the Santa Ana River watershed.

9. COMMUNITY & REGIONAL IMPACT

RP-1 is an economic enabler for the City of Ontario. By providing reliable wastewater treatment and affordable recycled water for industrial and landscape use, the facility supports local industry. The plant’s output is critical for the Chino Basin Watermaster’s recharge program, which replenishes the aquifer that serves as the primary drinking water source for the region.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES & RESOURCES

A. Related Infrastructure

• Regional Plant No. 4 (RP-4): Located in Rancho Cucamonga; sends solids to RP-1.
• Regional Plant No. 5 (RP-5): Serving the southern service area (Chino).
• Inland Empire Regional Composting Authority (IERCA): Receives dewatered cake from RP-1.

B. Resources

• Inland Empire Utilities Agency Official Website
• Santa Ana Regional Water Quality Control Board
• Directory of California Treatment Plants

12. FREQUENTLY ASKED QUESTIONS

Technical Questions

1. What is the solids retention time (SRT) for the anaerobic digesters at RP-1?

The digesters typically operate with a retention time of 15-20 days at mesophilic temperatures (approx. 98°F) to ensure volatile solids reduction (VSR) requirements are met for vector attraction reduction.

2. Does RP-1 use Membrane Bioreactors (MBR)?

No, RP-1 currently utilizes conventional activated sludge with gravity secondary clarifiers. However, IEUA utilizes MBR technology at other facilities, such as the Carbon Canyon Water Recycling Facility (CCWRF) and the new RP-5 expansion.

3. How is the recycled water from RP-1 distributed?

Effluent enters the Regional Recycled Water Distribution System (RRWDS). It is pumped to groundwater recharge basins or distributed via purple pipe for municipal landscape irrigation and industrial cooling towers.

4. What is the peak wet weather flow capacity?

While the design average is 44 MGD, the hydraulic peak capacity is significantly higher, capable of handling storm surges up to approximately 80 MGD through the primary and secondary trains before hydraulic constraints occur.

Public Interest Questions

5. Is the water leaving RP-1 safe to drink?

The water leaving RP-1 is recycled water, not potable (drinking) water. While it is highly treated and safe for human contact and irrigation, it is used for groundwater recharge. The soil acts as a final natural filter before the water eventually reaches aquifers used for drinking water supply.

6. Does the plant smell?

Wastewater treatment inherently generates odors, but RP-1 utilizes advanced chemical scrubbers and biofilters to capture and neutralize foul air before it leaves the site. IEUA maintains a strict odor monitoring program.

7. How much energy does the plant generate?

Through its cogeneration engines running on biogas and solar installations across the agency, IEUA aims for energy neutrality. RP-1 generates a significant portion of its own electricity needs onsite.