City Of San Diego North City Water Reclamation Plant

FACILITY BASIC INFORMATION

• Plant Name: North City Water Reclamation Plant (NCWRP)
• Location: 4949 Eastgate Mall, San Diego, San Diego County, CA 92121
• Operating Authority: City of San Diego Public Utilities Department
• Design Capacity: 52 MGD (Liquid Stream Expansion)
• Current Average Flow: ~30 MGD (Varies by seasonal demand and Pure Water operations)
• Population Served: Approx. 800,000 (Northern San Diego service area)
• Service Area: Northern San Diego City (approx. 49 sq. miles) including Del Mar, Poway, and Mira Mesa
• Receiving Body: Recycled Water System (Title 22), North City Pure Water Facility, or returned to Sewer System (Point Loma Outfall)
• NPDES/Waste Discharge Permit: Regional Water Quality Control Board Order No. 97-03 / Addendum No. 1
• Year Commissioned: 1997 (Major Expansion 2024)

TARGET AUDIENCE

• Municipal consulting engineers evaluating water reuse and scalping plant configurations
• Wastewater treatment plant operators and water reuse managers
• Regulatory officials regarding Title 22 compliance and IPR/DPR projects
• Engineering firms pursuing advanced water purification projects

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1. INTRODUCTION

The North City Water Reclamation Plant (NCWRP) is a critical component of the City of San Diego’s aggressive strategy to secure a local, drought-resilient water supply. Originally commissioned in 1997 with a capacity of 30 million gallons per day (MGD), the facility operates as an advanced “scalping” plant, diverting flow from the northern municipal collection system to produce high-quality tertiary treated water.

Ideally situated across I-805 from the Miramar Marine Corps Air Station, the plant has historically provided non-potable irrigation and industrial water via the distinct “purple pipe” network. However, its significance has elevated dramatically as the primary feedstock provider for the Pure Water San Diego program. Following a recent expansion to 52 MGD, the NCWRP now anchors Phase 1 of the Pure Water program, which aims to provide nearly half of San Diego’s water supply locally by 2035. It stands as a model of modern water resource management, bridging the gap between conventional wastewater treatment and advanced potable reuse.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The NCWRP serves the northern periphery of the City of San Diego, a region characterized by a mix of high-density residential zones, commercial technology parks (Sorrento Valley), and institutional hubs like UC San Diego. The collection system spans approximately 49 square miles. Unlike terminal treatment plants, NCWRP intercepts flow from the primary trunk sewers; any flow not treated—or solids generated during treatment—is returned to the sewer system and conveyed south to the Point Loma Wastewater Treatment Plant (PLWTP) for final treatment and ocean discharge.

B. Operational Capacity

Historically operating at an average flow of 22-24 MGD, the plant’s design capacity was recently uprated to 52 MGD to accommodate the influent requirements of the adjacent North City Pure Water Facility (NCPWF). The plant is designed to handle peak wet weather flows, though as a scalping plant, it has the operational flexibility to bypass excess flow back to the main collection system during extreme hydraulic events, protecting the biological biomass.

C. Discharge & Compliance

The facility produces Title 22 (California Code of Regulations) compliant tertiary recycled water. The effluent has three potential destinations:

1. Distribution System: Sold to customers for irrigation, cooling towers, and industrial processing.

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2. Pure Water Facility: Feedwater for the Advanced Water Purification Facility (Ozone/BAC/MF/RO/UV).
3. Return to Sewer: Excess tertiary water not needed for demand is returned to the Rose Canyon Trunk Sewer, effectively diluting the sewage flowing to Point Loma and improving that facility’s influent quality.

3. TREATMENT PROCESS

The NCWRP utilizes a conventional activated sludge process followed by tertiary filtration and disinfection. The specific treatment train is designed to meet strict California Title 22 standards for unrestricted reuse.

A. PRELIMINARY TREATMENT

The headworks utilizes mechanical bar screens to remove large debris, plastics, and rags. Following screening, flow enters aerated grit chambers where inorganic solids (sand, gravel, coffee grounds) settle out. The grit is washed and dewatered before being hauled to a landfill. Odor control at the headworks is robust, utilizing chemical scrubbers (packed towers) to neutralize H₂S, essential due to the plant’s proximity to commercial zones.

B. PRIMARY TREATMENT

Wastewater flows into rectangular primary sedimentation tanks. These tanks utilize chain-and-flight mechanisms to scrape settled sludge to hoppers and skim floating grease/scum from the surface.
Key Specification: The primary effluent is targeted to reduce TSS and BOD by approximately 50-60% and 25-30% respectively, easing the load on the secondary system. Primary sludge is not processed on-site; it is pumped back into the sewer system for treatment at the Point Loma facility or the Metro Biosolids Center.

C. SECONDARY TREATMENT

The biological engine of the plant is an activated sludge process operating in plug-flow aeration basins.

• Aeration: The plant utilizes fine-bubble diffusers to maximize oxygen transfer efficiency. The expansion project added new aeration zones to handle the increased 52 MGD load.
• Selectors: Anoxic selector zones are utilized to control filamentous bacteria and promote the growth of settling-friendly floc, while also achieving partial denitrification.
• Clarification: Mixed liquor flows to secondary clarifiers where biological solids settle. Return Activated Sludge (RAS) is pumped back to the aeration basins, while Waste Activated Sludge (WAS) is thickened via dissolved air flotation (DAF) or returned directly to the sewer trunk line for downstream processing.

D. TERTIARY TREATMENT

To meet Title 22 standards, secondary effluent undergoes filtration to reduce turbidity to typically less than 2 NTU.

• Filtration Technology: Deep-bed anthracite coal filters. These gravity filters effectively trap remaining suspended solids.
• Demineralization (Partial): A portion of the flow historically passed through an Electrodialysis Reversal (EDR) unit to reduce salinity (Total Dissolved Solids) for specific irrigation customers, though the new Pure Water facility utilizes Full Advanced Treatment (FAT) including Reverse Osmosis.

E. DISINFECTION

The tertiary effluent enters chlorine contact basins (CCB). The plant uses sodium hypochlorite for disinfection. The serpentine channel design ensures sufficient contact time (modal contact time of >90 minutes) to deactivate pathogens, meeting the 2.2 MPN/100mL coliform standard required for unrestricted access irrigation.

F. SOLIDS HANDLING

Unique Engineering Feature: NCWRP acts as a liquid-stream-only facility regarding final disposal. It does not contain anaerobic digesters or dewatering centrifuges for final biosolids disposal.

• Primary sludge and thickened WAS are discharged into the Metro Biosolids Center (MBC) dedicated pipeline or returned to the sewer.
• The MBC, located adjacent to the Miramar Landfill, is a separate regional facility that processes solids from both NCWRP and the Point Loma WWTP.

G. PROCESS CONTROL

The facility is managed via a distributed control system (DCS/SCADA) integrated with the City’s specific Comnet system. Real-time monitoring of turbidity, chlorine residual, and flow is critical for regulatory reporting.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The site occupies approximately 75 acres. The architecture is notable for its extensive use of xeriscaping and modern industrial design that blends with the surrounding “Golden Triangle” business district. Key structures include the Operations Building, the new Pure Water pump station, and the massive tertiary filter gallery.

B. Energy Systems

The City of San Diego prioritizes energy independence.

• Solar: The site features a 245 kW rooftop photovoltaic system.
• Cogeneration Integration: While NCWRP consumes grid power, it is energetically linked to the nearby Metro Biosolids Center, which utilizes landfill gas from the Miramar Landfill and digester gas to generate up to 6.4 MW of power, offsetting the regional pumping costs.

C. Odor Control

Given the high-value commercial real estate surrounding the plant, odor control is a zero-tolerance operational parameter. The facility employs a multi-stage approach, including covering headworks and primary clarifiers, and utilizing high-capacity chemical scrubbers and activated carbon polishing units to treat foul air before release.

5. RECENT UPGRADES & MAJOR PROJECTS

North City Water Reclamation Plant Expansion (Pure Water Phase 1)

Project Value: ~$356 Million (Plant Expansion component)
Timeline: 2019 – 2024 (Construction Phase)
Status: Commissioning/Operational

To support the Pure Water San Diego program, which aims to produce 30 MGD of potable water, the NCWRP required a massive capacity increase from 30 MGD to 52 MGD to ensure sufficient feedwater for the purification process.

Project Scope & Technical Highlights:

• Influent Pump Station (IPS): Upgraded with higher capacity pumps and VFDs to handle increased hydraulic loading.
• Primary Treatment: Construction of new primary sedimentation tanks and chemically enhanced primary treatment (CEPT) capabilities.
• Secondary Process: Addition of new aeration basins and secondary clarifiers. Retrofitting of existing basins with higher efficiency diffusers.
• Tertiary Filtration: Expansion of the filter gallery with new anthracite media filters to handle the 52 MGD peak flow.
• Pure Water Feed: Construction of a dedicated secondary effluent pump station to deliver water to the North City Pure Water Facility located across the street.

Contractors: The project was executed under a Construction Manager at Risk (CMAR) delivery method, with Kiewit-Shea serving as a primary joint venture for major components of the North City expansions.

North City Pure Water Facility (NCPWF)

While physically a separate structure adjacent to NCWRP, this facility is operationally integrated. It takes the tertiary effluent from NCWRP and treats it via:

1. Ozonation
2. Biological Activated Carbon (BAC)
3. Membrane Filtration (MF)
4. Reverse Osmosis (RO)
5. Ultraviolet Light / Advanced Oxidation (UV/AOP)

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under requirements set by the San Diego Regional Water Quality Control Board.

• Title 22 Recycled Water: Must meet < 2 NTU turbidity (24-hour average) and Total Coliform < 2.2 MPN/100mL.
• NPDES: While primarily a reclamation permit, the interaction with the Point Loma NPDES permit is critical, as NCWRP reduces the BOD/TSS load sent to the ocean outfall.

B. Compliance History

NCWRP consistently maintains a high level of compliance. It has received multiple “Plant of the Year” awards from the California Water Environment Association (CWEA) and the WateReuse Association for operational excellence and safety.

C. Environmental Stewardship

By recycling 30+ MGD, the plant significantly reduces the volume of treated wastewater discharged into the Pacific Ocean, directly benefiting the marine environment of the Point Loma kelp beds. Furthermore, the recycled water offsets imported water from the Colorado River and Northern California, reducing the energy footprint associated with water transport.

7. CHALLENGES & FUTURE PLANNING

A. Brine Management

The new Pure Water facility generates a brine stream (RO concentrate). Managing this high-salinity stream requires careful hydraulic integration with the return-to-sewer line to ensure it does not disrupt the biological processes at the downstream Point Loma plant.

B. Diurnal Flow Management

As a scalping plant, NCWRP relies on the diurnal flow patterns of the collection system. Ensuring a constant 52 MGD flow to feed the Pure Water plant requires sophisticated flow equalization strategies and potentially harvesting flow from wider reaches of the collection system during low-flow nighttime hours.

C. Phase 2 Planning

With Phase 1 nearing full operation, planning is underway for Phase 2 (Central Area Project), which will connect NCWRP infrastructure with future facilities at the airport/Harbor Drive area, creating a completely interconnected regional reuse grid by 2035.

10. TECHNICAL SPECIFICATIONS SUMMARY

12. FAQ SECTION

Technical Questions

1. Does NCWRP have anaerobic digesters on site?
No. NCWRP is a scalping plant. Solids (primary sludge and waste activated sludge) are returned to the sewer system or pumped via dedicated pipeline to the Metro Biosolids Center (MBC) for thickening and digestion.

2. What is the relationship between NCWRP and the Pure Water Facility?
NCWRP acts as the provider. It treats raw wastewater to a tertiary level. This tertiary effluent is then pumped across the street to the North City Pure Water Facility (NCPWF) for advanced purification (Ozone/RO/UV) to become potable water.

3. What happens to the brine from the Pure Water process?
The RO concentrate (brine) from the Pure Water facility is directed back into the sewer collection system, where it flows south to the Point Loma Wastewater Treatment Plant for ocean discharge.

Public Interest Questions

4. Can I tour the facility?
Yes. The City of San Diego operates a very popular tour program for the “Pure Water Demonstration Facility” located at the site. This allows the public to taste the purified water and see the technology.

5. Does the plant smell?
Odor control is a top priority. The plant uses advanced chemical scrubbers and covers major process tanks to prevent odors from escaping, as it is located near high-end commercial and retail areas.