Attch. 04A CDO-R9-2025-0139.pdf

CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD

SAN DIEGO REGION

CEASE AND DESIST ORDER NO. R920250139

UNITED STATES SECTION OF THE

INTERNATIONAL BOUNDARY AND WATER COMMISSION

SOUTH BAY INTERNATIONAL WASTEWATER TREATMENT PLANT

DISCHARGE TO THE PACIFIC OCEAN THROUGH THE SOUTH BAY OCEAN OUTFALL

The California Regional Water Quality Control Board, San Diego Region (San Diego Water Board) finds the following:

BACKGROUND

1. The United States Section of the International Boundary and Water Commission (USIBWC) owns and operates a number of facilities that comprise a federallyowned treatment works. These consist of the South Bay International Wastewater Treatment Plant (SBIWTP); five canyon collectors located at Stewart’s Drain, Silva Drain, Canyon del Sol, Smuggler’s Gulch, and Goat Canyon; Hollister Street Pump Station; Goat Canyon Pump Station; Junction Box 1; Junction Box 2; the South Bay Land Outfall (SBLO); the South Bay Ocean Outfall (SBOO); and other associated infrastructure, such as the pipes and conveyances between the diversion structures, pump stations, and the wastewater treatment plant. USIBWC and City of San Diego jointly own the SBLO and SBOO.

2. The SBIWTP receives domestic and industrial wastewater from the City of Tijuana’s municipal collection system; dry weather flows captured by the five canyon collectors; and occasional dry weather transboundary flows collected by vacuum trucks from other locations.

3. USIBWC discharges secondarytreated wastewater from the SBIWTP to the Pacific Ocean first via the SBLO and then finally through the SBOO. The discharge is regulated by Order No. R920210001, as amended, National Pollutant Discharge Elimination System (NPDES) Permit No. CA0108928, Waste Discharge Requirements for the United States Section of the International Boundary and Water Commission, South Bay International Wastewater Treatment Plant, Discharge to the Pacific Ocean Through the South Bay Ocean Outfall (NPDES Permit). The NPDES Permit establishes waste discharge requirements for the discharge of secondarytreated wastewater from the SBIWTP, including a maximum permitted effluent flow limitation of 25 million gallons per day (MGD).1

1 All references to a MGD flow limitation is expressed as a monthly average.

4. The City of San Diego also discharges secondarytreated wastewater effluent from its South Bay Water Reclamation Plant (SBWRP) through the SBOO under a separate NPDES permit that contains waste discharge requirements specific to the SBWRP.

5. USIBWC contracts with Veolia Water North America to operate and maintain the SBIWTP and associated infrastructure. However, the NPDES Permit is issued solely to USIBWC. USIBWC is responsible for any discharges originating from the SBIWTP and for meeting requirements of the NPDES Permit and associated enforcement orders.

6. On May 12, 2021, the San Diego Water Board adopted Order No. R920210001, which prescribed waste discharge requirements for the facility. Since the San Diego Water Board had determined, based on effluent data, that the SBIWTP discharge threatened to violate effluent limitations in Order No. R920210001, the San Diego Water Board also issued a cease and desist order (CDO) the same day, Order No. R920210107 (2021 CDO). The 2021 CDO established a time schedule for USIBWC to complete necessary maintenance and repairs, and other deliverables to achieve compliance with effluent limitations in its NPDES Permit. The CDO was amended on December 8, 2021, as requested by USIBWC on October 14, 2021.

7. On March 8, 2023, the San Diego Water Board adopted Order No. R920230009, which amended Order No. R920210001 in accordance with the terms of a settlement agreement between the San Diego Water Board and USIBWC that resolved a lawsuit filed by USIBWC.

8. In August 2023, Tropical Storm Hilary brought record rainfall to San Diego County and Baja California. The storm exacerbated infrastructure and system vulnerabilities and resulted in damage at the SBIWTP. At the September 2023 San Diego Water Board meeting, the USIBWC Commissioner described investments USIBWC had made in rehabilitation at the SBIWTP, described poststorm conditions, and explained that USIBWC would need additional funding and time to complete necessary repairs and capital improvement projects to achieve compliance with effluent limitations in its NPDES Permit.

9. In December 2023, the San Diego Water Board adopted a time schedule order (TSO), Order No. R920230189. The TSO established a revised time schedule for USIBWC to complete necessary maintenance and repairs to achieve compliance with effluent limitations in the NPDES Permit by August 15, 2024.

10. After considerable prioritization of and investment in rehabilitation of the SBIWTP, USIBWC attained compliance with all effluent limitations in its NPDES Permit in November 2024. Since that time, USIBWC has reported two effluent violations: 1) settleable solids instantaneous maximum of 5 milliliters per liter (ml/L) exceeded effluent limitation of 3 ml/L and 2) 30day average total suspended solids (TSS) percent removal of 84.09% did not meet minimum required removal of 85%.

11. The NPDES Permit expires on June 30, 2026. The terms and conditions of an expired NPDES Permit continue in force until the effective date of a new permit if USIBWC submits a complete Report of Waste Discharge (permit application) to the San Diego Water Board at least 180 days prior to the NPDES Permit expiration date and the San Diego Water Board is not able to reissue the NPDES Permit prior to the expiration date.

12. The SBIWTP is part of a regional wastewater collection, conveyance, and treatment system that is hydraulically interconnected but primarily maintained, operated, upgraded, and funded in a disjointed manner by various agencies in the United States and Mexico due to the crossborder and crosswatershed configuration. It is the San Diego Water Board’s understanding that wastewater in this region primarily reaches the ocean via three significant discharge points:

· Punta Bandera. A combination of treated, partially treated, and untreated wastewaters are discharged to a coastal shoreline discharge point in Mexico, approximately five miles south of the U.S.Mexico border. The treatment and discharges are managed by Baja California’s water utility for the City of Tijuana, Comisión Estatal de Servicios Públicos de Tijuana (CESPT). Government agencies in the U.S. have no authority to regulate discharges at Punta Bandera.

· Tijuana River Mouth. The magnitude of transboundary flows through the main channel and tributaries in the Tijuana River Valley varies and cannot be directly controlled or predicted by government agencies in the U.S. Dry weather transboundary tributary flows that do not exceed canyon collector capacities must be captured by USIBWC and conveyed to the SBIWTP for treatment. However, USIBWC has no infrastructure to capture or treat transboundary flows in the main channel of the Tijuana River. The flows contain untreated sewage that cause significant water quality impacts in the river, estuary, and coastal waters, where they ultimately discharge. Associated air quality impacts also significantly affect residents in and around the Tijuana River Valley.

· SBIWTP via the SBOO. Treated wastewater from the SBIWTP is discharged over three miles off the coastal shoreline via the SBOO.2 Government agencies in the U.S. possess the authority to regulate the SBIWTP discharge in accordance with U.S. federal and State of California (State) laws and regulations. As described above, the effluent discharged via the SBIWTP is regulated by the NPDES Permit.

There have been no indications that the SBOO plume reaches the coastal shoreline in areas where recreation is likely to take place.

13. Limitations within Tijuana’s collection and conveyance system result in discharges of wastewater to the concretelined main channel of the Tijuana River in Tijuana. The Mexican Section of the International Boundary and Water Commission (MxIBWC) and CESPT own and operate infrastructure, including pump stations, in Tijuana to divert dry weather flows in the Tijuana River to Punta Bandera. However, the pump stations have limitations. This frequently results in polluted transboundary flows through the main channel that reach the Tijuana River Valley, Tijuana River Estuary, and the Pacific

2 The SBOO is approximately 3.52 miles (3.06 nautical miles) long, but the terminus lies within State of California (State) waters because it is angled towards the U.S.Mexico border.

Ocean shoreline adjacent to the river mouth. Consequently, designated beneficial uses of the river, estuary, and coastal waters, including contact and noncontact water recreation (REC1 and REC2), are significantly impaired. The lower Tijuana River, the Tijuana River Estuary, and several downstream Pacific Ocean shorelines are listed as impaired on the Clean Water Act (CWA) section 303(d) List of Water Quality Limited Segments (303(d) List).

14. For many years, the U.S. beach shoreline from the U.S.Mexico border (Border Field State Park) to Imperial Beach has been closed on an ongoing basis, and since December 8, 2021, it has been closed almost continuously.

15. Transboundary flow water quality monitoring results indicate the presence of untreated sewage. Many bacteria, viruses, and other pathogenic microorganisms commonly present in sewage lead to severe, even lifethreatening, infections. This includes bacterial infections such as cholera, dysentery, salmonella, shigella; viral infections such as hepatitis A and E and those caused by the rotavirus and norovirus; and infections from parasites such as giardia and cryptosporidium.

16. Transboundary flows occur daily through the main channel of the Tijuana River. On July 25, 2025, USIBWC reported that its river gage had measured approximately 47.3 billion gallons of transboundary flows through the main channel since October 2023.

17. The United StatesMexicoCanada Agreement (USMCA) Implementation Act, signed in January 2020, appropriated funds to the U.S. Environmental Protection Agency (USEPA) for implementation of wastewater infrastructure projects at the U.S.Mexico border and authorized USEPA, in coordination with eligible public entities, to plan, design, and construct treatment projects in the Tijuana River area. USEPA and USIBWC refer to these projects collectively as the USMCA Mitigation of Contaminated Transboundary Flows Project. One of the projects chosen to reduce the occurrence of Tijuana River transboundary flows and reduce discharges of untreated wastewater at Punta Bandera is an expansion of treatment capacity at the SBIWTP.

18. In July 2022, the U.S. and Mexican governments entered into an international agreement, IBWC Minute 328, Sanitation Infrastructure Projects in San Diego, California – Tijuana, Baja California. Minute 328 outlines respective responsibilities for border projects, including expansion of treatment capacity at the SBIWTP. Minute 328 aims to provide benefits on both sides of the border, including reductions in untreated wastewater in the Tijuana River Valley and Pacific Ocean.

19. In November 2022, USEPA and USIBWC released their Final Programmatic Environmental Impact Statement (PEIS) on the USMCA Mitigation of Contaminated Transboundary Flows Project. In June 2023, USEPA and USIBWC signed a joint Record of Decision (ROD) for the PEIS. One of the core projects of the ROD, Project A, is an expansion of the SBIWTP. USIBWC plans to expand the SBIWTP to treat up to 50 MGD (full secondary treatment) and as funds become available, further expand the treatment capacity. While Minute 328 and the ROD have different roles, several of the projects specified in the ROD are the same as, or similar to, those included in Minute 328.

20. In September 2024, USEPA formally transferred USMCA funds to USIBWC for SBIWTP rehabilitation and expansion. In a July 24, 2025, press release, USIBWC stated that it expects to complete the expansion to 50 MGD by 2027.

21. In December 2024, the San Diego Water Board adopted Resolution No. R920240155, approving the Lower Tijuana River Indicator Bacteria and Trash Advance Restoration Plan (ARP). The ARP is centered on the San Diego Water Board’s expectation that USIBWC will work with USEPA to implement the projects identified in the ROD, including SBIWTP expansion, to significantly reduce transboundary flow pollution.

22. On May 20, 2025, USIBWC and USEPA announced a planned 10MGD expansion of the SBIWTP treatment capacity from 25 MGD to 35 MGD and projected completion and startup within 100 days, by August 28, 2025. USIBWC proposes to treat up to 35 MGD of influent wastewater through advanced primary treatment followed by 25 MGD of secondary treatment using existing activated sludge processes. The advanced primary treatment will consist of chemicallyenhanced primary treatment (CEPT), using coagulants to increase solids removal. Secondary treatment will consist of existing activated sludge processes. USIBWC proposes to blend the bypassed 10 MGD advanced primary effluent with the 25 MGD secondary effluent prior to discharge to the Pacific Ocean via the SBLO and SBOO.

23. On June 17, 2025, the San Diego Water Board sent a letter to USIBWC describing its understanding of USIBWC’s proposal and outlining key steps that would be required for an NPDES Permit amendment authorizing the expansion to be considered.

24. On July 16, 2025, USIBWC sent a letter to the San Diego Water Board requesting an amendment to their NPDES Permit to treat up to 10 MGD of increased flow. USIBWC’s letter explained that accepting more wastewater from Tijuana’s municipal system will eliminate dry weather transboundary flows in the Tijuana River. USIBWC again reiterated that its target date to receive the 10 MGD increase is by August 28, 2025.

25. The San Diego Water Board has determined that USIBWC’s target date to treat up to 10 MGD of increased flow by August 28, 2025, does not provide sufficient time for the Board to amend USIBWC’s NPDES Permit. However, the San Diego Water Board will consider amending the NPDES Permit prior to its expiration date to account for the expansion from 25 MGD to 35 MGD.

26. The San Diego Water Board finds that USIBWC’s proposed incremental expansion from 25 MGD to 35 MGD and inability to treat more than 25 MGD to secondary treatment standards, requiring a partial bypass of secondary treatment, will violate or threatens to violate the NPDES Permit and other requirements of the San Diego Water Board for the facility:

· USIBWC’s proposed increase will violate the average monthly effluent limitation for flow of 25 MGD.

· Modeling conducted by USIBWC to predict TSS and fiveday carbonaceous biochemical oxygen demand (CBOD5) concentrations in the CEPT effluent and the blended effluent indicated that USIBWC will violate or threaten to violate TSS and CBOD5 effluent limitations.

· USIBWC’s proposal includes the intentional diversion (bypass) of up to 10 MGD of CEPT effluent from secondary treatment. Section 1.7.2 of the Standard Provisions (Attachment D) of the NPDES Permit only allows a bypass to occur if: 1) it will not cause exceedances of effluent limitations and is for essential maintenance to ensure efficient operation, or 2) conditions in section 1.7.3 of the Standard Provisions (Attachment D) of the NPDES Permit are met. USIBWC’s proposal does not meet these conditions. Therefore, USIBWC’s proposed increase will violate provisions prohibiting bypass.

27. On August 4, 2025, USIBWC submitted PLUMES2.0 plume modeling results to the San Diego Water Board. The purpose of the modeling was to determine if the dilution factor of 94.6 in the NPDES Permit will still be applicable when up to 10 MGD of additional flow is discharged through the SBOO. USIBWC plans to open 64 additional ports on the southern leg of the SBOO diffuser for a total of 136 open ports prior to initiating the incremental expansion. The modeling results indicate that under these conditions, the additional discharge will not reduce dilution and that the 94.6 dilution factor will still be applicable.

28. On August 4, 2025, USIBWC submitted a report to the San Diego Water Board to certify that the proposed changes to SBIWTP treatment will not compromise the ability for the SBIWTP and SBOO to operate adequately under assumptions and planned circumstances of the 10MGD incremental expansion with blended effluent. The certification report was prepared and signed by a State licensed civil engineer.

29. USIBWC has expressed its commitment to ensuring that all essential operational and maintenance demands, including critical SBIWTP preventative maintenance and rehabilitation, will be met. Prior to startup of the incremental expansion, USIBWC will finalize a modified agreement with its contracted SBIWTP operator, Veolia Water North America, to include all required modifications to operations and maintenance for the increased flow and partial bypass of secondary treatment.

REGULATORY AUTHORITY AND PURPOSE

30. Water Code section 13301 authorizes the San Diego Water Board to issue a CDO when it finds that a waste discharge is taking place, or threatening to take place, in violation of requirements or discharge prohibitions prescribed by the San Diego Water Board. The San Diego Water Board may, in a CDO, direct that those persons not complying with the requirements or discharge prohibitions to comply forthwith, comply in accordance with a time schedule set by the San Diego Water Board, or, in the event of a threatened violation, take appropriate remedial or preventive action. CDOs may be issued directly by the San Diego Water Board, after notice and hearing.

31. On August 4, 2025, USIBWC submitted modeling results that predict concentrations of pollutants in the blended effluent. The model, which ties together biological, chemical, and physical processes, concentrates on conventionally regulated wastewater parameters, such as CBOD5, TSS, and ammonia. The results indicate that USIBWC will be out of compliance with CBOD5 and TSS effluent limitations in the NPDES Permit.

The expected overall increase in solids in effluent will likely lead to noncompliance with settleable solids and turbidity as well. The model does not estimate all parameters with effluent limitations in the NPDES Permit. For those parameters with effluent limitations in the NPDES Permit not estimated by the model, the San Diego Water Board conservatively estimated concentrations in the blended effluent based on mass balance calculations using historical influent data and secondary effluent data. These estimates indicate that USIBWC should continue to achieve compliance with the respective concentrationbased NPDES Permit effluent limitations once the planned modified treatment plant processes and modified SBOO diffuser operations are in effect. With respect to concentrationbased effluent limitations, USIBWC should only be out of compliance with those for CBOD5, TSS, settleable solids, and turbidity. Although USIBWC is expected to achieve compliance with concentrationbased effluent limitations for the remaining parameters, that assumption cannot be confirmed since currently there are no data that are fully representative of the blended effluent.

Therefore, at this time, it is not appropriate to establish interim concentrationbased effluent limitations for those remaining parameters; it is appropriate to hold USIBWC to the final concentrationbased effluent limitations in the NPDES Permit for those parameters. Due to 1) the expected concentrationbased exceedances for CBOD5, TSS, settleable solids, and turbidity, and/or 2) the planned exceedance of the 25 MGD flow rate limitation, the San Diego Water Board expects that USIBWC may not achieve compliance with NPDES Permit Mass Emission Rate (MER) (massbased) limitations for any given parameter with MER limitations.

32. As a result of the increased influent flow rate beyond the design capacity of the secondary treatment process and based on the analyses using historical monitoring data and predictive modeling results for certain parameters, the San Diego Water Board finds that a discharge of waste is taking place or threatening to take place in violation of requirements or discharge prohibitions prescribed by the San Diego Water Board.

USIBWC will not be able to comply with the final concentrationbased effluent limitations in the NPDES Permit for CBOD5, TSS, settleable solids, and turbidity until USIBWC’s longerterm facility modifications, which will phase out bypass/blending, are complete.

USIBWC may also be out of compliance with NPDES Permit MER limitations.

Additionally, USIBWC does not have control over the quality of SBIWTP influent (e.g., no industrial pretreatment program), nor can it independently control flow rate into the SBIWTP, both of which can pose additional threats to achieving compliance. This Order requires USIBWC to take appropriate remedial and preventative action and to comply in accordance with the time schedule set forth below. This Order is in the public interest given the significant environmental benefits associated with capturing and treating additional dry weather transboundary flows.

33. Water Code section 13383 authorizes the San Diego Water Board to “establish monitoring, inspection, entry, reporting, and recordkeeping requirements . . . for any person who discharges, or proposes to discharge, to navigable waters, any person who introduces pollutants into a publicly owned treatment works, any person who owns or operates, or proposes to own or operate, a publicly owned treatment works or other treatment works treating domestic sewage, or any person who uses or disposes, or proposes to use or dispose, of sewage sludge. . . .” The San Diego Water Board may also require any such persons “to establish and maintain monitoring equipment or methods, including, where appropriate, biological monitoring methods, sample effluent as prescribed, and provide other information as may be reasonably required.”

CEQA, PUBLIC NOTICE, AND PETITION PROCESS

34. This Order concerns an existing facility and does not significantly alter the status with respect to the facility. The issuance of this Order is an enforcement action by a regulatory agency and is being taken for the protection of the environment. Therefore, issuance of this Order is exempt from the provisions of the California Environmental Quality Act (CEQA) (Public Resources Code section 21100 et seq.) in accordance with sections 15061(b)(3), 15301, 15306, 15307, 15308, and 15321(a)(2) of Title 14 of the California Code of Regulations.

35. The San Diego Water Board has notified USIBWC and interested agencies and persons of its intent to issue this Order concerning compliance with the NPDES Permit. The San Diego Water Board accepted written comments, and heard and considered all comments and evidence pertaining to this matter in a public hearing.

36. Any person aggrieved by this action of the San Diego Water Board may petition the State Water Resources Control Board (State Water Board) to review the action in accordance with California Water Code section 13320 and California Code of Regulations, title 23, sections 2050 and following. The State Water Board must receive the petition by 5:00 p.m., 30 days after the date of this Order, except that if the thirtieth day following the date of this Order falls on a Saturday, Sunday, or state holiday, the petition must be received by the State Water Board by 5:00 p.m. on the next business day. Copies of the law and regulations applicable to filing petitions may be found on the Internet at http://www.waterboards.ca.gov/public_notices/petitions/water_quality or will be provided upon request.

THEREFORE, IT IS HEREBY ORDERED that, pursuant to Water Code sections 13301 and 13383, USIBWC shall comply with the following requirements to address discharges of waste in violation or threatened violation of its NPDES Permit, Order No. R920210001, as amended:

1. USIBWC shall comply immediately with the effluent limitations prescribed in its NPDES Permit, except for parameters specified in Table 1, below.

2. USIBWC shall comply with interim effluent limitations for parameters specified in Table 1, below, from August 28, 2025, to June 30, 2026, for blended effluent.

http://www.waterboards.ca.gov/public_notices/petitions/water_quality

Table 1. Interim Effluent Limitations3

Parameter Units Si x M on th

M ed ia n

Av er ag e M on th ly

Av er ag e W ee kl y

M ax im um D ai ly

In st an ta ne ou s

M ax im um

Flow MGD 35

CBOD5

milligram per liter (mg/L)

110 128

CBOD5

pounds per day (lb/day)

32,130 37,387

CBOD5 % removal ≥73%

TSS mg/L 62 81

TSS lb/day 18,109 23,659

TSS % removal ≥82%

Settleable solids milliliter per liter (ml/L)

2 3 5

Turbidity nephelometric turbidity units

(NTU)

135 180

Oil and Grease lb/day 7,298 11,676 21,893

Total Residual Chlorine lb/day 55.4 221 1,670

Copper, Total Recoverable lb/day 28.4 280 783

Mercury, Total Recoverable lb/day 1.1 4.42 11.1

3 CBOD5 and TSS interim effluent limitations are based on mass balance calculations using USIBWC effluent modeling results.

Parameter Units Si x M on th

M ed ia n

Av er ag e M on th ly

Av er ag e W ee kl y

M ax im um D ai ly

In st an ta ne ou s

M ax im um

Benzidine lb/day 0.00193

Chlordane lb/day 0.000641

DDT lb/day 0.00475

Heptachlor Epoxide lb/day 0.000559

Hexachlorobenzene lb/day 0.00587

PCBs lb/day 0.000531

TCDD Equivalents lb/day 0.000000109

Toxaphene lb/day 0.00587

Table note: The acronyms DDT, TCDD, and PCBs refer to dichlorodiphenyltrichloroethane, tetrachlorodibenzodioxin, and polychlorinated biphenyls, respectively.

3. USIBWC shall comply with the following remedial actions and preventative actions according to the time schedule in Table 2 of this Order.

Table 2. Time Schedule for Remedial Actions and Preventative Actions

Prescribed Action Deadline

1. Modify SBOO diffuser configuration such that the dilution factor remains at or above

94.6. Submit certification statement

confirming that the modification is complete.

Modify by August 28, 2025, or at least 10 days prior to initiating incremental expansion. Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

2. Update and implement protocols for coordination with agencies in Mexico to manage SBIWTP influent such that the monthly average effluent flow rate does not exceed 35 MGD. Submit certification statement confirming that the update is complete.

Update by August 28, 2025, or at least 10 days prior to initiating incremental expansion. Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

3. Update and implement protocols for operation of new junction box gates, Update protocols and submit certification statement by December 31, 2025.

Prescribed Action Deadline troubleshooting (e.g., gates jammed, debris blocking gates), and connections to Supervisory Control and Data Acquisition (SCADA) system, and alarms, such that SBIWTP influent is adequately managed and the monthly average effluent flow rate does not exceed 35 MGD. Submit certification statement confirming that the update is complete.

4. Design and operate the SBIWTP CEPT system such that ferric chloride and polymer dosing rates, rapid mixing, and effluent blending ratios are adequate to achieve interim effluent limitations. Submit certification statement confirming that the design is complete.

Finalize design by August 28, 2025, or at least 10 days prior to initiating incremental expansion. Implement on an ongoing basis. Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

5. Reinstate and operate skimming system on the SBIWTP primary effluent channel.

Monitor for and remove floatable debris at the SBIWTP headworks, primary sedimentation tanks, primary effluent channel, activated sludge tanks, and secondary settling tanks such that excess debris does not clog or otherwise create detrimental effects to the SBIWTP, SBLO, or SBOO. Submit certification statement confirming that the system is reinstated.

Reinstate by August 28, 2025, or at least 10 days prior to initiating incremental expansion. Monitor for and remove debris on an ongoing basis. Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

6. Install and operate additional equipment to thicken and dewater SBIWTP waste activated sludge such that sludge removal is increased to achieve interim effluent limitations and increased solids production is adequately managed. Submit certification statement confirming that the installation is complete.

Install by August 28, 2025, or at least 10 days prior to initiating incremental expansion. Operate on an ongoing basis.

Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

7. Identify all needs for changes in operation and maintenance (O&M) and provide guidance to the contracted operator to meet new O&M needs. This includes, but is not limited to, additional operators to run new treatment plant systems/equipment, temporary equipment O&M manuals, flow set points, chemical dosing, control

Identify needs and provide guidance by August 28, 2025, or at least 10 days prior to initiating incremental expansion.

Implement on an ongoing basis. Submit certification statement by September 15, 2025, or within 10 days after initiating incremental expansion.

Prescribed Action Deadline descriptions, and wiring diagrams. Ensure that new expectations and resources are reasonable for the contracted operator to meet comprehensive O&M demands, including ongoing preventative maintenance and critical rehabilitation needs. O&M must be adequate to protect the SBIWTP, SBLO, SBOO, and receiving waters to the highest extent practicable, including achieving interim effluent limitations. Submit certification statement confirming that the needs are identified and guidance has been provided.

8. Develop and implement standard operating procedures (SOPs) for SBIWTP headworks (i.e., channels, coarse screens, mechanical raking system, influent monitoring system, grit system), CEPT, skimmings system on the primary effluent channel, expanded solids handling, primary effluent bypass, and effluent blending. SOPs and their implementation must be adequate to protect the SBIWTP, SBOO, and receiving waters to the highest extent practicable, including achieving interim effluent limitations. Submit certification statement confirming that the SOPs have been developed.

Develop SOPs and submit certification statement by December 31, 2025.

4. Prior to initiating incremental expansion, USIBWC shall submit the final modified agreement between USIBWC and its contracted SBIWTP operator, Veolia Water North America, describing operations and maintenance for the increased flow and partial bypass of secondary treatment.

5. By March 1, 2026, USIBWC shall submit a technical report prepared and signed by a Statelicensed civil engineer to verify assumptions made for design, operation, maintenance, and contingency plans prior to initiating the incremental expansion and to assess performance of the incremental expansion of treatment and discharge. The technical report will verify the pre startup assumptions USIBWC made for the proposed incremental expansion in its August 4, 2025 certification report, which informed the development of this Order. The San Diego Water Board may use the post startup technical report to support an amendment to this Order and/or the NPDES Permit.

6. USIBWC shall upload document submittals required by this Order using the State Water Resources Control Board’s California Integrated Water Quality System (CIWQS) program website at https://www.waterboards.ca.gov/water_issues/programs/ciwqs/.

Submittals must be signed and certified as described in section 5 of the Standard Provisions (Attachment D) of the NPDES Permit.

7. All document submittals provided pursuant to this Order shall be signed by a person described in Standard Provisions – Reporting 5.2.2 of the NPDES Permit or by a duly authorized representative of that person. Each submittal shall include the following certification:

I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system or those persons directly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for submitting false information, including the possibility of fine and imprisonment for knowing violations.

8. If USIBWC fails to comply with any provision of this Order, the San Diego Water Board may take any further action authorized by law. The San Diego Water Board may also refer any violations to the Attorney General for judicial enforcement, including injunctive and civil monetary remedies.

9. No term or condition of the NPDES Permit is superseded or stayed by this Order.

10. The San Diego Water Board may reopen this Order at its discretion or at the request of USIBWC or interested persons, if warranted. Lack of progress towards compliance with this Order may be cause for the San Diego Water Board to modify the terms and conditions of this Order.

11. This Order is effective and final upon issuance by the San Diego Water Board.

I, David W. Gibson, do hereby certify the foregoing is a full, true, and correct copy of an order adopted by the California Regional Water Quality Control Board, San Diego Region on August 27, 2025.

David W. Gibson Executive Officer