The new Region 4 Commercial, Industrial, and Institutional (CII) Stormwater Permit creates stormwater requirements for certain privately owned CII properties within the Dominguez Channel/Los Angeles and Long Beach Inner Harbor Watershed and the Los Cerritos Channel/Alamitos Bay Watershed. Coverage depends on watershed location, property characteristics, acreage, and existing stormwater permit status-not simply a Los Angeles County address.
SoCal Stormwater Solutions can help property owners and operators evaluate potential coverage and navigate the compliance process, including site assessment, SWPPP and enrollment support, sampling and monitoring, compliance-option evaluation, and ongoing reporting.
Not every commercial, industrial, or institutional property in Los Angeles County is covered. The first question is whether the site is located within one of the two watershed areas regulated by the permit. From there, facility type, ownership, acreage, existing NPDES coverage, and parcel configuration must be evaluated.
Is the property within the Dominguez Channel/Los Angeles and Long Beach Inner Harbor Watershed or the Los Cerritos Channel/Alamitos Bay Watershed?
Does the property meet the permit definition of a privately owned commercial, industrial, or institutional site? Residential facilities are excluded.
IGP coverage, a No Exposure Certification (NEC), a Notice of Non-Applicability (NONA), or partial NPDES coverage does not automatically end the CII applicability review.
The review may need to account for contiguous parcels, campus configurations, and portions of a facility that are or are not already covered by another applicable stormwater permit.
The relevant property information is reviewed together to determine the appropriate next step.
If you are unsure whether the Region 4 CII Stormwater Permit applies to your property, an applicability screening provides a practical starting point before moving into a broader compliance engagement. SoCal Stormwater Solutions can review the factors that determine potential CII coverage, including:
The purpose is to identify likely applicability and the appropriate next compliance step based on the property’s circumstances.
The CII Permit establishes different coverage provisions depending on property characteristics and existing stormwater permit status.
Privately owned CII sites within the covered watershed areas that are not covered by another NPDES stormwater permit may require CII coverage when they have 5 or more acres of impervious surface.
Certain CII sites already covered by another NPDES stormwater permit may require CII coverage when they have 5 or more acres of total area, including the specific circumstances addressed below.
Facilities operating under an Industrial General Permit NEC may need CII coverage for the acreage covered by the NEC when the CII Permit criteria are met.
Facilities with an Industrial General Permit NONA may need CII coverage for acreage not covered by the NONA, subject to the CII Permit’s applicability criteria.
Where another NPDES stormwater permit covers only part of a facility, the remaining portion may require CII coverage when the applicable criteria are met.
Parcel configuration can affect the analysis. The CII Permit addresses privately owned parcels or contiguous parcels and provides for certain multi-parcel campus arrangements.
Important exclusion: A facility with an individual NPDES permit containing requirements at least as stringent as the CII Permit is not required to obtain separate coverage under this General Permit. Because these rules depend on both site characteristics and existing coverage, acreage alone should not be used to make a final applicability determination.
The CII Permit takes effect on October 31, 2026. Existing and new dischargers follow different enrollment schedules.
The deadlines correspond to 12 months, 18 months, and three and one-half years after the permit’s effective date.
New dischargers must submit the required NOI, SWPPP, initial sampling laboratory results, and Compliance Option Documents at least 45 days before commencement of the authorized discharge.
Starting the applicability review early can provide time to evaluate the property, prepare required documents, plan initial sampling, and assess the appropriate compliance option before the applicable deadline.
Existing dischargers seeking coverage must submit:
Obtaining and maintaining coverage involves more than filing an NOI. The permit establishes pollution-prevention, monitoring, documentation, and reporting requirements, with additional requirements depending on the selected compliance option.
Permit Registration Documents are submitted through the Stormwater Multiple Application and Report Tracking System (SMARTS). Required documents include the NOI, site-specific SWPPP, initial sampling laboratory results, and applicable Compliance Option Documents according to the permit schedule.SoCal Stormwater Solutions can provide SMARTS and permitting support to help organize and prepare applicable enrollment and reporting information.
Covered facilities must develop and implement a site-specific Stormwater Pollution Prevention Plan. Among other requirements, the SWPPP addresses facility information, the Stormwater Pollution Prevention Team, site mapping, potential pollutant sources, and minimum Best Management Practices (BMPs).SoCal Stormwater Solutions provides PRD and SWPPP preparation support for stormwater compliance programs.
The site-specific compliance process includes identifying drainage conditions, potential pollutant sources, relevant activities, and BMPs. Accurate site information also supports later monitoring and compliance-option planning.
The permit establishes minimum BMP requirements for covered facilities. BMP implementation, evaluation, maintenance, and corrective actions become part of the facility’s ongoing compliance record.
Initial sampling is required regardless of which of the three compliance options is selected. The permit requires representative sampling and analysis to provide information for the Los Angeles Water Board’s reasonable-potential evaluation.Initial sampling should not be confused with the recurring direct-compliance monitoring required under Compliance Option 3.
Covered facilities must maintain the applicable visual-observation, BMP, training, monitoring, and other records required by the permit and their selected compliance option.
The CII Permit requires dischargers to select one of three pathways for complying with applicable water quality-based effluent limitations. The appropriate pathway depends on site conditions, watershed/project availability, infrastructure, operational considerations, and monitoring requirements.
Option 1 involves entering into a legally binding agreement with the applicable local Watershed Management Group or its Fiduciary Agent to fund or partially fund eligible regional watershed project(s).
Participation depends on the facility being within the area modeled by the reasonable assurance analysis supporting the applicable Watershed Management Program and on the relevant project context. Option 1 therefore should not be assumed to be available to every covered facility.
Watershed Management Group eligibility, project availability, agreement requirements, funding obligations, and ongoing reporting responsibilities.
Option 2 requires facility-specific stormwater controls with effective capacity to capture and use, infiltrate, divert to the sanitary sewer, and/or evapotranspire applicable flows and the runoff volume produced up to and during an 85th-percentile 24-hour storm event.
This pathway can involve engineering, construction or implementation, operation, maintenance, testing, and monitoring of onsite stormwater controls. Applicable hydrologic analyses, hydraulic calculations, and design-standard operating parameters must be certified by a California-licensed civil engineer in accordance with the permit requirements.
A facility choosing Option 2 cannot change compliance options for two years unless the Executive Officer approves the change.
Under Option 3, facility discharges must meet the applicable water quality-based effluent limitations, with monitoring and reporting used to demonstrate direct compliance.
The monitoring framework includes sampling two Qualifying Storm Events (QSEs) during July 1–December 31 and two QSEs during January 1–June 30, with samples collected from each drainage area at all discharge locations as required by the permit.
Because the three pathways carry different technical, operational, infrastructure, monitoring, and documentation considerations, compliance-option selection should be based on facility-specific evaluation rather than a one-size-fits-all recommendation.
CII permit compliance can involve several stages. SoCal Stormwater Solutions can support the process from the initial applicability question through recurring compliance activities.
Review watershed location, acreage, parcel configuration, existing permit status, and other relevant coverage factors.
Evaluate site conditions relevant to stormwater management, drainage, pollutant sources, existing controls, and subsequent compliance planning.
Support preparation of the site-specific SWPPP and applicable enrollment information for submission through SMARTS.
Evaluate the requirements and site considerations associated with Options 1, 2, and 3 to support an informed compliance pathway.
Support applicable inspections, monitoring, documentation, reporting, and updates as the facility implements its stormwater compliance program.
The exact scope of support depends on the facility, selected compliance option, and applicable permit requirements.
Existing stormwater permit documentation does not necessarily resolve CII applicability. The new permit expressly addresses certain facilities that already have other NPDES stormwater coverage.
Existing Industrial General Permit coverage does not automatically resolve whether the CII Permit also applies. Facilities with IGP-related coverage should review the acreage and portions of the property covered by their existing permit status against the CII Permit’s separate applicability provisions.
For qualifying facilities with an NEC under the Industrial General Permit, the CII Permit states that coverage must be obtained for the acreage covered by the NEC when the CII Permit’s applicability requirements are met.
For facilities with an IGP NONA, the CII Permit addresses coverage for acreage not covered by the NONA when the CII criteria apply.
Where only part of the property is covered by another NPDES stormwater permit, the remaining portion requires separate evaluation under the CII Permit.
Contiguous parcels and campus arrangements can require additional review of ownership, operation, drainage, acreage, and existing coverage boundaries.
If your facility already has an Industrial SWPPP, NEC, NONA, or other stormwater permit status, the practical first step is to determine what acreage is already covered and what acreage, if any, remains subject to CII requirements.
The Region 4 CII Permit is new, but many of the tasks involved in implementing it draw on established California stormwater compliance disciplines.
SoCal Stormwater Solutions provides practical support across:
Support for site-specific stormwater planning and permit-related documentation based on applicable requirements.
Assistance organizing and preparing stormwater permit and reporting information for SMARTS workflows.
Field-oriented support for stormwater inspections, sampling, monitoring, and related documentation.
Stormwater requirements vary by facility. SoCal Stormwater Solutions focuses on site-specific conditions, applicable permit requirements, and practical next steps rather than a one-size-fits-all compliance approach.
For the new CII Permit, that experience can support the progression from applicability screening through enrollment, monitoring, reporting, and ongoing compliance.
Order R4-2026-0226 / NPDES Permit CAS004005 is a Los Angeles Regional Water Quality Control Board General NPDES Permit regulating stormwater and authorized non-stormwater discharges from certain privately owned commercial, industrial, and institutional sites in two specified watershed areas. It takes effect October 31, 2026.
No. The permit applies to qualifying CII sites within the Dominguez Channel/Los Angeles and Long Beach Inner Harbor Watershed and the Los Cerritos Channel/Alamitos Bay Watershed. A city or Los Angeles County address alone does not establish coverage.
No. There are different acreage tests. CII sites not covered by another NPDES stormwater permit are evaluated using 5 or more acres of impervious surface. Certain CII sites already covered by another NPDES stormwater permit are subject to provisions based on 5 or more acres of total area. Other applicability conditions also need to be considered.
Not necessarily. The CII Permit specifically addresses NEC acreage, acreage not covered by a NONA, and portions of facilities not covered by another NPDES stormwater permit. Existing status should therefore be reviewed as part of the CII applicability analysis.
Existing dischargers seeking coverage must submit a complete NOI and site-specific SWPPP within 12 months of the permit’s October 31, 2026 effective date—by October 31, 2027. Initial sampling results and Compliance Option Documents have later deadlines.
A new discharger must submit the NOI, SWPPP, required initial sampling laboratory results, and applicable Compliance Option Documents at least 45 days before commencement of the authorized discharge.
Yes. The permit requires initial sampling and analysis regardless of the compliance option selected. This initial characterization requirement is separate from the recurring monitoring associated with specific compliance options.
Yes. A site-specific SWPPP meeting the permit requirements forms part of the Permit Registration Documents.
In simplified terms, Option 1 uses an eligible Watershed Management Group agreement to support regional project(s); Option 2 uses facility-specific stormwater controls meeting the permit’s design requirements; and Option 3 uses monitoring and reporting to demonstrate direct compliance with applicable water quality-based effluent limitations. Eligibility, implementation requirements, and ongoing obligations differ among the options.
The permit requires an annual report through SMARTS for each July 1–June 30 reporting year by the following December 15, regardless of the selected compliance option. Additional monitoring and reporting deadlines apply depending on the option.
The screening considers factors such as watershed location, facility type, property and parcel configuration, applicable acreage, and existing NPDES/IGP, NEC, NONA, or partial coverage to help identify likely CII applicability and the appropriate next step.
The first step does not need to be a full compliance engagement. Start by determining whether the Region 4 CII Stormwater Permit is likely to apply to your facility and what the next compliance action should be. Provide basic property and existing-permit information so SoCal Stormwater Solutions can begin the screening process.
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Applicability screening provides technical compliance support based on available property and permit information. It does not guarantee a particular regulatory determination or compliance outcome.
For facilities that need additional stormwater support, related SoCal Stormwater Solutions resources include:
SMARTS & Permitting Application Services Full support for stormwater permitting through California’s
Compliance Document Preparation & Permit Registration in Los Angeles Expertly prepared SWPPP
Construction Inspection & Monitoring Services in California Stay compliant with California’s CGP
Industrial SWPPP Services in California Managing stormwater compliance in industrial settings is