Is a Numeric Action Level Exceedance Actually a Stormwater Violation?

Stormwater Legal & Compliance Center / Article

Under California's Industrial General Permit, a permit-defined Numeric Action Level exceedance is not, by itself, a violation of that permit. But it can trigger enforceable response requirements, and the same facts may be relevant to a different permit obligation. The correct answer is therefore neither "every exceedance is a violation" nor "an exceedance does not matter."

The first step is to identify the actual permit, parameter, threshold, and provision being discussed.

An action level and an effluent limit have different functions

The amended Industrial General Permit uses Numeric Action Levels, or NALs, to evaluate pollutant-control performance and trigger further assessment and response. Finding 77 explains that the defined NAL and TMDL Numeric Action Level exceedances are not, in themselves, permit violations. It also states that failure to comply fully with required Level 1 or Level 2 Exceedance Response Actions is a violation.

Numeric effluent limitations are different. Where an applicable limitation governs the discharge, an exceedance is evaluated under that limitation and its compliance provisions. The fact that another provision uses an action level does not turn an enforceable limit into a nonbinding benchmark.

The Industrial General Permit also contains other obligations, including controls, receiving-water requirements, sampling, and reporting. Those must be analyzed independently rather than assumed satisfied because an NAL exceedance alone is not a violation.

Check whether the permit defined exceedance occurred

A single laboratory value above a reference number is not always the same as a permit-defined annual or instantaneous maximum NAL exceedance. Under the Industrial General Permit, annual NAL assessment uses the specified reporting-year averaging method. The instantaneous maximum framework uses its own criteria, including the number of results above the threshold or outside the applicable pH range.

Review the actual data, units, sample locations, reporting period, and calculation method. Determine whether the relevant number is an NAL, a TMDL Numeric Action Level, an effluent limitation, or another criterion. An error in that classification can lead to an incorrect legal conclusion in either direction.

Technical review should be documented. Do not discard a result merely because it is inconvenient or inconsistent with expectations. Investigate analytical or transcription concerns with qualified professionals and use the appropriate correction process.

Identify the response obligations

Where the permit's criteria are met, the facility may move into a higher Exceedance Response Action status for the affected parameter. The required evaluation, reports, plans, technical demonstrations, and timing depend on the permit and the facility's status.

Qualified Industrial Stormwater Practitioner involvement may be required. The business should identify the applicable tasks and deadlines and confirm that required certifications and submissions are completed. A technical report prepared but never properly submitted may not satisfy the filing obligation.

It is important to distinguish completing a response requirement from proving that every other requirement has been met. The legal review should consider both the response itself and any separate allegations about conditions at the facility.

Do not use the NAL distinction as a blanket defense

For a broader view of disputes over industrial stormwater records and alleged violations, read our California industrial stormwater defense article.

An agency or plaintiff may point to sampling results as part of a broader claim involving inadequate controls, receiving-water effects, or another requirement. Whether the evidence supports that claim depends on the governing language and facts.

For example, a notice might inaccurately label an NAL exceedance as an automatic numeric-limit violation while separately identifying a genuinely missed response deadline. Correcting the first characterization would not necessarily resolve the second allegation. Each claim should be assessed on its own terms.

Likewise, assertions about background pollutants or runoff from a neighboring property need technical and legal support. The permit provides specific demonstration procedures; a general statement that pollution came from elsewhere is not a substitute for satisfying them.

Keep other permits separate

This explanation concerns the California Industrial General Permit. The Construction General Permit and the Los Angeles CII permit have their own thresholds, monitoring requirements, and compliance rules. The CII permit's water quality-based effluent limitations should not be described as though they were industrial NALs.

Before responding to a notice, verify which order and provision apply to the facility and discharge at issue. Do not rely on a general internet explanation without that connection.

Frequently asked questions

For help evaluating a disputed result or notice, visit Industrial General Permit counsel, 60-day notice defense, or Get A Case Evaluation.

This information is educational and is not a facility-specific determination of compliance or liability.

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