Benchmark values differ from permit limits. In a typical wastewater NPDES permit, limits may be specified for chemical parameters; if any of the limits are exceeded, it becomes a violation of the permit and may be subject to enforcement action.
Benchmark values, in the context of stormwater NPDES permits, are intended to provide a measurement of the effectiveness of the stormwater pollution prevention plan (SWPPP). Exceeding a benchmark does not directly result in a permit violation.

However, permits typically require facilities to reevaluate their SWPPP and to take prompt corrective action after a benchmark value is exceeded. Failure to take prompt corrective action if a benchmark value is exceeded can be a permit violation and subject to enforcement action. Multiple exceedances of a benchmark could result in a State requiring that the facility apply for an individual stormwater discharge permit. In this case, legally enforceable stormwater discharge limits may be written into the permit.

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