Stormwater Benchmarks Compared to Permit Limits

Benchmark values differ from permit limits, sometimes referred to as "effluent 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. Certain typical of stormwater discharges have federally enforceable Effluent Limits, with are Incorporated into stormwater general permits (such as a MSGP) or into individual NPDES permits.

Benchmark values 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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Caltha LLP maintains a library of Stormwater Monitoring Plan templates to meet individual State requirements, and can provide ad hoc technical guidance in development of stormwater monitoring programs.

For further information contact Caltha LLP at info@calthacompany.com or Caltha LLP Website