Tuesday, May 4, 2010

Comparison Between NPDES Benchmarks and Effluent Limits

How are "benchmark values" in my NPDES permit different than my "effluent limits"?

Benchmark values differ from 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.

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.

Click here for more information on stormwater benchmarks

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