On January 28, 2011, the California State Water Resources Control Board proposed a draft industrial stormwater discharge general permit. The draft General Permit amends a number of the existing requirements for permitted facilities and adds some new requirements.
One of the more significant changes to the California General NPDES Permit is the incorporation of quantitative
Action Levels and
Effluent Limits which could apply to any discharger. In 2006, the State Water Board convened a blue ribbon panel of storm water experts that submitted a report entitled, “The Feasibility of Numeric Effluent Limits Applicable to Discharges of Storm Water Associated with Municipal, Industrial and Construction Activities,”. The panel concluded that numeric limits or action levels are technically feasible to control industrial storm water discharges, provided that certain conditions are considered. The draft permit incorporates two types of quantitiative action levels/limits:
Numeric Action Levels (NALs) are derived from the US EPA Multi-Sector General Permit’s benchmarks, and are used as numeric thresholds for corrective action. Exceedances of an NAL are not a violation of the permit; however, exceedance of specific NAL Corrective Action Triggers requires the facility to enter into Level 1 Corrective Action.
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More information on US EPA benchmarks, and comparison to historic industrial sector monitoring results]
Numeric Effluent Limits (NELs) are could also apply to any facility. Dischargers in Corrective Action Level 3 (see below) are subject to a numeric effluent limitation (NEL) that will be the same value as the applicable pollutant NAL. A daily average exceedance of the NEL is a violation of the General Permit and may subject the discharger to
mandatory minimum penalties.
NAL Corrective Action Triggers are defined in the draft general permit as follows:
1. The Daily Average (DA) for any one constituent exceeds the NAL value for two or more storm events of a reporting year, or;
2. The DA for any two constituents exceed the NAL values for any single storm event within a reporting year, or;
3. The concentration for any one constituent exceeds 2.5 times the NAL value for any one individual or allowable combined sample (or is more than one pH unit outside the NAL pH range)
In the event that any of the NAL Corrective Action Triggers are met, the facility will need to complete Level 1 Corrective Actions. The need to do further corrective actions will depend on subsequent monitoring results.
Level 1 - Operational Source Control Corrective Actions
Upon the first occurrence meeting any of the NAL corrective action triggers, the discharger will be required to valuate areas of the facility to identify where additional operational source control BMPs and/or SWPPP implementation measures are necessary to prevent or reduce pollutants in storm water discharges in compliance with BAT/BCT. Based upon the facility evaluation, the facility will certify that the pollutant source(s) have been identified and 1) additional operational source control BMPs and/or SWPPP implementation measures have been included in the SWPPP , 2) no additional operational source control BMPs or SWPPP implementation measures are required , or 3) pollutant source(s) causing the exceedance are not related to the facility’s industrial activities. A Level 1 NAL Exceedance Evaluation Report will need to be prepared and submitted.
Level 2 Structural and/or Treatment Corrective Actions
If in any subsequent reporting year the sampling results meet an NAL corrective action trigger, the discharger is require to take addition action. If the NAL corrective action trigger is for a constituent that had not been included in a previous Level 1 NAL Exceedance Evaluation Report, the discharger go through Level 1 Corrective Actions.
If the NAL corrective action trigger is for one or more of the constituents previously addressed in a Level 1 NAL Exceedance Evaluation Report, the discharger would need to evaluate and select additional structural source control BMPs and/or treatment BMPs with the goal of achieving the applicable NAL value(s) in future discharges. A Level 2 NAL Exceedance Evaluation Report will need to be prepared and submitted and more frequent monitoring is required.
Level 3 Imposition of Numeric Effluent Limits
If in any subsequent reporting year the sampling results meet an NAL corrective action trigger for the same constituents subject to the Level 2 corrective actions, the discharger shall the applicable NAL(s) will become an NEL(s), and starting October 1 of the following compliance year, the discharger will be required to sample every qualifying storm event.
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