Traditionally, EPA has regulated storm water differently than point source discharges.  Regulators recognized that it was easier to install new technology to reduce pollutant loading from a specific industrial process with a specific "end of pipe" discharge point.  Storm water was much more unpredictable.

Therefore, U.S. EPA regulated storm water using general NPDES permits without specific numeric limits.  Instead, the general permit would require the development of a storm water pollution prevention plan (SWPPP) which required companies to institute "best management practices" (BMPs) to reduce pollution from run-off.  The effectiveness of BMPs were evaluated by monitoring pollutant levels in run-off. but permits did not contain specific numeric effluent limits that had to be met.

EPA recognized the difficulties in trying to establish a numeric effluent limit for storm water discharges due to the variables involved.  For instance, due to the variability of the size and nature of storm events, the amount of pollutant leaving a site in run-off was difficult to evaluate.

In 2002, EPA issued guidance that stated numeric limits would only be used "rarely" in storm water NPDES permits.  However, EPA believe technology has improved and has signaled a shift toward numeric limits for storm water control. In 2010, EPA issued a controversial revision to that guidance indicated numeric values may be appropriate.  (See, "Guidance on Establishing TMDL Waste Load Allocations for Storm Water Discharges in NPDES Permits"  EPA November 2010)

Benchmarks Versus Numeric Limits

The first step toward numeric limits is EPA’s use of "benchmarks" in storm water permits.  EPA makes clear that benchmarks are not effluent limits.  This means an exceedence of the numeric value is not a violation.  However, the exceedence is evidence that BMPs need to be improved to reduce pollutant loading.

In December 2011, Ohio EPA followed U.S. EPA lead and incorporated benchmarks into its final version of the new NPDES General Permit for Industrial Activity.  This permit differs from the previous General NPDES Permit companies  in two significant ways. 

First, the permit contains industry specific requirements (which is why the permit is 141 pages long).  Second, it uses benchmarks tied to specific industrial activity that will be used to determine the effectiveness of BMPs.

Ohio EPA’s new General  Permit became effective starting January 1, 2012.   However, facilities will still be covered by their old general permits, as long as they are still effective.  Existing facilities will begin the transition to the new permit upon notification from Ohio EPA. 

Ohio EPA will send written instructions to existing covered facilities on how to continue their general permit coverage with the submittal of a “re-notification” of intent to be covered. The existing facility will have 90 days to submit the re-notification.

Benchmark Monitoring

The new permit is effective for five years.  During the first four years of the permit, facilities to which the industry specific benchmarks apply, will monitor their compliance with the benchmarks.

In the first three years of the permit, monitoring and reporting is required for four out of the 12 quarters.  In year number four, the data is averaged and compared to applicable benchmarks for that industrial activity. If facilities are still exceeding the benchmarks after four years, they will be forced to review their BMPs, storm water control plans and house keeping activities to further reduce pollutant loading.

How Far will Facilities Need to Go to Comply with Benchmarks?

The permit makes very clear that the benchmarks are not enforceable effluent limits.  Therefore, an exceedence is not a violation which could subject the facility to an enforcement action.  However, the expectation is the facility will continue to improve storm water controls if the benchmarks are not met. 

The final permit does contain language that allows faculties to assert they have done all they feasibly can to reduce pollutants.  The permits states that facilities can demonstrate that “no further pollutant reductions are technologically available and economically practicable and achievable in light of best industry practice to meet the control measures/best management practices (BMPs) in Part 2 of this Permit.”

The determination must be documented and retained with the (SWPPP, and provide notification of this determination to Ohio EPA at the due date for the next benchmark monitoring report.  Of course, a company’s determination as to what is economically practicable may not be the same as the Agency’s. 

(For more information on Ohio EPA’s NPDES General Permit for Industrial Activityclick here)