NUMERICAL EFFLUENT LIMITS IN STORM WATER DISCHARGE PERMITS

Posted on December 7, 2011 by Kevin Beaton

In recent years, the states and EPA have placed greater emphasis on regulating storm water discharges from various industrial and municipal sources under the Clean Water Act.  These discharges are typically regulated by a general NPDES Permit issued by EPA or an authorized state.  The standard approach required in these general permits is for a facility to develop a storm water pollution prevention plan (SWPPP) incorporating best management practices (BMPs) that will be followed to reduce pollutant impacts to storm water discharged from the facility.  Typically some type of periodic monitoring is required during storm events.  The monitoring can be just visual monitoring and less frequently chemical analysis of certain pollutants associated with the particular industry.  In lieu of numerical effluent limits, typically the general permit will establish “benchmark levels” for industry specific pollutants that are not to be exceeded.  If a benchmark level is exceeded, the facility is required to undertake and document corrective measures to address the problem.  Typically corrective measures involve modifications to BMPs.  Unlike a numerical effluent limit in non-storm water NPDES permits, benchmark levels are not enforceable effluent limits under the Clean Water Act.  Therefore exceeding a benchmark level by itself does not subject a facility to an enforcement action by EPA, an authorized state or a third party citizen suit.

Over the past five years there has been a significant increase in Clean Water Act storm water enforcement actions.  The emphasis has been on actions against the home construction industry as well as confined animal feeding operations (CAFOs).  The typical enforcement action has been focused on facilities that failed to obtain a required general permit or failed to comply with SWPPS and related paperwork requirements.  Also in the West we have witnessed a significant increase in third party citizen suits for violation of general storm water permits.

Over the past 15-20 years, the BMP approach in general permits has provided relative certainty of the requirements and ease of implementation for permittees.  EPA has taken the position, however, that the BMP approach to storm water permits is just a first phase in the program while the agency gathers data to support future actual numerical limits.  The future is now here.  An EPA Guidance document entitled “Guidance on Establishing TMDL Waste Load Allocations for Storm Water Discharges in NPDES Permits (EPA November 2010),” although not finalized, is already being implemented by EPA to establish numerical criteria. 

For those not familiar with “TMDLs” and “waste load allocations,” some brief background may be helpful.  The total maximum daily load (TMDL) program is dictated by Section 303(d) of the Clean Water Act.  The program requires states to identify impaired waters not meeting water quality standards and to then develop TMDLs to bring the waters back into compliance.  TMDLS are basically pollution reduction plans that identify the loading capacity (with a margin of safety) of a water body which is the level of particular pollutant causing the impaired condition that will bring the water body back into compliance with water quality standards.  The TMDL thus requires reductions of pollutant loading from both point sources (known as “waste load allocations” or “WLAs”) and nonpoint sources (known as “load allocations”).  Typical of Clean Water Act programs, the regulatory onus of complying with TMDLs falls on point sources through the NPDES permit program.  Nonpoint sources are not regulated by EPA and state nonpoint source programs are generally based on a non-regulatory approach.  Also typical of Clean Water Act programs involving water quality standards, a states’ identification of impaired waters and development of TMDLs are subject to EPA review, approval or disapproval.  In many instances EPA will actually develop a TMDL in the face of state inaction.

In the past storm water NPDES permits were often overlooked by the states and EPA in establishing TMDLs.  EPA’s recent Guidance makes clear that storm water permits will be considered when EPA reviews state TMDLs.  In fact the Guidance makes clear that it is EPA’s intent in approving TMDLS to ensure that numerical WLAs are included in general storm water NPDES Permits.  Although the Guidance suggests some flexibility in such an approach by stipulating that WLAs will only be included in storm water permits when “practical,” we all know that “practicality” is in the eye of the beholder.

Inserting WLAs into storm water permits raises a host of technical and compliance issues.  First, because of the variability of storm events it is often difficult to quantify the actual loading of pollutants from a particular facility.  Often times the data on such loading is lacking and is therefore based on modeling which may or may not predict actual conditions.  Thus if EPA implements this Guidance in storm water permits the cost and frequency of monitoring storm water discharges is likely to increase substantially.  Secondly, it is often very difficult to control the concentration or loading of a particular pollutant during storm events absent the installation of expensive wastewater treatment controls.  Thus the cost of compliance may increase substantially once this Guidance is implemented.  Finally, once WLAs or numeric effluent limits do find their way into general storm water NPDES permits, exceedence of these limits will subject facilities to EPA, state or third party citizen suits enforcement actions.

Despite these concerns, numerical limits or WLAs in storm water discharge permits appear to be the next wave of regulation.  Practitioners in this area should make sure that clients with regulated storm water discharges to impaired waters become involved in the TMDL development at the state level to ensure that they receive a reasonable WLA that can be consistently complied with and which will not be too costly to achieve.



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