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Regulatory Alert - RA 02-22 - EEPA MEMORANDUM ON TMDL WASTELOAD ALLOCATIONS FOR MUNICIPAL STORMWATER PERMITS

Member Pipeline - Regulatory - Alert (RA 02-22)

To: Members & Affiliates, Wet Weather Issues Committee, Legal Affairs Committee, Water Quality Committee
From: National Office
Date: December 11, 2002
Subject: EPA MEMORANDUM ON TMDL WASTELOAD ALLOCATIONS FOR MUNICIPAL STORMWATER PERMITS
Reference: RA 02-22

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On November 22, the U.S. Environmental Protection Agency’s (EPA’s) Office of Wastewater Management and Office of Wetlands, Oceans & Watersheds released a joint policy memorandum to the Regions clarifying existing requirements for establishing total maximum daily load (TMDL) wasteload allocations (WLAs) for municipal stormwater discharges. A copy of the policy memorandum can be downloaded from AMSA’s web site at http://www.amsa-cleanwater.org/private/legreg/outreach/112202final-wwtmdl.pdf. This Regulatory Alert provides a summary of the major points in the policy memorandum as well as AMSA’s background concerns on these issues. AMSA believes that, overall, the policy memorandum provides some useful support for using an iterative best management practices approach to reducing stormwater pollutants, but continues to provide permitting authorities with too much discretion on the use of numeric limits.

Background
Due to the unique constraints of municipal stormwater programs and the largely unpredictable nature of urban runoff, the performance of stormwater controls, and storms in general, the Clean Water Act established a specialized pollutant reduction standard (i.e., “maximum extent practicable”, or “MEP”) for municipal separate storm sewer systems (MS4s). Federal Water Pollution Control Act, 33 §1342(p)(3)(B). AMSA believes that Congress, recognizing these uniquely urban constraints, intended that municipalities achieve the MEP standard through progressive implementation of best management practices (BMPs) tailored to the specific system, as opposed to strict compliance with specific numeric criteria. The iterative use of BMPs has been an approach strongly advocated by EPA in its previous guidance documents, such as the Interim Permitting Approach for Water Quality-Based Effluent Limitations in Storm Water Permits (see 61 Federal Register 43761, August 26, 1996).

AMSA’s interpretation of the Clean Water Act’s MEP standard was endorsed in 1999 by the Ninth Circuit Court of Appeals in Defenders of Wildlife v. Browner (see AMSA Legal Alert at http://www.amsa-cleanwater.org/private/legalalerts/leg99-5.cfm). The court held that the Clean Water Act “unambiguously demonstrates that Congress did not require municipal storm sewer discharges to comply strictly with [water quality standards].” However, the court did acknowledge that the permitting authority has the discretion to impose numeric water quality limits if necessary. AMSA believes that the permitting authority’s discretion is still confined by the limit of practicability that is embodied in the MEP standard (e.g., “maximum extent practicable”). Therefore, in AMSA’s opinion, a permitting authority would be required to demonstrate that a decision to require compliance with any numeric water quality standard is practicable and achievable, a demonstration that will be impossible in most if not all instances.

Numeric Limits and TMDLs
An area where the issue of numeric standards is especially controversial is in the TMDL program. In developing the TMDL, permitting authorities must ultimately determine how best to allocate load reduction responsibilities among contributing sources, including a decision on how much of a specific pollutant is coming from what source or what quantity must be reduced by those sources. Where MS4 discharges are contributing to noncompliance with water quality standards, it is inevitable that the regulatory authority will need to contend with how to assign a specific allocation or WLA to those sources. The challenge for these permitting authorities will be to reconcile the tensions between the need to allocate numeric pollutant reduction requirements to sources of impairment within a watershed and the need to recognize that strict compliance with numeric limits for MS4 discharges using BMPs as the primary control technology is not practicable. Notwithstanding past EPA guidance recommending progressive BMP implementation as the mechanism for achieving MEP, AMSA is concerned that permitting authorities may abandon the BMP approach in favor of specific numeric standards or numeric load reductions for individual MS4 dischargers. Specific numeric limits resulting from a WLA have already been required for several MS4 dischargers, including the District of Columbia (see AMSA’s Legal Alert 02-5 at http://www.amsa-cleanwater.org/private/legalalerts/leg02-5.cfm) and numerous municipalities in California. With this background in mind, EPA’s policy memorandum provides a glimpse into the Agency’s current thinking in determining the proper balance between the TMDL and MS4 permit programs.

EPA’s Policy Memorandum - Summary of Key Aspects
EPA’s policy memorandum seeks to clarify the options available for quantifying TMDL allocations for MS4 discharges to impaired streams, and to outline the recommended approach for converting these allocations into effluent limits in individual permits. The memorandum is organized into three sections covering the regulatory basis for including NPDES-regulated stormwater discharges in WLAs, options for addressing stormwater in TMDLs, and determining effluent limits in NPDES permits for stormwater discharges consistent with the WLA. This section highlights the latter two sections.

Quantifying WLAs for Municipal Stormwater Discharges (Section II)
For impaired streams, WLAs express the required load reduction from either individual point source discharges or broad categories of point sources. The Agency clarifies in its policy memorandum that permitted stormwater sources are to be treated as any other point source discharge in the allocation process. Section II, p. 4. Some MS4 permitholders take issue with this approach arguing that municipal stormwater sources are more appropriately treated as nonpoint sources considering the nature of urban runoff, the emphasis of the program on BMPs, and the overall lack of precision regarding removal efficiencies. According to EPA’s policy memorandum, the only municipal stormwater sources that are to be treated as nonpoint sources, and therefore to be given load allocations (LAs) instead of WLAs, are those that are currently unregulated in the NPDES program.

EPA recognizes in the policy memorandum that WLAs for regulated MS4 discharges will need to be fairly rudimentary due to the limited amount of actual data and the overwhelming reliance on modeled estimates of loadings. As a result, EPA believes that outfall-specific WLAs will often not be possible. Instead, EPA recommends “expressing the [WLA] ... as either a single number for all NPDES-regulated stormwater discharges, or when information allows, as different WLAs for different identifiable categories.” Section II, p. 4.

Approach for Determining Effluent Limits for MS4 Discharges (Section III)
EPA also articulates how WLAs should be transformed into effluent limits in individual NPDES stormwater permits. In general, once a TMDL has been developed and approved, the effluent limits of each permitted source must be adjusted consistent with the WLA. EPA indicates that the traditional form for expressing effluent limits is numeric, but acknowledges that MS4 limits should be treated differently. Recognizing that storm events are “highly variable in frequency and duration and are not easily characterized,” EPA recommends that MS4 effluent limits be expressed as BMPs, rather than numeric limits. Section III, p. 4. This recommendation is consistent with AMSA’s stated positions.

The Agency also reiterates its belief, based on the 1996 “Interim Permitting Approach Policy,” that an iterative approach is necessary to control pollutants from urban runoff, and that BMPs should be adjusted over time to reflect improved data and information. EPA justifies this position by observing that the “variability in the system and minimal data generally available make it difficult to determine with precision or certainty actual and projected loadings for individual discharges or groups of discharges.” Section III, p. 4. EPA also points out that the iterative process is consistent with the recent National Research Council (NRC) report on the TMDL program regarding the use of an “adaptive implementation” approach for implementing required pollutant reductions (i.e., “a cyclical process in which TMDL plans are periodically assessed for their achievement of water quality standards ... and adjustments made as necessary”). Section III, p. 5.

The policy memorandum also suggests that the permitting authority must determine whether effluent limits are expressed more appropriately using a BMP approach or numeric limits. Section III, p. 5. AMSA is concerned that EPA may be leaving too much discretion to the permitting authority here by not pointing out that any decision to use numeric limits must be confined within the limits of practicability, consistent with the MEP standard for MS4s. The policy memorandum leaves this decision to the permitting authority without acknowledging the limits of the MEP standard.

The remaining portions of Section III are dedicated to recommending the type of information that should accompany the permit to support the BMP approach. For instance, EPA recommends that the permit include a mechanism for requiring the “use of expanded or better-tailored BMPs when monitoring demonstrates they are necessary to implement the WLA and protect water quality.” Section III, p. 5. A discussion also should be included in the administrative record of the particular BMPs selected and the assumptions used. In addition, the permit must include requirements for sufficient monitoring to assure compliance with the effluent limits, and provisions for the collection of data to demonstrate the actual performance of BMPs. Section III, p. 5.

AMSA encourages its members to contact the National Office if your permitting authority is contemplating or has used numeric limits or numeric pollutant load reductions in your MS4 permit. AMSA will continue to track developments in this area and provide comments to EPA when necessary. For more information, contact Greg Schaner, AMSA at 202/296-9836 or gschaner@amsa-cleanwater.org.