The goal of the TMDL program is arguably simple - to develop watershed level conservation plans designed to restore impaired waters and attain applicable water quality standards – but its development and implementation has not been simple. In an attempt to bring new clarity to the process of incorporating TMDLs into stormwater permits, the EPA issued a revised guidance document last November entitled “Establishing Total Maximum Daily Load (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on Those WLAs”.
This new policy is a revision of agency guidance originally issued in 2002, and revised in 2010, and supersedes both. It now incorporates changes due to recent legal rulings and agency policy shifts, and appears to incorporate responses from an informal public comment period held in 2011 related to the 2010 document.
The 2010 guidance placed a greater emphasis on utilizing numeric water quality limits for stormwater discharges, reinforced the use of stormwater pollutant surrogates (e.g. stormwater flows) in stormwater permits, and generally moved away from prior emphasis on using an iterative approach for Best management Practice (BMP) implementation to meet TMDL requirements.
A number of changes occurred since the issuance of the 2010 guidance. In 2013, the U.S. District Court stated that surrogates such as stormwater flow could not be used in place of applicable water quality standards in the TMDL program in the Accotink Creek TMDL case (Virginia Department of Transportation v. EPA). The EPA also indefinitely deferred action on developing a national stormwater rule, favoring a more localized approach that will incorporate increased incentives, greater emphasis on the use of green stormwater infrastructure, and both enhancing and strengthening municipal permit programs.
The new guidance has removed reference to the use of TMDL surrogate pollutant parameters such as stormwater flows. The use of numeric water quality based effluent limits (WQBELs) where feasible remains, but there is also the incorporation of elements from the 2002 guidance that promotes the implementation of stormwater BMPs using an iterative approach. When utilizing this BMP based compliance approach, it must be demonstrated that implementation of specific BMPs can be reasonably expected to achieve the TMDL water quality goal.
The new guidance also discusses disaggregating elements of a WLA when opportunity exists, allowing for localized targeting of “hot spot areas”, establishing target goals at the sub-watershed level, and/or assigning WLAs for individual MS4s within a geographic area. New to this guidance is the inclusion of permitted industrial discharges and additional guidance on how TMDL effluent limits should be applied and implemented within that regulatory construct. Examples of TMDL implementation language from current permits and programs that incorporate the various approaches recommended in the guidance are provided in the guidance document, as well as reference to EPA’s recent MS4 Compendium on incorporating WLAs into stormwater permits
As stormwater permits are renewed in coordination with the regional EPA offices, we should expect to continue to see TMDL based effluent limits and restoration goals being incorporated. In fact, we already see the result of such efforts and actions in portions of the United States. For example, activities once considered voluntary - such as urban tree planting - are now being listed in stormwater permits with numeric goals for tree establishment. Regional permit program inspections and enforcement activities are increasing as well.
At the end of the day, it’s clear that this guidance promotes a number of options for states and local resource managers to refer to on how to meet TMDL requirements. While there is greater emphasis on meeting water quality standards with the use of WQBELs, the flexibility of utilizing the historical iterative approach for implementing stormwater BMPs remains. Such an approach offers the best of both worlds in an increasingly regulated sector where the ultimate measure of success remains the satisfaction of water quality standards.