Abstract

Helping subscribers and practitioners increase their understanding of the Total Maximum Daily Load (TMDL) process, and reducing the uncertainty in all phases of the process is a high priority for the Water Environment Research Foundation (WERF). WERF has therefore undertaken several studies to explore the TMDL process that would assist water quality professionals. Three of these reports provide key information for water quality professionals, and are the subject of this manuscript. With the knowledge and tools provided by these reports, TMDL practitioners will be able to implement a process that is practical, reasonable, and scientifically defensible.The first project, Navigating the TMDL Process: Listing and Delisting, reviewed the science underlying the processes for placing waters on the 303(d) impairment list, and also for removing them from the list. This report presents alternative, scientific approaches for listing and delisting waters to help reduce and manage uncertainty and increase confidence that the appropriate waters are targeted for water quality improvement via the TMDL process.There is a set of tiered recommendations for actions that state programs can take to minimize uncertainty in each of the four components of the listing and delisting process. This includes a minimum set of actions that should be taken to promote a scientifically defensible process that considers and addresses all the potential sources of uncertainty or variability. Researchers recommend that states adopt as comprehensive an approach that time, resources and policies permit by implementing as many additional actions as possible. Such efforts can increase certainty that appropriate waters have been placed on the 303(d) list for appropriate reasons. It is also recommended that U.S. EPA include an additional sub-category under Category 4 in the 2002 Listing Guidance—water bodies that are impaired due to unknown causes.Whereas the first project addresses issues of whether a water body should be listed or delisted (and hence determines whether a TMDL is required), the second project, Navigating the TMDL Process: Evaluation and Improvements, reviews the existing TMDL process and develops enhanced protocols for TMDL development. The study presents recommendations for key improvements to the TMDL process. These focus on specific issues that address identified weaknesses.Practitioners will benefit most from guidance on ten topics, including several approaches to quantifying and allocating pollutant loads, selecting critical conditions, addressing wet weather sources in a TMDL, guidance on modeling, implementation, and a discussion of the potential for using adaptive watershed management in the TMDL process.The third project, Navigating the TMDL Process: Method Development for Addressing Narrative Criteria, provides a thorough review of the use of narrative criteria in TMDLs and offers broad guidance on how to handle narrative criteria in the TMDL process. The determination of water quality impairment and the development of TMDLs is typically a quantitative activity, defining numeric allowable loads necessary to meet a numeric water quality objective. The lack of specific numerically defined objectives in narrative criteria confounds the determination of impairment and development of TMDLs.The project addresses the three major categories of narrative criteria (toxicological, ecological, and aesthetic) and identifies issues specific to these categories within the three steps of developing a TMDL that have proven most difficult for TMDL practitioners working with narrative criteria—making a determination of impairment, identifying the cause of impairment and setting appropriate TMDL targets. The research team suggests guiding principles for addressing narrative criteria in the TMDL process based on their review and analysis of 120 TMDLs.WERF's commitment to addressing TMDL-related research continues. Using the three core projects discussed above, the insights of WERF's research council, and drawing insights from several additional sources, WERF has identified new areas for research. WERF is currently researching sediment toxicity identification and the relationship to the TMDL process, and is planning to examine TMDLs for common yet complicated impairments such as bacteria in upcoming research cycles.

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