Narrative water quality criteria are an integral component of States' water quality standards but they pose special problems when incorporated into the TMDL process. The TMDL process is typically a quantitative activity, defining numeric allowable loads necessary to meet a numeric water quality objective. Narrative criteria confound development of quantitative TMDLs, due to the absence of these numeric criteria. The objective of this research was to improve the methods for addressing narrative water quality criteria in the TMDL process. The problems associated with narrative criteria in the TMDL process are known in general terms but, prior to this research, there has not been a thorough review of the use of narrative criteria in TMDLs nor broad guidance on how to address narrative criteria in the TMDL process. The approach taken for this research was to define the range of problems associated with all types of narrative criteria by means of a comprehensive review of 120 narrative TMDLs, and provide guiding principles to help address these problems.Adherence to these guiding principles is expected to significantly improve the evaluation of water bodies for impairment of a designated use based on non-attainment of narrative water quality criteria, resulting in more accurate 303(d) lists with a greater focus on those water bodies truly impaired. Also, adherence to these guiding principles will contribute to improvements in the TMDL development process, resulting in a greater degree of success in attaining designated uses when a TMDL is implemented . This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below

TMDLs, or total maximum daily loads, are required under the Clean Water Act, Section 303(d), for waterbodies that do not attain water quality standards. The objective of this research was to review the existing TMDL process and to develop an improved design for TMDL development where improvements are needed. This objective was accomplished through: (1) Identifying and verifying problems with the existing TMDL program; (2) Formulating a range of recommended improvement options on specific topics that address identified weaknesses; and (3) Providing case studies examples that highlight these recommended changes to improve the TMDL process. The research team identified ten specific areas for improvement, based on a review of approved TMDLs, a survey of state programs, and an in-depth review of specific case study examples. These topics relate to specific steps and/or methods employed in the TMDL development process. They include: estimating background pollutant loads; quantifying nonpoint source loads using simple methods; incorporating urban wet weather sources; selecting critical conditions; guiding principles for modeling; estimating the TMDL margin of safety; approaches to the allocation of loads; linking best management practices to load reduction; implementation planning, tracking, and adaptation; and adaptive watershed management. Each topic is addressed in a separate chapter of the report, with a discussion, recommendation of improved approaches where appropriate, and specific examples to help guide water quality professionals when developing or reviewing TMDLs.