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Are TMDL program mandated upgrades likely to result in significantly improved water quality? The answer could be a resounding NO! An examination of the TMDL development and implementation process for several tidally influenced coastal plain water bodies reveals the TMDL process is ripe with multiple opportunities for regulatory agencies to make inappropriate technical decisions. A technical flaw in the basis for any one of these decisions could translate to unnecessary direct or indirect expenditures - resulting in only the counting of an additional regulatory bean rather than in meaningful water quality improvement. This paper identifies, based upon examination of the TMDLs for four coastal plain water bodies, several critical TMDL process decisions and the potential of each to negatively impact the TMDL program outcome.

The first opportunity for a poor technical decision is associated with the identification and use of one or more inappropriate water quality standards and/or targets as the water quality goal for the process. As a result of TMDL schedules set forth in various TMDL consent order settlements, some regulatory agencies have taken the position that it is appropriate to use an existing standard and/or target because it is the best, or all, that there is. Unfortunately, these agencies have taken this position in the face of widely available scientific data indicating a particular standard is inappropriate.

Secondly, the authors observed different interpretation and application of the identical standard within one agency during the TMDL development for two separate, but similar, water bodies. All other factors being equal, the net effect is to treat water bodies with the same water quality standard differently. This practice has the potential to lead to inappropriate more restrictive source controls in one water body and less restrictive source controls in the other.

Selection and interpretation of the applicable standard and/or target greatly influences the required characteristics of the calibrated simulation model used to establish maximum available loads. For example, there seems to be a great deal of variation in identifying what “average” means. In the case of dissolved oxygen, the required characteristics, capabilities and even the level of calibration of a model being used to simulate attainment of an average standard could be significantly different depending on the interpretation of the word average. Does average mean average of all grab samples taken over the course of a day, a month or even a season? Or alternatively, does it mean the average of all values from a continuously monitored (or modeled) system?

The decision on how to allocate allowable loads between point and non-point sources and whether or not to allow trading of loads between point and non-point sources can also greatly impact the outcome of the TMDL program.

Document Type: Research Article


Publication date: January 1, 2003

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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