TR-549 Review of Total Maximum Daily Load Methods to Address Dissolved Oxygen Impairments Final Report
Authors: Taylor Jordan, Michael Schramm, Duncan Kikoyo and Amanda Tague
Among non-legacy contaminants, depressed dissolved oxygen (DO) is the second most frequent cause of water quality impairments in Texas. While much of the current focus of water quality efforts has been to address fecal indicator bacteria, substantial opportunity exists for addressing DO impairments. This report provides a review of methods and approaches used for developing DO Total Maximum Daily Loads (TMDLs) in the US Environmental Protection Agency (EPA) Regions 4 and 6. While many different approaches and models are available, TMDL development appears to have coalesced around only a few mechanistic models. In general, the use of linked watershed and receiving water body models is most common, with the choice of receiving water body model varying among the QUAL2E, WASP, and EFDC models. The development of frameworks for choosing modeling approaches using expertise available among agencies, universities and other stakeholders will help build consensus in decision-making prior to TMDL development. Due to the data requirements and model complexity in some of the identified approaches, additional discussion is needed to identify preliminary data needs for DO TMDL development. With anticipation of future DO TMDL (and other water quality planning efforts) development, this study suggests following a model similar to the previously convened Bacteria TMDL Task Force for providing expert guidance and building high-level consensus of approaches and data requirements for developing DO TMDLs within Texas.