The Role of Stakeholder-Funded Microbial Source Tracking Studies in Bacteria TMDL Development

An astonishing number of the nation's waterways are categorized as impaired by bacteria sources. Unfortunately, in most cases the sources of bacteria to impaired waterbodies are unidentified, or at least uncharacterized, which can lead to large capital expenditures for implementation requirements associated with Total Maximum Daily Loads (TMDLs) which are developed under the Clean Water Act. As such, in order to inform TMDL and implementation plan development, some stakeholder groups have funded source assessment studies based on microbial source tracking (MST). By conducting scientific studies prior to TMDL development, the accuracy of the developed TMDL and likelihood of success of the corresponding implementation plan can be increased. However, there are challenges associated with integrating MST studies into TMDLs, due to the fact that (i) currently there are no standard methods for MST technologies, (ii) some regulatory agencies are skeptical of MST due to recent comparison studies in which certain methods performed very poorly, (iii) many MST methods target microorganisms that differ from those on which the water quality criteria are based (e.g. Bacteroidales versus E. coli) and (iv) very few epidemiological studies have been performed using MST methodologies. Nonetheless, when applied and interpreted appropriately, MST studies provide meaningful and useful data for regulatory agencies and stakeholders. Thus, the role of MST data in TMDL and implementation plan development hinges on one critical aspect: the context in which the data are used.This paper reviews two stakeholder-funded MST studies that were designed by the authors and performed in cooperation with state and federal regulatory agencies to support TMDL and implementation plan development. A total of nine 303(d)-listed waterbodies in California were investigated, which are being addressed through two separate TMDL reports. The applied MST assays were based on quantitative polymerase chain reaction (qPCR) and targeted Bacteroidales and human-specific viruses (adenovirus and enterovirus). One of the studies was long-term (samples were collected for a period of over one-year) while the other was intensively (over 600 samples were collected) conducted over one summer. The land uses of the investigated watersheds were highly varied, ranging from predominantly open to agricultural to urban. In addition, the waterbody types were variable, including tidally-influenced creeks, natural and manmade sloughs, and highly-engineered concrete channels. The results of the MST studies, along with the approach to (and challenges with) integrating those results into the corresponding regulatory framework, will be discussed. This presentation should be of interest to an array of individuals/ agencies challenged with attaining bacteria standards in 303(d)-listed watersheds.