The influence of socioeconomic and spatial variables on total maximum daily load progress in the United States

The total maximum daily load (TMDL) program requires each state in the United States to assess their water bodies, list those that are impaired, and develop TMDL plans or programs to restore them. However, the impact that spatial and socioeconomic variables have on TMDL progress is unknown. This study seeks to fill this gap through a nation-wide analysis of the influence of spatial and socioeconomic variables on indicators of TMDL progress. To do so, data were collected and analyzed for each state, including indicators of TMDL progress, spatial variables, and socioeconomic data. Then, these data were applied to identify overall trends and to define the relationships between indicators of TMDL progress and spatial and socioeconomic variables. Results indicate that the size of a state, the length of total streams, and median household income are related to the percentage of streams that are assessed within a state. In addition, states largely followed similar patterns in TMDL progress based on the US Environmental Protection Agency region that they were within, indicating that location plays a large role. Overall, this study helps to contextualize progress in TMDL development and aid in our understanding of factors that influence the implementation of water quality programs.