Risk-Based Prioritization for Investigating Illicit Discharges Along TxDOT ROW Prepared by: G.O.A.T. – Geographers of Austin Texas INTRODUCTION MAPS METHODS This study has analyzed the flow of illicit discharges into the Right Of Way (ROW) and Municipal Separate Storm Sewer Systems (MS4’s) in San Marcos (shown in the figure below). The San Marcos MS4 is a conveyance system owned by the state of Texas to control pollution discharges. Priority locations include areas with the highest susceptibility to pollution from the expansion and maintenances of the city, like the Edwards Aquifer Recharge Zone and Spring Lake. After researching similar projects conducted in other states we have made two assumptions: high population density and industrial areas increase the probability of illicit discharge (Schaftlein, 2015;Brown, Caraco, 2004;Johnson, 1998). To calculate the potential threat of illicit discharge, we had to find variables that showed a higher probability for a possible pollutant to occur. We took into consideration a number of different factors such as neighborhoods, flood plains, water bodies, and slope. The two that had the most impact on our findings were the buildings that surrounded the outfalls, and the city zone that the outfalls were located in. Certain businesses; such as gas stations and car washes, have a higher probability for illicit discharge than any other variable. After assigning a threat level to each zone and building in the urbanized area, we were then able to create an outfall layer that combined those threat levels, generating a final map showing the outfalls with highest probability for illicit discharge. Outfalls and their potential risk levels overlaid on the Edwards Aquifer. Zoomed in map of categorized building threat levels. Zoning threat levels by using threat levels of each building and their concentrations. CONCLUSION We highlighted the importance of information over outfall locations in San Marcos, Texas as to reduce the illicit discharges’ along the ROW. This is important to the city as to reduce pollution to the surrounding environment which includes endangered species and sensitive water locations. It is difficult to determine all pollution discharges without doing field work. This acts as a pre-plan to determine illicit discharges along the ROW in Texas, so further projects can include testing the water of the outfall sites as well as the outfall sources to connect common chemicals. This project is aimed to assist all ROWs in all DOT systems, and it attempts to create a methodology that can be implemented across the United States. DATA The bulk of data was collected, downloaded, and loaded into the ArcGIS software from the San Marcos website. Other data was required from the Program Manager of TxDOT, and the North American Datum 1983 (NAD 1983) was also used. No projection changes between maps were necessary, and no field data was collected. Flow direction of discharge according to the San Marcos contour lines and potential risk levels of each outfall. Final map showing potential risk levels of illicit discharge to each outfall. Created by: Elizabeth Garcia, Jacqueline Lara, Austin Holman, Max Higgins, George Sanchez