IDOT needed to comply with an Environmental Protection Agency mandate to track illicit discharges into roadway drainage systems and map all storm sewer systems and outfalls. Through Professional Transportation Bulletin (PTB) 147, IDOT solicited qualified firms to provide survey, mapping, database, and GIS expertise in order to accomplish this goal, as well as to expand upon the existing GIS capabilities of the Department.

The team of R.E. Hamilton Consulting Engineers and Great Arc was selected for this project. Following project kickoff, the project team held a workshop with IDOT to perform a needs assessment of the various user groups within the Department and to determine the overall approach for the implementation of the NPDES GIS database.

Based on the input from the needs assessment, Great Arc completed the database design for the system. The database design included the appropriate feature classes, tables, and domains for both the immediate needs for outfall mapping and illicit discharge investigation as well as the planned future inclusion of storm water conveyance structures as well as scalability to accommodate data from all IDOT Districts state-wide.

A pilot area served as the initial focus for the data collection effort. R.E. Hamilton performed a GPS survey of the pilot area using survey-grade data collectors. Digital photographs and field notes were taken at each location for inclusion in the system as well. Following the field collection, Great Arc loaded the spatial and tabular data into the database. Scanned images of IDOT Location Drainage Study plans were linked to the appropriate segments of the pilot area for reference within the system.

To facilitate access to the information provided by the system, Great Arc developed a web-based application which allows users to view, query, and edit NPDES data. In this way, IDOT staff can access data without having desktop GIS installed on their workstations, and without the need for GIS expertise.