Using Geodatabases to Track NPDES Permit Requirements

Many state and municipal agencies are required to develop a stormwater management program as part of their National Pollutant Discharge Elimination System (NPDES) permit. Custom field tools, like the geodatabase KCI developed for transportation agency clients, not only maps the organization’s statewide Municipal Separate Storm and Sewer System (MS4) and logs water quality investigations, but also facilitates organized storage and future analysis of pertinent information.

Geodatabase Water Quality Investigation FormKCI’s customized geodatabase contains both attribute information (e.g., pipe materials) as well as geographic coordinate-based locations. It also produces accurate map renderings and opens many doorways to both spatial analysis and advanced queries.

While all the elements required for the NPDES permit can be incorporated into a geodatabase, this article focuses on applying a customized database specifically for the illicit discharge detection and elimination (IDDE). The IDDE evaluation takes into consideration multiple factors, such as land use and the structure’s proximity to streams and aging sanitary lines. Using available geographic information system (GIS) layers, pertinent attributes such as age can be queried in order to perform a proximity analysis with the MS4. Targeted features can be exported and maps created for field crews to use for screening.

While the scientist’s focus is on identifying flow, odor or staining to detect potential illicit discharges (PIDs), we have found that field notes on the surrounding area are useful in documenting ease of access for the structure or other potential concerns for the area. Crews use the customized geodatabase to record all the field observations and access a running history of prior visits and the issues identified.

In addition to detecting PIDs during dry weather screening, we receive reports through two other avenues: our MS4 inventory/inspection field team and external reports (e.g., public works staff, citizens). Housing the report source information within the geodatabase serves a greater purpose than good documentation practice. It functions as a tool for statistically evaluating the most frequently used reporting avenue, which can then support certain resource allocations. For example, if the statistics indicated MS4 reports as the most frequently used avenue, then we may consider devoting a few more resources to the MS4 task.

Investigate PID. In addition to the visual observations, the team conducts field testing on select parameters when dry weather flow is observed. These parameters, such as detergents, have pre-established benchmarks, and if any of the results exceed those benchmarks, a sample is sent to a certified lab for further analysis. Each parameter result is housed as a field in the database, allowing for in-depth analysis of all previous investigations for either a single parameter or a combination of them.

Water Quality Investigation

Track/Source the Flow. After a discharge has been determined to be illicit, it’s time to investigate the source. The permit requires mapping of the outfalls, but we have found that mapping the entire system allows for a quick assessment of the system’s extent, and can show what type of drainage structures are involved. Our teams also take advantage of camera-on-a-stick  technology that allows for the viewing of underground drainage pipes, which can lead to the identification of additional discharge sources that would not otherwise be visible, such as a polyvinyl chloride (PVC) pipe punched into the side of a larger pipe. The photos taken are then housed directly in the geodatabase, which enhances the organization and thoroughness of each of our investigations.

Eliminate the Source. Once the source of the discharge has been identified, efforts are then made to eliminate it. Part of this work includes a significant public awareness effort, which may require door hangers to be distributed to houses near the affected area. These door hangers identify the type of illicit discharge detected and provide general information on good residential practices, such as not rinsing paint brushes in the catch basins. We record the type of discharge and the number of door hangers distributed in the NPDES database to help quantify efforts to educate the public and eliminate illicit discharges. This information is required by the NPDES permit to be included in the annual report to regulatory agencies.

Affected Water Bodies. NPDES permits require permittees to name and depict the location of all waters that receive outfall discharges. Our geodatabase can be used to query the number of outfalls discharging to a particular waterbody, or perform a spatial analysis using our MS4 data and the available stream layer. We can even take it a step further and use our stream distance field to perform statistical analysis on the distance of outfalls to the nearest stream.

Reporting/Documentation. The most significant advantage to using a geodatabase to manage NPDES data is through documentation and reporting. The database stores all the information in a centralized and organized location, thereby facilitating an efficient summarization of all IDDE activities. A well-developed geodatabase can also be a powerful asset during a regulatory agency NPDES audit. Whether documentation for the last 20 IDDE investigations, or for one particular determination is requested, the information can be found in one location through a relatively quick process. The characteristics of a geodatabase also open doorways to other opportunities, such as producing auto-populated report templates, which reduce documentation efforts and enable field teams to dedicate more time toward investigating a PID.

Geodatabase Water Quality Report

Additional Uses and Power of the Database. A robust database can be leveraged for workflows outside of the IDDE Program. For instance, delineating drainage areas for outfalls or Best Management Practices (BMPs) without the use of a formal stormwater report can be conducted with a higher accuracy when the surrounding MS4 data is available in GIS format. This GIS data can be used in conjunction with a contours layer to help identify areas where a subsurface drainage system negates the natural path water would travel. Additionally, a geodatabase can be used to organize inventory, inspection and maintenance information for BMPs. This not only aides in meeting the post-construction stormwater management requirements of the NPDES permit, but also serves as an additional source of information for future construction projects. The historical inspections provide valuable insight to the effectiveness of a BMP at various points during its lifespan.

Benefits of Customized Database. KCI’s customized geodatabase is proving to be a one stop-shop for tracking NPDES permit requirements. The possibilities have extended beyond the MS4 Inventory or IDDE Programs to the integration of other intra-departmental modules, such as stormwater design and pesticide management.