Urban Non-point-source Pollution Assessment Using a Geographical Information System

This paper present a micro-approach for establishing an effective mitigation strategy to control urban non-point-sources pollution. It also discusses the potential of using a geographical information system (GIS) to obtain precise estimates of pollutant loadings for individual sewersheds. In this micro-approach, a total of 11 sewersheds were delineated from digital versions of existing sewer maps. The pollutant loadings of individual land use polygons, derived as the collection unit from individual street blocks, were aggregated to get the total pollutant loadings of each sewershed. The SLAMM model was used to estimate pollutant loadings of five priority pollutants. To facilitate management and transfer of land use data for the non-point-source model, a GIS was used. Using GIS overlay analysis and database management capabilities, all the input data were generated for each land use polygon, and each polygon was assigned to appropriate sewersheds. Based on the model output, a critical sewershed was located. The pollutant loadings at major sewer junctions within the critical sewershed were estimated to establish a mitigation strategy. The selected strategy was the installation of wet ponds. Two different approaches were investigated: a regional approach using a large area to build a wet pond at the major sewer outfalls, and a multi-site approach using a number of smaller sites for each major sewer junction. The cost analysis shows the regional approach to be more cost effective, though providing less pollutant control.