Gasp IV urban model of cadmium flow

The 60-square-mile region of extreme northwest Indiana, which includes the cities of Gary and East Chicago, is a highly urbanized and industrialized area. Pollution data over the region show high levels of cadmium, a toxic metal. There are several hundred sources of cadmium in the area, and the impact of each type of source is unclear. An accurate representation of the flow of cadmium would make it possible to structure a reasonable and efficient policy for controlling cadmium pollution. This paper describes a GASP IV computer model for that flow. The basic model is an aggregate continuous model which displays the time behavior of cadmium levels in each of nineteen compartments over a two-year period. This aggregate model raises several ques tions regarding the effects of discrete events such as rainfall. Since the GASP IV language is capable of combined continuous-discrete simulation, these new factors are easily incorporated into the model. Results of the simulation show the relative impact of the various types of sources and provide some insight into control policies. A continuous model was first constructed. Then modifications based on real-world data were implemented as discrete events. The successive forms of the model proved useful for studying at least two of the characteristics of cadmium flow in an urban ecosystem.