Chapter 4 aims at quantication of generation, transport, and loads of constituents in stormwater runoff originating from urban impervious surfaces and roads. This chapter will deal with pollutants in terms of their origin and transport and their characteristics at the point where they are discharged and enter into the environment or treatment facilities. It is considered important to focus on methods for estimation of the loads in this respect. This chapter will also give examples of what are considered characteristic levels of the pollutants well knowing that such levels are subject to a considerable variability (cf. Section 2.4). Last, it is important to include expressions and formulations that can be applied for modeling the pollutant loads. The subjects dealt with here are a continuation of the more general descriptions and concepts dealt with in Chapters 2 and 3.