Area sources contribute to 26 percent of all man-made air toxic emissions according to EPA estimates.
Other area sources of air pollution are: Water pollution manifestations of an area source—often called nonpoint source pollution—include: In the 1950s or earlier hydrology transport models appeared to calculate surface runoff, primarily for flood forecasting.
Beginning in the early 1970s computer models were developed to analyze the transport of runoff carrying water pollutants, which considered dissolution rates of various chemicals, infiltration into soils and ultimate pollutant load delivered to receiving waters.
One of the earliest models addressing chemical dissolution in runoff and resulting transport was developed in the early 1970s by the United States Environmental Protection Agency.
[3][full citation needed] This computer model formed the basis of much of the regulatory framework that led to strategies for water pollution control via land use and chemical handling techniques.