 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.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.