Green infrastructure concepts originated in mid-1980s proposals for best management practices that would achieve more holistic stormwater quantity management goals for runoff volume reduction, erosion prevention, and aquifer recharge. In 1987, amendments to the U.S. Clean Water Act introduced new provisions for management of diffuse pollutant sources from urban land uses, establishing the regulatory need for practices that unlike conventional drainage infrastructure managed runoff "at source." The U.S. Environmental Protection Agency (EPA) published its initial regulations for municipal separate storm sewer systems ("MS4") in 1990, requiring large MS4s to develop stormwater pollution prevention plans and implement "source control practices". EPA's 1993 handbook, "Urban Runoff Pollution Prevention and Control Planning", identified best management practices to consider in such plans, including vegetative controls, filtration practices and infiltration practices (trenches, porous pavement). Regulations covering smaller municipalities were published in 1999. MS4s serve over 80% of the US population and provide drainage for 4% of the land area.