In 1972, Congress amended the Federal Water Pollution Control Act (commonly referred to as the Clean Water Act (CWA)) which prohibited the discharge of any pollutant to waters of the United States from a "point source" unless the discharge is authorized by a National Pollutant Discharge Elimination System permit. A "point source" is a single identifiable localized source of pollution such as an industry, business or a sewer system.
In 1987, the CWA was amended and established a $400 million program for States to develop and implement, on a watershed basis, nonpoint source management, because water quality studies showed sparse sources of water pollution were also significant causes of pollution. They called these sparse sources of pollutants a "nonpoint source.” A "nonpoint source" pollution is water pollution that is difficult to trace to a specific discharge point because it comes from many sources. Examples of common nonpoint source pollutants include fertilizers, pesticides, sediments, oils, salts, trace metals, and litter. Nonpoint sources come from locations such as farms, yards, roofs, construction sites, automobiles and streets.
Phase I of the U.S. Environmental Protection Agency’s (EPA) storm water program was promulgated in 1990 under the CWA. Phase I relies on National Pollutant Discharge Elimination System (NPDES) permit coverage to address storm water runoff from: (1) “medium” and “large” municipal separate storm sewer systems (MS4s) generally serving populations of 100,000 or greater, (2) construction activity disturbing 5 acres of land or greater, and (3) ten categories of industrial activity. On Sept. 17, 1998, control over storm water permitting shifted from EPA’s National Pollutant Discharge Elimination System (NPDES) program to Texas’ version, the Texas Pollutant Discharge Elimination System (TPDES).
Phase II rules for small municipalities and construction activity were finalized in December 1999. The TCEQ issued the Phase II MS4 Permit on Aug. 13, 2007, to small municipalities with residential populations under 100,000 (according to the 1990 Census Bureau). Phase II requires permit coverage for all small MS4s located within urbanized areas, where an urbanized area is defined by the U.S. Census Bureau as “a land area comprising one or more places — central place(s) — and the adjacent densely settled surrounding area — urban fringe — that together have a residential population of at least 50,000 and an overall population density of at least 1,000 people per square mile."