The United States Environmental Protection Agency (EPA) developed the National Pollutant Discharge Elimination System (NPDES) program in response to the 1987 Amendments to the Clean Water Act.  The goal the NPDES storm water program is to reduce the amount of pollution in the nation's storm water runoff and is requiring communities to develop a comprehensive storm water quality management for preventing local waterways from becoming polluted storm water runoff.  Phase I of the NPDES storm water program was developed in 1990 for medium and large Municipal Separate Storm Sewer Systems (MS4s) (incorporated places or counties with populations of 100,000 or more), industrial activities, and construction activities that disturbed five or more acres of land.  Phase II was developed in 1999 and required NPDES permit coverage for discharges from small MS4s and construction activities disturbing between one and five acres of land.  The City of Gary is covered under the requirements of Phase II.

The State of Indiana, through the Department of Environmental Management (IDEM), enacted what is commonly known as Rule 13 (in 327 IAC, Article 15) in 2003 to comply with the NPDES program.  All MS4’s entities in Indiana must adhere to in order to be in compliance.