Phase I:

The National Pollutant Discharge Elimination System (NPDES) Phase I storm water program, initiated in 1990, required discharges from large construction sites, certain industrial activities and operators of "medium" or "large" MS4s (MS4s that serve a population of 100,000 or greater), to obtain permits and implement a storm water management program as a means to control polluted discharges from these activities. Since 1984, the Rhode Island Department of Environmental Management (RIDEM) has been the delegated authority to implement the NPDES program in Rhode Island (referred to as RIPDES).

Phase II:

The Environmental Protection Agency (EPA) finalized on December 8, 1999, the Storm Water Phase II Rule, that requires MS4s to obtain permits and establish a storm water management program that is intended to improve waterbodies by reducing the quantity of pollutants that can enter storm sewer systems during storm events.

The Storm Water Phase II Rule extends the coverage of the NPDES storm water program to include "small" MS4s. The Phase II Rule automatically covers on a nationwide basis all small MS4s located in "urbanized areas" (UAs) as defined by the Bureau of the Census. Small MS4s located outside of UAs may be subject to future designation on a case-by-case basis.

The RIPDES Program amended the RIPDES Regulations and has included Phase II storm water requirements (amended February 5, 2003)