This is the federal stormwater program. In 1972, the NPDES program was essentially the regulatory mechanism
of the Clean Water Act (CWA) which the Environmental Protection Agency (EPA) used to focus on industrial process wastewater
and municipal sewage discharges. These sources were identified as being responsible for severely degraded water quality. In
1987, in an effort to mitigate diffuse sources of pollution conveyed in stormwater runoff, Congress enacted the Water Quality
Act, an amendment to the CWA a comprehensive program to regulate stormwater.
EPA promulgated the Phase I stormwater rule on November 16, 1990. This rule targeted stormwater discharges
from communities with a population of at least 100,000 (termed by EPA as medium and large municipal separate storm sewer systems
or MS4s), as well as stormwater discharges associated with certain industrial activities and construction sites impacting five
acres or more of land. In Arizona, there were 8 entities targeted by the Phase I stormwater program. They included, Phoenix,
Mesa, Tempe, Glendale, Scottsdale, Tucson, Pima County and the Arizona Department of Transportation (ADOT).
The Phase II stormwater rule was promulgated on December 8, 1999 and focused on small MS4s. Small MS4s were
communities serving a population of less than 100,000 or communities greater than 100,000 (based on the 2000 census) not captured
by the Phase I program that are located in an “urbanized” area or designated by the permitting authority. In addition to the MS4s,
Phase II also focused on federal and state facilities including prisons, hospitals and universities, municipally owned/operated
industrial facilities and lastly construction sites greater or equal to one acre and less than five acres in size.
It is the unincorporated areas of Maricopa County within the urbanized area that are the areas regulated by
the Phase II permitting program.