United States
                           Environmental Protection
                                 Office of Water                 EPA 833-F-00-003
                                    (4203)    January 2000 (revised December 2005)
                                                                Fact Sheet 2.1
Storm water  Phase   II
Final  Rule
  Stormwater Phase II
  Final Rule
  Fact Sheet Series
  1.0 - Stormwater Phase II Final
  Rule: An Overview
  Small MS4 Program
  2.0 - Small MS4 Stormwater
  Program Overview
  2.1 - Who's Covered? Designation
  and Waivers of Regulated Small
  2.2 - Urbanized Areas: Definition
  and Description
     Minimum Control Measures

  2.3 - Public Education and

  2.4 - Public Participation/

  2.5 - Illicit Discharge Detection
  and Elimination

  2.6 - Construction Site Runoff

  2.7 - Post-Construction Runoff

  2.8 - Pollution Prevention/Good
  2.9 - Permitting and Reporting:
  The Process and Requirements
  2.10 - Federal and State-Operated
  MS4s: Program Implementation

  Construction Program
  3.0 - Construction Program
  3.1 - Construction Rainfall
  Erosivity Waiver

  Industrial "No Exposure"
  4.0 - Conditional No Exposure
  Exclusion for Industrial Activity
                           Who's  Covered?  Designation and
                           Waivers of Regulated Small  MS4s
   Who Is Affected by the Phase II Small MS4 Program?

      The Stormwater Phase II Final Rule applies to operators of regulated small municipal
      separate storm sewer systems (MS4s), which are designated based on the criteria discussed
   in this fact sheet. In this fact sheet, the definition of an MS4 and the distinction between small,
   medium, and large MS4s is reviewed. Conditions under which a small MS4 may be designated
   as a regulated small MS4, as well as the conditions for a waiver from the Phase II program
   requirements, are outlined. This fact sheet also attempts to clarify possible implementation
   issues related to determining one's status as an operator of a regulated small MS4.

   What Is a Municipal Separate Storm Sewer System (MS4)?

   \\ 7"^ constitutes an MS4 is often misinterpreted and misunderstood. The term MS4 does
    W not solely refer to municipally-owned storm sewer systems, but rather is a term of art with
   a much broader application that can include, in addition to local jurisdictions, State departments
   of transportation, universities, local sewer districts, hospitals, military bases, and prisons.  An
   MS4  also is not always just a system of underground pipes - it can include roads with drainage
   systems, gutters, and ditches. The regulatory definition of an MS4 is provided below.
          According to 40 CFR 122.26(b)(8), "municipal separate storm sewer
          means a conveyance or system of conveyances (including roads with
          drainage systems, municipal streets, catch basins, curbs, gutters, ditches,
          man-made channels, or storm drains):

             (i)  Owned or operated by a State, city, town, borough, county,
                 parish, district, association, or other public body (created by or
                 pursuant to State law)...including special districts under State law
                 such as a sewer district, flood control district or drainage district,
                 or similar entity, or an Indian tribe or an authorized Indian tribal
                 organization, or a designated and approved management agency
                 under section 208 of the Clean Water Act that discharges into
                 waters of the United States.

             (ii)  Designed or used for collecting or conveying stormwater;

             (iii) Which is not a combined sewer; and

             (iv) Which is not part of a Publicly Owned Treatment Works
                  (POTW) as defined at 40 CFR 122.2."

Fact Sheet 2.1 - Who's Covered? Designation and Waivers of Regulated Small MS4s
                                            Page 2
What Is a Small, Medium, or Large MS4?

Q   EPA's NPDES (National Pollutant Discharge
     Elimination System) stormwater permitting program
     labels MS4s as either "small," " medium," or "large" for
     the purposes of regulation.

Q   A small MS4 is any MS4 that is not already covered by
     the Phase I stormwater program. Small MS4s include
     Federally-owned systems, such as military bases.

Q   The Phase I stormwater program covers medium
     and large MS4s. Phase I MS4s were automatically
     designated nationwide as medium MS4s if they were
     located in an incorporated place or county with a
     population between 100,000 - 249,999 or as large MS4s
     if located in an incorporated place or county with a
     population of 250,000 or greater.  Many MS4s in areas
     below 100,000 in population, however, have
     been individually brought into the Phase I program by
     NPDES permitting authorities. Such already regulated
     MS4s do not have to develop a Phase II program.

Are All Small MS4s Covered by the Phase II
Final Rule?

    No. The universe of small MS4s is quite large since it
    includes every MS4 except for the approximately 900
medium and large MS4s already regulated under the Phase I
stormwater program. Only a select sub-set of small MS4s,
referred to as regulated small MS4s, is covered by the
Phase II Final Rule, either through automatic nationwide
designation or designation on a case-by-case basis by the
NPDES permitting authority.

How Is  A Small MS4 Designated as a Regulated
Small MS4?

A    small MS4 can be designated by the permitting authority
    as a regulated small MS4 in one of three ways:

O Automatic  Nationwide Designation

    The Phase II  Final Rule requires nationwide coverage
    of all operators of small MS4s that are located within
    the boundaries of a Bureau of the Census-defined
    "urbanized area" (UA) based on the latest decennial
    Census. Once a small MS4 is designated into the
    program based on the UA boundaries, it cannot be
    waived from  the program if in a subsequent UA
    calculation the small MS4 is no longer within the UA
    boundaries. An automatically designated small MS4
    remains regulated unless,  or until, it meets the criteria
    for a waiver.
    Urbanized Areas
     An urbanized area (UA) is 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. It is a calculation used by the
     Bureau of the Census to determine the geographic
     boundaries of the most heavily developed and
     dense urban areas.
    EPA has developed a set of digitized maps for each
    urbanized area as defined by the 2000 U.S. Census.
    These maps are organized by state and are available
    at http://www.epa.gov/npdes/stormwater/urbanmaps.
    Additionally, information about urbanized areas is
    available directly from the U.S. Bureau of the Census
    at http://www.census.gov/geo/www/ua/
Potential Designation by the NPDES Permitting
Authority - Required Evaluation

An operator of small MS4 located outside of a UA may
have been designated as a regulated small MS4 if the
NPDES permitting authority determined that its
discharges cause, or have the potential to cause, an
adverse impact on water quality.  The Phase II Final Rule
required the NPDES permitting authority to develop a set
of designation criteria and apply them, at a minimum,
to all small MS4s located outside of a UA  serving a
jurisdiction with a population of at least 10,000 and a
population density of at least 1,000 people/square mile.

Q  Designation Criteria
    EPA recommended that the NPDES permitting
    authority use a balanced consideration of the
    following designation criteria on a watershed or
    other local basis:

       •   Discharge to sensitive waters;
       •   High population density;
       •   High growth or growth potential;
       •   Contiguity to a UA;
       •   Significant contributor of pollutants to
            waters of the United States; and
       •   Ineffective protection of water quality
            concerns by other programs.

Fact Sheet 2.1 - Who's Covered? Designation and Waivers of Regulated Small MS4s
                                                 Page 3
    Potential Designation by the NPDES Permitting
    Authority - Physically Interconnected

    Under the final rule, the NPDES permitting authority was
    required to designate any small MS4 located outside of a
    UA that contributes substantially to the pollutant loadings
    of a physically interconnected MS4 regulated by the
    NPDES stormwater program.  The final rule did not set a
    deadline for designation of small MS4s meeting this
   Physically interconnected means that one MS4 is
   connected to a second MS4 in such a way that it
   allows for direct discharges into the second system.
State and EPA permitting authorities can be contacted to
obtain a full list of regulated MS4s, including both
automatically designated MS4s and those that were
additionally designated.

Are Waivers from the Phase II Permit/Program
Requirements Possible?

    Yes, two waiver options are available to operators of
    automatically designated small MS4s if discharges do not
cause, or have the potential to cause, water quality

The first applies where:

   (1)  the jurisdiction served by the system is less than
        1,000 people;

   (2)  the system is not contributing substantially to the
        pollutant loadings of a physically interconnected
        regulated MS4; and

   (3)  if the small MS4 discharges any pollutants identified
        as  a cause of impairment of any water body to which
        it discharges, stormwater controls are not needed
        based on wasteload allocations that are part of an
        EPA approved or established  "total maximum daily
        load" (TMDL) that addresses the pollutant(s) of
      TMDLs are water quality assessments that
      determine the source or sources of pollutants of
      concern for a particular waterbody, consider the
      maximum amount of pollutants the waterbody
      can assimilate, and then allocate to each source
      a set level of pollutants that it is allowed to
      discharge (i.e., a "wasteload allocation"). Small
      MS4s that are not given a wasteload allocation
      would meet the third criterion above.
The second applies where:

   (1)  the jurisdiction served by the system is less than
        10,000 people;

   (2)  an evaluation of all waters of the U.S. that receive a
        discharge from the system shows that stormwater
        controls are not needed based on wasteload
        allocations that are part of an EPA approved or
        established TMDL that addresses the pollutant(s)
        of concern or an equivalent analysis; and

   (3)  it is determined that future discharges from the small
        MS4 do not have the potential to result in
        exceedances of water quality standards.

The NPDES permitting authority is required to periodically
review any waivers granted to MS4 operators to determine
whether any information required for granting the waiver has
changed. Minimally, such a review needs to be conducted
once every five years.

Are There Allowances for Phasing-in Permit

    Yes. Small MS4s serving a jurisdiction with a population
    under 10,000 can be phased-in for permit coverage,
following establishment of a State watershed permitting
approach. NPDES permitting authorities that choose this
option must establish a schedule to phase-in permit coverage
annually for approximately 20 percent  of all small MS4s that
qualify for such phased-in coverage. Where this option is
followed, all regulated small MS4s are required to have
permit coverage no later than March 8, 2007.

Fact Sheet 2.1 - Who's Covered?  Designation and Waivers of Regulated Small MS4s
                                              Page 4
Can More than One MS4 in the Same Political
Jurisdiction Be Automatically Designated?

    Yes.  Since the final rule provides automatic coverage
    of all small MS4s within a UA, the result would likely be
coverage of several governments and agencies with multiple,
perhaps overlapping, jurisdictions.  For example, a city that is
located within a UA and operates its own small MS4 could be
designated alongside the State's department of transportation
(DOT) and the county's DOT if the State and county operate
roads that are within the borders of the city. All three
entities would be responsible for developing a stormwater
management program for the portion of their respective
MS4s within the city limits. In such a case, the permittees
are strongly encouraged to work together to form a unified
stormwater management program.

Who Is Responsible  if the Small MS4 Operator
Lacks the Necessary Legal Authority?

   Some regulated small MS4s may lack the necessary legal
   authority to implement one or more of the required
minimum control measures that comprise the Phase II
storm water management program.  For example, a local
government that is a small MS4 operator may be in a State
that does not have an enabling statute that allows local
regulatory  control of construction site runoff into the sewer
system.  Another example is a State DOT that may not have
the legal authority to require and enforce controls on illicit
discharges into its system.  In these situations the small MS4
is encouraged to work with the neighboring regulated small
MS4s. As co-permittees, they could form a shared
stormwater management program in which each permittee is
responsible for activities that are within their individual legal
authorities and abilities.
            For Additional Information

"^ U.S. EPA Office of Wastewater Management
    http ://www. epa. gov/npdes/stormwater
    Phone: 202-564-9545

"^ Your NPDES Permitting Authority. Most States and
    Territories are authorized to administer the NPDES
    Program, except the following, for which EPA is the
    permitting authority:
    District of Columbia
    New Hampshire
    New Mexico
    American Samoa
Johnston Atoll
Midway and Wake Islands
Northern Mariana Islands
Puerto Rico
Trust Territories
    A list of names and telephone numbers for each EPA
    Region and State is located at http://www.epa.gov/
    npdes/stormwater (click on "Contacts").
Reference Documents
"^ EPA's Stormwater Web Site
    http ://www. epa. gov/npdes/stormwater
      •  Stormwater Phase II Final Rule Fact Sheet Series
      •  Stormwater Phase II Final Rule (64 FR 68722)
      •  National Menu of Best Management Practices
        for Stormwater Phase II
      •  Measurable Goals Guidance for Phase II Small
      •  Stormwater Case Studies
      •  EPA Urbanized Area Maps: http://www.epa.gov/
"^ Census 2000 Urbanized Area Information
      •  General Information: http://www.census.gov/
      •  Maps: http://www.census.gov/geo/www/maps/