United States	Office of Water	EPA 833-F-99-004

Environmental Protection	(4203)	April 1999

Agency	Fact Sheet 2.2

SEPA

Storm Water Phase II
Proposed Rule
Fact Sheet Series

Overview

1.0 - Storm Water Phase II
Proposed Rule Overview

Small MS4 Program

2.0	- Small MS4 Storm Water
Program Overview

2.1	- Who's Covered? Designation
and Waivers of Regulated Small
MS4s

2.2	- Urbanized Areas: Definition
and Description

Minimum Control Measures

2.3	- Public Education and
Outreach Minimum Control
Measure

2.4	- Public Participation/
Involvement Minimum Control
Measure

2.5	- Illicit Discharge Detection and
Elimination Minimum Control
Measure

2.6	- Construction Site Runoff
Control Minimum Control Measure

2.7	- Post-Construction Runoff
Control Minimum Control Measure

2.8	- Pollution Prevention/Good
Housekeeping Minimum Control
Measure

2.9	- Permitting and Reporting:
The Process and Requirements

2.10	- Federal and State-Owned
MS4s: Program Implementation

Construction Program

3.0 - Construction Program
Overview

Industrial "No Exposure"

4.0 - Conditional No Exposure
Exemption for Industrial Activity

Storm Water Phase II
Proposed Rule

Urbanized Areas:

Definition and Description

This fact sheet is based on the Storm Water Phase II Proposed Rule. Therefore, the information provided herein is subject to
change upon publication of the final Phase II rule in November 1999. A revised series of fact sheets will be provided at that
time. A comprehensive list of the current fact sheets is in the text box at left.

As discussed inFact Sheet 2.1, Who's Covered? Designation and Waivers of Regulated Small
MS4s, the proposed Phase II regulations would cover all small municipal separate storm sewer
systems (MS4s) located within an "urbanized area" (UA). Based on the 1990 Census, there are 405
UAs in the United States that cover 2 percent of total U.S. land area and contain approximately 63
percent of the Nation's population. These numbers include Puerto Rico - the only U.S. Territory with
UAs.

UAs constitute the largest and most dense areas of settlement. UA calculations delineate boundaries
around these dense areas of settlement and, in doing so, identify the areas of concentrated
development. UA designations are used for several purposes in both the public and private sectors.
For example, the Federal Government has used UAs to calculate allocations for transportation
funding, and some planning agencies and development firms use UA boundaries to help ascertain
current, and predict future, growth areas.

What Is an Urbanized Area (UA)?

The Bureau of the Census determines UAs by applying a detailed set of published UA criteria
(see 55 FR 42592, October 22, 1990) to the latest decennial census data. Although the full UA
definition is complex, the Bureau of the Census' general definition of a UA, based on population and
population density, is provided below.

An urbanized area 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.

The basic unit for delineating the UA boundary is the census block. Census blocks are based on
visible physical boundaries, such as the city block, when possible, or on invisible political boundaries,
when not. How an urbanized area is determined varies slightly on the geographic entity, be it a place,
county, Federal Indian reservation, or minor civil division (towns and townships), as explained below:

~ Place. A "place," whether an incorporated place or a Census-designated place, is included in its
entirety even if all of its census blocks are not densely settled. Therefore, this part of the UA
determination is based on place boundaries. In rare cases (128 places), a place is not included in
its entirety, but rather only partly included within the UA, usually due to the existence of large
expanses of vacant or very sparsely populated territory within its incorporated area.


-------
Fact Sheet 2.2 - Urbanized Areas: Definition and Description

Page 2

~	County/Federal Indian reservation. A county is
included in its entirety only if all of its census blocks,
based on the county's unincorporated area, meet the UA
criteria. Unlike a place, a county is often "split" into
urbanized and non-urbanized portions, with no regard for
political boundaries. Only small MS4s in the urbanized
portion of a split county would be automatically covered
under the Phase II Proposed Rule. If a county or sewer
district, for example, operates a small MS4 that runs
throughout a split county, it would only be required to
implement the storm water program in the portion of the
county that is within the UA. The same situation applies to
split Federal Indian reservations, as well as minor civil
divisions (see below).

~	Minor Civil Division (towns & townships). Twenty
states have functioning subdivisions of counties called
minor civil divisions (MCDs). MCDs are towns or
townships, depending on the State. Like a county, a MCD
is included in its entirety only if all of its census blocks
meet the urbanized area criteria. A MCD is often "split"
into urbanized and non-urbanized portions, with no regard
for political boundaries. Only small MS4s in the urbanized
portion of a split MCD would be automatically covered
under the storm water Phase II proposal. Where a small
MS4 runs throughout a split MCD, the owner/operator of
the small MS4 would only be responsible for implementing
the storm water program in the portion of the MCD that is
within the UA.

How Can Status as a Regulated Small MS4 Be
Determined?

The drawing below (see Figure 1) is a simplified UA
illustration that demonstrates the concept of UAs in relation
to the proposed storm water Phase II regulations. The "urbanized
area" includes within its boundaries incorporated places, a portion
of a Federal Indian reservation, an entire MCD, a portion of
another MCD, and portions of two counties. Any and all owners
or operators of small MS4s located within the boundaries of the
UA would be covered under the Phase II Proposed Rule,
regardless of political boundaries. Owners and operators of small
MS4s located outside of the UA would be subject to potential
designation into the Phase IIMS4 program by the NPDES
permitting authority.

Once the concept of a UA is understood, the owner or operator
can proceed to determining their location in relation to a UA.

Figure 1

Pvvj Central Place
o Incorporated Place

Federal Indian Reservation (FIR)

Unincorporated "Urbanized
Area" Portion of a Town
(MCD) or County

	Urbanized Area

	Town or Township as a

functioning Minor Civil Division
(MCD). An MCD is the primary
subdivision of a County.

	 County

1719D

_ J


-------
Fact Sheet 2.2 - Urbanized Areas: Definition and Description

Page 3

Owners and operators of small MS4s can determine if they are
located within a UA, and therefore covered by the Phase II storm
water program as proposed, through the following two steps:

—	STEP 1 —

Refer to a listing of incorporated places, MCDs, and counties in
UAs. Such a listing, based on the 1990 Census, can be found in
Appendix 6 in the preamble to the proposed rule, although it does
not include MCDs or governmental entities already permitted
under Phase I. A similar listing, based on the 2000 Census, may
be published with the storm water general permit for regulated
small MS4s. If a small MS4 is located in a listed incorporated
place, then it would be covered by the Phase II program. If a
small MS4 is not located in a listed incorporated place, but is
located in a listed MCD or county, then the owner or operator of
the small MS4 would need to follow step (2) below. (Note:
Listings of Phase II incorporated places, MCDs, and counties
located entirely or partially within a UA can be obtained from the
EPA Office of Wastewater Management or downloaded from the
OWM web site.)

—	STEP 2 —

Some owners and operators of small MS4s may find their
counties or MCDs on the list but not know, due to the occurrence
of split counties and MCDs, if their systems are within the
urbanized portion of the county or MCD. In such a case, they
should contact one or more of the following institutions for more
detailed information on the location of the UA boundary:

~ The State/NPDES Permitting Authority (may be the
State or the U.S. EPA Region)

Storm Water Coordinators: The NPDES permitting
authority may be the State or the U.S. EPA Region.
The Storm Water Coordinators for each U.S. EPA
Region are listed in the For Additional Information
section in Fact Sheet 2.9. These regional contacts
can assist with UA information and provide the
names of State storm water contacts. Regional and
State contact information can also be obtained from
the EPA Office of Wastewater Management.

State Data Centers: Each State's Data Center
receives listings of all entities that are located in
UAs, as well as detailed maps and electronic files
ofUA boundaries. The Bureau of the Census web site
includes a list of contact names and phone numbers
for the data centers in each State
(www .census .gov/sdc/www/).

State Planning/Economic/Transportation Agencies:
These agencies typically use UAs to assess current
development and forecast future growth trends and,
therefore, should have detailed UA information
readily available to help determine the exact UA
boundaries in any given area.

~	County or Regional Planning Commissions/ Boards

As with State agencies, these entities are likely to
already have detailed UA data and maps to help
determine UA boundaries.

~ The Bureau of the Census

Urbanized Areas Staff: 301 457-1099

Web Site: www.census.gov
The site provides information on purchasing UA
maps and electronic files for use with computerized
mapping systems. Obtain free UA cartographic
boundary files (Arc/Info export format) for
Geographical Information System (GIS) use at:
www.census.gov: 80/geo/www/
cob/ua.html.

UA Maps: Detailed UA maps are available for
purchase with a $25 minimum order ($5 per map
sheet). Each map sheet measures 36 by 42 inches.
For prices and a listing of UAs, visit
www.census.gov/mp/www/geo/msgeo 12.html. Order
from the Department of Commerce, Bureau of the
Census (MS 1921), P.O. Box 277943, Atlanta, GA
30384-7943 (Phone: 301 457-4100; Toll-free fax:
1-888-249-7295).

~	The Local Library (or State Data Center) for Book of
UA Maps

The following book contains small maps of each UA
and detailed listings of all geographic entities located
within them:

1990 Census of Population and Housing.
Supplementary Reports. Urbanized Areas
of the United States and Puerto Rico.
1990 CPH-S-1-2 (2 sections, sold as a set).

The UA book also can be ordered from the
Government Printing Office by calling 202 512-1800
(approximate cost is $56).


-------
Fact Sheet 2.2 - Urbanized Areas: Definition and Description

Page 4

How Will the Year 2000 Census Affect the
Determination of Status as a Regulated Small MS4?

he listing of incorporated places and counties located

within UAs in the United States and Puerto Rico, found
in Appendix 6 of the proposed rule, is based on the 1990
Census. New listings for UAs based on the 2000 Census
are scheduled to be available by July or August of 2001.
Once the official 2000 Census listings are published by the
Bureau of the Census, owners or operators of small MS4s
located within the revised boundaries of former 1990 UAs,
or in any newly defined 2000 UAs, would be required to
seek NPDES storm water permits.

Additional automatic designations of small MS4s based on
the Year 2000 Census and subsequent census years would
be governed by the Bureau of the Census' definition of a
UA in effect for that year and the UA boundaries
determined as a result of the definition.

Once a small MS4 is designated into the Phase II storm
water program based on the UA boundaries, it would not 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 will remain regulated
unless, or until, it meets the criteria for a waiver (see Fact
Sheet 2.1 for more information on the regulated small MS4
waiver option).

Contact

U.S. EPA Office of Wastewater Management
• Phone : 202 260-5816
E-mail: SW2@epa.gov
Internet: www.epa.gov/owm/sw2.htm

Reference Documents

Storm Water Phase II Proposed Rule Fact Sheet
Series.

Contact the U.S. EPA Water Resource Center at
202 260-7786 or at waterpubs@epa.gov
Internet: www.epa.gov/owm/sw2.htm

For Additional Information

Storm Water Phase II Proposed Rule, published on
Jan. 9, 1998 in the Federal Register (63 FR 1536).
Internet: www.epa.gov/owm/sw2.htm


-------