Storm Water Phase II

Final Rule 

Fact Sheet Series

Overview

1.0 – Storm Water Phase II Final

Rule: An 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

2.4 – Public Participation/

Involvement

2.5 – Illicit Discharge Detection

and Elimination

2.6 – Construction Site Runoff

Control

2.7 – Post-Construction Runoff

Control

2.8 – Pollution Prevention/Good

Housekeeping

2.9 – Permitting and Reporting: 

The Process and Requirements

2.10 – Federal and State-Operated

MS4s: Program Implementation

Construction Program

3.0 – Construction Program

Overview

3.1 – Construction Rainfall

Erosivity Waiver

Industrial “No Exposure”

4.0 – Conditional No Exposure

Exclusion for Industrial Activity

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.

 	
 
  	  

	 
 
! "###

$
% 	
 & '

	
	



	

	




	


As discussed in Fact Sheet 2.1, Who’s Covered? Designation and Waivers of Regulated

Small MS4s, the Phase II Final Rule covers 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.

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. An urbanized area can comprise places, counties, Federal Indian

Reservations, and minor civil divisions (MCDs - towns and townships).

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 Phase II Final Rule. 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 operators of small MS4s

located within the boundaries of the UA are covered under the Phase II Final Rule, regardless of

political boundaries. Operators of small MS4s located outside of the UA are subject to potential

designation into the Phase II MS4 program by the NPDES permitting authority.
Fact Sheet 2.2 — Urbanized Areas: Definition and Description Page 2

1719D

County A

County B

FIR

Town B

Town A

Central Place

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

Figure 1

Operators of small MS4s can determine if they are located

within a UA, and therefore covered by the Phase II storm

water program, through the following two steps:

— STEP 1 —

Refer to a listing of incorporated places, MCDs, and counties

that are located entirely or partially within a UA. Such a

listing, based on the 1990 Census, can be found in Appendix

6 to the Preamble of the Phase II Final Rule; it does not

include governmental entities already permitted under

Phase I. If a small MS4 is located in a listed incorporated

place, MCD, or county, then the operator of the small MS4

should follow step (2) below. (Note: Appendix 6 can be

obtained from the EPA Office of Wastewater Management

(OWM) or downloaded from the OWM web site.)

— STEP 2 —

Some operators of small MS4s may find that they are located

within an entity listed in Appendix 6 but not know if their

systems are within the urbanized portion of the listed entity. 

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 or 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 OWM.

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 of UA boundaries. 

The Bureau of the Census web site includes a list of

contact names and phone numbers for the data in each

State at 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 UA boundaries in any

given area.

 County or Regional Planning Commissions/

Boards

As with State agencies, these entities are likely to have

detailed UA data and maps to help determine UA

boundaries.
Fact Sheet 2.2 — Urbanized Areas: Definition and Description Page 3

For Additional Information

Contact

 U.S. EPA Office of Wastewater Management

• Phone: (202) 564-9545

• Internet: www.epa.gov/npdes/stormwater

Reference Documents

 Storm Water Phase II Final Rule Fact Sheet Series

• Internet: cfpub.epa.gov/npdes/stormwater/swfinal.cfm

 Storm Water Phase II Final Rule (64 FR 68722)

• Internet: www.epa.gov/npdes/regulations/phase2.pdf

 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/msgeo12.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).

 U.S. EPA

EPA is modifying a web-based geographic program

called Enviromapper. This will allow MS4 operators

to enter a location and see a detailed map of the UA

boundary. Information about Enviromapper will be

available at www.epa.gov/owm/phase2.

How Will the Year 2000 Census Affect the

Determination of Status as a Regulated Small

MS4?

The listing of incorporated places, MCDs, and counties

located within UAs in the United States and Puerto Rico,

found in Appendix 6, 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, operators of small MS4s located within the revised

boundaries of former 1990 UAs, or in any newly defined

2000 UAs, become regulated small MS4s and must develop a

storm water management program.

Any additional automatic designations of small MS4s based

on subsequent census years is 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 can 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).