United States
Environmental Protection
Agency
Office of Water
(4203)
EPA 833-F-99-003
April 1999
Fact Sheet 2.1
vvEPA
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
Who's Covered? Designation and
Waivers of Regulated Small MS4s
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.
Who Would Be Affected by the Proposed Phase II Small MS4 Program?
The Storm Water Phase II Proposed Rule would apply to public owners or operators of regulated
small municipal separate storm sewer systems (MS4s), which are determined by specific criteria
as discussed in this fact sheet. To aid in determining whether an MS4 would meet these criteria, this
fact sheet reviews the definition of an MS4 and distinguishes between small, medium, and large
MS4s. 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 owner or
operator of a regulated Phase II small MS4.
What Is a Municipal Separate Storm Sewer System (MS4)?
What constitutes an MS4 is often misinterpreted and misunderstood. An MS4 is not meant to
refer to municipally-owned storm sewer systems only, but rather it is a term of art with a much
broader application. Owners or operators of MS4s, in addition to local jurisdictions, could be State
and Federal departments of transportation, universities, local sewer districts, hospitals, military bases,
and prisons. Also, an MS4 is not necessarily merely a system of underground pipes. It also can
include roads with drainage systems, gutters, and ditches. The existing 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 to 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 storm water;
(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."
The Phase II Proposed Rule would add Federal systems, such as military bases and prisons, to the
existing regulatory definition of an MS4 by changing paragraph 122.26(b)(8)(i) (see above) to read:
"Owned or operated by the United States, a State, city, town, borough, county...."
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Fact Sheet 2.1 - Who's Covered? Designation and Waivers of Regulated Small MS4s
Page 2
What is a Small, Medium, or Large MS4?
Urbanized Areas
Q
Q
Q
EPA's national storm water program labels MS4s as either
"small," " medium," or "large" for the purposes of
regulation.
A small MS4 is any MS4 that is not already covered by the
existing Phase I storm water program.
The Phase I storm water program covers medium and large
MS4s. Phase I MS4s were automatically designated
nationwide as medium MS4s if the systems served a
population between 100,000 - 249,999 people or as large
MS4s if the systems served a population of 250,000 or
more. Many MS4s that serve a population below 100,000,
however, have been individually brought into the Phase I
program by NPDES permitting authorities and are
considered medium or large MS4s, and not small MS4s,
regardless of the size of the population served.
Would All Small MS4s Be Covered by the Phase II
Proposed 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 storm water
program. Only a select sub-set of small MS4s, referred to as
regulated small MS4s, would be covered by the Phase II
Proposed Rule, either through automatic nationwide designation
or designation on a case-by-case basis by the NPDES permitting
authority.
How Would A Small MS4 Be Designated as a
Regulated Small MS4?
A small MS4 could be designated as a regulated small MS4 in
one of three ways:
O Automatic Nationwide Designation
The Phase II Proposed Rule would require nationwide
coverage of all owners or 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 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 would remain regulated unless, or
until, it meets the criteria for a waiver.
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.
At the time of permit issuance (not to exceed 3 years and
90 days after publication of the final Phase II rule), UA
calculations based on the 2000 Census are scheduled to
be completed and the regulated universe then would be
based on these new calculations. For more information
on UAs, see Fact Sheet 2.2.
Appendix 6 to the Preamble of the Phase II
Proposed Rule
Appendix 6 is a listing of all incorporated places and
counties that are fully or partially located within a UA
according to the 1990 Census. The list is meant to serve
as a general geographic reference for owners or operators
of small MS4s that are trying to determine their status in
regard to the Phase II criterion (located within a UA) for
automatic designation. Appendix 6 can be obtained from
the EPA Office of Wastewater Management or
downloaded from the OWM web site. See Fact Sheet 2.2
for more information on UAs and how to determine
potential coverage under the Phase II program.
It is important to note that Appendix 6 is not a listing of
all the Phase II regulated small MS4s. Because a
Phase II regulated small MS4 would be any small MS4
located within the boundaries of a UA, providing an
accurate nationwide list of these entities is not feasible at
this time.
In addition, Appendix 6 does not include incorporated
places and counties already permitted under Phase I.
Any small MS4s located in a Phase I incorporated place
or in the UA portion of a Phase I county (e.g., a Federal
prison), however, would be covered under the Phase II
program. This is particularly important to note in the
case of Federally owned or operated MS4s since they
were not covered nationally under Phase I and may exist,
unpermitted, in Phase I areas. A list of Phase I counties
and incorporated places can be obtained from the EPA
Office of Wastewater Management or downloaded from
the OWM web site.
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Fact Sheet 2.1 - Who's Covered? Designation and Waivers of Regulated Small MS4s
Page 3
Appendix 6 also does not include minor civil divisions
(towns and townships). A list of the minor civil divisions
that are functioning governmental entities and are entirely
or partially located within a U A can be obtained from the
EPA Office of Wastewater Management or downloaded
from the OWM web site.
Potential Designation by the NPDES Permitting
Authority (Required Evaluation)
Owners or operators of small MS4s located outside of a UA
could be designated as regulated small MS4s if the NPDES
permitting authority determines that the discharges from the
small MS4 cause, or have the potential to cause, an adverse
impact on water quality. The Phase II Proposed Rule would
require 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 an area with a
population of at least 10,000 and a population density of at
least 1,000 people per square mile.
Q Designation Criteria
EPA recommends 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 control of water quality
concerns by other programs.
Q Appendix 7 to the Preamble of the Phase II
Proposed Rule
Appendix 7 is a listing of all incorporated places and
counties, located outside of a UA, that have a population
of at least 10,000 and a population density of at least
1,000 people per square mile. As with Appendix 6, the
list is meant to serve as a geographic reference only.
Owners or operators of small MS4s located within a
listed area should be aware that they could be examined
by their NPDES permitting authority for potential
designation into the Phase II program. Appendix 7 can
be obtained from the EPA Office of Wastewater
Management or downloaded from the OWM web site.
It is important to note that Appendix 7 is not a complete
listing of all potentially designated small MS4s because
the NPDES permitting authorities may require any small
MS4 that is contributing pollutants to waters of the U.S.
to be permitted.
Q Deadline for Designation
The NPDES permitting authority would be required to
designate small MS4s meeting the designation criteria
within 3 years and 90 days of publication of the final
rule, or within 5 years if a watershed plan is in place.
Potential Designation by the NPDES Permitting
Authority
Under the proposed rule, the NPDES permitting authority
would be required to designate any small MS4 located outside
of a UA that contributes substantially to the storm water
pollutant loadings of a physically interconnected MS4
regulated by the NPDES storm water program. The proposed
rule does not set a deadline for designation of small MS4s
meeting this criterion.
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.
Does the Proposal Provide a Waiver from the
Phase II Permit/Program Requirements?
Yes, if a regulated small MS4's discharges have been
determined to not cause, or have the potential to cause, water
quality impairment. A waiver option would be available to
owners or operators of automatically designated small MS4s
where:
(1) the jurisdiction served by the system is less than 1,000
people;
(2) the system is not contributing substantially to the storm
water pollutant loadings of a physically interconnected
regulated MS4; and
(3) the owner or operator can certify that storm water
controls are not needed based on "total maximum daily
loads" (TMDLs) assessments or a comprehensive
watershed plan that includes the equivalents of TMDLs.
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.
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Fact Sheet 2.1 - Who's Covered? Designation and Waivers of Regulated Small MS4s
Page 4
To obtain a waiver, the owner or operator would be responsible
for certifying on a form, provided by the NPDES permitting
authority, that the three waiver criteria have been met
and therefore implementation of storm water controls is not
necessary. Since the waiver is indefinite, the owner or operator
would not need to recertify every 5 years.
Could Multiple Jurisdictions in the Same
Urbanized Area Be Designated?
Yes. Since the proposed rule would provide 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
would be designated alongside the State's department of
transportation (DOT) and the county's DOT if the State and
county own or operate roads that are within the borders of the
city. All three entities would be responsible for developing a
storm water management program for the portion of their
respective MS4s within the city limits. In such a case, the
permittees would be strongly encouraged to work together to form
a unified storm water management program.
Who Would Be Responsible if the Small MS4
Owner/Operator Lacks the Necessary Legal
Authority?
For Additional Information
Contact
^ U. S. EPA Office of Wastewater Management
• Phone: 202260-5816
E-mail: SW2@epa.gov
Internet: www.epa.gov/owm/sw2.htm
Reference Documents
ISP 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
"^ 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
Some regulated small MS4s may lack the necessary legal
authority to implement one or more of the required minimum
control measures that comprise the proposed 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. In such cases, the
NPDES permitting authority would be responsible for
implementation of the particular minimum control measure.
Another example is a State DOT that may not have the legal
authority to require and enforce controls on illicit discharges into
its system. Since the regulated portion of a DOT system would
likely run through the area of, or connect to, another regulated
small MS4, the DOT would be encouraged to work with the
neighboring regulated small MS4. As co-permittees, they could
form a shared storm water management program in which each
permittee is responsible for activities that are within their
individual legal authorities and abilities.
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