United States Environmental
Protection Agency and the
EPA Region III states of
Pennsylvania, Maryland,
Delaware, District of Columbia,
Virginia and West Virginia
EPA833-F-07-009
Understanding Impaired Waters and Total
Maximum Daily Load (TMDL) Requirements
for Municipal Stormwater Programs
January 2008
Does your municipal separate storm sewer system (MS4)
contribute a pollutant of concern to an impaired waterbody,
a waterbody with an approved Total Maximum Daily Load
(TMDL), or to a tributary of the Chesapeake Bay? If so, you most
likely need to take steps to modify your municipal stormwater
management program to meet state and federal National
Pollutant Discharge Elimination System
(NPDES) regulations.
This document describes
how municipal stormwater
managers can determine
if their storm drain
system discharges to
an impaired waterbody
and how to update their
stormwater management
program to address the TMDL.
\t r o d (A ft to
Sources of fecal coliform
in Four Mile Run, Virginia
In the Mid-Atlantic Region, stormwater runoff is a leading source
of stream impairments. Stormwater runoff contributes to the
primary pollutants impairing the Chesapeake Bay— nitrogen,
phosphorus, and sediment.
Section 303(d) of the Clean Water Act requires that states
develop impaired waters lists for rivers, lakes, coastal waters,
and estuaries that do not meet water quality standards. These
303(d) lists are published biannually and are available at the web
link listed in the Resources section of this document. TMDLs,
developed for waterbodies placed on the list, specify the maximum
amount of a pollutant that a waterbody can receive in order to
meet water quality standards. Regulations governing the TMDL
program (40 CFR 130.2 and 130.70) define the TMDL as "the sum
of the individual wasteload allocations (WLAs) for point sources
and load allocations (LAs) for nonpoint sources." Mathematically
the TMDL can be represented by the following equation:
TMDL = ZtVLA +
Where MOS is the margin of safety.
+ MOS
WLAs are generally expressed in numeric form (e.g., 500 Ibs/day
phosphorus). Municipal stormwater sources, which are regulated
as point sources under the NPDES program, are included as part
of the wasteload allocations. Non-NPDES permitted areas are
included as LAs.
If your MS4 is affected by a TMDL, a numeric WLA will be
assigned and your NPDES permit, when it is reissued or revised,
will include effluent limits consistent with the requirements
of the WLA. These TMDL requirements convey the goal of the
Clean Water Act and the implementing NPDES regulations
which is to not cause or contribute to exceedance of water
quality standards. However, EPA recognizes the difficulty in
characterizing stormwater discharges because of the highly
variable frequency and duration of storm events. Therefore, EPA
issued a memorandum on November 22, 2002 that recommends
initially expressing NPDES permit requirements (effluent limits)
for NPDES-regulated municipal stormwater sources as best
management practices (BMPs) rather than as numeric effluent
limits.www.epa.gov/npdes/pubs/final-wwtmdl.pdf
This BMP approach provides more flexibility to MS4s, but
requires that MS4s monitor and evaluate BMPs. When
BMPs are not found to be effective, expanded or better-
tailored BMPs may be necessary to attain water quality.
-to Address TMPL
gut renews i* M S4 P emits
The following five steps will help you determine if TMDL
requirements apply to you and, if so, how to comply with those
requirements. The first two steps describe how to determine if
your MS4 discharges to an impaired waterbody. If your MS4 does
not discharge to an impaired waterbody, you will only need to
complete steps 1 and 2.
1. Determine if the waterbody into which your MS4 discharges is
impaired, has a TMDL assigned, or drains to the Chesapeake
Bay
2. Determine what requirements apply to your MS4
3. Update your stormwater management program
4. Implement programs and practices to address the TMDL
5. Assess effectiveness of the stormwater program in
addressing pollutant(s) of concern
Step 1: Determine if the waterbody into which your
MS4 discharges is impaired, has a TMDL assigned,
or drains to the Chesapeake Bay
The first step is to identify the waterbodies into which your MS4
discharges. Most MS4s have developed maps of their outfalls and
receiving waters. You should use your maps to develop a list of
all the named and unnamed waterbodies into which your outfalls
discharge. To facilitate the process to determine impairment
status, you should include stream codes as assigned by states.
One source of information on waterbodies is EPA's Enviromapper
for Water (www.epa.gov/waters/enviromapper/index.html). This
Web-based system can map receiving waters in your jurisdiction.
Once you have the list of waterbodies into which your MS4
discharges, you will need to determine if any of these waterbodies
-------
EPA833-F-07-009
Understanding Impaired Waters and Total Maximum Daily Load (TMDL) Requirements for Municipal Stormwater Programs
are impaired, have been assigned a TMDL or drain to the
Chesapeake Bay and therefore are covered by a state Tributary
Strategy. This determination can be made by reviewing your state
303(d) list, state TMDL list, Chesapeake Bay Program web site or
contacting your state stormwater coordinator or TMDL coordinator.
Links to state 303(d), TMDL lists, and Chesapeake Bay Program
website are included in the Resources section of this document.
EPA's EnviroMapper for Water
Step 2: Determine what requirements apply to your
MS4
Review your NPDES MS4 permit to identify specific TMDL
allocations or requirements pertaining to MS4 stormwater
discharges to impaired waterbodies. You will most likely find
these requirements under the Special Conditions section of
your MS4 NPDES stormwater permit. Keep in mind that NPDES
permits have five year permit terms; therefore, your requirements
for discharges to impaired waters might change as your state
reissues your MS4 stormwater permit.
Impaired waterbodies for which a TMDL has not yet been
developed. Contact your state TMDL coordinator to determine
the schedule for TMDL development. You may be asked to
participate in or supply information for the TMDL development
process for impaired waterbodies that do not yet have an
approved TMDL. Your participation in the TMDL process will likely
mean attending public meetings as a stakeholder and providing
information that will assist in characterizing your MS4 system.
TMDL development is a data-intensive exercise; therefore you
should provide the best available data related to your stormwater
discharges, such as outfall locations, drainage areas, types
and locations of structural and non-structural BMPs, as well as
the expected or measured pollutant load reductions from the
BMPs. This information supports calculation of an accurate and
reasonable WLA for your system.
Impaired Waterbodies with approved TMDLs. Review TMDL
reports and supporting documents to identify WLA(s) assigned
to your MS4 and review the approach and assumptions used to
calculate the WLA(s). Depending on the availability of information
and the technical approach used to develop the TMDL, a
TMDL might assign your MS4 a specific WLA or use a broader
approach, such as assigning an aggregate WLA to several MS4s.
In some cases, the TMDL might assign an aggregate WLA to all
permitted stormwater sources (e.g., MS4s, industrial facilities,
and construction sites) because data are not available to make
source-specific allocations.
Given the general WLAs assigned to MS4s, it is often beneficial
to estimate more specifically the pollutant loads and reductions
needed within and across the MS4. For more examples of
methods to estimate MS4 contributions, please refer to
"Summary of 17 TMDLs with Stormwater Sources" listed in the
resources section of this document. The following are some
suggestions for estimating your MS4's specific contribution to
the impaired waterbodies pollutant(s) of concern:
• General estimation: Assess to what extent your MS4
discharge contributes to the water quality impairment
listed in the 303(d) list, TMDL or Chesapeake Bay Tributary
Strategy. Land use patterns, in particular, impervious cover
and vegetation, influence the volume and rate of runoff and
the type of pollutants found in stormwater runoff. Assessing
the amount and location of industrial and commercial, light
medium and dense residential areas, etc., provides a rough
indication of the amount and type of pollutant loads to
anticipate from these areas. The Chesapeake Bay Program
web site and EPA published reports on urban stormwater
contain common pollutant levels found in urban storm water
runoff based on land use.
• More refined estimation: Once you have an indication of the
types of pollutant loads that may emanate from your MS4
during a storm, you may either directly monitor your discharge
and/or estimate through simple calculations or models,
to get a better sense of what is causing the water quality
standard exceedances and where in your jurisdiction are the
anticipated hotspots. This effort can include reviewing existing
monitoring data (if available) or conducting new stormwater
outfall monitoring, estimating pollutant loads using common
computational methods such as the Simple Method
(www.stormwatercenter.net/monitoring%20and%20
assessment/simple%20meth/simple.htm), or modeling
using any number of computer models. EPA's SWMM Model
is one such model that simulates stormwater runoff quantity
and quality in any given area (www.epa.gov/ednnrmrl/
models/swmm/index.htm). Additional TMDL models are
available from EPA's Watershed and Water Quality Modeling
Technical Support Center (www.epa.gov/athens/wwqtsc/).
Getting a better sense of your MS4's specific contribution to the
pollutants of concern will enable you to design and implement the
most appropriate controls in the best locations across your MS4.
For example, several TMDLs have been established for
waters within for the city of Portland, Oregon and surrounding
municipalities. These TMDLS include WLAs for all urban areas,
within and adjacent to the MS4 boundaries (Portland's NPDES
permit is available at www.deq.state.or.us/wq/stormwater/
municipalphl.htm). As a result, the aggregated WLA assigned to
Portland includes contributions from areas outside their control
and does not separate allocations to each MS4 jurisdiction
separately. The City of Portland and its co-permittees refined the
WLAs in the TMDLs by delineating the land area within each MS4
-------
EPA833-F-07-009
Understanding Impaired Waters and Total Maximum Daily Load (TMDL) Requirements for Municipal Stormwater Programs
boundary, estimating the stormwater runoff for each jurisdiction,
and apportioning the WLA for each MS4.
For additional examples of how TMDLs have been implemented
through stormwater permits, the following reports may be
useful: "Summary of 17 TMDLs with Stormwater Sources"
(www.epa.gov/owow/tmdl/17_TMDLs_Stormwater_Sources.pdf)
and "Total Maximum Daily Loads and National Pollutant
Discharge Elimination System Storm Water Permits for Impaired
Water Bodies: A Summary of State Practices" (www.epa.gov/
region5/water/wshednps/topic_tmdls.htm).
Step 3: Update your stormwater management
program
You should consider updating your MS4 stormwater management
program and associated legal documents (e.g., stormwater
ordinances) to address the allocations in the TMDL (relevant
WLAs). For those waterbodies that do not yet have a TMDL
issued, consult your MS4 NPDES permit and your state
stormwater coordinator to determine what intermediate steps
can be taken to address those impairments.
Updates to your MS4 stormwater management program will
be based on estimations of pollutant loads emanating from
various land uses across your MS4 as described in Step 2 and
an understanding of what BMPs can be put in place to target
those pollutants. There are several resources available to assist
with the design of appropriate BMPs to reduce pollutant loads.
For instance, the International Stormwater BMP Database
(www.bmpdatabase.org) or the SWMM model mentioned above,
can be used as aids in this process to help the municipality
devise a suite of BMPs that will meet the requirements of the
effluent limits based on the TMDL or reduce the pollutants of
concern in the impaired waterbody.
In addition to revising your stormwater management program,
you may be invited to participate in the development of a TMDL
Implementation Plan to specifically address implementation of
any TMDLs in your watershed. Maryland, Virginia and Delaware
currently require development of TMDL Implementation Plans (in
Delaware, these plans are called Pollution Control Strategies).
An Implementation Plan describes and quantifies the types of
activities to be implemented, along with a time frame to meet the
WLA. Because most TMDLs cross multiple jurisdictions, these
TMDL Implementation Plans are often developed by a group of
stakeholders. Additional information on TMDL implementation
plans can be found at:
• Virginia - www.deq.virginia.gov/tmdl/implement.html
• Maryland - www.mde.state.md.us/Programs/
WaterPrograms/TMDL/implementation.asp
• Delaware - www.dnrec.state.de.us/water2000/Sections/
Watershed/ws/pcs.htm
An example of how an MS4 updated its program to address
TMDLs is once again provided by the city of Portland, Oregon. In
Portland, TMDLs and wasteload allocations have been developed
for two watersheds. Pollutants include among others, bacteria,
phosphorus and pesticides.
To comply with the effluent limits based on the TMDL WLAs,
Portland conducted a thorough review of its existing MS4
stormwater management program and identified additional
activities necessary to fulfill new MS4 permit requirements for
stormwater discharges to waters with assigned TMDLs. The city
developed performance measures for each BMP and numeric
benchmarks for each pollutant as required by the permit (e.g.
reduction of 436 Ibs/day of phosphorous), as well as modified
the existing stormwater monitoring program to evaluate progress
towards achieving the benchmarks. The city used the GRID
model to model pollutant loads and develop benchmarks.
BMPs included such things as instream flow control, riparian
tree protection and planting, culvert replacement, streambank
restoration, and water quality facilities. If any new TMDLs
are developed and approved for impaired waters within the
MS4 boundary, the city of Portland will have 18 months to
again review and update its existing stormwater management
program to ensure current BMPs adequately address new WLAs.
Information on Portland's stormwater management program is
available at www.portlandonline.com/bes/index.cfm?c=31892.
Step 4: Implement programs and practices to
address the TMDL
The crucial step is to implement the programs and practices
described in your updated stormwater management plan to
address the effluent limits based on the TMDL and to reduce
the pollutant(s) of concern. These programs can range from
tailoringyour public education and outreach to pet owners in
order to reduce fecal coliform, to installing a series of BMPs
such as porous pavement, percolation trenches, and biofilters in
dense residential areas to capture the first flush and reduce any
number of pollutants including nutrients, BOD or sediment.
Implementation will require proper budgeting and oversight to
ensure BMPs are built or enacted appropriately and effectively.
Step 5: Assess Effectiveness of the Stormwater
Program in Reducing Pollutant(s) of Concern
Because implementation of most MS4 WLAs will be BMP-based,
it is critical to assess the effectiveness of those BMPs and your
stormwater management program in meeting the effluent limits
based on the WLA. NPDES regulations require such assessment.
The EPA document Evaluating the Effectiveness of Municipal
Stormwater Programs describes different approaches available to
evaluate effectiveness of the stormwater management program.
Some steps you can take to evaluate the effectiveness of your
program in reducing the pollutants of concern include:
• Track BMPs. Develop a process to inventory the type and
quantity of existing structural and non-structural BMPs and
determine the current pollutant load reductions from these
practices based on estimated or modeled reduction estimates.
It is also helpful to track the year of installation and applicable
design standards, where available. This information will help
you to document compliance with the TMDL.
• /Assess BMP monitoring data for the pollutant(s) of concern.
Review BMP performance data collected through monitoring
-------
EPA833-F-07-009
Understanding Impaired Waters and Total Maximum Daily Load (TMDL) Requirements for Municipal Stormwater Programs
programs, including BMP performance data collected
regionally. Conduct early reviews of BMP monitoring data
to gauge whether BMPs are generating the expected flow
volume and pollutant load reductions anticipated. Address
BMP performance issues if early data indicate that BMPs are
not performing as expected. Implement additional BMPs, if
necessary, to provide additional pollutant load reductions.
/Assess water quality monitoring data for the pollutant(s) of
concern, and/or data on TMDL surrogates such as flow or
percent impervious cover. Review data from outfall monitoring
and/or ambient water quality monitoring, to determine the
impact of stormwater discharges on water quality. Other
possible sources of local data to help characterize discharges
from your MS4 include local watershed management
plans, university studies and reports, or reports generated
by departments with stormwater management related
responsibilities (e.g., public works department catch basin
cleaning or street sweeping reports).
M i(e
TMPL
rettd
MS4
Watershed Overview
Four Mile Run is one of the most urbanized watersheds in
Northern Virginia and has been included in Virginia's 303(d) list
as being impaired by bacteria. In May 2002, EPA approved the
Fecal Coliform TMDL for Four Mile Run (available at
www.novaregion.org/bacteriatmdl.htm).
Four Mile Run TMDL Map
-»
Arlington
County
County
Regulated MS4s in the Four Mile Run Watershed
The Fecal Coliform TMDL for Four Mile Run documents bacteria
contributions from Fairfax and Arlington Counties, which are
both Phase I MS4s covered under individual permits, as well
as Alexandria and Falls Church, which are both Phase II MS4s
covered under general permits.
Four Mile Run TMDL Wasteload Allocations for
MS4s
The technical approach used to develop the TMDL focused on
modeling runoff from impervious surfaces in the watershed to
determine wasteload allocations for the MS4s. The wasteload
allocation assigns all MS4s one aggregate wasteload allocation
(average annual fecal coliform loadings of 9.61E+14 counts/year
for pervious lands, and 2.04E+13 counts/year for impervious
lands). The TMDL modeling estimated that bacteria will need to
be reduced by 98% from human and canine sources to achieve
water quality standards for bacteria.
TMDL Implementation Plans
The Four Mile Run TMDL Implementation Plan (available at
www.novaregion.org/bacteriaimplementation.htm), finalized
in May 2004, documents the commitments of each jurisdiction
to address bacteria contributions. Many of the activities
documented in the implementation plan are activities that
were already required under each jurisdiction's respective
MS4 permit (e.g., illicit discharge detection and elimination).
The implementation plan focuses on pollution prevention
practices (such as illicit discharge controls and proper pet waste
disposal), mitigation measures (such as stormwater treatment
using sand filters), and indirect measures (such as general
outreach). The implementation plan also
includes a timeline for implementation and
monitoring/evaluation measures.
Connecting Chesapeake
Bay Requirements to TMDL
Implementation and MS4
Stormwater Management Programs
Each MS4 in the Four Mile Run watershed
is subject to Virginia's 1988 Chesapeake
Bay Preservation Act and, subsequently,
has a local Chesapeake Bay Preservation
Ordinance that requires the assessment
of stormwater impacts from development
and redevelopment on local tributaries to
the Chesapeake Bay. These stormwater
management efforts, tied to local
Chesapeake Bay Preservation Ordinances
are incorporated into each jurisdiction's
MS4 stormwater management program
and documented in the Four Mile Run
TMDL Implementation Plan.
Four Mile Run Watershed
-------
U.S. EPA-Paula Estornell
estornell.paula@epa.gov
Delaware—Peder Hansen
peder.hansen@state.de.us
EPA833-F-07-009
Understanding Impaired Waters and Total Maximum Daily Load (TMDL) Requirements for Municipal Stormwater Programs
Other Resources
Ventura, California, MS4 Permit
www.swrcb.ca.gov/rwqcb4/html/programs/stormwater/
State TMDL Websites venturaMs4.html
EPA Region 3 TMDL website: www.epa.gov/reg3wapd/tmdl/index.htm Portland, Oregon, MS4 Permit
Delaware: www.dnrec.state.de.us/water2000/Sections/Watershed/ www.deq.state.or.us/wq/stormwater/munlclpalphl.htm
TMDL/tmdlinfo.htm
District of Columbia: http://app.doh.dc.gov/services/administration_
offices/environmental/services2/water_division/report.shtm
Maryland: www.mde.state.md.us/Programs/WaterPrograms/TMDL/
index.asp
Pennsylvania: www.dep.state.pa.us/watermanagement_apps/tmdl
Virginia: www.deq.state.va.us/tmdl/develop.html
West Virginia: www.wvdep.org/item.cfm?ssid=ll&sslid=930
State 303(d) Lists
Reports and lists for all Region 3 states are available at: www.epa.gov/
reg3wapd/tmdl/303d.htm
General TMDL Information
EPA TMDL website: www.epa.gov/owow/tmdl
EPA November 22, 2002 Memorandum Establishing Total Maximum Daily
Loads (TMDL) Wasteload Allocations (WLAs) for Storm Water Sources and
NPDES Permit Requirements Based on Those WLAs.
www.epa.gov/npdes/pubs/final-wwtmdl.pdf
Tota/ Maximum Daily Loads and National Pollutant Discharge Elimination
System Storm Water Permits for Impaired Water Bodies: A Summary of
State Practices
www.epa.gov/r5water/wshednps/pdf/state_practices_report_fina!3_
09_07.pdf
Summary of 17 TMDLs with Stormwater Sources: www.epa.gov/reg3wapd/
tmdl/StormwaterResources
Region 3 TMDL Modeling Toolbox: www.epa.gov/athens/wwqtsc/
BMP Monitoring Guidance or Resources
Chesapeake Bay Program BMP Efficiencies and Definitions:
www.chesapeakebay.net/pubs/subcommittee/nsc/uswg/BMP_
Pollutant_Removal_Efficiencies.pdf
NOTE: This document is not law or regulation; it provides
recommendations and explanations that MS4s may consider in
determining how to comply with requirements of the CWA and
NPDES permit requirements.
Chesapeake Bay State Tributary Strategies Websites
Chesapeake Watershed Profile website www.chesapeakebay.net/
wshed.htm
Delaware: www.dnrec.state.de.us/water2000/Sections/Watershed/ws/
map_chesapeake.htm
District of Columbia: http://doh.dc.gov/doh/cwp/view,a, 1374,q,586841,
dohNav_GID,1802,dohNav, |33200 |33215|.asp
Maryland: www.dnr.state.md.us/bay/tribstrat/index.html and
www.dnr.state.md. us/bay/tribstrat/implementation_plan/urban.pdf
Pennsylvania: www.depweb.state.pa.us/chesapeake/cwp/view.asp?a=
3&Q=442886&chesapeakeNav= 1299581
Virginia: www.deq.virginia.gov/bay
West Virginia: www.wvnet.org
------- |