DRAFT

Chesapeake Bay Total Maximum Daily Load

September 24, 2010

U.S. Environmental Protection Agency

Region 3

Water Protection Division

Office of Regional Counsel

Philadelphia, Pennsylvania

U.S. Environmental Protection Agency

Region 3

Chesapeake Bay Program Office

Annapolis, Maryland

and

U.S. Environmental Protection Agency

Region 2

Division of Environmental Planning and Protection

New York, New York

in coordination with

U.S. Environmental Protection Agency

Office of Water

Washington, D.C.

and in collaboration with

Delaware, Maryland, New York,

Pennsylvania, Virginia,

West Virginia and the District of Columbia
DRAFT Chesapeake Bay TMDL

ii September 24, 2010

Draft Chesapeake Bay TMDL Executive Summary

Introduction

The U.S. Environmental Protection Agency has released the draft Chesapeake Bay Total 

Maximum Daily Load (TMDL), a ―pollution diet‖ that will compel sweeping actions to restore 

the Chesapeake Bay and its vast network of streams, creeks and rivers.

The TMDL was prompted by insufficient restoration progress over the last several decades in the 

Bay. The TMDL is required under federal law and responds to consent decrees in Virginia and 

D.C. dating back to the late 1990s. It is also a keystone commitment of a federal strategy to meet 

President Obama‘s Executive Order to restore and protect the Bay.

The draft TMDL – the largest ever developed by EPA – includes pollution limits to meet water 

quality standards in the Bay and its tidal rivers. The TMDL is designed to ensure that all 

pollution control measures to fully restore the Bay and its tidal rivers are in place by 2025, with 

60 percent of the actions completed by 2017. The final TMDL will be established December 31. 

On July 1, EPA set draft Bay watershed limits for nitrogen and phosphorus at 187.4 million and 

12.5 million pounds per year, respectively, and on Aug. 13 set a range of allowable sediment 

pollution levels at between 6.1 and 6.7 billion pounds per year. These pollution limits were 

further divided by jurisdiction and major river basin based on state-of-the-art modeling tools, 

extensive monitoring data, peer-reviewed science, and close interaction with state partners.

The TMDL is supported by accountability measures to ensure cleanup commitments are met, 

including short-and long-term benchmarks, a tracking and accounting system, and additional 

federal backstop measures, if necessary, to spur progress. 

EPA incorporated federal backstop measures into the draft TMDL because of deficiencies in the 

majority of draft pollution reduction plans submitted by the states and District of Columbia in 

early September. Most of these draft Watershed Implementation Plans (WIPs) did not identify 

programs to sufficiently reduce pollution to meet TMDL allocations and provide assurance the 

programs could be implemented. As a result, EPA‘s backstop measures focus on tightening 

controls on federally permitted point sources of pollution, such as wastewater treatment plants, 

large animal agriculture operations and municipal stormwater systems. 

EPA proposed more extensive backstop allocations for Pennsylvania, Virginia, New York, 

Delaware and West Virginia. Only minor changes were made to the plans for Maryland and the 

District of Columbia. The jurisdictions will have the opportunity to revise and strengthen their 

plans before final versions are due on November 29. During this time, EPA will engage 

jurisdictions to share best approaches from the WIPs across the jurisdictions and provide EPA 

guidance on the most effective pollution controls. When those final WIPs are submitted, EPA 

will again evaluate the plans to determine if EPA backstop allocations can be replaced with 

sufficiently improved state commitments.

The release of the draft TMDL begins a 45-day public comment period that will include 18 

public meetings in all six watershed states and the District of Columbia. The public meeting 
DRAFT Chesapeake Bay TMDL

iii September 24, 2010

schedule, including registration links for webinars, is at http://www.epa.gov/chesapeakebaytmdl. 

The website provides instructions for accessing the draft TMDL and providing comments. 

TMDL Background

The Clean Water Act sets as a goal that all waters in the United States be ―fishable‖ and 

―swimmable,‖ and requires states and the District of Columbia to establish water quality 

standards to measure the health of water bodies relative to these primary environmental goals. 

The Clean Water Act also requires jurisdictions to develop a list of waterways that are impaired 

by pollutants and do not meet water quality standards. A Total Maximum Daily Load (TMDL) 

must be developed for certain waterways on the impaired list. A TMDL is essentially a 

―pollution diet‖ that identifies the maximum amount of a pollutant the waterway can receive and 

still meet water quality standards.

Most of the Chesapeake Bay and its tidal waters are listed as impaired because of excess 

nitrogen, phosphorus and sediment. These pollutants cause algae blooms that consume oxygen 

and create ―dead zones‖ where fish and shellfish cannot survive, block sunlight that is needed for 

underwater grasses, and smother aquatic life on the bottom. The high levels of nitrogen, 

phosphorus and sediment enter the water from agricultural operations, urban and suburban 

runoff, wastewater facilities, air pollution and other sources, including septic systems. Despite 

some reductions in pollution during the past 27 years of restoration due to extensive efforts by 

federal, state and local governments; non-governmental organizations; and stakeholders in the 

agriculture, urban/suburban and wastewater sectors, there has been insufficient progress toward 

meeting the water quality goals for the Chesapeake Bay and its tidal waters.

Since 2000, the seven jurisdictions in the Chesapeake Bay watershed (Delaware, District of 

Columbia, Maryland, New York, Pennsylvania, Virginia, and West Virginia) and the U.S. 

Environmental Protection Agency, who along with the Chesapeake Bay Commission are partners 

in the Chesapeake Bay Program, have been planning for a Chesapeake Bay TMDL. 

Since September 2005, the seven jurisdictions have been actively involved in decision-making to 

develop the TMDL. In the October 2007 meeting of the Chesapeake Bay Program‘s Principals‘ 

Staff Committee, the jurisdictions and EPA agreed that EPA would establish the TMDL. Since 

2008, EPA has sent official letters to the jurisdictions detailing all facets of the TMDL, 

including: schedules for developing the TMDL and pollution reduction plans, EPA‘s 

expectations and evaluation criteria for jurisdiction plans to meet the TMDL pollution limits, 

reasonable assurance for controlling nonpoint source pollution, and backstop actions that EPA 

could take to ensure progress.

The TMDL also resolves commitments made in a number of consent decrees, Memos of 

Understanding, and settlement agreements dating back to the late 1990s that address certain 

waters identified as impaired in the District of Columbia, Delaware, Maryland and Virginia. 

Additionally, President Obama issued Executive Order 13508 on May 12, 2009, which directed 

the federal government to lead a renewed effort to restore and protect the Chesapeake Bay and its 

watershed. The Chesapeake Bay TMDL is a keystone commitment in the strategy developed by 

federal agencies to meet the President‘s Executive Order.
DRAFT Chesapeake Bay TMDL

iv September 24, 2010

More than 40,000 TMDLs have been completed across the United States, but the Chesapeake 

Bay TMDL will be the largest and most complex thus far – it is designed to achieve significant 

reductions in nitrogen, phosphorus and sediment pollution throughout a 64,000-square-mile

watershed that includes the District of Columbia and large sections of six states. The TMDL is 

actually a combination of 92 smaller TMDLs for individual Chesapeake Bay tidal segments and 

includes pollution limits that are sufficient to meet state water quality standards for dissolved 

oxygen, water clarity, underwater grasses and chlorophyll-a, an indicator of algae levels. It is 

important to note that the pollution controls employed to meet the TMDL will also have 

significant benefits for water quality in the tens of thousands of streams, creeks and rivers 

throughout the region. EPA will establish the final Chesapeake Bay TMDL, after considering 

public comments and additional input from the jurisdictions, by December 31, 2010.

Developing the Chesapeake Bay TMDL

Development of the Chesapeake Bay TMDL required knowledge of the stream flow 

characteristics of the watershed, sources of pollution, distribution and acreage of the various land 

uses, appropriate best management practices, the transport and fate of pollutants, precipitation

data and many other factors. The TMDL uses a series of models, calibrated to decades of water 

quality and other data, and refined based on input from dozens of Chesapeake Bay scientists. 

Modeling is an approach that uses observed and simulated data to replicate what is occurring in 

the environment, and was a critical and valuable tool to develop the Chesapeake Bay TMDL.

The development of the TMDL consisted of three major steps. 

1. EPA provided allocations to the jurisdictions and major basins for nitrogen, phosphorus 

and sediment.

2. Jurisdictions developed draft Phase 1 Watershed Implementation Plans to achieve those 

basin-jurisdiction allocations. In these WIPs, jurisdictions made decisions on how to 

further sub-allocate the basin-jurisdiction loadings to various individual point sources and 

a number of point and nonpoint source sectors.

3. EPA evaluated the draft WIPs and where deficiencies existed, EPA provided backstop 

allocations in the draft TMDL that consisted of a hybrid of the jurisdiction WIP 

allocations modified by EPA allocations for some source sectors to fill gaps in the WIPs.

These draft TMDL loadings to the basin-jurisdictions are provided in table ES-1. These loadings 

were determined using the best peer-reviewed science and through extensive collaboration with 

the jurisdictions and informed by the Watershed Implementation Plans.
DRAFT Chesapeake Bay TMDL

v September 24, 2010

Table ES-1. Chesapeake Bay TMDL watershed nutrient and sediment draft allocations by 

jurisdiction and by major river basin [proposed standards]

Jurisdiction Basin

Nitrogen draft 

allocations

(million lbs/year)

Phosphorus 

draft allocations

(million 

lbs/year)

Sediment draft 

allocations

(million lbs/year)

Pennsylvania Susquehanna 71.74 2.31

1,758.20

Potomac 4.72 0.42

233.93

Eastern Shore 0.28 0.01

21.12

Western Shore 0.02 0.001

0.37

PA Total 76.77 2.74

2,013.62

Maryland Susquehanna 1.08 0.05

62.94

Eastern Shore 9.71 1.09 169.70

Western Shore 9.74 0.46 170.38

Patuxent 2.85 0.21 90.12

Potomac 15.70 0.90 682.33

MD Total 39.09 2.72 1,175.47

Virginia Eastern Shore 1.21 0.16 10.91

Potomac 17.46 1.47 810.07

Rappahannock 5.84 0.90 688.51

York 5.41 0.54 107.09

James 23.48 2.34 852.77

VA Total 53.40 5.41 2,469.35

District of Columbia Potomac 2.32 0.12 11.16

DC Total 2.32 0.12 11.16

New York Susquehanna 8.23 0.52 292.96

NY Total 8.23 0.52 292.96

Delaware Eastern Shore 2.95 0.26 57.82

DE Total 2.95 0.26 57.82

West Virginia Potomac 4.67 0.74 248.11

James 0.02 0.01 16.65

WV Total 4.68 0.75 264.76

Total Basin/Jurisdiction Draft Allocation 187.44 12.52 6,285.14

Atmospheric Deposition Draft Allocation 15.70 -- --

Total Basinwide Draft Allocation 203.14 12.52 6,285.14

a. Cap on atmospheric deposition loads direct to Chesapeake Bay and tidal tributary surface waters to be achieved 

by federal air regulations through 2020.

Since nitrogen and phosphorus loadings from all parts of the Bay watershed have an impact on 

most segments of the Bay, it was necessary for EPA to allocate the nitrogen and phosphorus 

loadings in an equitable manner to the states and basins. There were 3 basic guides that were 

used to divide these loads. 
DRAFT Chesapeake Bay TMDL

vi September 24, 2010

Allocated loads should protect living resources of the Bay and its tidal tributaries and 

result in all segments of the Bay mainstem, tidal tributaries and embayments meeting 

water quality standards for dissolved oxygen, chlorophyll a, water clarity and underwater 

grasses. 

Tributary basins that contribute the most to the Bay water quality problems must do the 

most to resolve those problems (on a pound per pound basis).

All tracked and reported reductions in nitrogen, phosphorus and sediment loads are 

credited toward achieving final assigned loads. 

In addition, EPA is committing to reducing air deposition of nitrogen to the tidal waters of the 

Chesapeake Bay to 15.7 million pounds per year. The reductions will be achieved through 

implementation of federal air regulations during the coming years.

To insure that these pollutant loadings will attain and maintain water quality standards, the 

TMDL calculations were developed to account for critical environmental conditions a waterway 

would face, future growth, and seasonal variation. An implicit margin of safety was also 

included in the TMDL. 

The TMDL is designed to ensure that by 2025 all practices necessary to fully restore the Bay and 

its tidal river are in place, with 60 percent of the actions taken by 2017. 

As mentioned above, a TMDL must be based on achieving established state water quality 

standards. In the case of the Bay TMDL, as the TMDL is being developed, the state water quality 

standards are being proposed for modification. So the loadings allocated to the states as 

identified above and the state WIPs are based on loadings to achieve the proposed state 

standards. 

However, the Chesapeake Bay TMDL document also provides allocations for attaining the 

current water quality standards. In order to achieve the current standards, the allocations happen 

to be more stringent that the allocations identified above. This set of TMDL allocations are 

important if the state standards are not modified before the completion of the Bay TMDL.

Furthermore, this TMDL provides information on the pollution control levels for a full backstop 

TMDL, in case such controls are needed in the final TMDL. 

EPA expects that the water quality standards and state WIPs are likely to change before this 

TMDL is finalized. So offering information on possible TMDL loadings under each of these 

options provides EPA with the flexibility, informed by the final WIPs and public comment, to 

finalize this TMDL based on the relevant information at the time the TMDL is finalized. And the 

final TMDL allocations could range from full WIP based loads to full backstop loads, depending 

on the strength of the final state WIPs.

Accountability and Goals

The Chesapeake Bay TMDL is unique because of the extensive measures included to ensure 

accountability for reducing pollution and meeting deadlines for progress. The TMDL will be 

implemented using an accountability framework that includes Watershed Implementation Plans 

(WIPs), two-year milestones, EPA‘s tracking and assessment of restoration progress and, as 
DRAFT Chesapeake Bay TMDL

vii September 24, 2010

necessary, specific federal backstop actions if the jurisdictions do not meet their commitments. 

The accountability framework is being established in part to provide demonstration of the 

reasonable assurance provisions of the Chesapeake Bay TMDL pursuant to both the Clean Water 

Act and the Chesapeake Bay Executive Order, but is not part of the TMDL itself. 

When EPA establishes or approves a TMDL that allocates pollutant loads to both point and 

nonpoint sources, it determines whether there is a ―reasonable assurance‖ that the nonpoint 

source load allocations will be achieved and water quality standards will be attained. Reasonable 

assurance for the Chesapeake Bay TMDL is provided by the numerous federal, state and local 

regulatory and non-regulatory programs identified in the accountability framework that EPA 

believes will result in the necessary point and nonpoint source controls and pollutant reduction 

programs. The most prominent program is the CWA‘s National Pollutant Discharge Elimination 

System (NPDES) permit program that regulates point sources throughout the nation. Many 

nonpoint sources are not covered by a similar federal permit program; as a result, financial 

incentives and other voluntary programs are used to achieve nonpoint source reductions. These 

federal tools are supplemented by a variety of state regulatory and voluntary programs and other 

commitments of the federal government set forth in the Executive Order strategy and identified 

in the accountability framework discussed above.

Beginning in 2012, jurisdictions (including the federal government) are expected to develop twoyear milestones to track progress toward reaching the TMDL‘s goals. In addition, the milestones 

will demonstrate the effectiveness of the jurisdictions‘ WIPs by identifying specific near-term 

pollutant reduction controls and a schedule for implementation (see next section for further 

description of WIPs). EPA will review these two-year milestones and evaluate whether they are 

sufficient to achieve necessary pollution reductions and, through the use of a Bay Tracking and 

Accountability System, determine if milestones are met.

If a jurisdiction‘s plans are inadequate or its progress is insufficient, EPA can invoke a suite of 

backstop actions to ensure pollution reductions. These include expanding coverage of NPDES

permits to sources that are currently unregulated, increasing oversight of state-issued NPDES 

permits, requiring additional pollution reductions from point sources such as wastewater 

treatment plants, increasing federal enforcement and compliance in the watershed, prohibiting 

new or expanded pollution discharges, redirecting EPA grants, and revising water quality 

standards to better protect local and downstream waters.

Watershed Implementation Plans

The cornerstone of the accountability framework is the jurisdictions‘ development of Watershed 

Implementation Plans (WIPs), which serve as roadmaps for how and when a jurisdiction plans to 

meet its pollution allocations under the TMDL. In their draft Phase I WIPs, the jurisdictions were 

expected to subdivide the Bay TMDL allocations among pollutant sources; evaluate their current

legal, regulatory, programmatic and financial tools available to implement the allocations; 

identify and rectify potential shortfalls in attaining the allocations; describe mechanisms to track 

and report implementation activities; provide alternative approaches; and outline a schedule for 

implementation. 
DRAFT Chesapeake Bay TMDL

viii September 24, 2010

EPA provided the jurisdictions with detailed expectations for WIPs in November 2009 and April 

2010. To assist with WIP preparation, EPA provided considerable technical and financial

assistance. Also last year, EPA announced target loads to allow the jurisdictions to begin 

developing WIPs. EPA worked with the jurisdictions to evaluate various ―what if‖ scenarios –

combinations of practices and programs that could achieve their pollution allocations.

After the draft Phase I WIP submittal deadline of September 1, a team of EPA sector experts 

conducted an intense evaluation process, comparing the submissions with EPA expectations.

Two goals were paramount in the EPA WIP review: achieving the basin-jurisdiction pollution 

allocations and providing a high level of assurance that reductions would be achieved, 

particularly for non-permitted sources like runoff from agricultural lands and currently 

unregulated stormwater from urban and suburban lands.

The EPA evaluation concluded that the pollution controls identified in two of the seven 

jurisdictions‘ WIPs could meet nitrogen and phosphorus allocations and five of the seven

jurisdictions‘ WIPs could meet sediment allocations for the jurisdiction as a whole. The 

evaluation by jurisdiction is:

Maryland: Some deficiencies – Meets overall statewide allocations for nitrogen (at 

allocation), phosphorus (at allocation) and sediment (0 percent under), but several

individual river basins exceed the allocations for nitrogen, phosphorus or sediment.

District of Columbia: Some deficiencies – Meets allocation for nitrogen (5 percent 

under) and phosphorus (3 percent under), but does not meet the sediment allocation (25 

percent over).

Delaware: Serious deficiencies – Does not meet allocations for nitrogen (17 percent 

over) and phosphorus (8 percent over), but does meet allocations for sediment (20 percent 

under).

New York: Serious deficiencies – Does not meet allocations for nitrogen (15 percent 

over) and phosphorus (14 percent over), but does meet allocations for sediment (17 

percent under.

Pennsylvania: Serious deficiencies – Does not meet allocations for nitrogen (0 percent 

under) and phosphorus (11 percent over), but does meet allocations for sediment (1 

percent over).

Virginia: Serious deficiencies – Does not meet allocations for nitrogen (6 percent over) 

and phosphorus (7 percent over), but does meet allocations for sediment (12 percent 

under).

West Virginia: Serious deficiencies – Does not meet allocation for nitrogen (18 percent 

over) or sediment (38 percent over), but does meet the allocation for phosphorus (6 

percent under).

The EPA evaluation also concluded that none of the seven WIPs provided sufficient reasonable 

assurance that pollution controls identified could actually be implemented to achieve the 

nitrogen, phosphorus and sediment reduction targets by 2017 or 2025. The shortfalls of the 

WIPs, which varied by jurisdiction, included:

Vague or no strategy for filling recognized program or resources gaps

Few enforceable or otherwise binding commitments
DRAFT Chesapeake Bay TMDL

ix September 24, 2010

Discrepancies between implementation levels in model input decks and strategies 

described in WIP

Reliance on pollution trading programs but no commitment to adopt critical trading 

drivers such as new regulations

Few dates for key actions and program-building milestones

EPA Backstop Allocations

Once EPA evaluated a WIP and found shortfalls in pollution loading reductions and/or assurance 

that reductions would be achieved, EPA included only the parts of the WIP that it determined to 

be adequate and appropriate in its TMDL allocation. EPA then determined how to make up that 

shortfall and/or insufficient amount of reasonable assurance for the remainder of the allocation. 

EPA considered varying levels of federal backstop allocations that adjusted loads delivered to 

the Bay to ensure water quality standards are met. The result is a draft TMDL that merges

jurisdictions‘ WIP allocations with varying degrees of federal backstop allocations in all seven 

jurisdictions, as well identification of additional federal actions that EPA is prepared to take if

jurisdictions do not achieve milestones on schedule. For the most part in making the hybrid 

allocations, EPA decreased the allocations to the point sources (over which EPA has or could 

assert regulatory control) and increased the load allocations to unregulated nonpoint sources. 

EPA identified backstop allocations at three levels:

Minor: EPA adjusted WIP pollution sector allocations to achieve the jurisdiction‘s 

overall and major river basin nitrogen, phosphorus and sediment allocations.

Moderate: WIP aggregate point source allocations for stormwater and animal agriculture 

(CAFO) sectors were adjusted to equate to the best approach that was proposed and 

determined adequate in other jurisdiction WIPs. More stringent wasteload allocations 

were applied to point source wastewater sources (regulated via federal programs); other 

nonpoint source allocations increased as feasible if there was insufficient assurance that 

reductions would be achieved. 

High: WIP aggregate allocations for point source stormwater and animal agriculture 

sectors were adjusted downward to equate to the best approach that was proposed and 

determined adequate in other jurisdiction WIPs; Very stringent wastewater allocations 

were applied to point source wastewater sources based on limit of technology 

concentrations (regulated via federal programs); other nonpoint source allocations 

increased as feasible if there was insufficient assurance that reductions would be 

achieved.

Backstop allocations focus on areas where EPA has the federal authority to control pollution 

allocations through NPDES permits. These backstops involve substituting a jurisdiction‘s 

proposed point source allocations with more stringent EPA ―backstop allocations‖ for point 

sources including wastewater treatment plants, stormwater permits, and animal agriculture 

operations. The draft TMDL reflects the following level of backstops for each jurisdiction:

Maryland: Minor-level backstop allocations primarily for Maryland‘s nonpoint source 

load allocations to meet nitrogen, phosphorus and sediment allocations in each major 

basin within Maryland. No changes to point source wasteload allocations that would 

affect NPDES permit conditions. 
DRAFT Chesapeake Bay TMDL

x September 24, 2010

District of Columbia: Minor-level backstop allocations to District of Columbia‘s 

wasteload allocations for urban stormwater so that the District meets upper range of 

sediment allocation. EPA will ensure that all allocations, including sediment, are met 

through the NPDES permits issued within the District.

Virginia: Moderate-level backstop allocations for Virginia point sources

o Wastewater treatment plants: 4 mg/L TN and .3 mg/L TP and design flow for 

significant municipal plants consistent with most aggressive WIP proposal 

(Maryland ENR Strategy).

o MS4s: 50 percent of urban MS4 lands meet aggressive performance standard 

through retrofit/ redevelopment; 50 percent of unregulated land treated as 

regulated, so that 25 percent of unregulated land meets aggressive performance 

standard; designation as necessary.

o Construction: Erosion and sediment control on all lands subject to Construction 

General Permit.

o CAFO production areas: Waste management, barnyard runoff control, mortality 

composting. Precision feed management for all animals. Same standards apply to 

AFOs not subject to CAFO permit except no feed management on dairies; 

designation as necessary.

o Additional adjustments to agriculture nonpoint sources as necessary to exactly 

meet nitrogen, phosphorus and sediment allocations.

Delaware: High-level backstop allocations for Delaware point sources

o Wastewater treatment plants: limit of technology (3 mg/L TN and .1 mg/L TP)

and design flow for significant municipal plants.

o MS4s: 50 percent of urban MS4 lands meet aggressive performance standard 

through retrofit/ redevelopment; 50 percent of unregulated land treated as 

regulated, so that 25 percent of unregulated land meets aggressive performance 

standard; designation as necessary.

o Construction: Erosion and sediment control on all lands subject to Construction 

General Permit.

o CAFO production areas: Waste management, barnyard runoff control, mortality 

composting. Precision feed management for all animals. Same standards apply to 

AFOs not subject to CAFO permits except no feed management on dairies; 

designation as necessary.

o Additional reductions from agricultural nonpoint sources necessary to meet 

nitrogen and phosphorus allocations that EPA will ensure occurs through 

additional federal backstop actions.

New York: High-level backstop allocations for New York point sources

o Wastewater treatment plants: limit of technology (3 mg/L TN and .1 mg/L TP) 

and design flow for significant municipal plants.

o MS4s: 50 percent of urban MS4 lands meet aggressive performance standard 

through retrofit/ redevelopment; 50 percent of unregulated land treated as 

regulated, so that 25 percent of unregulated land meets aggressive performance 

standard; designation as necessary.
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xi September 24, 2010

o Construction: Erosion and sediment control on all lands subject to Construction 

General Permit.

o CAFO production areas: Waste management, barnyard runoff control, mortality 

composting. Precision feed management for all animals. Same standards apply to 

AFOs not subject to CAFO permits except no feed management on dairies; 

designation as necessary.

o Additional reductions from agricultural nonpoint sources necessary to meet 

nitrogen, phosphorus and sediment allocations that EPA will ensure occurs 

through additional federal backstop actions. 

o Finer scale wasteload and load allocations (same level of detail as tidal states) to 

ensure NPDES permits will be consistent with Chesapeake Bay TMDL wasteload 

allocations.

Pennsylvania: High-level backstop allocations for Pennsylvania point sources

o Wastewater treatment plants: limit of technology (3 mg/L TN and .1 mg/L TP)

and design flow for significant municipal plants.

o MS4s: 50 percent of urban MS4 lands meet aggressive performance standard 

through retrofit/ redevelopment; 50 percent of unregulated land treated as 

regulated, so that 25 percent of unregulated land meets aggressive performance 

standard; designation as necessary.

o Construction: Erosion and sediment control on all lands subject to Construction 

General Permit.

o CAFO production areas: Waste management, barnyard runoff control, mortality 

composting. Precision feed management for all animals. Same standards apply to 

AFOs not subject to CAFO permits except no feed management on dairies; 

designation as necessary.

o Load from point source reductions redistributed to forest, septic, and agriculture 

sources as possible while still meeting nitrogen, phosphorus and sediment 

allocations.

o Finer scale wasteload and load allocations (same level of detail as tidal states) to 

ensure NPDES permits will be consistent with Chesapeake Bay TMDL wasteload 

allocations.

West Virginia: High-level backstop allocations for West Virginia point sources

o Wastewater treatment plants: limit of technology (3 mg/L TN and .1 mg/L TP) 

and design flow for significant municipal plants.

o MS4s: 50 percent of urban MS4 lands meet aggressive performance standard 

through retrofit/ redevelopment; 50 percent of unregulated land treated as 

regulated, so that 25 percent of unregulated land meets aggressive performance 

standard; designation as necessary.

o Construction: Erosion and sediment control on all lands subject to Construction 

General Permit.

o CAFO production areas: Waste management, barnyard runoff control, mortality 

composting. Precision feed management for all animals. Same standards apply to 

AFOs not subject to CAFO permits except no feed management on dairies; 

designation as necessary.
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xii September 24, 2010

o Additional reductions from agricultural nonpoint sources necessary to meet July 1 

and August 13 nitrogen, phosphorus and sediment allocations that EPA will 

ensure occurs through additional federal backstop actions. 

o Finer scale wasteload and load allocations (same level of detail as tidal states) to 

ensure NPDES permits will be consistent with Chesapeake Bay TMDL wasteload 

allocations.

The jurisdictions are encouraged to revise and strengthen their draft Phase I WIPs before final 

versions are due November 29 to meet the basin-state pollution allocations and provide 

reasonable assurance the allocations will be achieved. During this time, EPA will engage 

jurisdictions to share best approaches from the WIPs across the jurisdictions and provide EPA 

guidance on the most effective pollution controls. When final Phase I WIPs are submitted, EPA 

will again evaluate the plans to determine if EPA backstop allocations can be replaced with 

sufficiently improved state commitments.

In 2011, the jurisdictions are expected to submit Phase II WIPs that allocate the pollutant loads 

on a geographically smaller scale. Phase III WIPs in 2017 are expected to be designed to provide 

additional detail of restoration actions beyond 2017 and ensure that the 2025 goals are met.

Public Participation

The release of the draft Chesapeake Bay TMDL on September 24, 2010 began a 45-day public 

comment period that concludes on November 8, 2010. During the public comment period, there 

are 18 public meetings in all six watershed states and the District. A full public meeting 

schedule, including registration links for an online broadcast in each jurisdiction, is available at 

http://www.epa.gov/chesapeakebaytmdl. The website also provides a link for accessing and 

formally commenting on the draft TMDL. 

The TMDL is available for viewing at EPA Region III, 1650 Arch Street, Philadelphia, PA 

19103 with arrangements made in advance with the Region 3 library (215-814-5254 or libraryreg3@epa.gov), EPA Chesapeake Bay Program Office at 410 Severn Avenue Suite 112, 

Annapolis, MD 21403 (Contact Debbie Embleton 410-267-9856 or

Embleton.debbie@epa.gov) or EPA Docket Center, EPA/DC, EPA West, Room 3334, 1301 

Constitution Ave., NW., Washington, DC (Docket Number EPA-R03-OW-2010-0736 and 

reading room phone number (202) 566-1744).

Options for comment are:

Electronically, visit: www.regulations.gov. Docket ID No. EPA-R03-OW-2010-0736

In writing, mail to: Water Docket, EPA, Mail code: 2822T, 1200 Pennsylvania Ave., 

NW., Washington, D.C., 20460.

By hand, drop off from 8:30 a.m. - 4:30 p.m.: EPA Docket Center Public Reading Room, 

EPA Headquarters West, Room 3340, 1301 Constitution Ave., NW, Washington, D.C. 
DRAFT Chesapeake Bay TMDL

xiii September 24, 2010

Contents

SECTION 1. Introduction..................................................................................................... 1-1

1.1. TMDLs and the CWA............................................................................................................1-2

1.2 History of the Chesapeake Bay TMDL.................................................................................1-3

1.2.1 Regulatory and Management Initiatives............................................................................................ 1-3

1.2.2 Partnership Commitment to Develop the Chesapeake Bay TMDL ................................................... 1-5

1.2.3 President‘s Chesapeake Bay Executive Order ................................................................................... 1-6

1.3 Bay TMDL Process, Partner Coordination and Responsibilities.......................................1-7

1.3.1 CBP Partnership and Organizational Structure.................................................................................. 1-8

1.4 Legal Framework for the Chesapeake Bay TMDL...........................................................1-11

1.4.1. What is a TMDL?................................................................................................................................. 1-11

1.4.2. Why is EPA establishing this TMDL? ................................................................................................. 1-12

SECTION 2. WATERSHED and Impairment Description................................................. 2-1

2.1 General Watershed Setting....................................................................................................2-1

2.2 Chesapeake Bay TMDL Scope ..............................................................................................2-7

2.2.1 Pollutants of Concern......................................................................................................................... 2-8

2.2.2 Chesapeake Bay Program Segmentation Scheme.............................................................................. 2-8

2.2.3 Jurisdictions‘ 2008 303(d) Listings ................................................................................................. 2-15

2.2.4 2008 303(d) Listing Segments Compared to Consent Decree and MOU Segments........................ 2-16

SECTION 3. Chesapeake Bay Water Quality Standards .................................................... 3-1

3.1 Chesapeake Bay Water Quality Criteria and Designated Uses..........................................3-1

3.1.1 Tidal Water Designated Uses............................................................................................................. 3-4

3.1.2 Dissolved Oxygen Criteria................................................................................................................. 3-9

3.1.3 Chlorophyll a Criteria ...................................................................................................................... 3-11

3.1.4 Water Clarity/Underwater Bay Grasses Criteria.............................................................................. 3-12

3.2 Jurisdictions’ Current Chesapeake Bay Water Quality Standards Regulations ...........3-15

3.2.1 District of Columbia ........................................................................................................................ 3-16

3.2.2 Delaware .......................................................................................................................................... 3-17

3.2.3 Maryland.......................................................................................................................................... 3-17

3.2.4 Virginia ............................................................................................................................................ 3-17

3.3 Jurisdictions’ Pending Revisions to Chesapeake Bay Water Quality Standards 

Regulations.........................................................................................................................................3-18

3.3.1 District of Columbia ........................................................................................................................ 3-18

3.3.2 Delaware .......................................................................................................................................... 3-18

3.3.3 Maryland.......................................................................................................................................... 3-18

3.3.4 Virginia ............................................................................................................................................ 3-19

3.4 Assessing Attainment of Chesapeake Bay Water Quality Standards..............................3-19

3.4.1 Defining Total Exceedances............................................................................................................ 3-19

3.4.2 Defining Allowable Exceedances.................................................................................................... 3-21

3.4.3 Assessing Criteria Attainment ......................................................................................................... 3-23

SECTION 4. Sources of Nutrients and Sediment to the Chesapeake Bay ......................... 4-1

4.1 Jurisdiction Loading Contributions......................................................................................4-1
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xiv September 24, 2010

4.2 Major River Basin Contributions.........................................................................................4-3

4.3 Pollutant Source Sector Contributions.................................................................................4-6

4.4 Regulated Point Sources ........................................................................................................4-7

4.4.1 Significant and Nonsignificant Municipal and Industrial Facilities................................................... 4-8

4.4.2 Basinwide NPDES Permitting Approach .......................................................................................... 4-9

4.4.3 Data Sources.................................................................................................................................... 4-10

4.5 Regulated Point Source Load Summaries..........................................................................4-12

4.5.1 Municipal Wastewater Discharging Facilities................................................................................. 4-13

4.5.2 Industrial Discharge Facilities ......................................................................................................... 4-17

4.5.3 Combined Sewer Overflows............................................................................................................ 4-21

4.5.4 Sanitary Sewer Overflows ............................................................................................................... 4-24

4.5.5 NPDES Permitted Stormwater......................................................................................................... 4-24

4.5.6 Concentrated Animal Feeding Operations....................................................................................... 4-28

4.6 Nonpoint Sources..................................................................................................................4-30

4.6.1 Data Sources.................................................................................................................................... 4-30

4.7 Nonpoint Source Load Summaries.....................................................................................4-31

4.7.1 Agriculture....................................................................................................................................... 4-31

4.7.2 Atmospheric Deposition .................................................................................................................. 4-35

4.7.3 Forest Lands..................................................................................................................................... 4-39

4.7.4 On-site Wastewater Treatment Systems .......................................................................................... 4-39

4.7.5 Nonregulated Stormwater Runoff.................................................................................................... 4-41

4.7.6 Oceanic inputs ................................................................................................................................. 4-41

4.7.7 Streambank and Tidal Shoreline Erosion......................................................................................... 4-43

4.7.8 Tidal Resuspension.......................................................................................................................... 4-45

4.7.9 Wildlife ............................................................................................................................................ 4-46

4.7.10 Natural Background .................................................................................................................... 4-46

SECTION 5. Chesapeake Bay Monitoring and Modeling Frameworks ............................ 5-1

5.1 Technical Monitoring and Modeling Requirements ...........................................................5-1

5.2 Bay Monitoring Framework Overview ................................................................................5-2

5.2.1 Partnership‘s Chesapeake Bay Tidal Monitoring Network................................................................ 5-2

5.2.2 Partnership‘s Watershed Monitoring Network .................................................................................. 5-8

5.2.3 Data Quality and Access.................................................................................................................. 5-11

5.2.4 Data Submission and Quality Assurance ......................................................................................... 5-12

5.2.5 Monitoring Applications in Chesapeake Bay TMDL Development................................................ 5-15

5.3 Modeling Framework Overview .........................................................................................5-15

5.4 Chesapeake Bay Airshed Model..........................................................................................5-17

5.5 Chesapeake Bay Land Change Model................................................................................5-20

5.5.1 Motivations for Developing Future Land Use Estimates................................................................. 5-20

5.5.2 Scale of Chesapeake Bay Land Change Model Future Land Use Estimates................................... 5-21

5.5.3 Components of Chesapeake Bay Land Change Model Future Land Use Estimates........................ 5-23

5.6 Chesapeake Bay SPARROW Model...................................................................................5-24

5.7 Scenario Builder ...................................................................................................................5-26

5.8 Phase 5 Chesapeake Bay Watershed Model.......................................................................5-27

5.8.1 Segmentation ................................................................................................................................... 5-29

5.8.2 Model Setup..................................................................................................................................... 5-29

5.8.3 Pollutant Source Representation ...................................................................................................... 5-34
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xv September 24, 2010

5.8.4 Calibration ....................................................................................................................................... 5-35

5.9 Chesapeake Bay Water Quality and Sediment Transport Model....................................5-37

5.9.1 Nonpoint Source Loads ................................................................................................................... 5-39

5.9.2 Point Source Loads.......................................................................................................................... 5-39

5.9.3 Atmospheric Loads.......................................................................................................................... 5-39

5.9.4 Bank Loads...................................................................................................................................... 5-39

5.9.5 Wetlands.......................................................................................................................................... 5-39

5.9.6 Model Setup..................................................................................................................................... 5-39

5.10 CHESAPEAKE BAY CRITERIA ASSESSMENT PROGRAM..........................................5-40

5.11 CLIMATE CHANGE SIMULATION ....................................................................................5-41

SECTION 6. Chesapeake Bay TMDL Development ........................................................... 6-1

6.1 Establishing Model Parameters ............................................................................................6-1

6.1.1 Hydrologic Period.............................................................................................................................. 6-1

6.1.2 Critical Conditions............................................................................................................................. 6-3

6.1.3 Water Quality Standards.................................................................................................................... 6-4

6.1.4 Seasonal Variation ............................................................................................................................. 6-5

6.2 Interpreting Model Results....................................................................................................6-7

6.2.1 Criteria Assessment Procedures......................................................................................................... 6-7

6.2.2 Addressing Reduced Sensitivity to Load Reductions at Low Nonattainment Percentages ............... 6-9

6.2.3 Margin of Safety .............................................................................................................................. 6-12

6.2.4 Temporary Reserve.......................................................................................................................... 6-14

6.2.5 Daily Loads...................................................................................................................................... 6-15

6.3 Establishing Allocation Rules..............................................................................................6-18

6.3.1 Nutrient Allocation Methodology.................................................................................................... 6-18

6.3.2 Sediment Allocation Methodology .................................................................................................. 6-29

6.4 Assessing Attainment of Proposed Amended Chesapeake Bay WQS .............................6-30

6.4.1 Establishing Nutrient Load Caps to Attain the Proposed Amended Water Quality Standards........ 6-30

6.4.2 Determining the Sediment Load Caps to Achieve the Proposed Amended Water Quality Standards. 6-

46

6.5 Assessing Attainment of Current WQS..............................................................................6-50

6.5.1 Establishing Nutrient Basin-Jurisdiction Load Caps ....................................................................... 6-50

6.5.2 Establishing Sediment Load Caps ................................................................................................... 6-53

6.6 Setting Draft Basin-jurisdiction Allocations......................................................................6-54

6.6.1 Basin-jurisdiction Allocations to Achieve the Proposed WQS........................................................ 6-54

6.6.2 Basin-jurisdiction Allocations to Achieve the Current WQS .......................................................... 6-56

SECTION 7. Reasonable Assurance and Accountability Framework................................ 7-1

7.1 Reasonable Assurance............................................................................................................7-1

7.2 Accountability Framework....................................................................................................7-4

7.2.1 Watershed Implementation Plans ...................................................................................................... 7-5

7.2.2 Two-Year Milestones ........................................................................................................................ 7-8

7.2.3 Chesapeake Bay TMDL Accountability Tracking System................................................................ 7-9

7.2.4 Federal EPA Actions ...................................................................................................................... 7-11
DRAFT Chesapeake Bay TMDL

xvi September 24, 2010

SECTION 8. WATERSHED IMPLEMENTATION PLAN EVALUATION AND DRAFT 

BACKSTOP ALLOCATIONS .................................................................................................... 8-1

8.1 WIP Evaluation Methodology.................................................................................................8-2

8.2 WIP Evaluation Results ..........................................................................................................8-4

8.2.1 Target Nutrient/Sediment Allocation Gaps........................................................................................ 8-5

8.2.2 Insufficient Reasonable Assurance .................................................................................................... 8-6

8.2.3 Summary of Results of EPA Evaluation of Draft Phase I WIPs........................................................ 8-7

8.3 Draft Backstop Allocations......................................................................................................8-8

8.3.1 Methodology for Backstop Allocations............................................................................................. 8-9

8.3.2 Assumptions Supporting the Draft Bay TMDL Backstop Allocations........................................... 8-12

8.3.3 Summary of Backstop Allocations .................................................................................................. 8-17

SECTION 9. Chesapeake Bay TMDLs ................................................................................ 9-1

9.1 Bay Segment Annual and Daily Allocations to Meet Proposed Amended WQS ..............9-1

9.2 Bay Segment Annual and Daily Allocations to Meet Current WQS ...............................9-42

SECTION 10. TMDL Implementation and Adaptive Management.................................... 10-1

10.1 Future Growth......................................................................................................................10-1

10.1.1 Designating Target Loads for New or Increased Sources........................................................... 10-1

10.1.2 Offset Programs .......................................................................................................................... 10-1

10.1.3 Additional Offset Program Features ........................................................................................... 10-2

10.1.4 EPA‘s Oversight Role of State Offset Program .......................................................................... 10-3

10.2 Water Quality Trading ........................................................................................................10-3

10.3 Future Modifications to the Chesapeake Bay TMDL .......................................................10-4

10.4 Federal Facilities and Lands................................................................................................10-5

10.5 Factoring in Effects from Continued Climate Change .....................................................10-7

10.6 Sediments behind the Susquehanna River Dams ..............................................................10-7

10.7 Filter Feeders........................................................................................................................10-8

SECTION 11. Public Participation ...................................................................................... 11-1

11.1 Stakeholder and Local Government Outreach and Involvement ....................................11-1

11.1.1 Open Collaboration with Stakeholders ....................................................................................... 11-1

11.1.2 Outreach to Local Governments and Elected Officials............................................................... 11-1

11.1.3 Local Pilots ................................................................................................................................. 11-2

11.2 Public Outreach....................................................................................................................11-2

11.2.1 Public Meetings .......................................................................................................................... 11-2

11.2.2 Webinars to Expand Audiences.................................................................................................. 11-4

11.2.3 Chesapeake Bay TMDL Web Site .............................................................................................. 11-4

11.2.4 Public Notices............................................................................................................................. 11-5

11.3 Responses to Public Comments...........................................................................................11-5

SECTION 12. References ..................................................................................................... 12-1
DRAFT Chesapeake Bay TMDL

xvii September 24, 2010

SECTION 13. Glossary ......................................................................................................... 13-1

SECTION 14. Abbreviations................................................................................................. 14-1

Appendices

Appendix A Chesapeake Bay TMDL Contributors

Appendix B Index of Documents Supporting the Chesapeake Bay TMDL

Appendix C Record of Chesapeake Bay TMDL Related Chesapeake Bay Program Committee, 

Team and Workgroup and Partner/Stakeholder Meetings 

Appendix D Evaluation of the Most Protective Chesapeake Bay Dissolved Oxygen Criteria

Appendix E Summary of Initial Climate Change Impacts on the Chesapeake Bay Watershed 

Flows and Loads

Appendix F Determination of the Hydrologic Period for Model Application

Appendix G Determination of Critical Conditions for the Chesapeake Bay TMDL

Appendix H Criteria Assessment Procedures using Model Scenario Output with Bay 

Monitoring Data

Appendix I Documentation of the Reduced Sensitivity to Load Reductions at Low

Nonattainment Percentages

Appendix J Key Chesapeake Bay TMDL Reference and Management Model Scenarios: 

Definitions and Descriptions

Appendix K Allocation Methodology for Relating Relative Impact to Needed Controls

Appendix L Setting the Chesapeake Bay Atmospheric Nitrogen Deposition Allocations

Appendix M Chesapeake Bay Water Quality/Sediment Transport Model Management Scenario 

Attainment Assessment Results and 2008 303(d) Chesapeake Bay List 

Assessment Results

Appendix M-1 Chesapeake Bay Dissolved Oxygen Criteria Attainment 

Assessment Results

Appendix M-2 Chesapeake Bay Chlorophyll a Criteria Attainment 

Assessment Results

Appendix M-3 Chesapeake Bay Water Clarity/SAV Criteria Attainment 

Assessment Results

Appendix M-4 Chesapeake Bay Segments 2008 303(d) List Assessment 

Results

Appendix N Resolution of Segments Failing to Attain the Applicable Criteria

Appendix N-1 Resolution of Segments Failing to Attain the Dissolved 

Oxygen Criteria
DRAFT Chesapeake Bay TMDL

xviii September 24, 2010

Appendix N-2 Resolution of Segments Failing to Attain the SAV/Water 

Clarity Criteria

Appendix O Setting the Chlorophyll a Criteria-Based Nutrient Allocations for the James River 

Watershed

Appendix P Setting the Water Clarity/SAV Criteria-Based Sediment Allocations

Appendix Q Detailed Annual Chesapeake Bay TMDL WLAs and LAs

Appendix R Chesapeake Bay TMDL Daily WLAs and LAs

Appendix S Offsets for New or Increased Loadings of Nitrogen, Phosphorus and Sediment to 

the Chesapeake Bay Watershed

Appendix T Sediments behind the Susquehanna Dams Technical Documentation

Appendix U Accounting for the Benefits of Filter Feeder Restoration Technical 

Documentation

Appendix V Responses to Public Comments Received on the September 24, 2010, Draft 

Chesapeake Bay TMDL
DRAFT Chesapeake Bay TMDL

xix September 24, 2010

Tables

Table 1-1. URLs for accessing the seven Chesapeake Bay watershed jurisdictions‘ tributary 

strategies ...................................................................................................................................... 1-4

Table 1-2. Summary of Chesapeake Bay TMDL relevant actions agreed to by the CBP‘s 

Principals‘ Staff Committee during its October 1, 2007, meeting............................................... 1-6

Table 1-3. Virginia consent decree (CD) waters impaired for dissolved oxygen (DO) and/or 

nutrients that will be addressed by the Chesapeake Bay TMDL............................................... 1-15

Table 1-4. District of Columbia consent decree (CD) waters impaired for pH that will be 

addressed by the Chesapeake Bay TMDL................................................................................. 1-16

Table 2-1. The Chesapeake Bay 303(d) tidal segments with consent decree (CD)/memorandum 

of understanding (MOU) and 303(d) listing status by major river basin and jurisdiction......... 2-10

Table 2-2. Comparison of consent decree/MOU segments with total number of Bay segments.. 2-

16

Table 3-1. Chesapeake Bay water quality criteria and designated use related documentation and 

addenda ........................................................................................................................................ 3-2

Table 3-2. Five Chesapeake Bay tidal waters designated uses.................................................... 3-4

Table 3-3. Current tidal water designated uses by Chesapeake Bay segment ............................. 3-6

Table 3-4. Current Chesapeake Bay DO criteria ....................................................................... 3-11

Table 3-5. Summary of Chesapeake Bay water clarity criteria for application to shallow-water 

bay grass designated use habitats............................................................................................... 3-12

Table 3-6. Chesapeake Bay SAV restoration acreages and application depths—current WQS3-13

Table 3-7. Links for accessing the current WQS regulations for Delaware, the District of 

Columbia, Maryland, and Virginia ............................................................................................ 3-16

Table 3-8. District of Columbia designated uses for surface waters ......................................... 3-16

Table 3-9. Numeric criteria for the District of Columbia‘s tidally influenced waters............... 3-16

Table 3-10. Segment-specific chlorophyll a criteria for Virginia‘s tidal James River waters .. 3-18

Table 3-11. Estimated percent spatial criteria exceedances and associated cumulative 

probabilities................................................................................................................................ 3-20

Table 4-1. Percentage of total nitrogen from each major pollutant source sector by jurisdiction4-6

Table 4-2. Percentage of total phosphorus from each major pollutant source sector by jurisdiction

...................................................................................................................................................... 4-6

Table 4-3. Percentage of sediment from each source sector by jurisdiction ............................... 4-7

Table 4-4. Jurisdiction-specific definitions of significant municipal and industrial wastewater 

discharge facilities ....................................................................................................................... 4-8

Table 4-5. Significant and nonsignificant municipal and industrial wastewater discharging 

facilities by jurisdiction................................................................................................................ 4-8

Table 4-6. Nutrient permit tracking summary under the Basinwide NPDES Wastewater 

Permitting Approach, through June 2010 .................................................................................. 4-10

Table 4-7. Municipal wastewater facilities by jurisdiction........................................................ 4-13

Table 4-8. Model estimated 2009 municipal wastewater loads by jurisdiction delivered to 

Chesapeake Bay......................................................................................................................... 4-13

Table 4-9. Model estimated 2009 municipal wastewater loads by major river basin delivered to 

Chesapeake Bay......................................................................................................................... 4-14

Table 4-10. Industrial wastewater facilities............................................................................... 4-17

Table 4-11. 2009 Load estimates of industrial facility discharges ............................................ 4-17
DRAFT Chesapeake Bay TMDL

xx September 24, 2010

Table 4-12. 2009 Flow, total nitrogen, and total phosphorus load estimates of industrial 

wastewater facility discharges by major river basin .................................................................. 4-18

Table 4-13. Combined sewer system communities in the Bay watershed................................. 4-21

Table 4-14. NPDES stormwater permittees by jurisdiction and in the Chesapeake Bay watershed, 

summer 2009.............................................................................................................................. 4-27

Table 4-15. Federal numeric thresholds for small, medium, and large CAFOs........................ 4-28

Table 4-16. Estimated number of state or federal permitted CAFOs........................................ 4-30

Table 4-17. Estimated portion of deposited NOx loads on the Chesapeake watershed from four 

source sectors—EGUs, mobile sources, industry, and all other sources in 1990 and 2020 ...... 4-38

Table 4-18. Chesapeake Bay WQSTM simulated SAV acres under a range of sediment scoping 

scenarios compared with the 2010 Tributary Strategy scenario ................................................ 4-46

Table 5-1. Modeling tools supporting development of the Chesapeake Bay TMDL................ 5-16

Table 5-2. Phase 5.3 Chesapeake Bay Watershed Model land uses.......................................... 5-30

Table 6-1. Tributary strategy and proposed amended Bay WQS-based allocation scenarios TSS 

loads (millions of pounds) by jurisdiction ................................................................................... 6-8

Table 6-2. Different approaches available under the explicit and implicit MOS types............. 6-13

Table 6-3. Nitrogen and phosphorus temporary reserves by Chesapeake Bay watershed 

jurisdiction. ................................................................................................................................ 6-15

Table 6-4. Annual/Daily Maximum (ADMs) for calculating daily maximum loads-............... 6-17

Table 6-5. Relative effectiveness (measured as DO concentration per edge-of-stream pound 

reduced) for nitrogen and phosphorus for watershed jurisdictions by major river basin and above 

and below the fall line................................................................................................................ 6-21

Table 6-6. Pollutant sources as defined for the No Action and E3 model scenarios................. 6-27

Table 6-7. Chesapeake Bay designated use segments showing percent nonattainment of the 

applicable Bay DO WQS under the proposed basinwide nutrient target loadings (shaded column)

.................................................................................................................................................... 6-37

Table 6-8. Percent nonattainment of the current Chesapeake SAV-water clarity WQS for the 

Back, Chester and middle Pocomoke (Maryland) rivers under a range of nutrient and sediment 

reduction load scenarios............................................................................................................. 6-54

Table 6-9. Chesapeake Bay watershed nutrient and sediment draft allocations by major river 

basin by jurisdiction to achieve the proposed Chesapeake Bay WQS....................................... 6-55

Table 6-10. Chesapeake Bay watershed nutrient and sediment draft allocations by jurisdiction by 

major river basin to achieve the proposed Chesapeake Bay WQS............................................ 6-56

Table 6-11. Chesapeake Bay Allocations for Existing WQS by Jurisdiction............................ 6-58

Table 7-1. Eight elements of the jurisdictions‘ WIPs.................................................................. 7-6

Table 7-2. Comparison of elements within the Chesapeake Bay TMDL and Phase I, II, and III 

WIPs............................................................................................................................................. 7-7

Table 8-1. Thresholds for four evaluation tiers for assessing whether a jurisdiction met its 

nitrogen, phosphorus, and sediment target allocations................................................................ 8-3

Table 8-2. Thresholds for the four Phase I WIP evaluation tiers for the reasonable assurance 

assessment.................................................................................................................................... 8-4

Table 8-3. Comparison of the nitrogen, phosphorus, and sediment jurisdiction-wide allocations in 

the jurisdictions‘ draft Phase I WIPs with the target allocations for each pollutant.................... 8-5

Table 8-4. Comparison of the nitrogen, phosphorus, and sediment basinwide allocations in the 

jurisdictions‘ draft Phase I WIPs with the basinwide target nutrient (in millions of pounds per 

year [mpy]) and sediment allocations (mpy) for 2025................................................................. 8-6
DRAFT Chesapeake Bay TMDL

xxi September 24, 2010

Table 8-5. Draft Phase I WIP evaluation ratings by jurisdiction by the three major pollutant 

loading source sectors.................................................................................................................. 8-8

Table 8-6. Definitions of the backstop allocation options that EPA considered to replace 

jurisdictions‘ WIP point source allocations............................................................................... 8-11

Table 8-7. Summary of backstop allocations applied to the seven watershed jurisdictions in 

developing the draft Bay TMDL WLAs and LAs..................................................................... 8-18

Table 8-8. Chesapeake Bay watershed nutrient and sediment draft backstop allocations by 

jurisdiction and by major river basin to achieve the proposed amended Chesapeake Bay WQS . 8-

20

Table 8-9. Chesapeake Bay watershed nutrient and sediment draft allocations by jurisdiction and 

by major river basin to achieve the current Chesapeake Bay water quality standards. ............. 8-21

Table 9-1. Draft Chesapeake Bay TMDL total nitrogen (TN) annual allocationsa(pounds per 

year) by Chesapeake Bay segment for the proposed amended Chesapeake Bay WQS 9-2

Table 9-2. Draft Chesapeake Bay TMDL total phosphorus (TP) annual allocationsa(pounds per 

year) by Chesapeake Bay segment for the proposed amended Chesapeake Bay WQS .............. 9-9

Table 9-3. Draft Chesapeake Bay TMDL sediment (SED) annual allocationsa(thousands of 

pounds per year) by Chesapeake Bay segment for the proposed amended Chesapeake Bay WQS

.................................................................................................................................................... 9-15

Table 9-4. Individual WLAs (Annual) for the 483 significant permitted dischargers to meet 

TMDLs to address the proposed amended Chesapeake Bay WQS ........................................... 9-21

Table 9-5. Draft Chesapeake Bay TMDL total nitrogen (TN) annual allocationsa(pounds per 

year) by Chesapeake Bay segment for the current Chesapeake Bay WQS ............................... 9-42

Table 9-6. Draft Chesapeake Bay TMDL total phosphorus (TP) annual allocationsa(pounds per 

year delivered to tidal waters) by Chesapeake Bay segment for the current Chesapeake Bay WQS

.................................................................................................................................................... 9-49

Table 9-7. Draft Chesapeake Bay TMDL sediment (SED) annual allocationsa(thousands of 

pounds per year) by Chesapeake Bay segment for the current Chesapeake Bay WQS ............ 9-55
DRAFT Chesapeake Bay TMDL

xxii September 24, 2010

Figures

Figure 1-1. CBP‘s organizational structure. ................................................................................ 1-8

Figure 2-1. The Chesapeake Bay watershed with major rivers and cities. .................................. 2-2

Figure 2-2. Hydrogeomorphic regions of the Chesapeake Bay watershed.................................. 2-4

Figure 2-3. Chesapeake Bay watershed land cover. .................................................................... 2-6

Figure 2-4. Reported and projected human population growth in the Chesapeake Bay watershed 

1950–2030.................................................................................................................................... 2-7

Figure 2-5. The 92 Chesapeake Bay segments. ........................................................................... 2-9

Figure 2-6. The 92 Chesapeake Bay segment watersheds......................................................... 2-14

Figure 3-1. Conceptual illustration of the five Chesapeake Bay tidal water designated use zones.

...................................................................................................................................................... 3-5

Figure 3-2. DO (mg/L) concentrations required by different Chesapeake Bay species and 

biological communities.............................................................................................................. 3-10

Figure 3-3. Example cumulative frequency distribution (CFD) curve. ..................................... 3-20

Figure 3-4. Default reference curve used in the attainment assessment of Chesapeake Bay water 

quality criteria for which biologically based reference curves have not yet been derived. ....... 3-22

Figure 3-5. Example reference and assessment curves showing allowable and non-allowable 

exceedances................................................................................................................................ 3-23

Figure 3-6. Direct model assessment of open water (a), and deep water and deep channel (b) 

criteria. ....................................................................................................................................... 3-25

Figure 4-1. Modeled estimated total nitrogen loads delivered to the Chesapeake Bay by 

jurisdiction in 2009. ..................................................................................................................... 4-1

Figure 4-2. Model estimated total phosphorus loads delivered to the Chesapeake Bay by 

jurisdiction in 2009. ..................................................................................................................... 4-2

Figure 4-3. Model estimated total sediment loads delivered to the Chesapeake Bay by 

jurisdiction in 2009. ..................................................................................................................... 4-3

Figure 4-4. Model estimated total nitrogen loads delivered to the Chesapeake Bay by major 

tributary in 2009........................................................................................................................... 4-4

Figure 4-5. Model estimated total phosphorus loads delivered to the Chesapeake Bay by major 

tributary in 2009........................................................................................................................... 4-5

Figure 4-6. Model estimated total sediment loads delivered to the Chesapeake Bay by major 

tributary in 2009........................................................................................................................... 4-5

Figure 4-7. Significant wastewater treatment facilities in the Chesapeake Bay watershed....... 4-15

Figure 4-8. Nonsignificant municipal wastewater treatment facilities in the Chesapeake Bay 

watershed. .................................................................................................................................. 4-16

Figure 4-9. Significant industrial wastewater discharge facilities in the Chesapeake Bay 

watershed. .................................................................................................................................. 4-19

Figure 4-10. Nonsignificant industrial wastewater discharge facilities in the Chesapeake Bay 

watershed. .................................................................................................................................. 4-20

Figure 4-11. CSO communities in the Chesapeake Bay watershed........................................... 4-23

Figure 4-12. Phase I and II MS4s in the Chesapeake Bay watershed........................................ 4-26

Figure 4-13. 1985 and 2009 modeled total nitrogen, phosphorus, and sediments loads from 

agricultural lands across the Chesapeake Bay watershed. ......................................................... 4-32

Figure 4-14. 2007 Chesapeake Bay watershed poultry populations by jurisdiction.................. 4-33

Figure 4-15. 2007 Chesapeake Bay watershed livestock populations by jurisdiction............... 4-34
DRAFT Chesapeake Bay TMDL

xxiii September 24, 2010

Figure 4-16. Principle area of NOX emissions (outlined in blue) that contribute nitrogen 

deposition to the Chesapeake Bay and its watershed (solid blue fill) (the Bay airshed). .......... 4-37

Figure 4-17 Trend of estimated average nitrate and ammonia deposition concentrations in the 

Phase 5 Model domain from 1984 to 2005. .............................................................................. 4-38

Figure 4-18. Estimated 2001 annual total deposition of nitrogen (kg-N/ha) to North America and 

adjacent coastal ocean................................................................................................................ 4-43

Figure 4-19. Relative estimates of sources of erosion from land sources (crop, forest, or 

construction) or bank sources banks and ditch beds)................................................................. 4-44

Figure 4-20. Sources of total suspended solids in the Chesapeake including the two components 

of shoreline erosions, fastland and nearshore erosion. .............................................................. 4-45

Figure 4-21. Estimated tidal sediment inputs for 1990 from the Chesapeake Bay watershed and 

from shore erosion. Shoreline sediment inputs (here labeled bank load) are estimated to be about 

equal to watershed inputs (here labeled as nonpoint source)..................................................... 4-45

Figure 5-1. Tidal monitoring network stations. ........................................................................... 5-4

Figure 5-2. Shallow-water monitoring illustrating segment completion and latest rotation for 

Maryland...................................................................................................................................... 5-6

Figure 5-3. Example of results from the probability-based sampling distribution, 1998, to 

estimate habitat impairment through benthic community condition assessment......................... 5-7

Figure 5-4. One way of illustrating SAV mapping results. ......................................................... 5-8

Figure 5-5. Watershed monitoring network............................................................................... 5-10

Figure 5-6. Chesapeake Bay tidal and watershed water quality monitoring networks‘ participants 

arrayed by their role in sample collection, laboratory analysis, or data reporting..................... 5-14

Figure 5-7. Chesapeake Bay TMDL modeling framework. ...................................................... 5-17

Figure 5-8. Atmospheric deposition monitoring stations used in the airshed regression model. .. 5-

18

Figure 5-9. The CMAQ 12 km grid over the Phase 5 domain................................................... 5-19

Figure 5-10. The Land Change Model....................................................................................... 5-22

Figure 5-11. An example of SPARROW Model output showing delivered yield of total nitrogen 

in the Chesapeake Bay watershed during 1987. ........................................................................ 5-25

Figure 5-12. Scenario Builder conceptual process. ................................................................... 5-26

Figure 5-13. Segmentation and reach simulation of the Phase 5.3 Chesapeake Bay Watershed 

Model. ........................................................................................................................................ 5-28

Figure 5-14. Phase 5.3 Chesapeake Bay Watershed Model hydrology (upper panel) and water 

quality (lower panel) monitoring calibration stations overlaid on the Phase 5.3 river segments. . 5-

36

Figure 5-15. The detailed 57,000 cell grid of the Chesapeake Bay Water Quality and Sediment 

Transport Model......................................................................................................................... 5-38

Figure 6-1. Graphic comparison of allowable exceedance compared to actual exceedance. .... 6-10

Figure 6-2. Example of DO criteria nonattainment results from a wide range of nutrient load 

reduction model scenarios.......................................................................................................... 6-10

Figure 6-3. A graphical representation of how the persistent 1% nonattainment may arise in the 

criteria assessment of the Chesapeake Bay WQS...................................................................... 6-12

Figure 6-4. Relative effectiveness for nitrogen for the watershed jurisdictions and major rivers 

basins, above and below the fall line, in descending order........................................................ 6-22

Figure 6-5. Relative effectiveness illustrated geographically by subbasins across the Chesapeake 

Bay watershed for nitrogen........................................................................................................ 6-24
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xxiv September 24, 2010

Figure 6-6. Relative effectiveness for illustrated geographically by subbasins across the 

Chesapeake Bay watershed for phosphorus............................................................................... 6-25

Figure 6-7. Allocation methodology example showing the hockey stick and straight line 

reductions approaches, respectively, to wastewater (red line) and all other sources (blue line) for 

nitrogen. ..................................................................................................................................... 6-29

Figure 6-8.Principal areas of nitrogen oxide (blue line) and ammonia (red line) emissions that 

contribute to nitrogen deposition to the Chesapeake Bay and its watershed (dark blue fill)..... 6-31

Figure 6-9. Chesapeake Bay water quality model simulated DO criteria attainment under various 

nutrient loading scenarios. ......................................................................................................... 6-34

Figure 6-10. Example allocation methodology application for phosphorus.............................. 6-35

Figure 6-11. Example allocation methodology application for nitrogen................................... 6-36

Figure 6-12. Potomac River chlorophyll a monitoring data compared with the District‘s 

chlorophyll a water quality criteria............................................................................................ 6-41

Figure 6-13. James River nonattainment of the chlorophyll a standards at various load scenarios.

.................................................................................................................................................... 6-42

Figure 6-14. Tidal James River monitoring data for chlorophyll a at station TF5.5 (located in the 

upper tidal James River near Hopewell, Virginia) compared to Virginia‘s James River segmentseason specific chlorophyll a criteria......................................................................................... 6-43

Figure 6-15. Total nitrogen:total phosphorus exchanges based on anoxic volume days and 

varying total phosphorus loads. ................................................................................................. 6-45

Figure 6-16. Total nitrogen (TN): total phosphorus (TP) exchanges based on chlorophyll a 

concentrations and varying total phosphorus loads. .................................................................. 6-46

Figure 6-17. Chesapeake Bay SAV/Water Clarity WQS attainment from monitoring data 

assessment.................................................................................................................................. 6-47

Figure 6-18. Model simulated sediment loads by scenario compared with the draft range of 

sediment allocations (billions of pounds per year as total suspended sediments). .................... 6-48

Figure 6-19. Observed SAV acres in Virginia‘s lower Potomac River segment....................... 6-50

Figure 7-1. Relationship between WIPs and 2-year milestones. ................................................. 7-9
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xxv September 24, 2010

Foreword

This document describes the technical, legal, and policy underpinnings of the Chesapeake Bay 

Total Maximum Daily Load (TMDL). While EPA Regions 2 and 3 are establishing this TMDL, 

it represents the product of decades of monitoring and model development, and years of focused 

dialogue and analysis among EPA, our state partners, and numerous stakeholders. This document 

has benefited from input of hundreds of professionals dedicated to the restoration of the 

Chesapeake Bay. In accordance with the Clean Water Act and Executive Order 13508 (signed by 

President Obama on May 12, 2009), the Bay TMDL provides a critical plan to restore and 

maintain the living resources of the Chesapeake Bay.

A TMDL is required by the Clean Water Act for waters that are on state lists identifying waters 

that are not attaining state adopted water quality standards. Most of the waters of the Bay and its 

tidal tributaries are on the states‘ lists of impaired waters because of excess nitrogen, phosphorus, 

and sediment. The Chesapeake Bay TMDL identifies the loadings of nitrogen, phosphorus, and 

sediment that are necessary to achieve the applicable state water quality standards for the Bay 

and its tidal tributaries for dissolved oxygen, chlorophyll  ̳a‘ (an indication of algae), water 

clarity, and submerged aquatic vegetation (SAV, or underwater Bay grasses). For this reason, the 

Chesapeake Bay TMDL has been described as a pollution diet of pollutant loadings necessary to 

attain water quality and restore the aquatic life resources of the Chesapeake Bay.

The Chesapeake Bay drains streams and rivers from many jurisdictions in the mid- Atlantic 

region of the United States including: Delaware, District of Columbia, Maryland, New York, 

Pennsylvania, Virginia, and West Virginia. Since these waters drain to the Chesapeake Bay and 

therefore contribute to the pollutant loadings to the Bay, the Chesapeake Bay TMDL will 

establish total maximum daily loads allowable for these waters and jurisdictions. These loadings 

are further divided to each of the 92 segments that comprise the waters of the Chesapeake Bay 

and its tidal tributaries. Thus, the Chesapeake Bay TMDL is actually an assemblage of 92 

TMDLs, one for each segment, and also one for each pollutant including nitrogen, phosphorus 

and sediment.

The focus of the Chesapeake Bay TMDL is to identify the pollutant loadings needed to restore 

the Bay, and it thus allocates loading reductions to all source sectors in all parts of the Bay 

watershed. Because of the Bay-wide nature of these loading reductions, the water quality 

benefits from these reductions will not be limited to the Bay and its tidal tributaries. In fact, all 

waters from the point the reductions are made to the point that they enter the Bay should benefit 

from some measure of improved water quality. The controls necessary to reduce nutrients and 

sediment are also likely to reduce other pollutants.

While the Chesapeake Bay TMDL establishes the pollutant loadings for nitrogen, phosphorus, 

and sediment needed to restore and maintain a healthy Bay, the TMDL is an information and 

planning tool and does not by itself implement the needed controls. Other provisions of the Clean 

Water Act and state laws, regulations, and funding are needed to achieve these loading levels.

The Bay TMDL will be implemented using an accountability framework that includes state 

Watershed Implementation Plans (WIPs), two-year milestones, EPA‘s tracking and assessment 

of restoration progress and, as necessary, specific federal actions if the Bay jurisdictions do not 

meet their commitments. The WIPs are the opportunity for each state to set up a system of 

controls and allocations to attain the respective loading cap for that state basin, which EPA will 
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xxvi September 24, 2010

consider in making its TMDL allocation decisions. The accountability framework is being 

established in part to provide demonstration of the reasonable assurance provisions of the 

Chesapeake Bay TMDL pursuant to both Section 117(g)(1) of the CWA and Executive Order 

13508, but is not part of the Chesapeake Bay TMDL itself. The accountability framework is 

designed to help ensure that these nutrient goals and water quality requirements, as embodied in 

the Chesapeake Bay TMDL, are met.

An executive summary provides an overview of the TMDL, highlighting its more important 

aspects. For more specific information, readers should consult the main document which 

describes each aspect of the Chesapeake Bay TMDL in detail. Finally, for additional background 

and supportive material, the reader is referred to the numerous appendices and references 

contained in the main document.

____________ _________________________________________

Date Shawn M. Garvin, Regional Administrator

EPA Region III

_____________ _________________________________________

Date Judith A. Enck, Regional Administrator

EPA Region II
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xxvii September 24, 2010

Acknowledgements

This document was developed through the collaborative efforts of the U.S. Environmental 

Protection Agency (EPA) and its seven Chesapeake Bay watershed partners—Delaware, District 

of Columbia, Maryland, New York, Pennsylvania, Virginia and West Virginia—principally 

through the Chesapeake Bay Program‘s (CBP‘s) Water Quality Goal Implementation Team 

(WQGIT) (formerly the Water Quality Steering Committee), its principal workgroups and the 

former Nutrient Subcommittee. The CBP‘s Principals‘ Staff Committee made decisions on 

behalf of the partnership and provided policy direction to the WQGIT. Advice, direction and 

independent peer review were provided by the CBP‘s Scientific and Technical Advisory 

Committee (STAC), the Local Government Advisory Committee (LGAC) and the Citizen‘s 

Advisory Committee (CAC). Comments and recommendations gathered through the November–

December 2009 public meetings and webinars were instrumental in ensuring that the published 

allocations provide the most benefits to local streams and rivers and still achieve the 

jurisdictions‘ Chesapeake Bay water quality standards.

The document resulted from the collaborative expertise, input, and feedback of many individuals 

from the multitude of CBP partnering agencies and institutions, local governments, 

nongovernmental organizations, businesses, and many other involved stakeholders. Their 

individual and collective contributions are hereby acknowledged. Appendix A provides a 

detailed member listing of the various groups and committees who were instrumental in 

completing the Chesapeake Bay total maximum daily load or TMDL.

Special acknowledgment is made to past and present members the following CBP committees: 

WQGIT, Principals‘ Staff Committee, Management Board, STAC, LGAC, CAC, Agriculture 

Workgroup, Forestry Workgroup, Sediment Workgroup, Urban Stormwater Workgroup, 

Wastewater Treatment Workgroup, Watershed Technical Workgroup, TMDL Workgroup 

(formerly Reevaluation Technical Workgroup), and the former Nutrient Subcommittee.

Special acknowledgement is also made to the following individuals (in alphabetical order): 

Katherine Antos, EPA Region 3 CBP Office; Mike Barnes, Chesapeake Research 

Consortium/CBP Office; Rich Batiuk, EPA Region 3 CBP Office; Benita Best-Wong, EPA 

Office of Water; Carin Bisland, EPA Region 3 CBP Office; Chris Brosch, University of 

Maryland/CBP Office; Jon Capacasa, EPA Region 3 Water Protection Division; Peter Claggett, 

U.S. Geological Survey/CBP Office; Jeff Corbin, EPA Region 3 Office of Regional 

Administrator; Jim Curtin, EPA Headquarters, Office of General Counsel; Christopher Day, EPA 

Region 3 Office of Regional Counsel; Helene Drago, EPA Region 3 Water Protection Division; 

Mark Dubin, University of Maryland/CBP Office; Jim Edward, EPA Region 3 CBP Office; J. 

Charles Fox, EPA Headquarters Office of the Administrator; Shawn Garvin, EPA Regional 

Administrator; Kelly Gable, EPA Region 3 Office Regional Counsel; Aaron Gorka, Chesapeake 

Research Consortium/CBP Office; Mike Haire, EPA Office of Water; Suzanne Hall, EPA 

Region 3 Water Protection Division; Ruth Izraeli, EPA Region 2 Division of Environmental 

Planning and Protection; Jeni Keisman, University of Maryland/CBP Office; Victoria Kilbert, 

Chesapeake Research Consortium/CBP Office; Bob Koroncai, EPA Region 3 Water Protection 

Division; Lewis Linker, EPA Region 3 CBP Office; Felix Locicero, EPA Region 2 Division of 

Environmental Planning and Protection; Travis Loop, EPA Region 3 CBP Office; Larry Merrill, 

EPA Region 3 Water Protection Division; Linda Miller, EPA Region 3; Jenny Molloy, EPA 

Region 3 CBP Office/Water Protection Division; Sucharith Ravi, University of Maryland/CBP 
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xxviii September 24, 2010

Office; Jennifer Sincock, EPA Region 3 Water Protection Division; Gary Shenk, EPA Region 3 

CBP Office; Kelly Shenk, EPA Region 3 CBP Office; Rachel Streusand, Chesapeake Research 

Consortium/CBP Office; Jeff Sweeney, University of Maryland/CBP Office; Nita Sylvester, 

EPA Region 3 CBP Office; Peter Tango, U.S. Geological Survey/CBP Office; Tom Wall, EPA 

Headquarters Office of Water; Ping Wang, University of Maryland/CBP Office; Jing Wu, 

University of Maryland/CBP Office; John Wolf, U.S. Geological Survey/CBP Office; Rob 

Wood, EPA Region 3 CBP Office; and Ning Zhou, Virginia Polytechnical and State 

University/EPA Region 3 CBP Office.
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Members of the CBP‘s Water Quality Goal Implementation Team gather in Lancaster, 

Pennsylvania, in April 2009 to discuss development of the Chesapeake Bay TMDL.
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1-1 September 24, 2010

SECTION 1. INTRODUCTION

This document establishes total maximum daily loads (TMDLs) for nutrients (nitrogen and 

phosphorus) and sediment for the Chesapeake Bay and its tidal tributaries and embayments as 

required by section 303(d) of the Clean Water Act (CWA) and its implementing regulations at 

Title 40 of the Code of Federal Regulations (CFR) section 130.7. This TMDL represents the 

culmination of decades of collaboration among many partners and stakeholders and is the result 

of an analysis of water quality pollution and its solution on an unprecedented geographic, 

scientific, and political scale. While all TMDLs are unique, this TMDL is distinguished by the 

magnitude of the watershed it addresses and the wealth of data developed and analyses 

conducted over the course of the past decades that support its conclusions.

In an effort to keep the Bay TMDL document as clear and succinct as possible, discussion of the 

technical analyses and modeling that support the pollutant allocations are reasonably summary in 

nature with links provided to the more detailed technical support documentation. Because of the 

large size of the watershed and the many individual sources, load allocations (LAs) and 

wasteload allocations (WLAs) that are summarized in Section 9 are presented in greater detail in 

supporting appendices.

This document is organized into 11 sections as follows:

Section 1: CWA and regulatory, statutory, and historical background of the Chesapeake 

Bay TMDL

Section 2: Description of the Chesapeake Bay watershed, the Bay, and its impaired 

segments

Section 3: The jurisdictions‘ Chesapeake Bay water quality standards (WQS)

Section 4: The major sources of nutrients and sediment in the Bay, its watershed and its 

airshed

Section 5: The modeling tools used to develop the WLAs and LAs

Section 6: How the TMDL was developed, including the allocation methodology and 

related considerations

Section 7: Discussion of reasonable assurance, Bay TMDL implementation, and the Bay 

TMDL accountability framework

Section 8: The evaluation of jurisdictions‘ Watershed Implementation Plans (WIP) and 

decisions on backstop allocations

Section 9: The individual TMDLs for the 92 Bay tidal segments

Section 10: Adaptive management approach to Bay TMDL implementation

Section 11: Documentation of public participation, comments, and responses
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This document also contains three additional sections providing: a list of references (Section 12), 

a glossary (Section 13), and a list of abbreviations (Section 14).

Additional supporting information that is not part of this document, or its appendices, can be 

found as follows:

Technical documentation for each of the Chesapeake Bay TMDL models—airshed, land 

change, Scenario Builder, SPARROW, watershed, Bay water quality/sediment transport, 

oyster filter feeder and menhaden filter feeder—are provided via URL in Section 5.

Each of the jurisdictions‘ Phase I Watershed Implementation Plans (WIPs) is provided via 

URL in Section 7. The WIPs are part of the accountability framework meant to implement 

the Bay TMDL, but they are not part of the Bay TMDL itself. EPA also is reviewing the 

WIPs as part of the information to inform its allocation decisions.

Publicly accessible agreements, documents, reports, papers, meeting summaries, and 

correspondence developed during the decades and more recent years leading up to the 

Chesapeake Bay TMDL, which were instrumental in setting the scientific, policy, and legal 

foundation on which the Bay TMDL is built, are provided via URL in Appendix B.

1.1. TMDLs and the CWA

Section 303(c) of the 1972 CWA requires states, including the District of Columbia, (collectively 

referred to as jurisdictions) to establish WQS that identify each waterbody‘s designated uses and 

the criteria needed to support those uses. The CWA establishes a rebuttable presumption that all 

waters can attain beneficial aquatic life uses, i.e., fishable and recreational uses, i.e., swimmable.

Section 303(d) of the CWA requires states, including the District of Columbia, (collectively 

referred to as jurisdictions) to develop lists of impaired waters that fail to meet WQS set by 

jurisdictions even after implementing technology-based and other pollution controls. EPA‘s 

regulations for implementing CWA section 303(d) are codified in the Water Quality Planning 

and Management Regulations at 40 CFR Part 130. The law requires that jurisdictions establish 

priority rankings and develop TMDLs for waters on the lists of impaired waters (40 CFR 130.7).

A TMDL specifies the maximum amount of a pollutant that a waterbody can receive and still 

meet applicable WQS. A mathematical definition of a TMDL is written as the sum of the 

individual WLAs for point sources, the LAs for nonpoint sources and natural background, and a 

margin of safety [CWA section 303(d)(1)(C)]:

TMDL = ΣWLA + ΣLA + MOS

where

WLA = wasteload allocation, or the portion of the TMDL allocated to existing and/or future 

point sources.

LA = load allocation, or the portion of the TMDL attributed to existing and/or future 

nonpoint sources and natural background.

MOS = margin of safety, or the portion of the TMDL that accounts for any lack of 

knowledge concerning the relationship between effluent limitations and water 

quality, such as uncertainty about the relationship between pollutant loads and 
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1-3 September 24, 2010

receiving water quality, which can be provided implicitly by applying conservative 

analytical assumptions or explicitly by reserving a portion of loading capacity.

The process of calculating and documenting a TMDL involves a number of tasks and—

especially for a large, complex, multijurisdictional waterbody with multiple impairments—can 

require substantial effort and resources. Major tasks involved in the TMDL development process 

include the following:

Characterizing the impaired waterbody and its watershed

Identifying and inventorying the relevant pollutant source sectors

Applying the appropriate WQS

Calculating the loading capacity using appropriate modeling analyses to link pollutant 

loads to water quality

Identifying the required source allocations

The Bay TMDL report presents the results of the numerous analyses and model simulations and 

documents the informational elements described above. Because the Chesapeake Bay watershed 

is so large, and the analysis required for developing the Bay TMDL so extensive, the Chesapeake 

Bay TMDL and its supporting documentation consists of this report and additional supporting 

materials in the numerous appendices referenced throughout the report. The Bay TMDL is also 

supported by an extensive list of significant documents (Appendix B).

1.2 History of the Chesapeake Bay TMDL

The Chesapeake Bay watershed has been inhabited for thousands of years, but the population 

started to increase significantly with the arrival of European settlers in the 1600s. Settlers began 

clearing forests for timber and to make room for expanding agricultural activities, increasing soil 

erosion and nutrient delivery to the Bay and its tributaries (Curtin et al. 2001; Rountree et al. 

2007). As early as 1900, the oyster population began to decline. Throughout the 20th century, 

urban development and agricultural activities increased throughout the watershed. In the late 

1970s, Maryland Senator Charles Mathias sponsored a congressionally funded, 5-year study to 

analyze the rapid loss of aquatic life that was affecting the Bay. That study identified excess 

nutrient pollution as the main source of the Bay‘s degradation (USEPA 1982, 1983a, 1983b, 

1983c, 1983d).

1.2.1 Regulatory and Management Initiatives

In response to the Bay‘s decline, various regulatory and management initiatives have been 

undertaken aimed at Bay restoration, ranging from cooperative agreements among surrounding 

jurisdictions to regulatory and policy programs. Through the years, the agreements and alliances 

have become more formalized and inclusive to address the multitude of factors contributing to 

the deterioration in Chesapeake Bay water quality. The following paragraphs outline the major 

policy, legislative, and programmatic events that have led to the development of the Bay TMDL, 

including the management agreements and regulatory requirements that form the underpinning 

of the TMDL.
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1983 Chesapeake Bay Agreement

In 1983 the governors of Maryland, Virginia, and Pennsylvania; the mayor of the District of 

Columbia; the chairman of the Chesapeake Bay Commission; and EPA‘s Administrator signed 

the first Chesapeake Bay Agreement. In that agreement, the signatories acknowledged the 

decline in living resources of the Chesapeake Bay and agreed to establish the Chesapeake 

Executive Council (CEC) to ―assess and oversee the implementation of coordinated plans to 

improve and protect the water quality and living resources of the Chesapeake Bay estuarine 

systems‖ (Chesapeake Bay Partnership 1983).

1987 Chesapeake Bay Agreement

Faced with the need to take a more comprehensive and coordinated approach to restoring water 

quality and living resources of the Chesapeake Bay, the signatories to the 1983 agreement 

entered into the 1987 Chesapeake Bay Agreement (CEC 1987). The 1987 Chesapeake Bay 

Agreement set priority goals and commitments, of which a key goal was to ―reduce and control 

point and nonpoint sources of pollution to attain the water quality condition necessary to support 

the living resources of the Bay.‖ To achieve that goal, signatories to the 1987 Bay Agreement 

committed to reduce the controllable nitrogen and phosphorus loads delivered to the mainstem of 

the Chesapeake Bay by 40 percent by 2000 and to develop a Bay-wide implementation strategy 

to achieve those reductions (CEC 1987).

CWA Section 117 and the Chesapeake Bay Program (CBP)

In the 1987 amendments to the CWA, Congress—in section 117—authorized the formation and 

funding of the CBP within EPA Region 3. Congress directed the CBP to collect and disseminate 

information related to the environmental quality of the Bay, to ―coordinate state and federal 

efforts to improve Bay water quality, to evaluate sediment impacts on the Bay, and to determine 

the impact of natural and human-induced environmental changes on the living resources of the 

Bay.‖

1

1991 Reevaluation

A 1991 reevaluation of progress made toward the 1987 Bay Agreement‘s 40 percent nutrient 

reduction goal led to a detailed quantification of the original narrative goal. Each major river 

basin by jurisdiction received a ―tributary nutrient load allocation‖ as a ―40% controllable load 

reduction‖ for both nitrogen and phosphorus as the principal outcome of the reevaluation 

(Secretary Robert Perciasepe 1992). The 1991 reevaluation also introduced several concepts still 

applicable in the Bay TMDL: tributary strategies (WIPs), limit of technology (E3 scenario), 

recognition of air deposition (air allocation to tidal surface waters), and geographic-based 

allocations (relative effectiveness-based allocation methodology).

1992 Amendments to the Chesapeake Bay Agreement

The 1991 reevaluation led to several amendments to the 1987 Chesapeake Bay Agreement in 

1992, including an increased focus on the importance of tributaries in the Bay‘s restoration. The 

parties to the 1987 Chesapeake Bay Agreement were to begin by 1993 to develop and implement 

tributary-specific strategies to meet mainstem nutrient reduction goals, to improve water quality, 

and to restore living resources to the mainstem and tributaries (CEC 1992). The amendments

 

1 Clean Water Act section 117 (33 United States Code [U.S.C.] 1267).
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1-2 September 24, 2010

also established the distribution of submerged aquatic vegetation (SAV) as an initial measure of 

progress toward the water quality and living resource goals of the 1987 Agreement.

1997 Reevaluation

In 1997 the CBP conducted a year-long evaluation to assess what progress had been made 

toward the goal set in the 1987 Agreement of a 40 percent reduction in nitrogen and phosphorus 

delivered to the Bay by 2000 (CEC 1997). The 1997 reevaluation found that between 1985 and 

1996 phosphorus loads delivered to the Bay declined by 6 million pounds annually, and nitrogen 

loads delivered to the Bay declined by 29 million pounds annually. By 1996 phosphorus loads 

from wastewater dischargers had been reduced by 51 percent in the participating jurisdictions as 

a result of implementing effluent standards, upgrading wastewater treatment plants, and banning

phosphate laundry detergents. Wastewater nitrogen loads were reduced by 15 percent by

implementing biological nutrient removal at some major municipal wastewater treatment 

facilities and industrial wastewater treatment facility upgrades. Implementation of nutrient 

reduction best management practices (BMPs) reduced nonpoint source loadings of nitrogen and 

phosphorus to the Bay by 7 and 9 percent, respectively. There was no clear trend in Bay 

dissolved oxygen (DO) levels, however. Although progress was made, the 1997 reevaluation 

report stated, ―we must accelerate our efforts to close the gap on the year 2000 goal, maintain 

those reduced loading levels into the future and if necessary adjust the nutrient goals to help us 

achieve the water quality improvements needed to sustain living resources in the Bay‖ (CBP

1997).

1999 Integration of Cooperative and Statutory Programs

In September 1999, senior water quality program managers representing the jurisdictions and 

EPA outlined the Process for Integrating the Cooperative and Statutory Programs of the 

Chesapeake Bay and its Tributaries—Continuing the Watershed Partnership to Restore the 

Chesapeake Bay (CBP 1999). That consensus document laid the groundwork for the water 

quality goals and commitments within the Chesapeake 2000 Agreement. A decade in advance, it 

set the partnership on a course that culminated in the Bay TMDL.

Chesapeake 2000 Agreement

In June 2000 the governors of Maryland, Virginia, and Pennsylvania; the mayor of the District of 

Columbia; the Administrator of EPA; and the chairman of the Chesapeake Bay Commission

signed the Chesapeake 2000 Agreement (CEC 2000). To meet the goal of ―achieving and 

maintaining the water quality necessary to support the aquatic living resources of the Bay and its 

tributaries and to protect human health,‖ the signatories committed to specific actions, including:

Continue to achieve and maintain the 40 percent nutrient reduction goal agreed to 

in 1987.
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1-3 September 24, 2010

By 2010, correct nutrient- and sediment-related problems in the Chesapeake Bay 

and its tidal tributaries sufficiently to remove the Bay and the tidal portions of its 

tributaries from the list of impaired waters under the Clean Water Act. In order to 

achieve this:

1. By 2001, define the water quality conditions necessary to protect aquatic living 

resources and then assign load reductions for nitrogen and phosphorus to each 

major tributary;

2. Using a process parallel to that established for nutrients, determine the sediment 

load reductions necessary to achieve the water quality conditions that protect 

aquatic living resources, and assign load reductions for sediment to each major 

tributary by 2001;

3. By 2002, complete a public process to develop and begin implementation of 

revised Tributary Strategies to achieve and maintain the assigned loading goals;

4. By 2003, the jurisdictions with tidal waters will use their best efforts to adopt 

new or revised [WQS] consistent with the defined water quality conditions. 

Once adopted by the jurisdictions, the Environmental Protection Agency will 

work expeditiously to review the new or revised standards, which will then be 

used as the basis for removing the Bay and its tidal rivers from the list of 

impaired waters; and

5. By 2003, work with the Susquehanna River Basin Commission and others to

adopt and begin implementing strategies that prevent the loss of the sediment 

retention capabilities of the lower Susquehanna River dams.

2000 Six-Jurisdiction Memorandum of Understanding

In the fall of 2000, EPA, Delaware, the District of Columbia, Maryland, New York, 

Pennsylvania, and Virginia signed a Memorandum of Understanding (MOU) (Chesapeake Bay 

Watershed Partners 2000), with West Virginia joining as a signatory in June 2002, agreeing to

the following:

Work cooperatively to achieve the nutrient and sediment reduction targets necessary to 

achieve the goals of a clean Chesapeake Bay by 2010, thereby allowing the Chesapeake 

Bay and its tidal tributaries to be removed from the list of impaired waters.

Provide for an inclusive, open and comprehensive public participation process.

Collaborate on the development and use of innovative measures such as effluent trading, 

cooperative implementation mechanisms, and expanded interstate agreements to achieve 

the necessary reductions.

The signatories also agreed to report annually on progress toward achieving the goals of the 

agreement.

2003 Nutrient and Sediment Cap Load Allocations

In 2003 EPA and its watershed partners established nutrient and sediment cap loads on the basis 

of the Bay water quality model projections of attainment of the then EPA-proposed DO water 

quality criteria under long-term average hydrologic conditions (Secretary Tayloe Murphy 2003). 
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1-4 September 24, 2010

Reaching those cap loads was expected to eliminate the summer anoxic conditions in the deep 

waters of the Bay and the excessive algal blooms throughout the Bay and tidal tributaries 

(USEPA 2003b).

EPA and its watershed jurisdiction partners allocated the nutrient cap loads among the major 

river basins. Those jurisdictions with the highest impact on Bay water quality were assigned the 

highest nutrient reductions, while jurisdictions without tidal waters received less stringent 

reductions because they would not realize a direct benefit from the improved water quality 

conditions in the Bay (USEPA 2003b). Sediment allocations were based on the phosphorusequivalent allocations to each major river basin by jurisdiction (USEPA 2003b).

Although not original signatories of the Chesapeake 2000 Agreement, New York, Delaware, and 

West Virginia signed on as partners in implementing the cap loads; thus, all seven Bay 

jurisdictions were assigned allocations (Chesapeake Bay Watershed Partners 2000; USEPA 

2003b). The final total basinwide cap loads agreed to by the jurisdictions were 175 million 

pounds for nitrogen and 12.8 million pounds of phosphorus delivered to the tidal waters of the 

Bay (USEPA 2003b). The basinwide upland sediment cap load was 4.15 million tons (USEPA 

2003b).

2004–2006 Tributary Strategies

To implement the cap loads, the seven watershed jurisdictions developed what became known as 

the Chesapeake Bay Tributary Strategies (Table 1-1) (Secretary Tayloe Murphy 2003). The 

tributary strategies outlined river basin-specific implementation activities to reduce nitrogen, 

phosphorus, and sediment from point and nonpoint sources sufficient to remove the Chesapeake 

Bay and its tidal tributaries and embayments from the Bay jurisdictions‘ respective impaired 

waters lists. Many of the policies and procedures used in developing the Chesapeake Bay TMDL 

originated with the development of the 2003 nutrient and sediment cap loads and subsequent 

development of tributary strategies.

Table 1-1. URLs for accessing the seven Chesapeake Bay watershed jurisdictions’ tributary 

strategies

Jurisdiction Tributary strategy 

Delaware http://www.chesapeakebay.net/watershedimplementationplantools.aspx?menuitem=52044

District of 

Columbia

http://www.chesapeakebay.net/watershedimplementationplantools.aspx?menuitem=52044

Maryland http://www.dnr.state.md.us/bay/tribstrat/implementation_plan.html

New York http://www.dec.ny.gov/docs/water_pdf/cbaystratfinal.pdf

Pennsylvania http://www.chesapeakebay.net/watershedimplementationplantools.aspx?menuitem=52044

Virginia http://www.chesapeakebay.net/watershedimplementationplantools.aspx?menuitem=52044

West Virginia http://www.wvca.us/bay/files/bay_documents/8_9657_WV_Potomac_Tributary_Strategy_FIN

AL_from_web.pdf

2004–2005 Jurisdiction Adoption of Chesapeake Bay Water Quality Standards

In continued efforts to coordinate activities to address nutrient and sediment-based pollution in 

the Bay, the tidal jurisdictions of Maryland, Virginia, Delaware, and the District of Columbia 

adopted into their respective WQS regulations the EPA-published Chesapeake Bay water quality 

criteria for DO, water clarity, SAV, and chlorophyll a, along with criteria attainment assessment 
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1-5 September 24, 2010

procedures and refined tidal water designated uses (for details, see Section 3) (USEPA 2003a, 

2003c). EPA approved those WQS modifications pursuant to CWA section 303(c).

2007 Reevaluation

Secretary Tayloe Murphy‘s 2003 memorandum summarized the comprehensive set of 

agreements made by Bay watershed partners with regard to cap loads for nitrogen, phosphorus,

and sediment; new Bay-wide and local SAV restoration goals; and a commitment to reevaluate 

the allocations in 2007. The initiation of that reevaluation at a workshop in September 2005 laid 

the institutional groundwork for the collaborative work on the Bay TMDL (Chesapeake Bay 

Reevaluation Steering Committee 2005).

EPA and the seven jurisdictions reevaluated the nutrient and sediment cap loads in 2007, in 

response to the four Bay jurisdictions revising their WQS regulations for the Chesapeake Bay 

and its tidal tributaries (Secretary Tayloe Murphy 2003). The 2007 reevaluation found that 

sufficient progress had not been made toward improving water quality in the Chesapeake Bay to 

a level that the mainstem Chesapeake Bay and its tidal tributaries were no longer impaired by 

nutrients and sediment (Chesapeake Bay Reevaluation Steering Committee 2005).

1.2.2 Partnership Commitment to Develop the Chesapeake Bay TMDL

Throughout the Bay TMDL development process, EPA has worked in close and open partnership 

with all seven watershed jurisdictions, sharing decision making with the jurisdictions via the 

CBP structure described in more detail in Section 1.3. While EPA is developing the Bay TMDL, 

the seven watershed jurisdictions have been essential partners in the initiative, providing critical 

input and participating in deliberations and key decisions affecting the development process. The 

seven Bay watershed jurisdictions and EPA have been building the foundation for the 

Chesapeake Bay TMDL since signing the Chesapeake 2000 Agreement, which laid out the steps 

necessary to put in place an appropriate framework for a future Bay TMDL, including consistent 

jurisdictional Chesapeake Bay WQS (CEC 2000).

From September 2005 to the present, the seven watershed jurisdictions have been actively 

involved in decision making related to developing the Bay TMDL through participation in the 

CBP‘s Principals‘ Staff Committee (PSC), Water Quality Goal Implementation Team (WQGIT), 

and other decision-making committees and technical workgroups (see Section 1.3.1). The full 

records of the meetings and conference calls of those groups are accessible via the Internet—see 

Appendix C.

At the October 1, 2007, meeting of the PSC, the seven watershed jurisdictions and EPA reached 

consensus

2

that EPA would establish the Bay TMDL on behalf of the jurisdictions with a target 

restoration date of 2025 (CBP PSC 2007). Table 1-2 summarizes that and the other Bay TMDLrelevant consensus agreements reached by the partners during that meeting.

 

2 Consensus within the Principals‘ Staff Committee means that all parties present have either agreed on this as a 

course of action and/or that no party objected to it.
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1-6 September 24, 2010

Table 1-2. Summary of Chesapeake Bay TMDL relevant actions agreed to by the CBP’s Principals’ 

Staff Committee during its October 1, 2007, meeting

The Bay watershed TMDLs will be developed jointly between the six Bay watershed states, the 

District, and EPA and then established by EPA.

The Water Quality Steering Committee (WQSC) will draft nutrient and sediment cap load allocations 

by tributary basin by jurisdiction, and the PSC will formally adopt these allocations.

The watershed states and the District would have responsibility for further assigning loads —WLAs

and LAs—to sources consistent with EPA regulations and guidance.

These state/District suballocations (WLA/LA) would become part of the overall Bay watershed 

TMDLs report.

The final publication would contain all the required documentation supporting the EPA Bay 

watershed TMDLs in a single, integrated publication with extensive appendices.

EPA will provide the technical resources/analyses required to support development of the Bay 

watershed TMDLs through the CBP Office staff and EPA-funded contractor support.

The Bay watershed TMDLs must be completed and established by EPA no later than May 1, 2011.

The CBP partners will engage stakeholders and the public in a more extensive structured dialogue 

about the tributary strategy implementation challenges before us.

The CBP partners will focus on getting the programs in place by 2010 that we believe are required to 

achieve our water quality goals.

The CBP partnership‘s public announcement of initiation of work on the Bay watershed TMDLs will 

occur following the states‘ submission and EPA approval of the 2008 303(d) lists in the spring 2008 

time frame.

Eight principles will guide the reevaluation efforts by the WQSC and its workgroups (see Attachment 

A for more detailed version):

o Shared urgency to restore the Bay;

o Clear communication and common message;

o Focus and accelerate implementation (do no harm);

o Engage the public about the implementation challenge;

o Legal obligations will be met;

o Improving and applying the latest science;

o Flexibility of the sub-allocations within the major basins; and

o Keep healthy waters healthy.

The WQSC will proceed forward with the responsibility for carrying out the necessary preparation 

work following these eight guiding principles.

The state/EPA Reevaluation Technical Workgroup (RTWG) will be reconvened and operate under 

the direction of the WQSC.

The RTWG was charged with responsibility for resolving the existing technical issues in light of the 

desire to accelerate implementation at all scales. The WQSC will convene a parallel Implementation 

Workgroup and charge this group with the responsibility for ensuring that the reevaluation and 

TMDL development process results in acceleration of ongoing tributary strategy implementation.

Source: CBP PSC 2007

1.2.3 President’s Chesapeake Bay Executive Order

On May 12, 2009, President Barack Obama issued the Chesapeake Bay Protection and 

Restoration Executive Order 13508, which calls for the federal government to lead a renewed 

effort to restore and protect the Chesapeake Bay and its watershed. Critical among its directives 

were

Establish a Federal Leadership Committee to oversee the development and coordination of 

reporting, data management and other activities by agencies involved in Bay restoration.
DRAFT Chesapeake Bay TMDL

1-7 September 24, 2010

Require involved agencies to prepare and submit reports with recommendations on a wide 

range of Bay issues (EPA-HQ-OW-2009-0761; FRL-8978-8).

Require the Federal Leadership Committee to develop a Strategy for Protecting and 

Restoring the Chesapeake Bay by May 2010 (see 

http://executiveorder.chesapeakebay.net/).

Require the Federal Leadership Committee to publish an annual Chesapeake Bay Action 

Plan describing how Federal funding proposed in the President‘s Budget will be used to 

protect and restore the Chesapeake Bay during the upcoming fiscal year.

Require federal agencies to consult extensively with Bay jurisdictions in preparing their 

reports.

Pursuant to the Executive Order, on May 12, 2010, the Federal Leadership Committee—led by 

the EPA Administrator and secretaries from the Departments of Agriculture, Commerce, 

Defense, Homeland Security, Interior, Transportation and others—issued its coordinated strategy 

for restoring the Chesapeake Bay (FLCCB 2010). That strategy sets measurable goals for 

improving environmental conditions in the Bay for the following:

Clean water

Habitat

Fish and wildlife

Land and public access

Other supporting strategies address citizen stewardship, climate change, science, and 

implementation and accountability.

A key element of the approach for meeting water quality goals is the development of this TMDL 

for the Chesapeake Bay (FLCCB 2010).

Parallel to the issuance of the Executive Order, the jurisdictions and the federal government 

committed to implement all necessary measures for restoring water quality in the Bay by 2025 

and to meet specific milestones every 2 years (FRL-8955-4; Clean Water Act Section 303(d): 

Preliminary Notice of Total Maximum Daily Load (TMDL) Development for the Chesapeake 

Bay). To that end, EPA is developing an accountability framework to guide the overall 

restoration effort and to link it to implementation of the Chesapeake Bay TMDL. The 

accountability framework, which is discussed in more detail in Section 8, includes four elements:

Watershed Implementation Plans (WIPs)

Two-year milestones to demonstrate restoration progress

EPA‘s commitment to track and assess progress

Federal actions if the watershed jurisdictions fail to develop sufficient WIPs, effectively 

implement their WIPs, or fulfill their 2-year milestones

1.3 Bay TMDL Process, Partner Coordination and Responsibilities

EPA Region 3 is the lead federal office responsible for developing the Chesapeake Bay TMDL, 

with the Water Protection Division (WPD) having direct responsibility for publication of the Bay 

TMDL. In developing this TMDL, WPD has coordinated efforts with the CBP Office, the Air 
DRAFT Chesapeake Bay TMDL

1-8 September 24, 2010

Protection Division, and the Office of Regional Counsel (all within Region 3), EPA Region 2, 

and EPA Headquarters. Throughout the Bay TMDL development process, EPA has worked in 

close and open partnership with all seven watershed jurisdictions, numerous federal agency 

partners, and a diverse array of other partners and stakeholders through the CBP partnership. 

This section describes the different elements of the CBP organizational structure and provides 

additional description of the roles and responsibilities of the various entities and stakeholders 

involved in developing the Chesapeake Bay TMDL.

1.3.1 CBP Partnership and Organizational Structure

The CBP is a unique regional partnership within EPA Region 3 that includes Maryland, 

Pennsylvania, Virginia, the District of Columbia, the Chesapeake Bay Commission, EPA, federal 

agencies, and participating advisory groups. The headwater states of Delaware, New York, and 

West Virginia participate as full partners on issues related to water quality. Each of the CBP

partners agrees to use its own resources to implement projects and activities that advance Bay 

restoration.

The partnership defines its collective actions through formal, voluntary agreements and provides 

general policy direction through consensus documents, typically called directives. The CBP 

works through a series of Goal Implementation Teams with oversight provided by the CBP‘s 

Management Board. Extensive documentation of the CBP structure and governance is provided 

in Chesapeake Bay Program Governance—Managing the Partnership for a Restored and 

Protected Watershed and Bay (CBP 2009). Figure 1-1 shows the CBP organizational chart.

Source: CBP 2009

Figure 1-1. CBP’s organizational structure.
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1-9 September 24, 2010

Chesapeake Executive Council (CEC)

The top executive of each of the signatories of the Chesapeake 2000 Agreement (state governors, 

District of Columbia mayor, EPA Administrator, and Chesapeake Bay Commission Chair), form 

the CEC, which meets annually to set basinwide policies and the future directions for CBP. 

Delaware, New York, and West Virginia participate in CEC meetings and have full input status 

on all water quality-related matters. PSC members serve as advisors to their respective CEC 

members. The CEC has played a pivotal role in developing the Bay TMDL by signing the

Chesapeake 2000 Agreement and subsequent directives and by setting the partnership on a welldefined, 10-year path directly supporting development of the Bay TMDL (CEC 2000, 2003, 

2005).

Federal Leadership Committee

To bring the full weight of the federal government to address the Chesapeake‘s challenges, 

President Obama issued Executive Order 13508 on Chesapeake Bay Protection and Restoration 

and established the Federal Leadership Committee, which is chaired by the Administrator of the 

U.S. Environmental Protection Agency and includes senior representatives from the departments 

of Agriculture, Commerce, Defense, Homeland Security, Interior, and Transportation.

Principals’ Staff Committee (PSC)

The PSC provided policy and programmatic direction to the Management Board and the WQGIT 

on the development and adoption of the Chesapeake Bay nutrient and sediment targets and 

allocations for the Bay TMDL (Figure 1-1). The PSC is composed of cabinet-level 

representatives from each of the seven watershed jurisdictions, EPA Region 3‘s Regional 

Administrator, senior federal agency executives, the Chesapeake Bay Commission executive 

director and the director of the CBP Office. The Regional Administrator of EPA Region 3 

currently chairs the PSC. The Citizens, Local Governments, and the Scientific and Technical 

advisory committees all advise the PSC.

Management Board

PSC members provide policy and program direction to the Management Board which, in turn, 

provided strategic planning, priority setting, and operational guidance and direction to the 

WQGIT during the development of the Bay TMDL (Figure 1-1). The Management Board is 

composed of senior policy representatives from the seven watershed jurisdictions, the 

Chesapeake Bay Commission, the nine core federal agency partners,3and the chairs of the 

Citizens, Local Governments, and the Scientific and Technical advisory committees. The 

Management Board directs and coordinates the efforts of the six Goal Implementation Teams 

and Action Teams. The director of the CBP Office chairs the Management Board, and the CBP 

Office provides for the staff to support the work of all the Goal Implementation Teams and 

workgroups. Staffing for the three advisory committees is supported by EPA through cooperative 

agreements with nonprofit organizations.

Water Quality Goal Implementation Team

The WQGIT‘s purpose is to support efforts to reduce and cap the nutrient and sediment loads 

entering the Bay and to ensure that such reductions are maintained over time. It is composed of 

 

3 The Natural Resources Conservation Service, U.S. Forest Service, National Oceanic and Atmospheric 

Administration, U.S. Geological Survey, National Park Service, U.S. Fish and Wildlife Service, U.S. Army Corps of 

Engineers, U.S. Department of Defense, and EPA.
DRAFT Chesapeake Bay TMDL

1-10 September 24, 2010

the members of the former Water Quality Steering Committee and the Nutrient Subcommittee. 

The WQGIT provided advice and guidance to EPA related to the targets and allocations before 

they were brought to the PSC. The WQGIT consists of senior water program managers from 

each of the seven Bay watershed jurisdictions, EPA Headquarters and Regions 2 and 3, the 

Chesapeake Bay Commission, the Susquehanna River Basin Commission, and the Potomac 

River Basin Commission. The WQGIT provided technical direction to the Watershed Technical, 

Agriculture, Forestry, Wastewater Treatment, Sediment, and Urban Stormwater workgroups.

Watershed Technical Workgroup

The Watershed Technical Workgroup was created to provide a forum for communication among 

the jurisdictions and other CBP participants on technical issues related to tributary strategy

development, tracking and reporting. Members of the Watershed Technical Workgroup include 

technical staff and mid-level managers from the seven watershed jurisdictions, EPA, and point 

source and environmental stakeholder groups. For the Chesapeake Bay TMDL, the workgroup 

provided review and oversight in regards to application of the Bay Watershed Model.

Pollutant Source Workgroups

The Agricultural Workgroup coordinated and evaluated agricultural nutrient and sediment 

reduction measures throughout the jurisdictions and resolved issues related to tracking, reporting, 

and crediting conservation practices.

The Forestry Workgroup provided information on the effectiveness of different riparian forest 

buffer restoration and other forest management practices.

The Wastewater Treatment Workgroup provided a formal means of communication among 

federal agencies, state agencies/jurisdictions, and wastewater treatment plants.

The Sediment Workgroup provided technical and policy-related assistance to the CBP partners in 

setting the sediment allocations.

The Urban Stormwater Workgroup provided input related to all aspects of stormwater nutrient 

and sediment loads and management practices.

Science, Technical Analysis, and Reporting Team—Criteria Assessment Protocols 

Workgroup

The Criteria Assessment Protocols Workgroup had the lead responsibility for ensuring 

coordinated assessment of all Chesapeake Bay and tidal tributary/embayment waters related to 

the Bay jurisdictions‘ listing and delisting under CWA section 303(d). The workgroup also had 

the lead in developing, reviewing, and recommending to the WQGIT amendments to the original 

2003 Chesapeake Bay water quality criteria.

Science, Technical Analysis, and Reporting Team—Modeling Workgroup

The Modeling Workgroup, formerly the Modeling Subcommittee and now under the Science, 

Technical Analysis, and Reporting (STAR) team, oversaw the development, calibration, 

verification, and management application of the suite of computer-based Bay models that 

supported the development of the Bay TMDL. The models allowed managers to estimate the 

pollutant load reductions needed to achieve WQS and to assess the potential of different 

management scenarios to achieve the needed pollutant load reductions.
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1-11 September 24, 2010

Scientific and Technical Advisory Committee

The Scientific and Technical Advisory Committee (STAC) is composed of scientists from 

academic institutions from all seven watershed jurisdiction and federal science agencies, 

representing a diverse range of disciplines. STAC provides scientific and technical guidance and 

peer review to the CBP partnership on measures to restore and protect the Chesapeake Bay. 

STAC activities related to the Bay TMDL included providing for independent scientific peer 

reviews of all the Bay models (watershed, land change, estuarine water quality, estuarine 

sediment transport), Bay criteria assessment procedures, land use data, and reviewing and 

commenting on the draft Bay TMDL.

Local Governments Advisory Committee

The Local Governments Advisory Committee (LGAC) is a body of officials appointed by the 

governors of Maryland, Pennsylvania, Virginia, and the mayor of the District of Columbia to 

improve the role local governments can play in Bay restoration efforts and develop strategies to 

broaden local government participation in the CBP. The LGAC was directly involved in 

developing the Bay TMDL in the following ways: ensured the direct involvement of local 

elected officials in the decision-making processes, helped establish the local WIP pilots in 2010 

(before development of the Phase II WIPs in 2011), and helped inform the thousands of local 

governments across the watershed about the Bay TMDL.

Citizen’s Advisory Committee

The Citizens Advisory Committee (CAC) provided advice to the CEC, the PSC, the 

Management Board, and all the Goal Implementation Teams as needed in implementing the 

Chesapeake Bay Agreement. The CAC directly assisted the Bay TMDL development process by 

providing detailed recommendations on how to engage the nongovernmental components of the 

larger Bay watershed community and placing a strong focus on ensuring full accountability 

during the development and throughout the long-term implementation of the Bay TMDL.

Appendix A provides the membership lists of all the above described committees, teams, and 

workgroups at the time of publication of the Bay TMDL, fully acknowledging their individual 

and collective contributions.

1.4 Legal Framework for the Chesapeake Bay TMDL

1.4.1. What is a TMDL?

As discussed more fully in Section 1.1, a TMDL specifies the maximum amount of a pollutant 

that a waterbody can receive and still meet applicable WQS. Allocations to point sources are 

called WLAs, while allocations to nonpoint sources are called LAs. A TMDL is the sum of the 

individual WLAs (for point sources), LAs (for nonpoint sources and natural background) (40 

CFR 130.2), and a margin of safety [CWA section 303(d)(1)(C)]. Section 303(d) requires that 

TMDLs be established for impaired waterbodies ―at a level necessary to implement the 

applicable [WQS].‖4

TMDLs are ―primarily informational tools‖ that ―serve as a link in an implementation chain that 

includes federally regulated point source controls, state or local plans for point and nonpoint 

 

4

33 U.S.C. 1313(d)(1)(C).
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1-12 September 24, 2010

source pollutant reduction, and assessment of the impact of such measures on water quality, all 

to the end of attaining water quality goals for the nation‘s waters.‖5 Recognizing a TMDL‘s role 

as a vital link in the implementation chain, federal regulations require that effluent limits in 

NPDES permits be ―consistent with the assumptions and requirements of any available WLA‖ in 

an approved TMDL.6

In addition, before EPA establishes or approves a TMDL that allocates pollutant loads to both 

point and nonpoint sources, it determines whether there is reasonable assurance that the 

nonpoint source LAs will, in fact, be achieved and WQS will be attained (USEPA 1991a). If the 

reductions embodied in LAs are not fully achieved, the collective reductions from point and 

nonpoint sources will not result in attainment of the WQS.

The Bay TMDL will be implemented using an accountability framework that includes WIPs, 2-

year milestones, EPA‘s tracking and assessment of restoration progress and, as necessary, 

specific federal actions if the Bay jurisdictions do not meet their commitments. The 

accountability framework is being established, in part, to demonstrate that the TMDL is 

supported by reasonable assurance. The accountability framework is also being established 

pursuant to CWA section 117(g)(1). Section 117(g) of the CWA directs the EPA Administrator 

to ―ensure that management plans are developed and implementation is begun...to achieve and 

maintain...the nutrient goals of the Chesapeake Bay Agreement for the quantity of nitrogen and 

phosphorus entering the Chesapeake Bay and its watershed, [and] the water quality requirements 

necessary to restore living resources in the Chesapeake Bay ecosystem.‖7 In addition, Executive 

Order 13508 directs EPA and other federal agencies to build a new accountability framework 

that guides local, state, and federal water quality restoration efforts. The accountability 

framework is designed to help ensure that the Bay‘s nutrient goals, as embodied in the 

Chesapeake Bay TMDL, are met. While the accountability framework informs the TMDL 

section 303(d) does not require that EPA ―approve‖ the framework per se, or the jurisdictions‘ 

WIPs that constitute part of that framework.

1.4.2. Why is EPA establishing this TMDL?

In 1998 data showed the mainstem and tidal waters of the Chesapeake Bay to be impaired for

aquatic life resources. EPA determined that the mainstem and tidal waters of the Chesapeake 

Bay must be placed on Virginia‘s section 303(d) list. EPA therefore added the mainstem of the 

Chesapeake Bay to Virginia‘s final section 303(d) list. As described in Section 2, each river, 

tributary, and other waterbody that is part of the Chesapeake Bay TMDL is included on a 

jurisdiction‘s section 303(d) list.

EPA is establishing the Chesapeake Bay TMDL pursuant to a number of existing authorities, 

including the CWA and its implementing regulations, judicial consent decrees requiring EPA to 

address certain impaired Chesapeake Bay and tidal tributary waters, a settlement agreement 

resolving litigation brought by the Chesapeake Bay Foundation, the current Chesapeake Bay 

Agreement, and Executive Order 13508. In establishing the Bay TMDL, EPA has acted pursuant 

 

5

Pronsolino v. Nastri, 291 F.3d 1123, 1129 (9th Cir. 2002).

6

40 CFR 122.44(d)(1)(vii)(B).

7 Clean Water Act section 117(g)(1)(A)-(B), 33 U.S.C. 1267(g)(1)(A)-(B).
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1-13 September 24, 2010

to the consensus direction of the Chesapeake Executive Council‘s PSC and in partnership with 

each of the seven Chesapeake Bay watershed jurisdictions.

The CWA provides EPA with ample authority to establish the Chesapeake Bay TMDL. CWA 

section 117(g)(1) provides that ―[t]he Administrator, in coordination with other members of the 

[CEC], shall ensure that management plans are developed and implementation is begun by 

signatories to the Chesapeake Bay Agreement to achieve and maintain [among other things] the 

nutrient goals of the Chesapeake Bay Agreement for the quantity of nitrogen and phosphorus 

entering the Chesapeake Bay and its watershed [and] the water quality requirements necessary to 

restore living resources in the Chesapeake Bay ecosystem.‖ Because it establishes the Bay and 

tidal tributaries‘ nutrient and sediment loading and allocation targets, the Chesapeake Bay 

TMDL is such a management plan. In addition, the Bay TMDL‘s loading and allocation targets 

both inform and are informed by, a larger set of federal and state management plans being 

developed for the Bay, including the jurisdiction WIPs and the May 2010 Bay strategy.

CWA section 303(d) requires jurisdictions to establish and submit TMDLs to EPA for review. 

Under certain circumstances, EPA also has the authority to establish TMDLs. The circumstances 

of this TMDL do not necessarily identify the outer bounds of EPA‘s authority. However, where 

impaired waters have been identified on jurisdictions‘ section 303(d) lists for many years, where 

the states in question have decided not to establish their own TMDLs for those waters, where 

EPA is establishing a TMDL for those waters at the direction of, and in cooperation with, the 

jurisdictions in question, and where those waters are part of an interrelated and interstate water 

system like the Chesapeake Bay that is impaired by pollutant loadings from sources in seven 

different jurisdictions, CWA section 303(d) authorizes EPA authority to establish that TMDL8.

On May 12, 2009, President Barack Obama signed Executive Order 13508—Chesapeake Bay 

Protection and Restoration. The Executive Order‘s overarching goal is ―to protect and restore 

the health, heritage, natural resources, and social and economic value of the Nation‘s largest 

estuarine ecosystem and the natural sustainability of its watershed.‖ The Executive Order says 

the federal government ―should lead this effort‖ and acknowledges that progress in restoring the 

Bay ―will depend on the support of state and local governments.‖ To that end, the Executive 

Order directs the lead federal agencies, including EPA, to work in close collaboration with their 

state partners. To protect and restore the Chesapeake Bay and its tidal tributaries, the President 

directed EPA to ―make full use of its authorities under the [CWA].‖ In establishing the Bay 

TMDL, EPA is doing no more—or less—than making full use of its CWA authorities to lead a 

collaborative and effective federal and state effort to meet the Bay‘s nutrient and sediment goals.

A number of consent decrees, MOUs, and settlement agreements provide additional support for 

EPA‘s decision to establish the Chesapeake Bay TMDL addressing certain waters identified as 

impaired on the Maryland, Virginia, and District of Columbia‘s 1998 section 303(d) lists and on 

the Delaware 1996 section 303(d) list. EPA is establishing the Chesapeake Bay TMDL 

consistent with those consent decrees, MOUs, and settlement agreements, described below.

 

8

 Dioxin/Organochlorine Center v. Clarke, 57 F.3d 1517 (9

th Cir. 1995); Scott v. City of Hammond, 741 F.2d 992 

(7th Cir. 1984); American Canoe Ass’n. v EPA, 54 F.Supp.2d 621 (E.D.Va. 1999).
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1-14 September 24, 2010

Virginia–EPA Consent Decree

The American Canoe Association, Inc., and the American Littoral Society filed a complaint 

against EPA for failing to comply with the CWA, including section 303(d), regarding the TMDL 

program in the Commonwealth of Virginia. A consent decree signed in 1999 resolved the 

litigation.9The consent decree includes a 12-year schedule for developing TMDLs for impaired 

segments identified on Virginia‘s 1998 section 303(d) list. The consent decree requires EPA to 

establish TMDLs for those waters, by May 1, 2011, if Virginia fails to do so according to the 

established schedule. Virginia has requested that EPA establish TMDLs for the nutrient- and 

sediment-impaired tidal portions of the Chesapeake Bay and its tributaries in accordance with the 

Virginia consent decree schedule (CBP PSC 2007). Table 1-1 provides a list of the Virginia 

consent decree waters that will be addressed by the Chesapeake Bay TMDLs for nutrients and 

sediment.

 

9 American Canoe Association v. EPA, 98cv979 (June 11, 1999).
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1-15 September 24, 2010

Table 1-3. Virginia consent decree (CD) waters impaired for dissolved oxygen (DO) and/or 

nutrients that will be addressed by the Chesapeake Bay TMDL

Waterbody Name

CD 

Segment ID

Chesapeake Bay 

Segment ID

CD 

Impairment

Bailey Bay, Bailey Creek –

Tidal VAP-G03E JMSTF1 DO

Broad Creek VAT-G15E

ELIPH, WBEMH,SBEMH, 

EBEMH DO

Chesapeake Bay Mainstem Narrative a CB5MH, CB6PH, CB7PH Nutrients

Chesapeake Bay Mainstem VACB-R01E CB5MH, CB6PH, CB7PH DO

Elizabeth River – Tidal Narrative b

ELIPH, WBEMH,SBEMH, 

EBEMH Nutrients

Hungars Creek VAT-C14R CB7PH DO

James River – Tidal Narrative c

JMSTF2, JMSTF1, 

JMSOH, JMSMH, JMSPH Nutrients

King Creek VAT-F27E YRKPH DO

Mattaponi River – Tidal Narrative d MPNTF, MPNOH Nutrients

Messongo Creek VAT-C10E POCMH DO

North Branch Onancock Creek VAT-C11E CB7PH DO

Pagan River VAT-G11E JMSMH DO

Pamunkey River – Tidal Narrative ePMKTF, PMKOH Nutrients

Queen Creek VAT-F26E YRKMH DO

Rappahannock River Narrative f RPPMH Nutrients

Rappahannock River VAP-E25E RPPMH Nutrients

Rappahannock River VAP-E25E RPPMH DO

Rappahannock River VAP-E26E RPPMH Nutrients

Rappahannock River VAP-E26E RPPMH DO

Thalia Creek VAT-C08E LYNPH DO

Williams Creek VAN-A30E POTMH DO

York River Narrative gYRKMH, YRKPH Nutrients

York River VAT-F27E YRKPH DO

Source: American Canoe Association v. EPA, 98cv979 (June 11, 1999).

Notes:

a = Chesapeake Bay Mainstem (VACB-R01E) impaired for nutrients

b = Elizabeth River (VAT-G15E) impaired for DO, nutrients

c = James River (VAP-G01E, VAP-G03E, VAP-G02E, VAP-G04E, VAP-G11E, and VAP-G15E) impaired for nutrients

d = Mattaponi River (VAP-F24E and VAP-F25E) impaired for nutrients

e = Pamunkey River (VAP-F13E and VAP-F14E) impaired for DO, nutrients

f = Rappahannock River (VAP-E24E) impaired for DO

g = York River (VAT-F26E) impaired for nutrients

District of Columbia–EPA Consent Decree

In 1998 Kingman Park Civic Association and others filed a similar suit against EPA.

10

 The 

lawsuit was settled through the entry of a consent decree requiring EPA to, among other things,

establish TMDLs for the District of Columbia‘s portions of the tidal Potomac and tidal Anacostia 

rivers if not established by the District of Columbia by a certain date.

 

10 Kingman Park Civic Association v EPA, 98cv00758 (June 13, 2000).
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1-16 September 24, 2010

The impairment of the District of Columbia‘s portion of the upper tidal Potomac River by low 

pH is directly related to the Chesapeake Bay water quality impairments because the low pH is a 

result of excess nutrients causing algal blooms in the tidal river. Establishing a tidal Potomac

River pH TMDL is directly linked to establishing the Chesapeake Bay TMDL because of their 

common impairing pollutants (nutrients) and the hydrologic connection between the District‘s 

portion of the tidal Potomac River and the Chesapeake Bay. EPA and the Kingman Park

plaintiffs jointly sought, and received on February 12, 2008, a formal extension of the District of 

Columbia TMDL Consent Decree so that EPA could complete the Potomac River pH TMDL on 

the same schedule as the Chesapeake Bay TMDL. The District of Columbia requested that EPA 

establish the pH TMDL for the District‘s portion of the tidal Potomac River (CBP PSC 2007).

Table 1-4provides a list of the District‘s consent decree waters that will be addressed by the 

Chesapeake Bay TMDLs for nutrients and sediment.

In addition, Anacostia Riverkeeper and Friends of the Earth filed suit against EPA challenging 

more than 300 TMDLs for the District of Columbia, including the Anacostia River TMDLs, 

because the TMDLs did not contain daily loads. On May 25, 2010, the District Court for the 

District of Columbia ordered the vacatur of the District of Columbia‘s TMDL for pH for the 

Washington Ship Channel, with a stay of vacatur until May 31, 2011. With the Bay TMDL, the 

Washington Ship Channel pH impairment will be addressed and will supersede the pH TMDL 

for the Ship Channel approved by EPA on December 15, 2004.

Table 1-4. District of Columbia consent decree (CD) waters impaired for pH that will be addressed 

by the Chesapeake Bay TMDL

Waterbody Name CD Segment ID Chesapeake Bay 

Segment ID

CD 

Impairment

Washington Ship Channel DCPWC04E_00 POTTF_DC pH

Middle Potomac River DCPMS00E POTTF_DC pH

Source: Kingman Park Civic Association v EPA, 98cv00758 (June 13, 2000).

Delaware–EPA Consent Decree

In 1996 the American Littoral Society and the Sierra Club filed a suit against EPA to ensure that 

TMDLs were developed for waters on Delaware‘s 1996 section 303(d) list, one of which is a 

tidal Bay segment (Upper Nanticoke). The parties entered into a consent decree resolving the 

lawsuit.11 The consent decree required EPA to establish TMDLs if Delaware failed to do so 

within the 10-year TMDL development schedule. Although Delaware established TMDLs for the 

one listed tidal Bay segment (DE DNREC 1998), the TMDLs were established to meet prior 

WQS and are insufficient to attain Chesapeake Bay WQS.

Maryland–EPA MOU

In 1998 Maryland and EPA Region 3 entered into an MOU that, among other things, established 

a 10-year schedule for addressing waters on Maryland‘s 1998 section 303(d) list, with 

completion by 2008 (MDE 1998). Because of funding constraints, the complexity of some 

TMDLs, and limited staff resources, Maryland determined that it would not be able to address all 

1998 listed waters by 2008. Further, the Chesapeake 2000 Agreement established a goal of 

meeting water quality goals in the Chesapeake Bay by 2010 (CEC 2000). Many of the waters on 

 

11 American Littoral Society, et al. v EPA, et al., 96cv591 (D.Del. 1997).
DRAFT Chesapeake Bay TMDL

1-17 September 24, 2010

Maryland‘s 1998 section 303(d) list were open waters of the Bay or tidal tributaries to the Bay. 

Maryland determined that developing TMDLs for those tidal waters before the deadline 

established by the MOU, as would be required under the schedule established in 1998, ―would 

undermine the spirit of the agreement‖ because of a lack of integration between the CBP and 

Maryland efforts (MDE 2004). Therefore, Maryland decided to postpone development of 

TMDLs for Maryland‘s listed Chesapeake Bay and tidal tributary waters until the two programs 

could coordinate efforts.

In September 2004, Maryland and EPA Region 3 entered into a revised MOU that extended the 

schedule for TMDL development to 13 years (by 2011) (MDE 2004). Although neither 

Maryland nor EPA is under a consent decree for establishing TMDLs for Maryland waters, the 

state has requested that EPA develop the TMDLs for the Maryland portion of the Chesapeake 

Bay and tidal tributaries impaired by excess nutrients and sediment as recognized in the MOU 

between Maryland and EPA (CBP PSC 2007).

Chesapeake Bay Foundation Settlement Agreement

In January 2009, the Chesapeake Bay Foundation and others filed suit against EPA in U.S.

District Court for the District of Columbia (1:09-cv-00005-CKK) alleging, among other things, 

that EPA had failed to carry out nondiscretionary duties under CWA section 117(g) designed to 

restore and preserve the Chesapeake Bay. In May 2010, EPA signed a settlement agreement with 

the plaintiffs promising to take a number of actions to restore and preserve the Bay. In particular, 

EPA promised that by December 31, 2010, it would establish a TMDL for those segments of the 

Chesapeake Bay impaired by nitrogen, phosphorus, and sediment. EPA is establishing this 

TMDL, in part, to meet that commitment.
DRAFT Chesapeake Bay TMDL

2-1 September 24, 2010

SECTION 2. WATERSHED AND IMPAIRMENT 

DESCRIPTION

This section provides a general description of the watershed and the impairments addressed in 

the Chesapeake Bay TMDL. Section 2.1 provides a description of the basic history, geography, 

land uses, and recent development patterns and trends. Section 2.2 presents the scope of the 

TMDL including the parameters of concern, the specific impairment listings addressed, and the 

TMDL segmentation.

2.1 General Watershed Setting

The Chesapeake Bay watershed includes parts of six states—Delaware, Maryland, New York, 

Pennsylvania, Virginia, and West Virginia—and the entire District of Columbia (collectively, the 

jurisdictions). The Chesapeake Bay proper is approximately 200 miles long, stretching from 

Havre de Grace, Maryland, to Norfolk, Virginia. It varies in width from about 3.4 miles near 

Aberdeen, Maryland, to 35 miles near the mouth of the Potomac River. The easternmost 

boundary of the Chesapeake Bay with the Atlantic Ocean is represented by a line between Cape 

Charles and Cape Henry. Including its tidal tributaries, the Chesapeake Bay encompasses 

approximately 11,684 miles of shoreline.

About half of the Bay‘s water volume consists of saltwater from the Atlantic Ocean. The other

half is freshwater that drains into the Bay from its 64,000-square-mile watershed (Figure 2-1). 

Ninety percent of the freshwater is delivered from five major rivers: the Susquehanna (which is 

responsible for about 50 percent), Potomac, James, Rappahannock, and York rivers. In all, the 

watershed contains more than 100,000 streams and rivers that eventually flow into the Bay.
DRAFT Chesapeake Bay TMDL

2-2 September 24, 2010

Figure 2-1. The Chesapeake Bay watershed with major rivers and cities.

Runoff from the Bay‘s enormous watershed flows into an estuary with a surface area of 4,500 

square miles resulting in a land-to-water ratio of 14 to 1. That large ratio is one of the key factors 

in explaining why the drainage area has such a significant influence on water quality in the Bay.

Although the Chesapeake Bay is entirely within the Atlantic Coastal Plain, its watershed includes 

parts of the Piedmont and Appalachian provinces. The waters that flow into the Bay have 

different chemical identities, depending on the geology from which they originate (Figure 2-2).
DRAFT Chesapeake Bay TMDL

2-3 September 24, 2010

The Atlantic Coastal Plain is a flat, lowland area with a maximum elevation of about 300 feet. It 

is supported by a bed of crystalline rock, covered with southeasterly dipping wedge-shaped 

layers of relatively unconsolidated sand, clay, and gravel. Water passing through the loosely 

compacted mixture dissolves many of the minerals. The most soluble elements are iron, calcium,

and magnesium. The coastal plain extends from the edge of the continental shelf, to the east, to a 

fall line that ranges from 15 to 90 miles west of the Chesapeake Bay. The fall line, which is the 

location where free flowing streams enter tidal waters, forms the boundary between the Piedmont 

Plateau and the coastal plain. Waterfalls and rapids clearly mark this line, which is close to 

Interstate 95. At the fall line, the elevation rises to 1,100 feet.

The Piedmont Plateau extends from the fall line in the east to the Appalachian Mountains in the 

west. The area is divided into two geologically distinct regions by Parrs Ridge, which traverses 

Carroll, Howard, and Montgomery counties in Maryland and adjacent counties in Pennsylvania.

Several types of dense, crystalline rock—including slates, schists, marble, and granite—compose 

the eastern side of the Piedmont Plateau. That variety results in a very diverse topography. Rocks 

of the Piedmont tend to be impermeable, and water from the eastern side is low in calcium and 

magnesium salts. The western side of the Piedmont consists of sandstones, shales, and siltstones,

layered over by limestone. The limestone bedrock contributes calcium and magnesium to its 

water, making it hard. Waters from the western side of Parrs Ridge flow into the Potomac River, 

one of the Chesapeake Bay‘s largest tributaries.
DRAFT Chesapeake Bay TMDL

2-4 September 24, 2010

Source: USGS WRIR 00-424

Figure 2-2. Hydrogeomorphic regions of the Chesapeake Bay watershed.
DRAFT Chesapeake Bay TMDL

2-5 September 24, 2010

The Appalachian Province covers the western and northern part of the watershed and is rich in 

coal and natural gas deposits. Sandstone, siltstone, shale, and limestone form the bedrock. Water 

from that province flows to the Chesapeake Bay mainly via the Susquehanna River.

Earliest evidence of human inhabitants in the Bay watershed is of hunter-gatherers as long as 

10,000 years ago, while Native Americans began cultivating crops and settling in villages 

throughout the area around 1,000 years ago. European settlement less than 500 hundred years 

ago began a period of transformation of forests into farmland, while today many of those lands 

are undergoing retransformations into urban and suburban lands.

Over the past hundreds of years, forest clearing and urban development have resulted in the 

following land use breakdown in the watershed: 69.4 percent wooded/open, 22.1 percent 

agriculture, 7.1 percent developed, and 1.4 percent open water and extractive (Figure 2-3).

From 1950 through 2008, the Bay watershed‘s population doubled, increasing from 8.3 million 

to 16.8 million. The 8-year period from 2000 to 2008 witnessed population growth of 

approximately 7 percent from 15.7 million. Today, nearly 17 million people live in the 

watershed. According to census data, the watershed‘s population is growing by about 157,000 

per year. Projections through 2030 are for the population to reach approximately 20 million 

(Figure 2-4).
DRAFT Chesapeake Bay TMDL

2-6 September 24, 2010

Source: USGS CBPO 

Figure 2-3. Chesapeake Bay watershed land cover.
DRAFT Chesapeake Bay TMDL

2-7 September 24, 2010

Source: CBP Office Bay Barometer 2009

Figure 2-4. Reported and projected human population growth in the Chesapeake Bay watershed 1950–2030.

2.2 Chesapeake Bay TMDL Scope

The Chesapeake Bay TMDL is the largest, most complex TMDL in the country, covering a 

64,000-square-mile area in the seven jurisdictions. EPA is establishing a federal TMDL for the 

tidal segments of the Chesapeake Bay and its tidal tributaries and embayments that are impaired 

for aquatic life uses due to excessive loads of nutrients (nitrogen and phosphorus) and sediment 

and listed on the four tidal Bay jurisdictions‘ respective CWA 2008 section 303(d) lists of 

impaired waters. The Bay TMDL also allocates loadings of nitrogen, phosphorus, and sediment 

to sources contributing those pollutants in all seven jurisdictions in the Bay watershed—

Delaware, the District of Columbia, Maryland, New York, Pennsylvania, Virginia, and West 

Virginia.

As described more fully in Section 2.2.1 below, the Chesapeake Bay TMDL addresses only the 

restoration of aquatic life uses for the Bay and its tidal tributaries that are impaired from excess 

nitrogen, phosphorus, and sediment. If Bay segments are impaired for other pollutants, EPA 

expects that the jurisdictions will develop separate TMDLs to address those pollutants.

Thousands of previously approved TMDLs have been established to protect local waters across 

the Chesapeake Bay watershed. While many addressed other pollutants, some addressed

nitrogen, phosphorus, and/or sediment. For watersheds and waterbodies that have both local 

TMDLs and Chesapeake Bay TMDLs for nitrogen, phosphorus, and sediment, the more stringent 

of the TMDLs will apply. In some cases, the reductions required to meet local conditions shown 

in existing TMDLs may be more stringent than those needed to meet Bay requirements, and vice 

versa.

0

5

10

15

20

25

1950 1960 1970 1980 1990 2000 2010 2020 2030

Population Projections (Millions)
DRAFT Chesapeake Bay TMDL

2-8 September 24, 2010

2.2.1 Pollutants of Concern

The pollutants of concern for this TMDL are nutrients—nitrogen and phosphorus—and 

sediment. Excessive nutrients in the Chesapeake Bay and its tidal tributaries promote a number 

of undesirable water quality conditions such as excessive algal growth, low DO, and reduced 

water clarity (Smith et al. 1992; Kemp et al. 2005). The effect of nutrient loads on water quality 

and living resources can vary considerably by season and region.

Sediment suspended in the water column reduces the amount of light available to support healthy 

and extensive SAV or underwater Bay grass communities (Dennison et al. 1993; Kemp et al. 

2004). The relative contribution of suspended sediment and algae that causes poor light 

conditions varies with location in the Bay tidal waters (Gallegos 2001).

Sediment also can contain other pollutants. For example, Escherichia coli often clings to 

sediment. By reducing sediment, reductions in phosphorus deliveries to the Bay (and possibly 

other pollutants such as E. coli) will also occur. However, EPA is not providing allocations for E. 

coli or other additional pollutants in this TMDL.

If Bay segments are impaired for other pollutants, EPA expects that the jurisdictions will develop 

separate TMDLs to address those pollutants. Because of the actions taken to achieve the 

Chesapeake Bay TMDL, direct benefits to local water quality conditions in surface waters 

throughout the Chesapeake Bay watershed will also occur.

2.2.2 Chesapeake Bay Program Segmentation Scheme

For 27 years, the CBP partners have used various versions of a basic segmentation scheme to 

organize the collection, analysis, and presentation of environmental data relating to the 

Chesapeake Bay. The Chesapeake Bay Program Segmentation Scheme: Revisions, Decisions 

and Rationales provides documentation of the spatial segmentation scheme of the Chesapeake 

Bay and its tidal tributaries and the later revisions and changes over almost three decades

(USEPA 1983b, 2004b, 2005, 2008a).

Segmentation is the compartmentalization of the estuary into subunits on the basis of selection 

criteria (USEPA 2008a). The 92-segment scheme used in the Chesapeake Bay was derived from 

the 2004 published 78-segment scheme with additional jurisdictional boundary lines imposed to 

create 89 segments (USEPA 2004b, 2008a). The scheme includes only the split segments12

agreed on for the tidal James and Potomac rivers for a total of 92 segments (Figure 2-5) (Table 

2-1) (USEPA 2008a). The 92 individual watersheds that drain directly into one of the 92 

Chesapeake Bay segments are referred to in this document as Bay segment watersheds (Figure 

2-6).

Table 2-1 lists the eight major river basins draining to the Chesapeake Bay and their associated 

Bay segments with information related to each Bay segment‘s 2008 section 303(d) list status and 

whether the Bay segment is addressed by a consent decree or MOU. The 303(d) list categories 

are as follows:

 

12 A split segment refers to when an established tidal Bay segment was fully bisected for purposes of applying 

different water quality criteria specific to two different portions of the same segment—in the case of the James 

River, or different assessments of attainment of the same applicable criteria separately from the main river 

segment—in the case of the Potomac River.
DRAFT Chesapeake Bay TMDL

2-9 September 24, 2010

Source: USEPA 2008a

Figure 2-5. The 92 Chesapeake Bay segments.
DRAFT Chesapeake Bay TMDL

2-10 September 24, 2010

Category 1—attaining all WQS

Category 2—attaining some WQS

Category 3—insufficient information to determine if WQS are attained

Category 4—impaired or threatened waters that do not need or have already completed a 

TMDL

o 4a—TMDL has been completed

o 4b—Other pollution control requirements are reasonably expected to result in the 

attainment of the WQS in the near future

o 4c—Impairment is not caused by a pollutant

Category 5—impaired or threatened water that requires a TMDL

Most Bay segments are listed as category 5 (impaired for most/all designated uses); exceptions 

are noted in Table 2-1.

Table 2-1. The Chesapeake Bay 303(d) tidal segments with consent decree (CD)/memorandum of 

understanding (MOU) and 303(d) listing status by major river basin and jurisdiction

Major river

basin

JurisdictionChesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

Eastern

Shore

MD Big Annemessex River BIGMH -- 5

MD Bohemia River BOHOH MD MOU 4a for TN and TP

DE C&D Canal, DE C&DOH_DE -- 5

MD C&D Canal, MD C&DOH_MD MD MOU 5

MD Eastern Bay EASMH MD MOU 5

VA Eastern Lower 

Chesapeake Bay

CB7PH VA CD 5

MD Elk River ELKOH MD MOU 5

MD Fishing Bay FSBMH MD MOU 4a for TN and TP 

MD Honga River HNGMH MD MOU 5

MD Little Choptank River LCHMH MD MOU 5

MD Lower Chester River CHSMH MD MOU 5

MD Lower Choptank River CHOMH2 MD MOU 5

MD Lower Nanticoke River NANMH -- 5

MD Lower Pocomoke 

River, MD

POCMH_MD MD MOU 5

VA Lower Pocomoke 

River, VA

POCMH_VA VA CD 5

MD Manokin River MANMH MD MOU 4a for TN and TP

MD Middle Chester River CHSOH MD MOU 4a for TN and TP

MD Middle Choptank River CHOOH MD MOU 5

MD Middle Nanticoke River NANOH MD MOU 5

MD Middle Pocomoke 

River, MD

POCOH_MD MD MOU 5

VA Middle Pocomoke 

River, VA

POCOH_VA -- 5

MD Mouth of Choptank 

River

CHOMH1 MD MOU 5

MD Northeast River NORTF MD MOU 4a for TN and TP
DRAFT Chesapeake Bay TMDL

2-11 September 24, 2010

Major river

basin

JurisdictionChesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

MD Sassafras River SASOH MD MOU 4a for TP

MD Tangier Sound, MD TANMH_MD MD MOU 5

VA Tangier Sound, VA TANMH_VA -- 5

MD Upper Chester River CHSTF MD MOU 4a for TN and TP

MD Upper Choptank River CHOTF MD MOU 5

DE Upper Nanticoke, DE NANTF_DE DE CD

finished

5

MD Upper Nanticoke, MD NANTF_MD MD MOU 5

MD Upper Pocomoke River POCTF MD MOU 5

MD Wicomico River WICMH MD MOU 5

James VA Appomattox River APPTF -- 5

VA Chickahominy River CHKOH -- 5

VA Eastern Branch 

Elizabeth River

EBEMH VA CD 5

VA Lafayette River LAFMH -- 5

VA Lower James River JMSMH VA CD 5

VA Lynnhaven River LYNPH VA CD 5

VA Middle James River JMSOH VA CD 5

VA Mouth of Chesapeake 

Bay

CB8PH -- 5

VA Mouth of James River JMSPH VA CD 5

VA Mouth to mid-Elizabeth 

River

ELIPH VA CD 5

VA Southern Branch 

Elizabeth River

SBEMH VA CD 5

VA Upper James River -

Lower

JMSTF1 VA CD 5

VA Upper James River -

Upper

JMSTF2 VA CD 5

VA Western Branch 

Elizabeth River

WBEMH VA CD 5

Patuxent MD Lower Patuxent River PAXMH MD MOU 5

MD Middle Patuxent River PAXOH MD MOU 5

MD Upper Patuxent River PAXTF MD MOU 5

MD Western Branch 

Patuxent River

WBRTF MD MOU BOD TMDL completed 

for DO impairments; 4a 

for BOD

Potomac DC Anacostia River, DC ANATF_DC DC CD 3 for DO; 4a for BOD, 

TN, TP and TSS

MD Anacostia River, MD ANATF_MD MD MOU 4a for BOD, TN, TP and 

TSS

VA Lower Central 

Chesapeake Bay, VA b

CB5MH_VA bVA CD 5

MD Lower Potomac River, 

MD

POTMH_MD MD MOU 5

VA Lower Potomac River, 

VA

POTMH_VA VA CD 5

MD Mattawoman Creek MATTF MD MOU 5
DRAFT Chesapeake Bay TMDL

2-12 September 24, 2010

Major river

basin

JurisdictionChesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

MD Middle Potomac River, 

MD - Mainstem

POTOH1_MD MD MOU 5

MD Middle Potomac River, 

MD - Nangemoy Creek

POTOH2_MD MD MOU 5

MD Middle Potomac River, 

MD - Port Tobacco 

River

POTOH2_MD MD MOU 4a for TN and TP

VA Middle Potomac River, 

VA

POTOH_VA -- 3 for DO in Migratory 

Spawning and Nursery 

(MSN); 2 for SAV and DO 

in open water

MD Piscataway Creek PISTF MD MOU 5

DC Upper Potomac River, 

DC

POTTF_DC DC CD 3 for DO, 5 for pH 

MD Upper Potomac River, 

MD

POTTF_MD MD MOU 5

VA Upper Potomac River, 

VA

POTTF_VA -- 3 for DO in Migratory 

Spawning and Nursery; 2 

for SAV and DO in open 

water 

Rappahannock VA Corrotoman River CRRMH -- 5

VA Lower Rappahannock 

River

RPPMH VA CD 5

VA Middle Rappahannock 

River

RPPOH -- 3 for DO in Migratory 

Spawning and Nursery; 2 

for SAV and DO in open 

water 

VA Upper Rappahannock 

River

RPPTF -- 5

VA Western Lower 

Chesapeake Bayb

CB6PHbVA CD 5

Susquehanna MD Northern Chesapeake 

Bayb

CB1TFb MD MOU 5

Western

Shore 

MD Back River BACOH MD MOU 4a for TN and TP

MD Bush River BSHOH MD MOU 5

MD Gunpowder River GUNOH MD MOU 5

MD Lower Central 

Chesapeake Bay, MDb

CB5MH_MDb MD MOU 5

MD Magothy River MAGMH MD MOU 5 

MD Middle Central 

Chesapeake Bayb

CB4MHb MD MOU 5

MD Middle River MIDOH MD MOU 5

MD Patapsco River PATMH MD MOU 5

MD Rhode River RHDMH MD MOU 5

MD Severn River SEVMH MD MOU 5

MD South River SOUMH MD MOU 5 

MD Upper Central 

Chesapeake Bayb

CB3MHb MD MOU 5

MD Upper Chesapeake CB2OHb MD MOU 5
DRAFT Chesapeake Bay TMDL

2-13 September 24, 2010

Major river

basin

JurisdictionChesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

Bayb

MD West River WSTMH MD MOU 5

York VA Lower Mattaponi River MPNOH VA CD 5

VA Lower Pamunkey River PMKOH VA CD 5

VA Lower York River YRKPH VA CD 5

VA Middle York River YRKMH VA CD 5

VA Mobjack Bay MOBPH -- 5

VA Piankatank River PIAMH -- 5

VA Upper Mattaponi River MPNTF VA CD 5

VA Upper Pamunkey River PMKTF VA CD 5

Sources: American Canoe Association v. EPA; American Littoral Society, et al. v. EPA, et al.; DC DOE 2008; DE 

DNREC 2008; Kingman Park Civic Association, et al. vs. EPA; MDE 1998, 2004, 2008; USEPA 2008 a; VA DEQ 

2008

a. BOD = biological oxygen demand; DO = dissolved oxygen; TN = total nitrogen; TP = total phosphorus; TSS = total 

suspended solids

b. More than one river basin flows into this tidal segment
DRAFT Chesapeake Bay TMDL

2-14 September 24, 2010

Source: USEPA 2008a

Figure 2-6. The 92 Chesapeake Bay segment watersheds.
DRAFT Chesapeake Bay TMDL

2-15 September 24, 2010

2.2.3 Jurisdictions’ 2008 303(d) Listings

The Chesapeake Bay TMDL is based on the most recent EPA-approved tidal Bay jurisdictions‘ 

section 303(d) lists, which are the 2008 303(d) listings.13 Those section 303(d) lists document 

89 of the 92 Chesapeake Bay segments as impaired on either Category 4a (impaired, TMDL has 

been developed) or Category 5 (impaired, needs TMDL) because of various factors, including

low DO levels, insufficient SAV, excess chlorophyll a, biological/nutrient indicators, total 

nitrogen, total phosphorus, total suspended solids (TSS), biological oxygen demand (BOD), and 

pH (caused by excessive nutrients fueling algal blooms) (DC DOE 2008; DE DNREC 2008; 

MDE 2008; VADEQ 2008).

Three Chesapeake Bay segments are not listed in Category 4a or 5 on Virginia‘s 2008 integrated 

report:

Upper Potomac River (POTTF_VA)

Middle Potomac River (POTOH_VA)

Middle Rappahannock River (RPPOH)

Those three segments are listed as either Category 2 (some uses met, other uses have insufficient 

information to determine impairment) or Category 3 (insufficient information to determine if 

impaired) (VA DEQ 2008). Because their listing status raises a reasonable question as to whether 

those three segments are impaired, and because those segments are tidally interconnected with 

other impaired Bay segments, it is appropriate that they also be addressed by the Chesapeake 

Bay TMDL.

The first segment, Virginia‘s Upper Potomac River (POTTF_VA), encompasses a series of small 

tidal embayments that are tidally interconnected with Maryland‘s Upper Potomac River 

(POTTF_MD) segment and the District of Columbia‘s Upper Potomac River (POTTF_DC) 

segment (USEPA 2008a), both of which are listed as Category 5 of Maryland‘s and the District 

of Columbia‘s respective 2008 integrated reports (DCDOE 2008; MDE 2008). Loads originating 

in the watershed that drains directly Virginia‘s Upper Potomac River segment influence the 

water quality in the two adjacent Maryland and District of Columbia impaired tidal segments and 

other down-tide segments.

The second segment, Virginia‘s Middle Potomac River (POTOH_VA), also encompasses a 

series of small tidal embayments that are tidally interconnected with Maryland‘s Middle 

Potomac River (POTOH_MD) segment (USEPA 2008a), which is listed as Category 5 on 

Maryland‘s 2008 integrated report (MDE 2008). Loads originating in the watershed that drains 

directly to Virginia‘s Middle Potomac River segment influence the water quality in the adjacent 

Maryland impaired tidal segment and other down-tide segments.

The third segment, Virginia‘s Middle Rappahannock River (RPPOH), is tidally interconnected 

with both the Lower Rappahannock River (RPPMH) and the Upper Rappahannock River 

(RPPTF) segments (USEPA 2008a), both of which are listed as Category 5 on Virginia‘s 2008 

 

13 At the time EPA applied the Bay models for development of the allocations, the 2008 section 303(d) lists were the 

most recent lists. Although EPA subsequently received final 2010 section 303(d) lists for approval from all tidal 

jurisdictions except Virginia (Virginia draft 2010 section 303(d) list released for public review on August 23, 2010),

EPA used the 2008 lists in establishing the Bay TMDL to have a consistent basis for the TMDL.
DRAFT Chesapeake Bay TMDL

2-16 September 24, 2010

integrated report (VADEQ 2008). Loads originating in the watershed that drains directly to 

Virginia‘s Middle Rappahannock River segment influence the water quality in the adjacent 

Virginia impaired tidal segments and other down-tide segments.

As detailed in Section 9, TMDLs have been completed as part of the Chesapeake Bay TMDL for 

all 92 Chesapeake Bay segments listed in Table 2-1 (see Section 9) including the above 

described three Virginia Bay segments because they flow into impaired tidal Bay segments, and 

reductions in nutrient and sediment loadings from their respective watersheds, therefore, are 

necessary to achieve the Bay jurisdictions‘ Chesapeake Bay WQS.

2.2.4 2008 303(d) Listing Segments Compared to Consent Decree and 

MOU Segments

To ensure that TMDLs were completed for all Bay segments for which they are legally 

required—all 2008 listed segments, all Virginia, Delaware, and District of Columbia TMDL 

consent decree segments, and all Maryland MOU segments—EPA compared the 2008 listed 

segments with those included on those agreements (Table 2-1). In total, 77 segments are 

addressed by the Virginia and District of Columbia consent decrees and the Maryland MOU: 22 

segments are on the Virginia TMDL consent decree; 2 segments are on the Delaware consent 

decree; 2 segments are on the District of Columbia TMDL consent decree; and 51 segments are 

on the Maryland TMDL MOU (Table 2-2). The evaluation found that all the Virginia consent 

decree, Delaware consent decree, District of Columbia consent decree, and Maryland MOU 

segments are a subset of the total list of 92 Chesapeake Bay segments for which TMDLs have 

been established under the Bay TMDL.

Table 2-2. Comparison of consent decree/MOU segments with total number of Bay segments

Jurisdiction

Consent decree or 

MOU segments

Chesapeake Bay 

segments

Virginia 22 35

District of Columbia 2 2

Maryland 51 53

Delaware 2

a

2

Total 77 92

Adapted from Table 2-1.

a. Two consent decrees affect one Bay segment each in Delaware, but TMDLs have already been established for 

both segments.
DRAFT Chesapeake Bay TMDL

3-1 September 24, 2010

SECTION 3. CHESAPEAKE BAY WATER QUALITY 

STANDARDS

WQS consist of four basic elements: designated uses, water quality criteria, an antidegradation 

policy (to maintain and protect existing uses and high-quality waters), and general policies 

(addressing implementation issues such as low flows, variances, and mixing zones). Designated 

uses are a jurisdiction‘s goals and expectations for each of the individual surface waters (e.g., 

coldwater fisheries, public water supply, and primary contact recreation). EPA‘s WQS regulation 

defines designated uses as the ―uses specified in WQS for each waterbody or segment, whether 

or not they are being attained‖ (40 CFR 131.3). Water quality criteria may be numeric or 

narrative, and represent a quality of water that supports a particular use. When water quality 

criteria are met, water quality is expected to protect its designated use. Numeric water quality 

criteria are chemical-specific and are based on specific levels of pollutants consistent with the 

water‘s designated uses (e.g., physical or chemical characteristics like temperature, minimum 

concentration of DO, and the maximum concentrations of toxic pollutants).

Starting in 1986, EPA and its CBP partners embarked on a process to synthesize scientific 

evidence on the water quality requirements of hundreds of aquatic species and biological 

communities. The 1987 Chesapeake Bay Agreement includes a commitment to, ―develop and 

adopt guidelines for the protection of water quality and habitat conditions necessary to support 

the living resources found in the Chesapeake Bay system, and to use these guidelines in the 

implementation of water quality and habitat quality programs‖ (CEC 1987). The CBP

partnership initially published two syntheses of the available scientific findings supporting 

establishment of habitat requirements for 31 target species (CBP 1987; Funderburk et al. 1991). 

Those efforts spawned development and publication of synthesis documents focused on DO

requirements (Jordan et al. 1991) and underwater Bay grasses habitat requirements (Batiuk et al. 

1992, 2000). On the basis of that work, in part, EPA published as guidance the Chesapeake Bay 

water quality criteria (USEPA 2003a) and the Chesapeake Bay refined aquatic life designated 

uses and attainability document (USEPA 2003c). Guided by those efforts, Delaware, the District 

of Columbia, Maryland, and Virginia adopted jurisdiction-specific Chesapeake Bay WQS 

regulations in 2004–2005 consistent with the EPA published guidance. EPA then reviewed and 

approved the four tidal Bay jurisdictions‘ WQS submissions pursuant to CWA section 303(c).

Maryland, Virginia, and the District have each proposed very specific amendments to their 

respective Chesapeake Bay WQS regulations. The proposed amendments are described in 

Section 3.2.5.

3.1 Chesapeake Bay Water Quality Criteria and Designated Uses

The above described DO, underwater Bay grasses and Bay habitat requirements documents

(Batiuk et al 1992, 2000; CBP 1987; Funderburk et al. 1991; Jordan et al. 1991), supplemented 

by additional scientific research findings, provided the basis for developing the applicable water 

quality criteria guidance for the Chesapeake Bay. That guidance is in EPA‘s Bay criteria 

(USEPA 2003a) and designated uses/attainability (USEPA 2003c) documents and their 

subsequent addenda (USEPA 2004a, 2004b, 2004e, 2005, 2007a, 2007b, 2008a, 2010a). EPA 

Region 3 published those documents as guidance in accordance with CWA sections 117(b) and 

303 to derive water quality criteria specifically for addressing the critical nutrient and sediment 
DRAFT Chesapeake Bay TMDL

3-2 September 24, 2010

enrichment parameters necessary to protect designated aquatic life uses in the Bay (Table 3-1). 

These criteria serve as surrogate numeric criteria for nitrogen, phosphorus, and sediment.

Table 3-1. Chesapeake Bay water quality criteria and designated use related documentation and 

addenda

Document title Month/year 

published

Document content and description

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries. EPA 903-R-03-002. [USEPA 

2003a]

April 2003 Original Chesapeake Bay water quality 

criteria document.

Technical Support Document for 

Identification of Chesapeake Bay 

Designated Uses and Attainability. EPA 

903-R-03-004. [USEPA 2003c]

October 2003 Original Chesapeake Bay tidal waters 

designated uses document.

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries—2004 Addendum. EPA 903-R03-002. [USEPA 2004a]

October 2004 Addresses endangered species protection, 

assessment of DO criteria, derivation of sitespecific DO criteria, pycnocline boundary 

delineation methodology and updated water 

clarity criteria/SAV restoration acreage 

assessment procedures.

Technical Support Document for 

Identification of Chesapeake Bay 

Designated Uses and Attainability—2004 

Addendum. EPA 903-R-04-006. [USEPA 

2004e]

October 2004 Addresses refinements to Bay tidal waters 

designated use boundaries, segmentation 

boundaries, Potomac River jurisdictional 

boundaries, and documents SAV no-grow 

zones, restoration goal, and shallow-water 

acreages.

Chesapeake Bay Program Analytical 

Segmentation Scheme: Revisions, 

Decisions and Rationales 1983–2003.

EPA 903-R-04-008. CBP/TRS 268-04.

[USEPA 2004b]

October 2004 Details documentation on the history of the 

segmentation schemes and coordinates, 

georeferences and narrative descriptions of 

the 2003 segmentation scheme.

Chesapeake Bay Program Analytical 

Segmentation Scheme: Revisions, 

Decisions and Rationales 1983–2003: 2005 

Addendum. EPA 903-R-05-004. CBP/TRS 

278-06. [USEPA 2005]

December 

2005

Addresses methods used to subdivide the 

segments by jurisdiction and the coordinates, 

georeferences and narrative descriptions for 

those subdivided segments.

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries—2007 Addendum. EPA 903-R07-003. CBP/TRS 285-07. [USEPA 2007a]

July 2007 Addresses refinements to the Bay water 

quality DO, water clarity/SAV and chlorophyll 

a criteria assessment methodologies and 

documents the framework for Bay tidal 

waters 303(d) list decision making.

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries—2007 Chlorophyll Criteria 

Addendum. EPA 903-R-07-005. CBP/TRS 

288/07. [USEPA 2007b] 

November

2007

Publishes a set of numerical chlorophyll a

criteria for Chesapeake Bay and the 

supporting criteria assessment procedures.
DRAFT Chesapeake Bay TMDL

3-3 September 24, 2010

Document title Month/year 

published

Document content and description

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries—2008 Technical Support for 

Criteria Assessment Protocols Addendum. 

EPA 903-R-08-001. CBP/TRS 290-08. 

[USEPA 2008a]

September 

2008

Addresses refinements to the Bay water 

quality DO, water clarity/SAV and chlorophyll 

a criteria assessment methodologies and 

documents the 2008 92-segment scheme for 

Bay tidal waters.

Ambient Water Quality Criteria for Dissolved 

Oxygen, Water Clarity and Chlorophyll a for 

the Chesapeake Bay and Its Tidal 

Tributaries—2010 Technical Support for 

Criteria Assessment Protocols Addendum. 

EPA 903-R-10-002. [USEPA 2010a]

May 2010 Addresses refinements to procedures for 

defining designated uses, existing 

procedures for deriving biologically based 

reference curves for DO criteria assessment 

and chlorophyll criteria assessment 

procedures.

Before adoption into each Bay jurisdiction‘s WQS regulations, each set of criteria, criteria 

assessment procedures, designated uses, and proposed WQS were subject to extensive scientific, 

programmatic, and public review.

The original 2003 water quality criteria, assessment procedures, and designated uses went 

through independent scientific peer reviews sponsored by the CBP‘s STAC. The CBP‘s Water 

Quality Steering Committee‘s water quality criteria and designated use teams then reviewed and 

approved them. Finally, the CBP‘s Water Quality Steering Committee reviewed and approved 

them for EPA publication on behalf of the partnership.

Since the publication of the original Chesapeake Bay water quality criteria document (USEPA

2003a) and Chesapeake Bay designated uses and attainability document (USEPA 2003c), EPA 

has published significant changes to the water quality criteria and the criteria assessment 

procedures. Specifically, EPA has published five addenda—USEPA 2004a, 2007a, 2007b, 

2008a, 2010a—to the original 2003 Bay criteria document (USEPA 2003a), one addendum—

USEPA 2004e—to the original 2003 Bay designated use/attainability document (USEPA 2003c) 

and one addendum—USEPA 2005—to the original Bay segmentation document (USEPA

2004b) (see Table 3-1).

Those revisions have undergone independent scientific peer reviews, sponsored by the CBP‘s 

STAC, before review and approval by the CBP‘s Criteria Assessment Protocols Workgroup and 

then the Water Quality Steering Committee/Water Quality Implementation Team for EPA 

publication on behalf of the partnership. Examples include the cumulative frequency distribution

approach (STAC 2006) and the biological reference curves (STAC 2009).

WQS revisions incorporating the most recent of these addenda are pending in the District of 

Columbia, Maryland, and Virginia. Virginia‘s WQS revisions also will incorporate the 2007 and 

2008 addenda. Maryland, Virginia, Delaware, and the District of Columbia‘s processes for 

adopting amendments to their existing Chesapeake Bay WQS regulations require full public 

notice, public review and comment, and response to public comments before submission to EPA 

Region 3 for final EPA review and approval.

In this TMDL, EPA is proposing for public notice and comment two separate TMDLs—one 

based on current WQS and one based on changes to WQS being proposed by the tidal Bay 

jurisdictions. Those two sets of WQS are discussed more fully in Sections 3.2 and 3.3 below.
DRAFT Chesapeake Bay TMDL

3-4 September 24, 2010

3.1.1 Tidal Water Designated Uses

EPA and its seven watershed jurisdiction partners agreed on five refined aquatic life designated 

uses reflecting the habitats of an array of recreationally, commercially, and ecologically 

important species and biological communities (USEPA 2003c, 2004e, 2010a). The five tidal Bay 

designated uses are applied, where appropriate, consistently across Maryland, Virginia, 

Delaware, and the District of Columbia‘s portions of the Chesapeake Bay and its tidal tributary 

and embayment waters. The vertical and horizontal breadth and temporal application of the 

designated use boundaries are based on a combination of natural factors, historical records, 

physical features, hydrology, bathymetry, and other scientific considerations (USEPA 2003c, 

2004e, 2010a). Table 3-2 outlines the Chesapeake Bay tidal water designated uses, which are 

illustrated in Figure 3-1.

Table 3-2. Five Chesapeake Bay tidal waters designated uses

Tidal water designated use Chesapeake Bay habitats and communities protected

Migratory fish spawning and 

nursery

Migratory and resident tidal freshwater finfish during the late 

winter/spring spawning and nursery season in tidal freshwater to lowsalinity habitats.

Shallow-water bay grass Underwater bay grasses and fish and crab species that depend on the 

shallow-water habitat provided by underwater bay grass beds.

Open-water fish and shellfish Diverse populations of sport fish, including striped bass, bluefish, 

mackerel and sea trout, as well as important bait fish such as 

menhaden and silversides in surface water habitats within tidal creeks, 

rivers, embayments and the mainstem Chesapeake Bay year-round.

Deep-water seasonal fish and 

shellfish

Animals inhabiting the deeper transitional water column and bottom 

habitats between the well-mixed surface waters and the very deep 

channels during the summer months (e.g., bottom-feeding fish, crabs 

and oysters, as well as other important species, including the bay 

anchovy).

Deep-channel seasonal 

refuge

Bottom-sediment-dwelling worms and small clams that serve as food 

for bottom-feeding fish and crabs in the very deep channel in summer. 

Sources: USEPA 2003c, 2004e
DRAFT Chesapeake Bay TMDL

3-5 September 24, 2010

Source: USEPA 2003c

Figure 3-1. Conceptual illustration of the five Chesapeake Bay tidal water designated use zones.

Table 3-3 lists the designated uses for each of the 92 Chesapeake Bay segments pursuant to 

current WQS regulations.14 It originally was published as Table V-1 on pages 51–53 of the 

Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the 

Chesapeake Bay and Its Tidal Tributaries 2007 Addendum (USEPA 2007a), which is an updated

version of Table IV-3 originally published on pages 62–63 of the 2003 Technical Support 

Document for Identification of Chesapeake Bay Designated Uses and Attainability (USEPA 

2003c). The absence of an X in the shallow-water bay grass designated use column indicates that 

the Bay segment has been entirely delineated as an SAV no-grow zone and, therefore, the 

shallow-water Bay grass designated use does not apply to that Bay segment (USEPA 2004e).

 

14 Maryland is proposing adding the deep-water designated use to three Bay segments—MAGMH (Magothy River), 

SEVMH (Severn River), and SOUMH (South River)—as part of a set of proposed amendments to its Chesapeake 

Bay WQS regulations.
DRAFT Chesapeake Bay TMDL

3-6 September 24, 2010

Table 3-3. Current tidal water designated uses by Chesapeake Bay segment

CBP segment 

name

CBP 

segment Juris

Migratory 

spawning & 

nursery

Open 

water

Deep 

water

Deep 

channel

Shallow 

water

Feb. 1–May 31

YearroundJune 1–

Sept. 30

June 1–

Sept. 30

SAV 

growing 

season

Northern 

Chesapeake Bay 

CB1TF MD X X X

Upper 

Chesapeake Bay 

CB2OH MD X X X

Upper Central 

Chesapeake Bay 

CB3MH MD X X X X X

Middle Central 

Chesapeake Bay 

CB4MH MD X X X X X

Lower Central 

Chesapeake Bay 

CB5MH_

MD

MD X X X X

Lower Central 

Chesapeake Bay 

CB5MH_

VA

VA X X X X

Western Lower 

Chesapeake Bay 

CB6PH VA X X X

Eastern Lower 

Chesapeake Bay 

CB7PH VA X X X

Mouth of the 

Chesapeake Bay 

CB8PH VA X X

Bush River BSHOH MD X X X

Gunpowder River GUNOH MD X X X

Middle River MIDOH MD X X X

Back River BACOH MD X X X*

Patapsco River PATMH MD X X X X

Magothy River MAGMH MD X X X

Severn River SEVMH MD X X X

South River SOUMH MD X X X

Rhode River RHDMH MD X X X

West River WSTMH MD X X X

Upper Patuxent 

River 

PAXTF MD X X X

Western Branch 

(Patuxent R.) 

WBRTF MD X X X*

Middle Patuxent 

River 

PAXOH MD X X X

Lower Patuxent 

River 

PAXMH MD X X X X

Upper Potomac 

River 

POTTF_

DC

DC X X X

Upper Potomac 

River 

POTTF_

MD

MD X X X

Upper Potomac 

River 

POTTF_

VA

VA X X X

Anacostia River ANATF_

DC

DC X X X
DRAFT Chesapeake Bay TMDL

3-7 September 24, 2010

CBP segment 

name

CBP 

segment Juris

Migratory 

spawning & 

nursery

Open 

water

Deep 

water

Deep 

channel

Shallow 

water

Feb. 1–May 31

YearroundJune 1–

Sept. 30

June 1–

Sept. 30

SAV 

growing 

season

Anacostia River ANATF_

MD

MD X X X

Piscataway Creek PISTF MD X X X

Mattawoman 

Creek 

MATTF MD X X X

Middle Potomac 

River 

POTOH1 MD X X X

Middle Potomac 

River 

POTOH2 MD X X X

Middle Potomac 

River 

POTOH3 MD X X X

Middle Potomac 

River 

POTOH VA X X X

Lower Potomac 

River 

POTMH MD X X X X X

Lower Potomac 

River 

POTMH VA X X X X X

Upper 

Rappahannock 

River 

RPPTF VA X X X

Middle 

Rappahannock 

River 

RPPOH VA X X X*

Lower 

Rappahannock 

River 

RPPMH VA X X X X X

Corrotoman River CRRMH VA X X X

Piankatank River PIAMH VA X X

Upper Mattaponi 

River 

MPNTF VA X X X

Lower Mattaponi 

River 

MPNOH VA X X X*

Upper Pamunkey 

River 

PMKTF VA X X X

Lower Pamunkey 

River 

PMKOH VA X X X*

Middle York River YRKMH VA X X X

Lower York River YRKPH VA X X X

Mobjack Bay MOBPH VA X X

Upper James 

River-Lower

JMSTF1 VA X X X

Upper James 

River-Upper

JMSTF2 VA X X X

Appomattox River APPTF VA X X X

Middle James 

River 

JMSOH VA X X X

Chickahominy 

River 

CHKOH VA X X X
DRAFT Chesapeake Bay TMDL

3-8 September 24, 2010

CBP segment 

name

CBP 

segment Juris

Migratory 

spawning & 

nursery

Open 

water

Deep 

water

Deep 

channel

Shallow 

water

Feb. 1–May 31

YearroundJune 1–

Sept. 30

June 1–

Sept. 30

SAV 

growing 

season

Lower James 

River 

JMSMH VA X X X

Mouth of the 

James River 

JMSPH VA X X

Western Branch 

Elizabeth River 

WBEMH VA X

Southern Branch 

Elizabeth River 

SBEMH VA X

Eastern Branch 

Elizabeth River 

EBEMH VA X

Lafayette River LAFMH VA X

Mouth of the 

Elizabeth River 

ELIPH VA X X X

Lynnhaven River LYNPH VA X X

Northeast River NORTF MD X X X

C&D Canal C&DOH_

DE

DE X X X

C&D Canal C&DOH_

MD

MD X X X

Bohemia River BOHOH MD X X X

Elk River ELKOH MD X X X

Sassafras River SASOH MD X X X

Upper Chester 

River 

CHSTF MD X X X*

Middle Chester 

River 

CHSOH MD X X X

Lower Chester 

River 

CHSMH MD X X X X X

Eastern Bay EASMH MD X X X X

Upper Choptank 

River 

CHOTF MD X X

Middle Choptank 

River 

CHOOH MD X X X

Lower Choptank 

River 

CHOMH

2

MD X X X

Mouth of the 

Choptank River 

CHOMH

1

MD X X X

Little Choptank 

River 

LCHMH MD X X

Honga River HNGMH MD X X

Fishing Bay FSBMH MD X X X

Upper Nanticoke 

River 

NANTF_

MD

MD X X

Upper Nanticoke 

River 

NANTF_

DE

DE X X X*

Middle Nanticoke 

River 

NANOH MD X X X
DRAFT Chesapeake Bay TMDL

3-9 September 24, 2010

CBP segment 

name

CBP 

segment Juris

Migratory 

spawning & 

nursery

Open 

water

Deep 

water

Deep 

channel

Shallow 

water

Feb. 1–May 31

YearroundJune 1–

Sept. 30

June 1–

Sept. 30

SAV 

growing 

season

Lower Nanticoke 

River 

NANMH MD X X X

Wicomico River WICMH MD X X X

Manokin River MANMH MD X X X

Big Annemessex 

River 

BIGMH MD X X X

Upper Pocomoke 

River 

POCTF MD X X

Middle Pocomoke 

River 

POCOH_

MD

MD X X X*

Middle Pocomoke 

River 

POCOH_

VA

VA X X X*

Lower Pocomoke 

River 

POCMH

_MD

MD X X X

Lower Pocomoke 

River 

POCMH

_VA

VA X X X

Tangier Sound TANMH_

MD

MD X X

Tangier Sound TANMH_

VA

VA X X

An asterisk (*) indicates that no numerical SAV restoration acreage goal was published in 2003 for the shallow-water 

bay grass designated use of that segment (USEPA 2003c).

3.1.2 Dissolved Oxygen Criteria

Oxygen is one of the most essential environmental constituents supporting life. In the 

Chesapeake Bay‘s deeper waters, there is a natural tendency toward reduced DO conditions 

because of the Bay‘s physical morphology and estuarine circulation. The Chesapeake Bay‘s 

highly productive shallow waters, coupled with strong density stratification; long residence times 

(weeks to months); low tidal energy; and tendency to retain, recycle, and regenerate nutrients 

from the surrounding watershed all set the stage for low DO conditions.

Against that backdrop, EPA worked closely with its seven watershed partners and the larger Bay 

scientific community to derive and publish a set of DO criteria to protect specific aquatic life 

communities and reflect the Chesapeake Bay‘s natural processes that define distinct habitats 

(Figure 3-2) (USEPA 2003a; Batiuk et al. 2009). Working with the National Marine Fisheries 

Service, EPA also ensured that the criteria were protective of the shortnose sturgeon, a species 

listed as endangered by the Endangered Species Act (NMFS 2003).
DRAFT Chesapeake Bay TMDL

3-10 September 24, 2010

Source: USEPA 2003a

Figure 3-2. DO (mg/L) concentrations required by different Chesapeake Bay species and biological 

communities.

Criteria for the migratory fish spawning and nursery, shallow-water Bay grass and open-water 

fish and shellfish designated uses were set at levels to prevent impairment of growth and to 

protect the reproduction and survival of all organisms living in the open-water column habitats 

(Table 3-4) (USEPA 2003a). Criteria for deep-water seasonal fish and shellfish designated use 

habitats during seasons when the water column is significantly stratified were set at levels to 

protect juvenile and adult fish, shellfish, and the recruitment success of the Bay anchovy. Criteria 

for deep-channel seasonal refuge designated use habitats in summer were set to protect the 

survival of bottom sediment-dwelling worms and clams.
DRAFT Chesapeake Bay TMDL

3-11 September 24, 2010

Table 3-4. Current Chesapeake Bay DO criteria

Designated 

use

Criteria 

concentration/duration Protection provided

Temporal 

application

Migratory 

fish 

spawning

and

nursery use

7-day mean > 6 mg/L

(tidal habitats with 0–0.5 ppt 

salinity)

Survival/growth of larval/juvenile tidalfresh resident fish; protective of 

threatened/endangered species

February 1–May 

31

Instantaneous minimum > 5 

mg/L

Survival and growth of larval/juvenile 

migratory fish; protective of 

threatened/endangered species

Open-water fish and shellfish designated use criteria apply June 1–January 

31

Shallowwater bay 

grass use

Open-water fish and shellfish designated use criteria apply Year-round

Open-water 

fish and 

shellfish use

30-day mean > 5.5 mg/L

(tidal habitats with 0–0.5 ppt 

salinity)

Growth of tidal-fresh juvenile and 

adult fish; protective of 

threatened/endangered species

Year-round

30-day mean > 5 mg/L

(tidal habitats with >0.5 ppt 

salinity)

Growth of larval, juvenile, and adult 

fish and shellfish; protective of 

threatened/endangered species

7-day mean > 4 mg/L Survival of open-water fish larvae

Instantaneous minimum >

3.2 mg/L

Survival of threatened/endangered 

sturgeon speciesa

Deep-water 

seasonal 

fish and 

shellfish use

30-day mean > 3 mg/L Survival and recruitment of Bay 

anchovy eggs and larvae

June 1–

September 30

1-day mean > 2.3 mg/L Survival of open-water juvenile and 

adult fish

Instantaneous minimum >

1.7 mg/L

Survival of Bay anchovy eggs and 

larvae

Open-water fish and shellfish designated use criteria apply October 1–May 31

Deepchannel 

seasonal 

refuge use

Instantaneous minimum > 1 

mg/L

Survival of bottom-dwelling worms 

and clams

June 1–

September 30

Open-water fish and shellfish designated use criteria apply October 1–May 31

Source: USEPA 2003a

Notes: mg/L = milligrams per liter; ppt = parts per thousand salinity

a. At temperatures considered stressful to shortnose sturgeon (> 29 degrees Celsius), DO concentrations above an 

instantaneous minimum of 4.3 mg/L will protect survival of this listed sturgeon species.

3.1.3 Chlorophyll a Criteria

EPA‘s 2003 Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and 

Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (USEPA 2003a) describes the 

applicable narrative criteria for chlorophyll a:

Concentrations of chlorophyll a in free-floating microscopic aquatic plants 

(algae) shall not exceed levels that result in ecologically undesirable 

consequences—such as reduced water clarity, low dissolved oxygen, food 

supply imbalances, proliferation of species deemed potentially harmful to 

aquatic life or humans or aesthetically objectionable conditions—or otherwise 

render tidal waters unsuitable for designated uses.
DRAFT Chesapeake Bay TMDL

3-12 September 24, 2010

In 2007 EPA published numeric chlorophyll a criteria guidance protective of open-water 

designated use impairment by harmful algal blooms and provided recommended reference 

chlorophyll a concentrations for historic chlorophyll a levels, and DO and water clarity 

impairments (USEPA 2007a).

Delaware, the District of Columbia, Maryland, and Virginia all adopted EPA‘s narrative 

chlorophyll a criteria. Additionally, Virginia and the District of Columbia adopted EPA‘s 

numeric chlorophyll a criteria for certain tidal waters as detailed in Section 3.2.

3.1.4 Water Clarity/Underwater Bay Grasses Criteria

Underwater Bay grass beds create rich animal habitats that support the growth of diverse fish and 

invertebrate populations. Underwater Bay grasses, also referred to as submerged aquatic 

vegetation (SAV), help improve tidal water quality by retaining nutrients as plant material, 

stabilizing bottom sediments (preventing their resuspension) and reducing shoreline erosion. The 

health and survival of such underwater plant communities in the Chesapeake Bay and its tidal 

tributaries depend on suitable environmental conditions (Dennison et al. 1993; Kemp et al. 

2004).

The loss of SAV from the shallow waters of the Chesapeake Bay, which was first noted in the 

early 1960s, is a widespread, well-documented problem (Orth and Moore 1983; Orth et al. 2010). 

The primary causes of the decline of SAV are nutrient over-enrichment, increased suspended 

sediment in the water, and associated reductions in light availability (Kemp et al. 2004). To 

restore the critical habitats and food sources, enough light must penetrate the shallow waters to 

support the survival, growth, and repropagation of diverse, healthy, SAV communities

(Dennison et al. 1993).

EPA, working closely with its seven watershed partners and the larger Bay scientific community, 

derived and published Chesapeake Bay water clarity criteria to establish the minimum level of 

light penetration required to support the survival, growth, and continued propagation of SAV 

(USEPA 2003a). Chesapeake Bay-specific water clarity criteria were derived for low and higher 

salinity habitats using a worldwide literature synthesis, an evaluation of Chesapeake Bay-specific 

field study findings, and model simulation and diagnostic tools (Table 3-5).

Table 3-5. Summary of Chesapeake Bay water clarity criteria for application to shallow-water bay 

grass designated use habitats

Salinity 

regime

Water clarity 

criteria 

(percent lightthroughwater)

Water clarity criteria as Secchi deptha

Temporal 

application

Water clarity criteria application depths

(meters)

0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0

Secchi depth for above criteria application depth

(meters)

Tidal-fresh 13% 0.2 0.4 0.5 0.7 0.9 1.1 1.2 1.4 April 1–Oct 31

Oligohaline 13% 0.2 0.4 0.5 0.7 0.9 1.1 1.2 1.4 April 1–Oct 31

Mesohaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 April 1–Oct 31

Polyhaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 March 1–May 31

Sept 1–Nov 30

Source: USEPA 2003a

a. Based on application of the Equation IV-1published in USEPA 2003a, PLW = 100exp(-KdZ), where the appropriate 

percent light through water (PLW) criterion value and the selected application depth (see Table 3-6) are inserted and 
DRAFT Chesapeake Bay TMDL

3-13 September 24, 2010

the equation is solved for Kd. The generated Kd value is then converted to Secchi depth (in meters) using the 

conversion factor Kd = 1.45/Secchi depth.

The water clarity criteria, applied only during the SAV growing seasons, are presented in terms 

of the percent ambient light at the water surface extending through the water column and the 

equivalent Secchi depth by application depth (Table 3-5). The recommended percent lightthrough-water criteria can be directly measured using a Secchi disk or a light meter. A specific 

application depth is required to apply and determine attainment of the water clarity criteria

(Table 3-6).

SAV restoration acreage goals and water clarity application depths were developed based on 

historic and recent data on the distribution of SAV (USEPA 2003c). Detailed analyses using that

data—including historical aerial photographs—were undertaken to map the distribution and 

depth of historical SAV beds in the Chesapeake Bay and its tidal tributaries. The analyses led to 

the adoption of the single best year method that considers historical SAV distributions from the 

1930s through the early 1970s and more recent distributions since 1978 to the present mapped 

through annual SAV aerial surveys of the Bay‘s shallow-water habitats. Using that method, the 

CBP and its watershed partners established a Bay-wide SAV restoration goal of 185,000 acres

and Bay segment-specific acreage goals (Table 3-6) (USEPA 2003c).

Table 3-6. Chesapeake Bay SAV restoration acreages and application depths—current WQS

Segment description State Segment 

designator

SAV acreage 

restoration 

goal

Secchi 

application depth

(meters)

Northern Chesapeake Bay MD CB1TF2 12,149 2.0 

Northern Chesapeake Bay MD CB1TF1 754 1.0 

Upper Chesapeake Bay MD CB2OH 705 0.5 

Upper Central Chesapeake Bay MD CB3MH 1,370 0.5 

Middle Central Chesapeake Bay MD CB4MH 2,533 2.0 

Lower Central Chesapeake Bay MD CB5MH_MD 8,270 2.0 

Lower Central Chesapeake Bay VA CB5MH_VA 7,633 2.0

Western Lower Chesapeake Bay VA CB6PH 1,267 1.0

Eastern Lower Chesapeake Bay VA CB7PH 15,107 2.0 

Mouth of Chesapeake Bay VA CB8PH 11 0.5 

Bush River MD BSHOH 350 0.5 

Gunpowder River-Upper MD GUNOH2 572 2.0 

Gunpowder River-Lower MD GUNOH1 1,860 0.5 

Middle River MD MIDOH 879 2.0 

Back River MD BACOH 34015 0.5

Patapsco River MD PATMH 389 1.0 

Magothy MD MAGMH 579 1.0 

Severn River MD SEVMH 455 1.0 

South River MD SOUMH 479 1.0 

Rhode River MD RHDMH 60 0.5 

West River MD WSTMH 238 0.5 

Upper Patuxent River MD PAXTF 205 0.5 

Middle Patuxent River MD PAXOH 115 0.5 

 

15 Proposed revisions to Maryland‘s water quality standards regulations would revise this figure to 30 acres.
DRAFT Chesapeake Bay TMDL

3-14 September 24, 2010

Segment description State Segment 

designator

SAV acreage 

restoration 

goal

Secchi 

application depth

(meters)

Lower Patuxent River MD PAXMH1 1,459 2.0 

Lower Patuxent River MD PAXMH2 172 0.5 

Lower Patuxent River MD PAXMH4 1 0.5 

Lower Patuxent River MD PAXMH5 2 0.5 

Upper Potomac River MD POTTF_MD 2,142 2.0 

Piscataway Creek MD PISTF 789 2.0 

Mattawoman Creek MD MATTF 792 1.0 

Middle Potomac River MD POTOH1 1,387 2.0 

Middle Potomac River MD POTOH2 262 1.0 

Middle Potomac River MD POTOH3 1,153 1.0 

Lower Potomac River MD POTMH_MD 7,088 1.0 

Upper Potomac River VA POTTF_VA 2,093 2.0 

Middle Potomac River VA POTOH_VA 1,503 2.0 

Lower Potomac River VA POTMH_VA 4,250 1.0 

Upper Rappahannock River VA RPPTF 66 0.5 

Middle Rappahannock River VA RPPOH 4 0.5 

Lower Rappahannock River VA RPPMH 1,700 1.0 

Corrotoman River VA CRRMH 768 1.0 

Piankatank River VA PIAMH 3,479 2.0 

Upper Mattaponi River VA MPNTF 85 0.5 

Lower Mattaponi River VA MPNOH No Data 

Available

0.5 

Upper Pamunkey River VA PMKTF 187 0.5 

Lower Pamunkey River VA PMKOH No Data 

Available

0.5 

Middle York River VA YRKMH 239 0.5 

Lower York River VA YRKPH 2,793 1.0 

Mobjack Bay VA MOBPH 15,901 2.0 

Upper James River-Upper VA JMSTF2 200 0.5 

Upper James River-Lower VA JMSTF1 1,000 0.5 

Appomattox River VA APPTF 379 0.5 

Middle James River VA JMSOH 15 0.5 

Chickahominy River VA CHKOH 535 0.5 

Lower James River VA JMSMH 200 0.5 

Mouth of the James River VA JMSPH 300 1.0 

Lynnhaven River VA LYNPH 107 0.5 

Northeast River MD NORTF 89 0.5 

Chesapeake & Delaware Canal MD C&DOH_MD 7 0.5 

Bohemia River MD BOHOH 354 0.5 

Elk River MD ELKOH1 1,844 2.0 

Elk River MD ELKOH2 190 0.5 

Sassafras River MD SASOH1 1,073 2.0 

Sassafras River MD SASOH2 95 0.5 

Upper Chester River MD CHSTF 23016 0.5

 

16 Proposed revisions to Maryland‘s water quality standards regulations would revise this figure to 1 acre.
DRAFT Chesapeake Bay TMDL

3-15 September 24, 2010

Segment description State Segment 

designator

SAV acreage 

restoration 

goal

Secchi 

application depth

(meters)

Middle Chester River MD CHSOH 77 0.5 

Lower Chester River MD CHSMH 2,928 1.0 

Eastern Bay MD EASMH 6,209 2.0 

Middle Choptank River MD CHOOH 72 0.5 

Lower Choptank River MD CHOMH2 1,621 1.0 

Mouth of Choptank River MD CHOMH1 8,184 2.0 

Little Choptank River MD LCHMH 4,076 2.0 

Honga River MD HNGMH 7,761 2.0 

Fishing Bay MD FSBMH 197 0.5 

Middle Nanticoke River MD NANOH 12 0.5 

Lower Nanticoke River MD NANMH 3 0.5 

Wicomico River MD WICMH 3 0.5 

Manokin River MD MANMH1 4,294 2.0 

Manokin River MD MANMH2 59 0.5 

Big Annemessex River MD BIGMH1 2,021 2.0 

Big Annemessex MD BIGMH2 22 0.5 

Middle Pocomoke River MD POCOH_MD 2217 0.5

Lower Pocomoke River MD POCMH_MD 877 1.0 

Lower Pocomoke River VA POCMH_VA 4,066 1.0 

Tangier Sound MD TANMH1_MD 24,683 2.0 

Tangier Sound MD TANMH2_MD 74 0.5 

Tangier Sound VA TAHMH_VA 13,579 2

Sources: USEPA 2003c, 2004e; Code of Maryland Title 26 Subtitle 08, Chapter 2, Section 3; Code of Virginia 9 62.1-

44.15 3a; VAC 25-260-185; 7 Delaware Code Section 6010; 7 Delaware Administrative Code 7401; District of 

Columbia Municipal Regulations Title 21, Chapter 11.

Note: This table contains additional split segments beyond the 92 Chesapeake Bay segments listed in Table 3-3 

strictly for purposes of applying separate water clarity criteria application depths within the same segment (USEPA 

2004e).

3.2 Jurisdictions’ Current Chesapeake Bay Water Quality Standards 

Regulations

Delaware, the District of Columbia, Maryland, and Virginia each has adopted WQS consistent 

with EPA‘s published Chesapeake Bay water quality criteria, assessment procedures, and tidal 

water designated uses in its respective WQS regulations (Table 3-7). In some cases, a jurisdiction 

also has adopted more jurisdiction-specific designated uses or criteria or both; those cases are 

briefly described below.

 

17 Proposed revisions to Maryland‘s water quality standards regulations would revise this to be a no-grow zone.
DRAFT Chesapeake Bay TMDL

3-16 September 24, 2010

Table 3-7. Links for accessing the current WQS regulations for Delaware, the District of Columbia, 

Maryland, and Virginia

Jurisdiction WQS regulations URL address

Delaware 7 Delaware Code Section 6010; 7 Delaware Administrative Code 7401

<http://www.epa.gov/waterscience/standards/wqslibrary/de/de_3_wqs.pdf> 

District of 

Columbia

DC Municipal Regulations Title 21, Chapter 11

<http://www.epa.gov/waterscience/standards/wqslibrary/dc/dc_3_register.pdf> 

Maryland Code of Maryland Title 26 Subtitle 08, Chapter 2

<http://www.epa.gov/waterscience/standards/wqslibrary/dsd.state.md/md-ch2-

quality-20051130.pdf.us/comar/subtitle_chapters/26_Chapters.htm> 

Virginia Code of Virginia 9 62.1-44.15 3a; VAC 25-260 Virginia WQSs

<http://www.deq.virginia.gov/wqs/> OR

<http://epa.gov/waterscience/standards/wqslibrary/va/va_3_wqs.pdf>

3.2.1 District of Columbia

Table 3-8 summarizes the District of Columbia‘s designated uses for its surface waters. The 

District of Columbia has adopted EPA‘s narrative chlorophyll a water quality criteria but also 

adopted the Bay numeric chlorophyll a water quality criteria shown in Table 3-9 with respect to 

the District of Columbia‘s tidal Class C waters. Those numeric chlorophyll a criteria are subject 

to this Chesapeake Bay TMDL (see Table 2-1).

Table 3-8. District of Columbia designated uses for surface waters

Class of water Description

A Primary contact recreation

B Secondary contact recreation and aesthetic enjoyment

C Protection and propagation of fish, shellfish, and wildlife

D Protection of human health related to consumption of fish and shellfish

E Navigation

Source: District of Columbia Municipal Regulations Title 21, Chapter 11

Table 3-9. Numeric criteria for the District of Columbia’s tidally influenced waters

Constituent Numeric criteria

Temporal 

application

Designated 

use

Dissolved 

oxygen

7-day mean ≥ 6.0 mg/L

Instantaneous minimum ≥ 5.0 mg/L

30-day mean ≥ 5.5 mg/L

7-day mean ≥ 4.0 mg/L

Instantaneous minimum ≥ 3.2 mg/L

(At temperatures greater than 29 °C, in tidally 

influenced waters, an instantaneous minimum 

dissolved oxygen concentration of 4.3 mg/L will 

apply)

February 1–

May 31

June 1–

January 31

C

Secchi depth 0.8 m (seasonal segment average) April 1–

October 31

C

Chlorophyll a 25 μg/L (season segment average) July 1–

September 30

C

Source: District of Columbia Municipal Regulations Title 21, Chapter 11

Note: μg/L = micrograms per liter
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3-17 September 24, 2010

3.2.2 Delaware

The EPA-published Chesapeake Bay criteria and designated use documents and subsequent 

addenda apply to the tidal Nanticoke River and Broad Creek in Delaware, both of which are 

subject to this Chesapeake Bay TMDL (see Table 2-1). Delaware has adopted EPA‘s narrative 

chlorophyll a water quality criteria.

Delaware has adopted all the EPA-published Chesapeake Bay criteria and designated use 

documents and subsequent addenda listed in Table 3-1 by reference into its WQS regulations. As 

a result, no WQS changes are pending in Delaware.

3.2.3 Maryland

Maryland has adopted into its WQS regulations all the EPA-published Bay criteria, assessment 

procedures, and designated uses described previously to apply to all Chesapeake Bay, tidal 

tributary, and embayment waters of Maryland subject to this Chesapeake Bay TMDL. Maryland 

has adopted EPA‘s narrative chlorophyll a water quality criteria.

Several tidal Bay segment-specific applications of DO criteria are unique to Maryland. In the 

middle-central Chesapeake Bay segment (CB4MH), restoration variances18 of 7 and 2 percent 

apply to the application of the deep-water and deep-channel designated use DO criteria,

respectively. In the Patapsco River segment (PATMH), a restoration variance of 7 percent 

applies to the application of the deep-water criteria (COMAR 26.08.02.03-3(c)(8)(e)(vi). Such 

restoration variances are consistent with EPA-published guidance (USEPA 2003c) and were 

approved by EPA on August 29, 2005.

3.2.4 Virginia

The EPA-published Bay criteria, assessment procedures, and designated uses described 

previously apply to all Chesapeake Bay, tidal tributary, and embayment waters of Virginia and 

are subject to this Chesapeake Bay TMDL. The narrative chlorophyll a criteria guidance 

published by EPA (USEPA 2003a) as adopted by Virginia are applicable to Virginia‘s Bay tidal 

waters. Virginia also adopted the segment-specific numeric chlorophyll a criteria for the tidal 

James River listed in Table 3-10 into its WQS regulations. The criteria are based on various 

scientific lines of evidence published the original EPA 2003 Bay criteria document (USEPA

2003a) with additional river-specific considerations (VADEQ 2004). EPA approved the WQS 

regulations on June 27, 2005.

Virginia has additional site-specific DO and chlorophyll a criteria. In the tidal Mattaponi

(MPNTF, MPNOH) and Pamunkey (PMKTF, PMKOH) river segments, because of the seasonal 

lower DO concentration from the natural oxygen-depleting processes present in surrounding tidal 

wetlands, a site-specific criterion of greater than or equal to 4 mg/L 30-day mean DO (9 VAC 

25-260-185) is warranted and is consistent with the EPA-published criterion (USEPA 2004a).

 

18 A restoration variance is the percentage of allowable exceedance based on water quality modeling incorporating 

the best available data and assumptions. The restoration variances are temporary and will be reviewed at a minimum 

every 3 years, as required by the CWA and EPA regulations. The variances could be modified on the basis of new 

data or assumptions incorporated into the water quality model. COMAR 26.08.02.03-3(C)(8)(h).
DRAFT Chesapeake Bay TMDL

3-18 September 24, 2010

Table 3-10. Segment-specific chlorophyll a criteria for Virginia’s tidal James River waters

Designated 

use

Chlorophyll a

criterion

(μg/L) Chesapeake Bay segment

Temporal 

application

OpenWater10 Upper James River-Upper (JMSTF2) March 1–May 

15 Upper James River-Lower (JMSTF1) 31

15 Middle James River (JMSOH)

12 Lower James River (JMSMH)

12 Mouth of the James River (JMSPH)

15 Upper James River-Upper (JMSTF2) July 1–

23 Upper James River-Lower (JMSTF1) September 30

22 Middle James River (JMSOH)

10 Lower James River (JMSMH)

10 Mouth of the James River (JMSPH)

Source: Code of Virginia 9 section 62.1-44.15 3a; VAC 25-260

Note: μg/L = micrograms per liter

3.3 Jurisdictions’ Pending Revisions to Chesapeake Bay Water 

Quality Standards Regulations

Maryland, Virginia, and the District of Columbia are each in the process of proposing the 

modification of their respective WQS regulations directly relevant to the Bay TMDL.

3.3.1 District of Columbia

The District of Columbia has adopted the 2003 Chesapeake Bay water quality criteria document 

(USEPA 2003a) into its WQS regulations. The District of Columbia has proposed adoption of 

the EPA-published 2004, 2007, 2008, 2010 Bay criteria addenda (USEPA 2004a, 2007a, 2007b, 

2008a, 2010a) by reference. The proposal is pending public review and EPA approval.

3.3.2 Delaware

Delaware already has adopted the EPA-published 2010 Bay criteria addendum into its WQS 

regulations by reference. Therefore, no revisions to Chesapeake Bay WQS regulations are 

pending in Delaware.

3.3.3 Maryland

Maryland has adopted most of the EPA-published Chesapeake Bay criteria and designated use 

documents and subsequent addenda listed in Table 3-1 by reference into its WQS regulations. 

Maryland has proposed adoption of the EPA published 2010 Bay criteria addendum (USEPA 

2010a) by reference. The proposal is pending public review and EPA approval.

Maryland also has proposed the following amendments to its WQS regulations: adopting the 

EPA-published 2010 Bay criteria addendum; adopting a 14 percent restoration variance for the 

lower Chester River segment (CHSMH) deep-channel DO criteria application; adopting a sitespecific 4 mg/L 30-day mean DO criterion for the upper and middle tidal Pocomoke River 

(POCTF, POCOH_MD) segments; applying the deep-water designated use, in the presence of 

observed pycnoclines, in the South (SOUMH), Severn (SEVMH) and Magothy (MAGMH) river 

segments; a 30-acre SAV restoration acreage for the Back River (BACOH) segment; a 1-acre 

SAV restoration acreage for the upper Chester River (CHSTF) segment; and recognizing the 
DRAFT Chesapeake Bay TMDL

3-19 September 24, 2010

middle Pocomoke River segment (POCOH_MD) as an SAV no-grow zone (Appendix R-3). The 

proposal is pending public review and EPA approval.

3.3.4 Virginia

Virginia has adopted most of the EPA-published Chesapeake Bay criteria and designated use 

documents and subsequent addenda listed in Table 3-1 by reference into its WQS regulations. 

Virginia has proposed adoption of the EPA-published 2007, 2008, and 2010 Bay criteria 

addendum (USEPA 2010a) by reference. The proposal is pending public review and EPA 

approval.

3.4 Assessing Attainment of Chesapeake Bay Water Quality 

Standards

The Bay criteria assessment approach is designed to protect the living resources as defined by 

the designated uses (USEPA 2003a). The criteria levels themselves were largely based on 

scientific studies performed in laboratory settings or under controlled field conditions. The 

criteria establish the level of a given habitat condition that living resources need for survival. 

They do not account for many other environmental factors that could affect survival.

For all three tidal states and the District of Columbia, attainment of each jurisdiction‘s 

Chesapeake Bay WQS is determined by applying the same set of assessment procedures 

published in the original 2003 Chesapeake Bay criteria document (USEPA 2003a) and 

subsequent published addenda (USEPA 2004a, 2007a, 2007b, 2008a, 2010a) (see Table 3-1). 

Those consistent sets of criteria assessment procedures are formally adopted into each 

jurisdiction‘s WQS regulations by reference.

3.4.1 Defining Total Exceedances

Criteria attainment for DO, water clarity, and chlorophyll a is assessed in terms of the spatial and 

temporal extent of criterion exceedances—what volume or surface area of the Bay segment 

exceeds a given criteria and for how much time during the assessment period (USEPA 2003a, 

2004a). The allowable frequency with which criteria can be violated without a loss of the 

designated use is also considered. For each listing cycle, assessments are based on monitoring 

data collected over a 3-year period in each spatial assessment unit. Spatial assessment units are 

defined by Chesapeake Bay segments and applicable designated uses. Such assessment of the 

criteria as further described below is designed to provide reliable protection for the associated 

refined aquatic life use.

The spatial exceedances of criteria are determined using a grid cell-based data interpolation 

software application that enables estimation of water quality values for the entire Bay using 

monitored data at specific points (USEPA 2003a, 2007a). The interpolated data are compared to 

water quality criteria on a cell by cell basis, and the percent of surface area or volume exceeding 

the criterion in each spatial assessment unit is calculated. The percent spatial exceedances for 

each assessment unit are then compiled for each monitoring event conducted during the 3-year 

monitoring period.

The temporal extent of exceedances is determined by calculating the probability that an observed 

percent exceedance will be equaled or exceeded. To calculate that probability, the percent of 
DRAFT Chesapeake Bay TMDL

3-20 September 24, 2010

spatial exceedances are sorted and ranked, and a cumulative probability is calculated for each 

spatial exceedance value (USEPA 2003a). An example is shown in Table 3-11.

Table 3-11. Estimated percent spatial criteria exceedances and associated cumulative 

probabilities

Period of data

Percent area/volume 

exceeding criteria

(spatial) Rank

Cumulative probability [rank / (n + 1)]

(temporal)

100 0.00%

June 1998 75 1 7.69%

March 1998 72 2 15.38%

May 1999 67 3 23.08%

May 1998 65 4 30.77%

April 1998 55 5 38.46%

June 2000 50 6 46.15%

March 1999 49 7 53.85%

April 2000 39 8 61.54%

May 2000 35 9 69.23%

Apr 1999 34 10 76.92%

June 1999 25 11 84.62%

March 2000 20 12 92.31%

Source: USEPA 2003a

The spatial and temporal exceedances can be graphically illustrated by plotting the cumulative 

frequency distribution (CFD) curve, which is a plot of the temporal exceedance values on the Yaxis versus the spatial exceedance values on the X-axis (Figure 3-3) (USEPA 2003a, 2007a; 

STAC 2006).

Source: 

USEPA 2003a

Figure 3-3. Example cumulative frequency distribution (CFD) curve.

Cumulative Frequency Distribution Curve

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 10 20 30 40 50 60 70 80 90 100

% Area or Volume Exceeding Criteria

% of Time a Specified Area or Volume 

Equals or Exceeds Criteria

39% or more of the area/volume 

exceedes criteria in 62% of the 

sampling events during the threeyear assessment period
DRAFT Chesapeake Bay TMDL

3-21 September 24, 2010

3.4.2 Defining Allowable Exceedances

Reference curves were developed to provide a scientifically based, direct measure of the 

allowable criteria exceedances (USEPA 2003a). Those allowable exceedances are defined to be 

those that last a short enough time or cover a small enough volume/surface area to have no 

adverse effects on the designated use. It is assumed that the designated uses can be attained even 

with some limited level of criteria exceedances and thus, the reference curves define those 

criteria exceedances deemed to be allowable—chronic in time but over small volumes/surface 

areas, or infrequent occurrences over large volumes/surface areas. Exceedances that occur over 

large areas of space and time would be expected to have significant detrimental effects on 

biological communities, which would imply nonattainment of designated uses.

Reference curves are used in conjunction with the CFD to illustrate the time and space during 

which a given criteria can be allowably exceeded without resulting in harm to the designated use. 

For assessment purposes, two types of reference curves are used: a biological reference curve 

and a 10 percent default reference curve.

Biological reference curves are CFDs developed for a given criterion in areas for which 

monitoring data are available and in which healthy aquatic communities exist (USEPA 2003a). 

They represent the range of conditions that can reasonably be expected in a healthy community. 

As a result, the biological reference curve can be used to provide an understanding of what level 

of criteria exceedances are allowable without losing support of the designated use. Given the 

Bay‘s nutrient-enriched status, appropriate reference sites are limited. Biological reference 

curves have been published for and are used to assess allowable exceedances for the deep-water 

DO criteria (USEPA 2010a) and the water clarity criteria (USEPA 2003a).

In some cases, developing a biologically based reference curve is not possible because of a lack 

of data describing the health of the relevant species or biological communities and lack of 

appropriate reference sites. Such cases require a different approach. EPA recommends using a 

default reference curve in situations for which a biologically based reference curve is unavailable 

(USEPA 2007a). The default reference curve is defined as a hyperbolic curve that encompasses 

no more than 10 percent of the area of the CFD graph (percent of space multiplied by percent of 

time) (USEPA 2007a, page 13, Figure II-4 and Equation 1) (Figure 3-4).
DRAFT Chesapeake Bay TMDL

3-22 September 24, 2010

Source: USEPA 2007a

Figure 3-4. Default reference curve used in the attainment assessment of Chesapeake Bay water quality 

criteria for which biologically based reference curves have not yet been derived.

Once the CFD curve for a spatial assessment unit is developed from monitoring data (also 

referred to as the assessment curve), it is compared to the appropriate reference curve. The area 

on the graph above the reference curve and below the assessment curve is considered a nonallowable exceedance. Values on the assessment curve falling below the reference curve are 

considered allowable exceedances (Figure 3-5).
DRAFT Chesapeake Bay TMDL

3-23 September 24, 2010

Source: USEPA 2003a

Figure 3-5. Example reference and assessment curves showing allowable and non-allowable exceedances

3.4.3 Assessing Criteria Attainment

Dissolved Oxygen Criteria Assessment

EPA published DO criteria protective of migratory and spawning, open-water, deep-water, and 

deep-channel designated use habitats (

Table 3-4) (USEPA 2003a). DO criteria were established for Chesapeake Bay that varied in 

space and time to provide levels of protection for different key species and communities. The 

criteria were also designed around several lengths of time to reflect the varying oxygen 

tolerances for different life stages (e.g., larval, juvenile, adult) and effects (e.g., mortality, 

growth, behavior).

The DO criteria include multiple components, including a target DO concentration, the duration 

of time over which the concentration is averaged, the designated use area where the criterion 

applies, the protection provided, and the time of year when the criterion applies (USEPA 2003a, 

2003c). The four tidal Bay jurisdictions adopted these DO criteria into their respective WQS 

regulations.
DRAFT Chesapeake Bay TMDL

3-24 September 24, 2010

Assessing DO criteria attainment is challenging because of the complexity of both the criteria 

and the Bay itself. To fully assess all the criteria components, data needed to be collected at a 

spatial intensity that adequately represent the four designated use habitats of Chesapeake Bay 

tidal waters at different times of the year (USEPA 2003c, 2004e). Similarly, data were collected 

during all the applicable seasons and at frequencies sufficient to address the various criteria 

duration components. The different DO criteria apply to different designated use areas and 

multiple criteria apply to the same designated use area. The DO criteria components also apply 

over different periods to protect species during critical life stages or during particularly stressful 

times of the year. To fully assess each DO component in each designated use habitat over the 

appropriate periods will require an extensive monitoring program and a detailed assessment 

methodology. The CBP conducts extensive water quality and living resource monitoring 

throughout the Bay tidal waters (CBP 1989a, 1989b; MRAT 2009). The existing Bay water 

quality monitoring was not sufficient to cover all the criteria components, however, and some 

details in the assessment methodology remain unresolved (USEPA 2007a; MRAT 2009).

The DO criteria include 30-day, 7-day, and 1-day means along with an instantaneous minimum. 

The CBP partners have the capacity (data, assessment methodology) to assess only the 30-day 

mean open-water and deep-water DO criteria and, in the case of the deep-channel use, the 

instantaneous minimum DO criteria (USEPA 2003a, 2004a, 2007a, 2008a, 2010a). The 

remaining DO criteria are not assessed because the existing water quality monitoring programs 

and the published assessment methodologies are not yet adequate for full assessment.

Evaluation of Chesapeake Bay water quality/sediment transport model outputs have provided 

clear evidence that the 30-day mean open-water and deep-water and the instantaneous minimum 

deep-channel DO criteria are the criteria driving determination of nutrient loadings supporting 

attainment all the open-water (30-day mean, 7-day mean, instantaneous minimum), deep-water 

(30-day mean, 1-day and instantaneous minimum), and deep-channel (instantaneous minimum) 

DO criteria.

For both open-water and deep–water designated uses, the 30-day mean criteria had the highest 

nonattainment in all three scenarios (Figure 3-6). The 30-day mean open-water and deep-water 

criteria are, therefore, protective of the other two non-assessed dissolved oxygen criteria (openwater 7-day and instantaneous minimum, deep-water 1-day mean and instantaneous minimum) 

on average for the mainstem Bay segments. The deep–channel designated use has only one 

dissolved oxygen criterion, and it is currently assessed using monitoring data. The deep-channel 

criterion is also more protective, based on the levels of nonattainment recorded in Figure 3-6, 

than the deep-water and open-water criteria. The analyses documented in Appendix D provide 

clear evidence the 30-day mean open-water and deep-water dissolved oxygen criteria and the 

deep-channel instantaneous minimum criterion are the most protective criteria across all Bay 

segments and designated uses.
DRAFT Chesapeake Bay TMDL

3-25 September 24, 2010

Figure 3-6. Direct model assessment of open water (a), and deep water and deep channel (b) criteria.

Chlorophyll a Criteria Assessment

The procedures described in USEPA 2007b, and further refined in USEPA 2010a, apply to 

assessing Virginia‘s tidal James River and the District of Columbia‘s tidal waters numeric 

chlorophyll a criteria.

To assess attainment of the Virginia and District of Columbia‘s adopted numerical chlorophyll a

concentration-based criteria, it was necessary to establish a reference curve for use in the CFD 

criteria assessment (USEPA 2003a, 2007a). In the case of the numerical chlorophyll a criteria 

where a biologically based reference curve is not available (USEPA 2007b), EPA 

0.0%

0.1%

0.2%

0.3%

0.4%

0.5%

0.6%

0.7%

0.8%

0.9%

1.0%

Calibrated Model Moderate Reduction Large Reduction

Average Mainstem Non-Attainment

Direct model assessment of nonattainment—mainstem average

open water

DO Open Water Summer Instantaneous

DO Open Water Weekly

DO Open Water Summer Monthly

0%

5%

10%

15%

20%

25%

30%

Calibrated Model Moderate Reduction Large Reduction

Average Mainstem Non-Attainment

Direct model assessment of nonattainment—mainstem average

deep water and deep channel

DO Deep Water Instantaneous

DO Deep Water Daily

DO Deep Water Monthly

DO Deep Channel Instantaneous
DRAFT Chesapeake Bay TMDL

3-26 September 24, 2010

recommended—and Virginia and the District of Columbia adopted—using the default reference 

curve originally described in USEPA 2007a and illustrated in Figure 3-4.

The jurisdiction-adopted, concentration-based, chlorophyll a criteria values are threshold 

concentrations that should be exceeded infrequently (e.g., < 10 percent) because a low number of 

naturally occurring exceedances occur even in a healthy phytoplankton population (USEPA 

2007b). The assessment of chlorophyll a criteria attainment, therefore, uses the CFD-based 

assessment method described earlier that applies the default reference curve. Such concentrationbased Chesapeake Bay chlorophyll a criteria apply only to those seasons and salinity-based 

habitats for which they were defined to protect against applicable human health and aquatic life 

impairments (USEPA 2007b). Each season—Spring (March 1–May 31) and Summer (July 1–

September 30)—was assessed separately to evaluate chlorophyll a criteria attainment.

The chlorophyll a criteria are based on seasonal mean of observed chlorophyll data. The 

observed data are first transformed by taking the natural logarithm and then interpolated spatially 

to equally spaced points (representing interpolator cells) within the designated use area for each 

monitoring cruise. The interpolated value of each cell is averaged in time across the entire 

season, and then the spatial violation rate is calculated as the fraction of interpolator cells in a 

designated use area that fails the appropriate criterion (USEPA 2010a).

SAV/Water Clarity Criteria Assessment

Water clarity criteria and SAV restoration acreages are used to define attainment of the shallowwater bay grass designated use in Chesapeake Bay, its tidal tributaries, and embayments

(USEPA 2003a, 2003c). EPA published three measures for assessing attainment of the shallowwater SAV designated use for a Chesapeake Bay segment (USEPA 2007a):

1. Measure SAV acreage in the Bay segment from overflight data mapping analysis and 

compare with the SAV restoration goal acreage for that Bay segment (USEPA 2003b).

2. Measure water clarity acreage on the basis of routine water quality mapping using data from 

the Chesapeake Bay shallow-water monitoring program and, combined with measured acres 

of SAV, compare with the calculated water clarity acres for that segment (USEPA 2007a).

3. Measure water clarity criteria attainment on the basis of the CFD assessment methodology, 

again using shallow-water monitoring program data (USEPA 2003a, 2003c, 2007a, 2008a).

Without sufficient shallow-water monitoring data to determine the available water clarity acres 

(measurement 2 above) or to assess water clarity criteria attainment using the CFD-based 

procedure (measurement 3 above), EPA recommends that the jurisdictions assess shallow-water 

Bay grass designated use attainment using the acres of mapped SAV (measurement 1 above) 

(USEPA 2003a, 2003b, 2007a, 2008a).