Chesapeake Bay Total Maximum Daily Load 

for Nitrogen, Phosphorus and Sediment 

December 29, 2010 

U.S. Environmental Protection Agency 

Region 3 

Water Protection Division 

Air 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 

Office of Air and Radiation 

Office of General Counsel 

Office of the Administrator 

Washington, D.C. 

and in collaboration with 

Delaware, the District of Columbia, Maryland, New York, 

Pennsylvania, Virginia, and West Virginia 
Chesapeake Bay TMDL

CHESAPEAKE BAY TMDL EXECUTIVE SUMMARY 

INTRODUCTION 

The U.S. Environmental Protection Agency (EPA) has established the Chesapeake Bay Total 

Maximum Daily Load (TMDL), a historic and comprehensive “pollution diet” with rigorous 

accountability measures to initiate sweeping actions to restore clean water in the Chesapeake 

Bay and the region’s streams, creeks and rivers. 

Despite extensive restoration efforts during the past 25 years, the TMDL was prompted by 

insufficient progress and continued poor water quality in the Chesapeake Bay and its tidal 

tributaries. The TMDL is required under the federal Clean Water Act and responds to consent 

decrees in Virginia and the District of Columbia from the late 1990s. It is also a keystone 

commitment of a federal strategy to meet President Barack Obama’s Executive Order to restore 

and protect the Bay. 

The TMDL – the largest ever developed by EPA – identifies the necessary pollution reductions 

of nitrogen, phosphorus and sediment across Delaware, Maryland, New York, Pennsylvania, 

Virginia, West Virginia and the District of Columbia and sets pollution limits necessary to meet 

applicable water quality standards in the Bay and its tidal rivers and embayments. Specifically, 

the TMDL sets Bay watershed limits of 185.9 million pounds of nitrogen, 12.5 million pounds of 

phosphorus and 6.45 billion pounds of sediment per year – a 25 percent reduction in nitrogen, 

24 percent reduction in phosphorus and 20 percent reduction in sediment. These pollution limits 

are 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 jurisdiction partners. 

The TMDL is designed to ensure that all pollution control measures needed to fully restore the 

Bay and its tidal rivers are in place by 2025, with at least 60 percent of the actions completed by 

2017. The TMDL is supported by rigorous accountability measures to ensure cleanup 

commitments are met, including short-and long-term benchmarks, a tracking and accountability 

system for jurisdiction activities, and federal contingency actions that can be employed if 

necessary to spur progress. 

Watershed Implementation Plans (WIPs), which detail how and when the six Bay states and the 

District of Columbia will meet pollution allocations, played a central role in shaping the TMDL. 

Most of the draft WIPs submitted by the jurisdictions in September 2010 did not sufficiently 

identify programs needed to reduce pollution or provide assurance the programs could be 

implemented. As a result, the draft TMDL issued September 24, 2010 contained moderate- to 

high-level backstop measures to tighten controls on federally permitted point sources of 

pollution. 

A 45-day public comment period on the draft TMDL was held from September 24 to November 

8, 2010. During that time, EPA held 18 public meetings in all seven Bay watershed jurisdictions, 

which were attended by about 2,500 citizens. EPA received more than 14,000 public comments 

and, where appropriate, incorporated responses to those comments in developing the final 

TMDL. 

ES‐1 December 29, 2010
Chesapeake Bay TMDL

After states submitted the draft WIPs, EPA worked closely with each jurisdiction to revise and 

strengthen its plan. Because of this cooperative work and state leadership, the final WIPs were 

significantly improved. Examples of specific improvements include: 

 Regulated point sources and non-regulated nonpoint sources of nitrogen, phosphorus, and 

sediment are fully considered and evaluated separately in terms of their relative 

contributions to water quality impairment of the Chesapeake Bay’s tidal waters. 

 Committing to more stringent nitrogen and phosphorus limits at wastewater treatment 

plants, including on the James River in Virginia. (Virginia, New York, Delaware) 

 Pursuing state legislation to fund wastewater treatment plant upgrades, urban stormwater 

management and agricultural programs. (Maryland, Virginia, West Virginia) 

 Implementing a progressive stormwater permit to reduce pollution. (District of Columbia) 

 Dramatically increasing enforcement and compliance of state requirements for agriculture. 

(Pennsylvania) 

 Committing state funding to develop and implement state-of-the-art-technologies for 

converting animal manure to energy for farms. (Pennsylvania) 

 Considering implementation of mandatory programs for agriculture by 2013 if pollution 

reductions fall behind schedule. (Delaware, Maryland, Virginia) 

These improvements enabled EPA to reduce and remove most federal backstops, leaving a few 

targeted backstops and a plan for enhanced oversight and contingency actions to ensure progress. 

As a result, the final TMDL is shaped in large part by the jurisdictions’ plans to reduce pollution, 

which was a long-standing priority for EPA and why the agency always provided the 

jurisdictions with flexibility to determine how to reduce pollution in the most efficient, costeffective and acceptable manner. 

Now the focus shifts to the jurisdictions’ implementation of the WIP policies and programs that 

will reduce pollution on-the-ground and in-the-water. EPA will conduct oversight of WIP 

implementation and jurisdictions’ progress toward meeting two-year milestones. If progress is 

insufficient, EPA is committed to take appropriate contingency actions including targeted 

compliance and enforcement activities, expansion of requirements to obtain NPDES permit 

coverage for currently unregulated sources, revision of the TMDL allocations and additional 

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

animal agriculture operations and municipal stormwater systems. 

In 2011, while the jurisdictions continue to implement their WIPs, they will begin development 

of Phase II WIPs, designed to engage local governments, watershed organizations, conservation 

districts, citizens and other key stakeholders in reducing water pollution. 

TMDL BACKGROUND 

The Clean Water Act (CWA) sets an overarching environmental goal that all waters of the 

United States be “fishable” and “swimmable.” More specifically it requires states and the District 

of Columbia to establish appropriate uses for their waters and adopt water quality standards that 

are protective of those uses. The CWA also requires that every two years jurisdictions develop – 

with EPA approval – a list of waterways that are impaired by pollutants and do not meet water 

ES‐2 December 29, 2010
Chesapeake Bay TMDL

quality standards. For those waterways identified on the impaired list, a TMDL must be 

developed. 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 Bay 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 

stormwater runoff, wastewater facilities, air pollution and other sources, including onsite septic 

systems. Despite some reductions in pollution during the past 25 years of restoration due to 

efforts by federal, state and local governments; non-governmental organizations; and 

stakeholders in the agriculture, urban/suburban stormwater, and wastewater sectors, there has 

been insufficient progress toward meeting the water quality goals for the Chesapeake Bay and its 

tidal waters. 

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 Bay grasses and chlorophyll-a, an indicator of algae levels 

(Figure ES-1). It is important to note that the pollution controls employed to meet the TMDL 

will also have significant benefits for water quality in tens of thousands of streams, creeks, lakes 

and rivers throughout the region. 

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

Columbia, Maryland, New York, Pennsylvania, Virginia, and West Virginia), EPA and the 

Chesapeake Bay Commission, which 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. During the October 2007 meeting of the Chesapeake Bay Program’s 

Principals’ Staff Committee, the Bay watershed jurisdictions and EPA agreed that EPA would 

establish the multi-state TMDL. Since 2008, EPA has sent official letters to the jurisdictions 

detailing all facets of the TMDL, including: nitrogen, phosphorus and sediment allocations; 

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, the Chesapeake Bay Foundation settlement agreement of 2010, and settlement 

agreements dating back to the late 1990s that address certain tidal waters identified as impaired 

in the District of Columbia, Delaware, Maryland and Virginia. 

ES‐3 December 29, 2010
Chesapeake Bay TMDL

Figure ES-1. A nitrogen, phosphorus and sediment TMDL has been developed for each of the 92 

Chesapeake Bay segment watersheds. 

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 

11 federal agencies to meet the President’s Executive Order. 

ES‐4 December 29, 2010
Chesapeake Bay TMDL

DEVELOPING THE CHESAPEAKE BAY TMDL 

Development of the Chesapeake Bay TMDL required extensive 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 is informed by 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 to make future predictions, and was a critical and valuable tool to 

develop the Chesapeake Bay TMDL. 

The development of the TMDL consisted of several steps: 

1. EPA provided the jurisdictions with loading allocations for nitrogen, phosphorus and 

sediment for the major river basins by jurisdiction. 

2. Jurisdictions developed draft Phase I WIPs to achieve those basin-jurisdiction allocations. 

In those draft 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 pollution 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. 

4. The draft TMDL was published for a 45-day public comment period and EPA held 18 

public meetings in all six states and the District of Columbia. Public comments were 

received, reviewed and considered for the final TMDL. 

5. Jurisdictions, working closely with EPA, revised and strengthened Phase I WIPs and 

submitted final versions to EPA. 

6. EPA evaluated the final WIPs and used them along with public comments to develop the 

final TMDL. 

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

the impaired tidal segments of the Bay and its rivers, it was necessary for EPA to allocate the 

nitrogen and phosphorus loadings in an equitable manner to the states and basins. EPA used 

three basic guides to divide these loads. 

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

should 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 Bay 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) (Figure ES-2). 

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

toward achieving final assigned loads. 

ES‐5 December 29, 2010
Chesapeake Bay TMDL

Figure ES-2. Sub-basins across the Chesapeake Bay watershed with the 

highest (red) to lowest (blue) pound for pound nitrogen pollutant loading 

effect on Chesapeake Bay water quality. 

In addition, EPA has committed to reducing air deposition of nitrogen to the tidal waters of the 

Chesapeake Bay from 17.9 to 15.7 million pounds per year. The reductions will be achieved 

through implementation of federal air regulations during the coming years. 

To ensure that these pollutant loadings will attain and maintain applicable water quality 

standards, the TMDL calculations were developed to account for critical environmental 

conditions a waterway would face and seasonal variation. An implicit margin of safety for 

nitrogen and phosphorus, and an explicit margin of safety for sediment, also are included in the 

TMDL. 

Ultimately, the TMDL is designed to ensure that by 2025 all practices necessary to fully restore 

the Bay and its tidal waters are in place, with at least 60 percent of the actions taken by 2017. 

ES‐6 December 29, 2010
Chesapeake Bay TMDL

The 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 are informed by the jurisdictions’ Phase I WIPs. 

Table ES-1. Chesapeake Bay TMDL watershed nitrogen, phosphorus and sediment final 

allocations by jurisdiction and by major river basin. 

Nitrogen 

allocations 

Phosphorus 

allocations 

Sediment 

allocations 

Jurisdiction Basin (million lbs/year) (million lbs/year) (million lbs/year) 

Susquehanna 68.90 2.49 1,741.17 

Potomac 4.72 0.42 221.11 

Eastern Shore 0.28 0.01 21.14 

Western Shore 0.02 0.00 0.37 

Pennsylvania 

PA Total 73.93 2.93 1,983.78 

Susquehanna 1.09 0.05 62.84 

Eastern Shore 9.71 1.02 168.85 

Western Shore 9.04 0.51 199.82 

Patuxent 2.86 0.24 106.30 

Potomac 16.38 0.90 680.29 

Maryland 

MD Total 39.09 2.72 1,218.10 

Eastern Shore 1.31 0.14 11.31 

Potomac 17.77 1.41 829.53 

Rappahannock 5.84 0.90 700.04 

York 5.41 0.54 117.80 

James 23.09 2.37 920.23 

Virginia 

VA Total 53.42 5.36 2,578.90 

District of Potomac 2.32 0.12 11.16 

Columbia DC Total 2.32 0.12 11.16 

New York Susquehanna 8.77 0.57 292.96 

NY Total 8.77 0.57 292.96 

Delaware Eastern Shore 2.95 0.26 57.82 

DE Total 2.95 0.26 57.82 

Potomac 5.43 0.58 294.24 

James 0.02 0.01 16.65 

West Virginia 

WV Total 5.45 0.59 310.88 

Total Basin/Jurisdiction Draft 

Allocation 

185.93 12.54 6,453.61 

Atmospheric Deposition Draft 

Allocationa 

15.7 N/A N/A 

Total Basinwide Draft 

Allocation 

201.63 12.54 6,453.61 

a

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

by federal air regulations through 2020. 

ES‐7 December 29, 2010
Chesapeake Bay TMDL

ACCOUNTABILITY AND GOALS 

The Chesapeake Bay TMDL is unique because of the extensive measures EPA and the 

jurisdictions have adopted to ensure accountability for reducing pollution and meeting deadlines 

for progress. The TMDL will be implemented using an accountability framework that includes 

WIPs, two-year milestones, EPA’s tracking and assessment of restoration progress and, as 

necessary, specific federal contingency actions if the jurisdictions do not meet their 

commitments. This 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 (CWA) 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 point and 

nonpoint source loadings will be achieved and applicable 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, other voluntary programs and state-specific regulatory programs are used to achieve 

nonpoint source reductions. These federal tools are supplemented by a variety of state and local 

regulatory and voluntary programs and other commitments of the federal government set forth in 

the Executive Order strategy and identified in the accountability framework. 

Beginning in 2012, jurisdictions (including the federal government) are expected to follow 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 TMDL 

Tracking and Accountability System, determine if milestones are met. 

If a jurisdiction’s plans are inadequate or its progress is insufficient, EPA is committed to take 

the appropriate contingency 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 WIPs, 

which serve as roadmaps for how and when a jurisdiction plans to meet its pollutant allocations 

under the TMDL. In their Phase I WIPs, the jurisdictions were expected to subdivide the Bay 

TMDL allocations among pollutant sources; evaluate their current legal, regulatory, 

ES‐8 December 29, 2010
Chesapeake Bay TMDL

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. 

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

evaluation criteria in April 2010. To assist with WIP preparation, EPA provided considerable 

technical and financial assistance. EPA worked with the jurisdictions to evaluate various “what 

if” scenarios – combinations of practices and programs that could achieve their pollution 

allocations. 

The two most important criteria for a WIP is that it achieves the basin-jurisdiction pollution 

allocations and meets EPA’s expectations for providing reasonable assurance that reductions will 

be achieved and maintained, particularly for non-permitted sources like runoff from agricultural 

lands and currently unregulated stormwater from urban and suburban lands. 

After the draft Phase I WIP submittals in September 2010, a team of EPA sector experts 

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

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

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

draft WIPs could meet sediment allocations. The EPA evaluation also concluded that none of the 

seven draft Phase I 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. 

In response to its findings, EPA developed a draft TMDL that established allocations based on 

using the adequate portions of the jurisdictions’ draft WIP allocations along with varying degrees 

of federal backstop allocations in all seven jurisdictions. Backstop allocations focused on areas 

where EPA has the federal authority to control pollution allocations through NPDES permits, 

including wastewater treatment plants, stormwater permits, and animal feeding operations. 

Public Participation 

The draft Chesapeake Bay TMDL was developed through a highly transparent and engaging 

process during the past two years. The outreach effort included hundreds of meetings with 

interested groups; two rounds of public meetings, stakeholder sessions and media interviews in 

all six states and the District of Columbia in fall of 2009 and 2010; a dedicated EPA website; a 

series of monthly interactive webinars; notices published in the Federal Register; and a close 

working relationship with Chesapeake Bay Program committees representing citizens, local 

governments and the scientific community. 

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

comment period that concluded on November 8, 2010. During the comment period EPA 

conducted 18 public meetings in all six states and the District of Columbia. More than 2,500 

people participated in the public meetings. Seven of these meetings were also broadcast live 

online. During the six weeks that EPA officials traveled around the watershed, they also held 

dozens of meetings with stakeholders, including local governments, agriculture groups, 

homebuilder and developer associations, wastewater industry representatives and environmental 

ES‐9 December 29, 2010
Chesapeake Bay TMDL

organizations. EPA received more than 14,000 comments – most of which supported the TMDL 

– and the Agency’s response to those comments is included as an appendix to the TMDL. 

Final Watershed Implementation Plans and TMDL 

Since submittal of the draft WIPs and release of the draft TMDL in September 2010, EPA 

worked closely with each jurisdiction to revise and strengthen its plan. Because of this 

cooperative work and state leadership, the final WIPs were significantly improved. Examples of 

specific improvements include: 

 Committing to more stringent nitrogen and phosphorus limits at wastewater treatment 

plants, including on the James River in Virginia. (Virginia, New York, Delaware) 

 Pursuing state legislation to fund wastewater treatment plant upgrades, urban stormwater 

management and agricultural programs. (Maryland, Virginia, West Virginia) 

 Implementing a progressive stormwater permit to reduce pollution. (District of Columbia) 

 Dramatically increasing enforcement and compliance of state requirements for agriculture. 

(Pennsylvania) 

 Committing state funding to develop and implement state-of-the-art-technologies for 

converting animal manure to energy for farms. (Pennsylvania) 

 Considering implementation of mandatory programs for agriculture by 2013 if pollution 

reductions fall behind schedule. (Delaware, Maryland, Virginia) 

These improvements enabled EPA to reduce and remove most federal backstops, leaving a few 

targeted backstops and a plan for enhanced oversight and contingency actions to ensure progress. 

Backstop Allocations, Adjustments, and Actions 

Despite the significant improvement in the final WIPs, one of the jurisdictions did not meet all of 

its target allocations and two of the jurisdictions did not fully meet EPA’s expectations for 

reasonable assurance for specific pollution sectors. To address these few remaining issues, EPA 

included in the final TMDL several targeted backstop allocations, adjustments and actions. As a 

result of the jurisdictions’ significant improvements combined with EPA’s backstops, EPA 

believes the jurisdictions are in a position to implement their WIPs and achieve the needed 

pollution reductions. This approach endorses jurisdictions’ pollution reduction commitments, 

gives them the flexibility to do it their way first, and signals EPA’s commitment to fully use its 

authorities as necessary to reduce pollution. 

New York Wastewater – Backstop Allocation 

 EPA closed the numeric gap between New York’s WIP and its modified allocations by 

establishing a backstop that further reduces New York’s wasteload allocation for 

wastewater. EPA is establishing an aggregate wasteload allocation for wastewater 

treatment plants. 

 EPA calculated this backstop WLA using the nitrogen and phosphorus performance levels 

that New York committed to, but assumes that significant wastewater treatment plants 

(WWTPs) are at current flow rather than design flow. 

ES‐10 December 29, 2010
Chesapeake Bay TMDL

 EPA understands that New York plans to renew and/or modify WWTP permits upon 

completion of its Phase II WIP, consistent with the applicable TMDL allocations at that 

time. New York is reviewing engineering reports from WWTPs and, in its Phase II WIP, 

will provide information to support individual WLAs for these plants. 

Pennsylvania Urban Stormwater – Backstop Adjustment 

 EPA transferred 50 percent of the stormwater load that is not currently subject to NPDES 

permits from the load allocation to the wasteload allocation. The TMDL allocation 

adjustment increases reasonable assurance that pollution allocations from urban stormwater 

discharges will be achieved and maintained by signaling that EPA is prepared to designate 

any of these discharges as requiring NPDES permits. Urban areas would only be subject to 

NPDES permit conditions protective of water quality as issued by Pennsylvania upon 

designation. EPA will consider this step if Pennsylvania does not demonstrate progress 

toward reductions in urban loads identified in the WIP. EPA may also pursue designation 

activities based on considerations other than TMDL and WIP implementation. 

 EPA will maintain close oversight of general permits for the Pennsylvania stormwater 

sector (PAG-13 and PAG-2) and may object if permits are not protective of water quality 

standards and regulations. Upon review of Pennsylvania’s Phase II WIP, EPA will revisit 

the wasteload allocations for wastewater treatment plants, including more stringent 

phosphorus limits, in the event that Pennsylvania does not reissue PAG-13 and PAG-2 

general permits for Phase II MS4s and construction that are protective of water quality by 

achieving the load reductions called for in Pennsylvania’s Phase I WIP. 

West Virginia Agriculture – Backstop Adjustment 

 EPA shifted 75 percent of West Virginia’s animal feeding operation (AFO) load into the 

wasteload allocation and assumed full implementation of barnyard runoff control, waste 

management and mortality composting practices required under a CAFO permit on these 

AFOs. The shift signals that any of these operations could potentially be subject to state or 

federal permits as necessary to protect water quality. AFOs would only be subject to 

NPDES permit conditions as issued by West Virginia upon designation. EPA will consider 

this step if West Virginia does not achieve reductions in agricultural loads as identified in 

the WIP. EPA may also pursue designation activities based upon considerations other than 

TMDL and WIP implementation. 

 Based upon West Virginia's ability to demonstrate near-term progress implementing the 

agricultural section of its WIP, including CAFO Program authorization and permit 

applications and issuance, EPA will assess in the Phase II WIP whether additional federal 

actions, such as establishing more stringent wasteload allocations for wastewater treatment 

plants, are necessary to ensure that TMDL allocations are achieved. 

Enhanced Oversight and Contingencies 

While final WIPs were significantly improved and the jurisdictions deserve credit for the efforts, 

EPA also has minor concerns with the assurance that pollution reductions can be achieved in 

certain pollution sectors in Pennsylvania, Virginia and West Virginia. EPA has informed these 

jurisdictions that it will consider future backstops if specific near-term progress is not 

demonstrated in the Phase II WIP. 

ES‐11 December 29, 2010
Chesapeake Bay TMDL

Pennsylvania Agriculture 

 Based on Pennsylvania's ability to demonstrate near-term progress implementing the 

agricultural section of its WIP, including EPA approval for its CAFO program and 

enhanced compliance assurance with state regulatory programs, EPA will assess in the 

Phase II WIP whether additional federal actions, such as shifting AFO loads from the load 

allocation to the wasteload allocation or establishing more stringent wasteload allocations 

for WWTPs, are necessary to ensure that TMDL allocations are achieved. 

Pennsylvania Wastewater 

 EPA established individual wasteload allocations for wastewater treatment plants in the 

TMDL to ensure that sufficient detail is provided to inform individual permits for sources 

within the wasteload allocation. Individual allocations do not commit wastewater plants to 

greater reductions than what the state has proposed in its WIP. Provisions of the TMDL 

allow, under certain circumstances, for modifications of allocations within a basin to 

support offsets and trading opportunities. 

 EPA will assess Pennsylvania’s near-term urban stormwater and agriculture program 

progress and determine whether EPA should modify TMDL allocations to assume 

additional reductions from wastewater treatment plants. 

Virginia Urban Stormwater 

 If the statewide rule and/or the Phase II WIP do not provide additional assurance regarding 

how stormwater discharges outside of MS4 jurisdictions will achieve nitrogen, phosphorus, 

and sediment reductions proposed in the final Phase I WIP and assumed within the TMDL 

allocations, EPA may shift a greater portion of Virginia’s urban stormwater load from the 

load allocation to the wasteload allocation. This shift would signal that substantially more 

stormwater could potentially be subject to NPDES permits issued by the Commonwealth as 

necessary to protect water quality. 

West Virginia Urban Stormwater 

 If stormwater rules and/or the Phase II WIP do not provide additional assurance regarding 

how urban stormwater discharges outside of MS4 jurisdictions will achieve nitrogen, 

phosphorus, and sediment allocations proposed in the final Phase I WIP and assumed within 

the TMDL load allocations, EPA may shift a greater portion of West Virginia’s urban 

stormwater load from the load allocation to the wasteload allocation. The shift would signal 

that substantially more urban stormwater could potentially be subject to state permit coverage 

and/or federal Clean Water Act permit coverage as necessary to protect water quality. 

West Virginia Wastewater 

 EPA established individual wasteload allocations for significant wastewater treatment 

plants in the TMDL to ensure that sufficient detail is provided to inform individual permits 

for sources within the wastewater wasteload allocation. Individual allocations do not 

commit wastewater plants to greater reductions than what the state has proposed in its WIP. 

Provisions of this TMDL allow, under certain circumstances, for modifications of 

allocations within a basin to support offsets and trading opportunities. 

ES‐12 December 29, 2010
Chesapeake Bay TMDL

 EPA will assess West Virginia’s near-term agriculture program progress and determine 

whether additional federal actions consistent with EPA’s December 29, 2009 letter, such as 

modifying TMDL allocations to assume additional reductions from wastewater treatment 

plants, are necessary to ensure that TMDL allocations are achieved. 

Ongoing oversight of Chesapeake Bay jurisdictions 

EPA will carefully review programs and permits in all jurisdictions. EPA’s goal is for 

jurisdictions to successfully implement their WIPs, but EPA is prepared to take necessary actions 

in all jurisdictions for insufficient WIP implementation or pollution reductions. Federal actions 

can be taken at any time, although EPA will engage particularly during two-year milestones and 

refining the TMDL in 2012 and 2017. Actions include: 

 Expanding coverage of NPDES permits to sources that are currently unregulated 

 Increasing oversight of state-issued NPDES permits 

 Requiring additional pollution reductions from federally regulated sources 

 Increasing federal enforcement and compliance 

 Prohibiting new or expanded pollution discharges 

 Conditioning or redirecting EPA grants 

 Revising water quality standards to better protect local and downstream waters 

 Discounting nutrient and sediment reduction progress if jurisdiction cannot verify proper 

installation and management of controls 

FINAL TMDL 

As a result of the significantly improved WIPs and the removal and reduction of federal 

backstops, the final TMDL is shaped in large part by the jurisdictions’ plans to reduce pollution. 

Jurisdiction-based solutions for reducing pollution was a long-standing priority for EPA and why 

the agency always provided the jurisdictions with flexibility to determine how to reduce 

pollution in the most efficient, cost-effective and acceptable manner. 

Now, the focus shifts to jurisdictions’ implementation of the WIP policies and programs 

designed to reduce pollution on-the-ground and in-the-water. EPA will conduct oversight of WIP 

implementation and jurisdictions’ progress toward meeting two-year milestones. If progress is 

insufficient, EPA will utilize contingencies to place additional controls on federally permitted 

sources of pollution, such as wastewater treatment plants, large animal agriculture operations and 

municipal stormwater systems, as well as target compliance and enforcement activities. 

Federal agencies will greatly contribute to restoration of the Chesapeake Bay watershed, 

particularly through implementation of the new federal strategy created under President Obama’s 

Executive Order. Eleven federal agencies have committed to a comprehensive suite of actions 

and pursuit of critical environmental goals on the same 2025 timeline as the TMDL. 

Additionally, federal agencies will be establishing and meeting two-year milestones, with the 

specific charge of taking actions that directly support the jurisdictions in reducing pollution and 

restoring water quality. 

ES‐13 December 29, 2010
Chesapeake Bay TMDL

ES‐14 December 29, 2010

The jurisdictions are expected to submit Phase II WIPs that provide local area pollution targets 

for implementation on a smaller scale; the timeframe for these Phase II WIPs will be determined 

in early 2011. 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. 
Chesapeake Bay TMDL

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 .............................................. 1-8 

1.2.3 President’s Chesapeake Bay Executive Order .............................................................................1-10 

1.3 Bay TMDL Process, Partner Coordination and Responsibilities......................................1-11 

1.3.1 CBP Partnership and Organizational Structure............................................................................1-11 

1.4 Legal Framework for the Chesapeake Bay TMDL ............................................................1-15 

1.4.1 What is a TMDL? ........................................................................................................................1-15 

1.4.2 Why is EPA establishing this TMDL?.........................................................................................1-16 

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

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

2.2 Chesapeake Bay TMDL Scope ...............................................................................................2-6

2.2.1 Pollutants of Concern.................................................................................................................... 2-7 

2.2.2 Chesapeake Bay Program Segmentation Scheme ......................................................................... 2-7 

2.2.3 Jurisdictions’ 2008 303(d) Listings..............................................................................................2-14 

2.2.4 2008 303(d) Listing Segments Compared to Consent Decree and MOU Segments....................2-15 

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

3.1 Chesapeake Bay Water Quality Criteria and Designated Uses...........................................3-2 

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 ..........................................................................3-11 

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

3.2.1 Delaware ......................................................................................................................................3-15 

3.2.2 District of Columbia.....................................................................................................................3-15 

3.2.3 Maryland......................................................................................................................................3-16 

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

3.3 Assessing Attainment of Chesapeake Bay Water Quality Standards...............................3-18 

3.3.1 Defining Total Exceedances ........................................................................................................3-18 

3.3.2 Defining Allowable Exceedances ................................................................................................3-20 

3.3.3 Assessing Criteria Attainment......................................................................................................3-22 

SECTION 4. Sources of nitrogen, phosphorus and Sediment to the Chesapeake Bay.......... 4-1 

4.1 Jurisdiction Loading Contributions.......................................................................................4-1 

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

4.3 Pollutant Source Sector Contributions..................................................................................4-5 

4.4 Regulated Point Sources..........................................................................................................4-6 

4.4.1 Significant and Nonsignificant Municipal and Industrial Facilities.............................................. 4-7 

4.4.2 Basinwide NPDES Permitting Approach...................................................................................... 4-8 

4.5 Regulated Point Source Load Summaries.............................................................................4-9 

i December 29, 2010
Chesapeake Bay TMDL

4.5.1 Municipal Wastewater Discharging Facilities .............................................................................. 4-9 

4.5.2 Industrial Discharge Facilities......................................................................................................4-13 

4.5.3 Combined Sewer Overflows ........................................................................................................4-17 

4.5.4 Sanitary Sewer Overflows ...........................................................................................................4-21 

4.5.5 NPDES Permitted Stormwater.....................................................................................................4-22 

4.5.6 Concentrated Animal Feeding Operations ...................................................................................4-25 

4.6 Nonpoint Sources...................................................................................................................4-28 

4.6.1 Agriculture ...................................................................................................................................4-29 

4.6.2 Atmospheric Deposition ..............................................................................................................4-33 

4.6.3 Forest Lands.................................................................................................................................4-36 

4.6.4 On-site Wastewater Treatment Systems ......................................................................................4-37 

4.6.5 Nonregulated Stormwater Runoff................................................................................................4-38 

4.6.6 Oceanic Inputs .............................................................................................................................4-39 

4.6.7 Streambank and Tidal Shoreline Erosion.....................................................................................4-41 

4.6.8 Tidal Resuspension ......................................................................................................................4-42 

4.6.9 Wildlife ........................................................................................................................................4-43 

4.6.10 Natural Background .....................................................................................................................4-44 

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

5.2.2 Partnership’s Watershed Monitoring Network.............................................................................5-12 

5.2.3 Data Quality and Access ..............................................................................................................5-14 

5.2.4 Data Submission and Quality Assurance .....................................................................................5-16 

5.2.5 Monitoring Applications in Chesapeake Bay TMDL Development............................................5-18 

5.3 Modeling Framework Overview ..........................................................................................5-18 

5.4 Chesapeake Bay Airshed Model...........................................................................................5-21

5.5 Chesapeake Bay Land Change Model .................................................................................5-24 

5.5.1 Motivations for Developing Future Land Use Estimates .............................................................5-24 

5.5.2 Scale of Chesapeake Bay Land Change Model Future Land Use Estimates ...............................5-24 

5.5.3 Components of Chesapeake Bay Land Change Model Future Land Use Estimates ....................5-26 

5.6 Chesapeake Bay SPARROW Model....................................................................................5-27 

5.7 Chesapeake Bay Scenario Builder .......................................................................................5-28 

5.8 Phase 5.3 Chesapeake Bay Watershed Model.....................................................................5-30 

5.8.1 Bay Watershed Model Segmentation...........................................................................................5-30 

5.8.2 Bay Watershed Model Setup........................................................................................................5-32 

5.8.3 Pollutant Source Representation ..................................................................................................5-37 

5.8.4 Calibration....................................................................................................................................5-38 

5.9 Chesapeake Bay Water Quality and Sediment Transport Model.....................................5-38 

5.9.1 Nonpoint Source Loads................................................................................................................5-41 

5.9.2 Point Source Loads ......................................................................................................................5-41 

5.9.3 Atmospheric Loads ......................................................................................................................5-41 

5.9.4 Bank Loads ..................................................................................................................................5-42 

5.9.5 Wetlands ......................................................................................................................................5-42 

5.9.6 Model Setup.................................................................................................................................5-42 

5.10 Chesapeake Bay Criteria Assessment Program..................................................................5-43 

5.11 Climate Change Simulation..................................................................................................5-43 

ii December 29, 2010
Chesapeake Bay TMDL

SECTION 6. Establishing the Allocations for the Basin-Jurisdictions.................................. 6-1 

6.1 Establishing the Overall Model Parameters .........................................................................6-2 

6.1.1 Hydrologic Period......................................................................................................................... 6-2 

6.1.2 Seasonal Variation ........................................................................................................................ 6-3 

6.1.3 Daily Loads................................................................................................................................... 6-5 

6.2 Establishing the Nitrogen and Phosphorus Related Model Parameters.............................6-8 

6.2.1 Critical Conditions ........................................................................................................................ 6-8 

6.2.2 Assessment Procedures for DO and Chlorophyll a Standards ...................................................... 6-9 

6.2.3 Addressing Reduced Sensitivity to Load Reductions at Low Nonattainment Percentages..........6-10 

6.2.4 Margin of Safety ..........................................................................................................................6-13 

6.3 Methodology for Establishing the Basin-Jurisdiction Allocations for Nitrogen and 

Phosphorus.............................................................................................................................6-16 

6.3.1 Accounting for Relative Effectiveness of the Major River Basins on Tidal Water Quality.........6-17 

6.3.2 Determining Controllable Load ...................................................................................................6-20 

6.3.3 Relating Relative Impact to Needed Controls (Allocations)........................................................6-24 

6.4 Establishing the Basin-Jurisdiction Allocations for Nitrogen and Phosphorus...............6-25 

6.4.1 Setting the Atmospheric Nitrogen Deposition Allocation............................................................6-26 

6.4.2 Determining the Basinwide Nitrogen and Phosphorus Target Load Based on Dissolved 

Oxygen.........................................................................................................................................6-28 

6.4.3 Allocating Nitrogen and Phosphorus Loads to Jurisdictions within the Bay Watershed .............6-30 

6.4.4 Resolving Dissolved Oxygen and Chlorophyll a Nonattaining Bay Segments............................6-32 

6.4.5 Allocation Considerations for the Headwater Jurisdictions (New York and West Virginia).......6-38 

6.4.6 Nitrogen-to-Phosphorus Exchanges.............................................................................................6-39 

6.5 Establishing the Sediment-Related Model Parameters......................................................6-41 

6.5.1 Critical Conditions for Water Clarity and SAV ...........................................................................6-41 

6.5.2 Assessment Procedures for the Clarity and SAV Standards ........................................................6-42 

6.5.3 Addressing Reduced Sensitivity to Load Reductions at Low Nonattainment Percentages..........6-43 

6.5.4 Explicit Margin of Safety for Sediment .......................................................................................6-44 

6.6 Establishing the Basin-Jurisdiction Allocations for Sediment ..........................................6-44 

6.6.1 Methodology for Determining Sediment Allocations ..................................................................6-45 

6.6.2 Addressing Water Clarity/SAV Nonattaining Segments .............................................................6-45 

6.7 Basin-Jurisdiction Allocations to Achieve the Bay WQS...................................................6-48 

6.7.1 Basin-Jurisdiction Allocations Tables..........................................................................................6-48 

6.7.2 Correction of the West Virginia Sediment Allocation .................................................................6-48 

6.8 Attainment of the District of Columbia pH Water Quality Standard ..............................6-49 

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

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

7.1.1 Overview of the Accountability Framework................................................................................. 7-2 

7.1.2 Federal Strategy ............................................................................................................................ 7-3 

7.1.3 Funding ......................................................................................................................................... 7-4 

7.1.4 Air Emission Reductions. ............................................................................................................. 7-4 

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

7.2.1 Watershed Implementation Plans.................................................................................................. 7-6 

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

7.2.3 Chesapeake Bay TMDL Tracking and Accountability System ...................................................7-10 

7.2.4 Federal EPA Actions....................................................................................................................7-11 

iii December 29, 2010
Chesapeake Bay TMDL

SECTION 8. Watershed Implementation Plan Evaluation and Resultant Allocations ......... 8-1 

8.1 WIP Evaluation Methodology ................................................................................................8-3 

8.1.1 Quantitative Evaluation of the Final Phase I WIPs....................................................................... 8-3 

8.1.2 Qualitative Evaluation of the Final Phase I WIPs......................................................................... 8-4 

8.2 WIP Evaluation Results ..........................................................................................................8-5 

8.2.1 Target Allocation Attainment ....................................................................................................... 8-5 

8.2.2 Reasonable Assurance................................................................................................................... 8-9 

8.3 Allocation Methodology ..........................................................................................................8-9 

8.3.1 Backstop Allocation Methodology ..............................................................................................8-10 

8.3.2 Backstop Adjustment (Allocation Shift) Methodology................................................................8-10 

8.3.3 Assumptions Supporting the Allocations.....................................................................................8-12 

8.4 Allocations by Jurisdiction ...................................................................................................8-17 

8.4.1 Delaware ......................................................................................................................................8-17 

8.4.2 District of Columbia.....................................................................................................................8-19 

8.4.3 Maryland......................................................................................................................................8-20 

8.4.4 New York.....................................................................................................................................8-22 

8.4.5 Pennsylvania ................................................................................................................................8-24 

8.4.6 Virginia ........................................................................................................................................8-27 

8.4.7 West Virginia...............................................................................................................................8-30 

8.5 Allocation Summary Chart...................................................................................................8-33 

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

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

SECTION 10. 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 Jurisdictions’ Offset Programs ............................................................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 Sediment 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 Website.................................................................................................11-5 

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

iv December 29, 2010
Chesapeake Bay TMDL

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

11.4 Interaction with States, D.C. on Watershed Implementation Plans .................................11-6 

SECTION 12. References ......................................................................................................... 12-1 

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 

v December 29, 2010
Chesapeake Bay TMDL

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 Sediment behind the Susquehanna Dams Technical Documentation 

Appendix U Accounting for the Benefits of Filter Feeder Restoration Technical 

Documentation 

Appendix V Best Management Practice (BMP) Implementation Rates for Final Scenarios 

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

Chesapeake Bay TMDL 

Appendix X Staged Implementation Approach for Wastewater Treatment Facilities in the 

Virginia James River Basin 

vi December 29, 2010
Chesapeake Bay TMDL

Tables 

Table ES-1. Chesapeake Bay TMDL watershed nitrogen, phosphorus and sediment final 

allocations by jurisdiction and by major river basin..............................................ES-7 

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

tributary strategies.................................................................................................... 1-7 

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 ............... 1-9 

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

and/or nutrients addressed by the Chesapeake Bay TMDL................................... 1-18 

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

by the Chesapeake Bay TMDL.............................................................................. 1-19 

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................................................................................................................. 2-15 

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..................................................................... 3-10 

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 acreage goals and application depths.............. 3-12 

Table 3-7. Links for accessing the current waters quality standards (WQS) regulations 

for Delaware, the District of Columbia, Maryland, and Virginia.......................... 3-15 

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..................................................................................................................... 3-17 

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

probabilities............................................................................................................ 3-19 

Table 4-1. Percentage of total nitrogen delivered to the Bay from each jurisdiction by 

pollutant source sector ............................................................................................. 4-5 

Table 4-2. Percentage of total phosphorus delivered to the Bay from each jurisdiction 

by pollutant source sector ........................................................................................ 4-5 

Table 4-3. Percentage of sediment delivered to the Bay from each jurisdiction by 

pollutant source sector ............................................................................................. 4-6 

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

wastewater discharge facilities ................................................................................ 4-7 

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

discharging facilities by jurisdiction as of December 2010..................................... 4-8 

Table 4-6. Nitrogen and phosphorus permit tracking summary under the Basinwide 

NPDES Wastewater Permitting Approach, through December 2010 ..................... 4-9 

Table 4-7. Municipal wastewater facilities by jurisdiction ..................................................... 4-10 

vii December 29, 2010
Chesapeake Bay TMDL

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

to Chesapeake Bay................................................................................................. 4-10 

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

delivered to Chesapeake Bay................................................................................. 4-10 

Table 4-10. Industrial wastewater facilities .............................................................................. 4-14 

Table 4-11. 2009 Load estimates of industrial facility discharges............................................ 4-14 

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

wastewater facility discharges by major river basin.............................................. 4-14 

Table 4-13. Combined sewer system communities in the Bay watershed ................................ 4-18 

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

watershed, summer 2009 ....................................................................................... 4-25 

Table 4-15. Federal numeric thresholds for small, medium, and large CAFOs........................ 4-26 

Table 4-16. Estimated number of state or federal permitted CAFOs........................................ 4-28 

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....................................................................................... 4-36 

Table 4-18. Chesapeake Bay Water Quality and Sediment Transport Model -simulated 

SAV acres under a range of sediment scoping scenarios compared with the 

2010 Tributary Strategy scenario........................................................................... 4-44 

Table 5-1. Modeling tools supporting development of the Chesapeake Bay TMDL ............. 5-20 

Table 5-2. Phase 5.3 Chesapeake Bay Watershed Model land uses ....................................... 5-33 

Table 6-1. ADM for calculating daily maximum loads ............................................................ 6-7 

Table 6-2. Different approaches available under the explicit and implicit MOS types .......... 6-14 

Table 6-3. 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 .............................................. 6-19 

Table 6-4. Pollutant sources as defined for the No Action and E3 model scenarios .............. 6-23 

Table 6-5. Chesapeake Bay designated use segments showing percent nonattainment of 

the applicable Bay DO WQS under the basinwide nitrogen and phosphorus 

target loadings (million pounds per year) .............................................................. 6-33 

Table 6-6. Tributary strategy scenario and nitrogen and phosphorus-based allocation 

scenario’s total suspended solids loads (millions of pounds) by watershed 

jurisdiction ............................................................................................................. 6-43 

Table 6-7. Chesapeake Bay watershed nitrogen and phosphorus and sediment 

allocations by major river basin by jurisdiction to achieve the Chesapeake 

Bay WQS ............................................................................................................... 6-50 

Table 6-8. Chesapeake Bay watershed nitrogen and phosphorus and sediment 

allocations by jurisdiction by major river basin to achieve the Chesapeake 

Bay WQS ............................................................................................................... 6-51 

Table 7-1. Eight elements of the jurisdictions’ Watershed Implementation Plans ................... 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. Comparison between nitrogen, phosphorus, and sediment jurisdiction-wide 

allocations and final Phase I Watershed Implementation Plans, in millions of 

pounds per year........................................................................................................ 8-6 

viii December 29, 2010
Chesapeake Bay TMDL

Table 8-2. Comparison between the nitrogen, phosphorus, and sediment basinjurisdiction allocations and final Phase I Watershed Implementation Plans, in 

million pounds per year ........................................................................................... 8-7 

Table 8-3. Percent reductions in edge-of-stream loads to achieve urban stormwater 

WLAs..................................................................................................................... 8-14 

Table 8-4. EPA backstop allocations, adjustments, and actions based on assessment of 

final Phase I WIPs.................................................................................................. 8-16 

Table 8-5. Chesapeake Bay watershed nitrogen, phosphorus, and sediment allocations 

by jurisdiction and by major river basin, in millions of pounds per year .............. 8-33 

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

year) by Chesapeake Bay segment to attain Chesapeake Bay WQS ....................... 9-2 

Table 9-2. Chesapeake Bay TMDL total phosphorus (TP) annual allocations (pounds 

per year) by Chesapeake Bay segment to attain for the proposed amended 

Chesapeake Bay WQS ............................................................................................. 9-7 

Table 9-3. Chesapeake Bay TMDL sediment (TSS) annual allocations (pounds per 

year) by Chesapeake Bay segment to attain Chesapeake Bay WQS ..................... 9-12 

Table 9-4. Edge of Stream (EOS) WLAs (Annual) for the 478 significant permitted 

dischargers to meet TMDLs to attain the Chesapeake Bay WQS ......................... 9-17 

ix December 29, 2010
Chesapeake Bay TMDL

Figures 

Figure ES-1. A nitrogen, phosphorus and sediment TMDL has been developed for each 

of the 92 Chesapeake Bay segment watersheds.....................................................ES-4 

Figure ES-2. Sub-basins across the Chesapeake Bay watershed with the highest (red) to 

lowest (blue) pound for pound nitrogen pollutant loading effect on 

Chesapeake Bay water quality...............................................................................ES-6 

Figure 1-1. CBP’s organizational structure. ............................................................................. 1-12 

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

Figure 2-2. Hydrogeomorphic regions of the Chesapeake Bay watershed. ............................... 2-3 

Figure 2-3. Chesapeake Bay watershed land cover.................................................................... 2-5 

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

watershed 1950–2030. ............................................................................................. 2-6 

Figure 2-5. The 92 Chesapeake Bay segments........................................................................... 2-8 

Figure 2-6. The 92 Chesapeake Bay segment watersheds.......................................................... 2-9 

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

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

Figure 3-2. Dissolved oxygen concentrations (mg/L) required by different Chesapeake 

Bay species and biological communities. ................................................................ 3-9 

Figure 3-3. Example cumulative frequency distribution (CFD) curve..................................... 3-19 

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............................................................................................... 3-21 

Figure 3-5. Example reference and assessment curves showing allowable and nonallowable exceedances........................................................................................... 3-21 

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

(b) criteria............................................................................................................... 3-24 

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. ................................................................................................. 4-2 

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

major tributary in 2009. ........................................................................................... 4-3 

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

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

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

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

Figure 4-7. Significant wastewater treatment facilities in the Chesapeake Bay watershed. .... 4-11 

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

Bay watershed........................................................................................................ 4-12 

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

watershed. .............................................................................................................. 4-15 

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

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

Figure 4-11. CSO communities in the Chesapeake Bay watershed. .......................................... 4-20 

x December 29, 2010
Chesapeake Bay TMDL

Figure 4-12. Phase I and II MS4s in the Chesapeake Bay watershed. ....................................... 4-24 

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

agricultural lands across the Chesapeake Bay watershed...................................... 4-30 

Figure 4-14. 2007 Chesapeake Bay watershed poultry populations by jurisdiction. ................. 4-31 

Figure 4-15. 2007 Chesapeake Bay watershed livestock populations by jurisdiction. .............. 4-32 

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)................................................................................................................... 4-34

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

the Phase 5 Model domain from 1984 to 2005...................................................... 4-35 

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

and adjacent coastal ocean..................................................................................... 4-40 

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

construction) or bank sources banks and ditch beds)............................................. 4-41 

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

components of shoreline erosions, fastland and nearshore erosion. ...................... 4-42 

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). ............................................................................................... 4-43 

Figure 5-1. Tidal Chesapeake Bay water quality monitoring network stations. ........................ 5-4 

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

for Maryland. ........................................................................................................... 5-7 

Figure 5-3. 2003-2008 Chesapeake Bay stratified random benthic sampling sites used to 

estimate habitat impairment through benthic community condition 

assessment................................................................................................................ 5-8 

Figure 5-4. Flightlines for the annual Chesapeake Bay SAV Aerial Survey. ............................ 5-9 

Figure 5-5. Illustration of mapped SAV beds, individual bed coding, bed density 

estimates, and species identification (from ground surveys)................................. 5-10 

Figure 5-6. Chesapeake Bay watershed monitoring network................................................... 5-13 

Figure 5-7. Chesapeake Bay tidal and watershed water quality monitoring networks’ 

participants arrayed by their role in sample collection, laboratory analysis, 

and/or data reporting.............................................................................................. 5-17 

Figure 5-8. Chesapeake Bay TMDL modeling framework...................................................... 5-19 

Figure 5-9. Atmospheric deposition monitoring stations used in the Chesapeake Bay 

airshed nitrogen wet deposition regression model................................................. 5-22 

Figure 5-10. The Community Multiscale Air Quality Model’s 12 km grid over the Phase 

5.3 Chesapeake Bay Watershed Model county segmentation. .............................. 5-23 

Figure 5-11. 2006 Land cover conditions in the Chesapeake Bay watershed and 

intersecting counties............................................................................................... 5-25 

Figure 5-12. An example of the Chesapeake Bay SPARROW Model output showing 

delivered yields of total nitrogen in the Chesapeake Bay watershed..................... 5-28 

Figure 5-13. Scenario Builder conceptual process. ................................................................... 5-29 

Figure 5-14. Segmentation and reach simulation of the Phase 5.3 Chesapeake Bay 

Watershed Model................................................................................................... 5-31 

xi December 29, 2010
Chesapeake Bay TMDL

Figure 5-15. Phase 5.3 Chesapeake Bay Watershed Model hydrology (upper panel) and 

water quality (lower panel) monitoring calibration stations overlaid on the 

Phase 5.3 Bay Watershed Model’s river segments................................................ 5-39 

Figure 5-16. The detailed 57,000 cell grid of the Chesapeake Bay Water Quality and 

Sediment Transport Model. ................................................................................... 5-40 

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

exceedance. ............................................................................................................ 6-11 

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

and phosphorus load reduction model scenarios. .................................................. 6-12 

Figure 6-3. Example of a James River segment’s spring chlorophyll a WQS 

nonattainment results from a wide range of TN loading Chesapeake Bay 

Water Quality Model scenarios. ............................................................................ 6-13 

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

rivers basins, above and below the fall line, in descending order.......................... 6-20 

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

Chesapeake Bay watershed for nitrogen................................................................ 6-21 

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

Chesapeake Bay watershed for phosphorus........................................................... 6-22 

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.............................................................................. 6-25 

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). ................................................................................. 6-27 

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

various TN and TP loading scenarios. ................................................................... 6-29 

Figure 6-10. Example allocation methodology application for phosphorus............................... 6-31 

Figure 6-11. Example allocation methodology application for nitrogen.................................... 6-31 

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

summer seasonal mean chlorophyll a water quality criteria.................................. 6-36 

Figure 6-13. Tidal James River monitoring data for chlorophyll a at station TF5.5 (in the 

upper tidal James River near Hopewell, Virginia) compared to Virginia’s 

James River segment-season specific chlorophyll a criteria.................................. 6-37 

Figure 6-14. James River nonattainment of the chlorophyll a WQS at various load 

scenarios................................................................................................................. 6-38 

Figure 6-15. TN:TP exchanges based on anoxic volume days and varying TP loads................ 6-40 

Figure 6-16. TN: TP exchanges based on chlorophyll a concentrations and varying TP 

loads. ...................................................................................................................... 6-40 

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

assessment.............................................................................................................. 6-46 

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

sediment allocations (billions of pounds per year as total suspended 

sediment)................................................................................................................ 6-49 

Figure 6-19. District of Columbia’s Roosevelt Island station pH versus chlorophyll a 

monitoring data regression..................................................................................... 6-52 

Figure 7-1. Relationship between WIPs and 2-year milestones................................................. 7-9 

xii December 29, 2010
Chesapeake Bay TMDL

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 scientific research, monitoring, assessment, and model 

application, and years of focused dialogue and analysis among EPA, our six watershed state 

partners and the District of Columbia, and numerous stakeholders. This document has benefited 

from the input of thousands of professionals and citizens 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 Chesapeake 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 impaired – i.e., not attaining state adopted and EPA approved water quality standards. 

Most of the waters of the Chesapeake Bay and its tidal tributaries and embayments are on the 

three states’ (Maryland, Virginia, and Delaware) and the District’s lists of impaired waters 

because of excess nitrogen, phosphorus, and sediment pollution. The Chesapeake Bay TMDL 

identifies the loadings of nitrogen, phosphorus, and sediment that are necessary to achieve the 

applicable jurisdiction’s water quality standards for the Bay and its tidal tributaries and 

embayments for dissolved oxygen, chlorophyll a (an indicator 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 defining the pollutant loadings 

necessary to attain water quality standards and restore the aquatic life resources of the 

Chesapeake Bay. 

The Chesapeake Bay receives waters from thousands of streams and rivers within seven 

jurisdictions in the mid-Atlantic region of the United States: Delaware, the District of Columbia, 

Maryland, New York, Pennsylvania, Virginia, and West Virginia. These waters drain to the 

Chesapeake Bay and, therefore, contribute pollutant loadings to the Bay. The Chesapeake Bay 

TMDL also establishes total maximum daily loads from these watersheds and jurisdictions for 

each of the 92 impaired segments that comprise the waters of the Chesapeake Bay and its tidal 

tributaries and embayments. Thus, the Chesapeake Bay TMDL is actually an assemblage of 276 

TMDLs: individual TMDLs for each of the 3 pollutants— nitrogen, phosphorus, and sediment—

for each of the 92 segments (3 x 92 = 276). 

The purpose of the Chesapeake Bay TMDL is to identify the pollutant loading reductions needed 

to meet the applicable Bay water quality standards. The TMDL, thus, allocates loads to all

pollutant source sectors in all parts of the Bay’s 64,000 square mile watershed. Because of the 

watershed-wide nature of these loading reductions, the water quality benefits from these 

reductions will not be limited to the Bay and its tidal tributaries and embayments. In fact, the 

watershed’s headwaters from the location the pollutant reductions are made to the point they 

enter the Bay or its tidal tributaries should benefit from some measure of improved water quality. 

The controls necessary to reduce nitrogen, phosphorus, and sediment also are likely to reduce 

other pollutants like bacteria and chemical contaminants. 

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 essentially an 

xiii December 29, 2010
Chesapeake Bay TMDL

information and planning tool that does not, by itself, implement the needed controls. 

Implementation mechanisms available under other provisions of the Clean Water Act, Clean Air 

Act, state laws, and federal and state regulations, and local ordinances, as well as appropriate 

levels of funding, are needed to achieve these loading targets. The Bay TMDL will be 

implemented using an accountability framework that includes the seven jurisdictions’ Watershed 

Implementation Plans (WIPs), two-year milestones, EPA’s tracking and assessment of 

restoration progress and, as necessary, specific federal actions if the Bay watershed jurisdictions 

do not meet their targets and commitments. Although not itself an element of the Chesapeake 

Bay TMDL, the accountability framework is being established pursuant to both section 117(g)(1) 

of the Clean Water Act and Executive Order 13508, in part, to demonstrate reasonable assurance 

that the Chesapeake Bay TMDL allocations for nitrogen, phosphorus, and sediment and the 

jurisdictions’ water quality standards 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 references contained in the main document 

and numerous appendices. 

Shawn M. Garvin, Regional Administrator 

U.S. Environmental Protection Agency Region 3 

Judith A. Enck, Regional Administrator 

U.S. Environmental Protection Agency Region 2

xiv December 29, 2010
Chesapeake Bay TMDL

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, the 

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

principally through the Chesapeake Bay Program’s (CBP) 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/webinars, the monthly webinars scheduled during 2010, and the 

September—November 2010 public comment period 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, feedback, and formal comments 

of thousands of individuals from the multitude of CBP partnering agencies and institutions, local 

governments, nongovernmental organizations, businesses, many other involved stakeholders, and 

the general public. Their individual and collective contributions are hereby acknowledged. 

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 and Suburban Stormwater 

Workgroup, Wastewater Treatment Workgroup, Watershed Technical Workgroup, TMDL 

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

Scientific and Technical Analysis and Reporting Team, Criteria Assessment Procedures 

Workgroup, Modeling Workgroup, Nontidal Water Quality Workgroup, Tidal Monitoring and 

Analysis Workgroup, Analytical Methods and Quality Assurance Workgroup, and former 

Monitoring and Analysis Subcommittee. Appendix A provides a detailed member listing of these 

committees, teams, and workgroups who were instrumental in completing the Chesapeake Bay 

total maximum daily load (TMDL). 

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

their contributions to the development of the Bay TMDL, support of the development of the 

jurisdictions’ Phase I Watershed Implementation Plans (WIPs), evaluation of the draft and final 

Phase I WIPs, supporting public and stakeholder outreach, responding to thousands of public 

comments, and publication of this document: Greg Allen, EPA Region 3 CBP Office; Katherine 

Antos, EPA Region 3 CBP Office; Cheryl Atkinson, EPA Region 3 Water Protection Division 

(WPD); Seth Ausubel, EPA Region 2 Division of Environmental Planning and Protection; 

Michael Barnes, Chesapeake Research Consortium/CBP Office; Greg Barranco, EPA Region 3 

CBP Office; Richard Batiuk, EPA Region 3 CBP Office; Benita Best-Wong, EPA Office of 

Water; Carin Bisland, EPA Region 3 CBP Office; Ross Brennan, EPA Office of Water; Kevin 

Bricke, EPA Region 2 Division of Environmental Planning and Protection; Chris Brosch, 

University of Maryland/CBP Office; Brian Burch, EPA Region 3 CBP Office; Jon Capacasa, 

EPA Region 3 WPD; Ann Carkhuff, EPA Region 3 WPD; Peter Claggett, U.S. Geological 

xv December 29, 2010
Chesapeake Bay TMDL

Survey (USGS)/CBP Office; Jeff Corbin, EPA Region 3 Office of the Regional Administrator; 

James Curtin, EPA Office of General Counsel; Thomas Damm, EPA Region 3 WPD; 

Christopher Day, EPA Region 3 Office of Regional Counsel; Kevin DeBell, EPA Region 3 CBP 

Office; Robin Dennis, NOAA/EPA Office of Research and Development; Helene Drago, EPA 

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

CBP Office; Judith Enck, EPA Region 2 Regional Administrator; Leo Essenthier, EPA Region 3 

WPD; Barbara Finazzo, EPA Region 2 Division of Environmental Planning and Protection; 

Katie Foreman, University of Maryland/CBP Office; Kristin Foringer, Chesapeake Research 

Consortium/CBP Office; Debra Forman, EPA Region 3 WPD; J. Charles Fox, EPA Office of the 

Administrator; Michael Fritz, EPA Region 3 CBP Office; Elizabeth Gaige, EPA Region 3 WPD; 

Angie Garcia, EPA Region 3 WPD; Shawn Garvin, EPA Region 3 Regional Administrator; 

Kelly Gable, EPA Region 3 Office of Regional Counsel; Patricia Gleason, EPA Region 3 WPD; 

Peter Gold, EPA Region 3 WPD; Aaron Gorka, Chesapeake Research Consortium/CBP Office; 

Michelle Gugger, EPA Region 3 WPD; Michael Haire, EPA Office of Water; Denise Hakowski, 

EPA Region 3 WPD; Suzanne Hall-Trevena, EPA Region 3 WPD; James Hanlon, EPA Office of 

Water; Rachel Herbert, EPA Office of Water; Sara Hilbrich, EPA Office of Water; Amie Howe, 

EPA Region 3 Office of State and Congressional Relations; Nan Ides, EPA Region 3 WPD; Fred 

Irani, USGS/CBP Office; Ruth Izraeli, EPA Region 2 Division of Environmental Planning and 

Protection; Jackie Johnson, Interstate Commission on the Potomac River Basin/CBP Office; Jeni 

Keisman, University of Maryland/CBP Office; Victoria Kilbert, Chesapeake Research 

Consortium/CBP Office; Robert Koroncai, EPA Region 3 WPD; Caitlin Kovelove, EPA Office 

of Water; Amelia Letnes, EPA Office of Water; Mary Letzkus, EPA Region 3 WPD; 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; Michael Mallonee, Interstate 

Commission on the Potomac River Basin/CBP Office; Lori Mackey, EPA Region 3 CBP Office; 

David McGuigan, EPA Region 3 WPD; Evelyn MacKnight, EPA Region 3 WPD; Mike Mason, 

EPA Office of Water; Larry Merrill, EPA Region 3 WPD; Linda Miller, EPA Region 3 Office of 

State and Congressional Relations; Jenny Molloy, EPA Region 3 CBP Office/WPD; Francis 

Mulhern EPA Region 3 WPD; Elizabeth Ottinger, EPA Region 3 WPD; Andrew Parker, Tetra 

Tech; Reggie Parrish, EPA Region 3 CBP Office; Jeffrey Potent, EPA Office of Water; Lucinda 

Power, EPA Region 3 CBP Office; Andrew Prugar, EPA Office of Environmental Information; 

Teresa Rafi, Tetra Tech; Pravin Rana, EPA Office of Water; Sucharith Ravi, University of 

Maryland/CBP Office; Bill Richardson, EPA Region 3 WPD; Robert Rose, EPA Office of 

Water; Jennifer Sincock, EPA Region 3 WPD; Mike Shapiro, EPA Office of Water; Gary Shenk, 

EPA Region 3 CBP Office; Kelly Shenk, EPA Region 3 CBP Office; Rachel Streusand, 

Chesapeake Research Consortium/CBP Office; Jeff Strong, Tetra Tech; Fred Suffian, EPA 

Region 3 WPD; Gwen Supplee, EPA Region 3 WPD; Jeff Sweeney, University of 

Maryland/CBP Office; Nita Sylvester, EPA Region 3 CBP Office; Peter Tango, U.S. Geological 

Survey/CBP Office; Renee Thompson, USGS/CBP Office; Brian Trulear, EPA Region 3 WPD; 

Randy Waite, EPA Office of Air and Radiation; Tom Wall, EPA Office of Water; Ping Wang, 

University of Maryland/CBP Office; Howard Weinberg, University of Maryland/CBP Office; 

Steve Whitlock EPA Office of Water; Julie Winters, EPA Region 3 CBP Office; John Wolf, 

USGS/CBP Office; Robert Wood, EPA Region 3 CBP Office; Jing Wu, University of 

Maryland/CBP Office; Guido Yactayo, University of Maryland/CBP Office; Ning Zhou, 

Virginia Polytechnical and State University/CBP Office; Kyle Zieba, EPA Region 3 WPD; and 

Hank Zygmunt, EPA Region 3 WPD. 

xvi December 29, 2010
Chesapeake Bay TMDL

Special acknowledgement of the policy direction and guidance provided by Lisa Jackson, EPA 

Administrator; Robert Perciasepe, EPA Deputy Administrator; and Robert Sussman, Counselor 

to the Administrator. 

xvii December 29, 2010
Chesapeake Bay TMDL

Members of the Chesapeake Bay Program’s Water Quality Goal Implementation Team gather in Lancaster, 

Pennsylvania, in April 2009 to discuss development of the Chesapeake Bay TMDL. 

xviii December 29, 2010
Chesapeake Bay TMDL

SECTION 1. INTRODUCTION 

This document establishes total maximum daily loads (TMDLs) for nitrogen, 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, programmatic, and 

political scale. While all TMDLs are unique, this TMDL is distinguished by the magnitude of the 

watershed it addresses and the wealth of science synthesized, data developed, and analyses 

conducted over the course of the past decades that support its conclusions. 

In an effort to keep the Chesapeake Bay TMDL (Bay TMDL) document as clear and succinct as 

possible, discussion of the technical analyses and modeling that support the pollutant allocations 

are reasonably summarized 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) summarized in Section 9 are presented in 

greater detail in supporting appendices. 

This document is organized into 11 sections as follows: 

 Section 1: Clean Water Act 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 

 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 

 Section 9: The individual nitrogen, phosphorus, and sediment TMDLs for each of the 92 

Bay tidal segments 

 Section 10: Adaptive management approach to Bay TMDL implementation 

 Section 11: Documentation of public participation, comments, and responses 

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) and 24 Appendices. 

1‐1 December 29, 2010
Chesapeake Bay TMDL

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 and supporting 

tools—Bay airshed, land change, Scenario Builder, SPARROW, Bay watershed, Bay water 

quality and sediment transport, oyster filter feeder, and menhaden filter feeder—are 

provided via URL links in Section 5. 

 Access to each of the jurisdictions’ final 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 an element of the Bay TMDL itself. 

EPA reviewed the Phase I WIPs as part of the information used to inform its allocation 

decisions. 

 Publicly accessible agreements, documents, reports, papers, meeting summaries, 

correspondence, and data sets developed during the decades and more recent years leading 

up to the Chesapeake Bay TMDL, which were instrumental in setting the scientific, 

programmatic, policy, and legal foundation on which the Bay TMDL is built, are listed in 

Appendix B with electronic access to all through the provided URLs. 

1.1 TMDLS AND THE CWA 

Section 303(c) of the 1972 Clean Water Act (CWA) requires states, including the District of 

Columbia, (collectively referred to as jurisdictions) to establish water quality standards (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 (i.e., swimmable) uses. 

Section 303(d) of the CWA requires states, including the District of Columbia, to develop lists of 

impaired waters that fail to meet WQS set by jurisdictions even after implementing technologybased 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 wasteload allocations (WLAs) for point sources, the load allocation (LAs) for 

nonpoint sources and natural background, and a margin of safety (MOS)[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. 

1‐2 December 29, 2010
Chesapeake Bay TMDL

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 

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, and 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 numerous analyses and model simulations 

designed to calculate the Bay and its tidal tributaries and embayments’ pollutant loading capacity 

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 

nitrogen and phosphorus 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 new regulatory programs and policies. Through the years, the agreements and 

alliances have become more formalized and inclusive to address the multitude of factors 

1‐3 December 29, 2010
Chesapeake Bay TMDL

1‐4 December 29, 2010

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 statutory and regulatory 

requirements that form the underpinning of the Bay TMDL. 

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 Chesapeake Bay Program (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 achievement of 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 

(everything by everyone everywhere or E3 scenario), recognition of air deposition (air load 

allocation to tidal surface waters), and geographic-based allocations (relative effectiveness-based 

allocation methodology). 

 

1

 Clean Water Act section 117 (33 United States Code [U.S.C.] 1267). 
Chesapeake Bay TMDL

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 the 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 also established a goal of expanding 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 Chesapeake Bay Agreement of a 40 percent reduction by 2000 in 

nitrogen and phosphorus delivered to the Bay (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 by upgrading certain industrial wastewater treatment 

facilities. 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 Bay watershed 

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. 

1‐5 December 29, 2010
Chesapeake Bay TMDL

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. By 2001, 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; 

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, jurisdictions with tidal waters use their best efforts to adopt new or 

revised WQS consistent with the defined water quality conditions. Once 

adopted by the jurisdictions, EPA will expeditiously review the new or revised 

standards, which are 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 seven watershed jurisdictional partners established nitrogen, phosphorus, 

and sediment cap loads based on Bay water quality model projections of attainment of the then 

EPA-proposed dissolved oxygen water quality criteria under long-term average hydrologic 

conditions (Secretary Tayloe Murphy 2003). Reaching those cap loads was expected to eliminate 

1‐6 December 29, 2010
Chesapeake Bay TMDL

the summer no-oxygen conditions in the deep waters of the Bay and excessive algal blooms 

throughout the Bay, tidal tributaries and embayments (USEPA 2003c). 

EPA and its watershed jurisdiction partners allocated the nitrogen and phosphorus cap loads 

among the major river basins by jurisdiction. 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 2003c). Sediment allocations were based 

on the phosphorus-equivalent allocations to each major river basin by jurisdiction (USEPA 

2003c). 

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 watershed 

jurisdictions were assigned allocations (Chesapeake Bay Watershed Partners 2000; USEPA 

2003c). The final total basinwide cap loads agreed to by EPA and the seven watershed 

jurisdictions were 175 million pounds of nitrogen per year and 12.8 million pounds of 

phosphorus per year delivered to the tidal waters of the Bay (USEPA 2003c). The basinwide 

upland sediment cap load was 4.15 million tons per year (USEPA 2003c). 

2004–2006 Tributary Strategies 

To achieve the nitrogen, phosphorus, and sediment 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 pollutant loads 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 URL link

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_F

INAL_from_web.pdf

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Chesapeake Bay TMDL

2004–2005 Jurisdiction Adoption of Chesapeake Bay Water Quality Standards 

In continued efforts to coordinate activities to address nitrogen, phosphorus, 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 dissolved oxygen, water clarity, SAV, and chlorophyll a, along with 

criteria attainment assessment procedures and refined tidal water designated uses (for details, see 

Section 3) (USEPA 2003a, 2003d). EPA approved those four jurisdictions’ WQS regulations 

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 (Secretary Tayloe Murphy 2003). The initiation of that reevaluation at a 

partnership sponsored 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 watershed 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, its tidal tributaries and embayments in 2004-2005 (Secretary Tayloe Murphy 

2003). The 2007 reevaluation found that sufficient progress had not been made toward 

improving water quality to a level that indicated the mainstem Chesapeake Bay and its tidal 

tributaries and embayments were no longer impaired by nitrogen, phosphorus, and sediment 

pollution (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 Section 1.3. While EPA established the Bay TMDL, the seven 

watershed jurisdictions were essential partners in the initiative, providing critical input and 

participating in deliberations and making key decisions affecting the development process. The 

seven Bay watershed jurisdictions and EPA had 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 the September 2005 reevaluation workshop to the publication of the Bay TMDL in 

December 2010, the seven watershed jurisdictions were actively involved in 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, teams, and 

technical workgroups (see Section 1.3.1). The full records of the meetings and conference calls 

of those committees, teams, and workgroups are accessible via the Internet—see Appendix C. 

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Chesapeake Bay TMDL

At the October 1, 2007 meeting of the PSC, the seven watershed jurisdictions and EPA reached 

consensus that EPA would establish the Bay TMDL on behalf of the seven jurisdictions with a 

target date of 2025 when all necessary pollution control measures would be in place (CBP PSC 

2007). 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. Table 1-2 

summarizes that and the other Bay TMDL-relevant consensus agreements reached by the 

partners during that meeting. 

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 

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Chesapeake Bay TMDL

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. 

 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 (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 watershed 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 was 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 7, includes four elements: 

 Watershed Implementation Plans (WIPs) 

 Two-year milestones to demonstrate restoration progress 

 EPA’s commitment to track and assess progress 

1‐10 December 29, 2010
Chesapeake Bay TMDL

 Federal actions if the Bay watershed jurisdictions fail to meet expectations such as 

developing sufficient WIPs, effectively implementing their WIPs, and/or fulfilling 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 the lead responsibility within the Regional 

Office. In developing this TMDL, WPD coordinated efforts with the Chesapeake Bay Program 

Office, Air Protection Division, Office of Regional Counsel, Office of State and Congressional 

Relations, Office of Public Affairs, and Office of the Regional Administrator (all within EPA 

Region 3), EPA Region 2 (Division of Environmental Planning and Restoration and Office of the 

Regional Administrator), and EPA Headquarters (Office of Water, Office of General Counsel, 

Office of Air and Radiation, and Office of the Administrator). Throughout the Bay TMDL 

development process, EPA 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 descriptions 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 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 and watershed 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. 

1‐11 December 29, 2010
Chesapeake Bay TMDL

Source: CBP 2009 

Figure 1-1. CBP’s organizational structure. 

Chesapeake Executive Council 

The top executive of each of the signatories of the Chesapeake 2000 Agreement (state governors, 

the District of Columbia mayor, EPA Administrator, and Chesapeake Bay Commission Chair), 

form the Chesapeake Executive Council (CEC), which meets annually to set basinwide policies 

and the future directions for the CBP. Delaware, New York, and West Virginia participate in 

CEC meetings and have full input status on all water quality-related matters. Principals’ Staff 

Committee (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 well-defined, 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. 

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Chesapeake Bay TMDL

1‐13 December 29, 2010

Principals’ Staff Committee 

The Principals’ Staff Committee (PSC) provided policy and programmatic direction to the 

Management Board 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 provided policy and program direction to the Management Board which, in turn, 

provided strategic planning, priority setting, and operational guidance and direction to the Water 

Quality Goal Implementation Team (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,2

 and 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 nitrogen, phosphorus, and 

sediment loads entering the Bay and to ensure that such reductions are maintained over time. It is 

composed of the members of the former Water Quality Steering Committee and the former 

Nutrient Subcommittee. The WQGIT provided advice and guidance to EPA related to the draft 

target loads 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 Interstate Commission on the Potomac River Basin. 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 Bay watershed jurisdictions and other CBP participants on technical issues originally 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 

 

2

 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. 
Chesapeake Bay TMDL

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 facility owner/operators. 

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, tidal tributary and embayment waters related to 

the four 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 published by EPA. 

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. 

Scientific and Technical Advisory Committee 

The Scientific and Technical Advisory Committee (STAC) is composed of scientists 

representing a diverse range of disciplines from federal agencies and academic institutions in the 

seven watershed jurisdictions. STAC provides scientific and technical guidance and independent 

scientific peer review to the CBP on measures to restore and protect the Chesapeake Bay. STAC 

activities related to the Bay TMDL included independent scientific peer reviews of all the Bay 

models (watershed, land change, estuarine water quality, estuarine sediment transport, estuarine 

filter feeder), Bay criteria assessment procedures, and land use data, and reviewing and 

commenting on the draft Bay TMDL. 

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Chesapeake Bay TMDL

1‐15 December 29, 2010

Local Governments Advisory Committee 

The Local Governments Advisory Committee (LGAC) is a body of locally elected officials 

appointed by the governors of Maryland, Pennsylvania, Virginia, and the mayor of the District of 

Columbia. The LGAC was established to promote the role of local governments in Bay 

restoration efforts and develop strategies that ultimately 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 Watershed Implementation Plan (WIP) pilots in 2010 (before 

development of the Phase II WIPs starting 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) provides 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 wasteload allocations or WLAs, while allocations to nonpoint sources are called load 

allocations or LAs. A TMDL is the sum of the 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].”3

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 

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.”4

 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.5

 

3

 33 U.S.C. 1313(d)(1)(C). 

4

 Pronsolino v. Nastri, 291 F.3d 1123, 1129 (9th Cir. 2002). 5

 40 CFR 122.44(d)(1)(vii)(B). 
Chesapeake Bay TMDL

1‐16 December 29, 2010

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 1991b). 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 the 

jurisdictions’ 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 

Bay 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.”6

 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 nitrogen, phosphorus, 

and sediment 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 tributary waters of the Chesapeake Bay to be 

impaired for aquatic life resources. EPA determined that the mainstem and tidal tributary 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 tidal river, tributary, embayment, and other tidal waterbody that is part of the 

Chesapeake Bay TMDL is included on a jurisdiction’s section 303(d) list. 

EPA established 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 and embayment waters, a settlement 

agreement resolving litigation brought by the Chesapeake Bay Foundation, the 2000 Chesapeake 

Agreement, and Executive Order 13508. In establishing the Bay TMDL, EPA acted pursuant 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 

 

6

 Clean Water Act section 117(g)(1)(A)-(B), 33 U.S.C. 1267(g)(1)(A)-(B). 
Chesapeake Bay TMDL

1‐17 December 29, 2010

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 itself 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 Bay watershed jurisdictions’ WIPs and the May 2010 

Strategy for Protecting and Restoring the Chesapeake Bay (FLCCB 2010). 

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 – 

as here – impaired waters have been identified on jurisdictions’ section 303(d) lists for many years, 

where the jurisdictions in question 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 to establish that TMDL7

. 

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, memoranda of understanding (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 the District of 

Columbia’s 1998 section 303(d) lists and on the Delaware 1996 section 303(d) list. EPA 

established the Chesapeake Bay TMDL consistent with those consent decrees, MOUs, and 

settlement agreements, described below. 

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.8

 The consent decree includes a 12-year schedule for developing TMDLs for impaired 

 

7 Dioxin/Organochlorine Center v. Clarke, 57 F.3d 1517 (9th Cir. 1995); Scott v. City of Hammond, 741 F.2d 992 

(7th Cir. 1984); American Canoe Assn. v EPA, 54 F.Supp.2d 621 (E.D.Va. 1999). 8 American Canoe Association v. EPA, 98cv979 (June 11, 1999). 
Chesapeake Bay TMDL

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 and embayments in 

accordance with the Virginia consent decree schedule (CBP PSC 2007). Table 1-3 provides a list 

of the Virginia consent decree waters that were addressed by the Chesapeake Bay TMDLs for 

nitrogen, phosphorus, and sediment. 

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

nutrients 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 e PMKTF, 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 g YRKMH, 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 

1‐18 December 29, 2010
Chesapeake Bay TMDL

1‐19 December 29, 2010

District of Columbia–EPA Consent Decree 

In 1998 Kingman Park Civic Association and others filed a similar suit against EPA.9 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. 

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 (nitrogen and phosphorus) 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.10 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 1-4 provides a list of the District’s consent decree waters that were 

addressed by the Chesapeake Bay TMDLs for nitrogen, phosphorus, 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 were not expressed as 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, 2011.11 With publication of the 

Bay TMDL, the Washington Ship Channel pH impairment has been addressed and the pH 

TMDL for the Ship Channel approved by EPA on December 15, 2004 has been superseded. 

Table 1-4. District of Columbia consent decree (CD) waters impaired for pH 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 River). The parties entered into a consent decree resolving 

the lawsuit.12 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 

 

9 Kingman Park Civic Association v EPA, 98cv00758 (June 13, 2000). 10 Kingman Park Civic Association v. EPA, 98cv00758 (Order February 12, 2008). 

11 Anacostia Riverkeeper et al v. Jackson, 1:2009cv00098 (D.DC)( Mem. and Order May 25, 2010) 12 American Littoral Society, et al. v EPA, et al., 96cv591 (D.Del. 1997). 
Chesapeake Bay TMDL

1‐20 December 29, 2010

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 standards in the Chesapeake Bay by 2010 (CEC 2000). Many of the waters 

on Maryland’s 1998 section 303(d) list were open waters of the Bay or tidal tributaries and 

embayments 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 partnership and Maryland efforts (MDE 2004). Therefore, Maryland decided to 

postpone development of TMDLs for Maryland’s listed Chesapeake Bay and its tidal tributary 

and embayment 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 and embayments impaired by excess nitrogen, phosphorus, 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. 
Chesapeake Bay TMDL

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 Bay 

TMDL including the parameters of concern, the specific impairment listings addressed, and the 

Bay 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 and embayments, the Chesapeake Bay 

encompasses approximately 11,684 miles of shoreline, a length longer than the entire West Coast 

of the United States. 

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 10,000 streams and rivers that eventually flow into the Bay. 

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 characteristics, depending on the geology from which they originate 

(Figure 2-2). 

2‐1 December 29, 2010
Chesapeake Bay TMDL

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

2‐2 December 29, 2010
Chesapeake Bay TMDL

Source: USGS WRIR 00-424 

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

2‐3 December 29, 2010
Chesapeake Bay TMDL

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. 

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. 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 percent wooded/open, 22 percent agriculture, 

7 percent developed, and 2 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). 

2‐4 December 29, 2010
Chesapeake Bay TMDL

Source: Irani and Claggett 2010 

Figure 2-3. Chesapeake Bay watershed land cover. 

2‐5 December 29, 2010
Chesapeake Bay TMDL

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 across seven jurisdictions. EPA established 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 and embayments that are 

impaired from excess nitrogen, phosphorus, and sediment pollution. If Bay segments are 

impaired for other pollutants, EPA expects that the Bay watershed 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 where both local 

TMDLs and Chesapeake Bay TMDLs have already been developed or established 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. 

2‐6 December 29, 2010
Chesapeake Bay TMDL

2‐7 December 29, 2010

2.2.1 Pollutants of Concern 

The pollutants of concern for this TMDL are nutrients—nitrogen and phosphorus—and 

sediment. Excessive nitrogen and phosphorus 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 nitrogen and 

phosphorus 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, certain bacteria (e.g., Escherichia coli) 

often cling to sediment. By reducing sediment, reductions in phosphorus delivered to the Bay 

(and possibly other pollutants such as E. coli) also will 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 Bay watershed 

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 also will 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 thirty years (USEPA 

1983b, 2004b, 2005, 2008a). 

Segmentation is the compartmentalization of the estuary into subunits on the basis of selection 

criteria (USEPA 2008a). Generally, segments reflect certain unique physical, chemical or 

biological characteristics of a portion of a waterbody (e.g., salinity, influence of pollutant 

sources, etc.). 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 segments1

 agreed to by the 

CBP partnership 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). 

 

1

 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. 
Chesapeake Bay TMDL

Source: USEPA 2008a 

Figure 2-5. The 92 Chesapeake Bay segments. 

2‐8 December 29, 2010
Chesapeake Bay TMDL

Source: USEPA 2008a 

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

2‐9 December 29, 2010
Chesapeake Bay TMDL

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) Integrated 

Report listing categories are as follows: 

 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 already have completed a 

TMDL 

- 4a—TMDL has been completed 

- 4b—Other pollution control requirements are reasonably expected to result in the 

attainment of the WQS in the near future 

- 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 Jurisdiction 

Chesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

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 

Eastern 

Shore 

MD Middle Chester River CHSOH MD MOU 4a for TN and TP 

2‐10 December 29, 2010
Chesapeake Bay TMDL

2‐11 December 29, 2010

Major river 

basin Jurisdiction 

Chesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

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 

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 River, 

DE 

NANTF_DE DE CD 

finished 

5 

MD Upper Nanticoke River, 

MD 

NANTF_MD MD MOU 5 

MD Upper Pocomoke River POCTF MD MOU 5 

MD Wicomico River WICMH MD MOU 5 

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 

James 

VA Western Branch 

Elizabeth River 

WBEMH VA CD 5 

MD Lower Patuxent River PAXMH MD MOU 5 

MD Middle Patuxent River PAXOH MD MOU 5 

Patuxent 

MD Upper Patuxent River PAXTF MD MOU 5 
Chesapeake Bay TMDL

2‐12 December 29, 2010

Major river 

basin Jurisdiction 

Chesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

MD Western Branch 

Patuxent River 

WBRTF MD MOU BOD TMDL 

completed for DO 

impairments; 4a for 

BOD 

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 b VA 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 

MD Middle Potomac River, 

MD - Mainstem 

POTOH1_MD MD MOU 5 

MD Middle Potomac River, 

MD - Nanjemoy 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 

Potomac 

VA Upper Potomac River, 

VA 

POTTF_VA -- 3 for DO in 

Migratory 

Spawning and 

Nursery; 2 for SAV 

and DO in open 

water 

Rappa- VA Corrotoman River CRRMH -- 5 

hannock VA Lower Rappahannock 

River 

RPPMH VA CD 5 
Chesapeake Bay TMDL

2‐13 December 29, 2010

Major river 

basin Jurisdiction 

Chesapeake Bay 

303(d) segment Segment ID CD/MOU 2008 list statusa

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

CB6PHb VA CD 5 

Susquehanna MD Northern Chesapeake 

Bayb

CB1TFb MD MOU 5 

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 

Bayb

CB2OHb MD MOU 5 

Western 

Shore 

MD West River WSTMH MD MOU 5 

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 

York 

VA Upper Pamunkey River PMKTF VA CD 5 

Sources: American Canoe Association v. EPA; American Littoral Society, et al. v. EPA, et al.; DC DOH 1998; DC 

DOE 2008; DE DNREC 1996; DE DNREC 2008; Kingman Park Civic Association, et al. vs. EPA; MDE 1998, 2004, 

2008; USEPA 2008 a; VA DEQ 1998; 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 
Chesapeake Bay TMDL

2‐14 December 29, 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.2

 Those section 303(d) lists identify 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 nitrogen and phosphorus 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 possibility that they 

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 to 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 impaired 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 

integrated report (VADEQ 2008). Loads originating in the watershed that drains directly to 

 

2

 At the time EPA applied the Bay models for development of the allocations starting in 2009, the 2008 section 

303(d) lists were the most recent approved lists. Although EPA subsequently received 2010 section 303(d) lists for 

approval from all tidal jurisdictions, EPA used the approved 2008 lists in establishing the Bay TMDL to have a 

consistent basis for the TMDL. 
Chesapeake Bay TMDL

2‐15 December 29, 2010

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). These include TMDLs for 

the above described three Virginia Bay segments because they flow into impaired tidal Bay 

segments, and reductions in nitrogen, phosphorus, 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 EPA established TMDLs for all necessary Bay segments—all 2008 listed 

segments, all Virginia, Delaware, and the District of Columbia TMDL consent decree segments, 

and all Maryland MOU segments—EPA compared the 2008 listed segments with those included 

on those consent decrees and MOUs (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 TMDL 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 segments of the Virginia 

consent decree, Delaware consent decree, the District of Columbia consent decree, and Maryland 

MOU are included in the list of 92 Chesapeake Bay segments for which nitrogen, phosphorus, 

and sediment 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 2a 2 

Total 77 92 

Source: Adapted from Table 2-1. 

a. Two consent decrees affect one Bay segment in Delaware, but TMDLs have already been established for both 

waterbodies. 
Chesapeake Bay TMDL

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 generally chemical-specific and reflect specific levels of pollutants that, if found in 

the waterbody, do not impair its 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 inhabiting Chesapeake Bay and its tidal tributaries and embayments. The 1987 

Chesapeake Bay Agreement included 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. 1992) 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 (USEPA 

2003d) documents. 

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). 

Since 2005, Delaware, Maryland, Virginia, and the District of Columbia each has proposed and 

adopted very specific amendments to its respective Chesapeake Bay WQS regulations. Each 

jurisdiction’s process for amending its existing Chesapeake Bay WQS regulations requires full 

public notice, public review and comment, and response to public comments before submission 

to EPA Region 3 for final EPA review and approval. 

3‐1 December 29, 2010
Chesapeake Bay TMDL

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. The criteria assessment guidance is 

documented within EPA’s Bay criteria (USEPA 2003a), designated uses/attainability (USEPA 

2003d), and Bay segmentation (USEPA 2004b) documents and the subsequent seven addenda 

(USEPA 2004a, 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 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 2003d] 

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-R-03-002. [USEPA 

2004a] 

October 2004 Addresses endangered species 

protection, assessment of DO criteria, 

derivation of site-specific 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, and Potomac River 

jurisdictional boundaries; 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 provides 

coordinates, georeferences, and narrative 

descriptions of the 2003 segmentation 

scheme. 

3‐2 December 29, 2010
Chesapeake Bay TMDL

3‐3 December 29, 2010

Document title 

Month/year 

published Document content and description 

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 provides 

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-R-07-003. 

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. 

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. 

CBP/TRS 301-10. [USEPA 2010a] 

May 2010 Addresses refinements to procedures for 

defining designated uses, procedures for 

deriving biologically based reference 

curves for DO criteria assessment and 

chlorophyll a 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 all went 

through independent scientific peer reviews sponsored by the CBP’s STAC and public review. 

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), Chesapeake Bay designated uses and attainability document (USEPA 2003d), and 

Chesapeake Bay segmentation document (USEPA 2004b), EPA has published enhancements to 

the criteria assessment procedures, designated use boundaries, and Bay segmentation scheme. 

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 
Chesapeake Bay TMDL

the original 2003 Bay designated use/attainability document (USEPA 2003d), 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). 

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 2003d, 2004e, 2010a). The five tidal Bay 

designated uses are applied, where appropriate, consistently across Delaware, the District of 

Columbia, Maryland, and Virginia’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 2003d, 

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 channels in summer. 

Sources: USEPA 2003d, 2004e 

3‐4 December 29, 2010
Chesapeake Bay TMDL

Source: USEPA 2003d 

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 

Delaware, the District of Columbia, Maryland, and Virginia’s existing WQS regulations. 

Amended based on USEPA 2010a, Table 3-3 was originally 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 2003d). 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). 

3‐5 December 29, 2010
Chesapeake Bay TMDL

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

Migratory 

fish 

spawning 

& nursery 

Open 

water fish 

& shellfish

Deep 

water 

seasonal 

fish & 

shellfish 

Deep 

channel 

seasonal 

refuge 

Shallow 

water Bay 

grasses 

CB segment name CB segment Juris.

Feb. 1– 

May 31 Year-round

June 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 , MD 

CB5MH_MD MD X X X X 

Lower Central 

Chesapeake Bay, VA 

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 X 

Severn River SEVMH MD X X X X 

South River SOUMH MD X 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 

River 

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, DC POTTF_DC DC X X X 

Upper Potomac River, MD POTTF_MD MD X X X 

Upper Potomac River, VA POTTF_VA VA X X X 

Anacostia River, DC ANATF_DC DC X X X 

Anacostia River, MD ANATF_MD MD X X X 

Piscataway Creek PISTF MD X X X 

Mattawoman Creek MATTF MD X X X 

3‐6 December 29, 2010
Chesapeake Bay TMDL

3‐7 December 29, 2010

Migratory 

fish 

spawning 

& nursery 

Open 

water fish 

& shellfish

Deep 

water 

seasonal 

fish & 

shellfish 

Deep 

channel 

seasonal 

refuge 

Shallow 

water Bay 

grasses 

CB segment name CB segment Juris.

Feb. 1– 

May 31 Year-round

June 1–

Sept. 30 

June 1–

Sept. 30 

SAV 

growing 

season 

Middle Potomac River, 

MD-Mainstem 

POTOH1_MD MD X X X 

Middle Potomac River, 

MD-Nanjemoy Creek 

POTOH2_MD MD X X X 

Middle Potomac River, 

MD-Port Tobacco River 

POTOH3_MD MD X X X 

Middle Potomac River, VA POTOH_VA VA X X X 

Lower Potomac River, MD POTMH_MD MD X X X X X 

Lower Potomac River, VA POTMH_VA 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 

Upper Pamunkey River PMKTF VA X X X 

Lower Pamunkey River PMKOH VA 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 

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 
Chesapeake Bay TMDL

3‐8 December 29, 2010

Migratory 

fish 

spawning 

& nursery 

Open 

water fish 

& shellfish

Deep 

water 

seasonal 

fish & 

shellfish 

Deep 

channel 

seasonal 

refuge 

Shallow 

water Bay 

grasses 

CB segment name CB segment Juris.

Feb. 1– 

May 31 Year-round

June 1–

Sept. 30 

June 1–

Sept. 30 

SAV 

growing 

season 

Lynnhaven River LYNPH VA X X 

Northeast River NORTF MD X X X 

C&D Canal, DE C&DOH_DE DE X X X 

C&D Canal, MD 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 CHOMH2 MD X X X 

Mouth of the Choptank 

River 

CHOMH1 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, 

MD 

NANTF_MD MD X X 

Upper Nanticoke River, DE NANTF_DE DE X X X 

Middle Nanticoke River NANOH MD X X X 

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, 

MD 

POCOH_MD MD X X 

Middle Pocomoke River, 

VA 

POCOH_VA VA X X 

Lower Pocomoke River, 

MD 

POCMH_MD MD X X X 

Lower Pocomoke River, 

VA 

POCMH_VA VA X X X 

Tangier Sound, MD TANMH_MD MD X X 

Tangier Sound, VA TANMH_VA VA X X 

Sources: USEPA 2003d, 2004e, 2007a, 2010a 
Chesapeake Bay TMDL

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 (preventing 

reaeration); 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 DO criteria were protective of the shortnose sturgeon, a 

species listed as endangered by the Endangered Species Act (NMFS 2003; USEPA 2003b). 

Source: USEPA 2003a 

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

biological communities. 

3‐9 December 29, 2010
Chesapeake Bay TMDL

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. 

Table 3-4. Current Chesapeake Bay DO criteria 

Designated 

use 

Criteria 

concentration/duration Protection provided

Temporal 

application

7-day mean ≥ 6 mg/L 

(tidal habitats with 0–0.5 ppt 

salinity) 

Survival and growth of 

larval/juvenile tidal-fresh resident 

fish; protective of 

threatened/endangered species 

Instantaneous minimum 

≥ 5 mg/L 

Survival and growth of 

larval/juvenile migratory fish; 

protective of 

threatened/endangered species 

Migratory fish February 1–May 31

spawning 

and 

nursery use 

Open-water fish and shellfish designated use criteria apply June 1–January 31 

Shallow-water 

Bay grass use 

Open-water fish and shellfish designated use criteria apply Year-round 

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 

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 

Open-water 

fish and 

shellfish use 

Instantaneous minimum 

≥ 3.2 mg/L 

Survival of threatened/endangered 

sturgeon speciesa

Year-round 

30-day mean ≥ 3 mg/L Survival and recruitment of Bay 

anchovy eggs and larvae 

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 

June 1–September 

30 

Deep-water 

seasonal fish 

and shellfish 

use 

Open-water fish and shellfish designated use criteria apply October 1–May 31 

Instantaneous minimum 

≥ 1 mg/L 

Survival of bottom-dwelling worms 

and clams 

June 1–September 

30 

Deep-channel 

seasonal 

refuge use 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. 

3‐10 December 29, 2010
Chesapeake Bay TMDL

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.” 

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 2007b). 

Delaware, the District of Columbia, Maryland, and Virginia all adopted EPA’s narrative 

chlorophyll a criteria. Additionally, the District of Columbia and Virginia adopted numeric 

chlorophyll a criteria for certain tidal waters as detailed in Sections 3.2.2 and 3.2.7, respectively. 

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 nitrogen and phosphorus as plant 

material, stabilizing bottom sediment (preventing their resuspension) and reducing shoreline 

erosion. The health and survival of such underwater plant communities in the Chesapeake Bay 

and its tidal tributaries and embayments 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. 

2010b). 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 application model simulations and diagnostic tools (Table 3-5). 

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 

3‐11 December 29, 2010
Chesapeake Bay TMDL

equivalent Secchi depth by application depth (Table 3-5). The recommended percent light-throughwater 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 2003d). 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 and embayments. 

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 EPA 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 2003d). 

Table 3-5. Summary of Chesapeake Bay water clarity criteria for application to shallowwater Bay grass designated use habitats 

Water clarity criteria as Secchi deptha

Water clarity criteria application depths 

(meters) 

0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 

Salinity 

regimeb

Water clarity 

criteria 

(percent lightthroughwater) 

Secchi depth for above criteria application depth 

(meters) 

Temporal 

application 

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-1 published 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 

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. 

b. Tidal fresh = 0-0.5 ppt salinity; oligohaline = >0.5-5 ppt salinity; mesohaline = >5-18 ppt salinity; polyhaline = >18 

ppt salinity 

Table 3-6. Chesapeake Bay SAV restoration acreage goals and application depths 

Segment description State

Segment 

designator

SAV acreage 

restoration goal 

(acres) 

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

3‐12 December 29, 2010
Chesapeake Bay TMDL

3‐13 December 29, 2010

Segment description State

Segment 

designator

SAV acreage 

restoration goal 

(acres) 

Application 

depth 

(meters)

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 30 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 

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 

Upper Pamunkey River VA PMKTF 187 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 
Chesapeake Bay TMDL

3‐14 December 29, 2010

Segment description State

Segment 

designator

SAV acreage 

restoration goal 

(acres) 

Application 

depth 

(meters)

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 1 0.5 

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 River MD BIGMH2 22 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 2.0 

Sources: USEPA 2003d, 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. 

Notes: 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 Bay segment 

(USEPA 2004e). If a Bay segment was listed in Table 3-3, but it is not listed here, that entire Bay segment has been 

delineated as a SAV no-grow zone and the shallow-water bay grass does not apply (USEPA 2004e). 
Chesapeake Bay TMDL

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 adopted jurisdiction-specific designated uses or criteria or both; those cases are briefly 

described below. 

Table 3-7. Links for accessing the current waters quality standards (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-quality20051130.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 Delaware 

Delaware has adopted all the EPA-published Chesapeake Bay criteria, assessment procedures, 

designated use documents, and subsequent addenda listed in Table 3-1 by reference into its WQS 

regulations. The EPA-published Chesapeake Bay criteria, assessment procedures, 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 also adopted EPA’s narrative chlorophyll a water quality criteria. 

3.2.2 District of Columbia 

The District of Columbia has adopted all the EPA-published Chesapeake Bay criteria, 

assessment procedures, designated use documents, and subsequent addenda listed in Table 3-1

by reference into its WQS regulations. 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 numeric chlorophyll a water quality 

criteria shown in Table 3-9 with respect to the District of Columbia’s tidal Class C waters (those 

designated for the protection and propagation of fish, shellfish, and wildlife). Those numeric 

chlorophyll a criteria are subject to this Chesapeake Bay TMDL (see Table 2-1). 

3‐15 December 29, 2010
Chesapeake Bay TMDL

3‐16 December 29, 2010

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 > 29 °C, in tidally influenced 

waters, an instantaneous minimum DO 

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 

3.2.3 Maryland 

Maryland has adopted into its WQS regulations all the EPA-published Chesapeake Bay criteria, 

assessment procedures, and designated uses documents, and subsequent addenda listed in Table 

3-1. These WQS apply to all Chesapeake Bay, tidal tributary and embayment waters of 

Maryland, all of which are subject to this Chesapeake Bay TMDL (see Table 2-1). Maryland has 

also 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 variances1

 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 designated use DO criteria. In the lower Chester 

River segment (CSHMH), a restoration variance of 14 percent applies to the application of the 

deep-channel designated use DO criterion (COMAR 26.08.02.03-3(c)(8)(e)(vi). These 

restoration variances are consistent with EPA-published guidance (USEPA 2003d) and were 

 

1

 A restoration variance is the percentage of allowable exceedance of a WQS 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). 
Chesapeake Bay TMDL

approved by EPA on August 29, 2005 in the case of the two mainstem Bay and Patapsco River 

segments and December 27, 2010 in the case of the lower Chester River segment. 

In the tidal upper and middle Pocomoke River segments (POCTF, POCOH_MD), because of the 

seasonal lower DO concentration from the natural oxygen-depleting processes present in the 

extensive surrounding tidal wetlands, Maryland adopted a site-specific criterion of greater than 

or equal to 4 mg/L 30-day mean DO, consistent with the EPA-published criterion (USEPA 

2004a), and approved by EPA on December 27, 2010. 

3.2.4 Virginia 

Virginia has adopted into its WQS regulations all the EPA-published Bay criteria, assessment 

procedures, designated uses documents, and subsequent addenda listed in Table 3-1. These WQS 

apply to all Chesapeake Bay, tidal tributary and embayment waters of Virginia, all of which are 

subject to this Chesapeake Bay TMDL. The narrative chlorophyll a criteria guidance published 

by EPA (USEPA 2003a) was adopted by Virginia for application 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 in the original EPA 2003 Bay criteria document (USEPA 2003a) 

with additional river-specific considerations (VADEQ 2004). EPA approved Virginia’s WQS 

regulations on June 27, 2005 and approved additional amendments on December 28, 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 

10 Upper James River-Upper (JMSTF2) 

15 Upper James River-Lower (JMSTF1) 

15 Middle James River (JMSOH) 

12 Lower James River (JMSMH) 

12 Mouth of the James River (JMSPH) 

March 1–May 31

15 Upper James River-Upper (JMSTF2) 

23 Upper James River-Lower (JMSTF1) 

22 Middle James River (JMSOH) 

10 Lower James River (JMSMH) 

Open-Water

10 Mouth of the James River (JMSPH) 

July 1–September 30

Source: Code of Virginia 9 section 62.1-44.15 3a; VAC 25-260 

Note: μg/L = micrograms per liter 

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 the surrounding 

extensive tidal wetlands, Virginia adopted a site-specific criterion of greater than or equal to 4 

mg/L 30-day mean DO (9 VAC 25-260-185), consistent with the EPA-published criterion 

(USEPA 2004a) and approved by EPA on June 27, 2005. 

3‐17 December 29, 2010
Chesapeake Bay TMDL

3.3 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 four tidal jurisdictions, 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 were formally adopted into each jurisdiction’s WQS regulations by reference. 

3.3.1 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 criterion 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 

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. 

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 

Y-axis versus the spatial exceedance values (in area or volume) on the X-axis (Figure 3-3) 

(USEPA 2003a, 2007a; STAC 2006). 

3‐18 December 29, 2010
Chesapeake Bay TMDL

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 

 Source: USEPA 2003a 

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

3‐19 December 29, 2010
Chesapeake Bay TMDL

3.3.2 Defining Allowable Exceedances 

EPA developed reference curves for each water quality criterion (DO, water clarity, and 

chlorophyll a) to provide a scientifically based, direct measure of the time and space during 

which a particular criterion can be allowably exceeded – i.e., without resulting in harm to the 

designated uses(s) (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. 

For assessment purposes, EPA developed two types of reference curves: a biological reference 

curve and a 10 percent default reference curve for use when a biological reference curve is 

unavailable. 

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, however, 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. In those cases, EPA used a 10 percent default reference curve 

(USEPA 2007a). The 10 percent 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). 

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 (blue line) and below the assessment curve (red line) is 

considered a non-allowable exceedance. The area below the reference curve (yellow) is 

considered an allowable exceedance (Figure 3-5). 

3‐20 December 29, 2010
Chesapeake Bay TMDL

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. 

Source: USEPA 2003a 

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

3‐21 December 29, 2010
Chesapeake Bay TMDL

3.3.3 Assessing Criteria Attainment 

Dissolved Oxygen Criteria Assessment 

EPA published DO criteria protective of migratory fish spawning and nursery, open-water fish 

and shellfish, deep-water seasonal fish and shellfish, and deep-channel seasonal refuge 

designated use habitats. DO criteria were established for the Chesapeake Bay that varied in space 

and time to provide levels of protection for different key species and communities (Table 3-4). 

The criteria also were 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) (USEPA 2003a). 

The DO criteria include multiple components, including the 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, 2003d). The four tidal Bay jurisdictions adopted these DO criteria into their 

respective WQS regulations. 

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 represents 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, published 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 were not assessed because the existing water quality monitoring programs 

and the published assessment methodologies are not yet adequate for full assessment. 

Evaluation of the Chesapeake Bay Water Quality and Sediment Transport Model’s 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. 

3‐22 December 29, 2010
Chesapeake Bay TMDL

For both open-water and deep–water designated uses, the 30-day mean criteria had the highest 

nonattainment in all three scenarios illustrated in Figure 3-6. The 30-day mean open-water and 

deep-water criteria are, therefore, protective of the other non-assessed DO criteria (open-water 

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 DO 

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 deepwater and open-water criteria. The analyses documented in Appendix D provide clear evidence 

the 30-day mean open-water, 30-day mean deep-water DO criteria, and the deep-channel 

instantaneous minimum criterion are the most protective criteria across all Bay segments and 

designated uses. 

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 the 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 

recommends—and Virginia and the District of Columbia adopted—using the 10 percent 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 (< 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 10 percent default reference curve. Such 

concentration-based 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 means 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). 

3‐23 December 29, 2010
Chesapeake Bay TMDL

Source: Appendix D 

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

3‐24 December 29, 2010
Chesapeake Bay TMDL

3‐25 December 29, 2010

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 the Chesapeake Bay, its tidal tributaries and embayments 

(USEPA 2003a, 2003d). 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 2003d). 

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, 2003d, 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, 2003d, 2007a, 2008a). 
Chesapeake Bay TMDL

SECTION 4. SOURCES OF NITROGEN, PHOSPHORUS 

AND SEDIMENT TO THE CHESAPEAKE 

BAY 

Nitrogen, phosphorus, and sediment loads originate from many sources in the Bay watershed. 

Point sources of nitrogen, phosphorus, and sediment include municipal wastewater facilities, 

industrial discharge facilities, CSOs, SSOs, NPDES permitted stormwater (MS4s and 

construction and industrial sites), and CAFOs. Nonpoint sources include agricultural lands 

(AFOs, cropland, hay land, and pasture), atmospheric deposition, forest lands, on-site treatment 

systems, nonregulated stormwater runoff, streambanks and tidal shorelines, tidal resuspension, 

the ocean, wildlife, and natural background. Unless otherwise specified, the loading estimates 

presented in this section are based on results of the Phase 5.3 Chesapeake Bay Watershed Model 

(Bay Watershed Model). For a description of the Bay Watershed Model, see Section 5.8. 

Estimates of existing loading conditions are based on the 2009 scenario run through the Bay 

Watershed Model. 

4.1 JURISDICTION LOADING CONTRIBUTIONS 

Analysis of 2009 monitoring data and estimated modeling results shows that Pennsylvania 

provided the largest proportion of nitrogen loads delivered to the Bay (44 percent), followed by 

Virginia (27 percent), Maryland (20 percent), New York (4 percent), Delaware (2 percent) and 

West Virginia (2 percent), and the District of Columbia (1 percent) (Figure 4-1). Delivered loads 

are the amount of a pollutant delivered to the tidal waters of the Chesapeake Bay or its tributaries 

from an upstream point. Delivered loads differ from edge-of-stream loads becauese of in-stream 

processes in free-flowing rivers that naturally remove nitrogen and phosphorus from the system. 

DE

2%

DC

1%

MD

20%

NY

4%

PA

44%

VA

27%

WV

2%

Total Nitrogen

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Figure 4-1. Modeled estimated total nitrogen loads delivered to the Chesapeake Bay by jurisdiction in 2009. 

4‐1 December 29, 2010
Chesapeake Bay TMDL

The model estimated phosphorus loads delivered to the Bay were dominated by Virginia (43 

percent), followed by Pennsylvania (24 percent), Maryland (20 percent), New York (5 percent), 

West Virginia (5 percent), Delaware (2 percent), and the District of Columbia (1 percent) (Figure 

4-2). 

DE

2%

DC

1%

MD

20%

NY

5%

PA

24%

VA

43%

WV

5%

Total Phosphorus

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Figure 4-2. Model estimated total phosphorus loads delivered to the Chesapeake Bay by jurisdiction in 2009. 

Similar to the phosphorus loads, 2009 model estimated sediment loads delivered to the Bay are 

dominated by Virginia (41 percent), followed by Pennsylvania (32 percent), Maryland (17 

percent), West Virginia (5 percent), New York (4 percent), Delaware (1 percent), and the District 

of Columbia (< 1 percent) (Figure 4-3). 

DE

1% DC, <1%

MD

17%

NY

4%

PA

32%

VA

41%

WV

5%

Total Sediment

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Figure 4-3. Model estimated total sediment loads delivered to the Chesapeake Bay by jurisdiction in 2009. 

4‐2 December 29, 2010
Chesapeake Bay TMDL

4.2 MAJOR RIVER BASIN CONTRIBUTIONS 

The major river basins’ model-estimated contributions of total nitrogen loads delivered to the 

Bay in 2009 are illustrated in Figure 4-4. The Susquehanna River basin, draining parts of New 

York, Pennsylvania, and Maryland, is estimated to be responsible for almost half of the nitrogen 

loads delivered to the Bay (46 percent). The next major contributor, at 22 percent, is the Potomac 

River Basin, draining the entire District of Columbia and parts of Maryland, Pennsylvania, 

Virginia, and West Virginia. The James River Basin (draining parts of Virginia and West 

Virginia) contributes 12 percent of the nitrogen loads to the Bay; the Eastern Shore Basin 

(draining parts of Delaware, Maryland, and Virginia) contibutes 8 percent of the nitrogen loads 

to the Bay; and the Western Shore Basin (draining parts of Maryland) is estimated to be 

responsible for 6 percent of the nitrogen loading to the Bay. Smaller portions, 3 percent, 2 

percent, and 1 percent are contributed by the Rappahannock (Virginia), the York (Virginia) and 

the Patuxent (Maryland) river basins, respectively (Figure 4-4). 

8%

12%

1%

22%

3%

46%

6%

2%

Total Nitrogen

Eastern Shore of

Chesapeake Bay

James River Basin

Patuxent River Basin

Potomac River Basin

Rappahannock River

Basin

Susquehanna River Basin

Western Shore of

Chesapeake Bay

York River Basin

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Figure 4-4. Model estimated total nitrogen loads delivered to the Chesapeake Bay by major tributary in 2009. 

The major river basins’ model estimated contributions to total phosphorus loads to the Bay in 

2009 are illustrated in Figure 4-5. Three river basins—the Potomac (27 percent), the 

Susquehanna (26 percent), and the James (20 percent)—are estimated to account for about threequarters of the total phosphorus loading to the Bay. The Eastern Shore contributes 10 percent of 

the total phosphorus load, while the balance is provided by the Rappahannock (6 percent), the 

Western Shore (5 percent), the York (4 percent), and the Patuxent (2 percent) river basins 

(Figure 4-5). 

The major river basins’ model estimated contributions to total sediment loads to the Bay in 2009 

are illustrated in Figure 4-6. The Susquehanna (33 percent) and Potomac (32 percent) river 

basins are estimated to contribute the majority of the total sediment loads delivered to the 

Chesapeake Bay, followed by the James (16 percent) and the Rappahannock (9 percent) river 

4‐3 December 29, 2010
Chesapeake Bay TMDL

basins. The Eastern Shore (4 percent), Western Shore (3 percent), York (2 percent) and Patuxent 

(1 percent) river basins each contribute relatively small total sediment loads (Figure 4-6). 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

2009. 

4%

16%

1%

32%

9%

33%

3% 2%

Total Sediment

Eastern Shore of

Chesapeake Bay

James River Basin

Patuxent River Basin

Potomac River Basin

Rappahannock River

Basin

Susquehanna River Basin

Western Shore of

Chesapeake Bay

York River Basin

10%

20%

2%

27%

6%

26%

5% 4%

Total Phosphorus

Eastern Shore of

Chesapeake Bay

James River Basin

Patuxent River Basin

Potomac River Basin

Rappahannock River

Basin

Susquehanna River Basin

Western Shore of

Chesapeake Bay

York River Basin

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Figure 4-6. Model estimated total sediment loads delivered to the Chesapeake Bay by major tributary in 2009. 

4‐4 December 29, 2010
Chesapeake Bay TMDL

4.3 POLLUTANT SOURCE SECTOR CONTRIBUTIONS 

Table 4-1 and Table 4-2 provide model estimates of major pollutant sources of nitrogen and 

phosphorus, respectively, delivered to the Bay by each jurisdiction and by each major pollutant 

source sector. Nontidal deposition refers to atmospheric deposition direct to nontidal surface 

waters (e.g., streams, rivers). Table 4-3 provides estimates of major sediment sources by 

jurisdiction and by major pollutant source sector and represents the portion of sediment that is 

from land-based sources. Stream erosion is also a significant source of watershed sediment 

delivered to the Bay. Sufficient data do not exist to accurately quantify the portion of the total 

sediment load specifically from stream erosion. 

Table 4-1. Percentage of total nitrogen delivered to the Bay from each jurisdiction by 

pollutant source sector 

Jurisdiction Agriculture Forest 

Stormwater

runoff 

Point 

source Septic 

Nontidal 

deposition 

Delaware 3% 1% 1% 0% 2% 1% 

District of Columbia 0% 0% 1% 5% 0% 0% 

Maryland 16% 14% 28% 27% 36% 27% 

New York 4% 7% 3% 3% 5% 5% 

Pennsylvania 55% 46% 33% 25% 30% 42% 

Virginia 20% 27% 33% 39% 24% 25% 

West Virginia 3% 4% 2% 1% 2% 1% 

Total 100% 100% 100% 100% 100% 100% 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Note: Nontidal deposition refers to atmospheric deposition direct to nontidal surface waters. 

Table 4-2. Percentage of total phosphorus delivered to the Bay from each jurisdiction by 

pollutant source sector 

Jurisdiction Agriculture Forest

Stormwater

runoff

Point 

source Septic

Nontidal 

deposition

Delaware 4% 1% 1% 0% 0% 0% 

District of Columbia 0% 0% 1% 2% 0% 0% 

Maryland 19% 14% 28% 21% 0% 27% 

New York 5% 7% 3% 5% 0% 5% 

Pennsylvania 24% 25% 16% 28% 0% 27% 

Virginia 42% 45% 50% 42% 0% 38% 

West Virginia 6% 7% 2% 3% 0% 2% 

Total 100% 100% 100% 100% 100% 100% 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Note: Nontidal deposition refers to atmospheric deposition direct to nontidal surface waters. Although the percentage 

contribution of phosphorus from nontidal deposition is provided here, the overall amount of phosphorus contributed 

from nontidal deposition is considered to be insignificant. 

4‐5 December 29, 2010
Chesapeake Bay TMDL

4‐6 December 29, 2010

Table 4-3. Percentage of sediment delivered to the Bay from each jurisdiction by 

pollutant source sector 

Jurisdiction Agriculture Forest

Stormwater

runoff

Point 

source Septic

Nontidal 

deposition

Delaware 1% 0% 1% 0% -- -- 

District of Columbia 0% 0% 1% 27% -- -- 

Maryland 15% 13% 32% 11% -- -- 

New York 3% 8% 4% 3% -- -- 

Pennsylvania 35% 34% 21% 23% -- -- 

Virginia 41% 40% 39% 35% -- -- 

West Virginia 5% 5% 3% 1% -- -- 

Total 100% 100% 100% 100% -- -- 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Note: Only land-based sources of sediment were included in this table. Septic sources discharge to groundwater and 

nontidal deposition refers to atmospheric deposition direct to nontidal surface waters. 

The following sections provide additional details regarding the major pollutant source sectors, 

including descriptions of the extent/magnitude of the pollutant source, geographic distribution, 

and long-term trends relevant to the source sector. The significance of the source sector in terms 

of loading to the Bay relative to other sources is also discussed. 

4.4 REGULATED POINT SOURCES 

Point sources are defined as any “discernable, confined, and discrete conveyance, including...any 

pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated 

animal feeding operation, landfill leachate collection system, or vessel or other floating craft, 

from which pollutants are or may be discharged” [CWA section 502(14), 40 CFR 122.2]. That 

definition does not include agricultural stormwater discharges or return flows from irrigated 

agriculture, which are exempt from the definition of point source under the CWA. The NPDES 

program, under CWA sections 318, 402, and 405, requires permits for the discharge of pollutants 

from point sources. 

Two issues that directly affect modeling of the regulated point sources in the Bay watershed are 

the size of facility flows and permitted discharge limits. For purposes of the Chesapeake Bay 

TMDL analysis and modeling, regulated point sources in the Chesapeake Bay watershed have 

been evaluated under the following categories1

: 

 Municipal wastewater facilities 

 Industrial wastewater facilities 

 CSOs 

 NPDES permitted stormwater (MS4s, industrial, and construction) 

 NPDES permitted CAFOs 

 

1

 The universe of regulated point sources may change over time due to such actions as designation, compliance 

evaluation, or new permitting activities. 
Chesapeake Bay TMDL

The remainder of this section outlines the distinctions between significant and nonsignificant 

municipal and industrial wastewater discharge facilities in the Bay watershed, explains how the 

facilities were addressed in modeling, discusses the effect of the basinwide nitrogen and 

phosphorus permitting approach on point source modeling for the TMDL, and provides a 

summary of model-estimated loads associated with each of the regulated point source categories 

of nitrogen, phosphorus, and sediment to the Bay. Appendix Q includes the regulated point 

sources accounted for in the Bay TMDL. 

4.4.1 Significant and Nonsignificant Municipal and Industrial Facilities 

Municipal and industrial wastewater discharge facilities are categorized as significant or 

nonsignificant primarily on the basis of permitted or existing flow characteristics and comparable 

loads in the case of industrial discharge facilities. The Bay jurisdictions define significant 

facilities as outlined in Table 4-4. 

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

wastewater discharge facilities 

Jurisdiction 

Municipal wastewater facilities 

(million gallons per day) 

Industrial wastewater facilities 

(estimated loads, 

pounds per year) 

Delaware Design flow ≥ 0.4 

District of Columbia Blue Plains WWTP 

Maryland Design flow ≥ 0.5 

New York Design flow ≥ 0.4 

Pennsylvania Existing flow ≥ 0.4 

Design flow ≥ 0.5a

Design flow ≥ 0.1b

Virginia 

New facilities ≥ 0.04c

West Virginia Design flow ≥ 0.4 

≥ 3,800 total phosphorus 

 or ≥ 27,000 total nitrogen 

Source: USEPA 2010b 

Notes: a. Above the fall line/tidal line; b. Below the fall line/tidal line; c. Also includes expansion of flows ≥ 0.04 mgd. 

Jurisdictions also may identify specific facilities as significant in their WIPs (USEPA 2009c). 

Facilities not meeting the above criteria, and not otherwise identified in the jurisdictions’ WIPs, 

are considered nonsignificant facilities. Table 4-5 provides a jurisdictional breakdown of 

municipal and industrial discharging facilities in the Chesapeake Bay watershed. 

For the TMDL, facilities were represented using various flow and discharge concentrations 

depending on their status as significant or nonsignificant. Significant facilities received 

individual WLAs, except for New York and the Virginia James River Basin, which received an 

aggregate WLA. The New York WLA for wastewater is discussed further in Section 8.4.4, and 

the James River Basin WLA is discussed further in Appendix X. Nonsignificant facilities were 

generally included in the aggregate WLAs by Bay segment watershed (USEPA 2009c) and are 

discussed further in Section 8.3.3. 

4‐7 December 29, 2010
Chesapeake Bay TMDL

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

discharging facilities by jurisdiction as of December 2010 

Significant facility Nonsignificant facility 

Jurisdiction Municipal Industrial Total Municipal Industrial Total 

Total 

Facilities

DCa 1 0 1 1 9 10 11

DE 3 1 4 1 1 2 6

MD 75 12 87 163 477 640 727

NY 26 2 28 26 45 71 99

PA 183 30 213 1246 409 1655 1868

VA 101 24 125 1618 639 2257 2382

WVb 13 7 20 125 23 148 168

Total 402 76 478 3180 1603 4783 5261

Source: Facilities identified in the final phase 1 WIPs 

Notes: 

a. Blue Plains WWTP serves DC and parts of MD and VA, but is only counted once. 

b. Multiple facilities (4) share one NPDES permit in West Virginia. 

4.4.2 Basinwide NPDES Permitting Approach 

In 2004 EPA and the Bay watershed jurisdictions agreed to take a consistent approach to 

permitting all the significant municipal and industrial wastewater discharging facilities 

contributing nitrogen and phosphorus to the Chesapeake Bay watershed (USEPA 2004d). As part 

of that approach and on the basis of the jurisdictions’ revised Chesapeake Bay WQS, permits are 

to be reissued with nitrogen and phosphorus limits that are sufficient to achieve Bay WQS and 

that are consistent with the jurisdictions’ tributary strategies. The basinwide permitting approach 

also contains additional specific provisions for permitting of nitrogen and phosphorus in the Bay 

watershed, including the following: 

 Annual load limits—Unless such expressions would be impracticable, EPA’s regulations 

require NPDES permits for non-publicly owned treatment works to express effluent limits 

as maximum daily and average monthly limits [40 CFR 122.45(d)(1)] and require NPDES 

permits for POTWs to express effluent limits as average weekly and average monthly 

limits [40 CFR 122.45(d)(2)]. In the case of the Chesapeake Bay permitting for nitrogen 

and phosphorus, EPA has determined that because of the long hydraulic durations in the 

Bay, and the fact that the control of annual loading levels of nitrogen and phosphorus from 

wastewater treatment plants is much more relevant and appropriate in terms of the effect of 

nitrogen and phosphorus on Bay water quality criteria than daily maximums or weekly or 

monthly averages, expression of nitrogen and phosphorus effluent limits in short periods is 

impracticable and that, therefore, such effluent limits may be expressed as an annual load 

(USEPA 2004c). 

 Compliance Schedules—Compliance schedules that are consistent with jurisdiction 

tributary strategies may be incorporated into permits, where such compliance schedules are 

needed, appropriate, and allowable under jurisdiction WQS and federal NPDES 

requirements (USEPA 2004d). 

 Watershed permits/trading—Watershed permits, which may accommodate nitrogen and 

phosphorus trading, may be used if such an approach would ensure protection of applicable 

4‐8 December 29, 2010
Chesapeake Bay TMDL

jurisdiction WQS and would be consistent with existing EPA policy regarding trading 

(USEPA 2004d). 

In 2005 the seven Bay jurisdictions began implementing the new permitting approach. As of 

June 2010, the permits for the significant nitrogen and phosphorus sources have been issued with 

nitrogen and phosphorus limits consistent with the Tributary Strategy allocations (described in 

Section 1.2.1) (some of which may include compliance schedules) to 64 percent of the 

significant wastewater treatment facilities (305 out of the total 478), accounting for 74 percent of 

the total design flow, 76 percent of the total nitrogen loads and 91 percent of the total phosphorus 

loads from significant facilities (Table 4-6). 

By the end of 2011, EPA expects all 478 significant wastewater treatment facilities in the Bay 

watershed to have annual nitrogen and phosphorus load limits in place in their permits (some of 

which may have compliance schedules as well). 

Table 4-6. Nitrogen and phosphorus permit tracking summary under the Basinwide 

NPDES Wastewater Permitting Approach, through December 2010 

Jurisdiction 

Significant 

facility 

NPDES 

Permits 

drafted 

Permits 

issued 

Design flow of 

facilities 

permits 

issued 

Percent of design 

flow for permits 

issued/significant 

facilities 

DCa 1 1 1 152.5 100% 

DE 4 4 4 3.3 100% 

MD 87 72 51 357.7 42% 

NY 28 1 1 20.0 22% 

PA 213 141 103 434.1 67% 

VA 125 125 125 1,253.5 100% 

WVb 20 16 16 27.737 100% 

Total 478 364 305 2,259.7 74% 

Source: USEPA Region 3, Region 2, Facilities identified in the final Phase 1 WIPs 

Notes: 

Some industrial design flows are not available or not comparable and not listed in the database. Some permits may 

contain compliance schedules. 

a. Blue Plains WWTP serves DC and parts of MD and VA, but is only counted once. 

b. Multiple facilities (4) share one NPDES permit in West Virginia. 

4.5 REGULATED POINT SOURCE LOAD SUMMARIES 

This section presents load estimates for each major point source sector. 

4.5.1 Municipal Wastewater Discharging Facilities 

A municipal wastewater facility is defined as a facility discharging treated wastewater from 

municipal or quasi-municipal sewer systems. EPA identified 3,582 NPDES permitted facilities 

as discharging municipal wastewater into the Chesapeake Bay watershed. Table 4-7 provides a 

summary of municipal wastewater facilities by jurisdiction; a complete list is available in 

Appendix Q. 

4‐9 December 29, 2010
Chesapeake Bay TMDL

Table 4-8 and Table 4-9 summarize modeled 2009 municipal wastewater loading estimates by 

jurisdiction and major river basin, respectively, for total nitrogen and phosphorus loads delivered 

to the Chesapeake Bay. Modeled sediment loads for those facilities are not presented because 

wastewater discharging facilities represent a de minimis source of sediment (i.e., less than 0.5 

percent of the 2009 total sediment load). In 2009 municipal wastewater treatment facilities 

contributed an estimated 17 percent of the total nitrogen and 16 percent of the total phosphorus 

loads delivered to Chesapeake Bay. 

Table 4-7. Municipal wastewater facilities by jurisdiction 

Jurisdiction Significant Nonsignificant 

DC 1 1 

DE 3 1 

MD 75 163 

NY 26 26 

PA 183 1246 

VA 101 1618 

WV 13 125 

Total 402 3180 

Source: EPA Region 3, EPA Region 2 

Note: Blue Plains wastewater treatment plant serves DC and portions of Maryland and Virginia but is counted once in 

this table as a DC plant. 

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

Chesapeake Bay 

Jurisdiction 

Flow 

(mgd) 

Total nitrogen delivered

(lb/yr)

Total phosphorus delivered 

(lb/yr) 

DC 140 2,387,918 20,456

DE 2 42,529 4,984

MD 563 11,928,717 568,905

NY 62 1,360,684 159,096

PA 335 9,391,741 740,397

VA 585 16,926,806 1,047,998

WV 13 188,137 62,674

Total 1,698 42,226,535 2,604,509

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

delivered to Chesapeake Bay 

Basin 

Flow

(mgd)

Total nitrogen delivered

(lbs/yr)

Total phosphorus delivered

(lbs/yr)

Susquehanna River 383 10,556,831 835,426

MD Eastern Shore 25 696,872 70,540

MD Western Shore 254 7,279,406 331,362

Patuxent River 58 640,507 61,948

Potomac River 635 9,475,644 412,464

Rappahannock River 23 376,453 46,463

York River 20 691,550 45,012

James River 299 12,494,335 798,615

VA Eastern Shore < 1 14,937 2,679

Total 1,698 42,226,535 2,604,509

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

4‐10 December 29, 2010
Chesapeake Bay TMDL

Figure 4-7 and Figure 4-8 illustrate the prevalence and locations of significant and nonsignificant 

municipal wastewater discharge facilities, respectively, across the watershed. 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

4‐11 December 29, 2010
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

Data related to municipal and industrial facilities are in the Bay Watershed Model point source 

database maintained by the CBP and include information for the 478 significant industrial, 

municipal, and federal facilities discharging directly to the surface waters in the watershed. The 

wastewater data used to calibrate the Bay Watershed Model cover the 1984 to 2005 time frame and 

are updated annually as data become available. Data are largely supplied by the seven watershed 

4‐12 December 29, 2010
Chesapeake Bay TMDL

jurisdictions but are also obtained from NPDES permit databases, including EPA’s Permit 

Compliance System (PCS) and jurisdiction discharge monitoring reports (DMRs). For each facility 

outfall, the database includes monthly flow and monthly average concentrations for total nitrogen, 

ammonia, nitrate and nitrite, total organic nitrogen, total phosphorus, orthophosphate, total organic 

phosphorus, total suspended solids, biological oxygen demand, and DO. 

Because the Bay jurisdictions are required to submit monthly concentration and flow data to 

EPA for only significant dischargers, the Bay Watershed Model point source database does not 

include comprehensive information useful for characterizing the nonsignificant facilities 

(especially nonsignificant industrials) for the Bay TMDL. For nonsignificant municipal facilities, 

all Bay jurisdictions conducted a one-time data collection in 2008 for the nitrogen and 

phosphorus discharge data, and estimates are based on any available data sources and default 

values recommended in Chesapeake Bay Watershed Model Application and Calculation of 

Nutrient and Sediment Loadings – Appendix F: Phase IV Chesapeake Bay Watershed Model 

Point Source Load (CBP 1998). EPA supplemented this information by querying the Integrated 

Compliance Information System database (ICIS) for jurisdictions that have migrated to ICIS as 

of 2009 (District of Columbia, Maryland, Pennsylvania, and New York), querying the PCS 

database for jurisdictions that have not yet migrated to ICIS (Delaware, Virginia and West 

Virginia), and obtaining Maryland and Virginia facility information directly from Maryland 

Department of the Environment (MDE) and Virginia Department of Environmental Quality 

(VADEQ), respectively. 

For more information regarding the data used to represent municipal wastewater discharge 

facilities and how they were incorporated into modeling for the TMDL, see Section 7 of the Bay 

Watershed Model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169

Appendix Q provides facility-specific information including NPDES ID, location, and more for 

all wastewater dischargers accounted for in the Bay TMDL. 

4.5.2 Industrial Discharge Facilities 

Industrial discharge facilities are facilities discharging process water, cooling water, and other 

contaminated waters from industrial or commercial sources. EPA identified 1,679 NPDES 

permitted facilities discharging industrial wastewaters in the Chesapeake Bay watershed (Table 

4-10, Appendix Q), with 76 significant facilities (Figure 4-9) and 1,603 nonsignificant facilities 

(Figure 4-10). In 2009 industrial wastewater discharging facilities contributed an estimated 7.3 

million pounds of the total nitrogen and 1.27 million pounds of the total phosphorus loads 

delivered to Chesapeake Bay (Table 4-11 and Table 4-12) an estimated 3 percent and 8 percent, 

respectively, of all nitrogen and phosphorus loads delivered to the Chesapeake Bay. 

Table 4-12 summarizes modeled wastewater nitrogen and phosphorus loading estimates using 

2009 loading conditions. Modeled sediment loads for industrial or commercial facilities are not 

presented because their wastewater discharges represent a de minimis source of sediment (i.e., 

less than 0.5 percent of the 2009 total sediment load). 

4‐13 December 29, 2010
Chesapeake Bay TMDL

Table 4-10. Industrial wastewater facilities 

Jurisdiction Significant Nonsignificant 

DC 0 9 

DE 1 1 

MD 12 477 

NY 2 45 

PA 30 409 

VA 24 639 

WV 7 23 

Total 76 1,603 

Source: USEPA Region 3, Region 2 

Table 4-11. 2009 Load estimates of industrial facility discharges 

Jurisdiction 

Flow

(mgd)

Total nitrogen delivered

(lbs/yr)

Total phosphorus delivered

(lbs/yr)

DC 13 183,490 20,433

DE < 1 95,438 71

MD 48 1,989,243 267,093

NY 7 126,897 19,971

PA 179 2,010,639 260,140

VA 160 2,883,828 649,266

WV 14 55,213 53,592

 Total 422 7,344,748 1,270,566

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

wastewater facility discharges by major river basin 

Basin 

Flow 

(mgd) 

Total nitrogen delivered 

(lbs/yr) 

Total phosphorus delivered 

(lbs/yr) 

Susquehanna River 184 2,171,197 281,922 

MD Eastern Shore 5 302,210 45,626 

MD Western Shore 21 1,369,383 105,100 

Patuxent River 3 50,615 38,689 

Potomac River 71 779,885 420,997 

Rappahannock River 5 78,006 36,039 

York River 81 478,892 81,675 

James River 51 1,979,297 259,331 

VA Eastern Shore 1 135,211 1,160 

 Total 422 7,344,697 1,270,539 

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

4‐14 December 29, 2010
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

4‐15 December 29, 2010
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario. 

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

4‐16 December 29, 2010
Chesapeake Bay TMDL

Discharge Monitoring Report (DMR) data from the population of industrial facilities were used 

to derive loadings where available. The majority of nonsignificant industrial facilities do not 

have DMR data for nitrogen and phosphorus. However, the default values from typical pollutant 

concentrations (Tetra Tech 1999) were used to estimate the loads where DMR data are not 

available, except for power plants and other facilities with high flows. 

Industrial facilities, such as power plants, petroleum refineries, and steel mills, that were not on 

the significant facility list were considered as high-flow, nonsignificant facilities in the 

evaluation. Nitrogen and phosphorus loads resulting from the use of flue gas desulfurization 

units, effluent from coal ash ponds and biocide applications at high-flow facilities were estimated 

from available databases. Data sets queried include EPA’s PCS and ICIS permit systems, 316(b) 

cooling water intake structure regulation data, U.S. Department of Energy’s Energy Information 

Administration data, and EPA’s eGrid database. 

Thirty-two power plants were identified as being in the Chesapeake Bay watershed. Eight of 

those facilities use cooling towers as part of their cooling system. Of the 32 facilities, 18 use coal 

as a fuel source; 7 use a flue gas desulfurization, and 13 use ash ponds. Eighty-nine other highflow industrial sites were identified in the watershed and represent a variety of industrial 

activities. 

Pollutant loads were estimated for the eight facilities that use cooling towers. The PCS and ICIS 

databases were queried for blowdown flows, and cooling tower chemical vendors were consulted 

to estimate water quality conditions in the towers. Facility use rates were then obtained from 

EPA’s eGrid database to characterize utilization routines and variability in blowdown events. 

Similarly, flue gas desulfurization and ash pond loads were estimated using data obtained from 

the PCS and ICIS databases. 

4.5.3 Combined Sewer Overflows 

Combined sewer systems (CSS) are sewers that are designed to collect rainwater runoff, 

domestic sewage, and industrial wastewater in the same pipe. Normally, the systems transport 

wastewater to a treatment plant, where it is treated and discharged to surface waters. However, 

during heavy rainfall or snowmelt, flow volumes in a CSS can exceed the capacity of the sewer 

system or treatment plant. To avoid situations where excess flows overwhelm the sewer network 

or the treatment capacity of the treatment system, CSSs are designed to overflow during times of 

high volume, discharging untreated excess wastewater directly to nearby streams, rivers, or other 

waterbodies. 

Such overflows, called combined sewer overflows (CSOs), contain stormwater and untreated 

human and industrial waste, toxic materials, and debris. There are 64 CSO communities in the 

Chesapeake Bay watershed (Table 4-13 and Figure 4-11). 

4‐17 December 29, 2010
Chesapeake Bay TMDL

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

Jurisdiction River basin NPDES ID Facility name 

DC Potomac DC0021199 Washington, District of Columbia 

DE Eastern Shore DE0020265 Seaford Waste Treatment Plant 

MD Eastern Shore MD0020249 Federalsburg WWTP 

MD Eastern Shore MD0021571 City of Salisbury WWTP 

MD Potomac MD0021598 Cumberland WWTP 

MD Patapsco MD0021601 Patapsco WWTP 

MD Eastern Shore MD0021636 Cambridge WWTP 

MD Eastern Shore MD0022764 Snow Hill Water & Sewer Department 

MD Potomac MD0067384 Westernport CSO 

MD Potomac MD0067407 Allegany County CSO 

MD Potomac MD0067423 Frostburg CSO 

MD Potomac MD0067547 Lavale Sanitary Commission CSO 

NY Susquehanna NY0023981 Johnson City (V) Overflows 

NY Susquehanna NY0024406 Binghamton (C) CSO 

NY Susquehanna NY0035742 Chemung Co Elmira SD STP 

PA Susquehanna PA0020940 Tunkhannock Boro Municipal Authority 

PA Susquehanna PA0021237 Newport Boro STP 

PA Susquehanna PA0021539 Williamsburg Municipal Authority 

PA Susquehanna PA0021571 Marysville Borough WWTP 

PA Susquehanna PA0021687 Wellsboro WWTP 

PA Susquehanna PA0021814 Mansfield Boro WWTP 

PA Susquehanna PA0022209 Bedford WWTP 

PA Susquehanna PA0023248 Berwick Area Joint Sewer Authority WWTP 

PA Susquehanna PA0023558 Ashland WWTP 

PA Susquehanna PA0023736 Tri-Boro Municipal Authority WWTP 

PA Susquehanna PA0024341 Canton Boro Auth. WWTP 

PA Susquehanna PA0024406 Mount Carmel WWTF 

PA Susquehanna PA0026107 Wyoming Valley Sanitary Authority WWTP 

PA Susquehanna PA0026191 Huntingdon Borough WWTP 

PA Susquehanna PA0026310 Clearfield Mun. Auth. WWTP 

PA Susquehanna PA0026361 Lower Lackawanna Valley Sanitary Authority WWTP 

PA Susquehanna PA0026492 Scranton Sewer Authority WWTP 

PA Susquehanna PA0026557 Sunbury City Municipal Authority WWTP 

PA Susquehanna PA0026743 Lancaster City WWTP 

PA Susquehanna PA0026921 Greater Hazelton Joint Sewer Authority WWTP 

PA Susquehanna PA0027014 Altoona City Auth. - Easterly WWTP 

PA Susquehanna PA0027022 Altoona City Auth. - Westerly WWTF 

PA Susquehanna PA0027049 Williamsport Sanitary Authority – West Plant 

PA Susquehanna PA0027057 Williamsport Sanitary Authority – Central Plant 

PA Susquehanna PA0027065 LRBSA - Archbald WWTP 

PA Susquehanna PA0027081 LRBSA - Clinton WWTP 

PA Susquehanna PA0027090 LRBSA - Throop WWTP 

PA Susquehanna PA0027197 Harrisburg Advanced WWTF 

PA Susquehanna PA0027324 Shamokin Coal Twp Joint Sewer Authority 

PA Susquehanna PA0028631 Mid-Cameron Authority 

4‐18 December 29, 2010
Chesapeake Bay TMDL

4‐19 December 29, 2010

Jurisdiction River basin NPDES ID Facility name 

PA Susquehanna PA0028673 Gallitzin Borough Sewer and Disposal Authority 

PA Susquehanna PA0036820 Galeton Borough Authority WWTP 

PA Susquehanna PA0037711 Everett Area WWTP 

PA Susquehanna PA0038920 Burnham Borough Authority WWTP 

PA Susquehanna PA0043273 Hollidaysburg STP 

PA Susquehanna PA0046159 Houtzdale Boro Municipal Sewer Authority 

PA Susquehanna PA0070041 Mahanoy City Sewer Authority WTP 

PA Susquehanna PA0070386 Shenandoah Municipal Sewer Authority WWTP 

PA Susquehanna PAG062202 Lackawanna River Basin Sewer Authority. 

PA Susquehanna PAG063501 Steelton Boro Authority 

VA James VA0063177 Richmond 

VA James VA0024970 Lynchburg 

VA James VA0025542 Covington Sewage Treatment Plant 

VA Potomac VA0087068 Alexandria 

WV Potomac WV0020150 City of Moorefield 

WV Potomac WV0021792 City of Petersburg 

WV Potomac WV0023167 City of Martinsburg 

WV Potomac WV0024392 City of Keyser 

WV Potomac WV0105279 City of Piedmont 

CSOs are considered point sources and are assigned WLAs in this TMDL. EPA’s CSO Control 

Policy is the national framework for implementing controls on CSOs through the NPDES 

permitting program. The policy resulted from negotiations among EPA, municipal organizations, 

environmental groups, and state agencies. It provides guidance to municipalities and state and 

federal permitting authorities on how to meet the CWA’s pollution control goals as flexibly and 

cost-effectively as possible. The CSO policy was published in the Federal Register (FR) (59 FR 

18688, April 19, 1994). CSO communities are required to develop Long-Term Control Plans 

(LTCPs), detailing steps necessary to achieve full compliance with the CWA. 

EPA relied on various sources of information to characterize the prevalence of CSOs in the Bay 

watershed and to quantify their loads for the Bay TMDL. There are 64 CSO communities in the 

Bay watershed (Table 4-13). Overflow volume and pollutant loading from CSO communities are 

heavily dependent on the service area or catchment area of the combined system. Service area 

data obtained from the communities were used to calculate the loading from each community 

during high-flow events. Precipitation data observations were also obtained from weather 

monitoring stations proximate to each community to derive runoff volumes. Estimates of 

overflows and associated pollutant loads from CSO communities were then developed using 

various sources of water quality data including monitoring data and literature values. 
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

4‐20 December 29, 2010
Chesapeake Bay TMDL

For four of the largest CSO communities in the watershed—Alexandria, Virginia; Lynchburg, 

Virginia; Richmond, Virginia; and the District of Columbia—EPA relied heavily on readily 

available and relatively detailed LTCPs to characterize overflows. In addition, EPA ran 

simulations of existing sewer models for those communities to support developing overflow and 

water quality estimates. EPA used the District of Columbia’s CSS model to develop loading 

estimates for the CSOs. For the Alexandria, Richmond, and Lynchburg CSSs, various versions 

of EPA’s Storm Water Management Model (SWMM) were used to estimate overflows. CSO 

discharge monitoring data were available for the Alexandria and Richmond CSSs, but no 

samples were available from Lynchburg because the LTCP calls for complete separation of this 

system (i.e., separation of the storm sewers from sanitary sewers). 

Information related to loading from the other 60 CSO communities in the watershed includes 

spatial data collected as a result of a direct survey of the communities to support the TMDL, 

limited water quality and overflow data from some of the CSO communities in the watershed, 

and representative water quality concentrations available in the literature. For further information 

regarding the data used to estimated CSO loads, see Section 7 of the Chesapeake Bay Watershed 

Model documentation at http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169. 

To avoid the difficulty of measuring LTCP implementation progress with weather-dominated 

CSO loading estimates, EPA used the 10-year average CSO loads for 1991–2000, which 

correlates with the hydrologic period selected for the TMDL (see Section 6.1.1). The loads from 

that 10-year period were used as the baseline to assess CSO progress and WLAs. Any CSO 

implementation progress will be tracked and input in the model as a reduction factor to represent 

a reduction achieved from the baseline. Thus, any reduction will be from management actions 

only and not from climate variation. The CSS land use will be changed to urban area for 

stormwater simulation in the model if there is CSS separation in the implementation plan and the 

separation acreage is reported with the reduction factor for implementation progress tracking. 

4.5.4 Sanitary Sewer Overflows 

Properly designed, operated, and maintained sanitary sewer systems are meant to collect and 

transport all the sewage that flows into them to a WWTP. SSOs are illegal discharges of raw 

sewage from municipal sanitary sewer systems. Frequent SSOs are indicative of problems with a 

community’s collection system and can be due to multiple factors: 

 Infiltration and inflow contributes to SSOs when rainfall or snowmelt infiltrates through 

the ground into leaky sanitary sewers or when excess water flows in through roof drains 

connected to sewers, broken pipes, or badly connected sewer service lines. Poor service 

connections between sewer lines and building service lines can contribute as much as 60 

percent of SSOs in some areas. 

 Undersized systems contribute to SSOs when sewers and pumps are too small to carry 

sewage from newly developed subdivisions or commercial areas. 

 Pipe failures contribute to SSOs as a result of blocked, broken, or cracked pipes; tree roots 

growing into the sewer; sections of pipe settling or shifting so that pipe joints no longer 

match; and sediment and other material building up causing pipes to break or collapse. 

 Equipment failures contribute to SSOs because of pump failures or power failures. 

4‐21 December 29, 2010
Chesapeake Bay TMDL

SSOs represent a source of nitrogen and phosphorus to the Chesapeake Bay; however, 

information available to characterize their contribution to the overall nitrogen and phosphorus 

loads delivered to the Bay is limited largely because of their illegality and infrequency. Although 

the Bay Watershed Model does not specifically account for SSOs, the nitrogen and phosphorus 

load contributions from SSOs are part of the background conditions incorporated into the Phase 

5.3 watershed model and, therefore, such loads are accounted for in the data used for calibration 

of the Bay Watershed Model. Because SSOs are illegal, however, the Chesapeake Bay TMDL 

assumes full removal of SSOs and makes no allocation to them. 

4.5.5 NPDES Permitted Stormwater 

Urban and suburban stormwater discharges contain nitrogen, phosphorus, and sediment from 

sources such as pet wastes, lawn fertilizers, construction activity, impervious surfaces, and air 

contaminants. The in-stream bank and bed scouring caused by increased volumes and durations 

of stormwater discharges contribute additional sediment and nitrogen and phosphorus loads to 

the Bay and its tributaries. Those nitrogen, phosphorus, and sediment loads affect local water 

quality, habitats, and the Bay downstream and represent a significant proportion of nitrogen, 

phosphorus, and sediment loads to Bay. The CBP estimates that in 2009 stormwater from urban 

and suburban development contributed to 16 percent of the sediment loadings, 15 percent of the 

phosphorus loadings, and 8 percent of the nitrogen loadings to the Bay (Bay Watershed Model 

2009 Scenario). 

Under the federal stormwater regulatory program, three broad categories of stormwater 

discharges are regulated (see 40 CFR 122.26, CFR 122.30-37): 

 Stormwater discharges from medium and large Municipal Separate Storm Sewer Systems 

(MS4s) and small MS4s in Census Bureau defined urbanized areas 

 Stormwater discharges associated with construction activity 1 acre and larger 

 Stormwater discharges associated with specified categories of industrial activity 

In addition, EPA established a process for designating and requiring NPDES permit coverage for 

additional stormwater discharges, implementing section 402(p)(2)(E). This residual designation 

authority (RDA) of section 402(p)(2)(E) is in 40 CFR 122.26(a)(9)(i)(C) and (D). EPA retains 

additional authority in CWA section 402(p)(5) and (6) to designate additional point sources of 

stormwater. 

EPA’s intent in creating the MS4 Stormwater Program was to regulate stormwater discharges by 

requiring the municipalities to develop management programs to control stormwater discharging 

via the MS4, i.e., stormwater collected by the MS4 from throughout its service area. 

CWA section 402(p) establishes the framework for EPA to address stormwater discharges. In 

Phase I, EPA established NPDES permit requirements for stormwater discharges associated with 

 Industrial activity, including construction activity disturbing 5 acres or greater, including 

sites smaller than 5 acres if they are associated with a common plan of development or sale 

that is at least 5 acres in size 

 Discharges from MS4s serving populations of 100,000 or more 

4‐22 December 29, 2010
Chesapeake Bay TMDL

In Phase II, EPA established permit requirements for stormwater discharges from 

 Construction activity disturbing 1 to 5 acres, including sites smaller than 1 acre if they are 

associated with a common plan of development or sale that is at least 1 acre in size 

 Small MS4s serving populations of fewer than 100,000 in urbanized areas 

With respect to Phase II MS4s, EPA considers stormwater discharges from within the geographic 

boundary of the urbanized area (and designated areas) served by small MS4s to be regulated (64 

FR 68722, 68751-52 and 68804, Appendix 2, December 8, 1999). The reason for regulating 

small MS4s in urbanized areas was based on the correlation between the degree of development/ 

urbanization and adverse water quality impacts from stormwater discharged from such areas. 

EPA can and has designated additional stormwater discharges, such as those from impervious 

surfaces above a certain size threshold, using its residual designation authority under 40 CFR 

122.26(a)(9)(i)(C) and (D). At the discretion of the NPDES permitting authority, stormwater 

dischargers that require NPDES permits can either obtain individual permits or, with the 

exception of medium and large MS4s, obtain coverage under general permits (see 40 CFR 

122.28). Also, EPA has additional authority in CWA section 402(p)(5) and (6) to designate 

additional point sources of stormwater. 

Figure 4-12 shows the locations of Phase I and II MS4s in the Bay watershed. 

Unless stormwater discharges are identified in EPA’s Phase I or Phase II regulations or are 

designated pursuant to CWA section 402(p)(2)(E) or 402(p)(6), the discharges are not regulated 

under CWA section 402. As explained in EPA guidance, “stormwater discharges that are 

regulated under Phase I or Phase II of the NPDES stormwater program are point sources that 

must be included in the WLA portion of a TMDL” (USEPA 2002). Appendix Q includes the 

stormwater permits subject to this Bay TMDL. 

It is estimated that existing NPDES MS4 areas contributed approximately 7,027,362 lbs total 

nitrogen, 900,868 lbs total phosphorus, and 287,295 tons of sediment annually in 2009. That 

compares to the total load delivered annually to the Bay of 251,040,081 lbs total nitrogen, 

16,619,332 lbs total phosphorus and 4,000,118 tons sediment by all sources (Bay Watershed 

Model 2009 Scenario). 

The contribution from industrial stormwater discharges subject to NPDES permits has been 

estimated on the basis of data submitted by jurisdictions in their Phase I WIPs, including the 

number of industrial stormwater permits per county and the number of urban acres regulated by 

industrial stormwater permits. For the Bay TMDL, the permitted industrial stormwater load is 

subtracted from the MS4 load when applicable. Table 4-14 provides an accounting of the current 

individual and general stormwater NPDES permits issued within the Chesapeake Bay watershed. 

4‐23 December 29, 2010
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

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

4‐24 December 29, 2010
Chesapeake Bay TMDL

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

watershed, summer 2009 

NPDES Stormwater permit type 

Jurisdiction 

MS4 

Phase I 

MS4 

Phase II Industrial Construction Total 

% 

Permittees 

in the Bay 

Baywide 1 0 60 212 273 1.6%

DC Districtwide 1 0 60 212 273

Baywide 1 0 48 NA* 49 0.3% 

DE Statewide 14 3 337 1,375 1,729

Baywide 11 82 1,578 8,300 9,971 57.6%

MD Statewide 11 82 1,578 8,332 10,003

Baywide 0 34 122 470 626 3.6%

NY Statewide 1 502 1,393 7,251 9,147

Baywide 0 206 1,238 906 2,350 13.6%

PA Statewide 2 727 2,494 2,399 5,622

Baywide 11 75 975 2,252 3,313 19.2%

VA Statewide 11 90 1,432 2,851 4,384

Baywide 0 3 113 651 767 4.4%

WV Statewide 0 45 933 2,488 3,466

Bay 23 400 4,086 12,791 17,300 100%

Total States 40 1,449 8,227 24,908 34,624

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario 

Note: Numbers of permittees are not static, and especially for categories like construction are fluctuating regularly. 

* Not including Delaware 

Data used to characterize loads from regulated stormwater activities and to represent these 

sources in the model are available from the jurisdictions’ NPDES programs and from EPA 

Region 3’s NPDES permitting, the permitting authority in the District of Columbia and for 

federal facilities in Delaware. Details related to how loads for MS4s and NPDES-permitted 

construction and industrial stormwater activities were derived for the Bay TMDL are in Section 

7 of the Phase 5 Chesapeake Bay Watershed Model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169. 

4.5.6 Concentrated Animal Feeding Operations 

The NPDES program regulates the discharge of pollutants from point sources to waters of the 

United States. Concentrated Animal Feeding Operations (CAFOs) are included in the definition 

of point sources in CWA section 502(14). To be considered a CAFO, a facility must first be 

defined as an AFO. 

AFOs are agricultural operations where animals are kept and raised in confined situations. AFOs 

generally congregate animals, feed, manure, dead animals, and production operations on a small 

land area. Feed is brought to the animals rather than the animals grazing or otherwise seeking 

feed in pastures. Such operations are defined as AFOs if animals are confined for 45 or more 

4‐25 December 29, 2010
Chesapeake Bay TMDL

days per year in facilities where vegetation and other growth are not present during the normal 

growing season [40 CFR 122.42(b)(1)]. 

AFOs that meet the regulatory definition of a CAFO or that are designated as a CAFO are 

regulated under the NPDES permitting program and are required to seek NPDES permit 

coverage if they discharge or propose to discharge. The NPDES regulations define AFOs as 

CAFOs based primarily on the number of animals confined (Table 4-15) (for example, a large 

dairy CAFO confines 700 or more dairy cattle) [40 CFR 122.23(b)(2), (4), and (6)]. An AFO that 

is not defined as a CAFO may be designated as a CAFO if it meets certain conditions [40 CFR 

122.23(c)]. 

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

Size thresholds 

(number of animals)

Animal sector Large CAFOs Medium CAFOs Small CAFOs

Cattle or cow/calf pairs 1,000 or more 300–999 less than 300

Mature dairy cattle 700 or more 200–699 less than 200

Veal calves 1,000 or more 300–999 less than 300

Swine (weighing over 55 pounds) 2,500 or more 750–2,499 less than 750

Swine (weighing less than 55 pounds) 10,000 or more 3,000–9,999 less than 3,000

Horses 500 or more 150–499 less than 150

Sheep or lambs 10,000 or more 3,000–9,999 less than 3,000

Turkeys 55,000 or more 16,500–54,999 less than 16,500

Laying hens or broilers (liquid manure handling 

systems) 

30,000 or more 9,000–29,999 less than 9,000

Chickens other than laying hens (other than a 

liquid manure handling systems) 

125,000 or more 37,500–124,999 less than 37,500

Laying hens (other than a liquid manure 

handling systems) 

82,000 or more 25,000–81,999 less than 25,000

Ducks (other than a liquid manure handling 

systems) 

30,000 or more 10,000–29,999 less than 10,000

Ducks (liquid manure handling systems) 5,000 or more 1,500–4,999 less than 1,500

Source: 40 CFR 122.23(b) 

Under federal regulations, NPDES permits for CAFOs require CAFOs to implement the terms of 

a site-specific nutrient management plan (NMP) that includes a number of critical minimum 

elements [40 CFR 122.42(e)(1)]. Those requirements limit nitrogen and phosphorus loads from 

the production area as well as from the land application area, where manure, litter and process 

wastewater must be applied in accordance with site-specific practices to ensure that nitrogen and 

phosphorus in the manure will be used appropriately. NPDES permits for all CAFOs must 

include technology-based effluent limits in accordance with 40 CFR 122.44. Permitted Large 

CAFOs that land-apply manure, litter or process wastewater must comply with technology-based 

effluent limitations for land application per the effluent limitations guidelines (ELGs) at 40 CFR 

412 (C) and (D). Unpermitted Large CAFOs may not have any discharges except for agricultural 

stormwater discharges from the land application area. 

4‐26 December 29, 2010
Chesapeake Bay TMDL

Agricultural stormwater discharges are the precipitation-related discharges from CAFO land 

application areas where the CAFO land applies manure, litter or process wastewater in 

accordance with nutrient management practices “that ensure appropriate agricultural utilization 

of the nutrients in the manure, litter or process wastewater” applied to the land—i.e., for 

permitted CAFOs, the terms of an NMP concerning land application [40 CFR 122.23(e)(1)]. 

State technical standards are used in calculating the technology-based effluent limits in NPDES 

permits of Large CAFOs. Requirements for land application areas at small and medium CAFOs 

are based on the best professional judgment of the permit writer, and may also incorporate state 

technical standards. The agricultural stormwater exemption does not apply to a CAFO’s 

production area. As a nonpoint source, an agricultural stormwater discharge is not subject to 

NPDES permitting requirements or water quality-based effluent limitations (WQBELs). 

Any permit issued to a CAFO of any size must include a requirement to implement an NMP that 

contains, at a minimum, BMPs that meet the requirements specified in 40 CFR 122.42(e)(1). 

These include the following: 

 Ensuring adequate storage of manure, litter, and process wastewater, including procedures 

to ensure proper operation and maintenance of the storage facility. 

 Managing mortalities to ensure that they are not disposed of in a liquid manure, 

stormwater, or process wastewater storage or treatment system that is not specifically 

designed to treat animal mortalities. 

 Ensuring that clean water is diverted, as appropriate, from the production area. 

 Preventing direct contact of confined animals with waters of the United States. 

 Ensuring that chemicals and other contaminants handled on-site are not disposed of in any 

manure, litter, process wastewater, or stormwater storage or treatment system unless 

specifically designed to treat such chemicals and other contaminants. 

 Identifying appropriate site-specific conservation practices to control runoff of pollutants to 

waters of the United States. 

 Identifying protocols for appropriate testing of manure, litter, process wastewater, and soil. 

 Establishing protocols to land apply manure, litter, or process wastewater in accordance 

with site-specific nutrient management practices that ensure appropriate agricultural 

utilization of the nutrients in the manure, litter or process wastewater. 

 Identifying specific records that will be maintained to document the implementation and 

management of the minimum elements described above. 

EPA and the jurisdictions have estimated the number of state or federal permitted CAFOs in the 

Chesapeake Bay watershed, in part, on the basis of the jurisdictions’ respective final Phase I 

WIPs (Table 4-16). 

4‐27 December 29, 2010
Chesapeake Bay TMDL

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

Jurisdiction # State or federal 

permitted CAFOs 

Delawarea 165 

Marylanda 365 

New York 65 

Pennsylvania 325 

Virginia 30 

West Virginia 30 

Total 980 

Sources: State data submitted to EPA for the Senate Environment and Public Works Committee Hearing on the 

Chesapeake Bay on April 20, 2009, and EPA Office of Wastewater Management’s latest NPDES CAFO Rule 

Implementation Status quarterly national CAFO number update. http://www.epa.gov/npdes/pubs/tracksum1Q10.pdf. 

Note: 

a. The numbers of CAFOs in Maryland and Delaware with permits are estimated according to the number of Notices 

of Intent (NOIs) received as a result of the EPA February 2009 permit application deadline. The NOIs are being 

reviewed for permit requirement completeness. 

4.6 NONPOINT SOURCES 

The term nonpoint source means any source of water pollution that does not meet the legal 

definition of point source (see Section 4.5). Nonpoint source pollution generally results from 

land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrologic modification. 

For purposes of the Chesapeake Bay TMDL analysis and modeling, nonpoint sources in the 

Chesapeake Bay watershed have been evaluated under the following categories: 

 Agriculture (manure, biosolids, chemical fertilizer) 

 Atmospheric deposition 

 Forest lands 

 On-site wastewater treatment systems (OSWTSs) 

 Nonregulated stormwater runoff 

 Oceanic inputs 

 Streambank and tidal shoreline erosion 

 Tidal resuspension 

 Wildlife 

For the Bay TMDL, Scenario Builder was used to provide the land use-based scenario inputs to 

the Bay Watershed Model including forest lands, OSWTSs , nonregulated stormwater runoff, 

oceanic inputs, streambank and tidal shoreline erosion, tidal resuspension, and wildlife (see 

Section 5.7). Data sources for agriculture and atmospheric deposition in the Chesapeake Bay 

watershed are included in the relevant sections below. Scenario Builder provides estimates of 

nitrogen and phosphorus loads to the land and the area of soil available to be eroded. Loads are 

input to the Bay Watershed Model to generate modeled estimates of loads delivered to the Bay. 

Additional information related to Scenario Builder and its application in Bay TMDL 

development (USEPA 2010d) is at 

http://archive.chesapeakebay.net/pubs/SB_V22_Final_12_31_2010.pdf. 

4‐28 December 29, 2010
Chesapeake Bay TMDL

4.6.1 Agriculture 

Agricultural lands account for 22 percent of the watershed, making agriculture one of the largest 

land uses in the area, second only to forested and open wooded areas (69 percent). The Bay 

watershed has more than 87,000 farm operations and 6.5 million acres of cropland. However, the 

District of Columbia does not include any agricultural lands. 

Farms in the Chesapeake Bay watershed produce more than 50 named commodities. The area’s 

primary crops are pasture, hay, corn, wheat, soybeans, vegetables, and fruits. The eastern part of 

the region is home to a rapidly expanding nursery and greenhouse industry. 

Animal operations account for more than 60 percent of the region’s annual farm product sales. In 

the watershed, the six major types of animal operations are dairy cows, beef cattle, pigs, egg 

production, broilers, and turkeys. The three major animal production regions in the watershed, 

according to livestock concentration, are the lower Susquehanna River in Pennsylvania, the 

Shenandoah Valley in Virginia and West Virginia, and the Delmarva Peninsula in Delaware, 

Maryland, and Virginia. The Delmarva Peninsula is considered to be one of the country’s top 

poultry producing regions and, according to the 2002 Census, three Bay counties are among the 

top 20 poultry producing counties in the nation (for either poultry/eggs, broilers, or layers): 

Sussex County, Delaware; Lancaster County, Pennsylvania; and Wicomico County, Maryland. 

In addition, at least one Bay county is among the top 20 counties for production of the following 

farm commodities: turkeys; cattle and calves; milk and other cow dairy products; hogs and pigs; 

horses and ponies; corn for silage; snap beans; apples; short rotation woody crops; and nursery, 

greenhouse, floriculture, and sod. 

Agriculture is the largest single source of nitrogen, phosphorus, and sediment loading to the Bay 

through applying fertilizers, tilling croplands, and applying animal manure. Agricultural 

activities are responsible for approximately 44 percent of nitrogen and phosphorus loads 

delivered to the Bay and about 65 percent of sediment loads delivered to the Bay (Bay 

Watershed Model 2009 Scenario). Figure 4-13 compares modeled loads from agricultural lands 

for 1985 and 2009. 

Data sources used to estimate nitrogen, phosphorus, and sediment from agriculture-related 

sources include information related to livestock production and manure generation, crop 

production and nutrient management, fertilizer use and application, and implementation of 

BMPs. EPA in cooperation with the Chesapeake Bay Program’s Agricultural Nutrient and 

Sediment Reduction Workgroup and Modeling Subcommittee relied on the many sources of 

information to characterize loads related to agriculture that are summarized in Section 2 of the 

Scenario Builder documentation Estimates of County-Level Nitrogen and Phosphorus Data for 

Use in Modeling Pollutant Reduction(USEPA 2010d). Examples of data sources are the U.S. 

Department of Agriculture (USDA) Agricultural Census; USDA, state, and university nutrient 

management standards and handbooks; peer-reviewed journal articles; agricultural conservation 

data from state agricultural and environmental agencies; county agencies, and nongovernmental 

organizations; and extensive input from members of the Chesapeake Bay Program’s Agricultural 

Nutrient and Sediment Reduction Workgroup. 

4‐29 December 29, 2010
Chesapeake Bay TMDL

Source: Phase 5.3 Chesapeake Bay Watershed Model 1985 and 2009 Scenarios 

Figure 4-13. 1985 and 2009 modeled total nitrogen, phosphorus, and sediment loads from agricultural lands 

across the Chesapeake Bay watershed. 

Manure 

Animal populations vary across the Bay watershed by animal type and management. Pastures 

exist in the watershed for dairy and beef heifers, goats, hogs, and in some places even chickens 

and turkeys. Animal feed BMPs are recognized by the Chesapeake Bay watershed model, and 

managing manure from production areas can include a suite of BMPs for storage and handling. 

Land application of manure is an important nitrogen and phosphorus recycling process in 

agriculture. Because manure is so extensively used as a resource of nitrogen and phosphorus, it is 

considered as important as inorganic fertilizer and is an important source of nonpoint source 

pollution. Figure 4-14 and Figure 4-15 provide historical population data of poultry and nonpoultry animals in the watershed, respectively. 

4‐30 December 29, 2010
Chesapeake Bay TMDL

Annual manure production is calculated as a daily excreted amount per animal equivalent unit (1 

animal equivalent unit equals 1,000 lbs live animal weight). Animal units are estimated for 

counties on the basis of USDA Agricultural Census data. The total amount of manure produced 

is then distributed among the applicable land uses, which include pasture, AFO, and other row 

crop land uses. The percentage of time animals spend in pasture (based on state 

recommendations) is used to estimate the percentage of total manure produced on pasture lands. 

For example, 50 percent pasture time equates to 50 percent of the total manure production 

occurring on pasture lands. Manure produced that is associated with time spent confined is 

considered to be generated on AFO acres. A fraction of that amount, (15–21 percent depending 

on animal type) is assumed to remain on the AFO acres (i.e., not captured by storage and 

handling activities), while the rest is redistributed by land application to pasture and row crop 

lands. The model simulates AFO acres similarly to urban impervious areas. 

Biosolids 

Applying biosolids, the nutrient-rich organic materials resulting from treating sewage sludge, as 

fertilizer to croplands represents another source of nutrients to the Bay. Biosolids typically 

contain plant nutrients (nitrogen, phosphorus, and potassium), although the amount of nutrients 

available from biosolids are normally lower than the amounts from most commercial fertilizers 

(Huddleston and Ronayne 1990). Nitrogen and phosphorus are the most prevalent nutrients 

found in sewage sludge. 

Source: 2007 Agriculture Census 

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

4‐31 December 29, 2010
Chesapeake Bay TMDL

Source: 2007 Agriculture Census 

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

Regulations governing use, disposal and application of sewage sludge are in EPA’s Sewage 

Sludge Use or Disposal Regulation (Part 503), which provides a framework for permitting 

sewage sludge use or disposal. No jurisdictions in EPA Region 3 have applied for program 

authorization of the federal Part 503. Although all Bay jurisdictions have their own sewage 

sludge programs in place, only Virginia routinely submits to EPA information regarding land 

application of biosolids. As a result, information available to characterize biosolids as a source 

and to represent it in the model is limited. 

For model characterization, jurisdiction-specific data on biosolids application were used. Land 

uses receiving biosolids include crops and pasture/hay, with different monthly proportions based 

on seasonal growing patterns. Modeled application rates are the same as manure because 

biosolids are applied to land in the same fashion as manure. 

For additional information related to representation of biosolids in the Bay TMDL, see the Phase 

5.3 Chesapeake Bay Watershed Model documentation at

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169

Chemical Fertilizer 

Chemical fertilizer application practices across the watershed can be estimated through 

commercial sales information. Fertilizer sales data are prepared by the Association of American 

Plant Food Control Officials on the basis of fertilizer consumption information submitted by 

state fertilizer control offices. The consumption data include total fertilizer sales or shipments for 

4‐32 December 29, 2010
Chesapeake Bay TMDL

farm and non-farm use. Liming materials, peat, potting soils, soil amendments, soil additives, 

and soil conditioners are excluded. Materials used for the manufacture or blending of reported 

fertilizer grades or for use in other fertilizers are excluded to avoid duplicate reporting. A review 

of commercial fertilizer sales records (from 1982 to 2007) showed that in all states, the sales are 

increasing. The increase can be attributed to both yield increases and increasing application. 

Removing the yield increases resulted in persistent increasing trends in chemical fertilizer 

nutrient application (except in Maryland where the trend is flat). 

Model estimates of commercial fertilizer loads have been derived by back-calculating load from 

agricultural lands and determining the proportion of nutrient species applied from commercial 

fertilizer, manure, and atmospheric deposition. 

As phosphorus-based nutrient management plans increase, the reliance on nitrogen fertilizer is 

expected to increase because less manure will be legally permitted to be applied to agricultural 

lands. Therefore chemical fertilizers are and will remain a significant potential source of nitrogen 

and phosphorus to the Bay. 

4.6.2 Atmospheric Deposition 

Air sources contribute about one-third of the total nitrogen loads delivered to the Chesapeake 

Bay by depositing directly onto the tidal surface waters of Chesapeake Bay and onto the 

surrounding Bay watershed. Direct deposition to the Bay’s tidal surface waters is estimated to be 

6 to 8 percent of the total (air and non-air) nitrogen load delivered to the Bay. The nitrogen 

deposited onto the land surface of the Bay’s watershed and subsequently transported to the Bay 

is estimated to account for 25 to 28 percent of the total nitrogen loadings delivered to the Bay. 

Atmospheric loads of nitrogen are from chemical species of oxidized nitrogen, also called NOx, 

and from reduced forms of nitrogen deposition, also called ammonia (NH4

+

). Oxidized forms of 

nitrogen deposition originate from conditions of high heat and pressure and are formed from 

inert diatomic atmospheric nitrogen (N2). The principle sources of NOx are industrial-sized 

boilers such as electric power plants and the internal combustion engines in cars, trucks, 

locomotives, airplanes, and the like. 

Reduced nitrogen, or ammonia, is responsible for approximately one-third of the total nitrogen 

atmospheric emissions that eventually end up as loads to the Bay. Ammonia sources are 

predominately agricultural, and ammonia is released into the air by volatilization of ammonia 

from manures and emissions from ammonia based fertilizers. Minor sources include mobile 

sources, slip ammonia released as a by-product of emission controls on NOx at power plants, and 

industrial processes. 

Two types of atmospheric deposition—wet and dry—are input to the Bay Watershed and Bay 

Water Quality Models daily. Wet deposition occurs during precipitation events and contributes 

to nitrogen loads only during days of rain or snow. Dry deposition occurs continuously and is 

input at a constant rate daily in Bay Watershed and Bay Water Quality Models. 

Because the Bay Watershed and Bay Water Quality Models are mass balance models, all sources 

of nitrogen and phosphorus inputs to the tidal Bay must be accounted for. Given atmospheric 

deposition of phosphorus and organic forms of nutrients are minor inputs, the Bay Watershed 

4‐33 December 29, 2010
Chesapeake Bay TMDL

and Bay Water Quality Models account for estimated loads of phosphorus and organic nutrients 

to open surface waters only, on the assumption that all phosphorus and organic nutrients are 

derived from aeolian or wind processes, which result in no net change in organic nitrogen on 

terrestrial or land surfaces but result in a net gain when deposited directly on water surfaces. 

Organic nitrogen is simulated only as wet deposition as dissolved organic nitrogen because the 

magnitude of dry deposition of organic nitrogen is not well characterized in the literature. 

Therefore, the limited dry deposition of organic nitrogen simulated by the Bay Airshed Model is 

lumped into the oxidized nitrogen atmospheric dry deposition. 

Atmospheric deposition monitoring in the Chesapeake watershed is through National 

Atmospheric Deposition Program (NADP) and AirMon stations throughout the watershed. 

Measured deposition at these discrete stations is used to extrapolate to all the land and waters of 

the Chesapeake watershed through a wet deposition regression model developed by Grimm and 

Lynch (2000, 2005; Lynch and Grimm 2003). Dry deposition data are estimated through the 

Community Multiscale Air Quality Model (CMAQ) (Dennis et al. 2007; Hameedi et al. 2007) 

(for more details, see Section 5.4). 

Chesapeake Bay Airshed 

The Bay’s NOx airshed—the area where emission sources that contribute the most airborne 

nitrates to the Bay originate—is about 570,000 square miles, or nine times the size of the Bay’s 

watershed (Figure 4-16). Close to 50 percent of the nitrate deposition to the Bay is from air 

emission sources in Bay watershed jurisdictions. Another 25 percent of the atmospheric 

deposition load to the Chesapeake watershed is from the remaining area in the airshed. The 

remaining 25 percent of deposition is from the area outside the Bay airshed. The ammonia 

airshed is similar to the NOx airshed, but slightly smaller. 

Source: Dr. Robin Dennis, EPA/ORD/NERL/AMAD/AEIB 

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). 

4‐34 December 29, 2010
Chesapeake Bay TMDL

4‐35 December 29, 2010

Atmospheric Deposition Emissions Sources and Trends 

Between 1985 and 2005, the simulation period of the Bay Watershed Model, atmospheric 

deposition loads of nitrate (NOx) in the Chesapeake watershed have decreased by about 30 

percent (Figure 4-17). Considerable variability exists across the watershed, however, with the 

greatest reductions occurring in the northern and western portions (Grimm and Lynch 2000, 

2005; Lynch and Grimm 2003). Figure 4-17 shows the trend of estimated average nitrate and 

ammonia deposition concentrations in the Phase 5 Model from 1984 to 2005. The average annual 

concentration from 1984 to 2005 was used as an adjustment to smooth out the high- and lowrainfall years, which bring different amounts of deposition load to the watershed depending on 

the volume of precipitation. Much of the reduction has been from point source air emission 

reductions, particularly from electric generating units (EGUs) such as electric power plants. 

Reductions from mobile sources, such as cars and trucks, are another large contributor to the 

downward trend. 

Annual Concentrations in Atdep

y = -0.0007x + 1.5153

R2

 = 0.1076

y = -0.0053x + 11.012

R2

 = 0.5791

y = -0.0046x + 9.4962

R2

 = 0.6469

y = -0.0202x + 40.649

R2

 = 0.8628

y = -0.0281x + 56.761

R2

 = 0.8372

y = -0.008x + 16.112

R2

 = 0.7207

0

0.1

0.2

0.3

0.4

0.5

0.6

1980 1985 1990 1995 2000 2005 2010

Year

mg/l

NH3

NO3

DIN

NH3

NO3

DIN

Linear (NH3)

Linear (DIN)

Linear (NO3)

Linear (DIN)

Linear (NO3)

Linear (NH3)

Source: Phase 5.3 Chesapeake Bay Watershed Model. 

Figure 4-17. Trend of estimated average nitrate and ammonia deposition concentrations in the Phase 5 Model 

domain from 1984 to 2005. 

Table 4-17 shows the estimated portion of deposited NOx loads on the Chesapeake watershed 

from four sectors including EGUs, mobile sources, industry, and all other sources. From 1990 to 

2020, considerable reductions have been made in the power sector. In addition, both on road and 

off-road mobile sources have ongoing fleet turnover and replacement, which is putting cleaner 

spark and diesel engines in service, and that is expected to continue beyond 2030. Table 4-17
Chesapeake Bay TMDL

shows that in 1990, EGUs are the dominant source of NOx; in 2020, mobile sources will be the 

dominant sources of NOx with EGUs the least contributor of NOx. However Figure 4-17 shows 

that all sources will be decreasing their NOx emissions, and the total deposition load in 2020 will 

be less than the 1990 load. 

Average ammonia loads over the Phase 5 Chesapeake Bay Watershed Model domain have 

followed the trend in overall manure loads in the watershed and have remained steady over the 

1985 to 2000 simulation period (Figure 4-17). Ammonia deposition is very site-specific and 

strongly influenced by local emissions. Local and regional trends in manure, such as the rise of 

poultry animal units in the Eastern Shore and Shenandoah basins and reduction of dairy farms in 

the northern portions of the watershed in the late 1980s, affect regional ammonia deposition in 

the Chesapeake watershed. 

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

Source sector 1990 2020 

Power plants (EGUs) 40% 17% 

Mobile sources (on-road) 30% 32% 

Industry 8% 20% 

Other (off-road-construction; residential, commercial) 21% 31% 

Source: Dr. Robin Dennis, EPA/ORD/NERL/AMAD/AEIB 

4.6.3 Forest Lands 

Forested areas represent a significant portion of the Chesapeake Bay watershed (see Figure 2-3), 

as approximately 70 percent of the watershed is composed of forested and open wooded areas. 

This land use contributes the lowest loading rate per acre of all the land uses, however. 

Compared with other major pollutant source sectors in 2009, forest lands in the Bay watershed 

contributed an estimated 20 percent (49 million pounds per year) of total nitrogen, 15 percent 

(2.4 million pounds per year) of total phosphorus, and 18 percent (730,000 tons per year) of 

sediment of the total delivered loads to the Bay from the watershed (Bay Watershed Model 2009 

Scenario). 

Forest land differs from most land uses in that a significant portion of the loads that come off the 

land do not originate in the forests. Most of the nitrogen loads come from atmospheric deposition 

of nitrogen (Campbell 1982; Langland et al. 1995; Ritter and Chirnside 1984; Stevenson et al. 

1987; Nixon 1997; Castro et al. 1997; Goodale et al. 2002; Pan et al. 2005; Aber et al. 1989; 

2003; Stoddard 1994). Sediment and phosphorus loads originate from poorly managed forest 

harvesting with unprotected stream crossings and unhealthy forest biota (Riekerk et al. 1988; 

Clark et al. 2000). 

The Bay Watershed Model differentiates between harvested and un-harvested forest lands as 

distinct land uses. Un-harvested forest lands contributed 1.63 lbs of nitrogen, 0.08 lb of 

phosphorus, and 0.02 ton of sediment per acre, which is the lowest loading rate of any land use. 

In contrast, harvested forest contributes 10.30 lbs of nitrogen, 0.47 lb of phosphorus, and 0.19 

ton of sediment per acre. The loads from harvested forest can be greatly reduced by using forest 

4‐36 December 29, 2010
Chesapeake Bay TMDL

harvesting BMPs. The loads are estimated through model calibration, which estimates loading 

rate per area on the basis of monitoring stations in forested areas. 

For additional information related to the representation of forest lands, see the Bay Watershed 

Model documentation at http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169. 

4.6.4 On-site Wastewater Treatment Systems 

Onsite Wastewater Treatment Systems (OSWTS), commonly referred to as septic systems, have 

the potential to deliver nitrogen and phosphorus to surface waters directly because of system 

failure and malfunction and indirectly through groundwater. Septic systems treat human waste 

using a collection system that discharges liquid waste into the soil through a series of distribution 

lines that compose the drain field. In properly functioning (normal) systems, phosphates are 

adsorbed, or gathered onto the soil surface, and retained by the soil as the effluent percolates 

through the soil to the shallow, groundwater table. Therefore, functioning systems do not 

contribute nitrogen and phosphorus loads to surface waters directly. A septic system failure 

occurs when there is a discharge of waste to the soil surface where it is available for washoff. As 

a result, failing septic systems can contribute high nitrogen and phosphorus loads to surface 

waters. Short-circuited systems (those close to streams) and direct discharges to streams also 

contribute significant nitrogen and phosphorus loads. 

OSWTSs represented an estimated 6 percent of the total nitrogen load from the Chesapeake 

watershed in 2009 (Bay Watershed Model 2009 Scenario). Information on the watershed loads 

from OSWTSs is generally sparse. Detailed descriptions of data procedures, source information, 

and assumptions used in estimating those loads are in Palace et al. (1998). 

For the Chesapeake Bay Watershed Model, the number of OSWTSs in each modeling segment 

was estimated by calculating the number of households outside areas served by public sewer. 

One septic system was assumed to exist for each household. Digital maps of 2009 sewer service 

areas were provided by 257 of the 403 major wastewater treatment plants in the watershed 

contacted during a 2009 survey sponsored by EPA. Digital data were also provided by the 

Maryland Department of Planning for all of Maryland, Fairfax County, and the Washington 

Council of Governments. In 2008 the CBP Office contacted some local jurisdictions and 

collected sewer service area data for all three Delaware counties, Albemarle, Arlington, Henrico, 

Loudoun, and Rockingham counties in Virginia and for James City, Newport News City, 

Virginia Beach, and Richmond in Virginia. Data were also collected for Perry, Dauphin, 

Lancaster, Lycoming, and Cumberland counties in Pennsylvania, and for Broome County in 

New York. For those major wastewater treatment plants that did not provide data and were not 

included in data supplied by county or state agencies, the extent of their sewer service area was 

estimated on the basis of population density. 

EPA simulated the extent of existing sewer service areas using a thresholded and logtransformed raster data set of year 2000 population density. A population density raster was 

created using a dasymetric mapping technique with 2000 Census Block Group data and a 

secondary road density raster map (Claggett and Bisland 2004). A logarithmic transformation 

was used to normalize the population density data in the surface raster. The standard deviations 

in the data range were examined to find the optimal threshold for representing sewer service 

4‐37 December 29, 2010
Chesapeake Bay TMDL

areas in Maryland because statewide maps of existing sewer service areas were provided by the 

Maryland Department of Planning. A threshold of 1.5 standard deviations from the mean (> –

0.4177) was chosen and used to reclassify the surface raster into a binary grid. A low-pass filter 

(ignoring no data) was then used to smooth the data, and the output was converted from a 

floating point to an integer grid. The resulting integer grid was used to represent potential sewer 

service areas for wastewater treatment plants that did not submit digital data. Households in the 

Bay watershed were mapped using a similar dasymetric mapping technique and 2000 Census 

household data. The resulting raster data set of households was overlaid on the sewer service 

area map to estimate the number of households outside sewer service areas. The data were scaled 

from the year 2000 to the year 2009 using published annual county-level population estimates 

adjusted for changes in average household size. In addition, the data were scaled back through 

time using county-level population estimates and spatially distributed raster data sets 

representing 1990 and 2000 Census Block Group data on the total number of households. 

Using that methodology, the number of OSWTSs is estimated and the nitrate loads exported to 

the river from OSWTSs are simulated. Phosphorus loads are assumed to be entirely attenuated 

by the OSWTSs. Standard engineering assumptions of per capita nitrogen waste and standard 

attenuation of nitrogen in the septic systems are applied. Overall, the assumption of a load of 4.0 

kg/person-year is used at the edge of the OSWTS field, all in the form of nitrate. 

Using an average water flow of 75 gallons/person-day for a septic tank (Salvato 1982), a mean 

value of 3,940 grams of nitrogen/person-year for groundwater septic flow, 4,240 grams/personyear for surface flow of septic effluent, and typical surface/subsurface splits as reported by 

Maizel et al. (1995), a total nitrogen concentration of about 39 mg/L at the edge of the septic 

field was calculated. This concentration compares favorably with Salvato (1982) who calculated 

OSWTS total nitrogen concentrations of 36 mg/L. It is assumed that attenuation of the nitrate 

loads between the septic system field and the edge-of-river nitrate loads represented in the Bay 

Watershed Model is due to: (1) attenuation in anaerobic saturated soils with sufficient organic 

carbon (Robertson et al. 1991; Robertson and Cherry 1992); (2) attenuation by plant uptake 

(Brown and Thomas 1978); or (3) attenuation in low-order streams before the simulated river 

reach. Overall, the total attenuation is assumed to be 60 percent (Palace et al. 1998) that is 

applied to all OSWTS in the Bay watershed except for MD where the zone specific attenuation 

rates developed by MDE were used. MDE assumes an 80 percent delivery rate (or 20 percent 

attenuation) in critical areas; a 50 percent delivery rate within 1,000 feet from any perennial 

surface water; and a 30 percent delivery rate from distances greater than 1,000 feet from any 

perennial surface water 

(http://www.mde.state.md.us/assets/document/NutrientCap_Trading_Policy.pdf). 

Additional information related to how the number of OSWTSs is estimated and how they are 

represented in the model is available in the Bay Watershed Model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169

4.6.5 Nonregulated Stormwater Runoff 

The sources of nitrogen, phosphorus and sediment from nonregulated stormwater are generally 

the same as those from regulated stormwater. Sources include residential and commercial 

application of fertilizer, land disturbance and poorly vegetated surfaces, atmospheric deposition 

4‐38 December 29, 2010
Chesapeake Bay TMDL

of nutrients, pet wastes, and developed properties. Together with regulated stormwater, the 

nitrogen, phosphorus, and sediment loads affect local water quality and habitats and represent a 

significant proportion of nitrogen, phosphorus, and sediment loads to the Bay. The CBP 

estimates that, in 2009, urban and suburban development and runoff contributed to 16 percent of 

the sediment loadings, 15 percent of the phosphorus loadings, and 8 percent of the nitrogen 

loadings to the Bay (Bay Watershed Model 2009 Scenario). 

The regulated sources of stormwater are discussed in the point sources section above (4.5.5). For 

the purposes of the TMDL, urban and suburban runoff occurring outside the NPDES regulatory 

purview is considered nonpoint source loading and is a component of the LA. However, note that 

CWA section 402(p) provides the authority to regulate many of those discharges. If any of the 

discharges are designated for regulation, they would then be considered part of the WLA. As 

discussed in Section 8 some of the unregulated sources of stormwater are being shifted from the 

LA portion to the WLA portion of the TMDL as potential regulated sources to further increase 

the reasonable assurance that the TMDL reductions will be achieved. Some jurisdictions might 

have state stormwater regulatory programs and, therefore, could have little to no nonregulated 

stormwater sources. 

For additional details related to how the non-regulated stormwater runoff loads were estimated in 

the Bay Watershed Model, see Section 7 in the Bay Watershed Model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169. 

4.6.6 Oceanic Inputs 

The Chesapeake Bay is an estuary and, by definition, a mixture of fresh and salt water. The 

relative proportion of ocean water in any region of the Bay can be roughly estimated by its 

salinity because salt is a perfectly conservative tracer. The salinity of full strength seawater just 

outside the Chesapeake Bay mouth is about 35 parts per thousand (ppt). At mid-Bay around the 

where Potomac River enters the mainstem Bay, the salinity drops to about 15 ppt, or a mixture of 

about half seawater (43 percent) and at the Bay Bridge between Annapolis and Kent Island, 

Maryland, salinity drops to about 6 ppt or 20 percent seawater. While nitrogen, phosphorus and 

sediment concentrations are relatively low in ocean water, the large volume of seawater entering 

the Bay brings considerable nitrogen, phosphorus, and sediment loads to the Bay. 

Ocean input loads of nitrogen, phosphorus, and sediment to the Chesapeake Bay are determined 

by calibration to the three Bay water quality monitoring stations at the mouth of the Chesapeake 

Bay by using the Curvilinear-grid Hydrodynamic Three-Dimensional model (CH3D 

Hydrodynamic Model), which has a model grid and domain that extends about 10 km beyond the 

mouth of the Bay. Ocean boundary concentrations are set monthly in the Chesapeake Bay Water 

Quality and Sediment Transport Model (Bay Water Quality Model) to best represent the 

nitrogen, phosphorus, and total suspended solids concentrations of the monitoring stations at the 

Chesapeake Bay month on an incoming tide. 

A previous study of ocean boundary loads found that when accounting for all input loads to the 

Chesapeake Bay, including atmospheric deposition to tidal waters and ocean inputs, the ocean 

inputs were significant and accounted for about one-third of the total nitrogen and about half the 

total phosphorus loads to the Bay (Thomann et al. 1994). Ocean sediment inputs are 

4‐39 December 29, 2010
Chesapeake Bay TMDL

predominantly sand and have little influence on light attenuation beyond the Bay mouth and 

lower mainstem Bay. 

Several nutrient budgets of the ocean waters off the Chesapeake, also called the Middle Atlantic 

Bight, have been made (Fennel et al. 2006; Howarth et al. 1995; Howarth 1998). Howarth (1998) 

estimates that for the northeast coast of the United States, which includes the discharge of all 

watersheds from Maine to Virginia draining to the Atlantic, the watershed inputs of nitrogen to 

coastal waters are 0.27 teragram (1012 grams) from rivers and estuaries. Estimated inputs from 

direct atmospheric deposition to coastal waters are 0.21 teragram, and inputs from deep ocean 

upwelling are 1.54 teragrams for a total input to the coastal ocean of 2.02 teragrams. 

The direct atmospheric deposition loads are roughly equivalent to the watershed loads in the 

northeast United States. The estimated distribution of 2001 atmospheric deposition loads to 

North America and adjacent coastal ocean is shown in Figure 4-18. Using the Community Multiscale Air Quality (CMAQ) Model estimates of atmospheric deposition loads to the coastal ocean 

under different air scenarios provides a means of adjusting the ocean boundary loads to changes 

in atmospheric deposition. Appendix L describes how the ocean boundary loads were adjusted to 

reflect projected changes in nitrogen atmospheric deposition to the coastal ocean and, therefore, 

coastal ocean nitrogen loads delivered to Chesapeake Bay. 

Source: Dr. Robin Dennis, EPA/ORD/NERL/AMAD/AEIB 

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

ocean. 

4‐40 December 29, 2010
Chesapeake Bay TMDL

4.6.7 Streambank and Tidal Shoreline Erosion 

Steambank Erosion 

Streambank erosion is erosion from the reworking of streams and rivers, either as flow rates 

change as in the case of increased imperviousness in a watershed (Center for Watershed 

Protection 2003), because of long-term changes in the landscape (Walter and Merritts 2008; 

Trimble 1999), or as a natural process of river channel dynamics (Leopold et al. 1995). 

In the Chesapeake Bay watershed, the relative amounts of streambank erosion and erosion from 

the land is difficult to quantify (Gellis et al. 2009) because the water quality monitoring stations 

measure the total suspended sediment in the free-flowing rivers, which is composed of sediment 

from both sources. The Bay Watershed Model has estimates of land erosion derived from 

RUSLE estimates made in the National Resource Inventory 

(http://www.nrcs.usda.gov/technical/NRI/), which could be used to quantify that source of 

sediment relative to the scour and erosion simulated in the rivers, but both sources of information 

are thought to be too crude to estimate the splits in erosion loads on a segment basis. However, 

on a watershed-wide basis, both sources of information estimate that 70 percent of the sediment 

delivered to the Bay comes from erosion from land and 30 percent comes from bank erosion. 

That is consistent with other estimates from research and field studies that find a wide variance 

of the portions of delivered erosion from land surfaces and bank erosion but could be generalized 

to about one-third of the erosion as coming from bank erosion (Figure 4-19). 

23

0

77

0

0

31

0

17

29

23

9

32

46

13

0

0 10 20 30 40 50 60 70 80 90 100

Banks

Ditch bed

Crop

Forest

Construction

Percent

Sources of Erosion

Pocomoke River Mattawoman Creek L. Conestoga Creek

Source: Gellis et al. 2009 

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

bank sources banks and ditch beds). 

4‐41 December 29, 2010
Chesapeake Bay TMDL

Because sediment monitoring stations in the watershed collect all the sediment loads passing the 

station, including both land erosion and bank erosion sources, the stream bank load is accounted 

for, ultimately, both in the Chesapeake Bay watershed monitoring network and in the Bay 

Watershed Model, at least as part of the total combination of sediment from land and riverine 

sources. In the same way, streambank loads are also accounted for in tracking sediment load 

reductions from stream restoration actions and through reductions of nitrogen, phosphorus, and 

sediment tracked in the jurisdictions’ WIPs. 

Tidal Shoreline Erosion 

Tidal shoreline erosion is a combination of the erosion of fastland (or shoreline) and nearshore 

erosion. Figure 4-20 illustrates the tidal shoreline erosion process. Fastland and nearshore is 

subtidal and usually unseen. Subtidal erosion can be accelerated when shoreline protection 

activities such as stone revetment, a facing of stone placed on a bank or bluff to protect a slope, 

are used. That practice typically cuts off fastland erosion, but the reflected wave energy 

continues subtidal erosion until the wave energy no longer scours the bottom to the depth of a 

meter or more. 

Source: CBP Sediment Workgroup 

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

erosions, fastland and nearshore erosion. 

Estimates of shoreline erosion were provided for the Bay Water Quality Model. Estimates of the 

shore recession rate, the elevation of the fastland, and the subtidal erosion rate were used to 

develop the shoreline erosion estimates. Figure 4-21 demonstrates considerable variation in the 

sediment load delivered by sediment erosion from segment to segment. 

4.6.8 Tidal Resuspension 

The bottom of the Chesapeake Bay is covered by sediment that has been either carried into the 

estuary by rivers draining the Bay’s extensive watershed; eroded from the Bay’s lengthy 

shoreline; transported up-estuary from the Atlantic Ocean, through the mouth of the Bay; 

introduced from the atmosphere; or generated by primary productivity (Langland and Cronin 

2003). Tidal resuspension is generated by episodic wave or current energy that scours the bottom 

sediment and resuspends the surficial sediment layers. 

4‐42 December 29, 2010
Chesapeake Bay TMDL

Source: Chesapeake Bay Water Quality and Sediment Transport Model. 

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). 

In the Bay Water Quality Model, a wave resuspension model simulates such episodic events. In 

some regions of the Bay, resuspended sediment can be one of the most detrimental sediment 

loads to SAV restoration as shown in results of sediment scoping scenarios run on the Bay Water 

Quality Model (Table 4-18). The Bay Water Quality Model was run to compare the base 

scenario of the 2010 Tributary Strategy against model scenarios that individually eliminated 

watershed loads of total suspended sediment, fall line loads of total suspended sediment, shore 

erosion loads, sediment resuspension loads, and ocean sediment loads. The model scenarios were 

run to determine which sediment source was most important. In most of the mainstem Bay, 

sediment resuspension loads were relatively more detrimental to SAV growth than were other 

sediment sources. 

4.6.9 Wildlife 

Wildlife sources are rarely, if ever, considered in nitrogen and phosphorus TMDLs because 

wildlife only cycle nitrogen and phosphorus that already exist in the system. To the extent that 

wildlife increases the availability of nitrogen and phosphorus for runoff, wildlife nitrogen and 

phosphorus loads are inherently represented in land use sources. As a specific example, the loads 

4‐43 December 29, 2010
Chesapeake Bay TMDL

4‐44 December 29, 2010

Table 4-18. Chesapeake Bay Water Quality and Sediment Transport Model -simulated 

SAV acres under a range of sediment scoping scenarios compared with the 2010 

Tributary Strategy scenario 

CBSEG 

SAV 

acre 

No 

watershed 

loads % 

increase 

over base 

SAV 

acre 

No fall 

line loads 

% 

increase 

over base 

SAV 

acre 

No shore 

erosion 

loads % 

increase 

over 

base 

SAV 

acre 

No resuspension 

loads % 

increase 

over base 

SAV 

acres 

No ocean 

sed loads 

% 

increase 

over 

base 

CB1TF 11,253 23% 11,001 20% 9,751 6% 10,344 13% 9,173 0% 

CB2OH 212 63% 192 47% 177 36% 269 107% 138 6% 

CB3MH 609 44% 539 28% 478 13% 704 67% 450 7% 

CB4MH 1,150 30% 1,039 18% 1,096 24% 1,671 89% 980 11% 

CB5MH 9,432 9% 9,086 5% 10,341 20% 14,055 63% 9,177 6% 

CB6PH 825 21% 695 2% 701 3% 980 44% 728 7% 

CB7PH 14,236 4% 13,798 1% 13,959 2% 14,582 7% 14,162 4% 

CB8PH 6 25% 5 17% 5 5% 6 29% 5 18% 

a. The percentages are the percentage increase in simulated SAV acres over the 2010 Tributary Strategy scenario SAV acres. 

from the wooded land incorporate nitrogen and phosphorus loads that are cycled through 

wildlife. The overall loads from the watershed and each land use type are calibrated to observed 

data and literature load estimates, which also include loads cycled through wildlife. As a result, 

no explicit allocation to wildlife is necessary or appropriate in the Bay TMDL. 

4.6.10 Natural Background 

The Bay Airshed Model, Watershed Model, and Bay Water Quality Model all include the loads 

from natural background conditions because all the Bay models are mass balance models and are 

calibrated to observed conditions. For example, the atmospheric deposition loads are monitored 

principally at the NADP sites. The deposition measured at those sites includes NOx from natural 

sources, which includes lightning, forest fires, and bacterial processes such as nitrification, which 

oxidizes ammonia (NH3) to NO2 or NO3. Those sources compose about 1 percent of the NOx 

deposition in the Chesapeake region (USEPA 2010i). Natural background sources of ammonia 

are easily volatilized from land and water surfaces and are generated from the decay 

(ammonification) of natural sources of organic nitrogen. Those are likewise a relatively small 

portion, relative to anthropogenic sources, of the atmospheric loads estimated by the NADP sites. 

Natural loads of nitrogen, phosphorus, and sediment from forested land are also part of the 

monitored load at the free-flowing stream, river, and river input monitoring stations throughout 

the Chesapeake Bay watershed. Because the loads are part of the total loads to which the 

Chesapeake Bay Program’s mass balance models are calibrated, the natural nitrogen, 

phosphorus, and sediment loads in the system, while small, are fully accounted for in the Bay 

TMDL assessment. 

The natural background loads can best be estimated by simulating the All Forest scenario, which 

includes no point source, manure, or fertilizer loads. Atmospheric deposition loads in that 

scenario are set at estimated pristine levels. The scenario yields delivered nitrogen, phosphorus, 

and sediment loads that are more than an order of magnitude less than current conditions (see 

Appendix J).