DRAFT Chesapeake Bay TMDL

4-1 September 24, 2010

SECTION 4. SOURCES OF NUTRIENTS AND 

SEDIMENT TO THE CHESAPEAKE BAY

Nitrogen, phosphorus, and sediment loads originate from many sources in the Bay watershed. 

Point sources of nutrient 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. 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 modeling results shows that Pennsylvania provided the 

estimated 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 from in-stream 

processes in free-flowing rivers that remove nutrients from the system.

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.

Total Nitrogen

DE, 2%

WV, 2% DC, 1%

MD, 20%

NY, 4%

PA, 44%

VA, 27%
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4-2 September 24, 2010

The model estimated phosphorous 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).

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.

Total Phosphorus

DE, 2%

WV, 5% DC, 1%

VA, 43%

PA, 24%

NY, 5%

MD, 20%
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4-3 September 24, 2010

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).

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 Major River Basin Contributions

The major river basins’ model-estimated contributions to 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. At 12 percent and 8 percent, respectively, are the James River basin 

(entirely within Virginia) and the Eastern Shore basin (draining parts of Delaware, Maryland, 

and Virginia), while 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, 3

percent, and 1 percent are contributed by the Rappahannock (Virginia), the York (Virginia) and 

the Patuxent (Maryland) river basins, respectively (Figure 4-4).

Total Sediment

DC, <1%

DE, 1%

PA, 32%

VA, 40%

NY, 4%

MD, 17%

WV, 5%
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4-4 September 24, 2010

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, 

while the balance is provided by the Rappahannock (7 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 

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).

Total Nitrogen

46%

3%

22%

1%

12%

8%

3%

6%

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
DRAFT Chesapeake Bay TMDL

4-5 September 24, 2010

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.

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.

Total Phosphorus

2%

27%

7%

26%

20%

10%

5% 4%

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

Total Sediment

2% 3%

1%

32%

33%

9%

4%

16%

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
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4-6 September 24, 2010

4.3 Pollutant Source Sector Contributions

Table 4-1and Table 4-2 provide model estimates of major pollutant sources of nitrogen and 

phosphorus, respectively, delivered to the Bay by jurisdiction and by major pollution 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. 

Currently, 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 from each major pollutant source sector by jurisdiction

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%

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

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%

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

Note: The amount of phosphorus contributed from nontidal deposition is considered to be insignificant.
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4-7 September 24, 2010

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

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% -- --

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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 categories:

Municipal wastewater facilities

Industrial wastewater facilities

CSOs

NPDES permitted stormwater (MS4s, industrial, and construction)

NPDES permitted CAFOs

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 nutrient 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 nutrients and sediment to 
DRAFT Chesapeake Bay TMDL

4-8 September 24, 2010

the Bay. Appendix Q includes an inventory of 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

≥ 3,800 total phosphorus

or ≥ 27,000 total nitrogen

District of Columbia Blue Plains WWTP

Maryland Design flow ≥ 0.5 

New York Design flow ≥ 0.4 

Pennsylvania Existing flow ≥ 0.4 

Virginia Design flow ≥ 0.5a

Design flow ≥ 0.1b

New facilities ≥ 0.04c

West Virginia Design flow ≥ 0.4

Source: USEPA 2010b

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.

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

facilities by jurisdiction

Jurisdiction

Significant facility

Total

Nonsignificant

facility

Municipal Industrial Municipal Industrial Total

DC 1 0 1 0 3 3

DE 3 1 4 1 1 15

MD 76 10 86 165 556 721

NY 26 2 28 17 40 57

PA 187 30 217 1,240 388 1,628

VA 101 24 125 1,239 339 1,578

WV 10 12 22 132 102 234

Total 404 79 483 2,794 1,429 4,236

Source: Facilities identified in the Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

Note: There are multiple facilities sharing one NPDES permit in West Virginia.
DRAFT Chesapeake Bay TMDL

4-9 September 24, 2010

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; nonsignificant facilities were generally given aggregate WLAs by Bay

segment watershed (USEPA 2009c)

4.4.2 Basinwide NPDES Permitting Approach

In 2004 EPA and the Bay watershed jurisdictions agreed to take a consistent approach to 

permitting the 483 significant municipal and industrial wastewater discharging facilities 

contributing nutrients 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 nutrient 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 nutrients 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 nutrients, 

EPA has determined that because of the long hydraulic durations in the Bay, and the fact 

that the control of annual loading levels of nutrients from wastewater treatment plants is 

much more relevant and appropriate in terms of the effect of nutrients on Bay water quality 

criteria than daily maximums or weekly or monthly averages, expression of nutrient 

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 nutrient trading, 

may be used if such an approach would ensure protection of applicable 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 nutrient sources have been issued with nutrient limits 

consistent with the Tributary Strategy allocations (described above at Section 1.2.1) (some of 

which may include compliance schedules) to 63 percent of the significant wastewater treatment 

facilities (305 out of the total 483), 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, all 483 significant wastewater treatment facilities in the Bay 

watershed are expected to have annual nutrient load limits in place in their permits (some of 

which may have compliance schedules as well).
DRAFT Chesapeake Bay TMDL

4-10 September 24, 2010

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

Approach, through June 2010

Jurisdiction

Significant 

facilities

Permits 

drafted

Permits 

issued

Design flow 

of facilities 

permits 

issued

Percent of design 

flow for permits 

issued/sig 

facilities

DC 1 1 1 152.5 100%

DE 4 4 4 3.3 100%

MD 85 72 51 357.7 42%

NY 28 1 1 20.0 22%

PA 213 141 103 434.1 67%

VA 124 124 124 1,253.5 100%

WV 28 21 21 38.5 81%

Total 483 364 305 2,259.7 74%

Source: USEPA Region 3, Region 2

Note: Some industrial design flows are not available or not comparable and not listed in the database. Some permits 

may contain compliance schedules.

4.4.3 Data Sources

Information used to characterize loading from regulated point sources in the watershed was 

obtained from various sources as described below.

Municipal and Industrial Wastewater Facility Data

Data related to municipal and industrial facilities are in the Phase 5 Chesapeake Bay Watershed 

Model Point Source Database maintained by the CBP and include information for the 483 

significant industrial, municipal, and federal facilities discharging directly to the surface waters 

in the watershed. The wastewater data used to calibrate the Phase 5.3 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 jurisdictions but are also obtained from NPDES permit 

databases, including EPA’s Permit Compliance System (PCS) and jurisdiction discharge 

monitoring reports. 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 Phase 5 Chesapeake 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 nutrient 

discharge data for nonsignificant municipal facilities, 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 
DRAFT Chesapeake Bay TMDL

4-11 September 24, 2010

from Maryland Department of the Environment (MDE) and Virginia Department of 

Environmental Quality (VADEQ), respectively.

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 nutrients. However, the default values from typical pollutant concentrations (Tetra 

Tech 1999) were used to estimate the loads where DMR data are not available. For more 

information regarding the data used to represent municipal and industrial facilities and how they 

were incorporated into modeling for the Bay TMDL, see Section 7 of the Phase 5 Chesapeake 

Bay watershed model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169.

Power Plant and Other Industrial Facility Data

Nutrient 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. 

Industrial facilities such as power plants, petroleum refineries, and steel mills were the focus of 

that evaluation. 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 those facilities, 18 use coal 

as a fuel source; 7 use a flue gas desulfurization, and 13 use ash ponds. Eighty-nine other 

industrial sites were identified in the watershed and represent a variety of industrial activities.

Cooling tower loads were estimated for eight facilities. 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. Flue gas 

desulfurization and ash pond loads were estimated using data obtained from the PCS and ICIS 

databases.

Combined Sewer Outfall Data

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. In the Bay watershed are 64 CSO 

communities. For the full list of CSO communities, see Section 4.5.3. 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. Overflows and associated pollutant loads from CSO communities were 

then developed using various sources of water quality data including monitoring data and 

literature values.

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 Long-Term Control Plans (LTCPs) to characterize overflows. In 

addition, EPA ran simulations of existing sewer models for those communities to support 
DRAFT Chesapeake Bay TMDL

4-12 September 24, 2010

developing overflow and water quality estimates. EPA used the District of Columbia’s combined 

sewer system (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) model 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 Phase 5 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 

this 10-year period were used to assess CSO progress and WLAs. Any CSO implementation 

progress will be input 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.

Permitted Stormwater Facility and MS4 Data

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.

Permitted Concentrated Animal Feeding Operations Data

In the Chesapeake Bay watershed, EPA and the Bay jurisdictions have estimated the number of 

state or federal permitted CAFOs (see Section 4.5.6). Two sources of information used to 

generate these CAFO estimate are the 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 quarterly national update. As the jurisdictions finalize 

their Phase I WIPs in November 2010, the estimates will be updated to reflect a greater level of 

specificity according to how jurisdictions reflect WLAs for livestock and poultry operations.

4.5 Regulated Point Source Load Summaries

This section presents load estimates for each major point source sector.
DRAFT Chesapeake Bay TMDL

4-13 September 24, 2010

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 3,206 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.

Table 4-7. Municipal wastewater facilities by jurisdiction

Jurisdiction Significant Nonsignificant

DC 1 0

DE 3 1

MD 76 164

NY 26 17

PA 182 1,246

VA 101 1,248

WV 10 134

Total 399 2,810

Source: EPA Region 3

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 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 4-8. 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
DRAFT Chesapeake Bay TMDL

4-14 September 24, 2010

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

Figure 4-7 and Figure 4-8 illustrate the prevalence and locations of significant and nonsignificant 

municipal wastewater discharge facilities, respectively, across the watershed.

Appendix Q provides facility-specific information including NPDES ID, location, and more for 

all wastewater dischargers accounted for in the Bay TMDL.

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 

Phase 5 Chesapeake Bay watershed model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169
DRAFT Chesapeake Bay TMDL

4-15 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

4-16 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

4-17 September 24, 2010

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 1,534 NPDES 

permitted facilities discharging industrial wastewaters in the Chesapeake Bay watershed (Table 

4-10, Appendix Q), with 75 significant facilities (Figure 4-9) and 1,459 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 4-10. Industrial wastewater facilities

Jurisdiction Significant Nonsignificant

DC 0 6

DE 1 1

MD 9 566

NY 2 40

PA 30 394

VA 24 338

WV 9 101

Total 75 1,446

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

Error! Not a valid bookmark self-reference., Table 4-13 and Table 4-14 summarize modeled 

wastewater nutrient loading estimates using 2009 loading conditions. Modeled sediment loads 

for those facilities are not presented because wastewater discharges do not represent a significant 

source of sediment (i.e. less than 0.5 percent of the 2009 total sediment load).
DRAFT Chesapeake Bay TMDL

4-18 September 24, 2010

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
DRAFT Chesapeake Bay TMDL

4-19 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

4-20 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario.

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

4-21 September 24, 2010

4.5.3 Combined Sewer Overflows

CSSs 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).

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 W & S Dept.

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 Mun. Auth.

PA Susquehanna PA0021237 Newport Boro STP

PA Susquehanna PA0021539 Williamsburg Municipal Auth. 

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 Auth. 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 WWTF

PA Susquehanna PA0026310 Clearfield Mun. Auth. WWTP

PA Susquehanna PA0026361 Lower Lackawanna Valley San. Auth. WWTP

PA Susquehanna PA0026492 Scranton Sewer Authority WWTP

PA Susquehanna PA0026557 Sunbury City Mun. Auth. WWTP

PA Susquehanna PA0026743 Lancaster City WWTP

PA Susquehanna PA0026921 Greater Hazelton Joint Sewer Authority WWTP

PA Susquehanna PA0027014 Altoona City Auth. - Easterly WWTP
DRAFT Chesapeake Bay TMDL

4-22 September 24, 2010

Jurisdiction River basin NPDES ID Facility name

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 Auth. 

PA Susquehanna PA0028631 Mid-Cameron Authority

PA Susquehanna PA0028673 Gallitzin Borough Sew and Disp. Auth. 

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 Auth. WTP

PA Susquehanna PA0070386 Shenandoah Mun. Sewer Auth. WWTP

PA Susquehanna PAG062202 Lackawanna River Basin Sewer Auth. 

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
DRAFT Chesapeake Bay TMDL

4-23 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

4-24 September 24, 2010

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 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 LTCPs, detailing steps 

necessary to achieve full compliance with the CWA.

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 POTW. Sanitary sewer overflows (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.

SSOs represent a source of nutrients to the Chesapeake Bay; however, information available to 

characterize their contribution to the overall nutrient loads delivered to the Bay is limited largely 

because of their illegality and infrequency. Although the Phase 5.3 Chesapeake Bay watershed 

model does not specifically account for SSOs, the nutrient 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 nutrients 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 nutrient loads to the Bay and its tributaries. These 

nutrients and sediment affect local water quality, habitats, and the Bay downstream and represent 

a significant proportion of nutrient 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 (Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario).
DRAFT Chesapeake Bay TMDL

4-25 September 24, 2010

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 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) and (6). This ―residual 

designation authority‖ (RDA) is in 40 CFR 122.26(a)(9)(i)(C) and (D).

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

11 categories of industrial activity, one of which is 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

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).

Figure 4-12 shows the locations of Phase I and II MS4s in the Bay watershed.
DRAFT Chesapeake Bay TMDL

4-26 September 24, 2010

Source: Phase 5.3 Chesapeake Bay Watershed Model 2009 Scenario

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

4-27 September 24, 2010

Unless stormwater discharges are identified in EPA’s Phase I or Phase II regulations or are 

designated pursuant to either CWA section 402(p)(6) RDA, 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 provides an 

inventory of 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 (Phase 5.3 

Chesapeake Bay Watershed Model 2009 Scenario).

The contribution from industrial stormwater discharges subject to NPDES 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.

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

summer 2009

Jurisdiction

NPDES Stormwater permit type

MS4 

Phase I

MS4 

Phase II Industrial Construction Total

% 

Permittees 

in the Bay

DC

Baywide 1 0 60 212 273 1.6%

Districtwide 1 0 60 212 273

DE

Baywide 1 0 48 NA 49 0.3%

Statewide 14 3 337 1,375 1,729

MD

Baywide 11 82 1,578 8,300 9,971 57.6%

Statewide 11 82 1,578 8,332 10,003

NY

Baywide 0 34 122 470 626 3.6%

Statewide 1 502 1,393 7,251 9,147

PA

Baywide 0 206 1,238 906 2,350 13.6%

Statewide 2 727 2,494 2,399 5,622

VA

Baywide 11 75 975 2,252 3,313 19.2%

Statewide 11 90 1,432 2,851 4,384

WV

Baywide 0 3 113 651 767 4.4%

Statewide 0 45 933 2,488 3,466

Total

Bay 23 400 4,086 12,791 17,300 100%

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
DRAFT Chesapeake Bay TMDL

4-28 September 24, 2010

4.5.6 Concentrated Animal Feeding Operations

The NPDES program regulates the discharge of pollutants from point sources to waters of the 

United States. CAFOs are point sources, as defined by 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 

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)]. AFOs that 

are not defined as a CAFO may be designated as a CAFO if they meet certain conditions [40 

CFR 122.23(c)].

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

Animal sector 

Size thresholds

(number of animals)

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)]. These requirements limit nutrient 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 nutrients 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 
DRAFT Chesapeake Bay TMDL

4-29 September 24, 2010

process wastewater must comply with technology-based effluent limitations for land application 

per the effluent limitations guidelines (ELG) 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.

Agricultural stormwater discharges are the precipitation-related discharges from CAFO land 

application areas where the CAFO land applies 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

1.Ensuring adequate storage of manure, liter, and process wastewater, including procedures to 

ensure proper operation and maintenance of the storage facility.

2. 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.

3.Ensuring that clean water is diverted, as appropriate, from the production area.

4. Preventing direct contact of confined animals with waters of the United States.

5.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 rate such chemicals and other contaminants.

6.Identifying appropriate site specific conservation practices to control runoff of pollutants to 

waters of the United States.

7.Identifying protocols for appropriate testing of manure, litter, process wastewater, and soil.

8.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.

9.Identifying specific records that will be maintained to document the implementation and 

management of the minimum elements described above.

In the Chesapeake Bay watershed, EPA and the jurisdictions have estimated the number of state 

or federal permitted CAFOs (Table 4-16). As the jurisdictions finalize their Phase I WIPs in 

November 2010, the estimates will be updated to reflect a greater level of specificity according 

to how the jurisdictions reflect WLAs for livestock and poultry operations.
DRAFT Chesapeake Bay TMDL

4-30 September 24, 2010

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

Jurisdiction # State or federal permitted CAFOs

Delawarea122

Marylanda426

New York 90

Pennsylvania 325

Virginia 30

West Virginia 30

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.

a. The numbers of CAFOs in Maryland and Delaware with permits are estimated based on the number of Notices of 

Intent (NOIs) received as a result of the EPA February 2009 permit application deadline. These 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

Appendix Q provides an inventory of nonpoint sources represented in the Bay Watershed Model 

by various geographic scales (county, land-river segment, and such)

4.6.1 Data Sources

Information used to characterize loading from nonpoint sources in the Bay watershed was 

obtained from various sources.

Agriculture

Data sources used to estimate nutrients 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 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, September 2010 (USEPA 2010d). 
DRAFT Chesapeake Bay TMDL

4-31 September 24, 2010

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.

Atmospheric 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; 2007; 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).

Other Nonpoint Sources

For the Bay TMDL, Scenario Builder was used to provide the land use-based scenario inputs to 

the Phase 5.3 Chesapeake Bay Watershed Model including forest lands, OSWTSs , nonregulated 

stormwater runoff, oceanic inputs, streambank and tidal shoreline erosion, tidal resuspension, 

and wildlife (Section 5). Scenario Builder provides nutrient 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://www.chesapeakebay.net/modeling.aspx?menuitem=19303.

4.7 Nonpoint Source Load Summaries

4.7.1 Agriculture

Agricultural lands account for 22 percent of the watershed, making agriculture one of the largest 

land uses in the area, second only to forests (58 percent). The Bay watershed has more than 

87,000 farm operations and 6.5 million acres of cropland.

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, 3 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 
DRAFT Chesapeake Bay TMDL

4-32 September 24, 2010

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 (CBP Phase 5.3 

Chesapeake Bay Watershed Model 2009 Scenario). Figure 4-13 compares modeled loads from 

agricultural lands for 1985 and 2009.

Source: Phase 5.3 Chesapeake Bay Watershed Model 1985 and 2009 Scenarios

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

across the Chesapeake Bay watershed.

0

20,000,000

40,000,000

60,000,000

80,000,000

100,000,000

120,000,000

140,000,000

160,000,000

180,000,000

TN (lbs/yr) TP (lbs/yr)

Agricultural Loads

(Nutrients)

1985

2009

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

TSS (tons/yr)

Agricultural Loads

(Sediment)

1985

2009
DRAFT Chesapeake Bay TMDL

4-33 September 24, 2010

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 nutrient recycling process in agriculture. Because 

manure is so extensively used as a resource of nutrients, it is considered as important as 

inorganic fertilizer as a source of nonpoint source pollution. Figure 4-14 and Figure 4-15 provide 

historical population data of poultry and non-poultry animals in the watershed, respectively.

Source: 2007 Agriculture Census

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

4-34 September 24, 2010

Source: 2007 Agriculture Census

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

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 that is 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 significant 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; USEPA 1976, 1978). Nitrogen and phosphorus are 

the most prevalent nutrients found in sewage sludge.
DRAFT Chesapeake Bay TMDL

4-35 September 24, 2010

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 Phase 5.3 Chesapeake Bay 

Watershed Model, see Section 7 of the Scenario Builder 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 

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 increasing yields and increasing application. 

Removing the yield increases resulted in persistent increasing trends in 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 

nutrients to the Bay.

4.7.2 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 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.
DRAFT Chesapeake Bay TMDL

4-36 September 24, 2010

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 only nitrogen loads 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 nutrient 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 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 processes, which result in no net change in organic nitrogen on terrestrial 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.

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 seven 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.
DRAFT Chesapeake Bay TMDL

4-37 September 24, 2010

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).

Atmospheric deposition emissions sources and trends

Between 1985 and 2005, the simulation period of the Phase 5 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). In Figure 4-17, the average annual concentration over a 1984 to 

2005 period is used as an adjustment to smooth out the high- and low-rainfall years, which bring 

different amounts of deposition load to the watershed due primarily to the volume of 

precipitation. Much of the reduction has been from point source air emission reductions, 

particularly from electric generating units (EGUs). Reductions from mobile sources are another 

large contributor to the downward trend.
DRAFT Chesapeake Bay TMDL

4-38 September 24, 2010

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

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 1990.

Average ammonia loads over the Phase 5 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 and dairy’s diminishment 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

Annual Concentrations in Atmospheric Deposition

y = 2E-06x + 0.1795

R

2

 = 7E-07

y = -0.0053x + 10.971

R

2

 = 0.5641

y = -0.0053x + 10.791

R

2

 = 0.7061

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1980 1985 1990 1995 2000 2005 2010

Year mg/l

NH3

NO3

DIN

Linear (NH3)

Linear (DIN)

Linear (NO3)
DRAFT Chesapeake Bay TMDL

4-39 September 24, 2010

4.7.3 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 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 (Phase 5.3 Chesapeake 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 forest loads come from atmospheric deposition of 

nitrogen (Campbell 1982; Langland et al. 1995; STAC 1997; Ritter et al. 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 Phase 5.3 Chesapeake Bay Watershed Model differentiates between harvested and unharvested 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 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 Phase 5.3 

Chesapeake Bay watershed model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169.

4.7.4 On-site Wastewater Treatment Systems

OSWTSs, commonly referred to as septic systems, have the potential to deliver nutrients to 

surface waters because of system failure and malfunction. 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 and retained by the soil as the effluent percolates through the soil to the shallow, 

saturated zone. Therefore, functioning systems do not contribute nutrient loads to surface waters. 

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 nutrient loads to 

surface waters. Short-circuited systems (those close to streams) and direct discharges also 

contribute significant nutrient loads.

OSWTSs represented an estimated 6 percent of the total nitrogen load from the Chesapeake 

watershed in 2009 (Phase 5.3 Chesapeake 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 these loads are in Palace et al. (1998).
DRAFT Chesapeake Bay TMDL

4-40 September 24, 2010

For the Chesapeake Bay watershed model, the number of OSWTSs in each modeling segment 

was estimated by calculating the number of households outside areas currently 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.

The CBP Office 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 

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 nitrate loads discharged to the 

river 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/personyear 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/person-year for groundwater septic flow, 4,240 grams/person-year 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 
DRAFT Chesapeake Bay TMDL

4-41 September 24, 2010

between the septic system field and the edge-of-river nitrate loads represented in the Phase 5 

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).

Additional information related to how the number of OSWTSs is estimated and how they are 

represented in the model is available in the Phase 5.3 watershed model documentation at 

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169

4.7.5 Nonregulated Stormwater Runoff

The sources of nutrients 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 of nutrients, 

pet wastes, developed properties, and a variety of other pollutants. Together with regulated 

stormwater, the nutrients and sediment impact local water quality and habitats and represent a 

significant proportion of nutrient 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 (Phase 5.3 Chesapeake 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 these discharges. If any of the 

discharges are designated for regulation, they would then be considered part of the WLA. Some 

jurisdictions may have state stormwater regulatory programs and, therefore, could have little to 

no nonregulated stormwater sources.

For additional details related to how the loads were estimated in the Phase 5.3 Chesapeake Bay 

Watershed Model, see Section 7 in the Watershed Model Documentation at

http://www.chesapeakebay.net/model_phase5.aspx?menuitem=26169.

4.7.6 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 and at the Bay Bridge between Annapolis and Kent Island, Maryland, 

salinity drops to about 6 ppt or 20 percent seawater. While nutrient and sediment concentrations 

are relatively low in ocean water, the large volume of seawater entering the Bay brings 

considerable nutrient and sediment loads to the Bay.

Ocean input loads of nutrients 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 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 WQSTM to 
DRAFT Chesapeake Bay TMDL

4-42 September 24, 2010

best represent the nutrient 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 

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 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 M 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.
DRAFT Chesapeake Bay TMDL

4-43 September 24, 2010

Source: Dr. Robin Dennis, EPA/ORD/NERL/AMAD/AEIB

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

coastal ocean.

4.7.7 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 stream bank 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. On a 

watershed-wide basis, the estimate is for about 70 percent of the sediment delivered to the Bay 

from erosion from land and 30 percent from bank erosion. This 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).
DRAFT Chesapeake Bay TMDL

4-44 September 24, 2010

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).

Because sediment monitoring stations in the watershed collect all the sediment loads passing the 

station, including both land erosion and from 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 sediment and nutrients 

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 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.

Estimates of shoreline erosion were provided for the WQSTM. Estimates of the shore recession 

rate, the elevation of the fastland, and the subtidal erosion rate were used to develop these 

shoreline erosion estimates. Figure 4-21 demonstrates considerable variation in the sediment load 

delivered by sediment erosion from segment to segment.
DRAFT Chesapeake Bay TMDL

4-45 September 24, 2010

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.

Source: 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).

4.7.8 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
DRAFT Chesapeake Bay TMDL

4-46 September 24, 2010

2003). Tidal resuspension is generated by episodic wave or current energy that scours the bottom 

sediment and resuspends the surficial sediment layers.

In the Bay WQSTM, a wave resuspension model simulates these 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 WQSTM (Table 

4-18). The WQSTM was run to compare the base scenario of the 2010 Tributary Strategy against 

model scenarios that individually eliminated watershed loads of total suspended sediments 

(TSS), fall line loads of TSS, shore erosion loads, sediment resuspension loads, and ocean 

sediment loads. These model scenarios were run to determine which sediment source was the 

more important source of sediment. In most of the mainstem Bay, sediment resuspension loads 

were relatively more detrimental to SAV growth than were other sediment sources.

Table 4-18. Chesapeake Bay WQSTM 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.

4.7.9 Wildlife

Wildlife sources are rarely, if ever, considered in nutrient TMDLs because wildlife cycle only 

nutrients that already exist in the system. To the extent that wildlife increases the availability of 

nutrients for runoff, wildlife nutrient loads are inherently represented in land use sources. As a 

specific example, the loads from the wooded land incorporate nutrient 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.

4.7.10 Natural Background

The Bay Airshed model, Watershed model, and WQSTM 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 
DRAFT Chesapeake Bay TMDL

4-47 September 24, 2010

(ammoniafication) 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 nutrients and sediment from forested land are also part of the monitored load at 

the free-flowing stream, river and river input monitoring stations located throughout the 

Chesapeake Bay watershed. Because the loads are part of the total loads to which the Bay 

Program mass balance models are calibrated, the natural nutrient 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 nutrient and sediment 

loads that are more than an order of magnitude less that current conditions (see Appendix K).