WATER QUALITY

EPA Faces Challenges 

in Addressing Damage 

Caused by Airborne 

Pollutants 

Report to Congressional Requesters

January 2013 

GAO-13-39 

United States Government Accountability Office

GAO 
 United States Government Accountability Office 

Highlights of GAO-13-39, a report to 

congressional requesters 

January 2013 

WATER QUALITY 

EPA Faces Challenges in Addressing Damage Caused 

by Airborne Pollutants 

Why GAO Did This Study 

Atmospheric deposition, a process that 

transfers pollutants, including NOx, 

SO2, and mercury, from the air to the 

earth’s surface, can significantly impair 

the quality of the nation’s waters. EPA 

can potentially address atmospheric 

deposition through the CWA and the 

CAA, but concerns have been raised 

about its ability to do so. GAO was 

asked to examine EPA’s efforts to 

address atmospheric deposition of 

pollutants that impair waterbodies. 

This report examines (1) the extent to 

which atmospheric deposition of NOx, 

SO2, and mercury contributes to the 

impairment of the nation’s waters and 

identify the key sources of these 

pollutants; (2) the regulatory tools that 

EPA uses under the CWA to address 

the effects of atmospheric deposition, 

and the challenges, if any, that it faces 

in doing so; and (3) the regulatory tools 

that EPA uses under the CAA to 

address the effects of atmospheric 

deposition, and the challenges, if any, 

that it faces in doing so. To conduct 

this work, GAO reviewed EPA data, 

reports, and activities and interviewed 

agency officials and other experts. 

What GAO Recommends 

GAO recommends that EPA determine 

whether EPA can obtain in a timely 

manner the data it needs to establish 

secondary NAAQS adequate to protect 

against the effects of acid rain and, if 

not, identify alternative strategies to 

do so. EPA agreed with GAO’s 

recommendation. 

What GAO Found

Atmospheric deposition of nitrogen oxides (NOx), sulfur dioxide (SO2), and 

mercury contributes to the impairment of the nation’s waters, but the full extent is 

not known. For example, states provide EPA with data on the extent to which 

their waterbodies do not meet water quality standards, and some states have 

reported that some of their waterbodies are polluted because of atmospheric 

deposition. However, the states have not assessed all of their waterbodies and 

are not required to report on the sources of pollution. Similarly, federal studies 

show that atmospheric deposition of NOx, SO2, and mercury is polluting 

waterbodies but have data for only some waters. The main sources of NOx and 

SO2 are cars and other forms of transportation and coal-burning power plants. 

Power plants are also the largest U.S. source of mercury emissions, but 

international sources also contribute to the mercury deposited in U.S. waters. 

EPA has sought to address atmospheric deposition through Clean Water Act 

(CWA) programs but faces challenges in doing so. Specifically, states typically 

establish water quality standards—considering EPA recommended criteria—for 

each waterbody. If a waterbody does not meet standards, CWA generally 

requires the state to set a Total Maximum Daily Load (TMDL) that identifies the 

maximum amount of pollutant that can enter the waterbody and still meet 

standards. States are responsible for taking actions to ensure the TMDL is met. 

For point sources of pollution, such as a pipe from a sewer treatment plant, CWA 

requires new or renewed permits to be consistent with the TMDL. However, there 

is no similar statutory requirement for nonpoint sources of pollution, such as 

atmospheric deposition. States may take actions, such as providing technical or 

financial assistance to limit pollution from nonpoint sources, but face a challenge 

when atmospheric deposition pollution affecting their waters originates in 

emissions from a different state. 

EPA has also sought to address atmospheric deposition through Clean Air Act 

(CAA) regulations but faces challenges in doing so. EPA issued regulations that 

reduced emissions of NOx, SO2, and mercury and in turn the amount of pollution 

in waterbodies. Even with reduced emissions, NOx, SO2, and mercury continue to 

pollute the nation’s waterbodies. EPA’s recent attempt to address atmospheric 

deposition by establishing secondary National Ambient Air Quality Standards 

(NAAQS)—standards to protect public welfare—targeting the effects of acid rain 

caused by NOx and SO2 on water bodies was not successful. EPA stated that 

uncertainty regarding atmospheric modeling and limitations in available data 

prevented determination of secondary NAAQS adequate to protect against the 

effects of acid rain, and the agency has not identified alternative strategies. EPA 

has begun a 5-year pilot program to gather additional scientific data, but it is 

unclear whether or when the agency will be able to address scientific 

uncertainties to enable adoption of a protective secondary NAAQS. EPA also did 

not set secondary NAAQS to address nutrient over-enrichment in aquatic 

ecosystems caused by NOx because of the limited available scientific data. Many 

sources of nitrogen can contribute to nutrient over-enrichment in a waterbody, 

including sources of nitrogen unrelated to atmospheric deposition. EPA recently 

announced an effort that is to lead to the development of an integrated nitrogen 

research strategy that includes approaches to reducing atmospheric deposition 

of NOx into waters impaired because of nutrient over-enrichment by nitrogen. 

View GAO-13-39. For more information, 

contact David C. Trimble at (202) 512-3841 or 

trimbled@gao.gov. 
Page i GAO-13-39 Water Quality 

Letter 1 

Background 5

Air Pollution Affects U.S. Waterbodies and Transportation and 

Power Plants Are Its Key Sources 10

EPA Faces Challenges Using Clean Water Act Regulations to 

Address Atmospheric Deposition 21

Clean Air Act Regulations Address Atmospheric Deposition, but 

EPA Faces Challenges Addressing Effects on Waterbodies 32

Conclusions 43

Recommendation for Executive Action 44

Agency Comments and Our Evaluation 45

Appendix I Scope and Methodology 46 

Appendix II Comments from the Environmental Protection Agency 50 

Appendix III GAO Contact and Staff Acknowledgments 53

Table 

Table 1: Waterbodies Reported by States as Impaired by 

Atmospheric Deposition by Waterbody Type 11

Figures 

Figure 1: Atmospheric Deposition 6

Figure 2: Location of Acid-Sensitive Ecosystems in the United 

States 13

Figure 3: Mercury-related Fish Consumption Advisories, 2010 16

Figure 4: Estimated Contributions of NOx Emissions from 

Domestic Sources in 2008 17

Figure 5: Estimated Contributions of Sulfur Dioxide Emissions 

from Domestic Sources in 2008 18

Figure 6: Estimated Contributions of Mercury Emissions from 

Domestic Sources in 2008 19

Figure 7: Estimated Contributions of Global Mercury Emissions 

from Human-Caused Sources in 2005 21

Contents 
Page ii GAO-13-39 Water Quality 

Figure 8: Sources of Atmospheric Deposition of Mercury in the 

Northeast Region, 2002 26

Figure 9: Location of New York State Forest Preserve Lands in the 

Adirondacks 28

Figure 10: Location of NOx Airshed and Chesapeake Bay Watershed 31

Figure 11: NOx and SO2

 Emissions in 1990, 2000, and 2008 by 

Source 33

Figure 12: Mercury Emissions in 1990 and 2008 by Source 37

 
Page iii GAO-13-39 Water Quality 

Abbreviations 

ATTAINS Assessment, TMDL Tracking, and Implementation 

System 

EPA Environmental Protection Agency 

CAA Clean Air Act 

CENRS Committee on Environment, Natural Resources, and 

Sustainability 

CWA Clean Water Act 

MACT maximum achievable control technology 

MATS Mercury and Air Toxics Standards 

NAAQS National Ambient Air Quality Standards 

NADP National Atmospheric Deposition Program 

NAPAP National Acid Precipitation Assessment Program 

NEIWPCC New England Interstate Water Pollution Control 

Commission 

NESCAUM Northeast States for Coordinated Air Use Management 

NLFA National Listing of Fish Advisories 

NOAA National Oceanic and Atmospheric Administration 

NOX nitrogen oxides 

NPDES National Pollution Discharge Elimination System 

NSTC National Science and Technology Council 

NYSDEC New York State Department of Environmental 

Conservation 

PCBs polychlorinated biphenyls 

SO2 sulfur dioxide 

SO4 sulfate 

TMDL Total Maximum Daily Load 

UNEP United Nations Environment Programme 

This is a work of the U.S. government and is not subject to copyright protection in the 

United States. The published product may be reproduced and distributed in its entirety 

without further permission from GAO. However, because this work may contain 

copyrighted images or other material, permission from the copyright holder may be 

necessary if you wish to reproduce this material separately. 
Page 1 GAO-13-39 Water Quality 

United States Government Accountability Office

Washington, DC 20548 

January 24, 2013 

The Honorable Timothy H. Bishop 

Ranking Member 

Subcommittee on Water Resources and the Environment 

Committee on Transportation and Infrastructure 

House of Representatives 

The Honorable Eddie Bernice Johnson 

House of Representatives 

Atmospheric deposition—a process that transfers pollutants from the air 

to the earth’s surface—can significantly impair water quality in the 

nation’s rivers, lakes, bays, and estuaries, and harm human health and 

aquatic ecosystems. In particular, airborne pollutants can fall to the 

ground in precipitation or as a gas or particle and be deposited either 

directly onto the surface of a waterbody or onto land and then transported 

into a waterbody through runoff. Three airborne pollutants commonly 

associated with atmospheric deposition are nitrogen oxides (NOx), sulfur 

dioxide (SO2), and mercury. NOx and SO2—which cause acid rain—

threaten certain aquatic ecosystems, especially in lakes and streams in 

higher altitudes. In addition, NOx contributes to nutrient over-enrichment 

in estuaries, which can result in oxygen depleted areas known as “dead 

zones,” where fish and other organisms cannot survive. Once in water, 

mercury becomes concentrated in fish and can harm the health of 

individuals who consume these fish, particularly children. 

Because these pollutants are transferred from air to water, the 

Environmental Protection Agency (EPA), whose mission is to protect 

human health and the environment, can potentially address atmospheric 

deposition through the Clean Water Act (CWA) and the Clean Air Act 

(CAA).1

 The CWA provides EPA with responsibilities aimed at maintaining 

and improving the quality of the nation’s waters, including the 

 

1

The Federal Water Pollution Control Act Amendments of 1972, Pub. L. No. 92-500, 

§ 2, 86 Stat. 816 (amending the Act of June 30, 1948, ch. 758, 62 Stat. 1155) (codified as 

further amended at 33 U.S.C. ch. 26 §§ 1251-1387 (2012) and commonly referred to as 

the Clean Water Act); Clean Air Act Amendments of 1970, Pub. L. No. 91-604, 84 Stat. 

1676 (1970) (codified as amended at 42 U.S.C. §§ 7401-7671q (2011) (commonly 

referred to as the Clean Air Act). 

 
 

Page 2 GAO-13-39 Water Quality 

responsibility to establish recommended water quality criteria for specific 

pollutants. Authorized states, territories, and tribes—collectively referred 

to as states in this report—then use these recommended criteria along 

with designated uses and antidegradation provisions to establish statespecific water quality standards. States then apply these standards to 

individual waterbodies.2

 If a waterbody does not meet water quality 

standards, these entities are to establish a pollutant “budget”—or a total 

maximum daily load (TMDL)—at a level that ensures that applicable 

water quality standards can be met and maintained.3

 Once a TMDL is 

established, states are generally responsible for implementation, while 

EPA and states share responsibility to ensure that permitted discharges 

to a waterbody do not exceed the level established by the TMDL. 

Analogous to the CWA, the CAA provides EPA with tools for regulating 

the emissions of pollutants into the air. Among the pollutants that EPA 

regulates in certain emissions are NOx, SO2, and mercury. 

EPA and others have recognized atmospheric deposition as a 

contributing factor to degraded water quality for several decades. 

However, congressional concerns have been raised about EPA’s ability to 

address atmospheric deposition. In this context, you asked us to review 

EPA’s efforts to address the atmospheric deposition of pollutants that 

impair the water quality and aquatic ecosystems of the nation’s rivers, 

lakes, and bays. Specifically, our objectives were to examine (1) the 

extent to which atmospheric deposition of NOx, SO2, and mercury 

contributes to the impairment of the nation’s waters and identify the key 

sources of these pollutants; (2) the regulatory tools that EPA uses under 

CWA to address the effects of atmospheric deposition, and the 

challenges, if any, that it faces in doing so; and (3) the regulatory tools 

that EPA uses under the CAA to address the effects of atmospheric 

deposition, and the challenges, if any, that it faces in doing so. 

To examine the extent to which atmospheric deposition of NOx, SO2, and 

mercury impairs waters, we analyzed the most recently available data 

from EPA’s Assessment, TMDL Tracking, and ImplementatioN System 

 

2

The water quality standard for a water body consists of three components: criteria, 

designated uses, and antidegradation provisions. 

3

TMDL is a calculation of the maximum amount of a pollutant that a body of water can 

receive and still meet water quality standards. TMDLs allocate or apportion the “budget” 

among the various sources, including permitted dischargers as well as nonpoint sources 

of pollution, or polluted runoff. 
 

Page 3 GAO-13-39 Water Quality 

(ATTAINS), a database containing state-reported information on the 

extent to which waterbodies meet water quality standards. To assess the 

reliability of its data, we interviewed knowledgeable agency officials and 

conducted electronic testing of the data. We determined that although the 

data have limitations, they were sufficiently reliable to present reported 

atmospheric deposition impairment on assessed waters for selected 

categories of water bodies. We also reviewed studies from EPA and 

others to further examine the extent to which atmospheric deposition is 

contributing to the impairment of the nation’s waters. We assessed the 

reliability and methodology of these studies, including limitations and 

assumptions, and determined that they were sufficiently reliable for the 

purposes of examining the extent to which atmospheric deposition is 

contributing to the impairment of the nation’s waters. To identify key 

sources of NOx, SO2, and mercury emissions, we used estimates from 

EPA’s 2008 National Emissions Inventory (version 2)—a national 

database of sources and amounts of pollution emissions. We also 

interviewed officials and scientists from EPA and the Department of 

Commerce’s National Oceanic and Atmospheric Administration (NOAA); 

and academic, state, and private sector scientists. 

To examine tools EPA uses under the CWA to address atmospheric 

deposition and the challenges it faces, we reviewed the law, relevant EPA 

regulations and guidance, and other pertinent documents and interviewed 

relevant EPA and state officials. We chose to examine a nonprobability 

sample of three TMDLs in greater detail—the Northeast Regional TMDL 

for mercury atmospheric deposition, a New York State TMDL for acid rain 

in the Adirondacks, and the Chesapeake Bay TMDL for nitrogen 

atmospheric deposition—to illustrate challenges.4

 We selected each 

TMDL to represent a different effect caused by the atmospheric 

deposition of the three pollutants on which we are focusing. The three 

effects are acid rain, nutrient over-enrichment, and mercury 

contamination. We examined key documents about these TMDLs and 

interviewed EPA and state and regional officials responsible for 

developing and implementing them. 

 

4

Because we selected a nonprobability sample, our analysis is not generalizeable to all 

TMDLs but can illustrate the challenges faced by EPA in using this tool. 
 

Page 4 GAO-13-39 Water Quality 

Likewise, to examine the tools EPA uses under the CAA to address 

atmospheric deposition and the challenges it faces, we reviewed the law, 

relevant EPA regulations and guidance, and other pertinent documents 

and interviewed relevant EPA officials. We used data from the 2008 

National Emissions Inventory (version 2), a 2011 peer-reviewed EPA 

study that estimates the benefits and costs of the CAA amendments of 

1990,5

 and other information to identify reductions in NOx, SO2, and 

mercury that EPA has attributed to the CAA and the associated beneficial 

effects on water quality. We assessed the reliability and methodology of 

these sources of information, including limitations and assumptions, and 

determined that they were sufficiently reliable for the purposes of 

attributing estimates of some reductions in NOx, SO2, and mercury to the 

CAA. To understand the challenges that EPA faced in trying to develop 

an air quality standard to protect ecosystems sensitive to the effects of 

acid rain, we reviewed documentation developed as part of the rule 

making process and interviewed knowledgeable officials responsible for 

the rulemaking. To understand EPA’s integrated nitrogen research 

strategy, we reviewed pertinent documents and interviewed relevant EPA 

officials. Appendix I presents a more detailed description of our scope 

and methodology. 

We conducted this performance audit from September 2011 to January 

2013 in accordance with generally accepted government auditing 

standards. Those standards require that we plan and perform the audit to 

obtain sufficient, appropriate evidence to provide a reasonable basis for 

our findings and conclusions based on our audit objectives. We believe 

that the evidence obtained provides a reasonable basis for our findings 

and conclusions based on our audit objectives. 

 

5

U.S. Environmental Protection Agency, Office of Air and Radiation, The Benefits and 

Costs of the Clean Air Act from 1990 to 2020, Final Report (Washington, D.C.: March 

2011). 
 

Page 5 GAO-13-39 Water Quality 

This section discusses atmospheric deposition, its effect on waterbodies, 

and how the CWA and the CAA address it.6

Air pollution can be carried through the atmosphere and deposited on 

land, water, or man-made structures in a process known as atmospheric 

deposition. The pollutants can get into waterbodies through either direct 

deposition or indirect deposition as follows: 

 Direct deposition occurs when air pollutants are deposited directly 

onto a waterbody; and 

 indirect deposition occurs when air pollutants are deposited onto the 

watershed—the area of land surrounding the waterbody—and are 

transported to the waterbody through runoff, rivers, streams, and 

groundwater. 

Additionally, atmospheric deposition can be either wet or dry as follows: 

 Wet deposition occurs when pollutants are removed from the air and 

deposited via rain, snow, fog, or mist; and 

 dry deposition occurs when air pollutants are deposited in the 

absence of rain or snow as falling particles or as the gas form of the 

pollutant. 

The pollution deposited through atmospheric deposition can come from 

human-caused sources, such as power plants, or natural sources, such 

as volcanoes. Figure 1 depicts this process. 

 

6

This report focuses on the atmospheric deposition of pollutants and their effects on 

waterbodies, but atmospheric deposition of pollutants can also harm land-based 

ecosystems such as forests. 

Background 

Atmospheric Deposition Is 

the Transfer of Air 

Pollution to the 

Earth’s Surface 
 

Page 6 GAO-13-39 Water Quality 

Figure 1: Atmospheric Deposition 

Three airborne pollutants commonly associated with atmospheric 

deposition are NOx, SO2, and mercury but there are other pollutants. 

Examples include ammonia, which contributes to nutrient overenrichment; and lead, polychlorinated biphenyls (PCBs), and other toxic 

substances, which can harm human health. 
 

Page 7 GAO-13-39 Water Quality 

NOx and SO2 cause acid rain, and NOx contributes to nutrient overenrichment of waterbodies. Once in water, mercury becomes 

concentrated in fish and can harm individuals who consume 

contaminated fish. 

NOx and SO2 cause acid rain, which can threaten certain aquatic 

ecosystems.7

 NOx reacts chemically in the atmosphere to form nitric acid. 

SO2 reacts chemically in the atmosphere to form sulfuric acid.8

 When 

these chemicals fall to the ground, they are known as acid rain. Some 

aquatic ecosystems are sensitive to acid rain. They are often at higher 

elevations and have underlying geologic conditions that limit their ability 

to neutralize or buffer acid. Acid rain in these ecosystems can cause a 

range of harmful effects. For example, acidification of lakes and streams 

can reduce or eliminate fish populations and decrease the numbers and 

types of aquatic plants and animals. 

NOx can also contribute to the nutrient over-enrichment of waterbodies, 

which can harm or kill aquatic species. NOx is one of several sources of 

nitrogen that can contribute to nutrient over-enrichment. Other sources of 

nitrogen, such as runoff from agricultural and urban landscapes, do not 

enter water bodies through atmospheric deposition. Bays and estuaries 

are susceptible to the overabundance of nutrients, including an 

overabundance of nitrogen, because the growth of algae and plankton in 

these waters is generally limited by the availability of nitrogen. As nitrogen 

levels in the water increase, the growth of algae and plankton increases. 

When these organisms die, they are decomposed by bacteria that use the 

dissolved oxygen in the water. Dead zones characterized by low levels of 

dissolved oxygen in the water may result, harming or killing fish, crabs, 

shrimp, and other organisms. Benthic (bottom-dwelling) organisms such 

as oysters that are unable to move to more oxygenated waters are 

particularly susceptible. 

Mercury is toxic to humans and animals. Exposure to mercury can affect 

neurological development, especially in children and developing fetuses, 

which are especially susceptible to mercury exposure. Mercury exposure 

at high levels can also harm the brain, heart, kidneys, lungs, and immune 

systems of all ages. Eating contaminated fish and shellfish is the primary 

 

7

Acid rain is also known as acidic deposition. 

8

SO2 is a component of sulfur oxide, commonly referred to as “SOx”. 

Effects of Atmospheric 

Deposition on Waterbodies 

NOx and SO2

Mercury 
 

Page 8 GAO-13-39 Water Quality 

way humans are exposed to mercury. In mercury contaminated 

waterbodies, bacteria in soils and sediments convert mercury into 

methylmercury, a highly toxic form of mercury. It can then be taken up by 

tiny aquatic plants and animals. Fish that eat these plants and animals 

build up methylmercury in their tissue through a process known as 

bioaccumulation. According to EPA, large predatory fish may have 

mercury concentrations many times higher than the concentrations in the 

waterbody in which they live. Thus, a relatively small concentration of 

mercury in a waterbody can harm humans who eat fish from these 

waterbodies. 

Atmospheric deposition is the primary pathway for mercury to reach many 

waterbodies, although nonatmospheric sources of mercury, such as 

legacy gold mining, can be a significant source of mercury to some 

waterbodies. Once airborne, mercury can travel long distances or be 

deposited close to its source—depending in part on its chemical form. 

Elemental mercury is the most prevalent form of mercury in the 

atmosphere. Because it does not readily react with other chemicals in the 

atmosphere, elemental mercury generally stays aloft for longer periods of 

time and can travel around the globe as part of the “global pool” of 

mercury. Other forms of mercury more readily react with chemicals in the 

atmosphere and travel shorter distances before they deposit. Unlike NOx

and SO2, mercury persists in the environment indefinitely. Mercury that 

has been deposited on land, water, and other surfaces can repeatedly be 

reemitted into the atmosphere. 

The CWA establishes the basic structure for establishing water quality 

standards for surface waters of the United States and for regulating 

discharges of pollutants into those waters. Among other things, CWA 

requires EPA to establish criteria that are then to be used by states to 

establish water quality standards for individual waterbodies. These 

standards consist of three key components: the designated uses that a 

given waterbody is intended to serve, such as recreation, water supply, or 

industrial; the qualitative (narrative) or numeric standards in order for a 

waterbody to be suitable for its designated uses; and antidegradation 

requirements. Where water quality standards are not being met, the 

waterbody is identified as impaired. States are required to identify and 

report a list of waterbodies that do not meet water quality standards, and 

for which pollution controls are not stringent enough to meet such 

The Clean Water Act and 

the Clean Air Act Address 

Water and Air Pollution 
 

Page 9 GAO-13-39 Water Quality 

standards.9 In such cases, the CWA generally requires states to establish 

a TMDL for each pollutant causing a given waterbody to be impaired. The 

TMDL must identify allocations, i.e., the amount of the pollutant that will 

come from point sources (e.g., a pipe from sewage treatment plant) and 

nonpoint sources (e.g., atmospheric deposition or agricultural and urban 

runoff). The total amount of pollution from both types of sources must be 

at a level that ensures that applicable water quality standards for that 

waterbody can be met and maintained. States are generally responsible 

for developing and implementing TMDLs, but their TMDLs must be 

approved by EPA. As of August 2012, EPA has approved more than 

48,000 TMDLs ranging in size from a small segment of a river to a 

multistate region. Additionally, the CWA authorizes EPA or, if approved 

by EPA, the states to issue National Pollution Discharge Elimination 

System (NPDES) permits to a facility that discharges a pollutant from a 

point source into U.S. waters.10 Generally, the discharge restrictions 

established by NPDES permits must be consistent with the allocations in 

applicable TMDLs. The CAA establishes the basic structure for regulating 

the emissions of pollutants into the air. It requires that EPA develop 

National Ambient Air Quality Standards (NAAQS) for certain pollutants, 

including NOx and SO2.

11 These standards include primary standards 

intended to protect public health, including the health of sensitive 

populations such as asthmatics, children, and the elderly, and secondary 

standards intended to protect public welfare from adverse effects such as 

decreased visibility and damage to animals, crops, vegetation, and 

buildings. EPA has developed primary and secondary standards for NOx

 

9

Pollution controls include technology-based and water quality-based effluent limitations 

contained in discharge permits, as well as any required best management practices. 

10According to EPA, the agency has authorized 46 states to issue and enforce NPDES 

permit requirements under their state laws. For those states that are not so authorized 

(Idaho, Massachusetts, New Hampshire, New Mexico, the District of Columbia, American 

Samoa, the Commonwealth of Northern Mariana Islands, Guam, and Puerto Rico), EPA 

retains the authority to issue permits and enforce permit requirements. EPA may also 

issue a compliance order or bring a civil suit in U.S. district court against persons who 

violate the terms of a permit. Those responsible for point sources are required to maintain 

records and to carry out effluent monitoring activities. Permits are effective for up to 5 

years by which time permittees must apply for permit renewal. 

11EPA has set NAAQS for six pollutants, termed “criteria” pollutants: carbon monoxide, 

lead, NOx, ozone, particulate matter, and sulfur dioxides. EPA’s NAAQS for SO2 is 

designed to protect against exposure to all the components of sulfur oxide. Other 

components of sulfur oxide, such as sulfate (SO4), are found in the atmosphere but at 

concentrations much lower than SO2. 
 

Page 10 GAO-13-39 Water Quality 

and SO2. Through its regulatory process, EPA designed the current 

secondary NOx and SO2 standards to protect land-based ecosystems, not 

water quality or aquatic ecosystems. EPA is required, at 5-year intervals, 

to review current NAAQS and make revisions and promulgate new 

standards as appropriate. In addition, the CAA authorizes EPA to set 

certain limits on emissions of “air toxics”—such as mercury—which are 

certain pollutants that may present, through inhalation or other exposures, 

a threat to human health, such as cancer and birth defects, or cause 

adverse environmental effects. EPA has issued regulations that limit 

mercury emissions from certain industries. 

Atmospheric deposition associated with NOx, SO2, and mercury 

contributes to the impairment of many waters in the United States, but the 

full extent is not completely known. Emissions from transportation and 

domestic power plants are key sources of NOx, SO2, and mercury, but 

international sources also contribute to mercury deposition in the United 

States. 

Atmospheric deposition, including from NOx, SO2, and mercury, is a 

contributing source of pollution to many waterbodies that the states have 

identified as impaired—that is, do not meet CWA water quality 

standards—according to our analysis of EPA’s ATTAINS database.12 For 

example, about 53,300 square miles of the Great Lakes are reported to 

be impaired, in part, because of atmospheric deposition.13 Table 1 shows 

for select waterbody types the percentage of waterbodies assessed, the 

percentage of assessed waterbodies that are reported as impaired, and 

the percentage of impaired waterbodies for which atmospheric deposition, 

including from NOx, SO2, and mercury, is identified as a source of 

pollution. However, the ATTAINS database likely underestimates the 

extent of the problem because the states have not assessed all of their 

 

12As described earlier, ATTAINS is an EPA database containing state reported 

information on the extent to which waterbodies meet water quality standards, among other 

things. 

13This reference is to Great Lakes open water. ATTAINS collects separate data on Great 

Lakes shoreline, inland lake shoreline, and connecting channels. According to ATTAINS, 

there are about 60,500 square miles of Great Lakes open water. 

Air Pollution Affects 

U.S. Waterbodies and 

Transportation and 

Power Plants Are Its 

Key Sources 

Atmospheric Deposition 

Pollutes Many U.S. 

Waterbodies, but the Full 

Extent is Not Known 
 

Page 11 GAO-13-39 Water Quality 

waterbodies.14 The percentage of waterbodies assessed varies by 

waterbody type and ranges from about 1 percent of wetlands to about 88 

percent of the Great Lakes. Additionally, states may, but are not required, 

to report on the sources of a pollutant to a waterbody, including whether 

atmospheric deposition is a reason why water quality standards are not 

being met or the extent to which atmospheric deposition is contributing to 

the problem. 

Table 1: Waterbodies Reported by States as Impaired by Atmospheric Deposition 

by Waterbody Type 

Type of waterbody

Percentage of 

waterbodies 

assessed

Percentage of 

assessed 

waterbodies that 

are reported as 

impaired 

Percentage of impaired 

waterbodies for which 

atmospheric deposition 

was identified as a 

contributing source

Rivers and streams 28 53 20

Lakes and 

reservoirs 

46 69 37

Bays and estuaries 37 66 36

The Great Lakes 88 100 100

Source: GAO analysis of ATTAINS database. 

Notes: GAO’s analysis of ATTAINS database includes data on the 50 states, the District of Columbia, 

American Samoa, the Commonwealth of Northern Mariana Islands, Guam, Puerto Rico, and the 

Virgin Islands. The most recently available state data are the most current year that each state 

reported. These years varied from 2002 to 2010 because some states reported more recently than 

others. 

The table includes the percentage of assessed waterbodies that are reported as impaired by any 

pollutant, including NOx, SO2, and mercury and the percentage of impaired waterbodies for which 

atmospheric deposition of any pollutant, including NOx, SO2, and mercury, was identified as a 

contributing source. 

Federal studies also show that atmospheric deposition associated with 

NOx, SO2, and mercury is polluting waters in the United States. For 

example, a 2011 report from the National Acid Precipitation Assessment 

Program (NAPAP)—a federal interagency program that coordinates acid 

rain research—summarized the most recent studies on acid rain and 

identified waters in several acid-sensitive ecosystems that are most 

 

14States are required to identify those waters that are impaired—that is, waters for which 

pollution controls are insufficient to meet water quality standards—and report this list to 

EPA every 2 years. According to EPA, states have not assessed all their waterbodies 

because of limited resources, but many states target their limited resources to 

waterbodies that they suspect are impaired. 
 

Page 12 GAO-13-39 Water Quality 

vulnerable and that continue to receive harmful levels of acid rain.15

According to the report, from 2006 through 2008, over 550 lakes in the 

Adirondack Mountains and approximately 21,000 miles of streams in the 

Central Appalachian Mountains continued to experience levels of acid 

rain that exceeded their ability to neutralize the acid. However, according 

to an EPA document, there is relatively sparse data coverage in 

mountainous western areas where a number of sensitive ecosystems are 

located.16 Figure 2 shows acid-sensitive ecosystems in the United States. 

 

15National Science and Technology Council, National Acid Precipitation Assessment 

Program Report to Congress 2011: An Integrated Assessment (Washington, D.C.: 2011). 

The CAA Amendments of 1990 authorized NAPAP to, among other things, periodically 

assess the effectiveness of the Acid Rain Program and report its findings to Congress. 

NAPAP operates under the auspices of the National Science and Technology Council 

(NSTC) Committee on Environment, Natural Resources, and Sustainability (CENRS). The 

NAPAP member agencies are the EPA, the U.S. Department of Energy, the U.S. 

Department of Interior/U.S. Geological Survey, the U.S. Department of Interior/National 

Park Service, the National Aeronautics and Space Administration, and NOAA. 

16See EPA, Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and 

Sulfur; Proposed Rule, 76 Fed. Reg. 46,084, 46,134 (Aug. 1, 2011). 
 

Page 13 GAO-13-39 Water Quality 

Figure 2: Location of Acid-Sensitive Ecosystems in the United States 

A 2007 study by NOAA assessed the extent to which 99 estuaries across 

the country experienced symptoms associated with nutrient overenrichment, such as algal blooms.17 The study found that 29 of the 

 

17Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 

Effects of Nutrient Enrichment In the Nation’s Estuaries: A Decade of Change. NOAA 

Coastal Ocean Program Decision Analysis Series No. 26. National Centers for Coastal 

Ocean Science (Silver Spring, MD: 2007). The study initially chose 141 estuaries to 

assess but did not have sufficient data to assess 42 of them. 
 

Page 14 GAO-13-39 Water Quality 

estuaries experienced symptoms that affected at least 50 percent of the 

estuary and/or were persistent and that another 35 estuaries periodically 

experienced symptoms that affected a smaller portion of the estuary. The 

study identified atmospheric deposition as contributing source of nutrients 

for all coastal regions—except the Pacific coast, for which there were 

insufficient data—but did not quantify the relative amount of nitrogen, 

including NOx coming from atmospheric deposition. A 2011 NAPAP report 

did quantify the relative amount of nitrogen coming from atmospheric 

deposition.18 Summarizing other scientific studies, the report stated that 

the relative amount of nitrogen entering estuaries that comes from 

atmospheric deposition varied from about 15 percent to 25 percent in the 

Mississippi Delta region of the Gulf of Mexico, to 20 percent to 50 percent 

from the Chesapeake Bay to Tampa Bay, and as much as 60 percent to 

80 percent in some coastal river estuaries of northern New England.19

The report did not provide any data about West Coast estuaries. 

Similarly, studies show that mercury is contaminating waters in the United 

States, but the extent of the contamination is less well understood. 

According to the National Atmospheric Deposition Program (NADP)—a 

public-private cooperative program that monitors atmospheric deposition 

of mercury, among other pollutants—atmospheric deposition is the 

primary pathway by which mercury reaches waters in many parts of the 

 

18National Science and Technology Council, National Acid Precipitation Assessment 

Program Report to Congress 2011: An Integrated Assessment (Washington, D.C.: 2011). 

19The report summarized the following studies: McIsaac, G.F., M.B. David, G.Z. Gertner, 

and D.A. Goolsby, “Eutrophication: Nitrate flux in the Mississippi River,” Nature 414 

(2001):166–167; Boyer, E.W., C.L. Goodale, N.A. Jaworski, and R.W. Howarth, 

“Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the 

northeastern U.S.A.” Biogeochemistry 57/58(2002):137–169.; Poor, N., C. Pollman, P. 

Tate, M. Begum, M. Evans, and S. Campbell, “Nature and magnitude of total inorganic 

nitrogen and other inorganic species to the Tampa Bay watershed, FL, USA,” Water, Air, 

& Soil Pollution 170(2006):267–83; Whitall, D., S. Bricker, J. Ferreira, A.M. Nobre, T. 

Simas, and M. Silva, “Assessment of eutrophication in estuaries: Pressure-state-response 

and nitrogen source apportionment,” Environmental Management 40(2007):678–690; 

Alexander, R.B., R.A. Smith, G.E. Schwarz, E.W. Boyer, J.V. Nolan, and J.W. Brakebill, 

“Differences in phosphorus and nitrogen delivery to the Gulf of Mexico from the 

Mississippi River,” Environmental Science & Technology 42(2008):822–830; and Howarth, 

R.W., “Estimating atmospheric nitrogen deposition in the northeastern United States: 

Relevance to Narragansett Bay,” ch. 3, in A. Desbonnet and B. A. Costa-Pierce, eds. 

Science for Ecosystem based Management: Narragansett Bay in the 21st Century, 

Springer Series on Environmental Management (New York: Springer) 47-65. 
 

Page 15 GAO-13-39 Water Quality 

United States.20 Other studies report similar results. For example, a 2007 

report to Congress by NOAA concludes that atmospheric deposition of 

mercury is a significant source of mercury in the Great Lakes.21 However, 

measuring mercury atmospheric deposition, especially dry deposition, is 

scientifically challenging, and representatives from NADP told us that 

there are significant data gaps on the amount of dry deposition across the 

country. Additionally, there are factors other than the amount of mercury 

in a waterbody that affect the amount of mercury in fish tissue. For 

example, the amount of mercury that has been converted to 

methylmercury—the form of mercury that bioaccumulates in fish—is 

influenced by various factors such as the chemical composition of the 

water. The amount of mercury in fish tissue also varies by the size and 

species of fish present in the waterbody. Nevertheless, according to 

EPA’s 2010 National Listing of Fish Advisories, all 50 states reported 

mercury-related fish consumption advisories, and 25 states reported 

statewide freshwater advisories. Additionally, Alaska, Hawaii, all of the 

Gulf states, and most of the East Coast states, reported statewide coastal 

advisories. Figure 3 shows the extent of mercury-related fish consumption 

advisories in 2010. Statewide advisories are precautionary and warn the 

public of the potential contamination of certain fish types in specific 

waterbodies, resulting in a designated fish advisory for all rivers or lakes 

in the state. 

 

20NADP is a cooperative effort among groups— including federal, state, tribal, and local 

governmental agencies, educational institutions, private companies, and nongovernmental 

agencies—that monitor atmospheric deposition of mercury, among other pollutants. The 

federal agencies involved in NADP include the Agricultural Research Service and the 

Forest Service within the Department of Agriculture; the Bureau of Land Management, the 

Fish and Wildlife Service, the Geological Survey, and the National Park Service within the 

Department of the Interior; the National Aeronautics and Space Administration; the 

National Science Foundation; NOAA; EPA; and the Tennessee Valley Authority. 

21Cohen, M., R. Artz, and R. Draxler. Report to Congress: Mercury Contamination in the 

Great Lakes. NOAA Air Resources Laboratory (Silver Spring, MD: 2007). 
 

Page 16 GAO-13-39 Water Quality 

Figure 3: Mercury-related Fish Consumption Advisories, 2010 

According to 2008 data, domestic transportation is the largest source of 

NOx, and domestic power plants are the primary source of SO2 and the 

largest source of U.S. mercury emissions, but international sources of 

mercury are a significant contributor to mercury atmospheric deposition in 

the United States. 

Domestic Transportation 

and Power Plants Are 

Sources of NOx and SO2, 

and Other Countries 

Contribute to Mercury 

Deposition 
 

Page 17 GAO-13-39 Water Quality 

Domestic transportation is the largest source of NOx emissions in the 

United States, according to EPA’s 2008 National Emissions Inventory.22

Figure 4 shows that on-road vehicles, such as cars and trucks, and offroad transportation, such as commercial fishing vessels, passenger 

trains, and commercial aircraft, contributed approximately 63 percent of 

the total estimated 17.4 million tons of NOx emissions in the United 

States. Other sources of NOx emissions include fuel combustion, mainly 

from power plants and industrial boilers,23 which accounted for an 

estimated 28 percent of total estimated NOx emissions. According to an 

EPA official, the only international sources of NOx emissions of any note 

that reach the United States are in Canada and Mexico and, in general, 

emissions from these sources do not impact U.S. waters. 

Figure 4: Estimated Contributions of NOx Emissions from Domestic Sources in 

2008 

a

Miscellaneous includes sources such as gas stations, bulk gasoline terminals, and commercial cooking. 

b

Some military aircraft are not included in the transportation category but are instead included in the 

fuel combustion category. 

c

Other fuel combustion sources include residential, commercial, and institutional biomass and fossilfuel burning units. 

Ammonia emissions, like NOx, can contribute to the atmospheric 

deposition of nitrogen. When nitrogen in fertilizers and animal waste 

 

22The 2008 National Emissions Inventory (version 2) provides the most complete 

collection of emissions data. EPA is currently collaborating with state, local, and tribal 

agencies in preparing the 2011 inventory. 

23Industrial boilers are a type of electrical generating unit that burns fossil fuels. 

Domestic Transportation Is the 

Largest Source of 

NOx Emissions 
 

Page 18 GAO-13-39 Water Quality 

breaks down, it is converted to ammonia gas and released into the air, 

where it can deposit on land and water. Agriculture accounted for 

approximately 83 percent of the total estimated 4.4 million tons of 

ammonia emissions, according to the 2008 National Emissions Inventory. 

Ammonia emissions can contribute to nutrient over-enrichment in 

waterbodies and, in some areas of the country, ammonia can be the 

dominant source of atmospheric nitrogen, especially those areas with 

abundant agricultural land, according to the 2011 NAPAP report. 

Domestic power plants are the primary source of SO2 emissions in the 

United States, according to the 2008 National Emissions Inventory. Figure 

5 shows that fuel combustion, mainly from power plants, contributed 

approximately 87 percent of the total estimated 10.4 million tons of SO2

emissions in the United States.24 Industrial processes and transportation 

contributed approximately 8 percent and 3 percent, respectively. According 

to an EPA official, the only international sources of SO2 emissions of any 

note that reach the United States are in Canada and Mexico and, in 

general, emissions from these sources do not impact U.S. waters. 

Figure 5: Estimated Contributions of Sulfur Dioxide Emissions from Domestic 

Sources in 2008 

Note: These power plants are primarily coal-fired. 

a

Miscellaneous includes sources such as gas stations, bulk gasoline terminals and commercial cooking. 

b

Other fuel combustion sources include residential, commercial and institutional biomass and fossilfuel burning units. 

 

24Power plants contributed approximately 7.8 million tons of SO2, or about 75 percent of 

the total estimated 10.4 million tons of SO2 emissions. 

Domestic Power Plants Are the 

Primary Source of 

SO2 Emissions 
 

Page 19 GAO-13-39 Water Quality 

Domestic sources emitted about 61 tons of mercury, according to the 

2008 National Emissions Inventory. Figure 6 shows that fuel combustion 

from domestic power plants—mostly coal-burning power plants—

contributed approximately half of these emissions. The next three largest 

sources were electric arc furnaces, industrial, commercial, and 

institutional boilers and process heaters, and Portland cement 

nonhazardous waste.25

Figure 6: Estimated Contributions of Mercury Emissions from Domestic Sources in 

2008 

aPortland cement is the most common type of cement produced around the world. Portland cement 

kilns emit mercury, among other pollutants. 

b

Other sources of mercury emissions include gold mining, transportation, municipal waste 

combustors, medical waste incineration, and other types of incineration. 

 

25Electric arc furnaces are heating devices that produce highly luminous and intensely hot 

electrical currents that jump between electrical conductors in the form of an arc and are 

used for melting metals such as steel. Portland cement nonhazardous waste is waste 

produced from cement kilns that produce the most common cement around the world 

known as Portland cement. Industrial, commercial, and institutional boilers and process 

heaters are types of electrical generating units that burn fossil fuels. 

Domestic Power Plants Are the 

Largest Source of U.S. Mercury 

Emissions, but International 

Sources Contribute 

to Deposition 
 

Page 20 GAO-13-39 Water Quality 

While most of the NOx and SO2 that affects U.S. waters originates from 

human-caused domestic sources, this is not the case for mercury. Some 

of the mercury deposited in the United States comes from international 

and natural sources, such as volcanoes, and not all mercury emissions 

from domestic sources are deposited in the United States. According to a 

2010 EPA report, human-caused mercury emissions from the United 

States, southern Canada, and northern Mexico contribute about 20 to 30 

percent of the total mercury atmospheric deposition in the continental 

United States.26 The remainder comes from other foreign sources and 

natural sources. However, according to a 2008 EPA report, local sources 

can be the dominant contributor of mercury atmospheric deposition in 

areas where there are sources that emit large amounts of mercury.27 A 

2008 United Nations Environment Programme (UNEP) report estimated 

that human-caused mercury emissions from North America contributed 

about 8 percent of global human-caused mercury emissions in 2005 (see 

fig. 7).28 Asia, on the other hand, contributed about 67 percent of global 

mercury emissions. According to the report, in 2005 about 46 percent of 

global mercury emissions came from burning fossil fuels, primarily coal, to 

produce electricity and heat. Another 24 percent of global mercury 

emissions came from gold production. Other global sources of mercury 

emissions include metal production (excluding gold) and cement 

production. 

 

26The Environmental Protection Agency, Effects of Air Pollutants on Ecological 

Resources: Literature Review and Case Studies, Draft Report (Washington, D.C.: 

February 2010). In its literature review, EPA cited two studies: (1) Seigneur, C., K. 

Vijayaraghavan, K. Lohman, P. Karamchandani, and C. Scott, “Global Source Attribution 

for Mercury Deposition in the United States” Environmental, Science and Technology, 38 

(2004), 555-569, and (2) Selin, N.E., D.J. Jacob, R.J. Park, R.M. Yantosca, S. Strode, L. 

Jaegle, and D. Jaffe, “Chemical cycling of atmospheric mercury,” Journal of Geophysical 

Research (January 2007). Reemissions of mercury also contribute to mercury deposition 

in the United States, but the two studies that EPA reviewed either did not cite reemission 

contributions or included reemission contributions in the emission contributions from 

natural or human-caused sources. 

27The Environmental Protection Agency, Model-Based Analysis and Tracking of Airborne 

Mercury Emissions to Assist in Watershed Planning (Washington, D.C.: August 2008). 

28The United Nations Environment Programme, The Global Atmospheric Mercury 

Assessment: Sources, Emissions and Transport (Geneva, Switzerland: December 2008). 
 

Page 21 GAO-13-39 Water Quality 

Figure 7: Estimated Contributions of Global Mercury Emissions from HumanCaused Sources in 2005 

Note: Percentages do not add to 100 percent due to rounding. 

aThe Oceania region includes the islands of the southern, western, and central Pacific Ocean, such 

as Australia, New Zealand, Melanesia, Micronesia, and Polynesia. 

Listing impaired waters and TMDLs are the primary regulatory tools EPA 

uses under the CWA to identify water pollution resulting from atmospheric 

deposition, but EPA faces challenges in using these tools, as well as 

other nonregulatory tools, to address the effects of atmospheric 

deposition. Three TMDLs we reviewed illustrate the challenges 

associated with using these tools. 

EPA has regulatory and nonregulatory tools available under the CWA for 

addressing atmospheric deposition. 

EPA Faces Challenges 

Using Clean Water Act 

Regulations to 

Address Atmospheric 

Deposition 

Key Regulatory Tools Do 

Not Directly Regulate 

Atmospheric Deposition 
 

Page 22 GAO-13-39 Water Quality 

EPA’s key regulatory tools for considering the effects of atmospheric 

deposition on water quality are listing of impaired waters and TMDLs, but 

the CWA does not directly regulate nonpoint sources of pollution, 

including pollution resulting from atmospheric deposition. When states 

identify waterbodies that are impaired—that is, that do not meet CWA 

water quality standards with existing controls—the CWA requires states 

to formally identify them as impaired, and generally to set a TMDL for 

each pollutant that does not meet the standards. TMDLs are not selfimplementing and CWA does not expressly require they be implemented; 

states generally have the lead role for implementation. TMDL allocations 

for permitted point sources are typically implemented via NPDES permits. 

Relevant NPDES permits issued to facilities for point sources of that 

pollutant must be consistent with the allocations established by the 

TMDL, but there is no comparable permitting mechanism under the CWA 

directly limiting pollutants from nonpoint sources. Nevertheless, states 

must account for nonpoint sources of pollution in their TMDLs and may 

include estimated reductions from those nonpoint sources. Where a state 

provides EPA with “reasonable assurance” that the reductions from 

nonpoint sources of pollution identified in the TMDL will be achieved, EPA 

often can allow NPDES permits for point sources of pollution identified in 

the TMDL to be less stringent than they would have otherwise been.29

EPA makes “reasonable assurance” determinations based on factors 

such as whether practices to reduce the nonpoint source pollutant are 

technically feasible and likely to be implemented. While this creates an 

incentive for a state to reduce pollution from nonpoint sources, the CWA 

provides no direct requirement—such as permitting—that states 

implement such reductions. 

A further challenge in using TMDLs to address atmospheric deposition is 

that the pollution impairing a waterbody can originate outside of the state 

responsible for implementing the TMDL. For example, pollutants travel in 

the atmosphere and harm air quality and the environment in downwind 

communities. To help address this challenge, EPA allows states some 

flexibility in addressing these situations. Specifically, EPA allows states 

 

29EPA requires reasonable assurance to allow EPA to determine that the TMDL has been 

established at a level necessary to implement water quality standards. Under EPA 

guidance, reasonable assurance is only needed for TMDLs that include allocations for 

both point and nonpoint sources. A TMDL developed for waters impaired solely by point 

sources does not have to demonstrate reasonable assurance. Also, the NPDES permit, 

and the requirements associated with it, constitutes the reasonable assurance that a 

TMDL’s allocation for point sources will result in the attainment of water quality standards. 

Regulatory Tools 
 

Page 23 GAO-13-39 Water Quality 

with a waterbody impaired primarily from atmospheric sources of mercury 

to defer developing a TMDL for that waterbody if the state is carrying out 

a comprehensive mercury reduction program and demonstrates progress 

in reducing in-state mercury sources. This approach provides a public 

accounting of the status of mercury impaired waters and a way for states 

to demonstrate progress in reducing in-state mercury sources. According 

to an EPA document describing this approach, it may also be useful in 

situations where other pollutants are primarily from atmospheric 

deposition. However, according to EPA officials, this approach is intended 

to encourage states to address in-state sources of mercury, and EPA has 

not encouraged the use of this approach for other pollutants such as NOx

or SO2. 

According to EPA officials, despite these limitations of the CWA, TMDLs 

may play an important role in understanding the role of atmospheric 

deposition to impairment of a particular waterbody, such as identifying the 

contributions from air sources to water and the reductions needed in air 

sources in order to meet water quality standards. In addition, according 

to EPA officials, TMDLs may parse the contributions from various air 

sources to waterbodies, including separating the contributions from local 

and global sources, which may help states identify whether there are air 

sources that can be controlled at the state level. 

EPA also has nonregulatory tools available under the CWA to provide 

incentives and assistance to the states to address nonpoint source 

pollution and improve water quality. However their use in addressing 

atmospheric deposition presents challenges. The most notable of these 

tools is the nonpoint source management program known as the Section 

319 Program. Under this program, EPA offers technical and financial 

assistance to states and local agencies to develop projects to control 

nonpoint sources of water pollution.30 According to an EPA official, only a 

small portion of projects that have been funded in this program have 

addressed atmospheric deposition. According to the official, projects 

typically involve source control—slowing down stormwater flow to prevent 

erosion or building fences to keep livestock out of streams—but the 

source of atmospheric deposition can be diffuse, as is the case with cars, 

or originate in other countries, as is the case with mercury. According to 

 

30For more information, see GAO, Nonpoint Source Water Pollution: Greater Oversight 

and Additional Data Needed for Key EPA Water Program, GAO-12-335 (Washington, 

D.C.: May 31, 2012). 

Nonregulatory Tools 
 

Page 24 GAO-13-39 Water Quality 

the official, a local or state agency that deals with water quality issues 

does not have authority or tools to control these types of sources and 

would find it difficult to develop a project to control atmospheric 

deposition. 

Another CWA tool relevant to atmospheric deposition is the interstate 

management conference process,31 whereby states or regions can 

petition the EPA Administrator to convene a management conference of 

all states that contribute nonpoint source pollution to the state’s or 

region’s waterbodies. The purpose of the conference is to forge an 

agreement to reduce the sources of nonpoint source pollution from the 

states or regions contributing to the pollution. However, even if a 

conference is held, there is neither a requirement that an agreement to 

address the problem be reached nor is there a requirement that any 

agreement that is reached be binding. EPA granted the petition for one 

such conference on the atmospheric deposition of mercury, which took 

place in 2010. However, as discussed below, participants in this 

conference did not reach an agreement on steps to reduce atmospheric 

deposition of mercury. 

The three TMDLs that we reviewed illustrate the challenges that states 

face in mitigating sources of atmospheric deposition when these sources 

originate from outside of the state or region. These three TMDLs are the 

Northeast Regional TMDL for mercury, a New York State TMDL for acid 

rain in the Adirondacks, and the Chesapeake Bay TMDL for nitrogen.32

In the Northeast Region, more than 10,000 lakes, ponds, and reservoirs, 

and more than 46,000 river miles are listed as impaired for fish 

consumption primarily due to the presence of mercury—mostly from 

atmospheric deposition.33 A committee of representatives of each of the 

 

31See 33 U.S.C. § 1329(g) (2012). When a state petitions EPA for a conference, the 

provision does not give EPA specific responsibilities or authority beyond holding the 

conference. 

32In addition to nitrogen, the TMDL addresses other pollutants, but the atmospheric 

deposition of these other pollutants is not a significant source to the bay. 

33The Northeast Region, as referred to here, includes the New England states 

(Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont) and 

New York State. According to TMDL documents, about 98 percent of the mercury comes 

from atmospheric deposition. 

Three TMDLs Highlight 

Challenges in Addressing 

Atmospheric Deposition 

under the Clean Water Act 

Northeast Regional TMDL 

for Mercury 
 

Page 25 GAO-13-39 Water Quality 

Northeast states and the New England Interstate Water Pollution Control 

Commission (NEIWPCC) developed a TMDL for mercury and an 

implementing strategy to reduce the mercury concentration in fish in 

Northeast Region waterbodies.34 EPA approved the TMDL in 2007. 

However, the TMDL acknowledged that given the magnitude of the 

reductions required to implement the TMDL, the Northeast Region cannot 

reduce in-region sources further to compensate for insufficient reductions 

from out-of-region sources. According to the TMDL, prior mercury 

emission limits implemented by the Northeast Region had contributed to 

reducing in-region mercury deposition by approximately 74 percent from 

1998 to 2002. By 2002, most of the remaining mercury deposited in the 

region was from out-of-region sources, with roughly two-thirds from the 

global pool of mercury and the remaining from domestic sources, split 

roughly evenly between sources in the Northeast Region states and 

sources in 11 other states, according to our analysis of a 2008 study by 

the Northeast States for Coordinated Air Use Management 

(NESCAUM).35 Figure 8 depicts the out-of-region sources of atmospheric 

deposition in the Northeast Region as of 2002. 

 

34The NEIWPCC is a not-for-profit interstate agency, established by an act of Congress, 

which serves its member states individually and collectively by providing coordination, 

public education, research, training, and leadership in water management and protection 

in the New England region and New York State. 

35The Northeast States for Coordinated Air Use Management, Sources of Mercury 

Deposition in the Northeast United States (March 2008). This study presents numeric 

estimates of the amount of mercury deposited in the Northeast Region states and the 

sources of that mercury. These estimates were obtained from a report prepared for EPA in 

2006, based on 2002 data (ICF International, Model-Based Analysis and Tracking of 

Airborne Mercury Emissions to Assist in Watershed Planning (San Rafael, CA: Nov. 30, 

2006). According to the authors of the ICF report, the numeric estimates result from a 

model that includes some uncertainty, and the estimates should be used to show the 

relative amounts of mercury originating from, and depositing in, different states or 

originating from global sources. The most recent year for which this data is available is 

2002. 
 

Page 26 GAO-13-39 Water Quality 

Figure 8: Sources of Atmospheric Deposition of Mercury in the Northeast Region, 

2002 

To address domestic but out-of-region mercury sources, in 2008, 

Northeast Region officials used the CWA interstate management 

conference process discussed above and petitioned EPA to hold a 

conference with 11 states that, according to a 2008 NESCAUM study, 

were the states outside the region that contributed the most to the 

Northeast’s mercury problem. The conference participants discussed 

developing a “principles document” that would outline next steps. 

However, according to a NEIWPCC representative, there was not enough 

agreement among the states to move forward with the principles 

document, and no formal agreement was reached to reduce the 

atmospheric deposition of mercury. In the end, according to the 

representative, all of the participating states have made some efforts to 
 

Page 27 GAO-13-39 Water Quality 

reduce mercury, but the level of commitment varies by state. According 

to EPA officials, the conference brought together senior air and water 

program officials from upwind and downwind states and allowed 

participants to learn about successful mercury programs in other states. 

Over the last several decades, acid rain has resulted in the significant 

loss of fish populations in the Adirondacks Region located in northeast 

New York State. In 2006, the New York State Department of 

Environmental Conservation (NYSDEC) developed a TMDL for an acid 

rain restoration plan to address 143 impaired lakes on state-owned forest 

preserve lands in the Adirondacks.36 Figure 9 shows the forest preserve 

lands within the Adirondacks. 

 

36These lands are regulated by the New York State Constitution as being “forever wild.” 

Adirondacks Region Lakes 

TMDL for Acid Rain 
 

Page 28 GAO-13-39 Water Quality 

Figure 9: Location of New York State Forest Preserve Lands in the Adirondacks 

According to state officials, over the last two decades the state has 

reduced in-state emissions of SO2 by about 90 percent and reduced instate emissions of NOx to a lesser extent.37 This in turn has reduced acid 

rain and improved water quality in the Adirondack lakes. However, state 

 

37NOx emissions decreased from 30 percent to 90 percent depending on the emission 

source but there is not reliable data on the overall reduction. 
 

Page 29 GAO-13-39 Water Quality 

officials said that reducing acid rain to the levels called for in the TMDL 

remains a challenge because almost all of the NOx, SO2, and other sulfur 

oxides contributing to acid rain in the region can be attributed to out-ofstate sources—mostly from the Southeast, and Midwest United States 

and Canada. Specifically, data compiled by the NYSDEC in the mid1980s estimated that 83 to 87 percent of acid rain came from emissions 

of NOx, SO2, and other sulfur oxides originating out-of-state, and 

NYSDEC officials stated that this percentage is now likely higher as a 

result of the in-state reductions. According to NYSDEC officials, meeting 

the TMDL goals for acid rain is dependent on emissions reductions in 

other states, but they said the department will continue to address its 

responsibilities for improving air and water quality within the state through 

implementation of federal programs under the CAA, as well as state air 

programs, such as its Acid Deposition Reduction Program. According to 

NYSDEC officials, the state has not used other nonregulatory tools 

available under the CWA to help address acid rain, such as petitioning for 

conferences with other states, but they said that this is an option that 

needs to be considered. 

Most of the Chesapeake Bay and its tidal waters are impaired, in part 

because of the effects of excess nitrogen. According to TMDL 

documents, atmospheric deposition of NOx accounts for about 22 percent 

of the total nitrogen entering the bay. Other sources of nitrogen include 

agricultural (i.e., ammonia from chemical fertilizer and manure), municipal 

and industrial wastewater, and storm water runoff.38 The Chesapeake Bay 

watershed covers 64,000 square miles and includes parts of six states—

Delaware, Maryland, New York, Pennsylvania, Virginia, and West 

Virginia—and the District of Columbia. 

In December 2010, EPA established the Chesapeake Bay TMDL for 

nitrogen. Among other things, for each of the seven jurisdictions in the 

watershed, the TMDL sets an allocation for total nitrogen entering the bay 

watershed, including from atmospheric deposition, needed to reduce 

nitrogen to meet water quality standards.39 However, as with the 

Northeast and Adirondack TMDLs discussed, the jurisdictions that are a 

 

38Atmospheric deposition of ammonia accounts for about 11 percent of total nitrogen 

impacting the bay. 

39The total limit for the jurisdictions was set at about 186 million pounds, or about a 25 

percent reduction from previous limits. 

Chesapeake Bay TMDL 

for Nitrogen 
 

Page 30 GAO-13-39 Water Quality 

party to this TMDL can only control those pollution sources inside their 

own jurisdictions. The bay’s watershed is contained within the boundaries 

of the seven jurisdictions party to the TMDL, but the bay’s NOx airshed 

extends beyond the seven jurisdictions’ boundaries. According to EPA, 

about 50 percent of the NOx impacting the bay comes from sources 

outside of the seven jurisdictions. Figure 10 depicts the Bay’s watershed 

and NOx airshed—defined by the area from which 75 percent of the NOx

emissions that contribute to the bay originate.40

 

40According to EPA, 25 percent of NOx emissions that contribute to the bay come from 

outside the seven jurisdictions but within the NOx airshed, and 25 percent come from 

outside of the airshed. 
 

Page 31 GAO-13-39 Water Quality 

Figure 10: Location of NOx Airshed and Chesapeake Bay Watershed 
 

Page 32 GAO-13-39 Water Quality 

Implementation of CAA regulations has reduced emissions of NOx, SO2, 

and mercury and lessened the impact of atmospheric deposition on water 

quality and aquatic ecosystems. However, atmospheric deposition 

continues to affect water quality and harm aquatic ecosystems, and EPA 

faces challenges in using the CAA to further lessen the impact. 

Implementation of EPA’s CAA regulations has reduced emissions of NOx, 

SO2, and mercury, but most were designed to address the effect of these 

pollutants on air quality and related human health effects, not water 

quality and aquatic ecosystems. While not designed specifically to 

address water quality, reductions in emissions that have occurred as a 

result of the implementation of CAA regulations have had a beneficial 

effect on water quality. Even with these reductions in pollutants, 

atmospheric deposition continues to affect water quality and harm aquatic 

ecosystems. 

According to EPA’s 2008 National Emissions Inventory, domestic 

emissions of NOx declined from about 26 million tons in 1990 to about 17 

million tons in 2008—about 74 percent of this reduction came from 

reduced emissions from power plants and on-road vehicles. Also 

according to the inventory, emissions of SO2 declined from 23 million tons 

in 1990 to 10 million tons in 2008—about 64 percent of this reduction 

came from reduced emissions from power plants. Figure 11 shows the 

decline in NOx and SO2 emissions. 

Clean Air Act 

Regulations Address 

Atmospheric 

Deposition, but EPA 

Faces Challenges 

Addressing Effects on 

Waterbodies 

CAA Regulations Have 

Lessened the Effect of 

Atmospheric Deposition 

on Waterbodies, but Such 

Deposition Is 

Still Occurring 

NOx and SO2 Emissions 
 

Page 33 GAO-13-39 Water Quality 

Figure 11: NOx and SO2 Emissions in 1990, 2000, and 2008 by Source 

Note: Regarding the figure depicting SO2 emissions, the category “All other sources” includes on-road 

vehicles. According to the National Emissions Inventory, on-road vehicles emitted 503 tons of SO2 in 

1990 and 117 tons in 2008. 

EPA has identified the following three key regulations or programs as 

contributing to these reductions (1) CAA Title II emission standards for 

moving sources (i.e., vehicle emission standards), (2) actions designed to 

meet primary NAAQS,41 and (3) the Acid Rain Program. Neither the 

vehicle emissions standards nor the actions to meet primary NAAQS are 

 

41Actions designed to meet primary NAAQS include, for example, emissions reductions 

under the Clean Air Interstate Rule, as well as other state-led programs such as the NOx

Budget Program. 
 

Page 34 GAO-13-39 Water Quality 

designed to address the effect of NOx and SO2 on waterbodies.42 Vehicle 

emission standards limit certain vehicles’ emissions of pollutants, 

including NOx, to the greatest extent achievable through the application of 

available technology, giving appropriate consideration to cost, energy, 

and safety factors. Even with these reductions in pollutants, atmospheric 

deposition continues to affect water quality and harm aquatic ecosystems. 

EPA established primary NAAQS to provide public health protection, 

including protecting the health of “sensitive” populations such as 

asthmatics, children, and the elderly, for six principal pollutants, which are 

called “criteria” pollutants to protect public health based on scientific 

information on their effects.43 In contrast, the Acid Rain Program was 

designed, in part, to address the effect of NOx and SO2 on waterbodies. 

The program implements CAA requirements for significant decreases in 

the emissions of NOx and SO2 from power plants to improve air quality 

and protect ecosystems that have suffered damage from acid rain, 

including aquatic ecosystems. According to the 2011 NAPAP report, the 

mandated emission reductions have been achieved, and thus no 

additional reductions in emissions can be expected from this program.44

However, two broad trends—recent environmental regulations and 

changing market conditions—could affect emissions from power plants. 

Regarding environmental regulations, as we have previously reported, 

beginning in June 2010, EPA proposed or finalized two key regulations 

that would, among other things, reduce emissions of NOx and SO2 from 

coal-burning power plants, but the requirements and deadlines these 

 

42While EPA has not promulgated such regulations explicitly designed to address 

atmospheric deposition, EPA officials pointed out that EPA’s mobile source standards do 

in fact address impacts on public welfare, which would include impacts of air pollutants on 

waterbodies. These officials noted that mobile source standards are “applicable to the 

emission of any air pollutant...which may reasonably be anticipated to endanger public 

health or welfare.” The officials stated that they had addressed the mobile source 

standards’ impact on public welfare in their rulemakings. 

43EPA has also established secondary NAAQS. Secondary NAAQS can be specifically 

designed to address a pollutant’s impact on water quality and aquatic ecosystems, but the 

current secondary NAAQS for NOx and SO2 are designed to protect land-based 

ecosystems. 

44National Science and Technology Council, National Acid Precipitation Assessment 

Program Report to Congress 2011: An Integrated Assessment (Washington, D.C.: 2011). 
 

Page 35 GAO-13-39 Water Quality 

regulations may establish for power plants are uncertain.45 In particular, 

both regulations have been challenged in federal court. For example, 

EPA finalized the Cross-State Air Pollution Rule in August 2011. The 

regulation would have required reductions of certain emissions of air 

pollutants, including NOx and SO2, in 28 states. The U.S. Court of 

Appeals for the D.C. Circuit recently issued an opinion that would strike 

down the regulation, and EPA has asked the full court to rehear the case, 

creating uncertainty as to what may be required from power plants in the 

future to address such emissions.46 Regarding broader market conditions, 

important market drivers have been weighing on the viability of coalburning power plants. Key among these has been the recent decrease in 

the price of natural gas, which has made it more attractive for power 

companies to use natural gas instead of coal to generate electricity. 

Power plants that use natural gas instead of coal to produce electricity 

generally emit less NOx and SO2 per unit of electricity generated. 

Nevertheless, coal is likely to continue to be a key fuel source for 

electricity generation in the United States, although its share as a source 

of electricity is expected to decline.47

Additionally, there have recently been key mobile source standards, like 

the 2010 Emissions Control Area and the 2011 Heavy Duty Vehicle GHG 

standards, which provide large reductions in both NOx and SOx from 

ocean-going ships and heavy-duty trucks, respectively. In addition, 

according to EPA officials, the upcoming planned Tier 3 vehicle 

standards, which are scheduled to be proposed in 2013, will provide 

significant NOx reductions in the future. 

 

45See GAO, EPA Regulations and Electricity: Better Monitoring by Agencies Could 

Strengthen Efforts to Address Potential Challenges, GAO-12-635 (Washington, D.C.: July 

17, 2012). 

46As of December 2012, the court has not yet ruled on the petitions for rehearing. The 

Cross-State Air Pollution Rule is not in effect pending resolution of the case; rather, a 

predecessor rule, the Clean Air Interstate Rule, remains in effect. Specifically, in 2008 the 

U.S. Court of Appeals for the D.C. Circuit remanded the Clean Air Interstate Rule, but did 

not vacate it, finding that allowing the rule to remain in effect until it is replaced by a rule 

consistent with the opinion would at least temporarily preserve environmental values. The 

Cross-State Air Pollution Rule was EPA’s response to the court’s remand of the Clean Air 

Interstate Rule. 

47See Electricity: Significant Changes Are Expected in Coal-Fueled Generation, but Coal 

is Likely to Remain a Key Fuel Source, GAO-13-72 (Washington, D. C.: Oct. 29, 2012). 
 

Page 36 GAO-13-39 Water Quality 

The reduced domestic emissions of NOx and SO2 into the atmosphere are 

having a beneficial impact on water quality and aquatic ecosystems, 

according to EPA’s 2011 report on the benefits and costs of the CAA.48

The report analyzed how reductions in NOx and SO2 emissions 

attributable to the CAA are affecting the levels of acid rain and the 

amount of nitrogen contributing to nutrient over-enrichment in bays and 

estuaries, among other things. The analysis compared two scenarios for 

the time frame 1990 through 2020. The first scenario assumes that 

federal, state, and local air regulations promulgated from 1990 through 

September 2005 are implemented through 2020. The second scenario 

freezes federal, state, and local air pollution controls at the levels of 

stringency and effectiveness that prevailed in 1990. The analysis 

assumes that the geographic distributions of population and economic 

activity remain the same between the two scenarios. According to the 

report, air regulations limit levels of acid rain, and the greatest benefits for 

areas sensitive to acid rain occur in the Blue Ridge Mountains, the midAppalachian Region, western Virginia, and central Pennsylvania. The 

report also notes that air regulations limit nitrogen deposition, and the 

greatest benefits for estuaries occur along the southeastern coast, Gulf 

Coast, and Southern California coast. 

Mercury emissions from human-caused domestic sources declined from 

about 246 tons in 1990 to about 61 tons in 2008, according to the 2008 

National Emissions Inventory. More than half of this decline can be 

attributed to reduced emissions from municipal waste combustors and 

medical waste incineration.49 According to the inventory, in 1990, these 

two sources emitted about 108 tons of mercury; in 2008, they emitted less 

than 2 tons of mercury. Mercury emissions from power plants also 

declined from about 59 tons of mercury in 1990 to about 30 tons of 

mercury in 2008. Figure 12 shows the decline in human-caused domestic 

mercury emissions. 

 

48U.S. Environmental Protection Agency, Office of Air and Radiation, The Benefits and 

Cost of the Clean Air Act from 1990 to 2020, Final Report (Washington, D.C.: March 

2011). Section 812 of the 1990 Clean Air Act Amendments requires EPA to develop 

biannual reports that estimate the benefits and costs of the Clean Air Act. This report is 

the third in the Section 812 series. The previous two reports covered different time frames. 

49Municipal waste combustors are incinerators or facilities that generate energy from 

garbage. 

Mercury Emissions 
 

Page 37 GAO-13-39 Water Quality 

Figure 12: Mercury Emissions in 1990 and 2008 by Source 

Note: all other sources include electric arc furnaces; Portland cement nonhazardous waste; and 

industrial, commercial, and institutional boilers, and process heaters. 

EPA issued regulations in 1995 and 1997 under the CAA limiting mercury 

emissions from municipal waste combustors and medical infectious waste 

incinerators.50 They were not designed to address the effect of mercury 

on waterbodies but were instead technology-based standards, as directed 

 

50See EPA, Standards of Performance for New Stationary Sources and Emission 

Guidelines for Existing Sources: Municipal Waste Combustors, 60 Fed. Reg. 65,387 (Dec. 

19, 1995) and EPA, Standards of Performance for New Stationary Sources and Emission 

Guidelines for Existing Sources: Hospital/Medical/Infectious Waste Incinerators, 62 Fed. 

Reg. 48,348 (Sept. 15, 1997). 
 

Page 38 GAO-13-39 Water Quality 

by CAA.51 According to EPA, power plant emissions of mercury also 

declined. Specifically, according to EPA, power plant emissions declined 

primarily because of state rules targeting mercury emissions and CAA 

regulations targeting emissions of other pollutants that incidentally also 

reduced mercury emissions. Additionally, in February 2012, EPA 

promulgated the Mercury and Air Toxics Standards (MATS),52

establishing for the first time emission limitations on mercury and other 

toxic pollutants from existing and new power plants.53 The rule was 

challenged in federal court. Regarding the provisions for existing units at 

power plants, the legal challenges are pending before the U.S. Court of 

Appeals for the D.C. Circuit. Regarding the provisions applicable to 

certain new units at power plants, EPA granted a petition for 

reconsideration; the court proceedings are on hold, and the provisions will 

not take effect before EPA completes that process, expected in March 

2013. Similar to the regulations limiting mercury emissions from municipal 

waste combustors and medical waste incinerators, MATS are technologybased standards, as directed by CAA, and thus are not designed or 

established with the specific purpose of addressing the effect of mercury 

emissions on waterbodies. EPA projects that MATS will reduce future 

mercury emissions from power plants to about 9 tons by 2016, a 70 

 

51Each regulation sets maximum achievable control technology (MACT) standards. A 

MACT standard is a technical standard applying to a particular industry that releases 

hazardous air pollutants, such as mercury. MACT standards are designed to reduce 

emissions of hazardous air pollutants to a maximum achievable degree, taking into 

consideration the cost of reductions and other factors. 

52CAA required EPA to study the public health hazards from electricity generating units’ 

emissions of mercury and other hazardous air pollutants and to regulate those emissions 

under section 112 if it finds that such regulation is “appropriate and necessary.” EPA 

made such a finding regarding certain electricity generating units in 2000 but did not issue 

a regulation under section 112. In 2005, EPA reversed this finding and finalized a 

regulation under section 111 of the CAA regulating mercury emissions from certain 

electricity generating units, which a federal court later struck down. Pursuant to a 

settlement agreement to resolve a lawsuit for failing to meet the statutory deadline for 

issuing a section 112 regulation, EPA published the final MATS regulations in February 

2012. 

53See EPA, National Emission Standards for Hazardous Air Pollutants From Coal- and 

Oil-Fired Electric Utility Steam Generating Units and Standards of Performance for FossilFuel-Fired Electric Utility, Industrial-Commercial-Institutional, and Small IndustrialCommercial-Institutional Steam Generating Units; Final Rule, 77 Fed. Reg. 9304 (Feb. 16, 

2012). In addition to the new standards for emission of mercury and other air toxics, the 

rulemaking also included amendments to new source performance standards for several 

criteria pollutants. 
 

Page 39 GAO-13-39 Water Quality 

percent reduction from 2008.54 According to an EPA official, the reduced 

emissions of mercury have lessened the amount of mercury deposition 

into water because most mercury in water comes from atmospheric 

deposition, but estimates of the amount of mercury that has been 

prevented from depositing in water are difficult to determine. Even with 

these reductions in mercury, atmospheric deposition continues to affect 

water quality and harm aquatic ecosystems. 

EPA faces challenges in using air regulations to further address the 

effects of atmospheric deposition from NOx, SO2, and mercury. According 

to the agency, its recent efforts to establish secondary NAAQS to address 

acid rain and nutrient over-enrichment were not successful because of 

insufficient scientific data. Air regulations have limited and, are expected 

by EPA to further limit, domestic mercury emissions, but mercury 

emissions originating outside of the United States are also contaminating 

U.S. waters. 

As part of its most recent 5-year review of secondary NAAQS, EPA 

concluded in the 2011 notice for its proposed rule on secondary NAAQS 

that current levels of NOx and SO2 are sufficient to cause acidification of 

aquatic ecosystems through acid rain and contribute to nutrient overenrichment in estuaries, among other effects, and that existing secondary 

NAAQS for NOx and SO2 do not provide adequate protection from these 

effects.55 Ultimately, however, the agency did not establish any additional 

secondary NAAQS to protect against these effects for ecosystems, citing 

challenges in available sufficient scientific data to set standards.56

 

54EPA also projects that MATS will reduce SO2 emissions from power plants. 

55See EPA, Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and 

Sulfur; Proposed Rule, 76 Fed. Reg. 46,084 (Aug. 1, 2011). According to EPA, it based its 

proposed conclusions on the following assessments: U.S. EPA. Integrated Science 

Assessment for Oxides of Nitrogen and Sulfur Ecological Criteria, U.S. Environmental 

Protection Agency, Washington, DC, EPA/600/R-08/082F, 2008 and U.S. EPA, Risk and 

Exposure Assessment for Review of the Secondary National Ambient Air Quality 

Standards for Oxides of Nitrogen and Oxides of Sulfur, U.S. Environmental Protection 

Agency, Washington, D.C., EPA/452/R-09-008a, 2009. 

56EPA, Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and 

Sulfur; Final Rule, 77 Fed. Reg. 20,218 (April 3, 2012). 

EPA Faces Challenges in 

Addressing Atmospheric 

Deposition with 

Clean Air Act 

NOx and SO2 Emissions 
 

Page 40 GAO-13-39 Water Quality 

To address the effects of acid rain, EPA developed an innovative 

approach to establish a secondary NAAQS but faced challenges including 

insufficient scientific data to determine the degree of protectiveness that 

would likely be provided by such standards. Specifically, the CAA 

requires that NAAQS be both national in scope and provide the requisite 

degree of protection—that is, that the standards are neither more nor less 

stringent than necessary. Because many areas in the United States are 

naturally resistant to the effects of acid rain due to underlying geological 

conditions, EPA’s approach was to establish a secondary NAAQS that 

would apply nationwide but would account for differences in the sensitivity 

to acid rain of ecosystems across the country.57 As part of this approach, 

EPA identified 84 regions, referred to as ecoregions, based on ecological 

factors relevant to acid rain in aquatic ecosystems. The 84 ecoregions 

cover the contiguous United States. However, in the notice for its April 

2012 final rule on secondary NAAQS, EPA concluded that it could not 

determine with an acceptable degree of scientific certainty that the 

secondary NAAQS under this approach would provide the requisite 

degree of protection for each ecoregion because of uncertainties related 

to ecological and atmospheric modeling and limitations in available field 

data. An important piece of field data needed to determine the requisite 

degree of protection is “critical load”—the amount of acid rain that an area 

can experience before ecological damage occurs. The number of critical 

load estimates for the 84 ecoregions ranged from about 700 estimates for 

one ecoregion to less than five estimates for several ecoregions. 

To address the uncertainty related to modeling and field data, EPA has 

begun a 5-year field pilot program to enhance its understanding of the 

degree of protectiveness that would likely be afforded by a secondary 

NAAQS using its new approach. EPA described the pilot program in its 

April 2012 final rule notice, stating that the program would serve to inform 

future reviews of NAAQS to address acid rain. However, according to an 

EPA official, the pilot program is a “proof of concept” project and not 

designed specifically to obtain sufficient scientific data to meet applicable 

legal standards for establishing secondary NAAQS. The official said that 

three sites have been chosen from which to gather additional data, but 

that resource constraints prevent EPA from moving forward with two of 

those areas. It is unclear if the agency will be able to address the 

 

57EPA describes its new approach for developing NAAQS for acid rain at length in its 

2011 proposed rule. See 76 Fed. Reg. 46,084 (Aug. 1, 2011). 
 

Page 41 GAO-13-39 Water Quality 

scientific uncertainties related to ecological and atmospheric modeling 

and limitations in available field data in time for the next 5-year interval for 

reviewing NAAQS and establishing a secondary NAAQS under its 

innovative approach. According to agency officials, EPA has not identified 

alternative strategies to address the acidification of aquatic ecosystems if 

it cannot resolve the scientific uncertainties. 

EPA also faces challenges in addressing the contribution of NOx to 

nutrient over-enrichment under the CAA. EPA announced in its 2011 

notice for its proposed rule on secondary NAAQS that it would not 

consider establishing an additional secondary NAAQS to address other 

effects from atmospheric deposition associated with NOx and SO2, 

including the contributions of NOx to nutrient over-enrichment in aquatic 

ecosystems, because of the limited quantity and quality of available 

scientific data relative to that available for acid rain. According to an EPA 

official, establishing a secondary NAAQS for NOx to protect against 

nutrient over-enrichment in a waterbody would be difficult because there 

can be many sources of nitrogen unrelated to atmospheric deposition, 

and these sources can be the dominant contributor of nitrogen to the 

waterbody. 

Furthermore, in a 2011 report, the EPA Science Advisory Board made 

recommendations regarding the adverse effects of nitrogen from all 

sources on water quality and aquatic ecosystems, as well as the effects 

of nitrogen on biodiversity, forests, and human health, among other 

effects.58 In response, EPA announced in 2012 that it will develop a 

“Nitrogen Roadmap” that identifies how it will foster research, program 

implementation, and policy integration for nitrogen and other pollutants 

across the agency. According to EPA officials, the roadmap is a scoping 

document that will precede more concrete steps to develop an integrated 

nitrogen research strategy to address acidification and nutrient overenrichment. The goals of the strategy are to ensure coordination among 

research areas within EPA, and among EPA scientists and policy 

analysts. An EPA official also noted that developing partnerships with 

other federal agencies, state and local governments, and 

 

58The EPA Science Advisory Board is a federal advisory committee established by 

Congress in 1978 with a broad mandate to advise the agency on technical matters. The 

board’s recommendations are found in its report: Reactive Nitrogen in the United States: 

An Analysis of Inputs, Flows, Consequences, and Management Options – A Report of the 

EPA Science Advisory Board, EPA-SAB-11-013, August 2011. 
 

Page 42 GAO-13-39 Water Quality 

nongovernmental organizations, will be an important step that will help 

foster nonregulatory solutions to address nutrient over-enrichment. 

According to the official, the roadmap is scheduled to be released in 

2013, but the effort to address nutrient over-enrichment will likely be longterm. This effort may lead to more suitable approaches to address 

nutrient over-enrichment than establishing secondary NAAQS by 

themselves. 

EPA also faces challenges in addressing mercury contamination because 

most mercury atmospheric deposition within the continental United States 

comes from sources that are outside of the scope of EPA’s authority. 

According to a 2010 National Research Council report, studies suggest 

that 10 percent to 80 percent of the mercury deposited in the contiguous 

United States is from human-caused domestic emissions—depending on 

location—with an average of about 30 percent for the country as a 

whole.59 According to the report, the remainder comes from natural 

sources, human-caused emissions from other countries, and the global 

pool of mercury. The United States is responsible for a relative small 

percentage of the global mercury emissions that contribute to the global 

pool of mercury. According to the 2008 UNEP report, total global 

emissions of mercury from human activity in 2005 ranged from 1,300 tons 

to 3,200 tons.60 According to data EPA used for the MATS rule, domestic 

mercury emissions from human activity totaled about 105 tons in 2005. 

Thus, even without reductions in mercury emissions beyond the 2005 

level, over 90 percent of human-caused mercury emissions originate 

outside of the United States. 

EPA is involved in international negotiations to limit global mercury 

releases into the environment. In February 2009, the Governing Council 

of the UNEP agreed on the need to develop a global, legally binding 

agreement on mercury to reduce risks to human health and the 

environment, including reducing atmospheric emissions of mercury. The 

council outlined a negotiating process to reach an agreement. The first 

negotiation meeting was held in June 2010, and the fifth and final meeting 

 

59National Research Council, Global Sources of Local Pollution: An Assessment of LongRange Transport of Key Air Pollutants to and from the United States. (National Academies 

Press, Washington, D.C.: 2010). 

60The United Nations Environment Programme, The Global Atmospheric Mercury 

Assessment: Sources, Emissions and Transport Mercury Assessment (Geneva, 

Switzerland: December 2008). 

Mercury Emissions 
 

Page 43 GAO-13-39 Water Quality 

is scheduled to be held in 2013. The third negotiating session (held in 

October and November 2011) produced a draft text of the agreement. 

The draft text includes language for consideration that would call on 

parties to the agreement that have significant aggregate mercury 

emissions from listed source categories to adopt national or numeric 

emission reduction goals that are, at a minimum, consistent with best 

available practices for reducing and, where feasible, eliminating 

atmospheric mercury emissions from sources such as coal-burning power 

plants. Language for consideration in the draft text would also call on 

parties to (1) develop and maintain an inventory of these sources and 

reliable emissions estimates and (2) develop and implement an action 

plan that includes strategies and timetables for achieving emission 

reduction goals. 

EPA has long recognized atmospheric deposition as a problem and has 

sought to mitigate its effects; however, EPA’s efforts are being hindered 

by limitations in the regulatory tools available to it. The CAA provides EPA 

with regulatory tools to reduce airborne emissions—and this has reduced 

atmospheric deposition. Even with these reductions, atmospheric 

deposition continues to affect water quality and harm aquatic ecosystems. 

One CAA tool for airborne emissions is also currently available to EPA to 

directly address the effects of atmospheric deposition—secondary 

NAAQS—but EPA has not been successful in using secondary NAAQS to 

protect water quality and aquatic ecosystems from acid rain or nutrient 

over-enrichment. 

We acknowledge the innovative approach EPA developed for establishing 

secondary NAAQS to address acid rain. However, as of April 2012, EPA 

stated it did not have sufficient scientific data to determine with an 

acceptable degree of scientific certainty if its new approach would meet 

applicable legal standards to establish the secondary NAAQS. Further, 

the 5-year pilot program it has initiated to inform future reviews of NAAQS 

to address acid rain is not designed specifically to obtain these data. 

However, EPA has not identified alternative strategies to address the 

acidification of aquatic ecosystem if it cannot resolve the scientific 

uncertainties that prevented it from issuing the secondary NAAQS in April 

2012. Furthermore, secondary NAAQS may not be well suited to address 

acid rain because EPA must satisfy the legal requirement that secondary 

NAAQS provide the requisite degree of protection—that is, that the 

standards are neither more nor less stringent than necessary—for all 

parts of the nation, and some areas of the nation are sensitive to the 

effects of acid rain, while others are naturally resistant to them. 

Conclusions 
 

Page 44 GAO-13-39 Water Quality 

Additionally, EPA does not have the scientific data it needs to establish a 

secondary NAAQS to address the contribution of NOx to nutrient overenrichment in aquatic ecosystems. Because there can be many sources 

of nitrogen that contribute to nutrient over-enrichment in a waterbody, 

including sources of nitrogen unrelated to atmospheric deposition, 

secondary NAAQS by themselves may not be well suited to address 

nutrient over-enrichment. EPA announced in 2012 that it will develop a 

“Nitrogen Roadmap” that identifies how it will foster research, program 

implementation, and policy integration for nitrogen and other pollutants 

across the agency. This roadmap is intended to be a scoping document 

that is to precede more concrete steps to develop an integrated nitrogen 

research strategy to address nutrient over-enrichment. We encourage 

EPA to continue its effort to develop an integrated nitrogen research 

strategy, which may lead to more suitable approaches to address nutrient 

over-enrichment. 

Regarding mercury, because most emissions originate outside of the 

United States, EPA’s regulatory tools are of limited applicability to the 

majority of emissions, but the agency is involved in the UNEP 

negotiations to, among other things, reduce atmospheric emissions of 

mercury on a global scale. This will be an important step toward reducing 

mercury levels in our nation’s waters. 

To help ensure that EPA can address atmospheric deposition of NOx and 

SO2 impairing the nation’s waters, we recommend that the EPA 

Administrator determine whether EPA can obtain in a timely manner the 

data it needs to establish secondary NAAQS adequate to protect against 

the effects of acid rain and, if not, identify alternative strategies to do so. 

Recommendation for 

Executive Action 
 

Page 45 GAO-13-39 Water Quality 

We provided a draft of this report to EPA for comment. In written 

comments, which are reproduced in appendix II, EPA agreed with the 

recommendation in our report. EPA stated that under the CAA, it is 

required every 5 years to complete a thorough review of the latest 

scientific knowledge, and as necessary, make revisions to the NAAQS or 

promulgate new NAAQS. For NOx and SOx, it stated that it will continue 

to review the science, as it develops and gather new data as resources 

permit. Additionally, EPA provided technical comments to provide 

additional clarity and completeness to the report. An overview of these 

technical comments is included in the written comments reproduced in 

appendix II. We incorporated the technical comments as appropriate. 

As agreed with your offices, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies to the Administrator of the 

Environmental Protection Agency, the appropriate congressional 

committees, and other interested parties. In addition, the report will be 

available at no charge on the GAO website at http://www.gao.gov. 

If you or your staff members have any questions about this report, please 

contact me at (202) 512-3841 or trimbled@gao.gov. Contact points for 

our Offices of Congressional Relations and Public Affairs may be found 

on the last page of this report. GAO staff who made key contributions to 

this report are listed in appendix III. 

David C. Trimble 

Director 

Natural Resources and Environment 

Agency Comments 

and Our Evaluation 
Appendix I: Scope and Methodology 

Page 46 GAO-13-39 Water Quality 

Our objectives were to (1) examine the extent to which the atmospheric 

deposition of nitrogen oxides (NOx), sulfur dioxide (SO2), and mercury 

contributes to the impairment of the nation’s waters and identify the key 

sources of these pollutants;(2) identify the regulatory tools that the 

Environmental Protection Administration (EPA) uses under the Clean 

Water Act (CWA) to address the effects of atmospheric deposition, and 

the challenges, if any, that it faces in doing so; and (3) identify the 

regulatory tools that EPA uses under the Clean Air Act (CAA) to address 

the effects of atmospheric deposition, and the challenges, if any, that it 

faces in doing so. 

To examine the extent to which atmospheric deposition of NOx, SO2 and 

mercury contributes to the impairment of the nation’s waters, we analyzed 

EPA’s Assessment, TMDL (Total Maximum Daily Load) Tracking, and 

Implementation System (ATTAINS) database. To assess the reliability of 

its data, we interviewed knowledgeable agency officials and conducted 

electronic testing of the data. We determined that, although the data have 

limitations, as specified below, they were sufficiently reliable to present 

reported atmospheric deposition impairment on assessed waters for 

selected categories of water bodies. The ATTAINS data we analyzed 

were the most recent available data from states and not the most current 

reporting-cycle year, 2012, because these 2012 data are undergoing 

review. Because some states are more current than others in reporting, 

the state data we analyzed for a given state could be from any reporting 

cycle year from 2002 to 2010, depending on the state.1

 Our analysis also 

included data from the 50 states, the District of Columbia, Puerto Rico, 

Guam, the U.S. Virgin Islands, American Samoa, and the Commonwealth 

of Northern Mariana Islands. ATTAINS also included data from the 

Delaware River Basin Commission, but we excluded these data in our 

analysis because EPA does not include it in its reports or queries related 

to the quality of the nation’s waters. In analyzing the data, we first 

identified how many miles, acres, or square miles of waters in each 

waterbody category in ATTAINS were assessed and classified as 

impaired. The ATTAINS database contained 10 different categories of 

waters. However, we did not report on coastal waters, ocean and near 

coastal waters, wetlands, Great Lakes shoreline, inland lake shoreline, 

and Great Lakes connecting channels because states have only 

 

1

One state had data from reporting cycle 2002; one state had data from 2004; six states 

had data from 2006; six other states had data from 2008, and the rest of the states had 

data from reporting cycle 2010. 

Appendix I: Scope and Methodology 
Appendix I: Scope and Methodology 

Page 47 GAO-13-39 Water Quality 

assessed a small percentage of these waters, and there was insufficient 

data or, in the case of Great Lakes shoreline, because we were reporting 

on Great Lakes open water. We reported on impaired waters in the 

following four categories: 

 Streams, creeks and rivers; 

 Lake, reservoirs, and ponds; 

 Bays and estuaries; and 

 Great Lakes open water. 

We then identified what pollution sources the states associated with these 

impaired miles, acres, or square miles of waters and considered only 

those waters whose impairment was attributed by states to atmospheric 

deposition. Our analysis of ATTAINS data represents only those waters 

that states have assessed and associated with atmospheric deposition as 

an impairment source. It is possible that additional impairment due to 

atmospheric deposition has occurred, but that states either did not report 

atmospheric deposition as an impairment source in ATTAINS or reported 

it as unknown or unspecified. In addition, our findings represent waters 

impaired by the atmospheric deposition of all reported air pollutants and 

are not specific to the atmospheric deposition of NOx, SO2, and mercury. 

We examined data on the reported causes and pollutants for waters with 

impairment that the states associated with atmospheric deposition and 

found that we could not reliably report on the causes or pollutants, such 

as NOx and SO2, because of data inconsistencies. 

For additional information on the extent to which atmospheric deposition 

of these three pollutants contribute to the impairment of the nation’s 

waters, we reviewed studies from EPA and other federal agencies, the 

United Nations, and others. We assessed the reliability and methodology 

of these studies, including limitations and assumptions, and determined 

that they were sufficiently reliable for the purposes of examining the 

extent to which atmospheric deposition is contributing to the impairment 

of the nation’s waters. In addition, we examined state reported-data in 

EPA’s 2010 National Listing of Fish Advisories (NLFA) and assessed the 

reliability of the data. We determined that despite some NLFA 

limitations—such as states’ different monitoring methods for sampling 

contaminants in fish tissues and limited waters monitoring – the data were 

sufficiently reliable for the purposes of reporting the number of states with 

mercury-related fish advisories and the extent of mercury-related fish 
Appendix I: Scope and Methodology 

Page 48 GAO-13-39 Water Quality 

advisories for certain types of waters. We also interviewed officials and 

scientists from EPA’s offices, including the Office of Air and Radiation and 

the Office of Water; the Department of Commerce’s National Oceans and 

Atmospheric Administration; and academic, state, and private sector 

scientists. 

To identify the key sources of NOx, SO2, and mercury, we examined 

emission estimates from EPA’s National Emissions Inventory (version 

2)—a national database of air emissions information with input from 

numerous state and local air agencies, tribes, and industry. For source 

estimates on NOx, SO2, and mercury emissions, we used 2008 National 

Emissions Inventory estimates because EPA is currently collaborating 

with state, local, and tribal agencies in preparing the 2011 inventory. We 

also talked with EPA officials and reviewed National Emissions Inventoryrelated documentation on quality assurance to assess the reliability of 

National Emissions Inventory estimates. We determined that despite 

some limitations—such as methodological and modeling differences used 

in estimating emission across various years and versions of the 

inventory—the 2008 National Emissions Inventory data were sufficiently 

reliable for the purposes of identifying in the national aggregate the top 

emission sources of NOx, SO2, and mercury, and for reporting emission 

estimates from the top emitting sources. In addition, we reviewed EPA 

documents related to mercury emissions and sources, as well as a 2008 

United Nations Environment Programme (UNEP) assessment on global 

mercury sources, emissions, and transport. 

To examine the regulatory tools that EPA uses under the CWA to address 

the effects of atmospheric deposition, and the challenges, if any, it faces 

in doing so, we reviewed the law, relevant EPA regulations and guidance, 

and other pertinent documents, and interviewed relevant EPA and state 

officials. As a result, we identified listing impaired waters and the TMDL 

as the primary regulatory tools EPA uses to address the effects of 

atmospheric deposition. We also chose to examine a nonprobability 

sample of three TMDLs in greater detail to illustrate the challenges EPA 

faces in using CWA to address atmospheric deposition. We selected 

each TMDL because it addressed a different effect caused by the 

atmospheric deposition of the three pollutants on which we are focusing. 

Specifically, we chose the Northeast Regional TMDL because it is 

addressing mercury, including atmospheric deposition of mercury. We 

chose a New York State TMDL because it addresses acid rain caused by 

NOx and S02. Finally, we chose the Chesapeake Bay TMDL because it 

address nutrient over-enrichment, including from NOx. To describe these 

TMDLs and the challenges they present, we examined key documents 
Appendix I: Scope and Methodology 

Page 49 GAO-13-39 Water Quality 

and interviewed EPA, state, and regional officials responsible for 

implementing the TMDLs. 

To examine the regulatory tools that EPA uses under CAA to address the 

effects of atmospheric deposition and the challenges that it faces in doing 

so, we reviewed the law, relevant EPA regulations and guidance, and 

other pertinent documents and studies, and interviewed relevant EPA 

officials. We used data from the 2008 National Emissions Inventory and 

2011 EPA study on the benefits and costs of the CAA amendments of 

1990 to identify the reductions in NOx, SO2, and mercury, key regulations 

that contributed to the reductions, and the associated beneficial effects on 

water quality and aquatic ecosystems. We assessed the reliability and 

methodology of these sources of information, including limitations and 

assumptions, and determined that they were sufficiently reliable for the 

purposes of attributing estimates of some reductions in NOx, SO2, and 

mercury to CAA. We reviewed the CAA and pertinent regulations to 

determine the design of the regulations. To understand the challenges 

that EPA faced in trying to develop a secondary National Ambient Air 

Quality Standard (NAAQS) to reduce emissions of NOx and SO2 in order 

to protect ecosystems sensitive to the effects of acid rain, we reviewed 

documentation developed as part of the rulemaking process and 

interviewed knowledgeable officials responsible for the rulemaking. To 

understand EPA’s integrated nitrogen research strategy, we reviewed 

pertinent documents and interviewed relevant EPA officials. For 

challenges related to mercury, we reviewed a UNEP study on global 

mercury emissions, sources, and transport, and other UNEP mercuryrelated documents on global efforts to reduce mercury emissions and 

interviewed knowledgeable EPA officials. 

We conducted this performance audit from September 2011 to January 

2013 in accordance with generally accepted auditing standards. Those 

standards require that we plan and perform the audit to obtain sufficient 

and appropriate evidence to provide a reasonable basis for our findings 

and conclusions based on our audit objectives. We believe that the 

evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives. 
Appendix II: Comments from the 

Environmental Protection Agency 

Page 50 GAO-13-39 Water Quality 

Appendix II: Comments from the 

Environmental Protection Agency 
Appendix II: Comments from the 

Environmental Protection Agency 

Page 51 GAO-13-39 Water Quality 
Appendix II: Comments from the 

Environmental Protection Agency 

Page 52 GAO-13-39 Water Quality 
Appendix III: GAO Contact and Staff 

Acknowledgments 

Page 53 GAO-13-39 Water Quality 

David C. Trimble, (202) 512-3841 or trimbled@gao.gov

In addition to the individual named above, Barbara Patterson, Assistant 

Director; Elizabeth Beardsley; Greg Carroll; Bernice Hill Dawson; Charles 

Egan; Michelle Fejfar; Michael Hix; Catherine Hurley; Alison O’Neill; 

Madhav Panwar; Carla Rojas Paz; and Carol Herrnstadt Shulman made 

key contributions to this report. 

Appendix III: GAO Contact and Staff 

Acknowledgments 

GAO Contact 

Staff 

Acknowledgments 

(361335)
The Government Accountability Office, the audit, evaluation, and 

investigative arm of Congress, exists to support Congress in meeting its 

constitutional responsibilities and to help improve the performance and 

accountability of the federal government for the American people. GAO 

examines the use of public funds; evaluates federal programs and 

policies; and provides analyses, recommendations, and other assistance 

to help Congress make informed oversight, policy, and funding decisions. 

GAO’s commitment to good government is reflected in its core values of 

accountability, integrity, and reliability. 

The fastest and easiest way to obtain copies of GAO documents at no 

cost is through GAO’s website (http://www.gao.gov). Each weekday 

afternoon, GAO posts on its website newly released reports, testimony, 

and correspondence. To have GAO e-mail you a list of newly posted 

products, go to http://www.gao.gov and select “E-mail Updates.” 

The price of each GAO publication reflects GAO’s actual cost of 

production and distribution and depends on the number of pages in the 

publication and whether the publication is printed in color or black and 

white. Pricing and ordering information is posted on GAO’s website, 

http://www.gao.gov/ordering.htm. 

Place orders by calling (202) 512-6000, toll free (866) 801-7077, or 

TDD (202) 512-2537. 

Orders may be paid for using American Express, Discover Card, 

MasterCard, Visa, check, or money order. Call for additional information. 

Connect with GAO on Facebook, Flickr, Twitter, and YouTube. 

Subscribe to our RSS Feeds or E-mail Updates. Listen to our Podcasts. 

Visit GAO on the web at www.gao.gov. 

Contact: 

Website: http://www.gao.gov/fraudnet/fraudnet.htm 

E-mail: fraudnet@gao.gov

Automated answering system: (800) 424-5454 or (202) 512-7470 

Katherine Siggerud, Managing Director, siggerudk@gao.gov, (202) 512-

4400, U.S. Government Accountability Office, 441 G Street NW, Room 

7125, Washington, DC 20548 

Chuck Young, Managing Director, youngc1@gao.gov, (202) 512-4800 

U.S. Government Accountability Office, 441 G Street NW, Room 7149 

Washington, DC 20548 

GAO’s Mission 

Obtaining Copies of 

GAO Reports and 

Testimony 

Order by Phone 

Connect with GAO 

To Report Fraud, 

Waste, and Abuse in 

Federal Programs 

Congressional 

Relations 

Public Affairs 

Please Print on Recycled Paper.