Air Quality: Information on Tall Smokestacks and Their Contribution to Interstate Transport of Air Pollution
Published: 2011-05-11T00:00:00

Fast Facts:

Highlights:
section_title: Why GAO Did This Study
paragraphs: Tall smokestacks--stacks of 500 feet or higher, which are primarily used at coal power plants--release air pollutants such as sulfur dioxide (SO2) and nitrogen oxides (NOx) high into the atmosphere to help limit the impact of these emissions on local air quality. Tall stacks can also increase the distance these pollutants travel in the atmosphere and harm air quality and the environment in downwind communities. The 1977 amendments to the Clean Air Act encourage the use of pollution control equipment over dispersion techniques, such as tall stacks, to meet national air standards. Section 123 of the Act does not limit stack height, but prohibits sources of emissions from using the dispersion effects of stack heights in excess of a stack's good engineering practice (GEP) height to meet emissions limitations. GAO was asked to report on (1) the number and location of tall stacks of 500 feet or higher at coal power plants and when they began operating; (2) what is known about such stacks' contribution to the interstate transport of air pollution and the pollution controls installed at plants with these stacks; and (3) the number of stacks that were built above GEP height since 1988 and the reasons for this. GAO analyzed Energy Information Administration (EIA) data on power plants, surveyed states with tall stacks, and interviewed experts on the transport of air pollution. GAO is not making recommendations in this report. The Environmental Protection Agency and the Department of Energy stated they had no comments on this report
section_title: What GAO Found
paragraphs: According to analysis of EIA data, which were updated with GAO's survey results, a total of 284 tall smokestacks were operating at 172 coal power plants in 34 states, as of December 31, 2010. Of these stacks, 207 are 500 to 699 feet tall, 63 are 700 to 999 feet tall, and the remaining 14 are 1,000 feet tall or higher. About one-third of these stacks are concentrated in 5 states along the Ohio River Valley. While about half of tall stacks began operating more than 30 years ago, there has been an increase in the number of tall stacks that began operating in the last 4 years, which air and utility officials attributed to the need for new stacks when plants installed pollution control equipment. Stack height is one of several factors that contribute to the interstate transport of air pollution. According to reports and stakeholders with expertise on this topic, tall stacks generally disperse pollutants over greater distances than shorter stacks and provide pollutants greater time to react in the atmosphere to form ozone and particulate matter. However, stakeholders had difficulty isolating the exact contribution of stack height to the transport of air pollution because this is a complex process that involves several other variables, including total emissions from a stack, the temperature and velocity of the emissions, and weather. The use of pollution controls, which are generally installed in boilers or the duct work that connects a boiler to a stack, has increased in recent years at coal power plants. However, GAO found that many boilers remain uncontrolled for certain pollutants, including several connected to tall stacks. For example, GAO found that 56 percent of boilers attached to tall stacks lacked scrubbers to control SO2 and 63 percent lacked post-combustion controls to capture NOx emissions. In general, GAO found that boilers without these controls tended to be older, with in-service dates prior to 1980. GAO identified 48 tall stacks built since 1988--when GEP regulations were largely affirmed in court--that states reported are subject to the GEP provisions of the Clean Air Act and for which states could provide GEP height information. Of these 48 stacks, 17 exceed their GEP height, 19 are at their GEP height, and 12 are below their GEP height. Section 123 of the Clean Air Act defines GEP as the height needed to prevent excessive downwash, a phenomenon that occurs when nearby structures disrupt airflow and produce high local concentrations of pollutants. Officials reported that a variety of factors can influence stack height decisions. For example, some utility officials reported that stacks were built above GEP to provide greater protection against downwash or to help a plant's emissions clear local geographic features, such as valley walls. GAO was unable to obtain GEP height information for an additional 25 stacks that were built since 1988 for two reasons: (1) some of these stacks were exempt from GEP regulations, and (2) states did not have GEP information readily available for some replacement stacks because the GEP calculation was sometimes made decades earlier and a recalculation was not required at the time the replacement stack was built.

section_title: Letter
paragraphs: Tall smokestacks—which are used primarily at coal power plants—release  air pollutants such as sulfur dioxide (SO), and nitrogen oxides (NO) high  into the atmosphere to help disperse them and limit their impact on air  quality in local communities. However, because wind currents are  generally faster at higher elevations, tall stacks can increase the distance  that these pollutants travel, harming air quality in downwind communities.  When these pollutants are airborne, they can react in the atmosphere to  form particulate matter, acid rain, and ozone that can harm air quality,  human health, and the environment. For example, SO, ozone, and  particulate matter can cause or worsen respiratory diseases such as  emphysema, bronchitis, or asthma, while acid rain can damage vegetation  and aquatic ecosystems.
Under the Clean Air Act, the Environmental Protection Agency (EPA) is  responsible for setting National Ambient Air Quality Standards (NAAQS)  for certain pollutants considered harmful to public health and the  environment. EPA has set NAAQS for six such pollutants, known as  criteria air pollutants: SO, NO, particulate matter, ozone, carbon  monoxide, and lead. These standards are expressed as concentration  limits averaged over time, and compliance is determined through ground- level monitoring at a local level. States are responsible for developing and  implementing plans, known as State Implementation Plans (SIP), to  achieve and maintain these standards. In carrying out this duty, states set  emissions limitations for individual sources of air pollution, which are  based, in part, on the results of air quality models that show the impact  these sources will have on air quality. Since 1990, the Clean Air Act has  required the incorporation of these emissions limitations into operating  permits which collect all of the pollution control, recordkeeping, and  reporting requirements applicable to individual sources of air pollution.
In the early 1970s, power plants commonly installed tall stacks to reduce  pollutant concentrations at ground level to help attain NAAQS. The 1977  amendments to the Clean Air Act encouraged the use of pollution control  equipment and other control measures over dispersion techniques such as  tall stacks to meet NAAQS. For example, section 123 was added to  prohibit states from counting the dispersion effects of stack heights in  excess of a stack’s good engineering practice (GEP) height when  determining a source’s emissions limitation. Section 123 of the Clean Air  Act defines GEP height as the height needed to disperse pollutants to  prevent excessive “downwash,” a phenomenon that occurs when nearby  structures disrupt airflow and produce excessively high concentrations of  pollutants in the immediate vicinity of the source. Section 123 generally  applies to stacks built since December 31, 1970, but some stacks may be  exempt if they were built to replace stacks that were in existence on or  before this date. Since the GEP heights for smokestacks can be  determined using a calculation that accounts for the height and width of  the largest nearby structure, GEP heights vary accordingly. and NO, along with ozone and  particulate matter, decreased between 1990 and 2008. However, EPA  noted that in 2008, about 127 million people lived in counties where one or  more NAAQS––usually ozone or particulate matter––was exceeded. In  developing policy to control air pollution, EPA recognizes that emissions  from upwind states can contribute to the nonattainment—or  exceedances—of NAAQS in downwind states. EPA has taken steps to  reduce SO and NO emissions that contribute to the interstate transport of  air pollution through recent rule makings.
You asked us to provide information on the use of tall smokestacks at coal  power plants. Specifically, our objectives were to examine (1) the number  and location of smokestacks 500 feet or higher that are operating at coal  power plants across the United States, and when they began operating; (2)  what is known about these smokestacks’ contribution to the interstate  transport of air pollution and the pollution controls that have been  installed at coal power plants with these stacks; and (3) the number of  these smokestacks that were built above their GEP height since 1988, and  the reasons for this.
To identify the number and location of smokestacks at coal power plants  that were 500 feet or higher on December 31, 2010, we analyzed data on  power plants from the Department of Energy’s (DOE) Energy Information  Administration (EIA). We also used these data to determine when these  stacks began operating. To assess the reliability of the EIA data used in  this report, we reviewed documentation from EIA, interviewed relevant  officials who were involved in collecting and compiling the data, and  conducted electronic testing of the data. We determined that the data were  sufficiently reliable for our purposes. Because the EIA data were collected  in 2008, we also contacted all 50 states and the District of Columbia and  sent a survey to states with tall stacks to determine if any changes had  taken place in the number or operating status of stacks since that time. We  updated the relevant EIA data with more recent data from our survey  results. To determine what is known about tall stacks’ contribution to the  interstate transport of air pollution, we reviewed reports from EPA and  academics and spoke with stakeholders with expertise on this topic. These  stakeholders included EPA officials involved in modeling interstate  transport of air pollution from power plants, officials from utilities and  construction firms that design and build power plants, atmospheric  scientists who conduct research on this topic, and state officials who are  involved in permitting power plants and complying with federal  regulations governing the interstate transport of air pollution. We also  analyzed the EIA data to determine the pollution control equipment  installed at coal power plants with stacks 500 feet or higher. To determine  the number of tall stacks that have been built above their GEP height since  1988, we used survey responses from 22 states in which tall stacks have  been built since 1988 to obtain information about the GEP height for these  stacks. In this survey, we also asked for reasons that a stack was built  above GEP, when applicable. In those cases where state officials could not  provide a reason for why a stack was built above its GEP height, we  contacted several of the operators of these facilities to obtain this  information.
We conducted our work from July 2010 through May 2011 in accordance  with all sections of GAO’s quality assurance framework that are relevant  to our objectives. This framework requires that we plan and perform the  engagement to obtain sufficient, appropriate evidence to meet our stated  objectives and to discuss any limitations in our work. We believe that the  information and data obtained, and the analysis conducted, provide a  reasonable basis for any findings and conclusions. A more detailed  description of our scope and methodology is presented in appendix I.
subsections: section_title: Background
paragraphs: The five principal emissions from coal power plants are carbon dioxide,  SO, particulate matter, and mercury. For the purposes of this report,  we are focusing on power plants’ emissions of SO, NO, and particulate  matter since they, along with ozone, are the focus of a rule currently  proposed by EPA—the Transport Rule—which seeks to limit the interstate  transport of emissions of SO in order to abate violations of  particulate matter and ozone NAAQS in downwind states. According to an  EPA analysis, as of 2008, power plants emitted over 65 percent of SO  emissions and almost 20 percent of NO emissions, nationwide. These  emissions impact local air quality, but they can also travel hundreds of  miles to impact the air quality of downwind states. In developing the  Transport Rule, EPA has found that emissions of SO from 31  eastern states and the District of Columbia prevent downwind states from  meeting NAAQS for ozone and particulate matter. SO and NO emissions  contribute to the formation of fine particulate matter, and NO emissions  contribute to the formation of ozone, which can cause or aggravate  respiratory illnesses. the atmosphere, known as volatile organic compounds; and sunlight.  Cars and power  plants that burn fossil fuels are contributors of NO pollution. stack. In 1970, there were only 2 stacks higher than 500 feet in the United  States, but this number had increased to more than 180 by 1985.
While constructing a tall stack is a dispersion technique that helps to  reduce pollution concentrations in the local area, using tall stacks does  not reduce total emissions that can potentially be transported to  downwind states. The 1977 amendments to the Clean Air Act discouraged  the use of dispersion techniques to help attain NAAQS. Specifically,  section 123 prohibits states from counting the dispersion effects of stack  heights in excess of a stack’s GEP height when determining a source’s  emissions limitation. The Clean Air Act defines GEP as “the height  necessary to insure that emissions from the stack do not result in  excessive concentrations of any air pollutant in the immediate vicinity of  the source as a result of atmospheric downwash, eddies, or wakes which  may be created by the source itself, nearby structures, or nearby terrain  obstacles.” According to federal regulations, a stack’s GEP height is the  higher of  65 meters, measured from the ground-level elevation at the base of the  stack; a formula based on the height and width of nearby structure(s) (height  plus 1.5 times the width or height, whichever is lesser); or the height demonstrated by a fluid model or field study that ensures  the emissions from a stack do not result in excessive concentrations of  any air pollutant as a result of atmospheric downwash created by the  source itself, nearby structures, or nearby terrain features.
Downwash occurs when large buildings or local terrain distort or impact  wind patterns, and an area of more turbulent air forms, known as a wake.
Emissions from a stack at a power plant can be drawn into this wake and  brought down to the ground near the stack more quickly (see fig. 1).
States issue air permits to major stationary sources of air pollution, such  as power plants, and determine GEP for stacks when they set emissions  limitations for these sources. Emissions limitations may be reset when  plants undergo New Source Review. New Source Review is a  preconstruction permitting program which requires a company that  constructs a new facility or makes a major modification to an existing  facility to meet new, more stringent emissions limitation based on the  current state of pollution control technology. A stack’s GEP height is used  in air dispersion modeling that takes place when emissions limitations are  developed for a source as part of the permitting process.
Many sources contribute to levels of pollution that affect the ability of  downwind states to attain and maintain compliance with NAAQS, and  some of these pollutants may originate hundreds or thousands of miles  from the areas where violations are detected. The Clean Air Act’s “good  neighbor provisions” under section 110 of the Act require states to prohibit  emissions that significantly contribute to nonattainment or interfere with  maintenance of NAAQS in downwind states or which will interfere with  downwind states’ ability to prevent significant deterioration of air quality.  Section 126 of the Clean Air Act also allows a downwind state to petition  EPA to determine that specific sources of air pollution in upwind states  interfere with the downwind state’s ability to protect air quality and for  EPA to impose emissions limitations directly on these sources. As detailed  in the timeline below, Congress granted EPA increased authority to  address interstate transport of air pollution under the Clean Air Act, and  EPA acted on this authority.    1977 amendments to the Clean Air Act. These amendments contained  two provisions that focused on interstate transport of air pollution, the  predecessor to the current good neighbor provision of section 110 of  the Act and section 126. These amendments also established the New  Source Review program.   1990 amendments to the Clean Air Act. These amendments added the  Acid Rain Program (Title IV) to the Clean Air Act, which created a cap- and-trade program for SO emissions by 10 million tons from 1980 levels and  reducing annual NO emissions by 2 million tons from 1980 levels by  the year 2000.   1998 NO SIP Call. After concluding that NO emissions from 22 states  and the District of Columbia contributed to the nonattainment of  NAAQS for ozone in downwind states, EPA required these states to  amend their SIPs to reduce their NO emissions. EPA took this  regulatory action based on section 110 of the Clean Air Act.   2005 Clean Air Interstate Rule (CAIR). This regulation required SIP  revisions in 28 states and the District of Columbia that were found to  contribute significantly to nonattainment of NAAQS for fine particulate  matter and ozone in downwind states. CAIR required reductions for  SO emissions from 28 eastern states and the District of  Columbia and included an option for states to meet these reductions  through regional cap-and-trade programs. When the rule was finalized,  EPA estimated it would annually reduce SO and NO emissions by 3.8  million and 1.2 million tons, respectively, by 2015. The U.S. Court of  Appeals remanded CAIR to EPA in 2008 because it found significant  flaws in the approach EPA used to develop CAIR, but allowed the rule  to remain in place while EPA develops a replacement rule.   2010 Transport Rule. EPA proposed this rule to replace CAIR, which  aims to reduce emissions of SO from power plants. If  finalized as written, the rule would require emissions of SO to  decrease 71 percent over 2005 levels and emissions of NO to decrease  by 52 percent over 2005 levels by 2014.
As described above, EPA’s efforts to address the interstate transport of air  pollution from power plants have focused on reducing the total emissions  of SO from these plants. Unlike tall stacks, pollution controls  help to reduce the actual emissions from power plants by either reducing  the formation of these emissions or capturing them after they are formed.  At coal power plants, these controls are generally installed in either the  boiler, where coal is burned, or the duct work that connects a boiler to the  stack. A single power plant can use multiple boilers to generate electricity,  and the emissions from multiple boilers can sometimes be connected to a  single stack. Figure 2 shows some of the pollution controls that may be  used at coal power plants: fabric filters or electrostatic precipitators (ESP)  to control particulate matter, flue gas desulfurization (FGD) units—known  as scrubbers—to control SO emissions, and selective catalytic reduction  (SCR) or selective non-catalytic reduction (SNCR) units to control NO  emissions.
The reduction in emissions from a coal power plant by the use of pollution  controls can be substantial, as shown in table 1. The installation of  pollution control equipment can also be expensive. According to a  Massachusetts Institute of Technology study of coal power plants, it may  cost anywhere from $215,000 per megawatt to $330,000 per megawatt to  install controls at a coal power plant for particulate matter, SO.  For a typical coal power plant with a capacity of 500 megawatts, this  means that it could cost from $107 million to install these controls at a  newly built facility up to $165 million to retrofit these controls at an  existing facility. Additionally, pollution controls can require additional  energy to operate, known as an energy penalty.
section_title: Almost 300 Tall Smokestacks Operate in 34 States, and about Half Began Operating before 1980
paragraphs: According to our analysis of EIA data, which we updated with our survey  results, we found a total of 284 tall smokestacks were operating at 172 coal  power plants in 34 states, as of December 31, 2010. While about half of the  tall stacks began operating more than 30 years ago, there has been an  increase in the number of tall stacks that have begun operating in the last 4  years, which several stakeholders attributed to the need for new stacks  when retrofitting existing plants with pollution control equipment.
subsections: section_title: 284 Tall Stacks Were Operating at about 170 Coal Power Plants, with Approximately One-Third Located in the Ohio River Valley
paragraphs: As of December 31, 2010, we found a total of 284 tall stacks were operating  at 172 coal power plants in the United States. These tall stacks account for  about 35 percent of the 808 stacks operating at coal power plants in the  United States, and they are generally located at larger power plants.  Specifically, we found these stacks are associated with 64 percent of the  coal generating capacity.
We found that 207 tall stacks (73 percent) are between 500 and 699 feet tall  and that 63 stacks (22 percent) are between 700 and 999 feet tall. The  remaining 14 stacks (5 percent) are 1,000 feet tall or higher, with the tallest  stack at a coal power plant in the United States having a height of 1,038  feet at the Rockport Power Plant in Indiana. In figure 3, we show how a  tall stack compares to the heights of other well-known structures.
Thirty-five percent of the 284 tall stacks are concentrated in 5 states along  the Ohio River Valley—Kentucky, Ohio, Indiana, Illinois, and  Pennsylvania—at 59 coal power plants. Another 32 percent are located in  Alabama, Missouri, West Virginia, Michigan, Georgia, Wyoming, Wisconsin,  and Texas, while the remaining 33 percent of tall stacks are located across  21 other states. Figure 4 shows the location of coal power plants with  operating tall stacks. For counts of all tall stacks by state, see appendix II.
section_title: About Half of All Tall Stacks Began Operating before 1980, but an Increasing Number Have Gone into Service in the Last 4 Years
paragraphs: Forty-six percent of the 284 tall stacks operating at coal power plants in  the United States as of December 31, 2010, went into service before 1980.  Another 28 percent went into service in the 1980s, 7 percent went into  service in the 1990s, and 18 percent went into service since 2000. Of the  stacks that went into service since 2000, a vast majority went into service  in the last 4 years, as shown in figure 5.
section_title: Stack Height Contributes to Interstate Transport of Air Pollution, and the Emissions from Several Tall Stacks Remain Uncontrolled for Certain Pollutants
paragraphs: Stack height is one of several factors that contribute to the interstate  transport of air pollution. While the use of pollution controls has increased  in recent years at coal power plants, several boilers connected to tall  stacks remain uncontrolled for certain pollutants.
subsections: section_title: Stack Height Is One of Several Factors that Contribute to the Interstate Transport of Air Pollution
paragraphs: Stack height is one of several factors that contribute to the interstate  transport of air pollution. According to reports and stakeholders with  expertise on this topic, tall stacks generally disperse pollutants over longer  distances than shorter stacks and provide pollutants with more time to  react in the atmosphere to form ozone or particulate matter. However, the  interstate transport of air pollution is a complex process that involves  several variables—such as total emissions from a stack, the temperature  and velocity of the emissions, and weather—in addition to stack height. As  a result, stakeholders had difficulty isolating the exact contribution of  stack height to the interstate transport of air pollution, and we found  limited research on this specific topic. For example, EPA staff involved in  the modeling of interstate transport told us that it is difficult to determine  the different impacts that stacks of varying heights have on the transport  of air pollution. According to one atmospheric scientist we spoke with, the  interstate transport of air pollution is a complex process and stack height  represents just one variable in this process.
Stakeholders struggled to identify the precise impact of tall stacks, due in  part to the other factors that influence how high emissions from a stack  will rise. The temperature and velocity of a stack’s emissions, along with  its height, contribute to what is known as an “effective stack height.”  Effective stack height takes into account not only the height at which  emissions are released, but also how high the plume of emissions will rise,  which is influenced by the temperature and velocity of these emissions.  One atmospheric scientist told us the emissions from a shorter stack could  rise higher than a taller stack, depending on the temperature and velocity  of the emissions.
Weather also plays a key role in the transport of air pollution. A study by  the Northeast States for Coordinated Air Use Management (NESCAUM)–– a group that represents state air agencies in the Northeast––described  weather patterns that can contribute to high-ozone days in the Ozone  Transport Region, which includes 12 states in the Mid-Atlantic and New  England regions and the District of Columbia. These high-ozone days  typically occur in the summer on hot days, when the sun helps transform  NO and volatile organic compounds into ozone. Wind speeds and wind  direction also help to determine how emissions will travel. In the Mid- Atlantic United States, the wind generally blows from west to east during  the day, and wind speeds are generally faster at higher elevations. The  time of day can also influence the transport of air pollution. According to  the NESCAUM report and researchers we spoke with, ozone can travel  hundreds of miles at night with the help of high-speed winds known as the  low-level jet. This phenomenon typically occurs at night when an  atmospheric inversion occurs due to the ground cooling quicker than the  upper atmosphere. A boundary layer can form between these two air  masses several hundred feet off the ground, which can allow the low-level  jet to form and transport ozone and particulate matter with its high winds.  As the atmosphere warms the following day, this boundary layer can break  down and allow these transported emissions to mix downward and affect  local air quality.
Air dispersion models typically take into account stack height along with  these other factors when predicting the transport of emissions from power  plants. For example, EPA used the Comprehensive Air Quality Model with  Extensions (CAMx) to conduct the modeling to support the development  of the Transport Rule. CAMx is a type of photochemical grid model, which  separates areas into grids and aims to predict the transport of sources that  lie within these grids. Key inputs into this model include stack height, the  velocity and temperature of emissions, and weather data. EPA staff  involved in conducting this modeling for the Transport Rule said they use  the CAMx model to predict the actual impacts of air emissions, and they  have not used this model to estimate the specific impact of stack height on  interstate transport. They reported their modeling efforts in recent years  have been done in support of CAIR and the Transport Rule, and have been  focused on modeling the regional impacts of reducing total air emissions.
Several stakeholders we spoke with said total emissions is a key  contributor to interstate transport of air pollution, and the use of pollution  controls at coal power plants is critical to reducing interstate transport of  air pollution. Reducing the total emissions from a power plant influences  how much pollution can react in the atmosphere to form ozone and  particulate matter that can ultimately be transported.
section_title: Use of Pollution Controls at Coal Power Plants Has Increased in Recent Years, but Emissions from Some Plants, Including Several with Tall Stacks, Remain Uncontrolled for Certain Pollutants
paragraphs: The use of pollution control equipment, particularly for SO and NO  emissions, has increased over time, largely in response to various changes  in air regulations, according to stakeholders and reports we reviewed.  According to EIA data, the generating capacity of power plants that is  controlled by FGDs has increased from about 87,000 megawatts to about  140,000 megawatts from 1997 to 2008. Since coal power plants had about  337,000 megawatts of generating capacity in 2008, this means that about 42  percent of the generating capacity was controlled by a FGD in 2008.  Similarly, SCRs were installed at about 44,000 megawatts worth of  capacity from 2004 through 2009, with about one-third of these  installations occurring in 2009 alone, according to an EPA presentation on  this topic. EPA and state officials, along with electric utility officials, told  us that the increase in the use of these pollution controls is due to various  air regulations, such as the Acid Rain Program and CAIR, which focused  on reducing SO emissions.
However, while we found that the use of pollution controls at coal power  plants has increased in recent years, many boilers remain uncontrolled for  certain pollutants, including several connected to tall stacks. For example,  we found that 56 percent of the boilers attached to tall stacks at coal  power plants do not have a FGD to control SO emissions. Collectively, we  found that these uncontrolled boilers accounted for 42 percent of the total  generating capacity of boilers attached to tall stacks. Our findings on  FGDs are similar to EPA data on all coal power plants. In 2009, EPA  estimated that 50 percent of the generating capacity of coal power plants  did not have FGDs.
For NO controls, we found that while about 90 percent of boilers attached  to tall stacks have combustion controls in place to reduce the formation of  NO emissions, a majority of these boilers lack post-combustion controls  that can help to reduce NO emissions to a greater extent. Specifically, 63  percent of boilers connected to tall stacks do not have post-combustion  controls for NO, such as SCRs or SNCRs, which help reduce NO  emissions more than combustion controls alone. Collectively, we found  that these boilers without post-combustion controls accounted for 54  percent of the total generating capacity of boilers attached to tall stacks.  EPA data on all coal power plants show that 53 percent of the generating  capacity for coal power plants did not have post-combustion controls for  NO emissions in place in 2009.
Tall stacks that had uncontrolled SO emissions were generally  attached to older boilers that went into service prior to 1980. We found  that approximately 85 percent of boilers without FGDs that were attached  to tall stacks went into service before 1980. Similarly, over 70 percent of  the boilers without post-combustion controls for NO went into service  before 1980. Overall, we found that about 82 percent of the boilers that  lacked both a FGD and post-combustion controls for NO went into  service before 1980. Some stakeholders attributed the lack of pollution  controls on older boilers to less stringent standards that were applied at  the time the boilers were constructed. As discussed above, companies that  construct a new facility or make a major modification to an existing  facility must meet new emissions limitations based on the current state of  pollution control technology. Because pollution control technology has  advanced over time, the standards have become more stringent over time,  meaning that boilers constructed before 1980 would have had higher  allowable emissions and less need to install controls than boilers  constructed in 2010.
Unlike our findings on FGDs and post-combustion controls for NO  emissions, we found that 100 percent of boilers attached to tall stacks  were controlled for particulate matter. However, it is important to note  that plants with uncontrolled SO and NO emissions contribute to the  formation of additional particulate matter in the atmosphere.
section_title: Based on Available Information, 17 of 48 Tall Smokestacks Built Since 1988 Exceed Their GEP Height, and A Variety of Factors Can Influence Height Decisions
paragraphs: We identified 48 tall stacks built since 1988 that states reported are subject  to the GEP provisions of the Clean Air Act and for which states could  provide GEP height information. Of these 48 stacks, we found that 17  exceed their GEP height, 19 are at their GEP height, and 12 are below their  GEP height. We found that 15 of the 17 stacks built above GEP were  replacement stacks that were built as part of the process of installing  pollution control equipment. These stacks vary in the degree to which they  exceed GEP height, ranging from less than 1 percent above GEP to about  46 percent above GEP, as shown in table 2. The other 2 stacks built above  GEP exceed their GEP height by 2 percent or less.
When we followed up with utility officials regarding why these stacks  were built above GEP, they reported that a variety of factors can influence  stack height decisions. These factors included helping a plant’s emissions  clear local geographic features, such as valley walls. According to one  state air protection agency, three stacks were built above GEP to provide  further protection against downwash. Officials from two utilities said they  built stacks above GEP at coal power plants to account for the impact of  other structures, such as cooling towers, on the site. Other stakeholders  said that utilities may be hesitant to lower stack heights at their facilities  when replacing a stack because plant officials have experience with that  stack height and its ability to help protect against downwash. An official  from one company that builds stacks told us this practice has sometimes  occurred because utilities do not want the moisture-rich emissions from  the replacement stack to hasten the deterioration of the old stacks, which  are usually left in place and must be maintained. In addition, this moisture  can create large icicles on the older stacks, which can present a danger to  staff working at the power plant.
Other stakeholders highlighted factors that may play a role in making  stack height decisions. Some federal and state officials reported that  generally there is little incentive to build a stack above GEP because a  facility will not receive dispersion credit for the stack’s height above GEP.  Other stakeholders acknowledged that a stack could be built above GEP  for site-specific reasons, such as helping emissions clear nearby terrain  features. Some of these officials also noted that cost was another factor  considered when making stack height decisions, as it is generally more  costly to build a higher stack. For example, one utility official told us that  two replacement stacks that were recently built below their original  heights could meet their emissions limitations with these lower stack  heights because the utility was installing pollution control equipment and  did not want to incur the additional cost of building a taller stack.
We found that stacks built above GEP since 1988 generally were attached  to boilers that had controls in place for SO, and particulate matter, as  shown in table 3. We found similar results for stacks that were built at or  below their GEP heights.
We were unable to obtain GEP height information for an additional 25  stacks that were built since 1988 for two reasons. First, some of these  stacks replaced stacks that were exempt from the GEP regulations,  according to state officials. Section 123 of the Clean Air Act exempts stack  heights that were in existence on or before December 31, 1970, from the  GEP regulations; because the exemption applies to stack heights rather  than to stacks themselves, it covers both original and replacement stacks.  Second, states did not have GEP information readily available for some  stacks. According to state officials, they did not set new emissions limits at  the time these replacement stacks were built because they were part of  pollution control projects and emissions from these plants did not  increase. For example, one state reported that GEP could have been  calculated decades earlier for the original stacks when emissions  limitations were set, and they were unable to locate this information in  response to our request. According to EPA staff we spoke with about this  issue, states are not required to conduct a GEP analysis in these instances.  While we were unable to obtain GEP information for these stacks, our  analysis of the pollution controls installed at boilers connected to these  stacks yielded similar results to those stacks for which we did obtain GEP  information. Specifically, all of these boilers had controls for SO.
section_title: Agency Comments
paragraphs: We provided a draft of this report to EPA and DOE for review and  comment. Both EPA and DOE stated they had no comments.
As agreed with your office, 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 appropriate  congressional committees, Secretary of Energy, Administrator of EPA, and  other interested parties. In addition, this report will be available at no  charge on the GAO Web site at http://www.gao.gov.
If you or your staff have any questions regarding 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 major contributions to this  report are listed in appendix III.
section_title: Appendix I: Scope and Methodology
paragraphs: To identify the number and location of smokestacks at coal power plants  that were 500 feet or higher as of December 31, 2010, we analyzed data on  power plants from the Department of Energy’s (DOE) Energy Information  Administration (EIA). We also used these data to determine when these  stacks began operating. To determine the reliability of these data, we  reviewed documentation from EIA, interviewed relevant officials who  were involved in collecting and compiling the data, conducted electronic  testing of the data, and we determined that the data were sufficiently  reliable for our purposes. Because the EIA data were collected in 2008, we  contacted all 50 states and the District of Columbia to determine if they  had tall stacks and developed and administered a survey to those 38 states  with tall stacks to update the relevant EIA data and determine if any  changes had taken place in the number or operating status of stacks since  that time. We received e-mail addresses for each state from the Web site  of the National Association of Clean Air Agencies, which represents air  pollution control agencies in 53 states and territories, and developed a  survey that we sent to respondents as an e-mail attachment. Prior to  sending out this survey, we pretested the survey with officials from 2  states and revised some of the survey questions based on their input. We  received responses to our survey from all 38 states and we sent follow-up  questions based on their survey responses to clarify certain responses or  to ask for additional information. We updated the relevant EIA data with  these survey results to include the most recent information available on  tall stacks.
We did not include tall stacks that were used as bypass stacks only in  times of maintenance or emergencies in our count of tall stacks. State  officials reported that bypass stacks are rarely used and would not be used  at the same time as plants’ fully operating stacks. Additionally, we defined  multi-flue stacks—those with multiple flues running within a single  casing—as one stack, as opposed to counting each flue as a separate  stack. A state modeling official told us they consider multi-flue stacks as  single stacks when conducting dispersion modeling.
For the purposes of this report, we defined tall smokestacks to be those  that were 500 feet or higher. In our interviews with stakeholders, several  told us they considered 500 feet to be a “tall” stack. Some stakeholders  said that a typical boiler building at a coal power plant is about 200 feet  high. Given that the original formula for good engineering practice (GEP)  was 2.5 times height of nearby structures, this would equal about 500 feet.  Other stakeholders reported that they considered a stack built above GEP  to be “tall.”
To determine what is known about tall stacks’ contribution to the  interstate transport of air pollution, we reviewed reports from the  Environmental Protection Agency (EPA) and academics and spoke with  stakeholders with expertise on this topic. We conducted a literature  search of engineering and other relevant journals on the topic of stack  height and interstate transport of air pollution, and we reviewed the  limited amount of literature we identified. The stakeholders we  interviewed included EPA officials involved in modeling interstate  transport of air pollution from power plants, officials from utilities and  construction firms that design and build power plants, atmospheric  scientists who conduct research on this topic, and state officials who are  involved in permitting power plants and complying with federal  regulations governing the interstate transport of air pollution. We also  analyzed the EIA data and our survey results to determine the pollution  control equipment installed at coal power plants with stacks 500 feet or  higher. Specifically, we identified the control equipment that was  associated with boilers that were attached to tall stacks. Pollution control  equipment is not installed on stacks themselves; rather it is installed in the  boilers or the ductwork that connect the boiler to a stack. We also  interviewed stakeholders to learn about trends in installing pollution  control equipment and reviewed relevant reports on this topic.
To determine the number of tall stacks that have been built above their  GEP height since 1988, we used our survey to obtain information from  state officials about the GEP height for these stacks. Twenty-two states  had stacks that were over 500 feet that were built since 1988, and we  received survey responses from all of them. In our survey, we also asked  for reasons that a stack was built above GEP, when applicable. In cases  where state officials could not provide specific reasons, we contacted the  utilities that operate the plants with these stacks to obtain this  information. Specifically, we contacted utilities that were involved in  operating 15 of the 17 stacks that were built since 1988 and exceed GEP  height, and we were able to interview utilities operating 12 of these stacks.  We did not contact the utilities that operate the other 2 stacks, because the  stacks are each less than 2 feet above GEP. We also interviewed  companies that design and build power plants to ask about some of the  general factors that are considered when deciding on stack height. We  focused on stacks built since 1988, because that was the year that EPA’s  regulations for determining GEP height were largely affirmed by the  District of Columbia Court of Appeals. EPA began the process of  developing these regulations in the late 1970s, but the final regulations  were not issued until 1985. The regulations were then challenged in court  and were largely affirmed in 1988.
Finally, we conducted site visits to two coal power plants in Ohio. We  selected this state because it contained several coal power plants with tall  stacks, including some stacks that were built in 1988 or later. During this  visit, we interviewed utility officials that operated these plants, along with  state and local officials involved in permitting these plants.
We conducted this work from July 2010 through May 2011 in accordance  with all sections of GAO’s quality assurance framework that are relevant  to our objectives. This framework requires that we plan and perform the  engagement to obtain sufficient, appropriate evidence to meet our stated  objectives and to discuss any limitations in our work. We believe that the  information and data obtained, and the analysis conducted, provide a  reasonable basis for any findings and conclusions.
section_title: Appendix II: Distribution of Tall Stacks by State
paragraphs: Table 4 provides counts of the number of stacks 500 feet or higher—tall  stacks—by state. In addition, the table provides information on the  generating capacity of the boilers attached to these stacks.
section_title: Appendix III: GAO Contact and Staff Acknowledgments
subsections: section_title: GAO Contact
section_title: Staff Acknowledgments
paragraphs: In addition to the individual named above, key contributors to this report  include Barbara Patterson (Assistant Director), Scott Heacock, Beth Reed  Fritts, and Jerome Sandau. Important assistance was also provided by  Antoinette Capaccio, Cindy Gilbert, Alison O’Neill, Madhav Panwar, and  Katherine Raheb.