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entitled 'Air Pollution: Estimated Emissions from Two New Mexicali 
Power Plants Are Low, but Health Impacts Are Unknown' which was 
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Report to Congressional Requesters: 

United States Government Accountability Office: 

GAO: 

August 2005: 

Air Pollution: 

Estimated Emissions from Two New Mexicali Power Plants Are Low, but 
Health Impacts Are Unknown: 

GAO-05-823: 

GAO Highlights: 

Highlights of GAO-05-823, a report to congressional requesters: 

Why GAO Did This Study: 

Power plants emit pollutants that have been linked to various negative 
health effects. In 2003, two new power plants, owned by Sempra Energy 
and Intergen, began operations 3 miles south of the U.S.-Mexico border 
near Imperial County, California. The county does not meet some federal 
and state air quality standards and may be further impacted by the 
emissions from these plants. Although these plants export most of the 
electricity they produce to the United States, they are not currently 
required to meet any U.S. or California emissions standards. 

GAO was asked to determine (1) how emissions from the two plants 
compare with emissions from recently permitted plants in California and 
emissions from sources in Imperial County, and what emissions standards 
they would be subject to if they were located in Imperial County; (2) 
the health impacts of emissions from the plants on Imperial County 
residents; and (3) options available to U.S. policymakers to ensure 
that emissions from these plants do not adversely affect the health of 
Imperial County residents. 

In commenting on a draft of this report, DOE disagreed with our 
characterization of the limitations of their assessment of the health 
impact of pollution from the Sempra and Intergen power plants. We 
believe we have portrayed the limitations of this assessment 
accurately. 

What GAO Found: 

The estimated emissions from the Sempra and Intergen power plants near 
Mexicali are comparable with similar plants recently permitted in 
California and are low relative to emissions from the primary sources 
of pollution in Imperial County, California, which are dust and 
vehicles. However, if the plants were located in Imperial County, they 
would be required to take steps to improve air quality by reducing 
emissions from other pollution sources in the region, such as paving 
dirt roads, because the county is not meeting certain U.S. air quality 
standards. 

Although emissions generated from the Sempra and Intergen plants may 
contribute to various adverse health impacts in Imperial County, the 
extent of such impacts is unknown. The Department of Energy (DOE) 
estimated that emissions from these plants may increase asthma 
hospitalizations by less than one per year. However, DOE did not 
quantify any other asthma-related impacts, such as emergency room 
visits or increased use of medications, which, although less severe, 
are likely to occur more often. In addition, DOE did not determine 
whether increased emissions would cause other respiratory or 
cardiovascular problems and the impact of particulate matter on 
particularly susceptible populations. Finally, the potential health 
impacts associated with ozone could be greater than DOE estimated 
because some important data needed for modeling were not available. 

Existing laws and international agreements may not provide adequate 
mechanisms to address adverse health impacts resulting from power plant 
emissions. Policymakers could take some actions, such as requiring 
plants that seek to export electricity to the United States to use 
specified emission controls. While this action would have benefits, it 
would also have costs, such as possibly reducing energy supplies 
available to Southern California. Long-term policy options include the 
development of a binational pollution reduction program or a trust fund 
to provide grants and loans to support air quality improvement 
projects. However, substantial efforts on both sides of the U.S.-Mexico 
border would be required to establish the legal and management 
framework necessary for such programs to be effective. 

Map of the U.S.-Mexico Border Region Near the Sempra and Intergen Power 
Plants: 

[See PDF for image] 

[End of figure] 

www.gao.gov/cgi-bin/getrpt?GAO-05-823. 

To view the full product, including the scope and methodology, click on 
the link above. For more information, contact John B. Stephenson at 
(202) 512-3841 or stephensonj@gao.gov. 

[End of section]

Contents: 

Letter: 

Results in Brief: 

Background: 

Emissions from the Mexicali Plants Are Comparable to New Plants in 
California, but Offset Requirements Would Apply in Imperial County: 

Emissions Generated by the Sempra and Intergen Power Plants May 
Contribute to Various Adverse Health Impacts in Imperial County, but 
the Extent of Such Impacts Is Unknown: 

Policymakers Have Limited Options to Ensure That Emissions from the 
Sempra and Intergen Power Plants Do Not Adversely Affect the Health of 
Residents in Imperial County: 

Conclusions: 

Agency Comments and Our Evaluation: 

Appendix I: Objectives, Scope, and Methodology: 

Appendix II: Comments from the Department of Energy: 

GAO Comments: 

Appendix III: GAO Contact and Staff Acknowledgments: 

Tables: 

Table 1: Key Power Plant Pollutants and Potential Health Impacts: 

Table 2: Average Emissions from the Sempra and Intergen Power Plants 
Based on Third-party Testing: 

Table 3: Comparison of Estimated Sempra and Intergen Plant Emissions 
and the Emission Limits of Recently Permitted Power Plants in 
California: 

Table 4: Summary of Annual Emission Estimates for the Sempra and 
Intergen Power Plants Using Three Alternative Operating Assumptions 
(Tons per Year): 

Table 5: Estimated Annual Average Emissions in 2004 for Imperial 
County, California (Tons per Year): 

Table 6: Comparison of NOx Emission Rates from the Sempra and Intergen 
Plants and Power Plants in Imperial County and Baja California: 

Table 7: Potential Offsets in Imperial County, California, Identified 
by the Imperial County Air Pollution Control District: 

Table 8: Imperial County Air Quality Compared with National Standard 
for PM10 (1997-2003): 

Figures: 

Figure 1: Map of the Sempra and Intergen Power Plants and the 
Associated Transmission Lines: 

Figure 2: Electrical Production at the Sempra and Intergen Power 
Plants: 

Figure 3: Relative Emissions Contributions by Source Assuming the 
Sempra and Intergen Plants Operated at Maximum Allowable Emissions and 
All Emissions Reached Imperial County: 

Figure 4: Pyramid of Potential Health Impacts for Asthmatics: 

Abbreviations: 

BLM: Bureau of Land Management: 

CO: carbon monoxide: 

DOE: Department of Energy: 

EPA: Environmental Protection Agency: 

NAAEC: North American Agreement on Environmental Cooperation: 

NAFTA: North American Free Trade Agreement: 

NOx: nitrogen oxides: 

NH3: ammonia: 

PM: particulate matter: 

PPM: parts per million: 

VOC: volatile organic compounds: 

United States Government Accountability Office: 

Washington, DC 20548: 

August 12, 2005: 

The Honorable Hilda Solis: 
Ranking Member: 
Subcommittee on Environment and Hazardous Materials: 
Committee on Energy and Commerce: 
House of Representatives: 

The Honorable Bob Filner: 
House of Representatives: 

In 2003, two new power plants owned by American-based corporations, 
Sempra Energy and Intergen, began operations 3 miles south of the U.S.- 
Mexico border near Mexicali, Mexico, and Imperial County, California. 
These modern natural gas-fired plants use advanced pollution control 
technologies; nevertheless, they emit some pollutants such as nitrogen 
oxides and airborne particles, known as particulate matter. Some health 
studies have found that even the smallest incremental increase in the 
amount of particulate matter in the air corresponds with an increase in 
adverse health effects. 

The U.S.-Mexico border region is experiencing significant economic, 
industrial, and population growth, and that growth is expected to 
continue. Imperial County is one of the fastest growing counties in 
California and is expected to double in population by 2025. The county 
does not currently meet some federal and state air quality standards 
and has one of the highest asthma prevalence rates for children ages 1 
through 17 in the state. The increased demand for energy to meet the 
needs of the border region could lead to the construction of additional 
power plants, with the associated potential for increased air pollution 
and negative impacts on public health. 

In the United States, the Clean Air Act establishes the principal 
framework for federal, state, and local efforts to protect air quality. 
Under this act, the Environmental Protection Agency (EPA) establishes 
health-based air standards that the states must meet.[Footnote 1] EPA 
has issued air quality standards for six primary pollutants--carbon 
monoxide, lead, nitrogen dioxide,[Footnote 2] ozone, sulfur dioxide, 
and two categories of particulate matter (PM2.5 and PM10)[Footnote 3]-
-that have been linked to a variety of health problems. Agencies 
collect data on the levels of these pollutants to determine if air 
quality is meeting the federal standards. Areas that do not meet these 
federal standards are designated as "nonattainment" areas and are, as a 
result, generally subject to more stringent emission control 
requirements. Imperial County is currently designated as a 
nonattainment area for PM10 and ozone.[Footnote 4] New facilities being 
built within a nonattainment area that are expected to generate 
emissions above a certain threshold may be required to provide 
mitigation measures in the form of emission offsets. These offsets are 
designed to improve air quality in nonattainment areas by reducing 
emissions from other pollution sources in the region. They could 
include, for example, providing funds to update diesel engines or to 
pave dusty dirt roads. 

The Sempra power plant has a single power-generating unit with the 
capacity to produce a total of 650 megawatts of electricity per hour, 
all of which are designated for export to the United States.[Footnote 
5] The Intergen facility, which has a total capacity of 1,060 
megawatts, is composed of two units: one that produces power 
exclusively for the United States and a second that exports up to one- 
third of its power to the U.S. market. Because the plants are located 
in Mexico, Mexican agencies have the exclusive authority to regulate 
the permitting and construction, as well as the emissions resulting 
from their operation. Mexico regulates the emissions of several 
pollutants from its power plants but requires natural gas-fired plants, 
such as Sempra and Intergen, to report emissions of only nitrogen 
oxides. In part, because of the advanced technology and control 
equipment these plants are using, their estimated emissions of NOx are 
significantly lower than the established emission limit in Mexico. 

The electricity generated by these plants is transmitted into the 
United States over electric transmission lines authorized by 
presidential permits issued by the Department of Energy's (DOE) Office 
of Fossil Energy.[Footnote 6] These permits are required before 
electric transmission facilities are constructed, operated, maintained, 
or connected at the U.S.-Mexico border.[Footnote 7] DOE is responsible 
for reviewing permit applications and conducting an environmental 
evaluation as part of this review. DOE issued a final environmental 
impact statement on the Sempra and Intergen transmission lines in 
December 2004 that included an assessment of the potential health 
impacts associated with emissions from the power plants. 

In this context, you asked us to determine (1) how emissions from the 
Sempra and Intergen power plants compare to emissions from recently 
permitted plants in California and emissions from sources in Imperial 
County, and what emissions standards the plants would be subject to if 
they were located in Imperial County; (2) the health impacts of 
emissions from the power plants on Imperial County residents; and (3) 
what options exist for U.S. policymakers to ensure that emissions from 
these power plants do not adversely affect the health of Imperial 
County residents. 

To address these objectives, we visited the Sempra and Intergen plants 
near Mexicali, Mexico; interviewed plant representatives, various 
federal, state, and local air quality officials, and other key 
stakeholders; and reviewed relevant documents and studies. To address 
how emissions from the Sempra and Intergen power plants compare to 
emissions from recently permitted plants in California, we used data 
from emissions tests conducted at the plants by third-party 
contractors. We did this because Mexico does not require the plants to 
report actual emissions of pollutants other than nitrogen oxides. We 
assessed the reliability of the data by (1) reviewing documentation of 
test objectives and quality control procedures provided by the third- 
party contractors who conducted the tests, (2) talking with Sempra and 
Intergen officials to determine the scope and generalizability of the 
tests, and (3) reviewing reports of actual NOx emissions submitted to 
the Mexican government to verify consistency with the test results. We 
determined that the data were sufficiently reliable for the purposes of 
this report. We also obtained the permissible emission limits for 
comparable plants in California. Comparable plants were selected by 
identifying all natural gas power plants of similar size and 
specifications to the Sempra and Intergen plants that were permitted in 
California between 2000 and 2004. Because all California power plants 
are permitted on a case-by-case basis, emissions limits may vary with 
each project. Therefore, we used the entire range of emission limits 
for the 23 plants that were identified during our selection process. To 
determine how the emissions from the Sempra and Intergen power plants 
compared to emissions from sources in Imperial County, we utilized the 
2004 estimated annual average emissions inventory for the county 
developed by the California Air Resources Board, among other things. To 
address what emissions standards the plants would be subject to if they 
were located in Imperial County, we reviewed federal and California 
regulations for new power plants, interviewed EPA, state, and Imperial 
County air quality officials, and reviewed the emission limits and 
selected permitting conditions for power plants located in California. 
To identify the potential health impacts from plant emissions, we 
reviewed the health assessment methodology DOE used in its 
environmental impact statement, reviewed relevant studies, and met with 
health experts. To determine available policy options, we reviewed the 
Clean Air Act; environmental and trade agreements among the United 
States, Mexico, and Canada; and academic research. See appendix I for 
additional details on our scope and methodology. We conducted our work 
between September 2004 and August 2005 in accordance with generally 
accepted government auditing standards. 

Results in Brief: 

The emissions from the Sempra and Intergen power plants near Mexicali 
are comparable to emissions from similar plants recently permitted in 
California and are low relative to emissions from the primary sources 
of pollution in Imperial County--dust and vehicles. However, if the 
plants were located in Imperial County, they would be required, among 
other things, to offset their emissions to help improve regional air 
quality. Our review of emissions test data obtained from Sempra and 
Intergen indicates that estimated emissions from these plants generally 
fall within a range of allowable emission limits identified from 23 
plants of comparable size and specifications permitted in California 
between 2000 and 2004. Although the Sempra and Intergen plants will 
cause some increase in regional emissions of PM10 and nitrogen oxides 
(which contribute to ozone formation), the primary sources contributing 
to PM10 and ozone in Imperial County are various forms of dust and 
motor vehicles. In addition, based on the amount of energy produced per 
pound of NOx emissions, these plants are cleaner than other major fuel- 
fired plants operating in Imperial County or the border region of Baja 
California, Mexico. Nevertheless, if the plants were located in 
Imperial County, they would be required to offset their emissions 
because the county is a nonattainment area for PM10 and ozone. More 
specifically, Imperial County air quality rules would require that the 
operators of each plant provide emissions offsets of at least 1.2 tons 
for every ton of emissions released by the plant that contribute to 
area nonattainment status. 

Emissions generated by the Sempra and Intergen power plants, like any 
other source of emissions, may contribute to adverse health impacts in 
Imperial County, but the full extent of such impacts is unknown. In its 
December 2004 final environmental impact statement, DOE estimated an 
increase in asthma hospitalizations in Imperial County of less than one 
per year as the result of increased emissions from the two plants. 
However, DOE did not fully assess the plants' health impact because it 
did not quantify other asthma-related health impacts, such as emergency 
room visits, physician visits, and increased use of asthma medication, 
which, although less severe than hospitalization, are likely to occur 
more often, according to health experts. Also, the DOE study did not 
address the extent to which increased emissions of particulate matter 
would cause other adverse health impacts, such as other respiratory or 
cardiovascular conditions. In addition, DOE did not analyze the health 
impacts from increased power plant emissions on particularly 
susceptible populations, such as asthmatic children and low-income 
asthmatic adults. Imperial County is one of the poorest counties in 
California and low-income asthmatics adults are more susceptible to 
health problems, in part, because they have less access to health care. 
Finally, EPA officials are concerned about the accuracy of DOE's 
modeling of estimated ozone increases for its final environmental 
impact statement because comprehensive data on some key factors, such 
as temperature and relative humidity, were not available. According to 
EPA officials, if the modeled estimates of increased ozone are not 
correct, the impacts on air quality from these two plants could be 
significant, resulting in some adverse health impacts that were not 
reported by DOE. 

Policymakers have limited options to ensure that emissions from the 
Sempra and Intergen power plants do not adversely affect the health of 
residents in Imperial County. The Sempra and Intergen plants are not 
subject to the federal Clean Air Act or the California Clean Air Act 
and, therefore, are not required to offset their emissions. In 
addition, relevant agreements among the United States, Canada, and 
Mexico may not provide adequate mechanisms to address adverse health 
impacts resulting from emissions from these plants because they only 
require the countries to enforce their own environmental laws, not to 
implement specific pollution control requirements. Nevertheless, 
policymakers could take some actions. For example, the Congress could 
enact legislation restricting the importation of electricity generated 
by these plants if they do not meet certain U.S. emission and offset 
requirements. While this action would have benefits to air quality and 
health, it would also have costs, such as possibly reducing energy 
supplies available to Southern California. Similarly, DOE could modify 
its regulations to require permit applicants seeking to import 
electricity into the United States from Mexico to employ specified 
emission controls and obtain offsets. However, these two policy options 
may raise trade issues under the North American Free Trade Agreement. A 
third option would be to develop programs that provide economic 
incentives to reduce pollution in the U.S.-Mexico border region. Market-
based programs, such as EPA's program to reduce emissions that 
contribute to acid rain, have proven successful elsewhere in the United 
States in reducing emissions. Finally, another potential option is the 
development of a binational clean air trust fund that could provide 
grants and loans to support air quality improvement projects for cities 
along the U.S.-Mexican border. However, developing the legal and 
regulatory framework needed to create these binational programs is 
likely to require substantial time and effort. 

DOE commented on a draft of this report and generally disagreed with 
our characterization of the limitations of the health risk assessment 
done as a part of the environmental impact statement for the Sempra and 
Intergen power plants. Specifically, DOE did not agree with our 
assertion that it did not analyze all of the likely asthma-related and 
other health impacts of increased pollution from the power plants. 
However, DOE's environmental impact statement analyzed adverse health 
effects only for asthma hospitalization, which is just one in a 
continuum of adverse health impacts. DOE also disagreed with our 
assertion that it did not analyze the potential health impacts of 
pollution from the Sempra and Intergen power plants on susceptible 
populations in Imperial County. Although DOE said that its 
environmental impact statement included children in its asthma 
hospitalization estimates, asthmatic children are not the only 
susceptible population and asthma hospitalization is not the only 
potential health impact. Finally, DOE did not agree that health impacts 
from ozone formation may be larger than it estimated in its final 
environmental impact statement because of limitations in its ozone 
modeling analysis. However, in its comments on the final environmental 
impact statement, EPA said that it continues to support off-site 
mitigation efforts to ensure that there is no net increase in air 
pollution in Imperial County because of the ozone modeling limitations. 
For these reasons, we believe the report accurately characterizes the 
limitations of DOE's health assessment and have made no changes to the 
report in response to these comments. DOE's specific comments and our 
detailed responses are presented in appendix II of this report. 

Background: 

The Sempra and Intergen plants are located in close proximity to each 
other near Mexicali, Mexico--an area 3 miles south of the U.S.-Mexican 
border and Imperial County, California (see fig. 1). Final permitting 
and construction for both of the plants and the associated transmission 
lines to the United States began in 2001, and commercial operations 
commenced in July 2003. Fuel for the plants is provided by a 145-mile 
cross-border natural gas pipeline built by Sempra Energy, which began 
operating in September 2002. 

Figure 1: Map of the Sempra and Intergen Power Plants and the 
Associated Transmission Lines: 

[See PDF for image]

[End of figure]

The Sempra plant, known as Termoelctrica de Mexicali, consists of one 
natural gas-fired, combined-cycle power-generating unit with a total 
capacity of 650 megawatts. In this type of plant, electricity is 
produced by a combination of gas turbines and steam turbines. Heat from 
the gas turbine exhaust, which would otherwise be released to the 
atmosphere with exhaust gases, is captured and used by a heat recovery 
steam generator to produce steam, which in turn is used by the steam 
turbine to generate additional electricity. The Sempra plant operates 
with an export permit from the Mexican government and produces 
electricity exclusively for export to the United States. The facility 
is equipped with the latest pollution control technologies, including 
selective catalytic reduction systems to reduce NOx emissions and an 
oxidizing catalyst system to reduce carbon monoxide (CO) 
emissions.[Footnote 8]

The Intergen plant, which consists of two natural gas-fired combined- 
cycle units (collectively known as the La Rosita Power Complex), has a 
total capacity of 1,060 megawatts. The first unit provides two-thirds 
of its 750 megawatt capacity to Mexico, with the remaining one-third 
available for export to the United States. The second unit has a 
generating capacity of 310 megawatts, all of which is designated for 
export to the U.S. market. (See fig. 2.) Originally, only the second 
unit was designed to include a selective catalytic reduction system, 
but as of April 7, 2005, all four of the combustion turbines within the 
two units have been equipped with these systems to control NOx 
emissions. 

Figure 2: Electrical Production at the Sempra and Intergen Power 
Plants: 

[See PDF for image]

[End of figure]

Although no U.S. emissions requirements apply to these plants, Sempra 
and Intergen required a presidential permit to construct and connect 
the new transmission lines needed at the U.S.-Mexican border to export 
electricity into the United States. Because of the similarities of the 
proposals submitted by the companies, DOE decided to consider them 
together in a single environmental assessment, required as part of the 
permitting process.[Footnote 9] In December 2001, DOE completed the 
environmental assessment and issued a finding of no significant impact 
and presidential permits for both of the proposed projects. Following 
these decisions, Sempra and Intergen constructed the transmission lines 
and began commercial operations. However, as a result of subsequent 
litigation, on July 8, 2003, the U.S. District Court for the Southern 
District of California instructed DOE to prepare a more comprehensive 
environmental review, which included an assessment of the health 
impacts from the power plants as part of its analysis. DOE's 
environmental impact statement was issued in final form in December 
2004. DOE found that the proposed power plants presented a low 
potential for environmental impacts and published a record of decision 
in the Federal Register on April 25, 2005, authorizing presidential 
permits to be granted for both transmission lines to the respective 
power plants as presently designed. 

The operation of any fuel-fired power plant results in a variety of air 
pollutants. However, because natural gas is a relatively clean fuel, 
the primary emissions of concern from these plants are generally 
limited to nitrogen oxides (which contribute to ozone formation); 
particulate matter; and, in some cases, carbon monoxide. Nitrogen 
oxide, or NOx, is the generic term for a group of highly reactive 
gases, all of which contain nitrogen and oxygen in varying amounts. 
Ground level ozone, another primary pollutant, is not emitted from the 
plants directly but is formed in the presence of sunlight by a chemical 
reaction between NOx and various air pollutants known as volatile 
organic compounds (VOC). Particulate matter refers to dust, dirt, soot, 
smoke, and liquid droplets directly emitted into the air by various 
sources. Secondary formation of PM can also take place by the 
combination of NOx and ammonia (NH3).[Footnote 10] Carbon monoxide is a 
colorless and odorless gas that is formed when carbon in fuel is not 
burned completely. These four pollutants have been linked to a variety 
of negative health effects, including, but not limited to, aggravated 
asthma, reduced lung function and other respiratory illnesses, and 
aggravation of heart disease, as well as premature deaths (see table 
1). While emissions of sulfur dioxide are also a significant concern at 
some power plants, the use of natural gas at the Sempra and Intergen 
facilities greatly reduces sulfur dioxide emissions compared with other 
fuels such as coal or oil. For example, U.S. coal contains an average 
of 1.6 percent sulfur, and oil burned at electric utility power plants 
ranges from 0.5 percent to 1.4 percent sulfur; comparatively, natural 
gas has less than 0.0005 percent sulfur. 

Table 1: Key Power Plant Pollutants and Potential Health Impacts: 

Pollutant: Nitrogen oxides; 
Potential health impact: 
* Can irritate the lungs, cause bronchitis and pneumonia, and lower 
resistance to respiratory infections; 
* Contribute to the formation of ozone. 

Pollutant: Ozone; 
Potential health impact: 
* Triggers a variety of health problems, including aggravated asthma, 
even at very low levels; 
* Can cause permanent lung damage after long-term exposure; 
* Can contribute to premature death. 

Pollutant: Particulate matter; 
Potential health impact: 
* Can aggravate asthma; 
* Can cause increases in respiratory problems like coughing and 
difficult or painful breathing; 
* Can lead to chronic bronchitis or decreased lung function; 
* Can contribute to premature death. 

Pollutant: Carbon monoxide; 
Potential health impact: 
* Can cause harmful health effects by reducing oxygen delivery to the 
body's organs (like the heart and brain) and tissues; 
* Can cause chest pains in those with heart disease and other 
cardiovascular effects after repeated exposures; 
* High levels can lead to vision problems, reduced ability to work or 
learn, reduced manual dexterity, and difficulty performing complex 
tasks. 

Sources: EPA and the Southwest Consortium for Environmental Research 
and Policy. 

[End of table]

Emissions from the Mexicali Plants Are Comparable to New Plants in 
California, but Offset Requirements Would Apply in Imperial County: 

The emissions from the Sempra and Intergen power plants in Mexicali are 
comparable to emissions from similar plants recently permitted in 
California and are low relative to emissions from the primary sources 
of pollution in Imperial County, which are various forms of dust and 
motor vehicles. However, if the plants were located in Imperial County, 
they would be required, among other things, to offset their emissions 
by reducing emissions from other pollution sources in the region. 

Estimated Emissions from the Sempra and Intergen Plants Are Comparable 
to Emissions from New California Plants: 

Power plants in Mexico are not required to report to federal agencies 
in the United States on actual emissions of key pollutants generated 
during plant operations. Therefore, we believe that the best data 
available to estimate emissions from the Sempra and Intergen power 
plants comes from emission performance tests conducted by independent 
third-party contractors hired by the power plants. The average 
emissions from the Sempra and Intergen plants based on the results of 
the third-party testing are presented in table 2. 

Table 2: Average Emissions from the Sempra and Intergen Power Plants 
Based on Third-party Testing: 

Pollutant: NOx (ppm); 
Sempra results[A]: Turbine 1: 2.33; 
Sempra results[A]: Turbine 2: 2.08; 
Intergen results[B]: Turbine 1: 15.33[C]; 
Intergen results[B]: Turbine 2: 13.37[C]; 
Unit 1: Turbine 3: 2.41; 
Unit 2: Turbine 1: 3.14. 

Pollutant: PM10 (lbs/hr); 
Sempra results[A]: Turbine 1: 12.80; 
Sempra results[A]: Turbine 2: 11.86; 
Intergen results[B]: Turbine 1: 7.73; 
Intergen results[B]: Turbine 2: 3.18; 
Unit 1: Turbine 3: 3.09; 
Unit 2: Turbine 1: 7.10. 

Pollutant: CO (ppm); 
Sempra results[A]: Turbine 1: 0.00; 
Sempra results[A]: Turbine 2: 0.00; 
Intergen results[B]: Turbine 1: 0.71; 
Intergen results[B]: Turbine 2: 1.24; 
Unit 1: Turbine 3: 0.86; 
Unit 2: Turbine 1: 0.73. 

Pollutant: NH3 (ppm); 
Sempra results[A]: Turbine 1: 0.45; 
Sempra results[A]: Turbine 2: 0.41; 
Intergen results[B]: Turbine 1: [D]; 
Intergen results[B]: Turbine 2: [D]; 
Unit 1: Turbine 3: 1.24; 
Unit 2: Turbine 1: 1.73. 

Pollutant: VOC (lbs/hr); 
Sempra results[A]: Turbine 1: [E]; 
Sempra results[A]: Turbine 2: [E]; 
Intergen results[B]: Turbine 1: 0.07; 
Intergen results[B]: Turbine 2: 0.11; 
Unit 1: Turbine 3: 0.83; 
Unit 2: Turbine 1: 0.86. 

Legend: NOx = nitrogen oxides; ppm = parts per million; PM10 = 
particulate matter; lbs/hr = pounds per hour; CO = carbon monoxide; NH3 
= ammonia; VOC = volatile organic compounds. 

Sources: Sempra and Intergen. 

[A] These tests were conducted on June 4-6, 2003, and July 8-9, 2003. 

[B] These tests were conducted between September 20 and September 28, 
2004. 

[C] Selective catalytic reduction systems were installed on these 
turbines in March and April 2005, after these tests had been completed. 
These turbines have been emitting NOx at a level below 2.5 ppm since 
the installation of the new equipment. 

[D] NH3 is a by-product of selective catalytic reduction control 
technology and was not emitted by these turbines at the time the tests 
were conducted because the control technology had not yet been 
installed. 

[E] VOC emissions were undetectable at the plant during these tests. 

[End of table]

We were not able to compare emissions data from the Sempra and Intergen 
plants with emissions data from an individual plant in Imperial County 
to determine whether the plants would likely meet emissions 
requirements because no similar natural gas-fired power plant has 
recently been permitted for construction in the county. Therefore, we 
evaluated the Sempra and Intergen data against a range of allowable 
emission limits from the 23 natural gas-fired power plants of similar 
size and specifications that were given permits to operate elsewhere in 
California by the California Energy Commission between 2000 and 2004. 
These 23 plants are among the cleanest fuel-fired plants in the United 
States. We found that the levels of emissions for major pollutants 
(NOx, PM10, CO, NH3, and VOC) from the Sempra and Intergen plants are 
generally comparable to the range of emissions limits for the recently 
permitted California plants (see table 3). 

Table 3: Comparison of Estimated Sempra and Intergen Plant Emissions 
and the Emission Limits of Recently Permitted Power Plants in 
California: 

Pollutant: NOx (ppm)[C]; 
Range of CA emission limits[A]: 2.0 - 2.5; 
Sempra average[B]: 2.2; 
Intergen average[B](US Export): 2.8; 
Intergen average (Mexico): 14.4. 

Pollutant: PM10 (lbs/hr); 
Range of CA emission limits[A]: 3.0 - 18.5; 
Sempra average[B]: 12.3; 
Intergen average[B](US Export): 5.1; 
Intergen average (Mexico): 5.5. 

Pollutant: CO (ppm); 
Range of CA emission limits[A]: 2.0 - 10.0; 
Sempra average[B]: 0.0; 
Intergen average[B](US Export): 0.8; 
Intergen average (Mexico): 1.0. 

Pollutant: NH3 (ppm); 
Range of CA emission limits[A]: 5.0 - 10.0; 
Sempra average[B]: 0.4; 
Intergen average[B](US Export): 1.5; 
Intergen average (Mexico): [D]. 

Pollutant: VOC (lbs/hr); 
Range of CA emission limits[A]: 1.6 - 6.6; 
Sempra average[B]: [E]; 
Intergen average[B](US Export): 0.8; 
Intergen average (Mexico): 0.1. 

Legend: NOx = nitrogen oxides; ppm = parts per million; PM10 = 
particulate matter; lbs/hr = pounds per hour; CO = carbon monoxide; NH3 
= ammonia; VOC = volatile organic compounds. 

Sources: GAO analysis of data from the California Energy Commission, 
Sempra, and Intergen. 

[A] The range of emission limits is based on best available control 
technology requirements for 23 similar plants permitted in CA between 
2000 and 2004. Although these limits are based primarily on the use of 
modern emissions control equipment, best available control technology 
is determined on a case-by-case basis and may take into consideration 
factors such as potential economic impacts, as well as design or 
operational standards. 

[B] Sempra and Intergen emissions data are based on the average of 
emissions from the individual turbines recorded during testing. 

[C] ppm for the California plants are based on a 1 or 3-hour average, 
depending on the testing method required by the local air pollution 
control agency. NH3 levels are computed based on a 1, 3, or 24-hour 
average. 

[D] NH3, or ammonia, is a by-product of selective catalytic reduction 
control technology and was not being emitted at this unit at the time 
of the tests because the control technology had not yet been installed. 

[E] VOC emissions were undetectable during tests conducted at the 
plant. 

[End of table]

As shown in table 3, the average NOx emissions from the Intergen power 
plant were the only emissions that exceeded the range of emissions from 
recently permitted plants in California. This was the case, in part, 
because the plant was not originally designed to meet California 
requirements. However, as of April 7, 2005, all combustion turbines at 
the Intergen plant had been equipped with the selective catalytic 
reduction control technology for nitrogen oxide that is common in the 
newer California plants. With the exception of one turbine, which will 
continue to operate at a maximum NOx limit of 3.5 ppm, all other 
turbines are expected to emit NOx at a level below 2.5 ppm. According 
to Intergen plant officials, the last two turbines to be equipped with 
selective catalytic reduction systems have been meeting these levels 
since the systems became operational in March and April 2005, 
respectively. Data provided by plant officials, based on continuous 
monitoring of all emissions from these turbines over a 1 week period, 
also indicate that both turbines are achieving the expected NOx 
reductions. 

Estimated Annual Emissions from the Sempra and Intergen Plants Are Low 
Relative to Emissions from Sources in Imperial County: 

One way to assess the environmental impact of emissions from power 
plants is to examine the tons of pollutants they emit on an annual 
basis. The third-party performance tests discussed above provide the 
best available data to estimate annual emissions likely to occur during 
actual operations at the Sempra and Intergen plants because the data 
are based on observations of the actual equipment in operation. Other 
options for estimating annual emissions from these plants include using 
(1) the maximum allowable emissions levels for similar plants in 
California and (2) the emissions estimates that DOE developed during 
its environmental impact assessment of the Sempra and Intergen plants. 
Table 4 presents annual emissions estimates based on each of these 
three alternative operating assumptions. 

Table 4: Summary of Annual Emission Estimates for the Sempra and 
Intergen Power Plants Using Three Alternative Operating Assumptions 
(Tons per Year): 

Pollutant: NOx; 
Third-party testing: 374; 
Maximum allowable emissions levels in California: 610; 
DOE's environmental impact statement: 610. 

Pollutant: PM10; 
Third-party testing: 200; 
Maximum allowable emissions levels in California: 352; 
DOE's environmental impact statement: 1,210. 

Pollutant: CO; 
Third-party testing: 919; 
Maximum allowable emissions levels in California: 1,897; 
DOE's environmental impact statement: 3,089. 

Pollutant: NH3; 
Third-party testing: 86; 
Maximum allowable emissions levels in California: 518; 
DOE's environmental impact statement: 646. 

Pollutant: VOC; 
Third-party testing: 57; 
Maximum allowable emissions levels in California: 105; 
DOE's environmental impact statement: 1,026. 

Source: GAO analysis of data from Sempra, Intergen, the California 
Energy Commission, and DOE. 

[End of table]

Under the first scenario, annual emissions levels were estimated using 
the values determined by third-party contractors during turbine 
performance tests at the Sempra and Intergen plants. For the two 
Intergen turbines that did not have selective catalytic reduction 
systems installed when the testing was conducted, we estimated annual 
NOx emissions using the testing values recorded for the similar turbine 
that was operating with such equipment. We did so because these two 
turbines are now equipped with selective catalytic reduction systems 
and their future emissions are likely to be similar to those from the 
turbine that was using this technology during the tests. These 
estimates do not take into account start-up and shutdown operations of 
the plant, which may contribute to increased plant emissions for 
approximately 1 to 2 hours. However, the total annual estimate is based 
on the conservative assumption that the plants are operating at maximum 
emission levels, 24 hours a day, 365 days a year. The actual operation 
of the plants, and the resulting emissions, would be less than this 
because of scheduled maintenance, forced outages, and varying 
electrical demand in California. 

The second estimates of annual emissions were based on maximum 
allowable emissions determined during the permitting process for 
similar California plants. These maximum allowable emissions are higher 
than the estimates based on third-party testing data. California grants 
permits to construct power plants on a case-by-case basis. As a 
condition of receiving a permit, the state places limits on emissions 
of individual pollutants. These limits are based on the use of best 
available control technology and take into consideration energy, 
environmental, and economic impacts. Under this estimating scenario, 
the annual estimates also account for short term variations in 
emissions levels that may occur during start-up and shutdown operations 
and are based on the conservative assumption that the plants are 
operating at maximum emissions levels, 24 hours a day, and 365 days a 
year. 

The final, and highest, emissions estimates are based on the values DOE 
used in its environmental impact statement. DOE's estimates are based 
on either the maximum emissions allowable by permit from the Mexican 
government or the vendor guarantee limits, which are the maximum 
emissions levels specified by the manufacturer that a piece of 
equipment is likely to produce. These values tend to be much higher 
than the levels that typically occur during normal power plant 
operations. For example, the vendor guarantee limit of PM10 for 
turbines at the Intergen plant is 52.3 pounds per hour. However, the 
actual emissions of PM10 at plants using similar equipment are 
typically below 10 pounds per hour. In addition, DOE's estimates also 
assume that the Sempra and Intergen plants are operating at these 
levels 100 percent of the time, 365 days per year. Averaged on an 
annual basis, these estimates are likely to be significantly higher 
than the actual emissions resulting from operations at these plants. 

According to DOE's environmental impact statement, emissions from the 
Sempra and Intergen power plant would result in increases of ambient 
concentrations of NOx, PM10, and CO in Imperial County. However, it is 
difficult to determine the actual percentage of plant emissions that 
will reach Imperial County annually. For most of the year, the winds in 
the vicinity of the Sempra and Intergen plants travel predominantly 
from the United States to Mexico. However, during the months of June, 
July, and August, this trend reverses and the winds travel 
predominantly from Mexico to the United States. Even assuming the 
plants operate at the maximum emissions levels allowed in California, 
and that all of those emissions reach Imperial County, annual emissions 
from the plants are low compared with various forms of dust and 
emissions from motor vehicles--the primary sources contributing to 
nonattainment of the standards for PM10 and ozone in Imperial County 
(see fig. 3). 

Figure 3: Relative Emissions Contributions by Source Assuming the 
Sempra and Intergen Plants Operated at Maximum Allowable Emissions and 
All Emissions Reached Imperial County: 

[See PDF for image]

Note: 

Emissions contributions of less than 0.5 percent were not included in 
this figure. In the PM10 category, mobile sources (0.5 percent), the 
Sempra and Intergen power plants (0.4 percent), and fuel combustion 
(0.2 percent) emissions were omitted. 

[A] The "mobile sources" category includes emissions from sources such 
as on and off-road motor vehicles, airplanes, trains, boats, and farm 
equipment. 

[B] The "fuel combustion" category includes other stationary sources, 
such as electric utilities, manufacturing, food and agricultural 
processing, and service and commercial operations. 

[C] The "other sources" category includes all subcategories identified 
by the California Air Resources Board, such as farming, fires, waste 
burning, and mineral processing that contribute emissions not included 
in the other categories listed. 

[End of figure]

According to 2004 California emissions inventory estimates, road and 
windblown dust constituted almost 89 percent of total PM10 emissions 
within Imperial County. Mobile sources, which include both personal and 
commercial vehicles, accounted for 79 percent of total NOx emissions in 
the county. Even if they were located in Imperial County and operated 
at maximum allowable California emissions levels 24 hours per day, the 
plants would emit 352 tons per year of PM10, compared with nearly 
77,000 tons per year from road and windblown dust, and 610 tons per 
year of NOx, compared with almost 10,000 tons per year from mobile 
sources (see table 5). 

Table 5: Estimated Annual Average Emissions in 2004 for Imperial 
County, California (Tons per Year): 

Stationary sources: 

Emissions sources: Fuel combustion[A]; 
NOx: 2,537; 
PM10: 150; 
CO: 325. 

Emissions sources: Other stationary sources; 
NOx: 11; 
PM10: 1,011; 
CO: 22. 

Subtotal; 
NOx: 2,548; 
PM10: 1,161; 
CO: 347. 

Area-wide sources: 

Emissions sources: Paved and unpaved road dust; 
NOx: 0; 
PM10: 13,647; 
CO: 0. 

Emissions sources: Fugitive windblown dust; 
NOx: 0; 
PM10: 63,068; 
CO: 0. 

Emissions sources: Waste burning and disposal; 
NOx: 106; 
PM10: 799; 
CO: 4,395. 

Emissions sources: Other miscellaneous; 
NOx: 37; 
PM10: 7,194; 
CO: 252. 

Subtotal; 
NOx: 142; 
PM10: 84,709; 
CO: 4,647. 

Mobile sources: 

Emissions sources: On-road motor vehicles; 
NOx: 5,143; 
PM10: 139; 
CO: 25,831. 

Emissions sources: Other mobile sources; 
NOx: 4,847; 
PM10: 252; 
CO: 8,629. 

Subtotal; 
NOx: 9,990; 
PM10: 391; 
CO: 34,460. 

Total; 
NOx: 12,680; 
PM10: 86,260; 
CO: 39,454. 

Legend: NOx = nitrogen oxides; 
PM10 = particulate matter; 
CO = carbon monoxide. 

Source: GAO analysis of California Air Resources Board data. 

[A] The Fuel Combustion subcategory includes stationary sources such as 
existing electric utilities, manufacturing, food and agricultural 
processing, and service and commercial operations. 

[End of table]

Another way to examine the environmental impact of a power plant is to 
evaluate the amount of pollution emitted per unit of electricity 
produced. This calculation has been used within the energy industry to 
measure how efficiently power plants produce electricity. As 
illustrated in table 6, the Sempra and Intergen plants produce much 
lower emissions of NOx for each megawatt of energy generated than do 
other power plants operating in Imperial County and the border region 
of Baja California, Mexico. For example, Sempra's estimated emission 
rate for NOx of .04 pounds per megawatt of electricity is over 35 times 
lower than that rate at El Centro, the only major fuel-fired plant 
operating in Imperial County in 2002.[Footnote 11]

Table 6: Comparison of NOx Emission Rates from the Sempra and Intergen 
Plants and Power Plants in Imperial County and Baja California: 

Mexicali plants (2004): 

Power plants: Sempra; 
NOx emissions rate (lbs/MW): 0.04; 
Annual NOx emissions (lbs): 89,668; 
Net annual energy generation (MW): 2,389,549. 

Power plants: Intergen; 
NOx emissions rate (lbs/MW): 0.30[A]; 
Annual NOx emissions (lbs): 1,309,422; 
Net annual energy generation (MW): 4,306,690. 

Imperial County (2002): 

Power plants: El Centro; 
NOx emissions rate (lbs/MW): 1.45; 
Annual NOx emissions (lbs): 610,674; 
Net annual energy generation (MW): 421,736. 

Baja California (2002): 

Power plants: C.C.C. Presidente Juarez (Rosarito); 
NOx emissions rate (lbs/MW): 2.38; 
Annual NOx emissions (lbs): 4,942,713; 
Net annual energy generation (MW): 2,077,250. 

Power plants: C.TG. Presidente Juarez (Tijuana); 
NOx emissions rate (lbs/MW): 4.15; 
Annual NOx emissions (lbs): 2,694,021; 
Net annual energy generation (MW): 648,420. 

Legend: NOx = nitrogen oxides; 
lbs/MW = pounds per megawatt. 

Sources: GAO analysis of data from Sempra, Intergen, and the Commission 
for Environmental Cooperation. 

[A] Intergen's values represent emissions produced in 2004 before the 
installation of selective catalytic reduction technology on two of the 
four units. Future NOx emissions rates will likely be comparable to 
those at the Sempra plant. 

[End of table]

If the Plants Were Located in Imperial County, California, among Other 
Things, Standards Would Require Them to Offset Their Emissions: 

If the Sempra and Intergen plants were located in Imperial County, to 
help improve air quality, California regulations would require, among 
other things, offsets for all emissions from the plants that contribute 
to nonattainment of the PM10 and ozone standards in the county. Under 
the specific offsetting rules established by the Imperial County Air 
Pollution Control District, the operators of each plant would be 
required to reduce emissions from other pollution sources in Imperial 
County by at least 1.2 tons for every ton of emissions the plants 
released.[Footnote 12] In addition to offsetting emissions of PM10 and 
NOx generated by the plant, Sempra and Intergen would also be required 
to offset all emissions of VOC, which, in combination with NOx, 
contribute to the formation of ozone.[Footnote 13]

As shown in table 7, potential offsets identified by the Imperial 
County Air Pollution Control District in DOE's environmental impact 
statement include (1) paving roads, (2) retrofitting emission controls 
on existing power plants in Imperial County, (3) funding projects 
designed to increase the use of natural gas in motor vehicles, (4) 
controlling Imperial County airport dust, and (5) retrofitting diesel 
engines for off-road heavy duty vehicles. According to the Air 
Pollution Control District, repaving approximately 23 miles of roads 
could reduce PM10 emissions in Imperial County by about 650 tons per 
year--more than the estimated annual PM10 emissions from both plants 
based on the maximum allowable emissions levels in California. The 
District estimated the paving project would cost approximately $430,000 
per mile for a two-lane road, bringing the total cost to about $9.9 
million. 

Table 7: Potential Offsets in Imperial County, California, Identified 
by the Imperial County Air Pollution Control District: 

Potential offset: Paving roads; 
Description of project: 
* Pave 50 road segments in Imperial County, totaling 23 miles; 
Estimated cost: $9,890,000; 
Estimated emission reduction: 650 tons per year (PM10). 

Potential offset: Enhancing use of natural gas in motor vehicles; 
Description of project: 
* Fund maintenance of El Centro natural gas facility; Estimated cost: 
$150,000; 
* Fund natural gas facility to be constructed at the Calexico Unified 
School District; Estimated cost: $250,000; 
* Acquire land in Brawley, California, for construction of a new 
natural gas facility; Estimated cost: $250,000 to $500,000; 
* Replace/update fleet of fifteen Imperial Valley buses; Estimated 
cost: $4 million to $5 million; 
Estimated emission reduction: 0.1 tons per year[A] (PM10). 

Potential offset: Controlling Imperial County Airport dust; 
Description of project: 
* Begin treatment of bare desert soil with chemical dust retardants or 
cover soil with crushed rock in the most sensitive areas; 
Estimated cost: $150,000; 
Estimated emission reduction: 15 tons per year (PM10). 

Potential offset: Retrofitting diesel engines; 
Description of project: 
* Update the diesel engines of off-road vehicles used in agriculture, 
earthmoving, or construction; 
Estimated cost: $250,000; 
Estimated emission reduction: 3.3 tons per year (PM10). 

Potential offset: Retrofitting emission controls on existing power 
plants; 
Description of project: 
* Install selective catalytic reduction technology on one main unit of 
the existing steam plant at the Imperial Irrigation District, as well 
as all of the smaller units used only during periods of peak 
electricity demand; 
Estimated cost: Not Estimated; 
Estimated emission reduction: The main unit is already scheduled to be 
retrofitted in 2007-2008 (NOx). 

Legend: NOx = nitrogen oxides; 
PM10 = particulate matter. 

Source: DOE. 

[A] Estimated emission reduction applies only to the bus replacement 
project. Emission reductions from the other projects were not 
quantified. 

[End of table]

In addition to the potential offsets identified above for Imperial 
County, according to DOE, mitigation measures may be even more abundant 
and cost-effective if applied on the Mexican side of the border. Some 
potential projects include paving roads in Mexicali, Mexico; 
replacing older automobiles and buses with newer, less polluting ones; 
and converting brick kilns to run on natural gas. However, according to 
DOE, it does not have the authority to impose or enforce offsets in 
Mexico. 

Finally, if the power plants were located in California, the Intergen 
plant would likely be required to make additional equipment 
modifications to be consistent with other plants recently constructed 
in California. These modifications would include installing additional 
carbon monoxide control equipment and achieving a small reduction in 
NOx emissions in one of the plant's four combustion turbines. Although 
emissions testing data indicate that Intergen's carbon monoxide levels 
are generally comparable to those of California plants without this 
equipment, nearly all of the plants recently permitted in California 
have installed oxidizing catalyst systems to control carbon monoxide 
emissions. In addition, the Intergen plant would likely be required to 
lower the maximum NOx emissions in one turbine by 1.0 ppm--from 3.5 ppm 
to 2.5 ppm. Although this turbine is currently equipped with a 
selective catalytic reduction system to control NOx emissions, Intergen 
has stated that certain technical aspects of the design of the turbine 
prevent it from attaining emissions levels of 2.5 ppm. 

Emissions Generated by the Sempra and Intergen Power Plants May 
Contribute to Various Adverse Health Impacts in Imperial County, but 
the Extent of Such Impacts Is Unknown: 

Emissions from the Sempra and Intergen power plants may contribute to 
adverse health impacts in Imperial County, but the extent of those 
impacts is unknown for several reasons. First, in its environmental 
impact statement, DOE did not calculate the total health impacts in the 
county because it did not analyze all the likely asthma-related or 
other health impacts from the increased pollution caused by the Sempra 
and Intergen plants. Second, DOE did not analyze the health impacts 
from increased power plant emissions on particularly susceptible 
populations, such as asthmatic children and low-income populations. 
Finally, because of uncertainty in DOE's modeling of ozone increases 
due to emissions from the power plants, the health impacts related to 
ozone may be larger than DOE estimated. 

DOE Did Not Analyze All the Likely Asthma-Related and Other Health 
Impacts of Increased Pollution from the Sempra and Intergen Power 
Plants: 

In its December 2004 final environmental impact statement, DOE 
estimated that emissions from the Sempra and Intergen power plants 
would result in increased concentrations of NOx, PM10, and CO in 
Imperial County. DOE used EPA's "significant impact levels" to help 
assess the impact of these emissions increases on the residents of 
Imperial County. Generally, significant impact levels are thresholds 
below which the environmental and health impacts of air pollution are 
not viewed as significant; however, EPA designed them to be used only 
in areas that meet air quality standards.[Footnote 14] Although the 
plants will add more pollution to an area already violating the 
national standards for PM10 and ozone, DOE reported that because all 
pollution increases would be below EPA's significant impact levels, 
emissions from the plants would not produce any significant air quality 
impacts in Imperial County. Specifically, DOE calculated that emissions 
from the power plants would be expected to increase asthma 
hospitalizations in the county by less than one case per year. However, 
DOE's analysis did not quantify all of the health impacts from the 
increase in PM10 emissions. 

Health experts told us that the potential impact on asthmatics would be 
broader than the minimal increase in hospitalizations described in the 
environmental impact statement because hospitalization occurs only in 
the most acute asthma cases. According to these experts, an increase in 
PM10 pollution could exacerbate the underlying condition of anyone 
suffering from asthma. According to data from the 2003 California 
Health Interview Survey, 21,000 Imperial County residents, or 14 
percent of the county's population, have been diagnosed with 
asthma.[Footnote 15] Approximately 13,000 of these asthmatics 
experienced asthma symptoms during the previous year. The health 
experts we spoke with agreed that hospitalizations and other adverse 
health effects are part of a pyramid of potential adverse health 
effects. While the number of hospitalizations is represented at the top 
of the pyramid, other adverse health impacts such as emergency room 
visits, physician visits, asthma medication use, and increased asthma 
symptoms are layered vertically downward, with the number of people 
increasing in each subsequent group as you move to the bottom of the 
pyramid (see fig. 4). 

Figure 4: Pyramid of Potential Health Impacts for Asthmatics: 

[See PDF for image]

[End of figure]

In addition, the DOE study did not address the extent to which 
increased emissions of particulate matter would cause other adverse 
health impacts, such as other respiratory or cardiovascular problems. 
These impacts could include chronic obstructive pulmonary disease, 
pneumonia, cardiovascular disease, as well as increased symptoms of 
upper and lower respiratory disease, decreased lung function, or 
premature death. According to the project manager of DOE's analysis, 
the expected incidence of other adverse health effects resulting from 
PM10 exposure has not been quantified because of a lack of data. 

DOE Did Not Analyze the Health Impacts on Particularly Susceptible 
Populations in Imperial County: 

Studies funded by EPA, the Health Effects Institute,[Footnote 16] and 
others have concluded that certain groups are likely to be more 
susceptible to particulate matter than others, and therefore experience 
more adverse health effects. For example, these studies identified 
asthmatics, especially children, as a potentially susceptible 
subpopulation. According to data from the 2003 California Health 
Interview Survey, approximately 19 percent of Imperial County children 
ages 1 through 17 have been diagnosed with asthma, or about 9,000 
children. In addition, the relationship between socioeconomic factors 
and asthma exacerbation has been documented in various studies. 
Imperial County is ranked as one of the poorest counties in California, 
with some of the highest poverty and unemployment rates in the state. 
An estimated 22 percent of the overall population lives below the 
national poverty level, in comparison with 13 percent statewide. 
Results from a 2001 California asthma report indicate that asthmatic 
adults with family incomes below the national poverty level are nearly 
twice as likely to experience symptoms every day or every week as those 
with incomes three times the poverty level, in part, because they have 
less access to health care.[Footnote 17]

Finally, residents of Imperial County are currently exposed to airborne 
particulate pollution exceeding the Clean Air Act's health-based 
National Ambient Air Quality Standard for PM10. For instance, in 2003, 
Imperial County residents were exposed to an annual average 
concentration of PM10 that was 30 micrograms, or 63 percent higher, 
than the national standard of 50 micrograms per cubic meter of air, as 
shown in table 8. As a result, Imperial County residents can be 
expected to have higher incidence of adverse health effects caused by 
airborne particulate pollution than residents living in areas with less 
of that contaminant. 

Table 8: Imperial County Air Quality Compared with National Standard 
for PM10 (1997-2003): 

PM10: Maximum 24 hour concentration; 
Micrograms per cubic meter of air: National standard: 150; 
Micrograms per cubic meter of air: Imperial County: 1997: 532; 
Micrograms per cubic meter of air: Imperial County: 1998: 176; 
Micrograms per cubic meter of air: Imperial County: 1999: 227; 
Micrograms per cubic meter of air: Imperial County: 2000: 268; 
Micrograms per cubic meter of air: Imperial County: 2001: 647; 
Micrograms per cubic meter of air: Imperial County: 2002: 373; 
Micrograms per cubic meter of air: Imperial County: 2003: 840. 

PM10: Calculated days over national standard; 
Micrograms per cubic meter of air: Imperial County: 1997: 12; 
Micrograms per cubic meter of air: Imperial County: 1998: 12; 
Micrograms per cubic meter of air: Imperial County: 1999: 32; 
Micrograms per cubic meter of air: Imperial County: 2000: 38; 
Micrograms per cubic meter of air: Imperial County: 2001: 18; 
Micrograms per cubic meter of air: Imperial County: 2002: 21; 
Micrograms per cubic meter of air: Imperial County: 2003: 25. 

PM10: Annual average; 
Micrograms per cubic meter of air: National standard: 50; 
Micrograms per cubic meter of air: Imperial County: 1997: 77.7; 
Micrograms per cubic meter of air: Imperial County: 1998: 66.1; 
Micrograms per cubic meter of air: Imperial County: 1999: 77.8; 
Micrograms per cubic meter of air: Imperial County: 2000: 95.2; 
Micrograms per cubic meter of air: Imperial County: 2001: 86.2; 
Micrograms per cubic meter of air: Imperial County: 2002: 81.3; 
Micrograms per cubic meter of air: Imperial County: 2003: 80. 

Legend: PM10 = particulate matter. 

Source: DOE. 

[End of table]

In its environmental impact statement, DOE acknowledges that there are 
preexisting conditions of concern in Imperial County, such as asthmatic 
children and low-income populations, both of whom are particularly 
susceptible to health problems from pollution, and the fact that the 
county is a Clean Air Act nonattainment area for PM10. However, DOE did 
not fully explore these conditions to determine their potential health 
impacts. DOE believes that because the increases in emissions from the 
plants are below EPA's significant impact levels any health impacts 
will be negligible. However, some health studies have found that even 
the smallest incremental increase in particulate matter air pollution 
increases the incidence of adverse health effects. 

Health Impacts from Ozone Formation May Be Larger Than Estimated by 
DOE: 

DOE conducted air dispersion ozone modeling for the Imperial Valley- 
Mexicali air basin to determine what impact emissions from the Sempra 
and Intergen plants would have on the formation of ozone. DOE 
concluded, based on its modeling, that there would be no meaningful 
change in ozone levels as a result of the operation of the Sempra and 
Intergen power plants. Consequently, DOE concluded that the health 
impacts from ozone formation as a result of plant emissions would be 
minimal. However, if the modeling is not accurate, then the health 
impacts could be larger than DOE estimated. 

EPA officials have raised concerns about the accuracy of DOE's modeling 
of estimated ozone increases. In its comments on DOE's draft 
environmental impact statement, EPA stated that it is difficult to 
quantify the impact of a small number of facilities (i.e., the two 
power plants) on the maximum ozone concentration in an air basin. The 
lack of area-specific information, such as temperature, relative 
humidity, and levels of volatile organic compounds (an ozone 
precursor), in the Imperial County-Mexicali air basin makes modeling 
ozone formation particularly difficult. Because these data were not 
available, DOE used surrogate values from Phoenix, Arizona.[Footnote 
18] Furthermore, DOE's analysis relied on air monitoring data and the 
EPA ozone model to determine the potential influence of NO2 emissions-
-the primary pollutant emitted from the Sempra and Intergen power 
plants--on ozone concentrations in Imperial Valley. DOE concluded that 
increased NOx emissions from the plants could produce a decrease in 
ozone concentrations. In its comments on the draft environmental impact 
statement, EPA stated that peak ozone concentrations generally occur in 
areas away from sources of high NOx emissions, not at the monitor where 
high NO2 concentrations are measured. They emphasized that if modeled 
ozone projections are not correct, impacts to air quality from the 
plants' emissions could be significant. Recent research funded by EPA 
and others has found that increases in ozone pollution raise the risk 
of premature death. Finally, EPA recommended that DOE require Sempra 
and Intergen to implement mitigation measures to ensure that increased 
concentrations of ozone do not occur in the air basin. 

In response to EPA's comments, in its December 2004 final environmental 
impact statement, DOE presented a sensitivity analysis that indicated 
that power plant emissions could result in either increases or 
decreases in peak ozone concentrations depending on model input 
assumptions. However, DOE again concluded that its modeling of ozone 
formation did not indicate any meaningful change in ozone levels as a 
result of the operation of the Sempra and Intergen power plants and 
therefore chose not to require any mitigation requirements in its 
record of decision. According to DOE officials, although the record of 
decision states that mitigation of emissions is the preferred option, 
the sum total of emissions from the plants is so minimal that it is not 
cost-effective to require mitigation measures in the United States. 
However, DOE has not conducted any analysis to support its claim that 
mitigation measures are not cost-effective. Furthermore, DOE said that 
it does not have the resources needed to conduct a comprehensive 
monitoring program to ensure that mitigation projects are completed 
satisfactorily. Finally, DOE acknowledged in the environmental impact 
statement that mitigation measures may be more abundant and cost- 
effective in Mexico. However, DOE told us that while it has the 
authority to require the plants to take mitigation measures in the 
United States, it does not have the authority to require or enforce 
such measures in Mexico. 

Policymakers Have Limited Options to Ensure That Emissions from the 
Sempra and Intergen Power Plants Do Not Adversely Affect the Health of 
Residents in Imperial County: 

Because the Sempra and Intergen power plants are not subject to either 
the federal Clean Air Act or the California Clean Air Act, they are not 
required to provide offsets for their emissions. In addition, relevant 
agreements among the United States, Canada, and Mexico may not provide 
adequate mechanisms to address adverse health impacts resulting from 
emissions from these plants. As a result, policymakers have limited 
options to ensure that emissions from these plants do not adversely 
affect the health of residents in Imperial County. 

Existing Laws and Agreements May Not Provide Effective Mechanisms to 
Address Adverse Health Impacts: 

Existing U.S. law provides few options to ensure that emissions from 
the Intergen and Sempra plants do not adversely affect the health of 
residents in Imperial County. Because the Intergen and Sempra plants 
are not located in the United States, federal and California 
environmental agencies do not have authority over the plants. The 
federal Clean Air Act contains no language extending the statute's 
coverage to pollution sources that are located outside of the United 
States. Similarly, the text of the California Clean Air Act limits its 
application to pollution sources that are located in California. 
Because neither of these laws applies to the Sempra or Intergen plants, 
U.S. environmental agencies have no authority under existing law to 
require the plants to implement pollution control measures. 

Similarly, existing international agreements provide few options to 
ensure that emissions from the Sempra and Intergen plants do not 
adversely affect the health of residents of Imperial County. The 
governments of the United States and Mexico have ratified two 
agreements that are of particular importance to environmental 
conditions in the border region. The first was signed at La Paz, 
Mexico, in 1983. The La Paz Agreement creates a framework for promoting 
cooperation between the United States and Mexico on issues of 
environmental protection in the border region. For example, the 
agreement states that the United States and Mexico will "cooperate in 
the solution of the environmental problems of mutual concern in the 
border area," and that high officials from the two countries will meet 
annually to review the agreement's implementation. The agreement does 
not require either government to implement specific pollution control 
requirements or provide a course of action for either country to pursue 
if a particular project in the border region harms the health of border 
region inhabitants. 

The other environmental agreement, the North American Agreement on 
Environmental Cooperation (NAAEC), also provides few options to ensure 
that emissions from the Sempra and Intergen plants do not adversely 
affect the health of residents of Imperial County. The United States, 
Canada, and Mexico signed the NAAEC in 1993 to supplement the 
provisions of the North American Free Trade Agreement. The NAAEC 
provides a dispute resolution procedure under which the United States, 
Mexico, or Canada may request consultation with another party to the 
agreement regarding whether there has been a persistent pattern of 
failure by that other party to effectively enforce its environmental 
law. The parties must make every attempt to resolve the matter through 
the consultative process. However, if consultation fails to lead to a 
satisfactory resolution, then either party may take a series of steps 
that may culminate in the meeting of an impartial, five-member 
arbitration panel. This panel can determine whether the party 
complained against has persistently failed to enforce its environmental 
law. If the panel issues a decision finding such a persistent failure, 
it may formulate an action plan to remedy the enforcement failure and 
may ultimately impose monetary penalties if the enforcement failure 
persists. Thus, the NAAEC dispute resolution procedure provides an 
option for U.S. policymakers, but only if the Mexican government 
persistently fails to enforce the Mexican environmental laws that apply 
to the two plants. The NAAEC dispute resolution procedure does not 
provide a useful option for U.S. policymakers if the Intergen and 
Sempra plants comply with Mexican law, even if the plants adversely 
affect the health of the residents of Imperial County. 

Policymakers Have Limited Options to Protect Imperial County Residents 
from Adverse Health Impacts: 

There are some actions policymakers could take to protect Imperial 
County from increased emissions from the Sempra and Intergen power 
plants. For example, the Congress could enact legislation restricting 
the importation of electricity generated by power plants whose 
electrical output is dedicated exclusively to the United States if they 
do not meet certain U.S. emission and offset requirements. While this 
action would have benefits to air quality and health, it would also 
have costs, such as possibly reducing energy supplies available to 
southern California. In 2003 a bill was introduced in the Senate and 
House that would have prohibited the exportation of natural gas from 
the United States to Mexico for use in power plants near the U.S. 
border if the plants do not provide air quality protection that is at 
least equivalent to the protection provided by air quality requirements 
applicable in the United States. Each chamber referred the bill to 
committee; neither the Senate nor the House committee reported the bill 
to the full chamber for consideration. 

Similarly, DOE could modify its regulations that apply to applicants 
for presidential permit seeking to build new international transmission 
lines to import electricity into the United States from Mexico. The 
modified regulations could require that the lines connect to plants 
that employ specified emissions controls and obtain offsets in the 
United States. However, limiting the import of electricity from Mexico 
into California could jeopardize some electricity supplies for parts of 
southern California, which could be problematic especially during peak 
consumption periods. According to the California Independent System 
Operator, the demand for energy in California is growing at nearly 4 
percent annually. During the summer of 2004, the peak demand record set 
in 1999 was broken seven times, and the California Independent System 
Operator believes that the record will likely fall again during the 
summer of 2005. 

Moreover, both of the above options would need to be assessed to 
determine if they are compliant with the North American Free Trade 
Agreement (NAFTA). The agreement allows either the U.S. or Mexico to 
restrict energy imports for a range of reasons, including protection of 
human life or health. However, such import restrictions must meet a 
variety of conditions. For example, though NAFTA recognizes a country's 
right to license imports and exports of energy, any such licensing 
system must be consistent with NAFTA and not frustrate its overall 
objectives of eliminating trade barriers, promoting fair competition, 
and increasing investment opportunities. NAFTA also requires energy 
regulatory agencies to minimize disruptions to contractual 
relationships in applying their regulations. 

A third option would be for the United States and Mexico to expand 
cooperation under the existing binational initiative to address 
transboundary air pollution in the U.S.-Mexico border region by 
providing economic incentives, such as emissions trading, to reduce 
pollution. Such programs have proven successful in the United States in 
reducing emissions that contribute to acid rain. At the international 
level, the United States and Canada have developed an air pollution 
agreement that could possibly serve as a model for a similar agreement 
between the United States and Mexico. However, based on the Canadian 
example, developing the legal and regulatory framework needed to create 
a binational emissions trading program with Mexico is likely to take a 
significant amount of time. The United States and Canada initiated 
cooperative efforts in 1980 through a memorandum of understanding, and 
11 years later the 1991 U.S.-Canada Air Quality Agreement identified 
market-based mechanisms, including emissions trading, as areas for 
further discussion. In April 1997, the United States and Canada agreed 
on a joint plan of action for addressing transboundary air pollution, 
expanding the initial focus on acid rain to also examine ground-level 
ozone and particulate matter. In 2000, the Air Quality Agreement was 
formally expanded to address transboundary ground-level ozone issues. 
In 2004, the United States and Canada initiated a joint study to 
examine the feasibility of establishing a binational emissions trading 
program. Issues being addressed include the legal authority and the air 
pollution monitoring, assessment, and reporting system that would be 
needed to implement such a program. 

At the state level, Texas passed legislation in 2001 that authorized 
the state's environmental agency to accept reductions in emissions from 
brick kilns in Ciudad Juarez, Mexico, to satisfy new state emission 
control requirements passed by the Texas Legislature in 1999. In return 
for air emission allowances under Texas law, the local utility, El Paso 
Electric, arranged the destruction of older, high-polluting, open-top 
kilns and replaced them with less polluting closed-top kilns. This 
emission control project serves the Paso Del Norte air basin, which is 
officially recognized in the La Paz Agreement, and includes El Paso, 
Texas, and Ciudad Juarez, Mexico. 

Finally, another potential option is the development of a binational 
clean air trust fund that could provide grants and loans to support 
projects that would improve the air quality of U.S. and Mexican cities 
that share air basins in the border region. Implementing such a program 
could help offset emissions generated by a variety of sources, 
including power plants in Mexico that are not required to offset their 
emissions. Funds from a variety of sources, such as appropriations from 
both nations' legislatures, fast-lane fees for cars and trucks at ports 
of entry, and fees from airports and railroads operating along the 
border, could be held in a joint U.S.-Mexican trust fund for 
distribution to states, counties, cities, or local air pollution 
control districts along the shared border.[Footnote 19] The binational 
clean air trust fund could also potentially obtain funds from power 
plants located in the U.S.-Mexico border region that are looking for 
opportunities to offset their emissions, although they are not required 
to do so by law. Both Intergen and Sempra have shown an interest in 
supporting projects aimed at improving the air quality in the border 
region. For example, Intergen supports an applied research grant 
program to improve air quality in the California-Mexico border 
region,[Footnote 20] and Sempra is developing a fund to support the 
implementation of environmental projects, such as road paving, in the 
border city of Mexicali, Mexico, that it expects to implement before 
the end of 2005. 

Conclusions: 

The Sempra and Intergen plants near Mexicali, Mexico, are modern power 
plants that use advanced air pollution control technologies. As a 
result, the pollution they emit is comparable to that emitted by 
similar plants that have recently received permits to operate in 
California and is low relative to dust and emissions from vehicles, the 
primary sources of pollution in Imperial County. Nevertheless, the 
plants emit some pollutants into an air basin that already does not 
meet some air quality standards and is home to many asthmatic children 
and a low-income population that may be particularly susceptible to 
adverse health consequences from any level of pollution increase. DOE 
concluded in its environmental impact statement that pollution from the 
plants would not result in significant health impacts in Imperial 
County and therefore did not require the plants to offset their 
emissions. However, the DOE analysis did not fully examine several 
issues that could have led to an assessment of a larger adverse health 
impact in Imperial County. In addition, if the plants were located 3 
miles north in Imperial County, California, they would be required to 
fund projects to reduce pollution from other sources to offset their 
emissions regardless of whether there was a documented adverse health 
impact. However, now that DOE has determined that no offsets are 
required, options available to U.S. policymakers in the short term to 
directly address the existing health concerns are limited. In the long 
term, the United States and Mexico could implement an emissions trading 
program or a clean air trust fund to address pollution in the border 
area, but such programs are likely to take years, and require 
significant binational effort to develop. 

Agency Comments and Our Evaluation: 

We provided draft copies of this report to the Department of Energy 
(DOE) and to the Environmental Protection Agency (EPA) for their review 
and comment. We received a written response from DOE's Director, Office 
of Electricity Delivery and Energy Reliability. EPA provided technical 
comments which we incorporated in the report. 

DOE disagreed with our assertion that it did not analyze all of the 
likely asthma-related and other health impacts of increased pollution 
from the Sempra and Intergen power plants. Specifically, DOE stated 
that the environmental impact statement for the two plants (1) notes 
the full range of respiratory effects associated with exposure to 
airborne particulate matter (PM10) and (2) uses the number of potential 
additional asthma hospitalizations in Imperial County as a 
representative estimate of the number of potential health effects cases 
associated with power plant emissions of PM10. While DOE's 
environmental impact statement acknowledges that increases in PM10 
concentrations could have adverse health impacts such as increased 
asthma symptoms and chronic bronchitis, up to hospitalization and 
death, DOE did not quantify or report quantified estimates for any 
adverse health effects other than asthma hospitalizations. For example, 
DOE did not quantify the extent to which asthma sufferers would have 
increased doctor visits or medication use related to increased 
pollution. Furthermore, while asthma hospitalizations are one measure 
of potential adverse health impacts from increased emissions of 
particulate matter, there are many other adverse health effects that 
have been documented, such as chronic lung disease, chronic bronchitis, 
pneumonia, and cardiovascular disease that DOE did not quantify. For 
these reasons, asthma hospitalizations do not represent the "full 
range" of potential adverse health impacts in Imperial County. 

DOE also disagreed with our assertion that it did not analyze the 
potential health impacts of pollution from the Sempra and Intergen 
power plants on susceptible populations in Imperial County. According 
to DOE, because the environmental impact statement's estimate of 
increased asthma hospitalizations is based on data that include 
children ages 14 and under, it accounts for health impacts on 
susceptible populations. However, asthmatic children are not the only 
susceptible population mentioned in our report, and asthma 
hospitalization is not the only potential health impact. Moreover, 
DOE's analysis does not differentiate among different population 
subgroups in terms of their susceptibility to the effects of air 
pollution but instead characterizes potential adverse health effects 
for the population as a whole. Consequently, we continue to believe 
that DOE's environmental impact statement did not address the full 
range of potential health impacts on susceptible populations in 
Imperial County. 

Finally, DOE does not agree that the health impacts from ozone 
formation may be larger than it estimated in the environmental impact 
statement. DOE said that it addressed EPA's concerns regarding the 
uncertainty in the ozone modeling in the final environmental impact 
statement. However, while EPA acknowledged in its comments on the final 
environmental impact statement that the document clarified the 
limitations of the ozone modeling analysis, it also reiterated its 
support for off-site mitigation efforts to address these limitations to 
ensure that there is no net increase in air pollution in Imperial 
County. As a result, we continue to believe that ozone formation may 
have larger health impacts than estimated in the final environmental 
impact statement. DOE's specific comments and our detailed responses 
are presented in appendix II of this report. 

We are sending copies of this report to the Secretary of Energy, and 
the Administrator of the Environmental Protection Agency, and 
appropriate congressional committees. We will also provide copies to 
others upon request. In addition, the report will be available at no 
charge on the GAO Web site at http://www.gao.gov. 

If you or your staffs have any questions about this report, please 
contact me at (202) 512-3841 or stephensonj@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. 

Signed by: 

John B. Stephenson: 
Director, Natural Resources and Environment: 

[End of section]

Appendix I: Objectives, Scope, and Methodology: 

The objectives of this report were to determine (1) how emissions from 
the Sempra and Intergen power plants compare to emissions from recently 
permitted plants in California and emissions from sources in Imperial 
County, and what emissions standards the plants would be subject to if 
they were located in Imperial County; (2) the health impacts of 
emissions from the power plants on Imperial County residents; and (3) 
what options exist for U.S. policymakers to ensure that emissions from 
these power plants do not adversely affect the health of Imperial 
County residents. To address all three of these objectives we visited 
the Sempra and Intergen plants in Mexicali, Mexico; interviewed plant 
representatives, various U.S. federal, state, and local air quality 
officials, and other stakeholders; and reviewed relevant documents and 
studies. 

To determine emissions from the Sempra and Intergen plants we obtained 
data from emissions performance tests conducted at the plants by third 
party contractors (GE Mostardi Platt and Air Hygiene). These tests were 
designed to document the average emissions of selected pollutants 
(nitrogen oxide, particulate matter, carbon monoxide, volatile organic 
compounds, and ammonia) from the combustion turbines at each of these 
plants. The results of these tests were reported in standard units of 
measurement, namely parts per million or pounds per hour. According to 
the contractors, they completed the tests according to Environmental 
Protection Agency and California-approved methods and conducted quality 
assurance activities related to their test results. We assessed the 
reliability of the data by (1) reviewing documentation of test 
objectives and quality control procedures provided by the third party 
contractors, (2) conducting interviews with plant officials to 
determine the scope and generalizability of the tests, and (3) 
reviewing reports of actual NOx emissions submitted to the Mexican 
government to ensure consistency with the test results. Based on this 
assessment, we determined that the data were sufficiently reliable for 
the purposes of this report. 

To determine annual emissions estimates from these plants, we used the 
results from the emissions tests to calculate the annual tonnage that 
these plants would be likely to emit. We computed these values based on 
the conservative assumption that these plants would be operating 24 
hours a day, 365 days a year. In addition to the estimates obtained 
from the testing results, we also used the maximum allowable emission 
limits of comparable plants in California to develop a more 
conservative estimate of annual emissions from these plants. For 
Sempra, we utilized the Elk Hills power plant as the primary basis for 
developing comparative estimates. This natural gas-fired power plant is 
partially owned by Sempra Energy and utilizes very similar equipment 
and pollution control technology as the Mexicali plant. For the 
Intergen plant, we used a combination of comparable estimates because 
no similar, Intergen owned facilities were recently constructed in 
California. To estimate nitrogen oxide (NOx) and ammonia (NH3), we used 
vendor guarantee limits, which are the maximum emissions levels 
specified by the manufacturer that a specific piece of equipment is 
likely to produce (e.g. selective catalytic reduction systems). 
Particulate matter (PM10) was estimated using the average allowable 
emissions limit from all comparable plants in California permitted 
between 2000 and 2004. Because the Intergen plant is not equipped with 
an oxidation catalyst, carbon monoxide (CO) was estimated using a 
specific plant in California, permitted in 2000, that was the only one 
licensed without such control equipment. Finally, because some 
California permits establish volatile organic compounds (VOC) limits in 
parts per million and others do so in pounds per hour, we were not able 
to develop an average for all recently permitted plants in California. 
For this reason, we used emissions limits from the Elk Hills power 
plant to estimate annual emission levels of VOC at the Intergen plant. 

To determine how estimated emissions from the Sempra and Intergen 
plants compare to recently permitted plants in California, we developed 
a range of maximum allowable emission limits for all natural gas-fired 
power plants in California with similar specifications, licensed 
between 2000 and 2004. This time frame was chosen because it 
corresponded to the dates that the Sempra and Intergen plants in 
Mexicali were designed, permitted, and began commercial operations. 
Because all California power plants are permitted on a case-by-case 
basis, emissions limits may vary with each project. Therefore, we used 
the entire range of emission limits for the 23 plants that were 
identified during our selection process. We then compared the range of 
emission limits from the 23 plants that we identified with the third 
party testing results we obtained from the Sempra and Intergen plants. 

To determine how the emissions from these plants compare to emissions 
from sources in Imperial County we utilized the 2004 estimated annual 
average emissions inventory for Imperial County developed by the 
California Air Resources Board. We also met with officials from the 
California Air Resources Board and reviewed emissions reports for 
stationary sources obtained from the Imperial County Air Pollution 
Control District. To determine the levels of nitrogen oxide emissions 
from the Sempra and Intergen plants in relation to existing plants in 
Imperial County and Baja California, Mexico, we obtained reports 
developed for the Mexican government that included annual emissions of 
nitrogen oxides based on data from the continuous emissions monitoring 
system on each turbine. Comparable data for the El Centro plant in 
Imperial County and the two Baja California plants were obtained from a 
report produced by the Commission for Environmental Cooperation of 
North America.[Footnote 21] To assess the reliability of these data 
sources we (1) spoke with officials at the California Air Resources 
Board and reviewed documentation related to data collection and quality 
control procedures used to develop the annual emissions inventory, and 
(2) corroborated the emissions data related to the El Centro plant with 
the EPA Clean Air Markets database. Based on these assessments, we 
determined that the data were sufficiently reliable for the purposes of 
this report. 

To determine what emissions standards the plants would be subject to if 
located in Imperial County we reviewed the principal federal 
regulations applicable to new power plants located in the United States 
and the emission limits of similar plants recently permitted in 
California. The primary federal regulations we reviewed were those 
established under EPA's New Source Review program for new or modified 
major pollution sources. We reviewed selected state and local air 
pollution regulations because state and local agencies have 
responsibility for implementing specific permitting activities as part 
of the federal program. The state and local regulations we reviewed 
included the permitting conditions of several power plants licensed by 
the California Energy Commission to determine the standard permitting 
criteria and the air quality rules established by the Imperial County 
Air Pollution Control District for sources located in Imperial County. 

To identify the potential health impacts from emissions generated by 
the Sempra and Intergen power plants, we reviewed the health assessment 
in DOE's environmental impact statement. We met with the project 
manager of DOE's health assessment to gather additional information 
about the assessment methodology. We reviewed EPA's comments on the 
environmental impact statement, and interviewed EPA officials and 
health experts regarding DOE's health assessment methodology. In 
addition, we reviewed relevant EPA reports, and other health studies 
regarding the impacts of particulate matter and ozone on human health. 
Finally, we reviewed a recent California health survey to obtain 
current information on asthmatic populations in Imperial County and 
other California counties. 

To determine the policy options available to ensure that emissions from 
the Sempra and Intergen plants do not adversely affect the health of 
Imperial County residents, we reviewed the federal Clean Air Act, the 
California Clean Air Act, key provisions of the North American Free 
Trade Agreement, as well as environmental agreements between the United 
States and Mexico, such as the La Paz agreement, and a trilateral 
agreement between the United States, Mexico, and Canada--the North 
American Agreement on Environmental Cooperation; and academic research. 
We also participated in a transboundary air quality management 
conference where officials from various federal, state, and local 
agencies in the United States and Mexico met to discuss strategies to 
address binational air pollution. 

We conducted our work between September 2004 and August 2005 in 
accordance with generally accepted government auditing standards. 

[End of section]

Appendix II: Comments from the Department of Energy: 

Note: GAO comments supplementing those in the report text appear at the 
end of this appendix. 

Department of Energy: 
Washington, DC 20585: 

July 29, 2005: 

Mr. John B. Stephenson: 
Director, Natural Resources And Environment:
U.S. Government Accountability Office: 
441 G Street, N.W., Room 2T23A: 
Washington, DC 20548: 

Dear Mr. Stephenson: 

Thank you for the opportunity to comment on the Government 
Accountability Office's (GAO) draft report entitled, "Air Pollution: 
Estimated Emissions from Two New Mexicali Power Plants Are Low, but 
Health Impacts Are Unknown." The Department of Energy (DOE) has 
reviewed the draft and offers comments in the following three areas of 
the report. 

The GAO report noted on Page 27 that: DOE Did Not Analyze All the 
Likely Asthma-Related and Other Health Impacts of Increased Pollution 
from the Sempra and Intergen Power Plants. 

DOE Response: The environmental impact statement (EIS) notes the full 
range of respiratory effects associated with exposure to airborne 
particulate matter (PM10), ranging from asthma symptoms, chronic 
bronchitis, and lower respiratory effects, up to hospitalizations and 
death, and assumes a general 3% across-the-board increase in all such 
effects for each 10-mu g/m3 increase in PM10 as reported in Pope and 
Dockery (1999). This factor is based on a summary of results of 
epidemiological studies of acute exposures to particulate matter. The 
EIS uses the number of potential additional hospitalizations (less than 
one per year) in Imperial County as a representative estimate of the 
number of potential health effects cases associated with power plant 
emissions of PM 10. DOE used this measure of health effects rather than 
any of the other levels in GAO's "Pyramid of Potential Health Impacts 
for Asthmatics" (Figure 4 in GAO's draft report) because DOE considered 
hospitalizations to be the best parameter for representing impacts on 
asthma for two reasons. First, the actual number of baseline 
hospitalizations is well documented (compared to other parameters such 
as doctor visits or use of rescue inhalers). Second, hospitalizations 
are a measure of one of the most severe impacts and, thus, of high 
interest to stakeholders and decision makers. 

While the "Pyramid" is a useful tool for expressing the general idea 
that less severe effects have higher frequency, we think that it is not 
a useful model for computing actual numbers of effects. Take, for 
example, the 2003 report "Asthma in California, Findings from the 2001 
California Health Interview Survey," which GAO cites in its report. The 
report notes that the frequency of asthma symptoms is reduced by timely 
and regular use of medication, regular consultation with physicians, 
and education regarding the recognition of the onset of symptoms. 
Therefore, as the frequency of use of medication and physician visits 
increases, the frequency of asthma symptoms, emergency room visits, and 
hospitalizations would be expected to decrease and impacts from PM10 on 
one level of the "Pyramid" are not expected to be directly related to 
impacts on the next level in a simple and quantifiable way. DOE instead 
relied on verifiable baseline rates of hospitalizations to calculate 
additional cases of this representative health effect of PM10. 

Regarding the potential relationship between PM10 and increased 
cardiovascular effects, including coronary obstructive pulmonary 
disease, which the EIS does not discuss, DOE notes that the observed 
association for these diseases is relatively recent in the literature 
of impacts and is based on far fewer studies than the association 
between PM 10 and respiratory effects (Pope and Dockery 1999). 
Sufficient facts and research have not yet been published from which 
DOE can draw the inference that a statistically linear relationship 
exists between the small increase in PM 10 attributable to the power 
plants and an increased incidence of these cardiovascular diseases. 

The GAO report noted on Page 29 that: DOE Did Not Analyze the Health 
Impacts on Particularly Susceptible Populations in Imperial County. 

DOE Response: The EIS acknowledges such populations in the estimate of 
additional hospitalizations. The baseline hospitalization rate in 
Imperial County is the highest in the state and is nearly twice the 
state average computed from actual discharge rates in Imperial County 
over a three-year period (CDHS 2003). The EIS presents hospitalization 
rates for 0-14 year olds (p. 4-103) as well as for all ages to 
highlight the susceptibility of children to asthma. The EIS contains a 
computation (p. 4-104) of the estimate of additional hospitalizations 
in the county using the all-ages baseline rate, which implicitly 
accounts for contributions from all groups. The estimated impact in 
terms of additional hospitalizations accounts for susceptible 
populations because they are included in the baseline rate. 

The GAO report noted on Page 30 that: Health Impacts from Ozone 
Formation May be Larger Than Estimated by DOE. The section of the 
report goes onto discuss EPA's comments on the draft EIS in which it 
did raise concern about the uncertainty in ozone modeling. 

DOE Response: EPA's concerns regarding the uncertainty in ozone 
modeling in the draft EIS were addressed in the final EIS. Indeed, DOE 
included in the final EIS the results of sensitivity analysis to 
respond to EPA's comments. That analysis showed that the production of 
ozone was insensitive to changes in input assumptions for model 
parameters for which estimated values were used. These results reduce 
the uncertainties associated with the ozone modeling and support the 
conclusion reached that impacts to air quality would be minimal. That 
is, emissions from the power plants would be expected to have very 
little impact on the ozone levels in Imperial County. 

On page 30 of its report, GAO cites EPA's comment that "peak ozone 
concentrations generally occur in areas away from sources of high NOx , 
not at the monitor where high NO2 concentrations are measured." In 
response to the EPA comment, all references to air monitoring data with 
respect to ozone formation were removed in the final EIS. Therefore, 
citing the EPA comment regarding the location of peak ozone 
concentrations is not relevant since the ozone model (OZIPR) that DOE 
used estimates peak ozone concentrations, wherever they would occur. 

DOE appreciates the opportunity to comment on this draft report and 
looks forward to receipt of the final version. 

Sincerely,

Signed for: 

Kevin M. Kolevar:
Director: 
Office of Electricity Delivery and Energy Reliability: 

GAO Comments: 

The following are GAO's comments on DOE's written comments provided in 
their letter dated July 29, 2004. 

1. While DOE's environmental impact statement acknowledges that 
increases in PM10 concentrations could have adverse health impacts such 
as increased asthma symptoms and chronic bronchitis, up to 
hospitalization and death, DOE did not quantify any potential adverse 
health effects other than asthma hospitalizations. Instead, the EIS 
relies solely on comparisons to significant impact levels to gauge the 
magnitude of potential adverse impacts on human health. In doing so, 
DOE determined that emissions from the two plants were below 
significant impact levels, and therefore, these emissions would not 
produce any significant air quality or adverse health impacts in 
Imperial County. As we stated in our report, significant impacts levels 
were designed to be used only in areas that meet air quality standards; 
Imperial County is currently designated as a nonattainment area for 
PM10 and ozone because it does not meet air quality standards for these 
two pollutants. 

2. Asthma hospitalizations are just one measure of potential adverse 
health impacts from increased emissions of particulate matter. While 
asthma hospitalizations are more severe and likely to occur less often 
than doctor visits or increased medication use for asthma, they cannot 
be considered representative of the "full range" of potential adverse 
health impacts associated with asthma in Imperial County. In addition 
to asthma-related adverse health effects, numerous studies have linked 
increased exposure to particulate matter to other non-asthma-related 
adverse health effects, such as chronic bronchitis, chronic lung 
disease, pneumonia, and cardiovascular disease. 

3. We disagree with DOE that hospitalizations are the best parameter 
for representing impacts on asthma. While asthma hospitalizations in 
Imperial County may be well documented, the 2003 California Health 
Survey provides information on other asthma-related health impacts in 
Imperial County. For example, the survey contains information on the 
number of Imperial County residents who take medication to control 
asthma. In addition, the survey presents information on the number of 
Imperial County residents who had asthma symptoms within a specified 
time frame and who visited an emergency room or urgent care facility 
for asthma-related health problems during that time frame. Such 
information could have been used, along with information on 
hospitalizations, to create a more complete estimate of the potential 
asthma-related health effects from increases in pollution from the 
power plants. 

4. The report does not use the health effects pyramid, or suggest it 
should be used, to compute instances of potential health effects from 
air pollution. However, we believe that the health effects pyramid is 
useful for understanding the variety of ways in which increased 
pollution can aggravate asthma suffering in Imperial County. In so 
doing, it also highlights the full range of potentially quantifiable 
effects related to asthma. 

5. During our review of the health effects literature, we identified a 
number of studies that support a linear relationship between increases 
in particulate matter pollution and increased incidence of 
cardiovascular diseases. 

6. Asthmatic children are not the only susceptible population mentioned 
in our report, and asthma hospitalization is not the only potential 
health impact. Consequently, we continue to believe that DOE's 
environmental impact statement did not address the full range of 
potential health impacts on susceptible populations in Imperial County. 
DOE's quantification of just one adverse health impact for the entire 
population of Imperial County masks the differential effects that can 
beset more susceptible subpopulations in the County. 

7. In commenting on the final environmental impact statement, EPA 
acknowledged that DOE had clarified the limitations and uncertainties 
of the ozone modeling analysis. However, in its comments EPA said it 
continues to support and encourage off-site mitigation efforts to 
address the limitations in the ozone modeling to ensure that there is 
no net increase of air pollution in Imperial County. 

8. We believe that EPA's comment regarding peak ozone concentrations is 
relevant because it is presented in the context of EPA's comments on 
the draft environmental impact statement. We also note in the report 
that DOE took action in response to EPA's comment. 

[End of section]

Appendix III: GAO Contact and Staff Acknowledgments: 

GAO Contact: 

John B. Stephenson (202) 512-3841: 

Acknowledgments: 

In addition to the contact named above, Leo G. Acosta, Charles Bausell, 
Nancy Crothers, Brandon Haller, Ryan Lambert, Omari Norman, Kim Raheb, 
and Stephen Secrist made key contributions to this report. 

FOOTNOTES

[1] The standards are known as the National Ambient Air Quality 
Standards. 

[2] Nitrogen dioxide (NO2), a common air pollutant, is one of a group 
of gases collectively known as nitrogen oxides, or NOx. The term NOx is 
used commonly in both the United States and Mexico to describe these 
gases, but NO2 is sometimes monitored to report on the levels of all 
nitrogen oxide emissions in general. 

[3] PM2.5 and PM10, also known as fine and coarse particulate matter, 
respectively, refer to the size of the airborne particles measured at 
the diameter (in micrometers). 

[4] Ozone is formed at ground level by a chemical reaction of various 
air pollutants, including NOx, combined with sunlight. Ozone is a key 
ingredient in urban smog. 

[5] Independent of such factors as time of day, time of year, and 
geographical location, in general, one megawatt of electricity is 
sufficient to meet the needs of 750 to 1,000 households for 1 hour. 

[6] On April 13, 2005, the Secretary of Energy transferred the 
authority to grant presidential permits to the Office of Electricity 
and Energy Assurance. That office has subsequently been renamed the 
Office of Electricity Delivery and Energy Reliability. 

[7] Exec. Order No. 10485, 18 Fed. Reg. 5397 (Sept. 9, 1953) amended by 
Exec. Order No. 10238, 43 Fed. Reg. 4957 (Feb. 3, 1978). 

[8] Selective catalytic reduction is a post-combustion cleaning 
technology whereby NOx emissions chemically react with ammonia (NH3) to 
produce ordinary nitrogen and water vapor. An oxidizing catalyst is 
similar in concept to catalytic converters used in automobiles. The 
catalyst, normally coated with a metal, such as platinum, is used to 
promote a chemical reaction with the oxygen present to convert carbon 
monoxide into carbon dioxide and water vapor. 

[9] Because the proposed lines traverse land managed by the U.S. 
Department of the Interior, Bureau of Land Management, they also 
participated in the environmental assessment. 

[10] For this reason, ammonia (NH3) is often included in the review of 
potential impacts from power plants and is subject to emission limits 
as part of the permitting process conducted in California. NH3 
emissions, typically referred to as ammonia-slip, are released from 
power plants as a byproduct of selective catalytic reduction control 
technology. 

[11] North American Power Plant Air Emissions, Commission for 
Environmental Cooperation of North America, 2004. 

[12] Imperial County Air Pollution Control District, Rule 207, Section 
C.3 (Revised Sept. 14, 1999). 

[13] The border city of Calexico, California, is also in violation of 
the state ambient air quality standard for CO. Therefore, if the plants 
were located in Imperial County close enough to Calexico to impact the 
city's air quality, the plants would also be required to offset their 
emissions of CO. 

[14] EPA has established significant impact levels for NO2, SO2, CO, 
and PM10 in the context of permitting a major source or major 
modification to an existing pollution source in the United States. 40 
C.F.R.  51.165(b)(2). 

[15] The California Health Interview Survey--maintained at the UCLA 
Center for Health Policy Research in Los Angeles, California--is the 
state's largest health survey. The telephone survey of adults, 
adolescents, and children is a collaborative project of the UCLA Center 
for Health Policy Research, the California Department of Health 
Services, and the Public Health Institute, and is conducted every 2 
years. 

[16] The Health Effects Institute (HEI) is an independent, nonprofit 
corporation chartered in 1980 to provide impartial research on the 
health effects of air pollution. Supported jointly by the U.S. 
Environmental Protection Agency and industry, HEI has funded over 170 
studies and published over 100 research reports. HEI supported research 
has produced findings on the health effects of a variety of pollutants, 
such as carbon monoxide, nitrogen oxides, ozone, and most recently, 
particulate air pollution. 

[17] UCLA Center for Health Policy Research, Asthma in California: 
Findings from the 2001 California Interview Health Survey, November 
2003. 

[18] DOE used data from Phoenix, Arizona because it is one of the 10 
cities that was already built into the EPA ozone model (OZIPR) 
database, and they believe Phoenix, Arizona is the most representative 
proximate city in terms of climate, latitude, and physiography. 

[19] Richard Ryan, "Financing Clean Air on the Border: Establishing a 
Binational Clean Air Trust Fund (BiCAT)" (paper presented at the Border 
Institute VII, Transboundary Air Quality Management conference, in Rio 
Rico, Ariz., April 2005). 

[20] The program, known as the Border Ozone Reduction and Air Quality 
Improvement Program, is administered by a Harvard University-affiliated 
nonprofit organization, LASPAU: Academic and Professional Programs for 
the Americas. 

[21] The Commission for Environmental Cooperation of North America was 
established by the North American Agreement on Environmental 
Cooperation--one of the two side agreements to the North American Free 
Trade Agreement. 

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