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. The Sempra plant, known as Termoelèctrica 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. 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. ) 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. 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. 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. 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. 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. 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. Intergen average(US export) (Mexico) NOX (ppm) (ppm) VOC (lbs/hr) Legend: NOX = nitrogen oxides; ppm = parts per million; PM = particulate matter; lbs/hr = pounds per hour; CO = carbon monoxide; NH levels are computed based on a 1, 3, or 24- hour average. VOC emissions were undetectable during tests conducted at the plant. 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. 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. 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. 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. 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 PM and ozone standards in the county.