Frequently asked questions about the issues facing NGS
Since the plant commenced operation in the mid-1970s, environmental stewardship has been a priority for the owners of NGS. NGS is equipped with controls that eliminate over 99% of particulate matter (PM), 95% of sulfur dioxide (SO2), and 40% of nitrogen oxides (NOx) from the plant's emissions. The NOx emission controls were installed voluntarily by the owners in advance of any regulatory requirement.
The Environmental Protection Agency (EPA) has established primary National Ambient Air Quality Standards (NAAQS) to protect all exposed populations, including sensitive subpopulations such as asthmatics, children, and the elderly. EPA reviews these standards every five years, and using the best available science, sets the standards at levels that are protective of public health with an adequate margin of safety.
SRP has been monitoring ambient pollution levels for many years at a monitoring site located within a few miles of NGS. The monitoring data shows that air pollution levels consistently fall below the NAAQS, indicating that air quality around NGS is not harmful to public health. Furthermore, additional air quality monitors in Coconino County that are closest to NGS also show that NGS emissions are not causing exceedances of EPA's health-protective standards.
Fine particulate matter is frequently used as a metric to assess potential health effects from air pollution. Recently, the World Health Organization (WHO) compiled a database that compares urban outdoor particulate matter pollution levels in various cities throughout the world. The database represents human exposure primarily from urban residential and commercial areas.
In this study Clearlake, California was reported to have the best air quality in the United States. The city of Page was not included in the study. However, the particulate matter concentrations measured at the monitoring site near NGS were even lower than those reported in Clearlake. This suggests that the area around NGS has some of the best air quality in the country.
A recent report by the American Lung Association also confirms that Coconino County has some of the cleanest air in the United States. Out of 600 U.S. counties evaluated in this assessment, Coconino County was listed in the top 25 for the best fine particulate matter short-term and year-round air quality.
NGS is the largest coal-fired power plant on the western grid. It operates around the clock to provide affordable and dependable electricity. Although NGS is a large power plant, it is also very efficient. NGS produces fewer emissions for each ton of fuel used than many of the other coal-fired units in the nation.
When compared to other coal-fired power producing units, the units at NGS perform better than:
- 852 units in terms of SO2 emissions (lb/MMBtu)
- 510 units in terms of NOx emissions (lb/MMBtu)
- 656 units in terms of CO2 emissions (lb/MMBtu)
Note: Data obtained from the EPA's Air Markets Program Data 2012 database. NOx and SO2 data was available for 944 coal-fired power producing units, and CO2 data was available for 941 coal-fired power producing units.
There are a variety of sources of air pollution. Common sources of outdoor air pollution include windblown dust, wildfires, controlled burns, vehicle exhaust, road debris, and industrial emissions. Indoor air is also a significant source of air pollution exposure. Because people generally spend the majority of their time indoors, and indoor air pollutants can be confined for extended periods of time, these exposures may outweigh everyday outdoor air pollution exposures.
Indoor activities such as baking, frying, smoking, burning candles, using certain office equipment such as photocopiers, or burning coal for cooking and heating purposes contributes to air pollution exposures. The pollution levels attributed to these activities often exceed the EPA's health-protective NAAQS.
Asthma is a complex, multi-factor disease, with a multitude of known triggers and risk factors. There is evidence that recent increases in asthma prevalence is more likely linked to risk factors other than outdoor air pollution, including allergic status, lifestyle factors, and indoor air pollution. In fact, over the many years that outdoor air quality has been steadily improving, and particulate matter concentration levels falling, asthma rates have increased.
While various media reports claim that NGS contributes to health issues, these claims are unsubstantiated and are inconsistent with air quality data measured at local monitoring sites. Ambient air data collected at these sites shows that air quality in the area meets all of EPA's health-protective National Ambient Air Quality Standards, which suggests that emissions from NGS do not create health risks for residents living in the area.
The health issues reported in these media reports are based on a computer modeling analysis conducted by the Clean Air Task Force (CATF). The analysis is a complex assessment that fails to address many significant issues such as the use of uncertain, dated, or inaccurate inputs in addition to other modeling and methodological limitations. The combination of these factors creates an unreliable estimate of health impacts that is completely at odds with measured air quality levels, which are below the EPA's standards that protect public health.
Regional haze and visibility
The EPA's Regional Haze Rule is designed to return visibility in national parks and wilderness areas to natural background conditions by 2064. The rule is not designed to address public health. EPA has established other regulations and standards to protect public health.
The Regional Haze Rule is structured to make progress towards the long-term goal over 10-year planning periods and is specifically designed to improve visibility on the haziest days and prevent visibility deterioration on the clearest days.
In the first 10-year planning period of the rule, stationary sources like power plants are required to install Best Available Retrofit Technology (BART) to control emissions. Companies are required to follow a procedure that is prescribed by EPA to establish retrofit technology for power plants that are subject to the rule. The regulatory agency then reviews the company's proposal and determines whether it is acceptable, or whether additional controls are needed.
In the case of NGS, EPA is currently considering whether additional nitrogen oxide (NOx) emission controls should be installed.
EPA's current rulemaking process is focused on evaluating whether additional NOx emission controls are needed at NGS. NOx is formed during the combustion of coal when nitrogen in the air and coal combine with oxygen. NOx can impact visibility in two ways:
- NOx consists of nitrogen oxide (NO) and nitrogen dioxide (NO2). NO2 is a gas that absorbs light and is visible as a local brown plume.
- Additional reactions in the atmosphere between NOx and background ammonia that may be present due to other sources create ammonium nitrate particles. These particles last longer and can impact visibility as a component of regional haze.
Two main technologies are currently available to control NOx emissions:
- Low-NOx Burners and Separated Overfire Air (LNB/SOFA) are furnace modifications that control air-to-fuel ratios to reduce NOx formation during combustion. This type of control technology represents a cost-effective means to reduce NOx emissions by 40% without the need for costly chemicals and other potentially negative environmental consequences. LNB/SOFA were installed on all units at NGS between 2009 and 2011. Installation was completed at a cost of approximately $45 million.
- Selective Catalytic Reduction (SCR) consists of a reactor in which ammonia is injected to combine with NOx to form nitrogen and water. The cost of installing SCR on all three units would be approximately $544 million. If baghouses are required to mitigate the increase in emissions of other pollutants created by the SCR, the total cost of controls would rise to approximately $1.1 billion.
Point sources of NOx emissions, such as power plants, account for a minor portion of total NOx emissions. As illustrated by the Western Regional Air Partnership (WRAP) Electronic Data Management System (2005 Inventory), NOx emissions from NGS constitute only a fraction of the regional NOx emissions. Mobile sources, such as vehicles, are major contributors to total NOx emissions.
How much do NOx emissions from power plants affect visibility in Grand Canyon and other nearby national parks?
Extensive studies performed by the Grand Canyon Visibility Transport Commission and the Western Regional Air Partnership have shown that NOx emissions from power plants are a small contributor to visibility impairment on the Colorado Plateau, including Grand Canyon National Park. The same studies show that wildfires, control burns, windblown dust, and emissions from metropolitan areas account for the majority of visibility impairment in nearby parks and wilderness areas.To illustrate this concept, below is a pie chart that shows the various contributors to regional haze in the Grand Canyon. As shown in the chart, visibility impairment is caused by Rayleigh scattering (the natural scattering of light caused by nitrogen and oxygen in the atmosphere which makes the sky look blue), sulfates, nitrates, and other particles (the other particles come from windblown dust, wildfires and control burns, and combustion sources like diesel engines).
Nitrates, which are produced when nitrogen oxide (NOx) emissions from various sources react with other gases in the atmosphere, account for 4% of regional haze. Power plant NOx emissions only contribute a fraction of this 4%.
How would adding SCR controls at NGS affect visibility conditions in nearby parks? Would a park visitor see a difference?
Visibility improvement is measured in units called deciviews (dv). An EPA-approved modeling analysis showed that installing SCR on all three units at NGS would result in an average visibility improvement of approximately 0.4 dv at nearby national parks. The maximum improvement was modeled at 0.7 dv. The EPA's regional haze rule states that 1 dv is a "small but noticeable change in visibility under most circumstances." Since modeling results suggest that installing SCR would yield less than 1 dv of change, perceptible visibility improvements at any of the national parks or wilderness areas near NGS would not be expected.
Power plant emissions on the Colorado Plateau have been significantly reduced over the past several decades. Has visibility in the Grand Canyon improved as a result?
The graphic below shows the emission reductions that have occurred over the last several decades, as well as the visibility impairment (light haziness) in Grand Canyon National Park over the same time period.
The graphic shows two step change reductions in emissions (installation of scrubbers at NGS in the late 1990s, and shutdown of Mohave Generating Station in southern Nevada in late 2005). However, as can be seen in the graphic, there is no corresponding step change improvement in visibility as a result of those significant emission reductions.
The data in this graphic shows that other sources of emissions contribute more significantly to visibility impairment than power plants. Given that NOx emissions are a smaller contributor to visibility impairment than SO2, further reductions in power plant NOx emissions would be unlikely to lead to appreciable visibility improvement in the Grand Canyon.
While SCR may achieve additional NOx reductions, monitoring data collected near NGS indicates that air quality already meets all of EPA's National Ambient Air Quality Standards (NAAQS), which are established and periodically reviewed by EPA for the purpose of protecting public health within a margin of safety. Therefore, the current emission controls at the plant are already protective of public health.
Low-NOx-burners modify the combustion process, so there are no significant adverse effects resulting from this method of NOx removal. SCR, however, creates sulfuric acid mist that also impairs visibility. Because sulfuric acid mist is a regulated pollutant, EPA's regulations could require the injection of sorbents to mitigate the mist emissions. The addition of sorbents would increase the particulate matter (PM) load and potentially require installation of baghouses at a significant additional cost to reduce PM emissions.
SRP conducted a BART analysis for NGS. That analysis, which was performed according to EPA's guidelines, concluded that Low-NOx Burners (LNB) and Separated Over-Fire Air (SOFA) are the best retrofit technology for NGS. As part of its analysis, SRP ran a model that predicts visibility improvement for each emission control option. The model predicts that installing SCR would result in such a small visibility improvement that it would be imperceptible in nearby national parks such as Grand Canyon. Given the significantly higher cost of SCR, and that installing SCR is unlikely to yield a perceptible improvement in visibility, SRP's analysis concluded that LNB/SOFA is BART.
Ownership and economics
Many complex issues surround the continued operation of NGS:
- The initial term of the plant site lease (and other critical agreements) begin to expire in 2019. The NGS owners are currently renegotiating the terms of the lease amendment with the Navajo Nation. However, even once a consensus is reached on future lease terms, the new site lease cannot be issued until comprehensive Federal environmental reviews are completed.
- These reviews will require the coordination of 10 Federal agencies and 15 Native American Tribes. Once the review is completed, the Federal agencies will issue a Record of Decision (ROD) and the Secretary of Interior must decide whether to approve the extension of the lease.
- Because of the number of stakeholders involved, the complexity of the project, and the extensive public input that is expected, the Federal environmental reviews will likely take 5 years or longer, and will most likely be subject to litigation.
- In the meantime, EPA will be proposing a rule that may require the installation of additional controls at NGS. If the most stringent controls are required, the total cost is estimated to be $1.1 billion. The NGS owners are concerned that EPA's proposal will not allow sufficient time to get through the Federal environmental review process and anticipated litigation, secure the necessary air permits, and complete the design and construction of the additional controls.
- If EPA requires the installation of additional controls on a schedule that does not allow the NGS owners enough time to resolve the uncertainties facing the plant before having to make a substantial capital investment, the plant could be forced to shut down.
If the owners cannot be certain that operation of NGS will continue beyond 2019, they cannot assume that the costs of additional emission controls can be recovered beyond 2019. This circumstance presents significant risk to the owners, and they would not likely be willing to invest $1.1 billion in additional controls with so many uncertainties facing the future operation of the plant. In the case of the U.S. Bureau of Reclamation (a co-owner of NGS), the Bureau cannot legally invest in additional controls until the Federal environmental review is completed and a Record of Decision is issued.
NGS began operating over 35 years ago. Why would anyone want to make additional investments in a plant that age?
The maintenance performed at NGS throughout the years has set a solid foundation for the plant to continue operating past 2019 if the site lease extension is approved. Although the facility began operating in the mid-1970s, the equipment runs better, cleaner, more efficiently, and more dependably than when the plant was first built. In fact, NGS is considered among the best maintained and operated facilities in the business, and has been recognized by the energy industry for its reliability throughout the years.
Installation of updated equipment and regularly scheduled maintenance has kept NGS in prime operating condition. Every year one of the plant's three 750-megawatt units undergoes a minor overhaul, and every third year it receives a major overhaul. A minor overhaul ensures that all the ducts, fans, pumps, steam lines, turbine components, valves, boiler, bottom ash, precipitators and scrubbers are inspected and repaired as needed. During a major overhaul the entire turbine, generator, and other parts of the plant are completely disassembled, inspected, repaired, and reassembled.
Because NGS has been well cared for throughout its lifetime, the plant is expected to be a productive and efficient power source in the future. Thus, continuing to operate NGS past 2019 is a good investment.
Many complex issues surround the continued operation of NGS:
- The shutdown of NGS would have devastating consequences on the state of Arizona. NGS and the Kayenta Mine are estimated to contribute over $20 billion and 3,000 jobs each year on average due to indirect and induced economic benefits throughout the state.
- Closure of NGS would also jeopardize Indian water rights settlements for multiple central Arizona Indian Tribes since those settlements are funded by the sale of excess power from the plant.
Navajo tribal interests
The Navajo Tribal Utility Authority (NTUA) operates the electric power distribution system on the Navajo Nation reservation. This distribution system is lower voltage than the transmission systems used by the generating stations on the Navajo Nation. As a result, the two systems cannot be directly connected, so NTUA buys power that can be delivered to their substations at the correct voltage level. Periodically, the NTUA bids out the power supply contract and they select the best option, taking into account price and reliability. If the NTUA wanted to acquire power directly from NGS, they would need to add significant infrastructure that would cost several millions of dollars. These costs would have to be paid by NTUA customers through higher rates.
What are the NGS owners doing to help bring electricity to residents in the LeChee Chapter of the Navajo Nation?
The NGS owners recently committed to contributing up to $2 million to the NTUA to help facilitate power distribution to the LeChee residents surrounding NGS. This project will bring power to 62 homes in LeChee over the next three years.
NGS is a conventional power generation resource that provides continuous, reliable power and can operate at maximum output around the clock. Renewables, such as wind turbines or solar panels, are promising generation alternatives, but these resources are intermittent and can only provide power when the wind or sun is available. As a consequence, renewable resources often require fossil fuel backup to provide continuous power around the clock and under all types of weather conditions. While there are technologies available to store energy generated by intermittent resources, those technologies are still experimental and very expensive.
Because of intermittency issues, a solar plant approximately three times as large in megawatt (MW) capacity than NGS would have to be built in order to generate the equivalent amount of energy on an annual basis. In other words, to replace the three units at NGS (2,250 MW total), a solar plant that generates at least 6,750 MW would be needed. As a result, this could necessitate substantial transmission system upgrades and/or additions. The same issue exists with wind power.
As a result, constructing a renewable facility with enough capacity to replace NGS would come with a hefty price tag that substantially exceeds the expected costs to retrofit NGS with additional emissions controls. At the current prices for solar power, SRP's latest estimates indicate that it would cost approximately $12 billion to construct a new solar plant that would produce the same annual energy output as NGS. It would also cost about $12 billion to build a new wind plant that would produce the same energy as NGS on an annual basis.
Renewable resources generally require larger land area than conventional resources to generate equivalent amounts of energy. For example, a solar plant that generates the equivalent amount of energy as NGS would require over 50,000 acres of land. An equivalent wind farm would need to be over 1.1 million acres. The NGS site is only about 1,800 acres.
To put this land area in perspective, the map below shows the size of a wind farm needed to replace NGS relative to the Phoenix metropolitan area.
It is also important to note that while a significant number of jobs are created during construction of solar and wind plants, these facilities support significantly fewer permanent jobs on an ongoing basis for operation and maintenance.
When all of these factors are taken into account, the total costs of constructing a new facility and generating, integrating and delivering power using renewable resources is not practical and far exceeds the cost of conventional resources. As a result, renewables may represent good sources of clean energy, but they are currently only appropriate to supplement rather than replace conventional resources like coal-fired power plants.