When Prairie Creek Generating Station experienced a change in the one-hour SO2 standard, plus a change in monitor location, it faced the possibility that plant operation—and steam customers—might experience negative consequences. Sensible solutions avoided these problems—as well as negative regional impacts.

The U.S. Environmental Protection Agency (EPA) is obligated to review many different federal environmental standards on a recurring basis and update them if the agency deems it necessary for the protection of public health and welfare. As standards change, existing facilities operating in a consistent fashion for years may suddenly be faced with the challenge of an updated and more-stringent regulatory requirement that must be addressed.

One approach to addressing such a situation may be to defer attention to it until it is brought up during the review of a renewable permit or when requirements are imposed by a regulatory authority, potentially through a State Implementation Plan. Another approach is to be proactive and address the challenge head on.

Communication with regulators, local officials, customers, the general public, and other stakeholders can be a much more effective and productive approach to a difficult situation such as this. Alliant Energy takes a proactive approach in these types of situations. We have found that a successful strategy is to maintain positive and collaborative relationships with regulators while keeping communication open with local officials, customers, and the public. A good example is the proactive actions taken by Alliant Energy to address the recent challenge posed by the sulfur dioxide (SO2) National Ambient Air Quality Standards (NAAQS).

The Sulfur Dioxide Surprise

The original SO2 primary standards were established by the EPA in 1971 on a 24-hour basis of 140 parts per billion (ppb) and 30 ppb on an annual basis. These standards were reviewed in 1996, but they were left unchanged.

In 2010, the EPA reviewed the SO2 standard again and chose to revise it by lowering the acceptable concentration to 75 ppb on a 1-hour basis. The EPA revoked the two existing primary standards because they would not provide additional public health protection given by a 1-hour standard at 75 ppb. As a result, many facilities and localities, primarily those that use coal as a fuel source, were faced with a more stringent air quality standard that could result in additional restrictions brought about by a potential nonattainment area designation.

With the 1-hour SO2 standard, the EPA introduced two paths for states to make recommendations of attainment status: using monitoring data or using ambient air quality modeling. Traditionally, when monitoring data is used, information is collected by monitoring stations for a three-year period. In the case of the 1-hour SO2 standard, the fourth-highest daily maximum 1-hour concentration for each of the three years is averaged together to calculate an SO2 concentration to be compared against the standard of 75 ppb. If that value is above the standard, then a recommendation and designation of nonattainment is likely.

Alliant Energy is a Midwestern utility that serves approximately 950,000 electric and 410,000 natural gas customers in Iowa and Wisconsin through its utilities Interstate Power and Light and Wisconsin Power and Light. Additionally, Alliant Energy provides steam to industrial customers. Alliant Energy utilizes coal in its generation portfolio, along with natural gas and renewable assets. Alliant Energy’s Prairie Creek Generating Station (PCGS) in Cedar Rapids, Iowa, provides electricity and steam through the use of coal and natural gas. The plant is equipped with four coal/natural gas–fired boilers and two natural gas–fired boilers totaling approximately 250 MW.

The Matter of Parking a Monitor in a Park

In 2012, the local air quality district office, Linn County Public Health Department (LCPHD), was faced with a decision regarding the relocation of SO2 ambient air monitoring equipment to a location that would provide a better representation of SO2 concentrations in the area. The Iowa Department of Natural Resources (IDNR) directed the LCPHD to relocate an existing SO2 monitor that had been stationed near an industrial park containing a coal-fired power plant that had been shuttered by the floods of 2008 to another location with potential SO2 emitting sources. LCPHD examined its air emissions inventory and decided to locate the monitor near the facility that had reported the highest annual SO2 emissions levels in recent years. That was Alliant Energy’s Prairie Creek Generating Station.

LCPHD contacted Alliant Energy officials and discussed the possibility of locating the monitor near PCGS, noting that although the plant had the highest reported annual SO2 emission levels in the county, the area was also impacted by other SO2-emitting sources. The precise location had yet to be decided. Although both Alliant Energy and LCPHD had conducted ambient air quality modeling to assess potential impact areas, both sets of analyses indicated that the areas predicted to observe the highest concentrations of SO2 were in a wooded area away from public congregation.

LCPHD, as a public health protection agency, assessed its options and looked for an area to locate the monitor that might be more representative of where the public may be. That line of thought raised the possibility of locating the monitor in Tait Cummins Park, adjacent to PCGS (Figure 1).


1. New monitor location. The red arrow shows the new location of the SO2 monitor in Cedar Rapids’ Tait Cummins Park. Prairie Creek Generating Station can be seen in the foreground. Courtesy: Map data © 2016 Google

SO2 is a fairly localized air pollutant not typically subject to long-range transport like ozone or fine particulates. According to Shane Dodge, supervisor of the Air and Water Quality Branch for the LCPHD, by locating the monitor in the park, LCPHD would be able to assess local SO2 emission sources’ impact on an area where the public congregates.

The recommendation to locate the monitor in Tait Cummins Park was put before the IDNR and ultimately accepted. That location, because it wasn’t the area with the highest predicted concentrations of SO2, would not ultimately serve as an acceptable location to demonstrate attainment with the SO2 standard, but it would be responsive to LCPHD’s mission.

Locating a monitoring trailer in Tait Cummins Park presented some interesting questions for the LCPHD and Alliant Energy to work through. The park contains several baseball diamonds and a concession stand, which the monitoring trailer was intended to be located near. It was anticipated that the presence of the trailer would generate questions, not only from users of the park, but also from those who work at PCGS, regarding its purpose, as well as what the information it was collecting might be telling.

LCPHD and Alliant Energy worked with officials of the Linn County Parks Department to develop a flier (Figure 2; full version here) that would communicate the purpose of the monitor, how the SO2 standard was changed, how to obtain information on the monitor’s readings, and that there hadn’t been any significant increases in SO2 emission sources in the area. In addition, data that the monitor was collecting was added to LCPHD’s Air Quality Division’s webpage.


2. Level indicator. Local agencies and Alliant Energy worked together to develop an informational flier about the new SO2 monitor and what SO2 air quality levels mean. It included this graphic. Courtesy: Linn County Public Health Department

The flier also identified whom to contact with questions and was distributed by the Parks Department to recreation league officials and posted on the concession stand. Dodge says that very few questions ended up coming into his office as a result. Alliant Energy provided similar information to its employees, with similar results.

Modeling vs. Monitoring

The monitor began collecting data on January 1, 2014, and contrary to what the air quality models were predicting, it recorded four daily high concentrations above the 75 ppb standard in the first six weeks of operation. By the end of April, six days had exceeded the 75 ppb threshold. Though weather patterns and other matters may have influenced the data in an unexpected way, the data that was being recorded introduced the possibility that the area could be found to be in nonattainment with the SO2 standard.

When monitoring data is utilized, attainment demonstrations with the 1-hour SO2 standard are based upon 99% of the values recorded. This is done by air quality agencies by examining the hourly SO2 data over the course of a day and assigning the highest value for a given day that day’s value. Since the standard is based upon the 99th percentile, the highest three days are omitted from the analysis, and the fourth-highest daily value is then the value that is used for the year. An area would be found to be out of attainment with the standard if the three-year average of these values is over 75 ppb.

By the end of 2014, the monitor had recorded 13 daily readings that were above the 1-hour standard, with the fourth-highest reading being 113 ppb. A nonattainment designation appeared to be a possible outcome if this trend continued, which would create an undesirable burden on the local community and industry (Figure 3).


3. Raising the threat of nonattainment. The red line indicates the 75 ppb threshold for SO2. This chart covers all of 2014. Monitoring in the new location began January 1, 2014, and by the end of April, six days had exceeded the 75 ppb threshold. Courtesy: Alliant Energy

Alliant Energy elevated the monitoring data to the attention of local government and economic officials on several occasions so that they had an understanding of what a nonattainment designation could mean from a development perspective. It was clear that the situation required attention and that the data the monitor was collecting could likely have an impact on any future development plans for the area. The data also could affect the operations of industry that additional modeling would predict to have a contributing effect on the SO2 concentrations the monitor was detecting.

Designations of nonattainment with air quality standards require agencies with responsibility for air quality, such as the LCPHD and the IDNR, to develop programs intended to reduce pollutant levels and manage permits for new emissions source development so the predicted pollutant concentrations do not intensify.

Early action and transparent discussions led to a better understanding of the circumstances the area was facing. That communication helped to develop action plans to monitor the issue and prevent reoccurrence of monitored SO2 levels in excess of the 1-hour SO2 standard. Proactively working with officials, especially the LCPHD, developed a sense of commitment and confidence that Alliant Energy would be a partner in developing a strategy to prevent monitored concentrations above the standard.

A Necessarily Holistic View

To demonstrate this partnership, Alliant Energy commissioned a study by an independent research group to analyze the impact that an SO2 nonattainment designation in the area might have on economic development.

Internally, Alliant Energy initiated activities to analyze its potential impact on the monitored SO2 values and what the company might be able to do to mitigate its contribution. While it was clear that operations at PCGS could be affecting the data the monitor was collecting, it was also apparent that other SO2 emitting sources, including idling mobile sources, likely had an influence.

In developing a strategy, Alliant Energy determined that whatever steps it may decide to take would have to be holistically evaluated. There were several competing influences that might affect operations at PCGS as well as Alliant Energy’s electric and steam customers and the community. Those considerations included:


■ Additional emerging air, water, and solid waste environmental programs and forthcoming EPA requirements

■ Fuel availability

■ Contractual agreements

■ Operational performance

■ Regulatory impacts

■ Shareholder considerations


Developing a balance in these matters required a proactive approach to decision-making while maintaining frequent, collaborative, and transparent communications with stakeholder groups internally and externally.

Alliant Energy has an unyielding responsibility to provide safe, reliable, and responsible energy to its customers. Any decisions made to address the SO2 matter would need to be in line with that obligation. While other environmental regulations may affect future investments in PCGS, Alliant Energy analyzed the possibility of moving forward using a lower-sulfur coal than what the plant had been utilizing, coupled with some natural gas blending that could be accommodated under the plant’s current configuration, especially since other changes were anticipated.

Alliant Energy conducted several air quality modeling exercises to assess the impact that reductions in PCGS stack emissions might have on predicted concentrations of SO2, not only at the monitor, but also in the area where models were predicting the highest concentrations might occur. The modeling methods and results were shared with the LCPHD and the IDNR and were found to be consistent with their methods.

Although only the predicted PCGS emissions impacts were reviewed, the models determined that reductions in stack SO2 emission rates brought on by a fuel change within the current abilities of the plant could have a measurable effect on SO2 concentrations in the area. But before such a change could be implemented, Alliant Energy needed to understand whether using such fuel would have operational or other impacts on the plant and its ability to live up to its responsibilities.

The lower-sulfur coal was strategically introduced to the fuel stream to analyze operational effects and any impacts it might have on combustion byproducts, especially as they related to particulate matter and mercury collection efficiencies of the plant’s electrostatic precipitators necessary to meet the recently promulgated Utility Mercury and Air Toxics Standards (MATS). Although the use of lower-sulfur coal posed a few logistical issues to overcome, it was determined that the use of the fuel was feasible, and it was moved forward fully in 2015.


During 2015, the SO2 monitor in Tait Cummins Park did not register any hourly SO2 concentrations that were found to be above the 1-hour SO2 standard (Figure 4). The fourth-highest daily maximum 1-hour reading for the year ended up being 49.7 ppb, a significant difference from the year before.


4. Below the threshold. Monitored SO2 data for 2015 did not exceed the 75 ppb threshold. Courtesy: Alliant Energy

As of the writing of this article in late February, 2016 has continued that trend. While it cannot be said that the fuel changes are the sole reason that monitored SO2 concentrations have been considerably lower, the fuel change likely had a contributing effect. Time will tell whether future influences such as other SO2-emitting sources, the weather, and other contributors may affect the monitor’s readings.

Although the monitor’s data collection won’t provide LCPHD and the IDNR with the ability to recommend an attainment designation, the ambient air quality modeling that was conducted to support this decision-making will be a strong tool in making that recommendation in the near future. In addition, it now seems possible to avoid a nonattainment designation for the region.

The primary lesson learned is that a proactive, collaborative, and transparent approach to problem solving—coupled with a willingness to communicate with stakeholders—goes a tremendously long way.

Alliant Energy appreciates the willingness of its stakeholders—especially those officials in Linn County, Iowa, in this instance—to engage in productive discussions, develop well-thought-out messages, and assess the many options that may be in the best interest of those affected. By developing a clear understanding of the impacts and possibilities, an ability to develop smart and flexible solutions was created, with time to adapt before an undesirable result was upon us. Without this communication, competing objectives might have been developed that could have had a detrimental effect on the common goal. ■

Jeffrey Hanson, PE (jeffreyhanson @alliantenergy.com) is senior manager–environmental and decommissioning services for Alliant Energy. This case study was also shared at the 2016 EUEC conference.