The U.S. Environmental Protection Agency told the state of Georgia that it is rejecting air dispersion modeling from the Sierra Club and agreeing with the state that Georgia Power‘s Scherer coal plant is not causing the area around the plant to be out of SO2 NAAQS compliance.
EPA on Feb. 16 sent a series of letters to various states outlining preliminary decisions about SO2 NAAQS compliance for certain specific areas in those states. Under section 107(d) of the Clean Air Act (CAA), EPA must designate areas as either “unclassifiable,” “attainment,” or “nonattainment” for the 2010 one-hour sulfur dioxide (SO2) primary national ambient air quality standard (NAAQS). A nonattainment area does not meet the NAAQS or contributes to a violation in a nearby area. An attainment area is defined as any area other than a nonattainment area that meets the NAAQS. Unclassifiable areas are defined as those that cannot be classified on the basis of available information as meeting or not meeting the NAAQS.
Georgia submitted updated recommendations in September 2015, ahead of a July 2, 2016, deadline for the EPA to designate certain areas. This deadline is the first of three deadlines established by the U.S. District Court for the Northern District of California for the EPA to complete area designations for the 2010 SO2 NAAQS. That court decision came out of a lawsuit filed by environmental groups.
Georgia Power’s Plant Scherer is a stationary source that according to the EPA’s Air Markets Database emitted in 2012 either more than 16,000 tons of SO2 or more than 2,600 tons of SO2 and had an annual average emission rate of at least 0.45 lbs SO2/mmBTU. As of March 2, 2015, this stationary source had not met the specific requirements for being “announced for retirement,” which would exclude it from this process.
Specifically, in 2012, Scherer emitted 42,349.16 tons of SO2, and had an emissions rate of 0.372 lbs SO2/mmBTU. The 3,600-MW plant since the 1990s has been fired entirely with low-sulfur Powder River Basin coal. Plant Scherer has four sub-critical pulverized coal-fired boilers.
Pursuant to the March 2, 2015 court-ordered schedule, the EPA must designate the area surrounding the facility by July 2, 2016. In its submission, Georgia recommended that the area surrounding Plant Scherer, specifically the entirety of Monroe, Bibb, Jones, Jasper, Butts, Lamar, Upson and Crawford counties, be designated as unclassifiable/attainment based on an assessment and characterization of air quality from the facility and other nearby sources which may have a potential impact in the area of analysis where maximum concentrations of SO2 are expected. This assessment and characterization was performed using air dispersion modeling software, i.e., AERMOD, analyzing actual emissions.
Said a technical document supporting EPA’s Feb. 16 letter to the state: “After careful review of the state’s assessment, supporting documentation, and all available data, the EPA agrees, in part, that the area is attaining the standard, and intends to designate the majority of the state’s recommended area as unclassifiable/attainment, i.e., Monroe, Jones, Jasper, Butts, Lamar, Upson, and Crawford Counties. At this time, the EPA does not intend to designate Bibb County; instead, the Agency will designate this county and all other remaining undesignated areas of Georgia not addressed in this TSD by either December 31, 2017, or December 31, 2020, consistent with the deadlines of the final consent decree.”
Plant Scherer is located in central Georgia in the town of Juliette, which is in the northeastern part of Monroe County. The facility is located about three miles south of the center of Juliette, just north of Macon and approximately 70 miles south of Atlanta.
The state included Plant Scherer and no other emitters of SO2 within 50 kilometers in the area of analysis. The state evaluated offsite SO2 sources within 70 kilometers of Plant Scherer in any direction and determined that it was not necessary to include any offsite sources in order to adequately characterize air quality on the vicinity of Plant Scherer. This determination was based on the actual 2013 emissions at each facility and the distance of each facility from Plant Scherer. This distance was selected because the state believes that this area of analysis adequately represents the area where maximum concentrations of SO2 are expected.
Retirement of the coal-fired Plant Branch helped with this designation
Georgia Power’s Plant Branch coal facility in Putnam County is located about 49 kilometers northeast of Plant Scherer and 45 kilometers from the Monroe County border and reported emissions of 32,544 tons of SO2 in 2014. According to information available to the EPA, all units at Plant Branch were permanently shut down by April 2015 resulting in zero potential to emit. Plant Branch was not explicitly included in the modeling analysis for Plant Scherer, but rather was considered in the background concentrations accounting for impacts from nearby sources including Plant Branch’s historic actual emissions. In September 2013, Georgia Power retired Plant Branch Unit 2, and then Units 1, 3, and 4 in April 2015. Georgia Power certified under penalty of law that these retirements are permanent in the Retired Unit Exemption (RUE) forms submitted to the EPA.
The EPA noted that it received air dispersion modeling results from the Sierra Club, in which the club asserted that SO2 emissions from Plant Scherer, when considered alone or in tandem with other local sources, are causing a violation of the NAAQS. The Sierra Club modeling was performed using the most recent version of AERMOD, AERMET, and AERMINUTE, with data provided to the Sierra Club by regulatory air agencies and through other publicly-available sources. Sierra Club stated that the analysis was conducted in adherence to all available EPA guidance for evaluating source impacts on attainment of the 1-hour SO2 NAAQS via aerial dispersion modeling.
The state of Georgia evaluated Sierra Club’s modeling and provided an explanation in their modeling report why the conservative assumptions Sierra Club used in the modeling were not appropriate. The state said the Sierra Club modeling modeled all emissions (scrubbed and not scrubbed) out of the scrubber stack. “Clearly, this is not appropriate and will lead to unrealistically high modeled design values since uncontrolled SO2 emissions are modeled out of the shorter and cooler (less plume rise) stacks,” said the state. “As a result, the Sierra Club modeling shows modeled violations of the SO2 NAAQS while the Georgia Power modeling shows that the modeled design value is 36% below the NAAQS.”
Said EPA’s technical document: “The EPA agrees with Georgia’s assessment of the Sierra Club’s modeling. Emissions that have been scrubbed will be emitted from one of the shorter 847 feet tall stacks. Non-scrubbed emissions will emit from one of the taller 1,000 feet tall bypass stacks. The Sierra Club assumed that all emissions (scrubbed and non-scrubbed) are emitted from the shorter scrubber stacks (847 feet). This would not properly represent stack conditions when the scrubber is either not installed or turned off and the emissions are being vented to the taller bypass stack. As indicated in the excerpt above, if any portion of the actual emissions for Plant Scherer are not modeled from the appropriate stack, the difference in stack height and exit temperature could cause the model to predict reduced atmospheric dispersion therefore resulting in over-predictions of surface level ambient concentrations. Therefore, having reviewed Georgia’s modeling, Sierra Club’s modeling, and Georgia’s assessment, the EPA preliminarily agrees with Georgia’s assessment.”