New air emissions controls for the Big Stone coal plant in South Dakota are a help, but the U.S. Environmental Protection Agency still couldn’t declare the area around the plant as being in attainment for the SO2 NAAQS, though it didn’t declare the area in nonattainment either.
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). The CAA defines a nonattainment area as one that does not meet the NAAQS or that 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.
South Dakota submitted updated recommendations to EPA in September 2015, ahead of a July 2, 2016, deadline for the EPA to designate certain areas around the country established by the U.S. District Court for the Northern District of California in a March 2015 order. That order settled a lawsuit filed by two environmental groups. This July 2 deadline is the first of three deadlines established by the court for the EPA to complete area designations for the 2010 SO2 NAAQS. On Feb. 16, EPA sent a letter to North Dakota with its preliminary decision on the one affected area in the state.
The Grant County area contains 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 pounds of SO2 per one million British thermal units (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 consideration. In 2012, the coal-fired Big Stone Plant emitted 12,290 tons of SO2, and had an emissions rate of 0.81 SO2/mmBTU.
In its submission, South Dakota recommended that the area surrounding the Big Stone Plant, specifically the entirety of Grant County, be designated as attainment. Said EPA: “After careful review of the State’s assessment, supporting documentation, and all available data, the EPA does not agree with the State’s recommendation for the area, and intends to designate the area as unclassifiable. Specifically, based on available information we are not able to determine whether the area is meeting or not meeting the NAAQS, and our intended unclassifiable area consists of Grant County.”
The EPA said it recognizes that control strategies implemented after the release of a 2011 emissions assessment may not be reflected, or may warrant further discussion. In its designation recommendation, the state indicated that SO2 pollution controls required as part of the state’s regional haze plan (approved by EPA in April 2012) would be installed and operational at the Big Stone facility by fall of 2015. The regional haze State Implementation Plan (SIP )requires the installation of semi-dry flue gas desulfurization (FGD), which was estimated to reduce SO2 levels at the facility by 90%, for an estimated 1,880 tons/year of SO2 from the facility.
New air systems went commercial at end of December
The Big Stone air quality control system (AQCS) project was declared commercially operational on Dec. 29, completing six years of effort, plant operator Otter Tail Power told the Minnesota Public Utilities Commission in a Jan. 13 quarterly update. Testing of the systems and demolition of obsolete facilities will continue, but there is nothing foreseen that will keep the project from coming in at, or under budget, Otter Tail added. The commission had approved this project on this South Dakota power plant in January 2012.
The 475-MW Big Stone plant is majority owned by Otter Tail Power, with other shares held by NorthWestern Energy and Montana-Dakota Utilities. The AQCS project includes a scrubber and selective catalytic reduction.
Otter Tail Power, a subsidiary of Otter Tail Corp. (NASDAQ Global Select Market: OTTR), is headquartered in Fergus Falls, Minnesota. It provides electricity and energy services to more than a quarter million people in Minnesota, North Dakota, and South Dakota.