# SIERRA

_ _,CLUB

FOUNOL:O 189 2 September 17, 2015 Scott Mathias Associate Director Air Quality Policy Division U.S. Environmental Protection Agency Research Triangle Park, NC 27711 Re: Air Dispersion l 'vfodeling of Nebraska Sulfur Dioxide Pollution Dear Associate Director Mathias, Sierra Club is submitting the attached modeling reports for the U . S. Environmental Protection Agency's ("EPA") consideration as it evaluates area designations for the 1

- hour Sulfur Dioxide ("SO t ) National Ambient 

### Air Quality Standard (NAAQS) in Nebraska. Air dispersion modeling recently conducted by Wingra Engineering, S.C. on behalf of S ierra Club demonstrates tl1at ambient air concentrations caused by emissions &om tl1e Gerald Gentleman and Sheldon coal-fired power plants exceed the NAAQS, which is the maximum concentration of air pollution allowed to protect public health . Using a consistent and conservative approach to modeling tl1at follows EPA guidance and regulation, the S0 2 emissions from both Gerald Gentleman and Sheldon cause downwind 

# so 2 ambient air concentrations to exceed the 196.2 micrograms per cubic meter NAAQS . In particular, tl1e modeling shows peak concentrations as high as 217 . 5 micrograms per cubic meter from Gerald Gentleman, and 208.6 micrograms per cubic meter at Sheldon Station . Based on tl1ese results, a designation of non -attainment is appropriate . While Sierra Club used tl1e state's lowest monitored value as background, consistent with EPA guidance, it is important to point out that this monitor is in highly-populated Douglas County. Sierra Club reached out to the Nebraska Department of Environmental Quality ("NDEQ") to find out how the state makes up for a rather slim monitoring network when modeling plants in more rural areas. NDEQ notified Sierra Club that it uses the Trago, K.S monitor as a s tand-in for mral Nebraska. Use of tllis background would changeLetter to Associate Director Mathias September 17, 2015 Page 2
the o utcome of S ierra Club's modeling res ults, and s hould be an area of focus for EPA when it evaluate s the impact of Nebraska's coal-fired power plants and the appropr i ate modelin g protocols necessary to ensure public hea lth is protected. Finally, while actual emissions when co mbined with a l owe r backg round concentration may n ot call for a non- attainment de s ignation, it is worth noting that the allowable emissions f o r the p lants produc e a stro nomically high modeled concentrations worthy of further review. Allowable emissio ns are relevant in determ.in.ing whether the plants threaten public heald1 s ince emissions c an always reach allowab l e le ve ls. At Gerald Gentleman S ta tion, all owab le emiss i ons would cause an impact of 809.7 microgram s per cubic meter, and at Sheldon S tati o n, allowable emissions would cause an impact of 841.2 microgram s p er cubic meter. There is no que s tion that the plants pose a threat were the y to e mit at the levels allowed b y their permits . If E PA determines not to des ignate the areas as n o nattainme nt, E P A s hould ensure that allowable emiss io ns limits are designed to protect public health. Enclosed, please find the results of the modeling analyses, a l ong with th e corresponding modeling input and o utput files . Sierra Club urges the U.S . E nv ironmental Protectio n Agency tO co n s ider this information as it und e rtakes area designations in Nebraska for the 2010 revised primary S02 NAAQS . This information i s being pro v ided to b o th E P A R egio n 7 and to appropriate p erso nnel at the Nebra ska Departmen t of Enviro nmental Quality. In the meantime , plea se let u s kn o w if we can prov ide an y addi tional information. Thank yo u for yo ur attention to and consideration of thi s matter, and p lease do not he s itate to contact us if yo u would like to dis cu ss furth er .Letter to Associate Director Mathias Septe mber 1 7, 2015 Page 

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S incerel y,

Kristin A. Henry S ierra Club 85 Second S treet, 2" d Floor San Francisco, CA 94105 415-977-5716 kristin.hcnry@sicrrac l ub.org S unil Bector Sierra Club 85 Second Street, 2"d Flo o r San Fra nci sco, Ci\ 94105 415-977-5759 s unil.bector@sicrraclub.org