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 ("SOt ) National Ambient Air Quality Standard (NAAQS) in Nebraska. Air 

dispersion modeling recently conducted by Wingra Engineering, S.C. on behalf of Sierra 

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 S02 emissions from both Gerald Gentleman and Sheldon cause 

downwind so2 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 stand-in for mral Nebraska. Use of tllis background would change 
Letter to Associate Director Mathias 

September 17, 2015 

Page 2 

the outcome of Sierra Club's modeling results, and should be an area of focus for EPA when 

it evaluates the impact of Nebraska's coal-fired power plants and the appropriate modeling 

protocols necessary to ensure public health is protected. 

Finally, while actual emissions when combined with a lower background 

concentration may not call for a non-attainment designation, it is worth noting that the 

allowable emissions for the plants produce astronomically high modeled concentrations 

worthy of further review. Allowable emissions are relevant in determ.in.ing whether the 

plants threaten public heald1 since emissions can always reach allowable levels. At Gerald 

Gentleman Station, allowable emissions would cause an impact of 809.7 micrograms per 

cubic meter, and at Sheldon Station, allowable emissions would cause an impact of 841.2 

micrograms per cubic meter. There is no question that the plants pose a threat were they to 

emit at the levels allowed by their permits. If EPA determines not to designate the areas as 

nonattainment, EPA should ensure that allowable emissions limits are designed to protect 

public health. 

Enclosed, please find the results of the modeling analyses, along with the 

corresponding modeling input and output files. 

Sierra Club urges the U.S. Environmental Protection Agency tO co nsider this 

information as it undertakes area designations in Nebraska for the 2010 revised primary S02 

NAAQS. This information is being provided to both EPA Region 7 and to appropriate 

personnel at the Nebraska Department of Environmental Quality. In the meantime, please 

let us know if we can provide any additional information. 

Thank you for your attention to and consideration of this matter, and please do not 

hesitate to contact us if you would like to discuss further. 
Letter to Associate Director Mathias 

September 17, 2015 

Page 3 

Sincerely, 

Kristin A. Henry 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, CA 94105 

415-977-5716 

kristin.hcnry@sicrraclub.org 

Sunil Bector 

Sierra Club 

85 Second Street, 2"d Floor 

San Francisco, Ci\ 94105 

415-977-5759 

sunil.bector@sicrraclub.org