UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

The Honorable Martha E. Rudolph 

Director 

MAR 2 0 2015 

Colorado Department of Public Health and Environment 

4300 Cherry Creek Drive South 

Denver, Colorado 80246 

Dear Ms. Rudolph: 

OFFICE OF 

AIR AND RADIATION 

I am writing to update you on the status of the U.S. Environmental Protection Agency's progress in 

implementing the primary National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (S02) 

set in 20 I 0 at 75 parts per billion (ppb) as a !-hour average. In July 20 13, the EPA identified areas in 16 

states as nonattainment and expressed the intent to address designations for the remainder of the country 

in separate future actions. 

On March 2, 2015, the U.S. District Court for the Northern District of California accepted as an 

enforceable order an agreement between the EPA and Sierra Club and Natural Resources Defense 

Council to resolve litigation concerning the deadline for completing the designations. The court's order 

directs the EPA to complete designations in three additional rounds: the first round by July 2, 2016, the 

second round by December 31 , 2017, and the final round by December 31, 2020. The EPA will 

complete these designations by designating areas as either nonattainment, unclassifiable/attainment, or 

unclassi fiable. 

In the first round of designations, the EPA will designate two groups of areas: I) areas that have newly 

monitored violations of the 20 I 0 S02 standard, and 2) areas that contain any stationary source that 

according to the EPA's Air Markets Database either emitted more than 16,000 tons ofS02 in 2012 or 

emitted more than 2,600 tons of S02 and had an emission rate of at least 0.45 lbs S02/mmbtu in 2012 

and that has not been announced (as ofMarch 2, 2015) for retirement. In the enclosure to this Jetter, the 

EPA provides the schedule we intend to follow to meet the July 2, 2016, deadline. 

The EPA has identified the following electric power plant sources in your state as meeting the criteria 

established in the court's order: 

2012 S02 2012 S02 

State County Facility Name Emissions Emissions Rate 

(tons) (lb/mmbtu) 

co El Paso Martin Drake Power Plant 4,792 0.565 

co Morgan Pawnee· Generating station 13,510 0.762 

Internet Address (URL) • http://www.epa.gov 

Recycled/Recyclable • Printed with Vegetable Oil Based Inks on 100% Postconsumer. Process Chlorine Free Recycled Paper 
The EPA will use the most recent available information when making designation and boundary 

decisions for the indicated areas. If you would like to submit an updated recommendation and 

supporting information for the EPA to consider for the affected areas in your state, we request that you 

do so by September 18,20 15. 

The EPA has updated its March 24, 2011, designation guidance for the 2010 S02 standard to support 

analysis of designations and boundaries for these next rounds of designations. The updated guidance can 

be found on the EPA's website at htLp:l/epa.gov!airqualitv!sul{urdioxide/guidance.html. The EPA has 

also provided two technical assistance documents that provide advice on the use of modeling and 

monitoring data when determining if an area is meeting or not meeting the 2010 S02 standard. These 

documents can be found on the EPA's website at hllp:l!epa.gov/airqualitv/sul{urdioxidelimplement.htm/. 

The court's order directs the EPA to complete the second round of area designations by December 31, 

2017. These designations would address areas where states have not installed and begun operating a new 

S02 monitoring network meeting the EPA's specifications referenced in our proposed rule titled, "Data 

Requirements Rule for the !-hour S02 primary NAAQS". This rule, which was proposed in the Federal 

Register on May 13, 2014, would direct state and tribal air agencies to provide data to characterize 

current air quality in areas with large sources of S02 if such areas do not have sufficient air quality 

monitoring in place to identify maximum S02 concentrations. The data collected as a result of this 

proposed rule would be used in the designations process. Lastly, the cou1t's order directs the EPA to 

designate all remaining areas by December 31 , 2020. The EPA will provide states with additional 

information on the designations process associated with these later deadlines at a later date. 

We look forward to continued dialogue with you and your staff as we work together to implement the 

2010 S02 standard and achieve its intended public health protection. For additional information 

regarding designations for the 2010 so2 standard, please visit our website at 

www.epa.gov/so2designations. Should you have any questions, please do not hesitate to call me or Scott 

Mathias of my staff at 919-541-5310 and mathias.scott@epa.gov. 

Sincerely, 

Janet G. McCabe 

Acting Assistant Administrator 

Enclosure 

cc: Shaun McGrath 

EPA Region 8 Administrator 
ENCLOSURE 

TIMELINE FOR 2010 PRIMARY S02 NAAQS DESIGNATION PROCESS FOR AREAS 

ASSOCIATED WITH JULY 2, 2016, COURT-ORDERED DEADLINE* 

Milestone Date** 

Court Order March 2, 2015 

States may submit updated recommendations No later than September 18, 2015 

and supporting information for area 

designations to the EPA 

The EPA notifies states concerning any ola January 22, 2016, but absolutely no later 

intended modifications to their than 120 days prior to final designations, i.e. , 

recommendations ( 120-day letters) March 2, 2016 

The EPA publishes public notice Of state o/a February 3, 2016 

recommendations and the EPA's intended 

modifications and initiates 30-day public 

comment period 

End of 30-day public comment period o/a March 4, 2016 

States provide additional information to o/a April 8, 2016 

demonstrate why an EPA modification is 

inappropriate 

The EPA promulgates final S02 area No later than July 2, 2016 

designations (no later than 16 months from 

Court Order) 0 0 *The court's order directs the EPA to promulgate additiOnal rounds of designations by 

December 31, 2017, and by December 31 , 2020. 

* * o/a = on or about