2010 SO2 NAAQS (75 Fed. Reg. 35520)

District of Columbia Infrastructure SIP

June 2014

 

ATTACHMENT B

Section 110(a)(2)(D)(i): Interstate Transport Provisions, Part I

Include an explanation in support of the conclusion that no source will contribute significantly to 

nonattainment or interfere with maintenance of the SO2 NAAQS in another state. 

The District of Columbia (District) has recommended an unclassifiable designation for the 2010 sulfur 

dioxide (SO2) national ambient air quality standards (NAAQS). This is at least in part because no 

source in the District contributes significantly to nonattainment or interferes with maintenance of the 

2010 SO2 NAAQS in another state. No source has caused a violation of the 2010 SO2 NAAQS and no 

source emits quantities that are potentially of concern. 

No SO2 NAAQS Violations

To date, the District operates two ambient air monitors to measure SO2: one long-term monitor at the 

River Terrace site, and one new trace-SO2 monitor at the McMillan NCore site that was deployed in 

2011. The River Terrace monitor has never shown a violation of any SO2 standard, as demonstrated in 

Figure 1. 

Figure 1. Monitored SO2 Concentrations in the District Over Time
Insignificant Contribution

In the SO2 NAAQS final rule (75 Fed. Reg. 35520), the U.S. Environmental Protection Agency (EPA) 

ruled that it would be reasonable to expect states to demonstrate, at a minimum, that major SO2 sources 

(≥ 100 tpy) are not causing or contributing to violations of the 1-hour SO2 NAAQS.” 

A letter to the District Department of the Environment (DDOE) Director on April 12, 2012, from EPA

suggested that, “EPA’s discussions with stakeholders about how best to implement the NAAQS may 

result in changes to our previously described recommendations for implementing the SO2 standard in 

unclassifiable areas.” EPA recommended focusing on “the traditional infrastructure elements of Clean 

Air Act sections 110(a)(1) and (2), rather than on modeling demonstrations showing future attainment of 

the standard by a fixed date,” as initially required in the final SO2 NAAQS rule and further described in 

the draft implementation guidance.

EPA’s 2013 document1suggested a potential revision to the emissions threshold to 2000 to 3000 tons 

per year (tpy) for sources in densely populated areas that are part of a core-based statistical area (CBSA) 

of more than one million people.

In the District, there is only one source that has emitted relatively large amounts of SO2: the U.S. Capitol 

Power Plant (CPP). Total emissions of SO2 from the facility have been well below even half of EPA’s

potential threshold, or less than 1000 tons per year, since 2002. Historically, two of the large boilers at 

the facility have burned coal, which contains sulfur, as a fuel source. In recent years, the use of coal at 

CPP has dropped dramatically. Figure 2 demonstrates that the reduced use of coal has resulted in a 

similar drop in SO2 emissions in recent years.

Figure 2. Capitol Power’s Coal Use and SO2 Emissions

Emissions of SO2 from CPP are expected to remain low because of recently finalized air quality permit 

actions. On June 6, 2013, DDOE issued final permits that established facility-wide emission limits at 

CPP. The permits also allow for the installation of a highly efficient natural gas-fired cogeneration 

 

1 U.S. EPA, “Next Steps for Area Designations and Implementation of the Sulfur Dioxide National Ambient Air Quality 

Standard” (February 6, 2013), found at: http://www.epa.gov/airquality/sulfurdioxide/pdfs/20130207SO2StrategyPaper.pdf. 
system at the facility that will reduce its reliance on coal-burning units. The facility’s potential to emit 

SO2 is less than 3,900 tons per year, even with a cogeneration system fully constructed2. After the 

cogeneration plant is commissioned and operational, the facility is required to cease burning coal except 

in very infrequent force majeure situations.

3

 

There are only two other major source facilities in the District that typically emit more than one ton of 

SO2 per year: Pepco-Benning Road Generation Station and U.S. General Services Administration. The 

following chart shows SO2 emissions for each facility in recent years, primarily due to the usage of oil:

Figure 3. SO2 Emissions (tpy) from Other Facilities in the District

Facility 2008 2009 2010 2011 2012

Pepco-Benning 278.1 106.9 871.7 510.8 21

U.S. GSA 3 1.6 1.5 1.4 15.7

Pepco-Benning’s two electric generating units (EGUs) that emitted a majority of the facility’s SO2

emissions shut down in 2012. The closure was a permit condition submitted as part of a State 

Implementation Plan (SIP) revision to address the Clean Air Act’s requirements for Regional Haze, 

which was approved by EPA on February 2, 2012 (77 Fed. Reg. 5191).

SO2 emissions at GSA are not expected to substantially increase in the future, especially with the 

District’s new source review program (20 DCMR Chapter 2) and prevention of significant deterioration 

federal implementation plan (PSD FIP), which both control emissions due to facility changes. There is a 

plant-wide emission limit for SO2 in GSA’s Title V permit of 17 tons per year. 

Additional SO2 controls in the District’s SIP include sulfur content limits on fuel oil (20 DCMR § 801), 

a high enhanced inspection and maintenance (I/M) program (see 40 C.F.R. § 52.470(c)), and numerous 

Federal PM2.5 measures.

No Interference with Maintenance (Prong 2)

There are no nonattainment areas for SO2 within a 50-kilometer radius of the District, which is the 

standard distance generally considered by EPA for air dispersion modeling (Appendix W to 40 C.F.R. 

Part 51). The most recent design values (DVs) computed using quality-assured and certified ambient air 

modeling data, based on the Federal Reference Method or an equivalent monitoring measurement, and 

reported to EPA’s Air Quality System (AQS) in states bordering the District are in Figure 4:

Figure 3. Recent 1-Hour NAAQS Design Values at Monitors 

in Maryland and Virginia (in parts per billion)

State County Site ID

2008-

2010

2009-

2011

2010-

2012 

Maryland Garrett County 24-023-0002 41 31 19

Maryland Prince George's County 24-033-0030 21 15 11

 

2 The Capitol Power Plant does not have a plant-wide emission limit for SO2. According to their 2009 Title V permit 

application, their potential to emit SO2 was 3875.1 tpy. Construction of the cogeneration project would add 8.4 tpy.

3 DDOE, “District Issues Air Quality Permits for Cogeneration Equipment at the U.S. Capitol Power Plant” (June 6, 2013), 

found at: http://ddoe.dc.gov/release/district-issues-air-quality-permits-cogeneration-equipment-us-capitol-power-plant. 
State County Site ID

2008-

2010

2009-

2011

2010-

2012 

Virginia Charles City County 51-036-0002 50 43 34

Virginia Richmond city 51-760-0024 39 35 25

Virginia Roanoke County 51-161-1004 11 10 8

Virginia Rockingham County 51-165-0003 11 9 6

Source: “Design Values” on EPA website at: http://www.epa.gov/airtrends/values.html; 

only complete and valid data

All nearby DVs are well below the 2010 1-hour NAAQS for SO2 of 75 ppb. Since there are also no 

nearby areas violating the SO2 NAAQS, the District has no reason to believe that any monitors 

identified in the table above may have difficulty maintaining the SO2 standards, particularly as a result 

of emissions from the District.

Conclusion

Since the District’s largest sources of SO2 emissions emit far less than EPA’s initially proposed

threshold for study of 100 tpy, there is no reason to believe that any source in the District will contribute 

significantly to nonattainment or interfere with maintenance of the SO2 NAAQS in another state. 

Currently, the District is not aware of any plans to establish a source that emits substantial amounts of 

SO2 within its borders. Thus, it is reasonable to conclude that no source will contribute significantly to 

nonattainment or interfere with maintenance of the NAAQS in another state.