Attachment 1: Supplemental Technical Support for Missouri’s Area 

Recommendations for the 2010 1-hour SO2 Standard: July 2016 

Designations 

The state recommended area designations for three parts of the state: the areas surrounding the 

Sikeston Power Station, Sibley Generating Station, and Ameren Labadie Energy Center. The 

EPA identified these three areas as meeting the criteria specified in the March 2, 2015 Federal 

Consent Decree for the next round of SO2 designations. EPA’s February 16, 2016 letter served 

as notification to the state that EPA intends to modify Missouri’s original recommendation. This 

technical analysis provides detailed information that supports Missouri’s original 

recommendation as well as addresses the concerns and issues raised by EPA in the received 

letter and TSD. 

We have performed additional analyses including updating all modeling to reflect the most 

recent year of emissions and meteorological data (2015) that was not available at the time of our 

initial recommendations. We also utilized the most recent version of EPA’s dispersion model 

and processors to take advantage of improvements made in the most recent version (version 

15181). 

Our original area recommendations and the associated modeling files are available on our 

webpage: http://dnr.mo.gov/env/apcp/naaqsboundarydesignations.htm#SO2. The changes made 

to the previously submitted modeling are outlined in this technical documentation. Excerpts of 

updated modeling files are included in Attachment 3. The modeling performed for this updated 

technical support adheres to the modeling protocol submitted with the original recommendations. 

There has been a general decrease in SO2 emissions nationwide due to the implementation of 

other federal regulations that have affected the highest SO2 emitters. Therefore it is not 

surprising that updating our modeling to include 2015 emissions does result in a slight decrease 

in modeled impacts in most cases. As detailed in EPA’s February 2016 draft, SO2 NAAQS 

Designations Modeling Technical Assistance Document (TAD), the goal of modeling for 

designation purposes is to approximate actual conditions as if a monitor were present and had 

three years of quality assured data (an approximate design value) to compare to the standard for 

compliance determination. 

Attainment Area Recommendations: 

Sikeston Power Station 

For the area surrounding the Sikeston Power Station (Sikeston), the air program reaffirms the 

recommendation of an attainment designation for Scott County. EPA has indicated they agree 

with Missouri’s proposed area boundaries and attainment classification1. The previously 

submitted modeling has been updated to reflect the most recent emissions and meteorological 

data, 2013 through 2015. The resulting approximate design value for the area still demonstrates 

                                                            

1

 EPA has reviewed the state’s assessment, supporting documentation, and all available data. EPA agrees that the 

area is attaining the standard and intends to designate Scott County as unclassifiable/attainment. 
compliance with the standard at 96 μg/m3

 (or 37 ppb). The analysis further supports the 

recommended attainment designation for Scott County. 

Sibley Generating Station 

For the area surrounding the Sibley Generating Station (Sibley), the air program reaffirms the 

recommendation of an attainment designation for a portion of Jackson County. EPA has 

indicated they agree with Missouri’s proposed area boundaries, but has modified Missouri’s 

recommendation of attainment to unclassifiable. The previously submitted modeling has been 

updated to reflect the most recent emissions and meteorological data, 2013 through 2015. The 

resulting approximate design value for the area still demonstrates compliance with the standard 

at 189 μg/m3

 (or 72.7 ppb), and supports an attainment designation. 

EPA voiced concern regarding three sources in the vicinity of the Sibley plant that could 

potentially interfere with attainment: the Veolia Energy steam plant (Veolia), the Blue Valley 

plant, and the Missouri City plant. As mentioned in the original recommendations, the Veolia 

plant is being addressed through Missouri’s Jackson County nonattainment area (NAA) plan 

(submitted to EPA on October 9, 2015). The main control strategy of the Jackson County NAA 

plan is the new federally enforceable limit for the Veolia plant. As indicated in EPA’s letter, 

Veolia’s historical emissions do model violations, but the new limitations set through the NAA 

plan demonstrate compliance with the standard. The new limits have a compliance date of 

January 1, 2017, per EPA’s April 2014 Guidance for 1-hour SO2 Nonattainment Area SIP 

Submissions. EPA’s concern that this compliance date occurs after this round’s designation date 

of July 2, 2016 is the reason Veolia was included in Sibley’s modeling analysis as an interactive 

source at their actual emission rates as reported in 2014. This is despite the fact the actual 

emission rates are approximately 80% higher than the new emission limits. It should be noted 

that modeling the higher emission rates for Veolia does not cause modeled violations within the 

attainment area boundary proposed for the Sibley plant. 

Furthermore, the air program has evaluated monitoring value trends at the nearby Troost 

monitor. Recent fuel mixture changes at the Veolia plant have had an apparent effect on the 

latest Troost monitor values, as shown in the figure below. Since December 2015, the Veolia 

plant has reportedly changed fuel combustion mixtures. Previously, Veolia primarily burned a 

mixture of 95% coal/5% Natural Gas. On December 3, 2015, Veolia reportedly began burning a 

mixture of 80% Natural Gas/15% Coal due to the low cost of natural gas and to reduce their coal 

inventory. The Veolia plant has reportedly been burning 100% natural gas since January 7, 2016 

due to the continued low price of natural gas. Veolia plans to continue burning 100% natural gas 

unless it becomes cost prohibitive in which case they will resume burning coal until their new 

emission limits become effective. 

In the figure below, the last monitored exceedance and the last monitored value above 50% of 

the NAAQS are depicted. The chart indicates a strong correlation between decreases in 

monitored values and the recent changes in Veolia’s fuel mix as discussed above. This not only 

strongly indicates that the Jackson County nonattainment area will demonstrate compliance by 

the attainment date but also that the Veolia plant will not interfere with attainment around the 

Sibley plant. Attachment 2 includes a table of recent monitoring values for all Missouri’s SO2
monitors including Troost. As of April 4, 2016, the 99th percentile 1-hour average for Troost in 

2016 is 7 ppb, which is a drastic decrease from the 99th percentile 1-hour average for 2015 of 142 

ppb. 

Troost SO2 Daily Maximum 1-hour Average Trend for 01/01/2015 - 03/14/2016 

The Blue Valley plant was included in Sibley’s modeling analysis as an interactive source at 

natural gas combustion emission rates. EPA’s concern regarding the Blue Valley plant is that 

those emission rates were not federally enforceable at the time of our recommendations, even 

though Blue Valley had already switched to exclusively burning natural gas. In an email dated 

September 30, 2015, the Blue Valley Environmental Program Supervisor confirmed the fuel 

combustion changes reflected in the facility’s permit renewal as submitted June 17, 2015. Blue 

Valley’s three primary units were built to be tri-fuel units (oil, natural gas, and coal), and are 

subject to federal regulations. Units 1 & 2 are subject to the Industrial Boiler Maximum 

Achievable Control Technology (MACT) while Unit 3 is subject to the Mercury and Air Toxics 

Standard (MATS) which have compliance dates of January 31, 2016, and April 15, 2015, 

11/12/2015

(Last Monitored

Exceedance  of the NAAQS)

82.0 ppb

12/1/2015 (Last Monitored

above 50%  of the NAAQS)

46.1 ppb

0

25

50

75

100

125

150

175

1/1/2015

1/22/20152/12/2015

3/5/2015

3/26/20154/16/2015

5/7/2015

5/28/20156/18/2015

7/9/2015

7/30/20158/20/20159/10/201510/1/2015

10/22/201511/12/2015

12/3/2015

12/24/2015

1/14/2016

2/4/2016

2/25/2016

ppb

SO2 Conc. (Reported Fuel

Mixture ‐1)

SO2 Conc. (Reported Fuel

Mixture ‐2)

SO2 Conc. (Reported Fuel

Mixture ‐3)

50% of NAAQS

SO2 NAAQS
respectively. The compliance strategy for these units as documented in their permit renewal is to 

cease burning coal and burn exclusively natural gas after January 31, 2016. Blue Valley emptied 

their coal reserves as of September 9, 2015, and indicated they do not intend to purchase more 

coal. This means that at the time of our original recommendations and with no coal reserves, the 

three Blue Valley units were already effectively only natural gas units. The federal regulations 

provide the enforceability to Blue Valley’s documented early switch to exclusively burning 

natural gas. Together these points demonstrate that the Blue Valley plant will not interfere with 

attainment around the Sibley plant. 

Lastly, the Missouri City plant was not included in Sibley’s modeling analysis as an interactive 

source as they have reportedly shut down. The Missouri City plant ceased burning coal effective 

January 31, 2016 in order to comply with the Industrial Boiler MACT. This compliance strategy 

was detailed in a City of Independence letter to the department dated July 1, 2014. Since the 

plant is not capable of burning natural gas, the cessation of coal burning effectively is the 

shutdown of the plant. This is reflected in our modeling analysis by excluding them as an 

interactive source. Since this plant is no longer emitting SO2, it will not interfere with attainment 

around the Sibley plant. 

Given these updates to our technical analysis and supporting information, we reaffirm our 

recommendation of attainment for the portion of Jackson County containing the Sibley plant. 

Unclassifiable Area Recommendation:

Ameren Labadie Energy Center 

For the area surrounding the Ameren Labadie Energy Center (Labadie), the air program 

reaffirms the recommendation of an unclassifiable area designation. EPA has indicated they 

agree with Missouri’s proposed area boundaries, but has modified Missouri’s recommendation of 

unclassifiable to nonattainment. The previously submitted modeling was updated to reflect the 

most recent emissions and meteorological data, 2013 through 2015. These model results further 

support an unclassifiable classification. 

The air program performed two modeling scenarios to characterize the air quality around the 

Labadie facility. In the first scenario, the only change made to the modeling submitted with our 

original recommendation was to include 2015 hourly emissions and meteorological data. This 

scenario resulted in a decrease in the approximate design value of the area from 234 μg/m3

 (or 90 

ppb) to 201 μg/m3 (or 77 ppb). In the second scenario, units 3 and 4 were modeled as a single 

release, or merged plume, as described below. This resulted in an approximate design value of 

175 μg/m3

 (or 67 ppb) which is in compliance with the 1-hour standard of 75 ppb. 

Two EPA Model Clearinghouse Information Storage and Retrieval System records (MCHISRS), 

91-II-01 2

and 96-V-103 describe situations in which multiple stacks/flues were allowed to be 

                                                            

2 91‐II‐01, EPA Model Clearinghouse Information and Storage Retrieval System: EPA Region II Correspondence re

NJ PSD Source, August 1990.   

https://cfpub.epa.gov/oarweb/MCHISRS/index.cfm?fuseaction=main.resultdetails&recnum=91‐II%20%20‐01  
treated/modeled as a single source. Units 3 and 4 at Labadie are vented through two flues 

contained in a singular outer annulus or stack. This fits the description in the records of a multiflued stack that could be treated as a single source. In addition, EPA Region VII has indicated 

that treating the flues as one stack is reasonable for designation purposes in order to approximate 

actual dispersion conditions. To be complete, both scenarios, where the flues are modeled 

separately and as a single source, are included in this analysis. 

As described in the two referenced EPA records, it is reasonable to treat multi-flued stacks as a 

single source in most cases. When modeled as a single source the flow parameters are 

combined. A general guideline is if the flues/stacks are closer together than their respective 

widths/diameters then they may be treated as a single source. This is based upon the logic laid 

out in the GEP stack height guideline regarding treating buildings that are closer than their 

individual widths as a single building when using the stack height formula. 

The air program employed the below methodology when combining the flues. This facilitysupplied approach was determined to be a reasonable method for accurately combining the flues’ 

release parameters. 

1) Emission rate: The emission rate for Unit 3 and Unit 4 were summed. 

2) Temperature: The combined temperature for Units 3 and 4 was calculated from the 

weighted average of the: (Unit 3 temperature * Unit 3 velocity) + (Unit 4 temperature * 

Unit 4 velocity) / (Unit 3 velocity + Unit 4 velocity) 

3) Velocity: The combined velocity for Units 3 and 4 was calculated from the: sum of the 

Unit 3 and 4 velocities * (pi * (6.25 (single flue diameter)^2) / (pi * 8.84 (equivalent dual 

flue diameter)^2) 

In addition to these two modeling evaluations of the Labadie facility, preliminary data from new 

ambient SO2 monitors near the plant is available. Since the start of operation in April 2015, these 

monitors have been measuring SO2 concentrations below the 1-hour SO2 standard of 75 ppb. The 

state statute, Section 643.650, RSMo, (SB 445 and HB 92 from the 2015 legislative session), 

which became effective August 28, 2015, directs the department to consider SO2 monitoring data 

for sources that choose to monitor to characterize their air quality. Though the dataset from 

Labadie’s new SO2 monitors is not yet complete, it further supports the unclassifiable 

designation for the area and we must consider it, consistent with state law. Attachment 2 includes 

a table of recent monitoring values for all Missouri’s SO2 monitors including the two newly sited 

monitors near Labadie, the Valley and Northwest sites. 

Because it cannot be determined with certainty based on available information whether the area 

is or is not meeting the 1-hour SO2 standard, the air program again recommends an unclassifiable 

designation for the area near Labadie. 

 

                                                                                                                                                                                                3 96‐V‐10, EPA Model Clearinghouse Information and Storage Retrieval System: EPA Region V Correspondence re

Ohio Bubble, August 1996.   

https://cfpub.epa.gov/oarweb/MCHISRS/index.cfm?fuseaction=main.resultdetails&recnum=96‐V%20%20%20‐10