1

Review and Analysis of Sierra Club Submitted Zimmer Generating Station Evaluation of Compliance with the 1

- hour NAAQS for SO 2

Ohio EPA

Division of Air Pollution Control

Introduction

The United States Environmental Protection Agency (U.S. EPA) established a new National Ambient Air Quality Standard (NAAQS) for SO 2 on June 22, 2010, of 75 ppb, as the 99 th percentile of maximum daily values, averaged over three years. In addition, U.S. EPA revoked the primary annual and 24

- hour standards.

On August 5, 2013 (75 FR 47191), effective October 4, 2013, U.S. EPA promulgated the initial SO 2 nonattainment areas for the newly established SO 2 standard across the country. On March 2, 2015, the U.S. District Court for the Northern District of California accepted as an enforceable order an agreement between the U.S. EPA and Sierra Club and the Natural Resources Defense Council to resolve litigation concerning the deadline for completing designations. The court’s order directs U.S. EPA to complete designations in three st eps: the first by July 2, 2016; the second by December 31, 2017 and the third by December 31, 2020. As part of the first round of designations, U.S. EPA has identified areas with newly monitored violations of the standard, or areas that contain stationary sources that emitted more than 16,000 tons of SO 2 in 2012 or emitted more than 2,600 tons of SO 2 and had an emission rate of at least 0.45 lbs SO 2 /MMBtu in 2012. The U.S. EPA has identified two facilities in Ohio as meeting one or more of these criteria: the General James M. Gavin Plant and the W.H. Zimmer Generating Station.

On September 16, 2015, Ohio EPA submitted recommendations of attainment for both the General James M. Gavin (including Kyger Creek) and W.H. Zimmer Generating Station source areas bas ed on a five factor analysis, inclusive of refined dispers ion modeling. On this same date , Sierra Club submitted dispersion modeling results and a recommendation of nonattainment for both areas.

This document is Ohio EPA’s analysis and response to Sierra Club’s modeling and recommended designation for the W.H. Zimmer Generating Station source area

. Ohio EPA has included for completeness Sierra Club’s modeling analysis report for both the W.H. Zimmer and General James M. Gavin power plants as Appendix A.

Modeling Approach

Per U.S. EPA’s Modeling Technical Assistance Document ( TAD )

,

“ Since the purpose here pertains to designations, this guidance supports analyses of existing air quality rather than analyses of emissions limits necessary to provide for attainment

. Consequently, the guidance in this TAD differs in2

selected respects from the guidance published in Appendix W. These differences include:

 Placement of receptors only in areas where it is feasible to place a monitor vs. all ambient air locati ons (NSR, PSD, and SIP)

 Use of the most recent 3 years of actual emissions (designations) vs. maximum allowable emissions (NSR, PSD, and SIP)

 Use of 3 years of meteorological data (designations) vs. one to five years (NSR, PSD, and SIP)

 Use of actual stack height for designations using actual emissions vs. Good Engineering Practice (GEP) stack height for other regulatory applications (NSR, PSD, and SIP)”

The Sierra Club incorporated some, but not all, of the items listed above

. Contrary to the specifications identified above, the Sierra Club also modeled allowable SO 2 limits and proposed an emissions reduction for the W.H. Zimmer Generating Station, d espite the fact their modeling does not show the W.H. Zimmer Generating Station causing or contributing to any exceedance of the standard over the period modeled. Further, Sierra Club placed receptors in areas that would be considered “inside the fenceline” for all sources included in the modeling domain. These are severe flaws in th e analysis.

The a veraging period for the 2010 SO 2 NAAQS is the 99 th percentile of maximum monitored daily values, averaged over three years . Per t he Modeling TAD, three years of National Weather Se rvice data is sufficient to allow the modeling to simulate a monitor . Thus, the modeled form of the standard is expressed as the 99 th percentile of maximum daily values averaged over three years (herein referred to as “design value”) for the purposes of designation.

The recommended dispersion model for modeling for SO 2 designations is the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) modeling system. There are two input data processors that are regulatory components of the AERMOD modeling system: AERMET, a mete orological data preprocessor that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, and AERMAP, a terrain data preprocessor that incorporates complex terrain using United States Geological Survey (USGS ) Digital Elevation Data. Additionally, Sierra Club u tilized the AERMINUTE module to incorporate 1

- minute ASOS meteorological data into the hourly surface input file. Sierra Club utilized the most
up

- to

- date versions of AERMOD and the associated preproces sors available at the time of modeling analyses. Tho se versions used are as follows: AERMOD version 14134, AERMET version 14134, AERMINUTE version 142 37, and AERMAP version 11103

. Meteorological Data

M eteorological data from 2012

- 2014 from the Cincinnati , OH surface station (Station # 93814 ) located at the Cincinnati/Northern Kentucky International Airport and the Wilmington, OH up per air station (Station # 13841 ) located at the Wilmington Airborne Airpark were used in the Sierra Club analyses. These site s have previously been3

determined by Ohio EPA to be representative of Clermont County , OH and the surrounding region . AERSURFACE was run using twelve sectors and four seasons, centered on the location of the meteorological station, using average moisture

c onditions and continuous winter snow cover. T he Sierra Club used a meteorological data set for their modeling analyses consistent with what Ohio EPA would use to perform modeling in this area.

Background

A background concentration of 23.5  g/m 3 (8.98 ppb ), was included in all modeling analyses conducted by Sierra Club in the W.H

. Zimmer source area. This background

wa s based on the design value recorded at the Allen County air quality monitor, 39

- 003

- 0009. Sierra Club chos e this monitor because it recor ded the lowest monitored design value i n Ohio for the 2011

- 2013 period

. This is not a background monitor. This monitor is located downwind of the city of Lima, Ohio and a large refining/petrochemical facility. Additionally, there is a major interstate hi ghway close to this location. There are several other sources of information that would indicate a background SO 2 concentration of 28.776  g/m 3 for the specific source area, as used in the Ohio EPA modeling. Sierra Club utilized the 2011

- 2013 period, rather than 2012

- 2014, which would encompass those years actually modeled. Why this period was chosen is unclear

. T his source area has multiple SO 2 monitors which were active during the 2012

- 2014 period

. Ohio EPA further notes that the background used in Ohio’s recommended designation was 11 ppb (28.776  g/m 3 )

, and was based on a more local monitor with careful consideration of those sources not explicitly modeled in the domain.

Emission Sources

The Sierra Club modeled emissions from the W.H. Zimmer Generating Station, DTE St. Bernard, and the Spurlock Station. Of the three SO 2 sources at the W.H. Zimmer Generating Station, Sierra Club modeled only the main boiler. The single SO 2 source at DTE St. Bernard w as modeled as a single egress point, and th e four SO 2 sources at Spurlock Station were modeled as four separate egress points. The stack parameters for each source included in Sierra Club’s analyses are shown in Table 1.

Table 1 : Release point parameters for all sources i ncluded in Sierra Club modeling, W.H. Zimmer

source area.
Ohio EPA has serious reservations and concerns with respect to the quality of emissions data modeled and the choice of facilities to include in the modeling domain. These concerns are detailed here

.
Emissions Data4

Sierra Club used hourly variable emissions inputs for the W. H. Zimmer Generating Station and Spurlock Station for years 2012

- 2014. These data were obtained from U.S. EPA’s Air Markets Program Data. Ohio EPA does not consider Air Markets Program Data ideally acceptable for use as input into a refined dispersion model for multiple reasons. Firs tly, data reported to the Air Markets Program is done so for the accounting of emission allowance consumption , in accordance with Part 75 monitoring and reporti ng requirements . Accordingly, the data tends to overstate emissions when there are errors in the monitorin g equipment or periods of missing data , as described in the Part 75 monitoring and reporting requi rements. The data substitution methodologies employed via Part 75 requirements can lead to severe overestimations of emissions data. These data were never intended to serve as a repository for hourly emissions suitable for refined dispersion modeling. In addition to overstating emissions, the database does not contain hourly exit temperature values, which are a critical component necessary to accurately model hourly plume rise and exit velocities. The shortcomings of the Air Markets Program data are made more apparent when applied to stringent 1

- hour standards. The hourly emissions database utilized by the Ohio EPA

w as the result of extensive analysis and consultation with relevant plant operators and technical staff to identify spurious emissions data an d to compile a complete and accurate hourly database of emissions, exit temperatures, and exit velocities for each source included in the modeling domain. In addition to the use of inappropriate hourly emissions data, the Sierra Club modeled the DTE St. B ernard facility at a fixed emission
rate based on 2014 actual SO 2 emissions, averaged across 8,760 hours of operation

. Fixed emission rates are not representative of operations at this facility, and all but guarantee tha t worst

- case, unrealistic impacts a re generated

. This is particularly so when modeling for stringent 1

- hour standards.

Sierra Club states that their use of fixed maximum exhaust flow rates and temperatures tends to under

- predict impacts. Ohio EPA’s experience would indicate that this is n ot the case, and neglects the complexities of, for example, AERMOD’s treatment of the penetrated plume and the impact of temperature inversions on ground level impacts. Ohio EPA contends that an accurate treatment of actual emissions necessitates the incl usion of variable exhaust velocities and temperatures in addition to variable emissions. This is of particular importance when the intent of the designations modeling is to treat receptors as a surrogate for air quality monitors.

In the second portion of Sierra Club’s modeling analysis, allowable emissions were modeled for all sources listed in Table 1, above. Ohio EPA did not extensively analyze this portion of Sierra Club’s analysis, as the modeling of allowable emissions is inconsistent with intent of the both the consent decree and the final Data Requirements Rule. U.S. EPA’s March 20, 2015 memorandum entitled Updated Guidance for Area Designations for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard lists the following recommendations for designating source areas via modeling explicitly:

° using actual emissions as an input for assessing violations to provide results that reflect current actual air quality (i.e., modeling that simulates a monitor);5

° using 3 years of modeling results to calculate a simulated design value consistent with the 3

-

year monitoring period required to develop a design value for comparison to the NAAQS;

° placing receptors only in locations where a monitor could be pl aced; and

° using actual stack heights rather than following the Good Engineering Practice stack height policy when using actual emissions.

Thus, Sierra Club’s inclusion of allowable emissions is inconsi stent with U.S. EPA policy for the purposes of de signations and the conclusion drawn by Sierra Club from this modeling should be dismissed

. Further, there is no regulatory rationale for the Sierra Club ’s suggest ed emission reductions at the W.H. Zimmer facility based on these flawed results. Sierra Club’s own modeling indicates that the W.H. Zimmer facility does not cause or contribute to an exceedance of the standard over the 2012

- 2014 period.

E xplicitly Modeled Facilities

As stated previously, the Sierra Club modeled the DTE St. Bernard facilit y and Spurlock Station in addition to the William H. Zimmer Generating Station. While these facilities do fall within a 50 km radius of the source area, both facilities are located more than 40 km distant, and are highly unlikely to cause a significant co ncentration gradient within the area impacted by the William H. Zimmer Generating Station. Indeed, Sierra Club’s modeling analysis demonstrates this clearly. Further, DTE St. Bernar d is converting its single coal

- fired boiler to natural gas by the beginn ing of 2016 and accepting new federally enforceable permit limits (Appendix B ) . Under the Data Requirements Rule, any facility which will have a federally enforceable permit limit below 2,000 TPY of SO 2 in place by January 2017 can be excluded from the modeling domain. Further, DTE St. Bernard falls below the 2,000 TPY emission limit established in the Data Requirements Rule with 2014 SO 2 emissions of 1,666 tons. According to Appendix B , DTE St. Bernard anticipates its post

- conversion “potential” emissions to be less than 56 TPY. As such, it is inappropriate to include DTE St. Bernard in the modeling domain considering 2014 emissions place s the facility outside of the scope of the Data Requirements Rule

, the facility has exceptionally low post

- conversion emissions, and the facility is at a distance of greater than 40 kilometers from the source area

. Ohio EPA’s modeling experience with the 1

- hour SO 2 standard suggests that, even for sources much larger than DTE St. Bernard, ground level impacts decrease dramatically within a few kilometers of the

source

. If it was Sierra Club’s intention to model all major sources operating in the W.H. Zimmer source a rea during years 2012

- 2014, it is unusual and arbitrary that DTE St. Bernard would be included, while the W.C. Beckjord facility, the largest source of SO 2 in the source area during that time period , would be excluded. Sierra Club did not provide an expla nation for why DTE St. Bernard was included.

In addition to the DTE St. Bernard facility, the Sierra Club explicitly modeled emissions from the Spurlock power plant. This facility is located approximately 40 kilometers to the southwest of the W.H. Zimmer facility. Given this distance and considering the primary southwest to northeast of the prevailing winds in the source area, Ohio EPA determined that this facility was unlikely to contribute to a concentration gradient beyond6

what was accounted for in Ohi o EPA’s conservative and carefully considered background of 10 ppb. To demonstrate this, Ohio EPA conducted an analysis of the impacts of Spurlock station at all receptors demonstrating a concentration greater than

one

- half of the standard (98.1  g/m 3 and greater) in Sierra Club’s modeling analysis. To avoid double counting of the background concentration, Ohio EPA did not include Sierra Club’s background in this analysis. These results are shown in Figure 1, below.

Figure 1 : Sierra Club modeled impacts of Spurlock power plant on W.H. Zimmer source area, 2012

- 2014. Concentrations in  g/m 3 , without background.
Figure 1 demonstrates that the impacts of Spurlock station at critical receptors in the W.H. Zimmer source area are b etween 3 and 10  g/m 3 . Ohio EPA notes here that receptors to the north, near the DTE St. Bernard facility, were excluded from Figure 1 for clarity. Impacts at those receptors are between 2 and 5  g/m 3 . The maximum impact of the Spurlock facility in the critical receptor grid is 10.16  g/m 3 , or 3.9 ppb. Ohio EPA notes here tha t these impacts are based on an inappropriate and overly

conservative emissions database. It is likely that, were a refined an d representative emissions database utilized for the Spurlock facility, these impacts would lessen further. Ohio EPA also notes that, with a carefully considered and more representative7

background such as that used by Ohio EPA, the impacts of the Spurlock station on the W.H. Zimmer source area would be adequately and conservatively represented.

Receptors

The Sierra Club conducted modeling analyse s on a three

- tiered receptor grid consisting of 21,201 discrete receptors. The first grid is a grid of 10 0 meters spacing extending from the W.H. Zimmer Generating Station to 5 km. The second is a grid of 500 meters spacing extending to 10 k ilometers. The final gird has a 1,000 meters spacing and extends to 50 kilometers. The elevations of these receptors were determined using AERMAP v. 11103 and 1 arc

- second resolution National Elevation Dataset (NED) files. No attempt was made by Sierra Club to exclude receptors located in bodies of water, in locations where monitor placement would not be feasible, or in areas that would be considered “inside the fenceline” of the various sources. Figure 2 shows the receptor grid utilized by Sierra Club and the location of the explicitly modeled facilities. Note that Ohio EPA included an additional receptor at the location of AQS monitor 39

- 061

- 0040. Ohio EPA included this additional receptor as i t is cus tomary and appropriate modeling practice to include receptors at the location of ambient air quality monitor s whenever possible. Inclusion of relevant monitors provides a convenient, transparent, and scientifically valid means to evaluate and assess model performance, and is done so by Ohio EPA in all situations where a representative monitor is located within a modeling domain. Furthermore, this receptor falls within a “hotspot” of modeled SO 2 impacts and can be used to assess the accuracy of Sierra Club’ s modeling results

. Ohio EPA suggests that Sierra Club’s omission of this critical receptor represents an incomplete consideration of the particular aspects of the modeling domain, a lack of adherence and consideration of proper modeling practice s , and th e avoidance of a transparent and convenient evaluation of model performance in the source area. The location of this additional receptor is indicated in Figure 2

.8

Figure 2 : Sierra Club receptors and source locations, W.H. Zimmer source area.
Analysis

Using the model input supplied by Sierra Club, Ohio EPA replicated the results and analysis of actual emissions, years 2012

- 2014, as conducted by Sierra Club. It should be noted that at the time of evaluation, Ohio EPA had already up date d to AERMOD v. 15181. The difference in model versions did not impact final model results, and Ohio EPA was able to replicate those modeled values reported by Sierra Club. Note that the additional receptor at the location of monitor 39

- 061

- 0040 was t he only modification introduced by Ohio EPA. Ohio E PA also included the erroneous background determined by Sierra Club for this source area, 23.5  g/m 3

, as an additional source in AERMOD. This was done to simplify the analysis and graphical presentation of Sierra Club’s results.

Results

Ohio EPA’s replication of Sierra Club’s modeling results with variable emissions, years 2012

- 2014

, are in agreement with those results reported in Table 1 of Sierra Club’s submittal for the W.H. Zimmer source area . Sier ra Club modeled exceedances of the standard at 23 receptors, located near DTE St. Bernard. These receptors and their9

respective modeled design values, inclusive of a 23.5  g/m 3 background, are shown in Figure 3

.

Figure 3 : Receptors with design values exceeding the 1

- hour SO2 standard, 2012

- 2014, in the Sierra Club’s W.H. Zimmer source area modeling analysis.

Sierra Club modeling indicates a maximum modeled design value of 519.2  g/m 3

, approximately 3 kilometers to the northwest of DTE St. Bernard. At the additional receptor representing monitor 39

- 061

- 0040, a design value of 269.9  g/m 3 was modeled. Table 2 shows the maximum modeled design value reported by Sierra Club for each facil ity individually, as well as the cumulative modeled design value. For completeness, Ohio EPA has included the design values modeled at the location of monitor 39

- 061

- 0040 in Table 2.10 Sierra Club 2012

- 2014 Modeled Design Values, W.H. Zimmer

Source Area

Source Group MAX 1

- hour SO2

Design Value (  g/m 3 ) MAX 1

- hour SO2 Design

Value (  g/m 3 ) at
Monitor Location

W.H. Zimmer 132.6235 50.03979
DTE St. Bernard 519.1875 269.91089 Spurlock 71.20649 32.75963

ALL 519.1882 269.9111
Table 2 : Sierra Club maximum modeled design values and design values at location of monitor 39

- 061

- 0040, 2012

- 2014.

Ohio EP A notes that the maximum impacts obtained by Sierra Club across the entirety of the receptor grid and at the locati on of monitor 39

- 061

- 0040 are almost exclusively attributable to DTE St. Ber nard , as demonstrated by the results in Table 2 (comparing DTE St. Bernard results to those for source group ALL) . Further, Sierra Club modeling indicates that W.H. Zimmer does no t cause or contribute to any modeled exceedances of the standard. This is demonstrated in Figure 4 , which shows the maximum modeled design values from DTE St. Bernard emissions alone, which can be comp ared to Figure 3 for reference. It is clearly demonst rated that the emissions modeled by Sierra Club for DTE St. Bernard yield impacts nearly identical to those generated by the cumulative modeling at these monitors (Figure 3 ).11

Figure 4 : Receptors with design values exceeding the 1

- hour SO2 standard, 2012

- 2014, in the Sierra Club’s W.H. Zimmer source area modeling analysis, DTE St. Bernard contributions only.
Lastly, Ohio EPA notes that the design value modeled at the location of monitor 39

- 061

- 0040, 269.9  g/m 3 , or 103.2 ppb, is 2 9 ppb greater than the actual monitored 2012

- 2014 design value of 74 ppb. Ohio EPA interprets this as a clear demonstration that the Sierra Club’s modeling analysis severely over

- predicts SO 2 impacts.

Conclusion

The flawed m odeling submitte d by Sierra Club for the W. H. Zimmer source area indicates a maximum design value of 519.2  g/m 3 . Sierra Club’s m odeling also indicates that the sole contributor to all modeled exceedances of the standard is the DTE St. Bernard facility, which does not fall under th e criteria of Data Requirements Rule and is also exempted by a commitment to convert to natural gas which will occur by the end of 2015

. (Appendix B ) Further, this facility was modeled with a fixed emission rate, which is not representative of actual fa ci lity operations. Fixed emissions rates are likely to generate over

- predictions for an hourly standard , and are12

inappropriate for the analysis of the 1

- hour SO 2 standard in all but the rarest of instances

. Even further, post

- 2014 potential emissions will be below 56 TPY for this facility. Sierra Club also relied on emissions data from the Air Markets Program, which contains erroneous and overestimated Part 75 emissions data and lacks temperature and exit vel ocity data. These data are therefore unsuitable for direct use in a refined modeling analysis. Lastly, the overly conservative nature of Sierra Club’s modeling submittal is clearly demonstrated when a receptor placed at the location of a nearby air quali ty monitor over

- predicts the monitored design value by approximately 40%.

The modeling analysis and accompanying report submitted by Sierra Club for the W.H. Zimmer source area is a significant departure from what Ohio EPA would consider proper with res pec t to the area designations process , as described in U.S. EPA’s March 20, 2015 Updated Guidance for Area Designations for the 2010 Primary Sulfur Dioxide National Ambient Air Quality Standard . This guidance suggests that if an area is found to be nonattain ment of the standard, then a nonattainment area should be suggested based on jurisdictional boundaries or other easily definable features , as well as air quality data, emissions, meteorology, and geography. This five

- factor approach was utilized by Ohio E PA when establishing the recommended attainment area designation for the W.H. Zimmer source area in accordance with U.S. EPA guidance . Sierra Club did not attempt to follow this process. Rather, emission reductions were suggested for the W.H. Zimmer plan t based on allowable emissions, and no attempt to define a nonattainment area was made. Because Sierra Club provided U.S. EPA with a flawed and incomplete analysis for the purposes of designation, U.S. EPA cannot put any credence in Sierra Club’s submitta l and should rely on the analyses submitted by Ohio EPA.

In conclusion, there are multiple sources of error, over

- prediction, and erroneous data, and Sierra Club’s recommendation of nonattainment must be disregarded. This conclusion is strengthened and supported by Sierra Club’s own modeling of “actual” emissions, which shows that the W. H. Zimmer facility did not cause or contribute to any exceedance of the 2010 1

- hour SO 2 standard, and that the only source causing or contributing to exceedances of the standard is a unit that does not meet the emissions criteria of the Data Requirements Rule and is converting to natural gas prior to January 2017. Further, Sierra Club suggests that W.H. Zimmer be subj ected to emission reductions based on the modeling of allowable emission rates, when that same facility was demonstrated by Sierra Club to not cause or contribute to any exceedances of the NAAQS when following U.S. EPA’s guidance with respect to modeling a ctual emissions.

Ohio EPA believes that the arbitrary inclusion of DTE St. Bernard is not justified, most

notably in light of the fact that Sierra Club did not consider future operational changes

, nor was any attempt made by Sierra Club to establish a real istic and representative emissions database for this source . The southwest Ohio area has a number of ambient sulfur dioxide monitors in the urban area around Cincinnati. None of these monitors measure values above the ambient air quality standard, which is another reflection of the over

- predictive nature of the Sierra Club modeling. Ohio EPA also notes the inclusion of the Spurlock power plant in Sierra Club’s modeling, which has been demonstrated to impact critical receptors well below that which would b e represented by13

a carefully considered and representative background concentration. That Sierra Club also attempted to suggest emission reductions at the W.H. Zimmer facility without any rationale, except for the fact that the source is a coal

- fired elect ric generating unit

. As such, Ohio EPA contends that the modeling submitted by Ohio EPA Division of Air Pollution control is more technically sound and conforms more completely to U.S. EPA’s Data R eq uirements R ule. Further, Ohio EPA’s analysis presented a five factor analysis of the W.H. Zimmer source area in accordance with U.S. EPA guidance. Therefore, Ohio EPA reiterates here its original recommendation of attainment for the William H. Zimmer source area, as des cribed in Ohio’s September 16, 2015 submittal.1

Review and Analysis of Sierra Club Submitted Gavin Power Plant Evaluation of

Compliance with the 1

- hour NAAQS for SO 2

Ohio EPA

Division of Air Pollution Control

Introduction

The United States Environmental Protection Agency (U.S. EPA) established a new National Ambient Air Quality Standard (NAAQS) for SO 2 on June 22, 2010, of 75 ppb, as the 99 th percentile of maximum daily values, averaged over three years. In addition, U.S. EPA revoked the primary annual and 24

- hour standards.

On August 5, 2013 (75 FR 47191), effective October 4, 2013, U.S. EPA promulgated the initial SO 2 nonattainment areas for the newly established SO 2 standard across the country. On March 2, 2015, the U.S. District Court for the Northern District of California accepted as an enforc eable order an agreement between the U.S. EPA and Sierra Club and the Natural Resources Defense Council to resolve litigation concerning the deadline for completing designations. The court’s order directs U.S. EPA to complete designations in three steps: t he first by July 2, 2016; the second by December 31, 2017 and the third by December 31, 2020. As part of the first round of designations, U.S. EPA has identified areas with newly monitored violations of the standard, or areas that contain stationary sourc es that emitted more than 16,000 tons of SO 2 in 2012 or emitted more than 2,600 tons of SO 2 and had an emission rate of at least 0.45 lbs SO 2 /MMBtu in 2012. The U.S. EPA has identified two facilities in Ohio as meeting one or more of these criteria: the Ge neral James M. Gavin Plant and the W.H. Zimmer Generating Station.

On September 16, 2015, Ohio EPA submitted recommendations of attainment for both the General James M. Gavin (including Kyger Creek) and W.H. Zimmer Generating Station source areas based on a five factor analysis, inclusive of refined dispers ion modeling. On this same date , Sierra Club submitted dispersion modeling results and a recommendation of nonattainment for both areas.

This document is Ohio EPA’s analysis of

, and response to

, Sierra Club’s modeling and recommended designation for the General James M. Gavin source area

. Ohio EPA has included

, for completeness

, Sierra Club’s modeling analysis report for both the W.H. Zimmer and General James M. Gavin power plants as Appendix A of this submittal.

Modeling Approach

Per U.S. EPA’s Modeling Technical Assistance Document ( TAD )

,

“ Since the purpose here pertains to designations, this guidance supports

ana lyses of existing air quality rather than analyses of emissions limits necessary to provide for attainment

. Consequently, the guidance in this TAD differs in2

selected respects from the guidance published in Appendix W. These differences include:

 Placement of receptors only in areas where it is feasible to place a monitor vs. all ambient air locations (NSR, PSD, and SIP)

 Use of the most recent 3 years of actual emissions (designations) vs. maximum allowable emissions (NSR, PSD, and SIP)

 Use of 3 ye ars of meteorological data (designations) vs. one to five years (NSR, PSD, and SIP)

 Use of actual stack height for designations using actual emissions vs. Good Engineering Practice (GEP) stack height for other regulatory applications (NSR, PSD, and SIP)”

The Sierra Club incorporated some, but not all, of the items listed above

. Contrary to the specifications listed above, the Sierra Club also modeled allowable SO 2 limits and proposed an emissions reduction for th e General James M. Gavin plant . Further, S ierra Club placed receptors in areas that would be considered “inside the fenceline” for all sources included in the modeling domain. These are serious flaws in the analysis.

The a veraging period for the 2010 SO 2 NAAQS is the 99 th percentile of maximum monitored daily values, averaged over three years . Per t he Modeling TAD, three years of National Weather Se rvice data is sufficient to allow the modeling to simulate a monitor . Thus, the modeled form of the standard is expressed as the 99 th percentile of maximum daily values averaged over three years (herein referred to as “design value”) for the purposes of designation.

The recommended dispersion model for modeling for SO 2 designations is the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) modeling system. There are two input data processors that are regulatory components of the AERMOD modeling system: AERMET, a meteorological data preprocessor that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, and AERMAP, a terrain data preprocessor that incorporates complex terrain using United States Geological Survey (USGS) Digital Elevation Data. Ad ditionally, Sierra Club u tilized the AERMINUTE module to incorporate 1

- minute ASOS meteorological data into the hourly surface input file. Sierra Club utilized the most
up

- to

- date versions of AERMOD and the associated preprocessors available at the time of the modeling analyses. Tho se versions used are as follows: AERMOD version 14134, AERMET version 14134, AERMINUTE version 142 37, and AERMAP version 11103

. Meteorological Data

M eteorological data from 2012

- 2014 from the Huntington, WV surface station (Stat ion # 3860 ) located at the Huntington Tri

- State Airport and the Pittsburgh, PA up per air station (Station # 94823 ) located at the Greater Pittsburgh International Airport were used in the Sierra Club analyses. These sites have previously been determined b y Ohio3

EPA to be representative of Gallia County , OH and the surrounding region

. AERSURFACE was run using twelve sectors and four seasons, centered on the location of the surface meteorological station, using average moisture conditions and continuous winter snow cover

. The Sierra Club used a meteorological data set for their modeling analyses consistent with what Ohio EPA would use to perform modeling in this area.

Background

A b ackground concentration of 28.8  g/m 3 (11.01 ppb) was included in all modeling analyses conducted by Sierra Club in the Gavin source area. This background was based on the design value recorded at the Allen County air quality monitor, 39

- 003

- 0009. Sierra Club chose this monitor because it recorded the lowest monitored design value in Ohio for the 2011

- 2013 period. This is not a background monitor. This monitor is located downwind of the city of Lima, Ohio and a large refining/petrochemical facility. Add itionally, there is a major interstate highway close to this location. There are several other sources of information that would indicate a background SO 2 concentration of 26.16  g/m 3 for this specific source area, as was used in the Ohio EPA modeling. S ierra Club utilized the 2011

- 2013 period, rather than 2012

- 2014, which would encompass those years actually modeled. Why this period was chosen is unclear. This source area has multiple SO 2 monitors which were active during the 2012

- 2014 period. Ohio EP A further notes that the background used in Ohio’s recommended designation was 10 ppb (26.16  g/m 3 ), and was based on a more local monitor with careful consideration of those sources not explicitly modeled in the domain.

Emission Sources

The Sierra Club explicitly modeled emissions from th e General James M. Gavin plant, Kyger Creek Station, and the Mountaineer Power Plant . The two SO 2 sources at th e General James M. Gavin plant were modeled by Sier ra Club as two separate egress points, as the two boiler s vent emissions to individual stacks. The five emission sources at Kyger Creek were incorrectly modeled by Sierra Club as venting to a single common stack, with an incorrect diameter of 11.887 meters. A correct representation of the egress points at Kyg er Creek would represent the emissions from Units 1 and 2 as being emitted from a stack with a 7.53 meter diameter, and emissions from Units 3, 4, and 5 as being emitted from a stack with a diameter of 9.2 meters. Ohio EPA notes here that the modeling sub mitted to U.S. EPA by Ohio EPA as part of a five factor analysis on September 16, 2015 correctly represented the egress points at Kyger Creek Station. Sierra Club modeled the emissions from Mountaineer Plant from a single egress point. The stack paramete rs for each source included in Sierra Club’s analyses are shown in Table 1.4

Table 1 : Release point parameters for all sources included in S ierra Club modeling, Gen. James M.
Gavin source area.

Ohio EPA has serious reservations and concerns with respect to the quality of emissions data modeled and the choice of facilities to include in the modeling domain. These concerns are detailed here.

Emissions Data

Sierra Club used hourly variable emissions inp uts for the General James M. Gavin Plant, Kyger Creek Station, and Mountaineer Power Plant

, years 2012

- 2014. These data were obtained from U.S. EPA’s Air Markets Program Data. Ohio EPA does not consider Air Markets Program Data ideally acceptable for use as input into a refined disp ersion model for multiple reasons. First ly, data reported to the Air Markets Program is done so for the accounting of emission allowance consumption, in accordance with Part 75 monitoring and reporti ng requirements

. Accordingly, the data tends to overstate emissions when there are errors in the monitorin g equipment or during periods of missing data, as described in the Part 75 monitoring and reporting requirements. The data substitution methodologies employed via Part 75 requirements for the purpo ses of allowance accounting can lead to severe ove restimations of emissions data, and consequently ground level impacts determined from refined dispersion modeling. These data were never intended to serve as a repository for hourly emissions suitable for refined dispersion modeling. In addition to overstating emissions, the database does not contain hourly exit temperature values, which are a critical component necessary to accurately model hourly plume rise and exit velocities. The shortcomings of the A ir Markets Program data are made more apparent when applied to stringent 1

- hour standards.

It should be noted he re that the hourly emissions database utilized by the Ohio EP A for this round of designation modeling was the result of intensive analysis and consultation with relevant plant operators and technical staff to identify spurious emissions data and to compile a complete and accurate hourly database of emissions, exit temperatures, and exit velocities for each source i ncluded in the modeling domain. A description of the problematic data and subsequent r efinement of the emissions database used by Ohio EPA for the General James M. Gavin source area is provided as Appendix C of this submittal

. This document was originally submitted by Ohio EPA as an A ppendix to Ohio’s September 16, 2015 recommendation submittal.

In addition to using an inappropriate emissions database, Sierra Club states that their use of fixed maximum exhaust flow rates and temperatures tends to under

- predict impacts. Ohio EPA’s experience would indicate that this is not the case

, and neglects the complexities of, for example, AERMOD’s treatment of the penetrated plume and the impact of temperature inversions on ground level impacts . Ohio EPA contends that an5

accurate treatment o f actual emissions necessitates the inclusion of variable exhaust velocities and temperatures in addition to variable emissions

. This is of particular importance when the stated intent of the designations modeling is to treat receptors as a surrogate for air quality monitors.

In the second portion of Sierra Club’s modeling analysis, allowable emissions were modeled for all sources listed in Table 1, above. Ohio EPA did not extensively analyze this portion of Sierra Club’s analysis, as the modeling of allo wable emissions is well beyond the scope and intent of the both the consent decree and the final Data Requirements Rule. U.S. EPA’s March 20, 2015 memorandum entitled Updated Guidance for Area Designations for the 2010 Primary Sulfur Dioxide National Ambi ent Air Quality Standard lists the following recommendations for designating source areas via modeling explicitly:

° using actual emissions as an input for assessing violations to provide results that reflect current actual air quality (i.e., modeling that simulates a monitor);

° using 3 years of modeling results to calculate a simulated design value consistent with the 3

-

year monitoring period required to develop a design value for comparison to the NAAQS;

° placing receptors only in locations where a monitor could be placed; and

° using actual stack heights rather than following the Good Engineering Practice stack height policy when using actual emissions.

Thus, Sierra Club’s inclusion of allowable emissions is inconsistent with U.S. EPA policy for the purposes of designation and the conclusion drawn by Sierra Club from this modeling should be dismissed. Further, there is no regulatory rationale for the Sierra Club’s suggested emission reductions at the General James M. Gavin facility bas ed on these flawed results.

E xplicitly Modeled Facilities

As stated previously, the Sierra Club modeled Kyger Creek Station and the Mountaineer Power Plant in addition to the General James M. Gavin facility . While these facilities do fall within a 50 km radius of the source area, the Mountaineer Power Plant was determined by Ohio EPA to be too distant and having emissions not significant enough to impact the source area above background

. Ohio EPA contends that this conclusion is supported by Sierra Club ’s modeling, and is discussed further in the Results section of this document.

Receptors

The Sierra Club conducted modeling analyse s on a three

- tiered receptor grid consisting of 21,201 discrete receptors. The first grid is a grid of 100 meters spacing extending from th e General James M. Gavin Plant to 5 kilometers . The second is a grid of 500 meters spacing extending to 10 k ilometers. The final gird has a 1,000 meters spacing and extends to 50 kilometers. The elevations of these receptors were determ ined using6

AERMAP v. 11103 and 1 arc

- second resolution National Elevation Dataset (NED) files. No attempt was made by Sierra Club to exclude receptors located in bodies of water, in locations where monitor placement would not be feasible, or in areas that would be considered “inside the fenceline” of the various explicitly modeled sources. Figure 1 shows the receptor grid utilized by Sierra Club and the location of the explicitly modeled facilities. Note that Ohio EPA included an additional receptor at t he location of AQS monit or 39

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- 000 3 when conducting the analysis of Sierra Club’s modeling . This monitor is located approximately 13 kilometers to the northeast of the General James M. Gavin plant, and is situated such that prevailing winds from the sou thwest carry emissions from both the General James M. Gavin plant and Kyger Creek Station to the monitor location. Ohio EPA included this additional receptor as it is customary and appropriate modeling practice to include receptors at the location of ambie nt air quality monitors whenever possible. Inclusion of relevant monitors provides a convenient, transparent, and scientifically valid means to evaluate and assess model performance, and is done so by Ohio EPA in all situations where a representative moni tor is located within a modeling domain. Furthermore, this receptor falls within a “hotspot” of modeled SO 2 impacts and can be used to assess the accuracy of Sierra Club’s modeling results. Ohio EPA suggests that Sierra Club’s omission of this critical re ceptor represents an incomplete consideration of the particular aspects of the modeling domain, a lack of adherence and consideration of proper modeling practices, and the avoidance of model performance evaluation in the area around the source. The location of this additional receptor is indicated in Figure 1.7

Figure 1 : Sierra Club receptors and source locations, Gen. James M. Gavin source area.
Analysis

Using the model input supplied by Sierra Club, Ohio EPA r eplicated the results and analysis of actual emissions, years 2012

- 2014, as conducted by Sierra Club. It should be noted that at the time of evaluation, Ohio EPA had already update d to AERMOD v. 15181. The difference in model versions did not impact final model results, and Ohio EPA was able to replicate those modeled values reported by Sierra Club. Note that the additional receptor at the location of monitor 39

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- 0003 was the o nly modification introduced by Ohio EPA. Ohio E PA also included the erroneous background determined by Sierra Club for this source area, 28.8  g/m 3

, as an additional source in AERMOD. This was done to simplify the analysis and graphical presentation of S ierra Club’s results.

Results

Ohio EPA’s replication of Sierra Club’s modeling results with variable emissions, years 2012

- 2014

, are in agreement with those results reported in Table 1 of Sierra Club’s submittal for the General James M. Gavin source area . Sierra Club modeled

e xceedances of the standard at 8,608 receptors, including the additional receptor8

placed by Ohio EPA at the location of monitor 39

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- 0003. Exceedances were modeled within 14.5 kilometers of the General James M. Gavin Plant. These receptors and their respective modeled design values, inclusive of a 28.8  g/m 3 background, are shown in Figure 2.

Figure 2 : Receptors with design values exceeding the 1

- hour SO2 standard, 2012

- 2014, in the Sierra Club’s General James M. Gavin source area modeling analysis.

Sierra Club modeling indicates a max imum modeled design value of 318.5  g/m 3 approximat ely 2.8 kilometers to the northwest of the General James M. Gavin plant . At the additional rece ptor representing monitor 39

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- 00 0 3, a design value of 197.4

 g/m 3 was modeled. Table 2 shows the maximum modeled design value reported by Sierra Club for each facility individually, as well as the cumulative modeled design value. For completeness, Ohio EPA also included the design values modeled a t the location of monitor 39

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- 00 0 3 in Table 2.9 Sierra Club 2012

- 2014 Modeled D esign Values, General James
M. Gavin Source Area

Source Group MAX 1

- hour SO2

Design Value (  g/m 3 ) MAX 1

- hour SO2 Design

Value (  g/m 3 ) at
Monitor Locati on
Gen J.M. Gavin 291.5320 170.83095 Kyger Creek 101.1416 65.79408
Mountaineer 53.09317 38.95341

ALL 318.5353 197.38876
Table 2 : Sierra Club maximum modeled design values and design valu es at location of monitor 39

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- 00 0 3
, 2012

- 2014.

The flawed Sierra Club mod eling indicates that Kyger Creek Station and Mountaineer Power Plant do not cause any modeled exceedances of the standard , and that the General James M. Gavin Plant is the largest contributor to modeled exceedances of t he standard

. Further, modeled results at the location of monitor 39

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- 0003 demonstrate a modeled exceedance of the standard. Ohio EPA sited that monitor in the vicinity of the General James M. Gavin plant to specifically measure SO 2 impacts from that p lant. This source oriented monitor can be used as an indicator of model performance and ambient air quality in the area around the source.

Ohio EPA notes that monitor 39

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- 0003 is in attainment of the 1

- hour SO 2 standard, with a 2012

- 2014 monitored design value of 30 ppb, while Sierra Club modeling indicates a modeled design value of 75.5 ppb for the same period . This large discrepancy prompted Ohio EPA to conduct an analysis of modeled concentrations at the mon itor location against monitored values. Ohio EPA first compared the first through fifth highest modeled and monitored maximum daily values for each year 2012

- 2014. The results of this analysis are shown in Table 3.10 Year Rank Modeled

Concentration (ppb) Monitored Concentration (ppb)
39

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- 0003

2012 1 133 34

2 100 34

3 77 32

4 70 26

5 66 24

2013 1 86 63

2 75 55

3 73 50

4 71 33

5 70 33

2014 1 143 85

2 93 47

3 87 33

4 85 32

5 80 30
Table 3 : 1 st through 5 th highest modeled and monitored values at monitor location 39

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- 0003 , 2012

- 2014

. Table 3 demonstrates that Sierra Club’s modeling significantly over

- predicts the maximum daily values with respect to those recorded at monitor 39

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- 0003 and is not representative of actual air quality

. During the 2012

- 2014 period, only a single maximum daily concentration greater than 75 ppb was recorded at the monitor location

. Over the same period, Sierra Club modeled nine maxim um daily values greater than 75 ppb at the monitor location. To further assess the performance of Sierra Club’s modeling against the monitor data, Ohio EPA evaluated the modeled and monitor maximum daily values at the 95 th , 90 th , 75 th , 50 th , and 25 th perc entiles for each year of the 2012

- 2014 period. These results are shown Table 4.11 Year Percentile Modeled

Concentration (ppb) Monitored Concentration (ppb)
39

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- 0003

2012 95 th 51 17

90 th 44 9

75 th 31 5

50 th 18 2

25 th 12 1

2013 95 th 60 20

90 th 45 12

75 th 31 6

50 th 16 3

25 th 11 1

2014 95 th 65 23

90 th 55 17

75 th 33 9

50 th 16 4

25 th 12 1
Table 4 : Modeled and monitored maximum daily values at various percentiles at monitor location 39

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- 0003, years 2012

- 2014.

The results shown in Table 4 ind icate that Sierra Club modeling systematically over

predicts , in some cases severely, across a wide range of percentiles, for all years modeled. Ohio EPA interprets these data as indicative of a systemic conservative bias in the Sierra Club modeling. Based on Ohio EPA’s analysis of the modeling submittal

, this consistent ove r

- prediction originates from Sierra Club’s use of an inappropriate and overly conservative emissions database.

In addition to the sig nificant over

- prediction demonstrated by Sierra Club’s modeling, Ohio EPA does not believe that the inclusion of the Mountaineer Power Plant was appropriate for this source area. Ohio EPA determined that the relatively low emissions from the Mountaineer P lant, considering local meteorology and its distance from the General James M. Gavin Plant (4,411 TPY, 16.7 km), would not necessitate explicit modeling as it is unlikely to impact ambient SO2 concentrations in the source area beyond what is accounted for in the background concentration. This conclusion is supported by the fact that emissions from the General James M. Gavin Plant and Kyger Creek Station, which were approximately 11 times higher than Mountaineer Power Plant in 2014, did not demonstrate mode led exceedances of the standard, and had maximum impacts relatively close to the faci lities. Ohio EPA analyzed the impact of the Mountaineer Power Plant at the 8,608 receptors for which Sierra Club modeling indicating an exceedance of the standard, without further alteration to the modeling inputs. The results of this modeling for only the Mountaineer Power Plant are shown in12

Figure 3. Note that for clarity and to avoid double counting of the background, the concentrations shown in Figure 3 do not include a background.

Figure 3 : Mountaineer Power Plant impacts, 2012

- 2014 , without background

. The results shown in Figure 3 demonstrate that the impacts of the Mountaineer Plant on those receptors demonstrated by Sierra Club to exceed the standard are relatively low. Within the fine grid around the General James M. Gavin and Kyger Creek facilities where the largest impacts were modeled, the impacts of Mountaineer are between 5 and 8  g/m 3 . The greatest modeled impact of Mountaineer in this receptor grid was13

12.38  g/m 3 , or 4.7 ppb. Ohio EPA contends that had Sierra Club utilized a carefully consid ered and more representative monitor to derive a background for this analysis, then the impacts of the Mountaineer Power plant would be conservatively represented, eliminating the need to explicitly model this source. It should be noted that Ohio EPA’s ba ckground for this area, 10 ppb, adequately and conservatively represents the impacts of the Mountaineer Power Plant in the General James M. Gavin source area. Sierra Club’s inclusion of this source, in addition to a non

- representative background, provides an additional unnecessary and inappropriate level of conservatism in the modeling analysis.

Conclusion

Modeling submitted by Sierr a Club for the General James M. Gavin source area indicates a maximum design value of 318.5  g/m 3 . Sierra Club relied on emissions data from the Air Markets Program, which cont ains erroneous and overly conservative Part 75 substitution data, and lacks variable temperature and exit velocity data. These data are therefore unsuitable for direct use in a refin ed modeling analys is. T he overly conservative nature of Sierra Club’s modeling subm ittal is clearly demonstrated when modeled results are compared to monitor data recorded at monitor 39

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- 0003, located 13 kilometers away and sited to monitor emissions from both the Gener al James M. Gavin and Kyger Creek power plants. Ohio EPA’s analysis indicates that Sierra Club’s modeling severely over

- predicts maximum daily values for all years, across a broad range of percentiles. The modeled design value at the monitor location, 75 .5 ppb, is approximate ly two

- and

- half times greater than the monitored design value at the same location, years 2012

- 2014. Ohio EPA notes that if the maximum modeled design value obtained by Sierra Club, 318.5  g/m 3 is scaled by a factor of 2.5, a design value of 127  g/m 3 is obtained, inclusive of background. Although Ohio EPA acknowledges that such scaling is inappropriate for deriving valid design values, it is a striking indication of the overly conservative nature of Sierra Club’s modeling in this

source area.

In conclusion, there are multiple sources of error, over

- prediction, and erroneous data, and Sierra Club’s recommendation of nonattainment must be disregarded

. As such, Ohio EPA contends that the modeling submitted by Ohio EPA Divisio n of Air Pollution control is more technically sound and conforms more completely to U.S. EPA’s Data R eq uirements R ule. Therefore, Ohio EPA reiterates here its original recommendation of atta inment for the General James M. Gavin source area, as described in Ohio’s September 16, 2015 submittal.