Environmental

Resources Management

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www.erm.com 

### To: David Triplett

Company: Entergy Services , Inc.

From: Richard Hamel

File number: 0268066

Date: 17 November 2015

Subject: Analysis of Sierra Club Modeling of Entergy White
Bluff Steam Electric Station for 1

- hour SO 2 

### Compliance.

ERM was asked by Entergy Services, Inc. (Entergy) , to review a modeling demonstration submitted by Sierra Club showing modeled c oncentrations

associated with emissions from the 

### White Bluff Steam Electric Station (White Bluff) above the 1

- hour SO 2 NAAQS. The document submitted to the U.S. Environmental Protection Agency (USEPA) Region 6 and the Arkansas Department of Environmental Quality (ADEQ) by Sierra Club, titled “ White Bluff Plant, Redfield, Arkansas, Evaluation of Compliance with the 1

- hour NAAQS for

SO 2 “(August 9, 2015), along with the modeling files themselves, were received by ERM on October 22, 2015. This memorandum desc ribes the findings of that

review.

General Summary

Sierra Club’s modeling methodology is basic, with a minimal level of refinement, and their analysis is very general. For example, a review of four separate modeling reports submitted by Sierra Club relate d to the 1

- hour SO 2 NAAQS shows the modeling to be identical even to the point of including tables from one report to the next that are not relevant for the facility in the report. The explanations of their modeling approach are copied from report to repor t regardless of the site

- specific details. In addition, the discussion of meteorological data representativeness does not provide any site

- specific reason that the meteorological data site chosen is representative, just that it is “close” to the project si te, and this same reason is given whether the airport is 20 miles away or 100 miles away from the study site with no discussion of what “close”

means. The modeling also contains several errors and incorrect assumptions that render the modeling inaccurate.PAGE 2

Errors in the Sierra Club Modeling

Sierra Club made several errors and incorrect assumptions in the modeling for White Bluff, including the use of incorrect stack exhaust temperatures, unnecessary corrections to the stack height, the use of constant stack parameters, use of an older model version, failure to consider the facility fence line in determining the receptor grid, and the use of allowable emission rates in the modeling. The first error alone, regarding the use of the in correct stack exhaust temperatures for White Bluff, singlehandedly invalidates the modeling even in the absence of all of the additional problems with Sierra Club’s modeling. Each of the errors and incorrect assumptions in Sierra Club’s modeling are ident ified in the paragraphs below.

Erroneous Stack Exit Temperature Units

Sierra Club failed to convert the permitted stack exhaust temperatures in degrees

Fahrenheit for each of the two coal

- fired units to the model input units of Kelvin.

The exhau st temperature for the two units, according to the Title V operating permit for White Bluff, is 321 degrees Fahrenheit, which converts to 433.7 Kelvin, the required units for input into the AERMOD model. Sierra Club did not make the appropriate c onversion, but instead simply input the value 321 as the exhaust temperature in the modeling. This error understates the correct exhaust temperature by more than 110 Kelvin and significantly alters the model

predicted impacts.

ERM corrected this error and reran Sierra Club’s actual emissions modeling with no other changes or refinements. The results are shown in Table 1: Sierra Club’s modeling, with the proper unit conversion for the exhaust temperature, shows

that the modeled impacts from White Bluff, when added to an ambient background concentration, are below the 1

- hour SO 2 NAAQS.

Therefore when the exhaust temperature error is corrected, Sierra Club’s modeling with the three most recent years (2012

- 2014) of actual emissions data shows that emissions from White Bluff do not cause or contribute to any

modeled exceedances of the 1

- hour SO 2 NAAQS.

The fact that this basic error was not caught and fixed indicates that Sierra Club

did not undertake even the most rudimenta ry QA/QC review of the modeling before it was submitted to EPA and ADEQ.PAGE 3

Table 1: White Bluff Actual Emissions Modeling with Erroneous and Corrected Stack Exhaust Temperatures.

S.C modeling with errors S.C modeling Corrected

1

- hour SO2 NAAQS ( μ g/m 3 ) Exhaust Temperature (K)* Modeled Design Value w/Background ( μ g/m 3 ) Exhaust Temperature (K) Modeled Design Value w/Background ( μ g/m 3 )

321.0 233.6 433.7 156.6 196.5

*Sierra Club erroneously claimed that the temperature was in Kelvin in Table 4 of their modeling report.

Assertions regarding Good Engineering Stack Height at White Bluff

In section 2.2 of the Sierra Club modeling report, Sierra Club states:

“An evaluation of facility buildings and structures determined that the current stack height of 1,000 feet (305 meters) did not meet the Good Engineering Practice (GEP) stack height requirement. Allowable emissions were modeled using both this height and the lower GEP stack height of 207 meters.”

This assertion is incorrect. In accordance with USEPA’s Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack Height Regulations) (USEPA 1985) 1 , the physic al GEP height, (H GEP ), is determined from the dimensions of all buildings which are within the region of influence using the following equations, depending on the construction date of

the stack:

(1) For stacks in existence on January 12, 1979 and for which th e owner or operator had obtained all applicable permits or approvals required,

H GEP = 2.5 H,

provided the owner or operator produces evidence that this equation was actually relied on in establishing an emission limitation;

(2) For all other stacks:

H GEP = H + 1.5L

where:

H = height of the structure within 5L of the stack which maximizes H GEP ; and

L = lesser dimension (height or projected width) of the structure.

1 http://www3.epa.gov/scram001/guidance/guide/gep.pdfPAGE 4

For a squat structure, i.e., height is less than projected width, the formula reduces

to:

H GEP = 2.5H

In the absence of influencing structures, a “default” GEP stack height is creditable up to 65 meters (213 feet).

The main stack at White Bluff was in existence and all applicable permits had

been obtained prior to January 12, 1979 . Therefore, the GEP formula height is

H GEP = 2.5 H. The controlling structure for the main stack is the Unit 1 cooling tower, with a height of 400 feet. Thus, the GEP formula height for the main stack is 400 x 2.5 = 1000 feet, which is the true height of the stack. As a result, Sierra

Club’s calculated GEP sta ck height of 207 meters for the White Bluff units should be disregarded.

In addition, even if Sierra Club’s GEP stack height calculation were correct, it is unnecessary for 1

- hour SO 2 modeling. According to the SO 2 NAAQS Designations Modeling Technical As sistance Document 2 , for the purpose of categorizing air quality for the 1

- hour SO 2 NAAQS, modeling with the full stack height, regardless of the GEP formula height, is allowed. Therefore, Sierra Club’s discussion of GEP stack height is not relevant for 1

- h our SO 2 modeling.

Other Modeling Weaknesses

ERM’s review of the modeling showed the following additional weaknesses, generalizations, and incorrect claims. While some of these are not errors in the modeling per se, they demonstrate that Sierra Club faile d to perform the most basic of refinements commonly applied to modeling studies.

Constant Stack Parameters:

The Sierra Club modeling uses constant exhaust temperatures and exit velocities

for each of the two coal

- fired units based on permitted data, since detailed hour

by

- hour stack exhaust parameter data is not available from EPA’s Clean Air
Markets Database, 3 which was the source of emissions information used in the modeling. Sierra Club’s modeling assumed that the stack parameters for the two

coal

- fired units are identical , which tend to make the impacts from both units directly additive, causing higher imp acts than would be the case when the actual hourly stack parameters are used. Table 2 shows that the average stack temperatures of the Units varied by almost 16 Kelvin, while the exit velocities differ on average by about 1.5 m/s. Note also that the stack temperatures used by Sierra Club, based on permitted values, are considerably higher than the

2 http://www3.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdf

3 http://ampd.epa.gov/ampd/PAGE 5

average values in the CEMS data, explaining why the corrected Sierra Club modeling had model

- predicted impacts that were lower than those performed by ERM using t he CEMS data with hourly stack temperatures and velocities. Both
studies showed that emissions from White Bluff, when modeled with the 3 most recent years of actual emissions data, do not cause or contribute to any

exceedance of the 1

- hour SO 2 NAAQS.

Tabl e 2: Average hourly stack parameters from CEMS data vs. permitted stack
parameters.

UNIT CEMS* PERMIT Data Differences Temp (K) Vel. (m/s) Temp (K) Vel. (m/s) Temp (K) Vel. (m/s)

Unit 1 395.99 25.50 433.71 27.43 37.72 1.93

Unit 2 380.04 24.09 433.71 27.43 53.67 3.34

*Temperature and exit velocity are the average values over three years (2012

- 2014) of all
hours with a non

- zero emission rate.

Model Version

Sierra Club states that the most recent version of the model was used. The modeling was performed in August, 2015, at which time v.15181 was publicly
available. Since the Sierra Club used v.14134, this statement is incorrect.

Evaluation of other Sources in the Region

In listing assumptions that Sierra Club claimed would cause their modeling to underestimate concentrations, they stated “ No consideration of off

- site sources.
These other sources of SO 2 will increase the predicted impacts”, with the implication that such sources exist. As was fully documented in ERM’s “ SO 2 Air Dispersion Modeling Re port for White Bluff Steam Electric Station ” (August 2015), there are no other major sources of SO 2 emissions in the vicinity of White Bluff.

Ambient Background Data

The modeling uses ambient background data from 2011

- 2013 in combination

with emissions and meteorological data from 2012

- 2014. A single annual ambient background value was used: no seasonal

- diurnal refinement was performed. Section 2.2 of the Sierra Club report claims that the ambient background concentration used was “the most readily availabl e design value”. This statement is incorrect because the 2014 ambient monitoring data was finalized and was readily available to the public from EPA’s database in May 2015, months before the modeling was performed.PAGE 6

Flagpole Receptors

The modeling uses flag pole receptors set to 1.5 meters, to represent the “inhalation level”. This assumption does not conform to guidance for NAAQS modeling but serves to slightly increase modeled concentrations.

Operational Loads

Section 4.2 of the Sierra Club modeling report suggests that because loads of less
than 100% were not considered, the model under

- predicts impacts, citing lower flow rate and temperature for the lesser load cases. The report neglects to

address the fact that emissions are also lower when the units are operating at less than 100% load. The modeling performed by ERM using hourly CEMS data including concurrent hourly stack parameters captures all load cases as they happen and shows no particular increase in modeled impacts during those periods of lesser lo ads.

Receptor Grid

The receptor grid in Sierra Club’s modeling covers the entire White Bluff property and ignores the fence line of the plant. As a result, the modeling includes impacts that are within the ambient air boundary of the facility. According to the Guideline on Air Quality Models (GAQM, 40CFR Appendix W) (USEPA 2005) 4 , the area within a facility’s fence line to which the public is excluded from access is not “ambient air” and thus a facility cannot cause or contribute to an ambient air quality violation within this boundary. Therefore, receptors should not be placed within that boundary.

Meteorological D ata Processing

The meteorological data processing assumed default seasonal periods and average moisture throughout the 3

- year period. ERM’s modeling refined the meteorological data by resolving surface roughness and moisture by month.

Additionally, in sect ion 4.5.4 of the modeling report, Sierra Club concludes that “Since the Clinton National Airport is located close to White Bluff Plant, this meteorological data set was considered appropriate for this modeling analysis”.

There is no discussion of what “clo se” means or why the meteorological data are representative, and no maps, drawings or other figures showing the relative location of the facility and the meteorological data tower. In fact, in the four modeling reports related to SO 2 attainment reviewed by ERM recently, as well as

4 http://www3.epa.gov/ttn/scram/guidance/guide/appw_05.pdfPAGE 7

in past modeling reports by Sierra Club, section 4.5.4 is simply repeated in each report with only the name of the airport changed.

Allowable Emission Rate Modeling

Sierra Club’s report included modeling of White Bluff using the allowable permitted emission rate for each coal

- fired unit. Since, per the final Data Requirements Rule for the 2010 1

- Hour Sulfur Dioxide (SO 2 ) Primary National Ambient Air Quality Standard (NAAQS) (USEPA 2015), 5 the purpose of the modeling is to evaluate the current ambient air quality to determine attainment
of the 1

- hour SO 2 NAAQS, the use of continuous operation at maximum allowable emissions is irrelevant. Additionally, modeling of allowable emissions requires 5 years of meteorological data . Sierra Club only used 3 years of data.

Conclusion

There are numerous deficiencies in the Sierra Club modeling that render it incomplete. More important however are the errors to basic inputs in the modeling. These errors and deficiencies invalidate the modeling study as presented, and as a result, the attainment status of the White Bluff Steam Electric Station with respect to the 1

- hour SO 2 NAAQS cannot accurately be determined from Sierra Club’s modeling. If the most significant error in the Sierra Cl ub modeling (the incorrect stack gas exhaust temperature) is corrected, then the Sierra Club modeling predicts that emissions from the White Bluff Station do not cause or contribute to any exceedances of the 1

- hour SO 2 NAAQS.

Therefore, W hite Bluff Station does not cause or contribute to any modeled
exceedances of the 1

- hour SO 2 NAAQS.

5 http://www.gpo.gov/fdsys/pkg/FR

- 2015

- 08

- 21/pdf/2015

- 20367.pdf