Environmental

Resources Management

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- 7800

www.erm.com 

### To: David Triplett

Company: Entergy Services , Inc.

From: Richard Hamel

File number: 0268066

Date: 1 7 November 2015

Subject: Analysis of Sierra Club Modeling of Entergy Independence 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 concentrations

associated with emissions from the 

### Independence Steam Electric Station (Independence Station) 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 “ Independence Plant, Newark, Arkansas, Evaluation of Compliance with the 1

- hour NAAQS for SO 2 “(September 16, 2015), along with the modeling files themselves, were received by ERM on October 22, 2015. This memorandum describes 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 related to the 1

- hour SO 2 NAAQS shows the modeling to be identica l 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 report regardless of site

- specific details. In addition, the dis cussion 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 site, and this same reason is given whether the airport is 20 mil es 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. Furthermore, the modeling report draws

conclusions which canno t be supported by the modeling results without further refinement and a culpability analysis.PAGE 2

Errors in the Sierra Club Modeling

ERM found the following errors in its review of the Sierra Club modeling files and report for Independence Station.

Incorrect Conclusions regarding the 1

- hour SO 2 Compliance Status of Independence
Station

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

“ It was determined that based on either current allowable emissions or measured actual emissions, the Independence Plant is estimated to create downwind SO 2 concentrations which exceed the 1

- hour NAAQS.”

Sierra Club then not only fails to show that Independence Station contributes to air quality impacts above the NAAQS, but their own Table 1 shows that, in their
model ing of the Independence units’ 3 most recent years (2012

- 2014) of actual emissions, as allowed by the SO 2 NAAQS Designations Modeling Technical

Assistance Document 1 , the modeled impacts from Independence Station, when added to an ambient background concent ration, are well below the NAAQS (137.7 μ g/m 3 compared to the NAAQS of 196.5 μ g/m 3 ). Sierra Club’s modeling of FutureFuel Chemical Corporation results in impacts above the NAAQS, but the modeling is incomplete: Sierra Club did not perform a culpability analysis to determine whether Independence Station significantly contributes (that is, has modeled impacts greater than the 1

- hour SO 2 Significant Impact Level (SIL) of 7.9

μ g/m 3 ) to any of the modeled impacts that were predicted to exceed the NAAQS. Witho ut such a culpability analysis, Sierra Club has no basis to draw any conclusions about Independence Station’s contributions to the model

predicted NAAQS exceedances caused by FutureFuel.

To determine whether Independence contributed to any exceedances cau sed by emissions from FutureFuel, ERM performed a culpability analysis using Sierra Club’s modeling files. No changes of any kind were made to the Sierra Club modeling: all inputs, including meteorological data, receptors, emissions, and stack parameters r emained the same. As a first step, Sierra Club’s modeling was rerun and it was confirmed that the model results matched those presented in the Sierra Club modeling report.

Next, 

### a review of the results showed that there were a total of 2530
modeled exceed a nces of the NAAQS occurring at 371 receptors, spanning
down to the 35 th 

### ranking, and occurring to the north, west, and south of
FutureFuel.

1 http://www3.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdfPAGE 3



### All of the modeled exceedances were then reviewed using the
MAXDCONT feature of AERMOD to determine if the contri bution from Independence sources to the modeled exceedances was significant. A source significantly contributes to a modeled exceedance if its
contribution to the model

- predicted impacts is greater than the Significant Impact Level (SIL), which in the case of 1

- hour SO 2 

### is 7.9 μ g/m 3 

### . Per the MAXDCONT output, the maximum contribution from Independence sources to any of the model

- predicted exceedances was 0.0154 μ g/m 3



### .

Sierra Club’s own modeling with the three most recent years (2012

- 2014) of
actual emissions data shows that SO 2 emissions from Independence Station do
not cause an exceedance of the 1

- hour SO 2 NAAQS. Further, as demonstrated by ERM’s culpability analysis, Independence Station d oes not contribute to any model

- predicted exceedance of the NAAQS.

Assertions regarding Good Engineering Stack Height at Independence Station

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.”

Sierra Club’s assertion regarding GEP stack height is in correct. In accordance

with USEPA’s Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack Height Regulations) (USEPA 1985) 2 , the physical 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 the 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:

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

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.

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 Independence 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 2 cooling tower, with a height of 393 feet (119.8 m). Thus, the GEP formula height for the main stack is 119.8 x 2.5 = 299.5 meters, not the 207 meters claimed by Sierra

Club.

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 Assistance Document 3 , for the purpose of categorizing air quality for the 1

- hour SO 2 NAAQS, modeling with the full stack height, regardless of the GEP form ula height, is allowed. Therefore, the discussion of GEP stack height is not relevant for the purposes of 1

- hour SO 2 modeling.

Other Modeling Weaknesses

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

Constant Stack Parameters:

The Sierra Club modeling use s 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 are not available from EPA’s Clean Air

3 http://www3.epa.gov/airquality/sulfurdioxide/pdfs/SO2ModelingTAD.pdfPAGE 5

Markets Database, 4 which is the source of emissions information used in Sierra Club’s modeling. Sierra Club’s modeling assumed that the stack parameters for

the two coal

- fired units are identical, which tends to make the impacts from both units directly additive, causing h igher impacts than would be the case when the actual hourly stack parameters are used. Table 1 shows that the average stack temperatures of the Units varies by over 20 Kelvin, while the exit velocities differ on average by about 1 m/s.

Table 1: Average ho urly 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 1 425.95 24.32 433.71 27.43 7.76 3.11

Unit 2 405.75 25.05 433.71 27.43 27.96 2.38

*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.

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 available design value”. This stat ement 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.

Flagpole Receptors

The modeling uses flagpole 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.

4 http://ampd.epa.gov/ampd/PAGE 6

Operational Loads

Section 4.2 of the Sierra Club modeling report suggests that because loa ds 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 10 0% 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 loads.

Receptor Grid

The receptor grid in Sierra Club’s modeling covers the entire Independence Station 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. Per the

Guideline on Air Quality Models (GAQM, 40CFR Appendix W) (USEPA 2005) 5 , 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 b oundary. Therefore, receptors should not be placed within that boundary.

Meteorological Data Processing

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

- year period. ERM’s modeling refined the

meteo rological data by resolving surface roughness and moisture by month.

Additionally, in section 4.5.4 of the modeling report, Sierra Club concludes that “Since the Clinton National Airport is located close to Independence Station, this meteorological data se t was considered appropriate for this modeling analysis”. There is no discussion of what “close” means or why the meteorological data are representative and Sierra Club provides no maps, drawings or other figures showing the relative location of the facili ty and the meteorological data tower. In fact, in the four modeling reports related to SO 2 attainment reviewed by ERM recently, as well as 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.

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

Allowable Emission Rate Modeling

Sierra Club’s report included modelin g of Independence Station 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), 6 the pu rpose 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 yea rs of meteorological data. Sierra Club only used 3 years of data.

Conclusion

Sierra Club’s modeling shows that Independence Station , when modeled with 3 years of actual emissions data, as is allowed in the SO 2 NAAQS Designations Modeling Technical Assis tance Document , combined with an ambient background concentration, has modeled impacts that are below the 1

- hour SO 2 NAAQS. While Sierra Club’s modeling predicts that emissions from FutureFuel Chemical Corporation exceed the NAAQS, Sierra Club did not perf orm a culpability analysis to determine whether Independence Station contributes to those predicted exceedances. Therefore, no conclusions related to the cumulative impacts of FutureFuel and Independence can be made from Sierra Club’s modeling. The culpab ility analysis performed by ERM using Sierra Club’s inputs shows that Independence Station does not contribute to any modeled NAAQS
exceedances

.

Therefore, Independence Station does not cause or contribute to any modeled
exceedances of the 1

- hour SO 2 NAAQS.

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

- 2015

- 08

- 21/pdf/2015

- 20367.pdf