### Assessment Process
Indiana

- Kentucky Electric Corporation Clifty Creek Station Evaluation for 720 Operating Hour Site Rolling Average SO 2 

### Mass Emissions Limits Using Flue Gas Desulfurization (FGD)

Step 1: Facility Description and Modeled Limits

The Indiana

- Kentucky Electric Corporation’s (IKEC’s) Clifty Creek Station has six coal

- fired electric generating units (Units 1 through 6) that were placed into commercial operation in 1955 and 1956. All six units have pulverized

- coal, front

- wall

- fired, w et

- bottom boilers and a nameplate generating capacity of approximately 217 megawatts

.

Prior to being exhausted to the atmosphere, the flue gases from Units 1, 2, and 3 are combined and
scrubbed for SO 2 

### removal in a jet

- bubbling reactor (JBR) scrubber. Th e scrubber for Units 1, 2 and 3 is
referred to as JBR13 , and the combined scrubbed flue gases from these three units is exhausted through Common Stack CS013 (also known as Flue 13). The flue gases from Units 4, 5, and 6 are combined and
scrubbed in JBR46 prior to being exhausted through Common Stack CS046 (also known as Flue 46). The two flues associated with each scrubber are contained in one stack shell (Stack 14), and the emissions from each flue are represented of the combined scrubbed emissions from all six units

. The scrubbers were designed to allow the Clifty Creek Station to use local Illinois Basin coal with sulfur content in the 5 lb per mmBtu range.

For modeling purposes, IKEC identified an appropriate mass emissions limit as a site average fo r the Clifty Creek Generating Station that s models attainment of the 20 10 1

- hour primary NAAQS for SO 2 

### .

Per the request of IKEC )

, Mr . Dave Long

- at American Electric Power (AEP) performed modeling using
the representative Clifty Creek Station post scrubber emissions data supplied to him by OVEC. Based on numerous modeling runs

, Mr. Long determined that an emission value of 2,624.6 lbs/hour as a SITE average emissions rate as averaged over a 30 day period will assist the Indiana Department of

E nvironmental Management (IDEM) in complying with the 20 10 SO 2 

### NAAQS.

Step 2: Compile Representative Emissions Data Set

Data was obtained for hourly SO 2 

### mass emissions (lbs/hour) for each stack at the Clifty Creek Station from June 1, 2013 00:00 hour th rough December 31, 2015 23:00 hour. This starting date was chosen based upon the startup dates for each of the two JBR scrubber s that were placed into service at the Clifty Creek Station in 2013 (CS013: 3/20/2013, CS046: 5/15/2013). Since a site limit w as developed for
the entire Clifty Creek Generating Station, the following criteria were used to “clean up” the data set:

1. At least one unit on each stack had to be operating. Periods when only one single stack was in operation was discarded.

2. The data fro m each stack was obtained using either the primary or backup certified SO2 monitoring system. H ours when either stack had data generated using the missing data algorithm was discarded.

3. Two data sets were generated. One data set included all data meeting cr iteria 1 & 2 from June 1, 2013 00:00 hour through December 31, 2015 23:00 hour. The second data set included data

### meeting criteria 1 & 2

, but only for the years 2014 and 2015 , which IKEC believes is more

representative based on fuel source and operational mode

. The coal blend consumed in 2013 included a significant proportion of residual P owder R iver B asin coal , which is no longer consumed at the Clifty Creek Generating Station . This fuels source was still being consumed during 2013 due to contractual obl igations in place prior to the commencement of scrubber operation. Utilization of the data from this time period could result in a low biasing of SO2

emissions

, which would not have been representative of future operations , nor of the design
criteria for scrubbers themselves . The data for 2014 & 2015 was not impacted to a significant degree by any PRB fuel blending and therefore is more representative of expected longer term
fuel source and future operations.

Step 3: Calculate 720 Operating Hour Site Roll ing Average

After sum ming the hourly mass emissions for SO 2 

### from each stack , t his data was then used to calculate a 720 Operating Hour Site Rolling Average mass emission value for each hour in the data collection period.

T he “cleaned up” data set resulted in a 720 Operating Hour Site Rolling Average that did not include hours where valid data was not available from both stacks and did not include hours where only one stack was operating. It should be noted that there are n o values calculated for the first 720 hours of the
data set.

Step 4: Calculate the 99 th 

### Percentile Values
The 99 th 

### percentile values were calculated for the 1

- hour site emissions data set and the 720 Operating Hour Site Rolling Average. T he Site 1 Hour Da ta set the 99 th 

### Percentile value was determined to be 2,394 lbs/hour. T he 720 Operating Hour Site Rolling Average data set the 99 th 

### Percentile Value was determined to be 1,346 lbs/hour.

Step 5: Calculate the Ration of the 99 th 

### Percentile Values

Divid ing the 99 th 

### percentile value of the 720 Operating Hour Site Rolling Average by the 99 th 

### percentile
value for the Site 1

- Hour Data yields a quotient of 56.2%.

1,346 lbs/hour / 2,394 lbs/hour *100%= 56.2%

Discussion

The attached graph shows the 720 Operating Hour Site Rolling Average and the 2,624.5 lbs/hour modeled value trended alongside the 99 th 

### percentile value for this particular data set.

IKEC proposes that the value of 2,624.5 pounds per hour (2,624.5 lb/hr) Site Average mass SO 2 

### emission
rate be uti lized for the IDEM Commissioner’s Order. This compliance value would be an unweighted average calculated by IKEC using data collected by existing certified CEMS. Data used for determining this compliance value will be unbiased data. Additionally, data ge nerated the using Part 75 Missing Data Algorithms will not be used to determine compliance . This is analogous to the manner in which data is handled under the existing Part 60 and MATS programs, which are utilized by IKEC for Title V and MATS compliance de monstration. The hourly data should be calculated as a 720 operating hour site rolling

average. IKEC also believes the Commissioner’s Order should state that IKEC is not out of compliance during periods where the certified CEMS is not producing valid dat a for both stacks if the scrubber parametric data remains within the limits listed below:Normal operation of either JBR reactor s shall be deemed to be

(a) Slurry level at or between the range of 19.33 to 21.06 feet , and ;

(b) Slurry pH at or between 4. 0 S.U. to 6.5 S.U.0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Hourly Site SO2 Mass Emissions (pounds) from January 1, 2014 through December 31, 2015

Sum of Plant

SO2 lbs/hr

Emissions

99th Percentile
Value of Hourly

Data

Proposed Limit 5,000 lbs/hr Figure 4

0 500 1000 1500 2000 2500 24 Hour Rolling Average SO2 Mass Emissions (pounds) from January 1, 2014 through December 31, 2015

24 Hour Rolling Average

99th Percentile
Value of 24

Hour Rolling Average Data Figure 5

0 200 400 600 800 1000 1200 1400 1600 720 Hour Rolling Average SO2 Mass Emissions (pounds) from January 1, 2014 through December 31, 2015

720 Hour Rolling Average

99th Percentile
Value of 720

Hour Rolling Average Data Figure 60 2000 4000 6000 8000 10000 12000 14000 16000 Hourly Site SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

Sum of
Plant SO2 lbs/hr

Emissions

99th
Percentile
Value of Hourly Data Figure 1

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0 7000.0 8000.0 24 Hour Rolling Average SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

24 Hour Rolling Average

99th Percentile Value
of 24 Hour Rolling Average Data Figure 2

0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0 720 Hour Rolling Average SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

720 Hour Rolling Average

99th Percentile Value
of 720 Hour Rolling Average Data Figure 3