Attachment	A TSRIA	Petition	for	Reconsideration Page	A

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*Analysis	by	Bison	Engineering,	Inc. **ATTACHMENT A**  *****

**DESIGN VALUE CALCULATIONS FOR SO**  **2 AT COBURN ROAD** 

**1. I**  **NTRODUCTION**
EPA’s SO 2 nonattainment designation for the area surrounding the Coburn Road monitor was based on a design value calculation using data collected during calendar y ears 2009

– 2011. TSRI A recognizes that 40 CFR Part 50.17, Appendix T prescribes that design values a re to be calculated based on three calendar years. However, the 2010 SO 2 NAAQS did not become effective until August 23, 2010 . Therefore, i t is appropriate to calculate a design value based entirely on data collected **after** the standard became effective

. Since three full calendars ye ars have not yet elapsed, it is necessary to either calculate these design values using a start date within the y ear or to use calendar y ear data to date

. This Attachment describes the methodology used to calculate the design value using three alternatives

. The first design value calculation is made based on data from the most recent 3 calendar years with the caveat that calendar y ear 2013 is not quite complete. The data were made available b y the Montana Department of Environmental Quality (MDEQ) and go through November 3, 2013. The second design value calculation was made using the same most recent data but covers the most recent 36

- month period , again ending November 3, 2013

. The third design value is based on the m ost recent 3

- ye ar period, ending September 30, 2013, with validated data. The third design value represents the first 36

- month calculation that does not contain data from before the August 23, 2010 effective date of the standard. It is also the first thr ee
- ye ar period where all data were collected from the Coburn site using a 500 ppb span range, rather than the less precise 1000 ppb span range used previousl y.
**2. D**  **ESIGN V**  **ALUE**

**– C**  **ALENDAR Y**  **EARS 2011,**  **2012 AND**  **2013** A design value was calculated for the most re cent 3 calendar years, although the final 16% of ye ar 2013 is not complete. Assuming no out

- of

- character values are encountered, the design value for 2011

- 2013 would be as shown in Table 1.

**TABLE 1: D**  **ESIGN V**  **ALUE C**  **ALCULATION FOR 2011** 

**– 2013** *
**Ranking 2011**  **2 012**  **2013***

Value (ppb) Date Value

(ppb) Date Value

(ppb) Date

1 st high 142 09/05/11 129 09/13/12 73 10/25/ 1 3 2 nd high 113 09/11/11 93 03/11/12 51 01/16/13 3 rd high 85 10/30/11 84 07/18/12 46 07/21/13 **4 th**  **high 74**  09/30/11 **70 11/03/12**  **46 10/26/13**  5 th high 66 11/20/11 55 01/04/12 42 01/04/13Attachment	A TSRIA	Petition	for	Reconsideration Page	A - 2

6 th high 65 10/19/11 54 9/28/12 42 09/10/13 **99 th** 

**- percentile value**  **74 70**  **46 Design Value = (74 + 70 + 46 ) / 3 = 63 ppb**  * Through November 3, 2013
**3. D ESIGN**  **V ALUE**  **– E NDING**  **N OVEMBER**  **3, 2013**
Coburn Road maximum daily SO 2 concentration data through November 3, 2013 were recently made available b y M DEQ. 1 While th is new data are currentl y described as “preliminary ,” any subsequent changes to that dataset will involve the removal of suspect value s, rather than the addition of new values that were not present in the initial compilation. Therefore, the dataset in its current form contains all of the potential “high” SO 2 values that could be present after final review and validation; use of that dat aset for purposes of this evaluation actually represents a conservative approach. The newl y available data were used to develop a design value calculation using a November 1, 2010

– October 31, 2013 basis (36 consecutive months) . Effectively , the calculation presented in Section 3 has been shifted forward b y one month , making it even more representative of current conditions.
Because the full hourly dataset for October is not y et published in a public EPA database and has only been provided b y M DEQ , this design value analy sis for November 2010

– October 2013 is p resented in steps for clarity . First, Table 2 shows the six highest daily maximum values for the indicated November 1, 2010

– September 30, 2013 periods, for which all hourl y data were available. 2

**TABLE 2 :**  **M AXIMUM**  **D AILY**  **SO 2**  **V ALUES FOR**  **N OV**  **2010 – S EP**  **2013**
**Ranking Nov 2010** 

**– Oct**  **2011 Nov 2011** 

**– Oc**  **t 2012 Nov 2012** 

**– Sep 2013** 

Value (ppb) Date Value

(ppb) Date Value

(ppb) Date

1 st high 142 09/05/11 129 09/13/12 70 11/03/12 2 nd high 113 09/11/11 93 03/11/12 52 12/21/12 3 rd high 101 12/24/10 84 07/1 8/12 51 01/16/13 **4 th**  **high 86**  **12/21/10 66**  **11/20/11 49**  **11/07/12** 5 th high 85 10/30/11 55 01/04/12 46 07/21/13 6 th high 74 09/30/11 54 09/28/12 42 09/10/13

Next, in order t o obtain a complete result for the November 1, 2012

– October 31, 2013 period, applicable values for October 2013 must be integrated into the data shown above. MDEQ has

1 Email from Stephen Coe (MDEQ) to James M Parker (PPL) dated November 6, 2013 , attached at the end of this document.
2 Hourly data for October 2013 were not available at the time of this analysis. However, MDEQ has reported the 4 highest daily ma ximums for January through October 2013 as outlined in Table 3.Attachment	A TSRIA	Petition	for	Reconsideration Page	A - 3

reported the following four highest daily one
- hour maximums for January

– October 2013 (Table 3).

**TABLE 3 :**  **M AXIMUM**  **D AILY**  **SO 2**  **V ALUES**  **F OR**  **J AN**  **– O CT**  **, 2013 ***
**Ranking Jan 2013** 

**– Oct 2013**  *****

Value (ppb) Date

1 st high 73 10/25/ 13 2 nd high 5 1 01/16/ 13 3 rd high 4 6 07/21/ 13 **4 th**  **high 4**  **6 10/26/**  **13** * This includes data through November 3 In combination, the two datasets can now be su mmarized as shown in Table 4.

**TABLE 4: D**  **ESIGN V**  **ALUE C**  **ALCULATIONS FOR N**  **OV 2010 – O**  **CT 2013** 
**Ranking Nov 2010**  **– Oct 2011 Nov 2011**  **– Oct 2012 Nov 2012**  **– Oct 2013**

Value (ppb) Date Value

(ppb) Date Value

(ppb) Date

1 st high 142 09/05/11 129 09/13/12 73 10/25/13 2 nd high 113 09/11/11 93 03/11/12 70 11/03/12 3 rd high 101 12/24/10 84 07/18/12 52 12/21/12 **4 th**  **high 86**  **12/21/10 66**  **11/20/11 51**  **01/16/13** 5 th high 85 10/30/11 55 01/04/12 49 11/07/12 6 th high 74 09/30/11 54 09/28/12 46 07/21/13 & 10/26/13 **99 th** 

**- percentile value**  **86 66**  **51 Design Value = (86 + 66 + 51 ) / 3 = 68 ppb** 

**4. D ESIGN**  **V ALUE**  **– E NDING**  **S EPTEMBER**  **30, 2013**

A n updated design value was also calculat ed for the Coburn Road monitor with respect to the 2010 SO 2 NAAQS of 75 ppb based on three consecutive y ears ending before October 4, 2013, consisting of the following periods:

 Year 1: October 1, 2010

– September 30, 2011

 Year 2: October 1, 2011

– September 30, 2012

 Year 3: October 1, 2012

– September 30, 2013
Table 5 of this Attachment lists the six highest daily maximum one

- hour SO 2 concentrations observed at Coburn Road for each of those ye ars. The fourth highest value within each ye ar represents the 99 th

- percentile value that is the basis for design value calculations. Analysis of the data yi elds a design value of 74 ppb, as shown at the bottom of the table.Attachment	A TSRIA	Petition	for	Reconsideration Page	A - 4 **TABLE 5**  **: D**  **ESIGN V**  **ALUE C**  **ALCULATION F**  **OR O**  **CT 2010 – S**  **EPT 2013** 

**Ranking Oct 2010 –**  **Sep 2011 Oct 2011 –**  **Sep 2012 Oct 2012 –**  **Sep 2013**

Value (ppb) Date Value

(ppb) Date Value

(ppb) Date

1 st high 142 09/05/11 129 09/13/12 70 11/03/12 2 nd high 113 09/11/11 93 03/11/12 52 12/21/12 3 rd high 101 12/24/10 85 10/30/11 51 01/16/13 **4 th**  **high 89**  **10/22/10 84**  **07/18/12 49**  **11/07/12** 5 th high 87 10/03/10 66 11/20/11 46 07/21/13 6 th high 86 12/21/10 65 10/19/11 42 09/10/13 **99 th** 

**- percentile value**  **89 84**  **49 Design Value = (89 + 84 + 49 ) / 3 =**  **74 ppb**
The calculated design value of 74 ppb for the three

- ye ar period of October 2010

– September 2013 is below the 75 ppb standard, and shows the Coburn Road monitor location meets the ambient standard.
As a side note, if this analy sis had been conducted from August 22, 2010 (the effective date of the rule) through August 21, 2011 (and so forth), the same results (< 75 ppb design value) would be observed. In fact, this is true for an y continuous 36

- month period following the effective date of the standard.

The anal ys es presented in this Attachment show that if the most recent ly available three calendar ye ar data period is used for a design value calculation, 3 Yellowstone County is presently in attainment of the 2010 SO 2 NAAQS of 75 ppb by a considerable margin. Based o n past history and the 2013 monitor readings through the first week of November, it is highl y probable that the three calendar years following the effective date of the 2010 SO 2 NAAQS will be well below 75 ppb.

The results from all three methods demonstrat e attainment and support TSRI A’s contention that EPA should reconsider and repeal the Yellowstone SO 2 Designation

. The continuing reduction in emissions coupled with cle ar evidence that ambient concentrations are below the 2010 SO 2 NAAQS support such a request.

3 T he 2013 calendar year is based on data through November 3 only

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### DEQ **-Supplied Coburn Data – 2013**  ***** **Jan 1 through November 3**

* Email from Stephen Coe (MDEQ) to James M Parker (PPL) dated November 6, 20131 THIS EMAIL INCLUDED WITH PERMISSION FROM STEPHEN COE OF MDEQ

From: Coe, Stephen [ mailto:SCoe@mt.gov ] Sent: Wednesday, November 06, 2013 8:31 AM To: Parker, James M Cc: Merchant, Eric Subject: Coburn info

Jim,

I just wanted to share with you the monitoring data I have been tracking and bring you up to speed with where we are tracking with the 2013 data and 11

‐ 13 design value. Below are a couple graphs showing all the hourly data, and pointing out th e High 4 days (99 th percentile) and a showing the 4 th highest and the resulting design value should that 4 th highest stay the same. We still have two months to go, so anything could happen. I have also included a table with the wind direction and speed for the high values, as well as pollution roses for the high days, because the pollution roses are for the entire 24 hour period they are not as ac curate as the table below, but are still good information.

DISCLAIMER: Some of the data presented in this email is unqualified and has not yet been quality assured, these data are for discussion only and should not be used for official determinations.

The wind direction is coming from between 232.7

– 239.4 degrees and wind speed between 12 and 16 mph.

CB_Blgs Coburn Rd 12_SPEED 001h CB_Blgs Coburn Rd 13_WDIR 001h CB_Blgs Coburn Rd 21_SO2

‐ 1HRB 001h
Date Final Value Final Value Final Value 10/25/2013 2:00 AM 16.0293144 232.726698 73.2670833 1/16/2013 8:00 AM 15.0486642 239.353242 51.9269444 7/21/2013 7:00 AM 11.9557505 233.207781 46.62875 10/26/2013 9:00 AM 13.3493935 234.593146 45.608194423 -- This
are n sen d 

### Stephe n Senior Pl a Air Resou Montana (406) 782 scoe@mt

The info r of the re c agent re s received this mes s notify us

email and a
n ot the inten d d er. Thank y o 

### n Coe P.E.

a nning Engin e
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‐ 2689 ext. 2 0 .gov

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