### EXHIBIT 7 : G. Hoffnagle, TRC Environmental Corporation, Evaluation of Craig BART Modeling for Regional Haze Analysis

to

Tri-State Generation and Transmission Association, Inc.’s Detailed Comments to EPA Proposed Rule Published

at 77 Fed. Reg. 18052 to 18098

Submitted May 25, 2012

Docket ID No. EPA-R08-OAR-2011-0770

## Evaluation of Craig BART Modeling for Regional Haze Analysis

Rebuttal Report by Gale F. Hoffnagle, Sr. Vice President and Technical Director TR C Environmental Corporation

OVERVIEW

The i ntent of this report is to discuss the inaccuracy inherent in the air quality modeling for visibility impact of the Craig Station at the Mount Zirkel Wilderness Area and to address the nitrate contribution to visibility impairment and the role of Northwest Colorado NOx emissions in visibility extinction in Colorado Class I Areas. I adopt and incorporate the general comments that I made in my first report and in my testimony before the Air Quality Control Commission in connection with the November 18 – 19, 2010 hearing on BART issues.

Reality Check
The 5 year average visibility from the IMPROVE monitoring data collected at Mount Zirkel and the WRAP modeling in visibility extinction at Mount Zirkel (see technical Support Document for Mount Zirkel) is as follows:
TABLE 1 (in Inverse Megameters)

Mount Zirkel 20% Best Days 20% Worst Days

Measured (TOTAL) 11.7 Mm-1 28.6 Mm-1

Measured Nitrates 0.51 Mm-1 2.2 Mm-1
Natural Visibility (EPA) 10.56 Mm-1 19.04 Mm-1

Figure 1: Total and Component Extinction at Mount Zirkel (APCD TSD on Mount Zirkel); note, extinction from nitrates (red bar) is a minor contributor.2

WRAP Nitrates Modeling

Th e Western Regional Air Quality Partnership (WRAP) provided modeling of the entire West to evaluate the sources of contribution to the nitrate visibility extinction at Mt. Zirke l. Those results show the sources sequentially, as follows:

– 97.8% the Total is Anthropogenic 0.50 Mm-1 2.15 Mm-1

– 41.5% of “Anthro” is from Colorado 0.21 Mm-1 0.89 Mm-1

– 79.2% of Colorado share are Point Sources 0.16 Mm-1 0.82 Mm-1

71.3% of Colorado Point Sources are 0.12 Mm-1 0.59 Mm-1 External Combustion

Use of Inverse Megameter s
As I testified at the November hearing, we use inverse megameters to make it possible to linear comparison of extinction values which are less than 1 Deciview, i.e. negative numbers. The use of Deciviews also makes it difficult to compare modeled to measured values. Figure 2 is offered to explain to the reader this relationship. One Deciview equals 10 Mm-1 and a visual range of 400 kilometers, a longer visual range than is possible given the natural scattering by atmospheric gases. For comparison, 10 Inverse Megameters is equal to 1 Deciview and represents a visual range of 400 kilometers. When one looks at the above listing of Colorado’s share of visibility extinction at Mount Zirkel as modeled by the WRAP, one sees that all of the values of nitrate extinction are less than 1 Deciview and thus will not by themselves affect visibility.

Figure 2: Relationship of Extinction, Deciviews and Visual range (NPS Introduction to Visibility)

Eliminating NOx Emissions from Colorado Power Plants will not be Humanly Perceptible
By the WRAP model calculations which are listed at the top of this page, above, the largest potential contribution from Colorado power plant sources is 0.59 inverse megameters (because the Deciview is a log number when visibility impairment is very small the Deciviews go negative thus the equivalent of 0.59 Mm-1 is -28.3 Deciviews). If we take into account that the “natural visibility” based on EPA Guidance is 0.55 Deciviews (10.56 Mm-1) for the 20% Best3

days and 6.44 Deciviews (19.04 Mm1-) for the 20% Worst days, the WRAP’s modeling

c o ncludes that power plant contribution of nitrates is substantially smaller. Under the WRAP’s modeling, power plants derived nitrates are therefore responsible for 22.9% of the total nitrates and 1% of the total visibility impairment on the Best days and 2% of the visibility impairment on the Worst days. This value would be for all power plants in Colorado, not just Craig Station. These WRAP model results led the APCD to report in February 2009 to conclude that “Removing all Colorado SO2 and NOx emissions yields, at most, ~1 Deciview of visibility improvement”.
Craig Station cannot possibly be responsible for all of the power plant-related visibility impact at Mount Zirkel Wilderness Area; for example, work by the APCD indicates that the Hayden Station is tied to an equivalent modeled impact at Mount Zirkel. Plus, there are other power plant emissions in Colorado. Even by controlling 75% of the emissions at Craig by putting on SCR, there would only be calculated to be reductions of 0.03 Mm-1 on the 20% Best days and 0.15 Mm-1 of reductions on the 20% Worst days, if Craig were responsible for all the power plant impact at Mount Zirkel, but that cannot be the case, because there are other Colorado power plant emissions. These changes would not be observable at Mount Zirkel and are less than the natural visibility reduction of the atmosphere without pollutants.

The Model Options
The Interagency Workgroup on Air Quality Modeling (IWAQM) guidance (called FLAG) and the Colorado protocol are based upon conservative principals of modeling analysis because of their application to a wide number of sources and situations. The reasons that the modeling may over estimate the measured concentrations can be found among the conservative assumptions that are inherent in the proscribed techniques. Several factors which I believe should be applied to the modeling of NO x emissions from any source, as follows:

M easured ammonia concentrations:

Nitrate partitioning:
Ammonia limiting Method:

Puff splitting:
Visibility calculations method:

Ozone Concentration:
As I will show, these improvements and perhaps more are necessary in order to give decision makers reasonable understanding of the issues. The other option for decision makers is to4

recognize the tendency for CALPUFF to over predict impacts and thus the benefits of emission

r e ductions and to temper reliance on such model results.

Measured Versus Modeled Visibility Impacts
As I suggested in my November testimony, I have compared measured visibility impairment from the IMPROVE monitoring network to the CALPUFF modeled visibility impairment at the Mount Zirkel Wilderness Area. This shows an indication of the extent of the over predictive nature of the current CALPUFF modeling performed by APCD. I understand that under the auspices of APCD and the Regional Air Quality Counsel, a similar exercise is conducted in ozone modeling where the modeled ozone concentrations are compared to the monitored ozone values for those same days and the model is calibrated to the monitored data to help improve the model performance.

The measured data come from the IMPROVE website and consist of the measured extinction coefficient (B ext in Mm-1) to compare “Total Measured” visibility impairment to the “Total M o deled” visibility impairment. Also obtained was the percentage of nitrate of the total particulate (these are given on the web site in micrograms /cubic meter). Measurements are made every third day.

2005 APCD Modeling of Craig 1 and 2
The modeled data for the 2005 APCD modeling come from page 51 of the Technical Support Document “BART CALPUFF Class I Federal Area individual Source Attribution......Craig Station Units 1 and 2”. This lists the 25 highest days of modeled visibility impact for 2002 including the day, receptor, Total modeled Deciviews, background modeled Deciviews, Delta Deciviews and the % Nitrate contributing to the impairment.

The first result to review is the measured versus modeled data for Total Visibility impairment. That is done as shown in Figure 3, below. Figure 3 shows that the CALPUFF modeling for Craig units 1 and 2 cause impairment equal to a major component of the actual measured impairment shown in the data from the IMPROVE data base. Figure 3 shows the total visibility extinction from all sources of impairment (Total Visibility Impairment at the IMPROVE site). Recall the bar graph on page one above tells us the WRAP analysis concludes a small fraction of the total visibility impairment is attributed to nitrates, yet Figure 3 reveals that the CALPUFF modeling would have us believe that Craig Units 1 and 2 are a major contributor.5

The results of the overview comparison show that the 25 highest modeled days of Craig impact occur in the cold weather season as expected due to the conditions that are necessary for NOx to convert to nitrates (cooler atmospheric temperatures and moisture), and not in the warm weather season when the maximum visibility impairment actually occurs. Thus, even if the CALPUFF modeling were more accurate, reductions in Craig NOx emissions would not be projected to affect in any meaningful way the worst case visibility impairment. It should be noted that the magnitude of the modeled Craig impairment is similar to the measured values for the days when the modeled values are the maximum 25 modeled values, leaving no room for other sources to make contributions. As shown above at the top of page 2, the WRAP modeling states that all utility sources would add only 22.9% of the Total extinction.
Among the 25 maximum modeled days there were ten days when there were simultaneous Measured and Modeled value. The comparison of measured and modeled days shows that, on average, the modeled accounts for 98% of the measured and ranges from 80% to 140%.

But, to get a true comparison of the CALPUFF results to IMPROVE monitored data, one must zero in on nitrates and that is what is shown in Figure 4.6

For Nitrates the comparison is even more biased:

The bias of the modeled data is even more evident when one compares it to the nitrate readings in the IMPROVE data. The modeled visibility impact is 11.9 times the measured values for nitrates on the 10 days with simultaneous data. There is only one day where the measured nitrates even approach the modeled values (not a simultaneous day). As a result the model can be estimated to over predict the measured nitrate values by more than a factor of 11 and thus any resultant visibility improvement from emission reductions.
There are two obvious ways in which the above comparisons are not precise. The model predicts visibility impacts at receptors throughout the Wilderness Area while the measurement occurs at the southern end of the Wilderness Area. A review of the receptor locations for the 25 days shows that some are closer to Craig Station, more are further away and two are very close to the monitor location. Thus, no appreciable difference between measured and modeled results is expected due to location differences.
The second element of precision is the actual emissions on the 25 days versus the 24 hour maximum emissions used in the modeling. Craig Units 1 and two actually emitted more NOx on7

the 25 days in question than used by APCD in the 2005 modeling. In addition, Craig Station Unit 3 w as also operating at near full capacity on those 25 days. If Craig 3 had been included in that modeling the model would have overestimated the Craig visibility impact by a factor of 15 or

more.
In 2010, APCD redid the modeling for all the Craig units together. The comparison shows that the model overestimates Total visibility impairment by a factor of 1.9 and nitrate visibility impairment by a factor of 13.7 for the 7 days with simultaneous measured and modeled values.
In addition there are 6 days in 2002 when the model predicted that both Craig and Hayden made simultaneous impacts on visibility at Mount Zirkel. On those 6 days the model overestimated Total impact by a factor of 2 and nitrate impact by a factor of 20.8.

2010 APCD Modeling of all Three Craig Units
In 2010 APCD reran the CALPUFF model for all three Craig units. The emissions comparisons are as follows:
Emissions (lbs/hour) 2005 modeling 2010 modeling

Modeled Actual Modeled Actual

Unit 1 1466.8 1595.6 1519.9 1500

Unit 2 1466.8 1766.5 1489.7 1791

Unit 3 Not Modeled 1511.4 1679 1279

Total 2933.6 4874.5 4688.7 4570
Actual emissions on the top modeled impact days exceeded the modeled emissions in the 2005 modeling and Craig 3 is missing. If actual emissions were used in the modeling the model over prediction would have been higher. The emissions assumptions used in the 2010 CALPUFF modeling were close to the level of actual plant wide emissions; therefore the comparisons made in this report of “modeled” to “measured” are accurate.

The top 22 modeled days of each year were evaluated and compared to the measured data for those days. The result of this comparison is shown in Figures 5 and 6, below:8

A comparison on the days with measurements is shown as follows:9

It is clear that on many of these days (14 out of 19 days) the Total visibility reduction calculated for Craig Station is greater than the total measured extinction, sometimes by startling amounts. On average, the modeled Craig extinction is larger than the measured.

Turning to nitrates the results are as follows:10

Figure 8 shows the days for which we can make a direct comparison. Figure 8 shows the modeled visibility extinction significantly over predicts the measured visibility extinction due to nitrates.11

The average model over prediction is by a factor of 11.8 assuming that Craig is the only source of nitrates on those days which is clearly not correct. As before, the WRAP modeling indicated that utility sources were only responsible for 22.9% of the extinction.

Issues Raised by Dr. Middleton et al.

Reducing NOx at Craig will improve Visibility

As demonstrated above, a comparison of the modeled visibility from CALPUFF to the measured visibility data from the IMPROVE network show that this is simply not true. Any benefits will be insignificant in terms of extinction and no visible change will occur.

Cumulative Visibility Impacts
The same over prediction of nitrate extinction occurs at each Class I area. The nitrate contribution can be seen in the following figure from the APCD SIP document:12

Figure 9: Total and Component extinction at 6 Colorado IMPROVE sites (APCD SIP)
Note that all measurements, except Rocky Mountain National Park, have equivalent or less nitrates than Mount Zirkel. A major source of Rocky Mountain national park nitrates is known to be the East slope and not the West slope. The nitrate portion of visibility impairment at the nearer areas to Craig are significantly smaller than at Mount Zirkel, yet the APCD modeling yields nearly the same vastly over stated amounts of nitrates at those locations.

As distances increase and more terrain obstacles occur between the Craig and the Class I area, the model accuracy goes down. Thus, the supposed effects on visibility are not additive.

Combine the Units

The modeling reviewed above combines the units and shows no significant combined visibility impact.

Improve Ground Level Ozone
There is no evidence that the substantially rural Moffat County has any ozone non-attainment issue. Colorado started measuring ozone in Rifle and Mesa County in2008. The 4 th max values in

t h at year were 0.066 and 0.070 respectively. It will take two more years and a change in the NAAQS to see if there is a non-attainment issue there. But the Colorado River valley is a far cry from the Yampa River valley. As with all ozone ground level issues, tall stacks like Craig’s would make only small contributions to any ozone concentrations that do exist in the town of13

Craig. The implication that Craig NOx reductions will help Mesa County or the East slope with

a t taining the NAAQS is an artifact of over reliance on modeling.

Reduce Nitrogen Deposition

Dr. Middleton comments that nitrates are rising in the intermountain West. The data from Mount Zirkel reflect this rise, as follows:

However, the emissions from Craig have not risen over the period of record of the IMPROVE station at Mount Zirkel. Even if in the 1995 to 1999 period Craig were the only contributor, which it wasn’t, it is clear that the rise in nitrates is not due to Craig. This is especially interesting since the modeled years were 2001, 2002 and 2003 when higher nitrates, clearly not from Craig existed. In fact, NOx emissions at Craig decreased in 2003 and 2004 with the addition of low NOx burners and overfire air which would have led to a decreased portion of the above extinction.14

C o nclusion
The APCD BART CALPUFF modeling for Craig Station overestimates nitrate impact by more than a factor of 10 and in some cases by more than a factor of 20. This means that the application of controls on nitrogen dioxide emissions at Craig will have no discernable effect on visibility at the Mount Zirkel Wilderness Area and by extension on any other Class I area. The chemistry, transport and other conservative assumptions in the BART modeling protocol and the Forest Service guidance are so conservative as to be of little help to the decision maker in addressing real issues. The analysis by WRAP is supported by this analysis of measured visibility values from the IMPROVE monitoring data base versus modeled visibility impacts from the CALPUFF modeling. There is so little impact of nitrates at Mount Zirkel on visibility that reductions in nitrogen oxide emissions do not and cannot improve visibility, i. e. additional controls will not change or improve the visibility at Mount Zirkel. Similarly, the impact of Craig on other Class I areas, ground level ozone and nitrogen deposition, as posited by Dr. Middleton, is unfounded because it is based on faulty modeling or supposition.