Technical Comments on the Public Review Draft of the

Washington State Regional Haze State Implementation Plan

Reasonable Progress Goals

Although Ecology has improved its documentation of a four-factor analysis, it has not yet taken 

measures to reduce emissions of haze-causing pollutants beyond BART. Because Ecology’s 

Reasonable Progress Goals are substantially slower than the uniform rate of progress, the 

Regional Haze Rule requires states to further reduce its emissions or demonstrate why additional 

emission reductions are not reasonable at this time. Ecology has identified several source 

categories for which NOx and SO2 emission reductions may be reasonable including process 

heaters, FCCU/CO Boiler units at petroleum refineries, dry process cement kilns, industrial 

boilers, and Kraft pulping mills. Ecology states that it is not reasonable to require additional 

controls on these sources at this time because of there is not sufficient time to go through the rule 

making process, as would be required under Washington State Law. However, we note that 

Oregon was able to identify go through the rule making process to obtain controls under 

Reasonable Progress for the PGE Boardman Facility. 

Additionally, it is unclear why Ecology is setting the Reasonable Progress Goals for the 20% 

Least Impaired Days as no degradation (i.e., the same deciview value as baseline) when the 

WRAP modeling shows lower values are projected for all Class I areas in Washington. 

This is in contradiction to § 51.308 (d) (1) (vi) 

“(vi) The State may not adopt a reasonable progress goal that represents less visibility 

improvement than is expected to result from implementation of other requirements of 

the CAA during the applicable planning period.”

In Ecology’s “Federal Land Managers Comments and Ecology’s Response to Comments” 

document (Appendix B, p. B12), Ecology addresses the Forest Service concern that visibility 

conditions at the NOCA1 IMPROVE site are projected to deteriorate by 2018. The Forest 

Service acknowledges that the roughly 9,500 tpy of SO2 reductions apparently not included in 

the WRAP modeling are significant and would most likely influence the projected visibility 

conditions favorably. Indeed worst 20% day sulfate concentrations have been declining at most 

Washington Class I areas, including NOCA1, from 2000 to 2008. In the same time period, 

however, monitoring data shows that clearest 20% day sulfate values at NOCA1 are increasing. 

In discussing the FS comment on modeled increase in sulfate impacts at NOCA1, Ecology 

makes the following statement:

“Ecology’s investigation of the projected increases in visibility impairment at NOCA1 

concluded that the projected increase in visibility impairment is the result of the comparatively 

long residence time of air parcels near the monitor combined with the presence of large point 

sources of SO2.”
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In light of the worsening clear day sulfate concentrations, the confusion surrounding the WRAP 

modeling results, and Ecology’s own statement that increasing impairment at NOCA1 can be 

expected due to large nearby SO2 point sources, it would seem that these large point sources 

should be identified, and would be candidates for reasonable progress controls as soon as 

practicable.

TransAlta BART Determination

Flex Fuels plus Selective Catalytic Reduction

The BART rule (FR Vol. 70. No. 128/July 6, 2005), specifies the five-step process used in 

determining BART. These steps are as follows:

1. Identifying all available retrofit technologies;

2. Eliminate technically infeasible options;

3. Evaluate control effectiveness of remaining control technologies;

4. Evaluate impacts and document the results; and 

5. Evaluate visibility impacts. 

The process is very linear. Ecology appropriately identified both selective catalytic reduction 

(SCR) and selective non-catalytic reduction (SNCR) as available retrofit technologies for 

controlling NOx. However, it is unclear whether or not Ecology is stating that SCR is 

technically infeasible or not due to complications associated with the tight spacing at TransAlta’s 

Centralia facility. Ecology’s cites the following issues for not selecting SCR as BART 

(Appendix L of Public Review Draft of the WA RH SIP):

The tight construction site,

Potential difficulty in finding a location for ammonia storage that is safe, does not impede 

access to other components, or interfere with underground or above ground utilities and 

ducting,

Elevated construction location, and 

Difficulty in ducting exhaust gas from the boiler through the SCR units to the ESPs while 

achieving even flue gas distribution across the SCR catalyst beds and within the ESP. 

The final BART rule states (page 39165 of the July 6, 2006 FR/Vol. 70. No. 128) “where you 

conclude that a control option identified in Step 1 is technically infeasible, you should 

demonstrate that ... specific circumstances preclude its application to a particular emission unit. 

A demonstration of technical infeasibility may involve irresolvable technical difficulties with 

applying the control to the source (e.g., size of the unit, location of the proposed site, operation 
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problems related to specific circumstances of the source, space constraints, reliability, and 

adverse side effects on the rest of the facility). Where the resolution of technical difficulties is 

merely a matter of increased cost, you should consider the technology to be technically feasible. 

The cost of a control alternative is considered later in the process.”

However, in Ecology’s BART Determination Support Documentation for TransAlta Centralia 

Generation, LLC Power Plant (Revised April 2010) Ecology states that “The primary difficulties 

are lack of space for easy installation of the catalyst beds and ducts, leading to very high 

construction costs that far surpass ranges of acceptable cost effectiveness”. This implies that 

Ecology believes SCR is technically feasible, but was not selected as BART due to excessive 

costs. This is further supported by the statement that “Ecology concurs with TransAlta that the 

construction costs to overcome the technical difficulties of retrofitting an SCR system on its 

boilers, given its current configuration and installed emission controls, render this technology 

economically infeasible for implementation at this time.” 

TransAlta evaluated the cost of retrofitting SCR in a “hot, dirty” location, above the first ESPs, 

as a cost of $413/kW, based upon scaling the $200/kW using “engineering judgment”. Ecology 

compares this with the PGE Boardman’s SCR retrofit cost of $382/kW, prepared by PGE’s 

consultant. However, we note that the PGE cost estimate revised by Oregon DEQ, after hiring 

an independent third party engineering firm to analyze the costs (Eastern Research Group). ERG 

estimated the cost of an SCR retrofit at the PGE Boardman facility at approximately $250/kW, 

which is 35% less than the estimate prepared by PGE’s consultant. 

Today, we note a similar situation exists for the TransAlta Centralia power plant in which 

TransAlta has prepared a cost estimate, which varies greatly from estimates provided by the 

National Park Service and estimates in the ERG report to Oregon DEQ. Referring to the 

National Park Service references of costs for recent SCR retrofits, we note that “the overall 

range for these industry studies is $50/kW to $300/kW. The upper end of this range is for highly 

complex retrofits with severe space constraints, such as Belews Creek, reported to cost $265/kW, 

or Cinergy’s Gibson Units 2-4. Gibson, a highly complex, space-constrained retrofit in which 

the SCR was built 230 feet above the power station using the largest crane in the world only cost 

$251/kW in 2007”. Thus TransAlta’s cost estimate of $413/kW is suspect because it far 

surpasses not only the revised costs for installing SCR at the PGE Boardman facility, but at other 

highly complex sites as well. Ecology did not perform and document its own independent cost 

estimate. 

Using the $413/kW estimate, Ecology states that annualized costs for installing SCR on both 

units would have a cost effectiveness of $9091/ton NOx removed. Other states have found that 

$7300/ton is cost effective for NOx removal as BART. If TransAlta’s cost estimates are overinflated, by 35 - 65% greater than the upper range of costs for other complex SCR installations, it 
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appears that SCR installation at TransAlta would be reasonable. Ecology does not provide its 

own cost analysis which supports its rationale for dismissing SCR as infeasible due to excessive 

costs

Ecology’s BART determination is also lacking an evaluation of the visibility improvement which 

could be accomplished by Flex Fuels plus SCR. Thus the benefits associated with incurring the 

costs of adding SCR on both units is not quantified, thus the BART analysis is incomplete. 

Flex Fuels Plus Selective Non-Catalytic Reduction (SNCR) 

The rationale Ecology provides for not selecting Flex Fuels plus SNCR as BART for NOx is 

unconvincing. Ecology cites the combination of the following factors, when considered 

together; provide sufficient rationale for Ecology to dismiss this option as BART. These factors 

are:

Incremental cost effectiveness

energy and non-air quality environmental impacts

existing air pollution controls, 

remaining useful life of the facility, and 

Compliance with State climate change rules.

Each of these reasons is examined below.

Ecology states that the incremental cost effectiveness of Flex Fuels plus SNCR is $2145/ton. 

Yet, it does not provide any additional analysis, such as creating a least-cost envelope of 

dominant alternatives which would help one determine whether Flex Fuels plus SNCR is 

unreasonable. Ecology recognizes that the combination of Flex Fuels and SNCR would increase 

the level of visibility improvement at the 12 affected Class I areas, in some cases up to nearly 2.0 

deciviews of improvement. Ecology merely states that “While this additional project does result 

in some visibility benefit, we must also weigh other factors of the BART analysis to determine 

feasibility. 

Additionally, Ecology identifies the energy and non-air quality environmental impacts as another 

factor in not selecting this option as BART. Ecology states that this alternative would result in a 

parasitic load of 1.4 MW. The EPA BART rule states “...because energy penalties or benefits

can usually be quantified in terms of additional costs or income to the source, the energy impacts 

analysis can, in most cases, simply be factored into the cost impact analysis.”. It appears that 

Ecology is double counting energy penalties (i.e., parasitic load) in making its BART 

determination.
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Ecology also states that there is a potential for ammonia slip with SNCR, which would in turn 

contribute to visibility impacts. Ecology then states that this is a manageable impact. Ammonia 

slip may cause visibility impacts in an ammonia limited environment. However Ecology has not 

demonstrated that the atmosphere between Centralia and the affected Class I areas is ammonia 

limited, nor has it quantified the potential impact through the modeling evaluation. In fact, this 

is an air quality impact, not a non-air quality impact, under which it is claimed. Additionally, 

SNCR has been selected as BART for a number of coal-fired power plants, all of which face this 

same potential for ammonia slip (e.g., PGE Boardman, Oregon, Trigen Craig, CO, Golden 

Valley Electric Healy, AK, Basin Electric, Leland Olds Power Plant, ND, etc.). Apparently, 

other states believe this is a manageable issue. 

Ecology also considered the existing controls at the facility in making its BART determination. 

The BART rule allows for consideration of existing controls in the BART determination process. 

Existing controls are to be included as part of Step 1 (identify all available retrofit control 

techniques), and Step 2 (include control options that involve improvements to existing controls 

in addition to add on or complete replacement of existing controls.) If the existing controls were 

put in place after the baseline period, they could be evaluated as any other control alternative. 

The presence of existing controls by itself is not sufficient basis to dismiss other control 

technologies. Ecology already considers the comparative cost of existing controls and Flex Fuels 

plus SNCR in the incremental cost analysis. Ecology is double counting this factor as a rationale 

for not selecting Flex Fuels plus SNCR as BART.

Ecology also states that they believe the likely remaining useful life of the TransAlta Centralia 

facility is 15 years or less. Should this become an enforceable permit condition, then it can be 

included in the determination of annualized cost effectiveness, and not be considered as a 

separate factor. We refer Ecology to the most recent proposal by Oregon DEQ for early 

shutdown options for the PGE Boardman power plant as an example of the proper way to 

consider a shortened remaining useful life in determining BART. 

Finally, Ecology identifies a proposed 3-step process requiring TransAlta to comply with 

Executive Order 09-05 pertaining to State climate change regulations. Ecology states that this 

factor affects the remaining life of the facility. As such, Ecology needs to account for this in the 

annualize costs of potential BART alternatives, and not cite it as an independent factor. 

When only considering factors which are not double counted, Flex Fuels plus SNCR is not 

selected as BART solely because of the incremental cost effectiveness of $2145/ton. This value 

is within reasonable costs as identified by other states. Ecology should revise its BART 

determination.
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BART Exemption Modeling for Alcoa Wenatchee Aluminum Works

The US Forest Service has reviewed Ecology’s response to our previous comments on the 

acceptability of the use of fine-resolution CALMET wind fields in the Alcoa Wenatchee Works 

BART exemption modeling and information provided in Appendix I of the Public Review Draft 

of the Regional Haze SIP. Ecology’s response has not resolved our concerns about both 

procedural and technical issues with this analysis. 

General Issues:

Ecology argued that no lower limit exists to the application of CALMET examined applications 

of CALMET. Ecology stated: “After finding numerous references to analyses with CALPUFF 

using similar grid spacing in equally complex terrain between 1999 and 2007 and finding no mention 

of any lower limit to the acceptable meteorological grid spacing,” First, we would like to highlight 

the oversight in Ecology’s argument that, in each of the cases cited by Ecology, no corresponding 

performance evaluation was conducted that objectively documented that greater performance was 

achieved with the application of CALMET at a higher resolution. Rather, Ecology should have 

focused its review upon published cases that documented the improved performance of CALMET. 

Earth Tech (2001), RWDI (2002), and Scire et al. (2009) all documented evaluations of CALMET at 

high resolutions. In each case, poor performance was achieved when relying solely upon the ability 

of CALMET to induce specific features into the 3-D windfield. Chandresekar (2003) provides the 

best summary of CALMET’s capabilities: “...regions of complex terrain can introduce additional 

difficulties like inadequate density of observations, limitations of a diagnostic model to 

reproduce the observed features over complex terrain, and difficulties in fully resolving terrain 

features by using a coarse prognostic model over a complex terrain. The effectiveness of this 

approach may therefore be different for a region of complex terrain.”

Finally, it is important to note that EPA shifted its policy in 2009 regarding the resolution of 

CALMET wind fields as a direct response to the growing trend of applications of CALMET at higher 

resolutions with little or no scientific justification. 

Procedural Issues:

Ecology acknowledges that the Washington-Oregon-Idaho BART Modeling Protocol was 

developed to provide consistency between the BART modeling performed in the three states. 

But Ecology also states that “the authors of the protocol agreed that the document was to be a 

guideline, and that States have the ability to deviate from the guideline under certain 

circumstances”. There is no documented mechanism which allows for unilateral approval of 

deviations from the modeling protocol. 

Further, section 6 of the EPA Guidelines on Air quality Modeling (GAQM) published in 

Appendix W of Part 51 includes recommendations regarding the application of CALPUFF for 

visibility assessments for long range transport in general. The GAQM indicates that such 
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applications will require significant consultation with the appropriate reviewing authority and the 

affected FLM (Federal Land Manager). As indicated in our previous comments, the reviewing 

authority (US EPA Region 10) and the US Forest Service have both indicated the unacceptable 

nature of Ecology’s deviation from the modeling protocol. As such, Ecology has not followed 

established protocol or EPA guidance on this issue.

Technical issues:

Ecology’s justification for use of the 0.5 km grid resolution is not consistent with EPA’s 

guidance on this issue. The May 15, 2009 EPA Regulatory Air Quality Modeling Clearinghouse 

Memo states the following in addressing the use of finer resolution CALMET wind field. 

An argument for the use of finer resolution CALMET wind fields should address two 

components.

1. The prognostic meteorological data sets from numerical weather prediction (NWP) 

models lack sufficient resolution to capture the meteorological features of interest which 

would be responsible for transport of airborne contaminants from the source to the Class 

I area(s) of interest.

2. Diagnostic wind model (DWM) such as CALMET can enhance the NWP data used as the 

first-guess wind field (CALMET switch setting IPROG=14) sufficiently to adequately 

replicate the key meteorological features of interest. 

In addressing the first issue, it is necessary to identify the meteorological features of interest 

which are responsible for transport of airborne contaminants from Alcoa Wenatchee Aluminum 

Works to the Alpine Lakes Wilderness. In addressing this, (1) the meteorological conditions 

associated with transport of air pollutants from Alcoa Wenatchee Aluminum works to the Alpine 

Lakes Wilderness need to be identified, and (2) the scale of motion needs to be identified for 

these conditions. 

A general rule of thumb is that a prognostic meteorological model cannot physically resolve a 

meteorological feature that is less than five times the grid resolution (horizontally and vertically) 

(ref: NOAA COMET learning module on numerical weather prediction). Thus, if the horizontal 

grid resolution of the prognostic meteorological model is 4-km, it is reasonable to assume that it 

cannot resolve a meteorological feature less than 20-km in length or width. 

For example, if a cold air mass descends along the east side of the Cascades causing easterly 

flows during the winter time, which transports pollutants from the Alcoa Wenatchee Aluminum 

Works to the Alpine Lakes Wilderness, then the scale of this synoptic system may be on the 

order of hundreds of kilometers, a phenomenon easily resolved by a 4-km MM5 run. However, 

in the case of up-valley flows driven by difference in the local surface energy budgets, this 

phenomenon may be on the scale of the length of the valley of interest, something which may not 

be resolved by a 4-km MM5 model
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Thus, if the locally-forced flows (such as mountain-valley winds) are the meteorological feature 

of interest and the only meteorological features which drive the transport winds from the Alcoa 

Wenatchee Aluminum Works towards the Alpine Lakes Wilderness, and these flows are less 

than 20-km, indeed, the 4 km NWP data cannot resolve this phenomenon. However, there may 

be other meteorological phenomenon of 20-km or larger scale which can drive flows from the 

Alcoa Wenatchee Aluminum Works towards the Alpine Lakes Wilderness. These should also be 

addressed and a discussion of which meteorological feature is associated with worst-case haze 

impacts in the wilderness ought to be identified as well. 

The second component of EPA’s recommendation is to demonstrate that CALMET can enhance 

NWP data used as the first-guess wind field sufficiently to adequately replicate key 

meteorological features of interest. 

One of the key contentions made by Ecology is that use of the 4-km CALMET generated wind 

field creates “errors” in the surface wind field, which are resolved by use of the 0.5-km wind 

field. This is demonstrated in Figure I-2 and I-3 in which both the 4-km and 0.5-km surface 

winds are shown with the 0.5-km resolved terrain as background. Ecology states “...the finer 

resolution modeling provides a much more detailed spatial pattern in the winds which conforms 

more accurately to the terrain when compared with the wind fields from the lower resolution 

model runs. It is clear from these plots that the lower resolution runs will miss much of the 

terrain channeling within the modeling domain. More important, the failure of the 4-km grid to 

accurately represent peaks will allow air to flow unimpeded through regions that would 

otherwise deflect it.” In examining the validity of this statement, we note the following.

Ecology’s approach is based upon the flawed assumption that increased structural detail of the 

higher resolution wind field is an indication of improved performance of the wind model. In the 

IWAQM guidance reassessment (EPA, 2009), EPA warned of the temptation to apply this form 

of reasoning. EPA stated: “...the higher resolution CALMET simulations may increase the 

structural detail of the final wind fields; however, the majority of CALMET evaluations to date

have been subjective in nature and have relied upon the perceived increase in structural detail 

(i.e. “realism”). This evaluation relies upon the perceived increase in structural detail without 

any form of a statistical performance evaluation to verify the objective accuracy of high 

resolution wind fields. In short, a subjective assessment that a wind field is “realistic” is not 

sufficient to support the assumption that the wind field accurately reflects reality.” Ecology uses 

the exact same reasoning and arbitrarily concludes that the increased structural detail must in fact 

be the correct wind field realization without any means to support such. In essence, the argument 

is condensed into “we will apply CALMET at a higher resolution to justify a higher resolution of 

CALMET.” 

Evaluation of the 4-km and the 0.5-km wind field is performed by comparing it with the 0.5-km 

resolved terrain, not both the 4-km and 0.5-km terrain. Following this logic, it is reasonable to 

conclude that the 0.5-km winds should be evaluated by comparing them with terrain resolved at a 
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higher resolution, perhaps 10 meters. Under this evaluation scenario, if any locations occur 

where the 0.5-km winds appear to move towards the 10 meter resolved terrain, rather than 

tangential to the terrain, then the 0.5-km wind should be deemed inappropriate. Similarly, if 12-

km winds were plotted against a 4-km resolved terrain, and locations were found in which the 

12-km winds were found to flow towards the terrain, then they should be found to be 

inappropriate. Following this logic, it appears that plotting the winds created with the same 

resolution as the terrain will always be selected, especially if the performance is evaluated based 

upon terrain following flows. Is there a point of diminishing returns when the use of higher grid 

resolution no longer affects the results? If so, this has not been demonstrated. 

Ecology inherently assumes that any deviation from tangential airflow is unexpected and 

therefore in error. In fact, numerous forces operating at different scales of motion, determine 

the wind direction, making it one of the most difficult meteorological parameters to accurately 

predict because of small scale influences near the surface. 

Air can flow up and over terrain if it has sufficient amount of kinetic energy to overcome 

resistant forces. The behavior of the air flow is determined by the ratio of the amount of kinetic 

energy of the air flow to the resisting forces of gravity, buoyancy, (i.e., static stability) and 

terrain height (referred to as the local Froude number). Thus if the sufficient kinetic energy 

exists, the wind would be expected to travel up and over terrain, rather than around it. Even if 

sufficient kinetic energy did not exist, the wind direction may not necessarily be channeled 

directly through the terrain, as frictional forces, and small scale differences in surface albedo, 

and Bowen ratios would act to induce turbulence, resulting in unexpected wind directions. 

CALMET must rely on the limited surface and upper air observations in the computational 

domain to calculate the local Froude number. Recall, that CALMET must obtain the needed 

information from observation stations which may not be representative of the location of interest 

(in this case, the terrain between Wenatchee and Alpine Lakes Wilderness). Thus, the CALMET 

calculated wind behavior is not necessarily representative of reality. 

Additionally, the terrain height used may not be representative of actual terrain features of 

interest as it’s is based upon the terrain radius of influence (TERRAD) specified by the user. 

Additionally, the static stability used in the calculation of the local Froude Number is based upon 

the potential temperature lapse rate, determined from the domain representative upper-air station 

specified by the user. If the upper air station is far away from the local terrain of interest, it will 

not be representative of the local temperature structure of the complex terrain between 

Wenatchee and Alpine Lakes Wilderness. 

CALMET also lacks the necessary physics to balance the forces when air flows near terrain, as 

such it forces air to flow tangentially to the terrain. The tendency of CALMET to generate 

terrain following flows is a known limitation in the model. This has been documented by EPA in 

its discussion of the ability of diagnostic wind model (DWM) to enhance numeric weather 
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prediction (NWP) data to adequately replicate meteorological fields of interest (Section 2.2 of 

the Reassessment of IWAQM Phase 2 Summary report, draft May 27, 2009). In that discussion, 

EPA states that CALMET only contains algorithms for certain aspects of the valley wind system 

(drainage flows). Other portions of the wind system (cross-valley, up/down valley circulations) 

are neglected in the algorithm (Scire et al. 2000a). 

CALMET also does not adjust the velocity to represent the decrease in kinetic energy of an air 

parcel as it works to ascend the barrier. This creates another concern regarding the 

directionality of the wind determined by the Froude number adjustment. CALMET assumes that 

the resultant wind vector will flow tangentially to the terrain obstacle. This assumption is only 

valid for isolated terrain features. 

Given the limitations of diagnostic models to ensure dynamically consistent wind fields

(Seaman, 2000), there is legitimate concern that the increased structural detail in the horizontal

wind fields resulting from application of CALMET at higher grid resolutions may lead to

spurious effects on plume dispersion which may not be obvious, even from a detailed review of

horizontal wind fields. As such, the decrease in model-predicted results as a function of 

increasing horizontal grid resolution in CALMET may be caused by inappropriate changes in the 

vertical velocity fields which in turn may enhance vertical turbulence and plume dispersion. 

CALMET is a mass-consistent diagnostic wind field model (DWM) and uses divergence to 

calculate vertical motions in the atmosphere (given in equation 2-2 of the CALMET User’s 

Guide (Scire et al. 2000)). In order to maintain the constraint of mass-consistency, the vertical 

component of the wind must change in relation to changes in the horizontal resolution. 

Reviwing the CALMET source code shows that the change from 4-km resolution to 0.5-km will 

result in an order of magnitude change in the rate of change of the horizontal wind components 

(represented by du/dx and dv/dy in the divergence calculations). In order to maintain mass 

consistency, the vertical velocity must increase due to the increase in the horizontal resolution of 

the model. 

Ecology assumes that the slight decrease in model-predicted concentrations is a result of a longer 

plume trajectory resulting from the finer grid resolution. It does not consider the implications of 

enhanced vertical turbulence and plume dispersion which may occur as a result of increasing grid 

resolution within CALMET. Without performing a more detailed analysis which evaluates these 

phenomenons, the justification is purely theoretical and does not justify the use of the higher 

resolution grid spacing in CALMET as compared to the grid spacing of the NWP. 

Additionally, there are several other important meteorological variables which affect visibility. 

These parameters include vertical velocity and turbulence parameters which affect plume 

dilution, vertical temperature gradients, which affect which whether or not plumes will move 

over or follow terrain, and relative humidity which affects hygroscopic particle growth rates such 

as ammonium sulfate and ammonium nitrate. The Forest Service is particularly interested in 
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knowing whether or not the change in grid resolution from 4.0km to 0.5km resulted in a change 

in vertical wind velocity or turbulence which may have artificially altered the plume dilution. 

Finally, in assessing any model performance, one must use an appropriate standard for 

evaluation. In most cases, this is the actual observation of the parameter of interest (e.g., wind 

direction and speed, or a tracer study for air quality modeling). Due to an absence of valid 

meteorological data in the area of interest, Ecology was not able to conduct a quantitative model 

performance evaluation. Only a subjective analysis was performed, on a very limited number of 

hours out of the entire 3-year period, thus creating a low degree of confidence in the 

interpretation of the results. 

An objective analysis is needed to assess model performance. EPA has identified several 

methods for assessing model performance, all of which include a comparison with observation 

data. Statistical measures should be identified and compared with statistical benchmarks. 

Additionally, graphical evaluation tools such as time series plots of predicted wind speed, wind 

speed bias, root mean square error and Index of Agreement (IOA) are some examples of these 

recommended model performance metrics. Given the lack of a complete statistical model 

performance analysis, the subjective evaluation provided by Ecology does not provide a high 

degree of confidence in their interpretation of results.

In summary, Ecology has inappropriately exempted Alcoa Wenatchee Aluminum Works from 

BART based upon a technically flawed modeling analysis. As such, a BART analysis for this 

facility needs to be performed or the facility must take federally enforceable limits to reduce its 

contribution to haze in the Alpine Lakes Wilderness following the established BART modeling 

protocol.