## Washington State Regional Haze State Implementation Plan



# Appendix I

Use of 0.5-km Grid Spacing to Evaluate the Impacts of Best Available Retrofit Technology-Eli gible Units at Alcoa Wenatchee Works on the Alpine Lakes WildernessUse of 0.5-km Grid Spacing to Evaluate the Im pacts of Best Available Retrofit TechnologyEligible Units at Alcoa Wenatchee Works on the Alpine Lakes Wilderness

As discussed in section 11.4.1, Alcoa Wenatc hee Works proposed, and the Washington State Department of Ecology (Ecology) accepted, refi nements to the Washington-Oregon-Idaho BART Modeling Protocol 1 . Specifically, Ecology accepted an alternative meteorological data file, which used a finer grid size than the default grid size specified by the protocol, and the use of an

alternate version of CALPUFF. The reasons for accepting these refinements are discussed

below.

Alcoa Wenatchee Works is an aluminum smelter located within the Columbia River Valley (Figure 1). About 20 kilometers (km) upstream from the smelter, the valley forks with one branch heading northwest toward the Alpine La kes Wilderness while the other branch continues north along the Columbia River Valley. The topogr aphy allows southerly flow to be channeled from the smelter up the valley to the fork and then to the nort h and the northwest.

Terrain in this region is comple x. Elevations vary from 200 meters (m) elevation mean sea level (MSL) in the vicinity of the smelter to 2500 m elevation at so me peaks within the Alpine Lakes Wilderness (see Figure 6).

Alcoa Wenatchee Works initially followed the Washington-Oregon-Idaho BART Modeling Protocol and used 4-km meteorology to model th e impacts from the aluminum smelter on nearby

Class I Areas. However, close examination of the surface wind fields (for example, Figure 2)

showed numerous locations where the modeled wi nd directions (indicated by the blue wind barb in the lower left corner of the 4-km grids) did not reflect the effects of the topography. Figure 3 shows a portion of Figure 2 in greater detail. It ca n be seen that the 4-km wind field attempts to

cut across the terrain and fails to model the down-slope, down-valley flow normally observed early in the morning.

Alcoa Wenatchee Works believed that the appare nt errors in the wind field were due to unresolved features of the complex terrain. Figur e 4 shows terrain corresponding to a 4-km grid spacing. Alcoa Wenatchee Works proposed doing a dditional modeling at a higher grid resolution to improve the wind field fo r BART exemption modeling.

Ecology, through its membership in the Northwes t Regional Modeling Center, has over a decade of daily experience with mesoscale meteorological models with grid spacing ranging from 36-km down to 1.3- km and occasionally in special st udies down to 0.44-km. Ecology staff have seen the improvement in model performance that comes with refined grids and understand the conditions that require the sm allest grid spacing.

Based on accumulated experience, Ecology was inclin ed to entertain a proposal to model with a finer grid. The characteristic scale of the terrain affecting transport of emissions from the Alcoa Wenatchee Works smelter to the Alpine Lake s Wilderness is on the same order as that encountered in the Columbia River Gorge. Additionally, like the Columbia River Gorge the

1 T he Washington-Oregon-Idaho Modeling Protocol may be found in Appendix H.maximum impact occurs during the winter. Modeling wintertime flow through the Columbia River Gorge required the smallest grid spacing of 0.44 km to correctly characterize the flow 2

.

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 3 , Ecology concurred with Alcoa Wenatchee Works’ proposal and notified the affected Federal Land Managers (FLMs). The horizontal grid spacing of the fine grid CALMET/CALPUFF modeling domain was 0.5-km. The domain covered an area of 209-km by 143-km (Figure 4). The doma in includes the Alcoa Wenatchee Works, the Alpine Lakes Wilderness, and at least a 50-km bu ffer zone in each direction from the aluminum

smelter and this Class I Area.

The revised BART exemption modeling followed the Washington-Oregon-Idaho BART modeling protocol except for a finer grid spacing of 0.5-km in the meteorological pre-processor

and the use of CALPUFF version 5.8. EPA approved CALPUFF version 5.8 as a replacement for version 6.112 on June 28, 2007. The modeling used the same 3 years of 12-km mesoscale model wind fields as sp ecified by the protocol.

The two years, 2007 and 2008, saw numerous change s in CALPUFF as one version after another became accepted as a guideline model only to be replaced by another. At the time Ecology made our decision to accept the 0.5-km grid modeli ng there were two model versions used for regulatory analyses: Version 5.8 for permitting (the Guideline model) and Version 6.112, accepted for BART analyses. Each analysis approved by Ecology was conducted according to the guideline or protocol in effect at the time.

Figures 2 and 3 compare the wind field computed at the 4 kilometer spacing with the wind field computed at the 0.5-km spacing. A measure of th e frequency of misdiagnosed wind directions is depicted in Figure 2. The figure shows that ten of the 70 points on the 4-km grid shown in the figure had wind directions that failed to c onform to the topography. These ten points are correctly modeled at the 0.5-km spacing.

Figure 3 is an enlargement of the area of Figur e 2 outlined by a black box. Figure 3 shows in greater detail that the 4-km spacing produces a def ective wind field that ignores the influence of the terrain or produces convergence on the slope of the valleys rather than at the bottom. The former is illustrated by the 4-km grid indicated by a blue barb inside a black box on the right side of the figure. The latter can be seen in two 4-km grids in the center of the figure. The 0.5-km wind field seems to accurately reflect the influence of topographic features.

A vertical cross section of the terrain elevation along the east-west line in Figure 5 is shown in Figure 6. The terrain elevation is shown for 4 different resolutions corresponding to grid spacings of 12, 4, 0.5, and 0.1-km. The 12-km grid spacing corresponds to that of the mesoscale

2 Sharp, J and C Mass, The Mesoscale Meteorology of th e Columbia River Gorge, Ninth Conference on Mesoscale

Processes, 2001.

3 Chang, et al, 2003 used 0.25 km. State and Federal agencies and regional planning organizations have used the following grid spacing: Colorado - 0.5 km, VISTAS – 1 km, Georgia -1.5 km, EPA - 0.4 km, and California - 0.1 to

0.5 km.model used for the input mete orological wind fields, the 4- km terrain corresponds to the CALMET grid used in the initial runs, and the 0.5-km terrain was us ed in the final runs. Terrain at the high resolution 0.1 km grid spacing is provided for comparison.

The cross section at 4-km (plotted in cyan) smoo thes out the peaks and the valleys drastically. The highest elevation of 4-km terrain is onl y 1820 m, well below the maximum of 2340 m for 0.5 km terrain (plotted in mage nta). Many ridges and valleys are not resolved at 4-km resolution. The effects of smoothing are even mo re pronounced at the 12-km spacing (plotted in red).

The similarity of the 0.5-km and 0.1-km profile s confirms that the 0.5-km spacing adequately represents the terrain fo r modeling purposes.

Figure 3 clearly demonstrates that the 0.5-km resolved terrain pr ovides a much better representation of te rrain features and the wind field than does the 4-km resolution. Figures 2 and

3 show that the finer resolution modeling provides a much more de tailed spatial pattern in the winds which conforms more accurately to the terr ain when compared with the wind fields from

the lower resolution runs. It is clear from thes e plots that the lower re solution runs will miss much of the terrain channeling wi thin the modeling domain. More importantly, the failure of the 4-km grid to accurately represent peaks will a llow air to flow unimpeded through regions that

would otherwise deflect it.

The Environmental Protection Agency (EPA) has co mmented on the use of finer grid spacing in BART exemption modeling for the Otter Tail Power generating facili ty in Big Stone, SD 4 . The Clearinghouse memo set forth two components th at an argument must address to run the CALPUFF meteorological pre-proce ssor at a smaller grid spacing than the input meteorological

wind fields:

(1) The resolution of the mesoscale model is in sufficient to correctly characterize the transport of emissions between their source and the receptors of concern.

(2) The diagnostic wind model, CALMET, can enhance the mesoscale model data sufficiently to adequately replicate th e key meteorological features governing the transport of emissions between their source and the receptors of concern.

The first has been addressed above. The 4-kmwind field, produced to meet the WashingtonOregon-Idaho Modeling Protocol, was strongly influenced by the inpu t meteorological wind fields and has been shown to have a significan t fraction of misaligned wind directions. The terrain analysis shown in Figur e 6 satisfies the implied require ment of demonstrable terrain complexity stated in the Model Clearinghouse review of May 15, 2009.

The second is more difficult to satisfy directly in this analysis. There are no observations at sites along the path between the Alcoa Wenatchee Works and the Alpine Lakes Wilderness. Additionally, there were errors in the observations at Pangborn fi eld in Wenatchee. Therefore there is no direct way to assess the improvement in the wind field by using the finer grid. An

4 EPA, Model Clearinghouse Review of CALPUFF Modeling Protocol for BART, Memorandum from Tyler Fox, EPA-OAQPS, Research Triangle Park, NC, May 15, 2009.indirect argument must be made by combining ex perience with close scrutiny of the wind fields computed at the 0.5-km grid spacing. Figure 3 seems to indicate that th e wind field computed on the 0.5-km grid responds to the topography in a reasonable manner.

Figure I-7 shows the dates and changes of 98th percentile impacts at 4-km and 0.5-km grid spacings. The highest deciview impact, without regard to location within the Alpine Lakes

Wilderness Area, was used to characterize the im pact on every day at each of the two grid spacings used in the modeling. The 22 highest deci view values at each gr id spacing constitute the upper two percent of the calcula ted impacts. Each of these 44 values is paired with the highest deciview value at the othe r grid spacing on the same day.

For example, taking the isolat ed red point in early 2003, the 0.5- km grid spacing run produced a slightly higher maximum impact to the Alpine Lakes Wilderness Ar ea on one of the 22 days that make up the highest two percent of impacts than was computed us ing the 4-km sp acing. It can also be seen that computed impacts using the 4-km spacing during the first part of 2003 were not in the highest two percent.

Note that the highest impacts are in the winter regardless of the grid spacing used. It can also be

seen that ten of the 22 highest impacts on the 0.5 km gr id (shown by red dots above the black horizontal line indicating zero change) were between 0 and 1 deciview larger than the impacts on the same days calculated using th e 4 km grid. Ecology interprets this as meaning that modeling at the smaller grid spacing has al so redistributed the plume from the smelter rather than simply increasing its dispersion. Changes of less than 1 deciview are generally not noticeable.

Figure 8 does show an important difference in th e spatial location of im pacts between the 4-km grid and the finer grid. Impact s occur at the eastern and sout hern boundaries of Alpine Lakes Wilderness during the winter for both the 4-km a nd 0.5-km grid spacings. Impacts occur at the western boundary, which is west of the Cascade Cr est, only at the 4-km grid spacing. The spatial variation and differences in magnitude can be attr ibuted to the different effect that the more highly resolved terrain has on th e trajectories of emissions from the Alcoa Wenatchee Works aluminum smelter. Because the maximum impacts computed using the 0.5-km grid continue to occur during winter, we may concl ude that the predicted maximum impacts will occur in similar meteorological conditions at both grid scales.

In summary, Ecology’s decision to accept Alcoa We natchee Works’ use of 0.5-km grid resolution and CALPUFF 5.8 for BART exemption modeling of the Alcoa Wenatchee Works facility was based on an analysis showing that the finer grid resolution provided a more accurate result, given the complex terrain surrounding the Alcoa Wenatchee Works aluminum smelter.Figure I-1 Terrain near the Alcoa Wenatchee Works. The greenpushpin marks the location of theAlcoa Wenatchee Works aluminumsmelter in the Columbia River Valley. The Columbia River flows from north to south along the eastside of the Cascade Mountains. TheValley branches upstream from the smelter at Olds with one branchheading northwest to the Alpine Lakes Wilderness, which is outlined inyellow. The black rectangle outlines the area shown inFigure 2. North is up on all maps in this appendix.Figure I-2 Sample wind field (5 am on Jan 5, 2003. The ten small black squares show points where there is a significant difference indirection between the 4-km (blue barbs) and 0.5-km (red barbs)wind fields. The large black rectangle outlines the area shownin greaterdetail in Figure 3.Figure I-3 Close-up of 0.5-km terrain with 4-km (blue barbs at lower left of each 4-km grid square) and 0.5- km (red barbs) wind fields.Small black squares are drawn to emphasize where there is a significant difference in the wind fields.Figure I-4 Terrain at 4-km resolution withFLM-defined receptors in the Alpine LakesWilderness Class I Area. The location of the AlcoaWenatchee Works aluminum smelter is marked by the red dot. Notethe relative softness of the terrain compared with Figure 1.Manyfeatures that affect the transportof emissions into the Class I Areahave been smoothed and are missing.Figure I-5 Terrain at 0.5-km resolution with FLM-defined receptors in Alpine Lakes Wilderness Class I Area. The location of the AlcoaWenatchee Works aluminum smelter is marked by the red dot. Notethe better definition of terrain feature compared with Figure4,especially valleys and side channels, which are important indefining the transport of emissions into the Class I Area.Figure I-6 Terrain profile at four different resolutions along the east-west line in Figure 5.Elevations are in meters and distances are inkilometers. The horizontal scale isapproximately the same as Figure 5.Figure I-7 Dates and changes of 98th percentile impacts at 4-km and 0.5-km grid spacings. The highest deciview, without regardto locationwithin the Alpine Lakes Wilderness Area, was used to characterizethe impact on every day at eachof the two grid spacings usedin themodeling. Each of the 44 values constituting the upper two percentof each distribution is pairedwith the highest deciview value at the othergrid spacing on the same day. Ten of the 22 highest impacts on the 0.5 km grid (shown by red dots above the black horizontal line indicatingzero change) were between 0 and 1 deciview larger than the impacts on the same days calculatedusing the 4 km grid. (See text for moreexplanation)Figure I-8 Locations of the impacts in thehighest two percent. The open purple symbols show locations from the 4-km run and the solid redsymbols are locations from the 0.5-km run. The green pushpin shows the location of the Alcoa Wenatchee Works smelter. The Alpine LakesWilderness is outlined in yellow.Note that in addition to the impacted locations along the east and south wilderness boundaryfor both gridspacings, the 4-km run has high impacts along the west wilderness boundary, which is west of the crest of the Cascade Mountains.