# The Existence of Complex Wind Fields in the Region Surrounding the

Portland Power Plant Site

and the Use of CALPUFF

February 25, 2010

Bureau of Technical Services Division of Air Quality

## New Jersey Dept. of En vironmental Protection

Section 1. INTRODUCTION

This document discusses technical issues related to the use of the CALPUFF modeling system to model the impact of emissions from the Portland Generating Station on Ne w Jersey. The use of CALPUFF for near-field regulat ory applications involving “com plex winds” is addressed in Section 7.2.8(a) of the EPA’s Guideline on Air Quality Models (EPA, 2005).

“a. Inhomogeneous Local Winds. In many parts of the United Stat es, the ground is neither flat nor is the ground cover (or land use) uniform. Thes e geographical variations can generate local winds and circulations, and modify the preva iling ambient winds and circulations. Geographic effects are most apparent when the ambient winds are light or calm. In general these geographically induced wind circul ation effects are named after th e source location of the winds, e.g., lake and sea breezes, and mountain and valley winds. In very rugged hilly or mountainous terrain, along coastlines, or near large la nd use variations, the characterization of the winds is a balance of various forces, such th at the assumptions of st eady-state straight-line transport both in time and space are inappropriate . In the special cases described, the CALPUFF modeling system (described in Appendix A) ma y be applied on a case-by-case basis for air quality estimates in such complex non steady- date meteorological c onditions. The purpose of choosing a modeling system like CALPUFF is to fu lly treat the time and space variations of meteorology effects on transport and dispersion. The setup and a pplication of the model should

be determined in consultations with the a ppropriate reviewing aut hority (paragraph 3.0(b)) consistent with limitations of paragraph 3.2.2(e).”

In a 2008 memorandum issued by EPA (EPA, 2008) , EPA indicated that to use CALPUFF for near field applications, there s hould be a determination that co mplex wind fields exist at the location of the modeling. EPA also indicated that the treatment of complex winds is important when estimating design concentrations. This gui dance appears applicable only to the use of

CALPUFF under Condition 3 in paragraph 3.2.2(b) of the Guideline regulations and the subsequent requirements listed in paragraph 3.2.2(e). Justificati on for use of CALPUFF in the

near-field here is based on Cond ition 2 in paragraph 3.2.2(b) of the Guideline regulations (where a validation study demonstrates that an alte rnate model performs better), not Condition 3. Regardless, this report demonstrates the existe nce of complex wind flows in the Portland Power Plant air shed and their importance when modeling em issions from this facility. The existence of complex winds in this area is an additional reason that the use of CALPUFF is appropriate here.

Section 2 COMPLEX WIND DETERMINATION

Section 2.1 Local Terrain Features

In Figure 1 the elevation of the terrain in the immediate vicinity of the plant is shown. Terrain with elevations above the top of the 400 ft stacks venting Units 1 and 2 (694 ft amsl) is located as

close as 2 km to the east and to the southeast of the stacks. In addition, th e very high terrain onKittatinny Ridge that exceeds 1500 ft amsl is locate d to the north and northwest as close as 7 km

from the stacks.

Several 2008 aerial photos have been included in th is report to provide a greater understanding of the region’s terrain. Photo 1 shows the Portland Power Plant in the foreground and the surrounding terrain looking in a northwesterly direction towards Kittatinny Ridge. The higher terrain immediately to the east of the Portland Po wer Plant in New Jersey and the curvature of the Delaware River Valley are al so apparent. Photo 2 is a view of Portland Power Plant through the Delaware Water Gap in Kittatinny Ridge. P hoto 3 shows the Portland Power Plant in the foreground, the nearby terrain that exceeds stack top just across the Delaware River to the southeast of the plant, and in the background are Jenny Jump a nd Scotts Mountains, significant

terrain features with eleva tions over 1,000 ft amsl. The last photo, Photo 4, was taken looking

south. The Portland Power Plant is in the fore ground and the Martins Creek Power Plant, which is located approximately 7.5 miles south of Po rtland Power Plant, is in the background. These photos clearly show that there are significant terr ain features near Portland Power Plant. These terrain features generate the non -steady state wind fields that affect the transport and dispersion of plumes emitted from the Martins Creek and Portland Power Plants.

Section 2.2 Meteorological Measurements Collected Near the Portland Site

While not capturing the full three-dimensional local terrain and mesoscale wind fields, wind

measurements taken at one location near the Port land site can be of use in demonstrating the

existence of non-uniform vertical wind fields in and near Portland and the Delaware River Valley. From July 1993 through June 1994, meteorolog ical data was collect ed near the Portland Generating Station. This monitoring program c onsisted of a collocated 100-meter tower and Doppler SODAR. Tower measurements of wind dire ction and wind speed ar e available at 30 and 100 meters. The sodar provided wind directi on and wind speed for modeling purposes at 30- meter increment levels from 120 meters up to 5 10 meters. The monitoring program is described in detail in Appendix A.

As can be seen in Figure 3-1 of Appendix A, the measurement site is located 2.3 km west of the power plant site on terrain above the river valley at an elevati on of 610 ft amsl. The stack base

elevation of the Portland Power Plant stacks is 294 ft amsl. Wi nd roses were generated from wind measurements taken at three heights. Fi gure 2 shows the 30 mete r wind rose from the meteorological tower. Figure 3 shows the 150 meter SODAR winds. Figure 4 shows the 300

meter wind rose.

When examining these figures, the expected incr ease in wind speed at the higher levels is evident. However, there are also some obvious di fferences in wind direction that occur at the

three levels. The lower 30-meter level data cl early shows a much greater frequency of winds

from the north/north-northeast and south than that which occurs at the 150 and 300 meter levels. This generally north/south wind flow reflects the general north-south axis of the Delaware River at that location. At 150 meters, the winds reflect the occurrence of larger-scale, westerly synoptic winds and with an additional peak wind direc tion out of the northeas t. This northeast wind direction peak is likely due to the influence of Kittatinny Ridg e and its southwest to northeastorientation. In the 300 meter wind rose the synop tic winds out to the south-southwest through

north-northwest are even more evident.

In addition to vertically and horizontally vary ing winds, other meteorological conditions of

interest at the site are the n ear stagnation condition that accomp anies wind flow reversals near mid-days, especially in the summertime. As sp ecifically mentioned in paragraph 7.2.8(a) of the Guideline on Air Quality Modeling Analysis (EPA , 2005), “geographic effect s are most apparent when the ambient winds are light or calm.” Examination of the 150 meter SODAR winds provide a measure of the winds that directly impacting plumes emitted from Portland Power Plant. Winds measured at this height (1102 ft amsl ) are 400 ft above the top of the stacks. At this level, very low wind speeds less than 2 m/s o ccur 8.5 percent of the time. Wind speeds of less than 2.5 m/s occur over 12.8 percent of the time. An example of a vertical wind profile during such a low wind, stagnation episode is given in Table 1. The table shows the extreme variation in wind direction with height that occurred at th ese times. There is r oughly a 180 degree wind shift moving from the lower levels of the atmosphe re to the higher levels during both hours.

Table 1. Example of Profile Wi nd Direction/Speed Data Collected at the Portland Site (Hours 11 and 12, July 18, 1993)

Portland Site a

Hour Height of

Measurement above ground (m) Wind Direction (deg.) Wind Speed (m/s)

10 ND ND

30 274 1.74

90 291 1.61

120 257 0.77

150 247 0.68

180 253 0.50

210 284 0.24

240 328 0.32

270 336 0.33

300 35 0.49

330 47 0.82

360 46 1.15

390 52 1.21

420 63 1.25

450 58 1.24

480 45 1.15 11

510 36 1.06

10 ND ND

30 213 1.65

90 217 1.56

120 295 0.63

150 312 0.76

180 327 0.79 12

210 343 0.82Portland Site a

Hour Height of

Measurement above ground (m) Wind Direction (deg.) Wind Speed (m/s)

240 5 0.75

270 17 0.61

300 26 0.48

330 33 0.38

360 16 0.34

390 31 0.38

420 35 0.41

450 43 0.52

480 40 0.45 12

510 45 0.58

a. Measurement site on valley ridge 610 ft amsl.

ND = No data

Section 2.3 Meteorological Measurements Collected Near the Martins Creek Site

Meteorological data was collected from Ma y 1, 1992 through May 19, 1993 near the Martins Creek Power Plant. As can be seen in Figur e 5, Martins Creek is located approximately 7.5

miles south of the Portland Power Plant. It is in the same Delaware River Valley air shed as

Portland Power Plant and therefor e meteorological measurements taken at that location should be helpful in understanding the comp lex wind fields of the area.

The SODAR and 10 meter tower wind speed and wi nd direction data was taken at the AMS-4 site (see Figure 5). The AMS-4 site is located 2.5 km to the west-southw est of the Martins Creek

Power Plant. AMS-4 is within the Delaware Rive r valley at a base eleva tion of 320 feet. The SODAR data consists of wind speed and wind dire ction at 30 meter height increments from 90 meters to 420 meters above-ground.

Wind measurements were also taken at the AMS-8 meteorological tower. AMS-8 is located 6 km

to the northwest of the Martins Creek facility and 10.6 km sout hwest of the Portland Power Plant (see Figure 5). It is on the valley ridge to the west of the Delaware River at a base elevation of 810 feet. At AMS-8, tower temperature, wind speed and wind direction were collected at the 10

meter level.

Examining wind roses generated from this data can provide a better understanding of the complex wind flows within the Delaware River Va lley. Figure 6 contains a wind rose of the 10 meter AMS-4 data collected between May 1, 1992 and May 19, 1993. Not surprisingly, these low-level winds in the valley show a pronounced up-valley/down valley (northeast/southwest)

flow. The SODAR data from the 150m level at AMS-4 is shown in Figure 7. The 150 meter SODAR level (840 ft amsl) is approximately equiva lent in height above mean sea-level to thefollowing: the height of the AMS-8 10 meter mete orological data, the hei ght of the valley ridge running along the west of the Dela ware River, and 150 ft above the top of the stacks that vent

Units 1-2 at Portland Power Plant. Winds at th e 150m SODAR level still show a strong terrain influence and the resulting up-va lley/down valley winds. The 150 meter SODAR data collected to the west of the Portland Power Plant (Figure 3) shows much more fre quent west and northwest

winds.

The 300m SODAR wind rose from AMS-4 (shown in Figure 8) displays more of a synoptic pattern. Winds at this level, 1300 ft amsl, are ju st above the highest peaks to the east of the Delaware River Valley. A modest frequency peak of winds from the northeast indicates much less of a valley influen ce than at lower levels. However, at the 300 meter level west of the Portland Power Plant site (Figure 4) there is almo st no indication of a similar valley influence. The final wind rose in Figure 9 summarizes the 10 meter wind speed and direction data from AMS-8 (810 ft amsl). While taken at the same height above ground as the AMS-4 10 meter data (Figure 6), these winds show little of the in-v alley influence shown at AMS-4. The lower level winds at the AMS-8 ridge locatio n more closely resemble the re gional, synoptic wind direction distribution shown in Figure 8.

These seven wind roses combined (Figures 2 through 4 and 6 through 9) illustrate a wind field that varies dramatically in both the vertical and horizontal directions in the Delaware River Valley air shed where Portland Power Plant is located.

The sulfur dioxide monitoring data colle cted from May 1, 1992 through May 19, 1993 also indicate that low wind speed/nea r stagnation meteorological conditi ons of concern because of the high concentrations that result. Fi gure 5 shows the network of eight SO 2 monitoring stations where measurements were collected. These monitors are identified as AMS-5, AMS-7, AMS-8, AMS-9, AMS-10, AMS-11, AMS-12, and AMS-13.

The meteorological conditions that o ccurred when the highest 1-hour SO 2 concentrations were measured at these monitors was investigate d. Network wide, 12 of the 15 highest 1-hour SO 2 concentrations monitored occurred when th e 150 meter SODAR wind speed was less than 2.5 m/s. The 150 meter SODAR wind speed was less th an 2.5 m/s for more than half of the top 20 1-

hour SO 2 concentrations monitored at each of these sites. This supports the concern that high impacts occur during light wind speeds when geographic effects on th e wind field are most

apparent.

Section 3 DIFFICULTIES WITH MO DELING NEAR-FIELD IMPACTS USING

AERMOD

AERMOD is EPA’s recommended refined model for traditional point sources . As noted earlier, AERMOD is a steady-state (straight-line) plume model. A critical limitation of a steady-state model is its inability to respond to terrain-induced spatial variability in wind fields or to changes in dispersion conditions resulting from changes in surface characteristics. When transporting and dispersing a plume from a stack, AERMOD uses a spatially invariant wind field (the entire modeling grid is assumed to have one wind direc tion in both vertically and horizontally). The straight-line plume transport us ed by AERMOD is based on the wind observations from a singlelocation. Unlike CALPUFF, a variable or curved trajectory by the plume is not possible. Therefore, as a steady-state model, AERMOD ca nnot represent the three-dimensional variability in the meteorological fields, w ill not treat stagnation, will not tr ack plume (puff) transport over time, and cannot assess the impact of wind reve rsals. Accordingly, AERMOD is not appropriate for modeling impacts from Portland’s emissions given low/variable wind episodes and complex

vertical and horizontal wi nd fields discussed in the previous section.

AERMOD will not account for the time required for the plume to reach a receptor and will not track the plume over several hours. Therefore, wind reversals that bring the previously emitted plume back into an area of concern as well as puf fs that linger in the vicinity of the plant over several hours during stagnation cond itions would be ignored. In an hours travel time the plume will only be transported 2 km from the stack wh en wind speeds are 0.6 m/s, and only 1 km from the stack when the wind speed is 0.3 m/s.

Another concern about using AERMOD to quantify the impacts from the Portland Power Plant is the lack of a representative me teorological data set needed for such modeling. There is only a very limited set of meteorological data measurem ents taken near the Portland Generating Station. This data was collected from July 1993 to J une 1994. The meteorologica l site was designed to

collect data for the CTDMPlus model.

Guidance on the requirements of meteorological data used in AE RMOD is given in Appendix A. Section 8.3.c of the Guideline on Air Qu ality Models (EPA, 2005). It states:

“Of paramount importance is the require ment that all meteorological data used as input to AERMOD must be both la terally and vertically representative of the transport and dispersion within the analysis domain.”

Measurements of the meteorological conditions ta ken at a single point 2.3 miles west and 316 ft higher than the Portland Power Plan t site will not reflect the three-dimensional local terrain and mesoscale winds, temperature, and st ability variations in the modeli ng grid near the Portland site.

Section 4 ABILITY OF CALPUFF TO MODEL NEAR-FIELD IMPACTS

In this application, CALPUFF is used because it has the ability to treat certain important complex flow and dispersion conditions in a more refined way than other regulatory models. In the near-field, CALPUFF contains three important features that allow a refined treatment of impacts. One is the ability of CALPUFF to account for spatial variability in meteorological conditions such as wind speed and direction, stab ility, and temperature gradient variations over the domain. In complex terrain, winds often chan ge dramatically over short distances. When performing near-field analyses in such conditions, the use of a model such as CALPUFF provides advantages due to its ability to represen t complex spatially varyi ng flow conditions with variable and curved plume trajectories. Stea dy-state (straight-line) plume models such as AERMOD cannot represent the spatial variabil ity in the meteorological fields due to AERMOD’s steady-state assumption.The second important feature of the CALPUFF m odel is its ability to track emissions during stagnation and light wind speed conditions. In valley situations, nocturnal temperature inversions often develop that can trap pollutant s released over several ho urs. CALPUFF allows pollutants emitted under such conditions to be tr acked. Steady-state models do not allow for emissions during periods other than the current hour to be considered in the calculation of

concentrations.

REFERENCES

Environmental Protection Agency, 2005: Guide line on Air Quality Models. 40 CFR Part 51, Appendix W. Published in the Federal Register , Vol. 70, No. 216, November 9, 2005.

Environmental Protection Agency, 2008: Technical Issues Related to CALPUFF Near-field Applications, memorandum from Roger Brode and Brett Anderson, dated September 26, 2008.Figure 1. Terrain and Land Use near the Portland Power Plant (located at center of map)

### Figure 5. Location of Portland Power Plant, Martins Creek Power Plant, Meteorological Stations AMS-4 and AMS-8, and the Eight SO 2 

### Monitoring SitesPhoto 1. The Portland Powr Plant Looking in a Northw esterly Direction towards. Kittatinny RidgePhoto 2. View of Portland Power Plant through the Delaware Water Gap in Kittatinny RidgePhoto 3. The Portland Power Plant with the Nearby High Terrain across the Delaware River to the Southeast and Jenny Jump a nd Scotts Mountains in the BackgroundPhoto 4. Looking South, Portland Power Plant in the Foreground and the Martins Creek Power Plant in the Background

# APPENDIX A

Location of Portland Power Plant’s Meteorological DataThe following figure was taken directly from the document: SO 2 NAAQS Compliance Modeling Protocol for GPU’s Por tland Generating Station , prepared for GPU Genco, prepared by ENSR Corporation, April 1999.

Figure 3.1 Location of the Meteorological Site relative to Portland Power Plant