Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

This AERMOD modeling analysis was completed to demonstrate that use non-regulatory 

ADJ_U*is applicable in this instance. 

1-hour S02 modeling completed using AERMOD with regulatory default options and variable 

hourly emissions resulted in modeled 4th high 1-hour S02 concentrations nearby the Wagner 

power plant (Wagner) area and approximately 35 km to the northwest of the Wagner area in 

Baltimore County (Figure IA). 

Figure 1 A. Modeled 4th High 1-hour S02 Concentrations 

Within each of these areas of modeled 4th high 1-hour S02 concentrations, one or two of the 

highest reading receptors were chosen and closely looked at. The areas to the northwest of the 

Wagner area were assigned the letters A- H to represent the various modeled 4th high 1-hour 

S02 concentration areas. The group A-G receptors are shown in Figure 2A and Figure 3A shows 

the receptor group H. The receptors that will be further analyzed are represented by red dots. 

Areas of modeled 4th high 1-hour S02 concentrations located in the Wagner area are represented 

by receptor group's 1-N as seen in Figure 4A. 

A-1 

Copyrighted map removed
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Figure 2A. Receptor Groups A - G 

A-2 

Copyrighted map removed
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Figure 3A. Receptor Group H 

A-3 

Copyrighted map removed
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Figure 4A. Receptor Groups I - N 

A-4 

Copyrighted map removed
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Within the areas A-Na total of 18 receptors were further analyzed. For each of these receptors 

the elevation, Julian day, hour, surface friction velocity (U*) and wind speed without and with 

the adjustment to U* are in Table lA. 

Based on Table IA, the receptors in groups A-Hare all located in areas of complex terrain and 

the greatest distance from the Wagner area. In addition, hours of the maximum concentrations at 

these receptors are all between the hours when stable conditions are expected and winds are 

light. The application of the ADJ_U* option reduces the frequency of low surface friction 

velocity (U*) values that are known to result in over-predictions of modeled concentrations with 

AERMOD. Receptors in groups I- N are in the immediate Wagner area and not located in 

complex terrain. The surface friction velocities are similar during the hours when unstable 

conditions are expected. 

In addition, the data in Table lA and the fact that the modeled 4th high 1-hour S02 

concentrations in Baltimore County are located at such a far distance from the Wagner area calls 

the model's applicability into question. 

The Baltimore Washington International Thurgood Marshall (BWI) Airport wind rose (Figure 

5A) shows that the prevailing wind direction is from the west and west northwest. Based on the 

wind rose the frequency of strong winds needed to cause the high concentrations of 1-hour S02 

to affect an area 35 kilometers away is not supported. 

Figure 6A shows the modeling run that was completed using the exact same input parameters, 

except the non-regulatory ADJ_U* option was used. This particular scenario still resulted in 4th 

high 1-hour S02 modeled concentrations in the immediate Wagner area but the high 

concentrations approximately 35 kilometers to the northwest of the Wagner area in Baltimore 

County were no longer present. 

A-5 
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Table IA. Surface Friction Velocity (U*) With and Without the Adjustment 

Without ADJ U* With ADJ U* 

Surface Friction Wind Speed Surface Friction Wind Speed 

Velocity (U*) (Ws) Velocity (U*) (Ws) 

Julian 

Group x y Elevation Day Hour (m/s) (m/s) (m/s) (m/s) 

A 344732.83 4366325.66 212.8 247 20 0.081 2.25 0.15 2.25 

A 344982.83 4365825.66 209.6 247 20 0.081 2.25 0.15 2.25 

B 343232.83 4368325.66 213.7 247 20 0.081 2.25 0.15 2.25 

B 343232.83 4368075.66 210.3 55 22 0.026 0.79 0.095 0.79 

c 347982.83 4367575.66 209.1 19 5 0.036 1.08 0.095 1.08 

c 347953.75 4367592.5 208.34 19 5 0.036 1.08 0.095 1.08 

D 348232.83 4367825.66 205.3 60 22 0.031 0.86 0.097 0.86 

E 347482.83 4368825.66 217.5 19 5 0.036 1.08 0.095 1.08 

E 347232.83 4369325.66 219.5 273 19 0.050 1.37 0.095 1.37 

F 346232.83 4370075.66 219.4 19 5 0.036 1.08 0.095 1.08 

G 348232.83 4365075.66 201.2 128 20 0.069 1.94 0.126 1.94 

H 349953.75 4349092.5 159.13 273 20 0.047 1.30 0.094 1.30 

I 365075 4337890 9.39 358 13 0.118 1.55 0.118 1.55 

J 369375 4336940 7.69 363 13 0.179 1.99 0.179 1.99 

K 368075 4334890 9.16 61 16 0.165 2.04 0.165 2.04 

L 369075 4335390 7.84 64 10 0.094 0.69 0.094 0.69 

M 368075 4336140 6.51 33 13 0.118 1.30 0.118 1.30 

N 367275 4336840 14.04 274 6 0.148 3.00 0.187 3.00 

A-6 
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

\\ 'C ROS: Pl.OT DISPLAY 

Station #93721 -BALTIM~EIBLT-WASHNGTN INT'l, MD Wind Speed 

' ' 

' ' ' ' 

' 

' 

' 

, 

, 

, 

' 

' ' ' ' ' 

' 

' 

, , 

, 

, 

' 

, 

' ' 

, 

, 

: : I 

f .... --.......... --....... .. ·!--· 

:WEST : ' ' ' . ' ~ . . . 

. . 

' . . 

' ' 

' ' . 

-' 

CO!lVlNTS 

' . 

' ' ' 

' ' . 

WRPl.OTVln ·l.a

Direction (blowing fnm) 

......... --.. ------fNORTH .. .. --- -- -- ' ' ' ' 

. . 

-. 

(' _,. --- ~- .. ·- ~ 

.,. ,,,, ,. : -- ' .. " : 

, , 

, 

-' 

--

·-

. ,, .. , .. ------1---.... .. _ 

,--

' ' ' ' __ ....... -~--- ' ..... 

----

·-

--- --

8% 

8% 

' ' 

10% 

. 

' . . 

' 

. 

' 

' ' ' ' 

. ' ..... --.... .1 ...... ---- -:-- - ---- -l-- -- - -- -· ; : ! EAST: 

, 

, 

--

~ I I I 

' ' ' 

: 

' ' ' ' ' ' ' ' ' ' 

' , 

, ' : 

' ' ' ' ' ' ' 

... .. .. .. -.. ----:----.. .. ...... , , 

, 

, , 

--- ----...... 

. ' 

. 

' ' ' ...... :,. .......... - ' ' ' ' ------ :soUTH .. .. ............ ! .... --

Cli A PfJUOC 

Start Date: 111/2013 - 00:00 

End Date: 1213112016 - 23:69 

CAl.lol" . OS 

1.49% 

- ' , 

. , , . .-- ,, ........ ,. , , , ,. - --- __ .. .. 

CJCllN..vr ~ 

l.IOCElflt 

TOTAl.COU .. T 

28270hrs. 

WllD SPEED 

(Knots) 

• >• 21 58 

• 17.11 - 21 58 

• 11.08- 17.11 

• 700 - 11 .'JS 

D 4.os.1.00 

D o.97-4 oa 

CUN!: 49'.4 

AVG W. C Sl'EE:l Co\~ PftOJ!CT..0 

6.99Knots 312412016 

Figure 5A. BWI Airport Wind Rose 

A-7 
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

Figure 6. Non-Regulatory Default ADJ_U* 4th High I-Hour Modeling Results 

A-8 

Copyrighted map removed
• 

Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

The completed modeling analysis demonstrates that the use of the regulatory default options and 

non-regulatory default ADJ_U* option results in very similar modeled 4th high I-hour S02 

concentrations. The only difference between the two is that the modeled 4th high I-hour S02 

concentrations 35 kilometers away in Baltimore County are no longer present using the nonregulatory default ADJ_U* option. As previously mentioned, the 4th high 1-hour S02 modeled 

concentrations are not highly probable based on the low wind speeds observed during the hours 

in question based on the available meteorological data. In addition, this same conclusion was 

reached by Raven Power based on the comments they submitted. In those comments, Raven 

Power says "it is impossible for the plume to travel that distance within the model's 1-hour 

averaging time" (Raven Power Comments on EPA's Proposed S02 Non-Attainment Designation 

for H.A. Wagner Power Plant, March 3I, 20I6). In conclusion, Maryland should be granted 

approval to use the non-regulatory default ADJ_U* option in this particular instance. 

A-9 
Attachment A 

Modeling Analysis to Support Use of ADJ_U* Option 

References 

Raven Power Comments on EPA's Proposed S02 Non-Attainment Designation for H.A. Wagner 

Power Plant, Baltimore, MD, Submitted by Raven Power, A Subsidiary of Talen Energy, March 

31, 2016. Docket#EPA-HQ-OAR-2014-0464. 

A-10 

. ..