April 23, 2003 

To: Arthur Carbonell 

Mechanical Engineering Section 

From: Ralph DeSiena 

Monitoring and Technical Services Section 

Subject: Otay Mesa Generating Co., LLC 

Application No. 978379 

 

An Air Quality Impact Analysis (AQIA) was performed for the Otay Mesa Generating Project 510 

MW natural gas-fired, combined cycle electric generating project by Sierra Research for Otay 

Mesa Generating Company, LLC in support of requested modifications to the Final Determination 

of Compliance (FDOC). The FDOC was previously revised in April 2002 (Amendment 1A) and 

included a revised site layout, increased stack heights, reduced PM10 emissions, and the addition 

of two wet surface air coolers. Additional design changes that affect the air quality impact 

assessment were included in a new submittal dated July 2002 (Amendment 1B). Design changes 

that were included are: 

• The facility layout was modified, resulting in changes in stack and structure locations. 

• The stacks for the two turbines are now separated and raised in height an additional 16 feet to 

the new stack height of 160 feet. 

• 388.1 MMBtu/hr (HHV) duct burners will be added to each HRSG. 

• The addition of an auxiliary boiler. 

The facility potential to emit emissions per this amendment, as compared to the original project, 

are as follows: 

POLLUTANT ORIGINAL AMENDMENT CHANGE

Nitrogen oxides 100 TPY 100 TPY 0 TPY 

Carbon monoxide 281.8 TPY 316 TPY +34 TPY 

Sulfur dioxide 39.4 TPY 12.8 TPY -26.6 TPY 

Particulate matter 159.6 TPY 99.5 TPY -60.1 TPY 

Volatile organic compounds 29.2 TPY 47.5 TPY +18 TPY 

The facility is a major stationary source and PSD source for Particulate Matter (PM10), Nitrogen 

oxides (NOx), and Carbon Monoxide (CO). 
Dispersion modeling was conducted for ongoing operational emissions of NO2, CO, SO2, and 

PM10. The applicant and their consultant (Sierra Research) worked closely with the District in 

developing modeling and analysis procedures in support of demonstrating compliance with all 

applicable requirements. Various modeling techniques were employed including ISCST3, 

ISC_OLM, and AERMOD. Table 1 summarizes the model and meteorological data employed for 

impact analysis of the various pollutants and averaging times. 

TABLE 1 

AIR QUALITY MODEL 

AND METEOROLOGICAL DATA 

USED FOR AQIA 

POLLUTANT AVERAGE PERIOD MODEL MET DATA

NO2 1 Hour ISC_OLM MIRAMAR 92-94

NO2 Annual ISCST3 MIRAMAR 92-94

CO All ISCST3 MIRAMAR 92-94

PM10 24 Hour AERMOD OTAY 94-96

PM10 Annual ISCST3 MIRAMAR 92-94

To ensure the impacts analyzed were for maximum emission levels and worst-case dispersion 

conditions, a screening procedure was used to determine the inputs for the maximum impact 

modeling. The screening analysis showed that impacts were maximized for each pollutant when 

the turbines operated at 100% load with duct firing at low ambient temperature conditions. The 

turbine emissions and stack parameters during these operating conditions are summarized in 

Table 2. 

TABLE 2 

TURBINE EMISSIONS AND STACK PARAMETERS 

PRODUCING WORST CASE IMPACTS 

DURING NORMAL OPERATING CONDITIONS 

Stack Diameter

 (Feet) 

Stack Height

 (Feet) 

Exhaust Temp

 (deg K) 

Exhaust Velocity

 (m/s) 

NOx 

lb/hr 

SO2 

lb/hr

CO 

lb/hr 

PM10

lb/hr 

 18.5 160 354.1 19.26 15.95 1.55 29.1 11.5

During ongoing operations, turbine shutdown and startups will occur. Facility impacts were 

evaluated with one turbine in startup operating at the emission and stack parameters (60% load) in 

Table 3 and one turbine at peak load as defined in Table 2. 

TABLE 3 

TURBINE EMISSIONS AND STACK PARAMETERS 

DURING STARTUP CONDITIONS 

Stack Diameter

 (Feet) 

Stack Height

 (Feet) 

Exhaust Temp

 (deg K) 

Exhaust Velocity

 (m/s) 

NOx 

lb/hr 

SO2 

lb/hr

CO 

lb/hr 

PM10 

lb/hr 

 18.5 160 347.0 12.78 239.9 0.9 2706 7.5
An auxiliary boiler was added to the facility in this amendment. The auxiliary boiler may be 

operated while 1 turbine is operating in peak mode, while the other turbine is in startup mode. The 

auxiliary boiler emissions and stack parameters during these ongoing operating conditions are 

summarized in Table 4. 

TABLE 4 

AUXILIARY BOILER EMISSIONS AND STACK PARAMETERS 

DURING A TURBINE STARTUP 

Stack Diameter

 (Feet) 

Stack Height

 (Feet) 

Exhaust Temp

 (deg K) 

Exhaust Velocity

 (m/s) 

NOx 

lb/hr 

SO2 

lb/hr

CO 

lb/hr 

PM10 

lb/hr 

 2.5 85 435.9 27.0 0.96 0.06 3.26 1.65

The maximum facility impacts were determined by evaluating impacts while both turbines were 

operating under various load and ambient conditions with and without duct burners firing. 

Additionally, facility modeling was performed with 1 turbine at peak load, 1 turbine in startup mode, 

and the auxiliary boiler operating. Maximum predicted short-term impacts for NO2 and CO are 

seen with 1 turbine in startup mode since these emissions are elevated. SO2 and PM10 emissions 

are not elevated during turbine startups and, therefore, maximum impacts for these pollutants are 

seen while both turbines are operating at peak load conditions. The maximum predicted facility 

impact for any of the various on-going operation scenarios modeled is presented in Table 5. 

Worst case background pollutant concentrations were added to the predicted maximum pollutant 

impacts and compared to Federal and California Ambient Air Quality Standards.

TABLE 5 

MODELED MAXIMUM IMPACTS 

FOR ONGOING FACILITY OPERATION 

Pollutant 

Averaging

Period 

Maximum 

Modeled 

Impact6

 (mg/m3) 

Background1

(mg/m3) 

Total Predicted 

Concentration 

(mg/m3) 

CAAQS 

(mg/m3)

NAAQS 

(mg/m3) 

NO2 1-Hour 2015

205 406 470 ------

NO2 Annual 0.652

37.6 38.25 ------ 100

SO2 1-Hour 9.1 392.6 401.7 655 -----

SO2 3-Hour 7.7 183.2 190.9 ----- 1300

SO2 24-Hour 1.5 62.8 64.3 105 365

SO2 Annual 0.08 10.5 10.58 ----- 80

CO 1-Hour 9025 8245 17270 23,000 40,000

CO 8-Hour 1797 4398 6195 10,000 10,000

PM10 24-Hour 4.84

103 107.8 503150

PM10 Annual8

0.98 32 33 ----- 50

PM10 Annual7

0.98 29 30 303-----

1 Maximum concentration observed at the Chula Vista Monitoring station (1993-1997). 

2

The predicted annual NOx increase is 0.87 μg/m3. Using the ARM default value of 0.75, this is reduced to 0.65 

μg/m3. 

3

The project area is designated as non-attainment for the state PM10 standards. 

4

Value from AERMOD. 

5

Value from ISC_OLM. 

6 Values from ISCST3 modeling unless noted otherwise. 

7 Geometric mean 

8 Arithmetic mean 
The results of the modeling indicate that ongoing facility operation will not result in exceedances of 

Federal and California standards with the exception of the California 24-Hour standard for PM10, 

for which the project area is designated non-attainment. Since background PM10 values exceed 

this standard in the project vicinity, modeling was performed to determine whether operation of the 

facility would result in additional violations of the California 24 Hour PM10 standard. 

Since the maximum predicted impact for the facility was 4.8 μg/m3, AERMOD modeling was 

performed for all days in the 1994-1996 period that PM10 background concentrations were greater 

than 45 μg/m3 but less than or equal to 50 μg/m3(California Standard). The results are presented 

in Table 6. The results demonstrate that ongoing facility operations would not cause additional 

violations of the California 24-hour Ambient Air Quality Standard for PM10. 

TABLE 6 

MODELING RESULTS FOR DAYS 

WITH CHULA VISTA 24-HOUR PM10 CONCENTRATIONS 

GREATER THAN 45 μg/m3 BUT LESS THAN THE CAAQS 

Date of High Background

Chula Vista 

Background (mg/m3)

Highest Daily 

Prediction 

(mg/m3) 

Total PM10 

(mg/m3) 

August 31, 1995(day 243) 46 1.8 47.8 

November 5, 1995(day 309) 46 2.5 48.5 

November 30, 1995(day 334) 46 1.0 47.0 

October 6, 1996(day 280) 48 1.2 49.2 

October 18, 1996(day 292) 46 2.0 48.9 

During the initial commissioning period, CO and NOx emissions are expected to be much higher 

since the control system will not yet be optimized. 1-Hour CO, 8-Hour CO, and 1-Hour NOx

emissions were modeled to determine whether the Federal and California Ambient Air Quality 

Standards for CO and NO2 would be violated during commissioning. SO2 and PM10 emissions 

are not elevated during this period and, therefore, were not evaluated. 

Since emissions will vary during this period dependent upon control equipment status, and 

whether one or both turbines are operating, an assumption was made to assume that the total 

emissions were released from a single stack for this modeling. It was also assumed that the 

auxiliary boiler would not be operating at this time. The turbine emissions and stack parameters 

during the commissioning period operation are summarized in Table 7. 

TABLE 7 

TURBINE EMISSIONS AND STACK PARAMETERS 

DURING COMMISSIONING 

Stack Diameter

 (Feet) 

Stack Height

 (Feet) 

Exhaust Temp

 (deg K) 

Exhaust Velocity

 (m/s) 

NOx 

lb/hr 

SO2 

lb/hr

CO 

lb/hr 

PM10 

lb/hr 

 18.5 160 365.3 13.53 1133 N/A 270635N/A
The maximum predicted facility impacts modeled for the commissioning period are presented in 

Table 8 below. Worst case background pollutant concentrations were added to the predicted 

maximum pollutant impacts and compared to Federal and California Ambient Air Quality 

Standards. The ISC_OLM model was used to determine NO2 maximum 1-Hour predicted 

concentrations. The ISCST3 model was used to determine the predicted 1-Hour and 8-Hour CO 

impacts. 

TABLE 8 

MODELED MAXIMUM IMPACTS 

FOR COMMISSIONING PERIOD FACILITY OPERATION 

Pollutant 

Averaging

Period 

Maximum 

Modeled 

Impact3

 (mg/m3) 

Background 

(mg/m3) 

Total Predicted 

Concentration 

(mg/m3) 

CAAQS 

(mg/m3)

NAAQS 

(mg/m3) 

NO2 1-Hour 4052

211426 470 ------

CO 1-Hour 8035 8245 16280 23,000 40,000

CO 8-Hour 3882 4398 8280 10,000 10,000

1 NO2 concentration observed at the Chula Vista Monitoring station for max impact hour (993040104). 

2

Value from ISC_OLM. 

3 Values from ISCST3 modeling unless noted otherwise. 

The results demonstrate that facility operations during the commissioning period will not cause 

violations of California or Federal Ambient Air Quality Standard for CO or NO2. 

In conclusion, the Air Quality Impact Analysis results demonstrate that facility operations during 

the commissioning period and normal ongoing operations will not cause violations of either the 

California or Federal Ambient Air Quality Standards for CO, NO2, SO2, and PM10. 

Ralph DeSiena 

Air Pollution Meteorologist 

San Diego Air Pollution Control District