## IOWA DEPARTMENT OF N**ATURAL RESOURCES Environmental Services Division** 

**Air Quality Bureau Modeling Group**  

## MEMORANDUM
**DATE: 12**  **- 1**  **8 -** **2007 TO:**  **WENDY RAINS FROM:**  **AMY SCOTT RE:**  **EM ERGENCY EVENT GENE**  **RATORS CC:**  **LORI HANSON, CHRIS R OLING, ANNE PREZIOSI** **, JIM MCG RAW**  **AN AL** **YSIS RESULT**  **S** Passed / Acceptable . Changes required that affect the permits (see below for details ) Does not pass / Not acceptable **AN AL** **YSIS SUMM ARY**  

### Modeling has been conducted in support of a rule requested by MidAmerican and Alliant utilities to allow alternate electricity generation in a disaster situation. The model was set up with one 2 - MWportable generator as a representative maximum sized emission unit operating at 100% load . Emissio n rates and stack parameters for the representative emission unit were provided by the utilities . Table 1 lists the parameters used to evaluate the emission unit . Down -wash was not included in the model because:  t he emission units are reported to be hous ed in non - solid structure s ( portable generator units are on wheels),  portability of the emission units to any location in the state does not allow for the development of a representative “facility plan” for purposes of identifying the presence or absence of adjacent buildings with the potential to impact the plume. N o property line credit was given and the terrain was assumed to be flat. T he analysis was completed for all ten Iowa meteorological datasets. As a conservative measure, t he representative emi ssion unit was modeled as operating 24 hours/day, 8760 hours/year, which exceeds the proposed 250 hour operational limit per site. Provided there are no downwash impacts on the stack, the results from the AMS/EPA Regulatory Model (AERMOD , dated 0 7026 ), ind icate that the PM 10 

### , SO 2 

### , NO X 

### and CO emissions from this facility will cause predicted concentrations that are less than the applicable PM 10 

### , SO 2 

### , NO X 

### and CO NAAQS. The modeling results are listed in Table 2. It should be noted that I have not checked the correctness of the parameters used in the modeling, including the emission rates.

### Table 1. Modeled Emission Rates and Stack Parameter **– Point Source** 

Em ission Point PM 10 SO 2 * NO X CO Stack Height Stack Gas

Exit Temperature Stack Tip

Diam eter Stack Gas

Fl ow Rate (lb/hr) (lb/hr) (lb/hr) (lb/hr) (ft) (  F) (in) (acfm) EP1 D iesel Engine Generator2 MW 1.04 1.03 36.21 1.09 13.80 975 18.0 17,300 * SO 2 em ission rate based on No. 2 Diesel F uel with a maximum sulfur content of 0.05% . 

### Table **2. Wors t**  **Case Modeling Results** Pollutant Averaging

Period Year and

location in which event occurred Predicted

Concentration* Background

Concentration Total

Concentration NAAQS
( g/m 3 ) ( g/m 3 ) ( g/m 3 ) ( g/m 3 ) PM 10 24 - hour 200 1 ( Sioux Falls ) 12. 04 45 57.04 150 Annual 2002

(Sioux Falls) 1.1 2 22 2 3 .1 2 5 0 SO 2 3 - hour 200 0 (Omaha ) 24. 6 7 20 4 4 . 6 7 1,300 24 - hour 200 1

( Sioux Falls ) 11.93 20 31.93 365 Annual 2002

(Sioux Falls) 1. 11 20 21.11 80 NO X Annual 200 2 (Sioux Falls) 39 . 06 11 50. 06 100 CO 1 - hour 2003 (Waterloo ) 28.65 0 28.65 40,000 8 - hour 200 4

( Sioux Falls ) 21.96 0 21.96 10,000 * The short-term concentration s are the highest- second - highest predicted value s . T he annual concentration s are the highest predicted value s .