## Appendix C

1. CALPUFF Modeling System The CALPUFF Modeling System is the required model f or determining visual impacts at long distances from sources. This model was used in accordance wi th the guidelines found in the Best Available Retrofit Technology (BART) Modeling Protocol to Det ermine Sources Subject-to-BART in the State of Minnesota, Final 1 , with the modifications found in Appendix B.
The CALPUFF system consists of three main component s (CALMET, CALPUFF and CALPOST) and a number of pre-processing programs. These pre-proces sing programs are designed to prepare available meteorological and geophysical data for input into CALMET. Each of these modeling components are described below:

• CALMET is a meteorological model that develops hour ly wind and temperature fields on a threedimensional gridded modeling domain. Associated two -dimensional fields such as mixing heights, terrain elevations, land use categories an d dispersion properties are also included in the file produced by CALMET.

• CALPUFF is a transport and dispersion model that fo llows the “puffs” of material emitted from one or more sources as they travel downwind. CALPU FF simulates dispersion and chemical transformations as each puff moves away from the so urce, using the multi-dimensional grids generated by CALMET.

• CALPUFF produces an output file containing hourly c oncentrations of pollutants which are processed by CALPOST to yield estimates of ambient air extinction coefficients and related measures of visibility impairment at selected avera ging times and locations.
Lambert conformal coordinates (LCC) were used in th e modeling. To accommodate this coordinate system, it was necessary to use CALPUFF version 5.7 11a. To allow the use of larger meteorological set s and overcome other size limitations, CALPUFF was re compiled with several size parameters increased.

1 MPCA, Final March 2006. Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject to BART in the State of Minnesota.

### CALMET

Three years (2002-2004) of MM5 prognostic mesoscale meteorological data, surface weather data, precipitation data, and upper air data were used to generate the CALMET data set for use in the CALPUFF model. The CALMET computational grid was 1 75 grid cells (east-west) by 120 grid cells (north-south) with a grid spacing of 12 km. This g rid encompasses Northshore Mining Company (NMC) sources, the BWCAW and Voyageurs National Park. US GS digital elevation maps (DEMs) and land use land cover (LULC) files required by CALMET were obt ained from the MPCA.


### CALPUFF
CALPUFF model input files were set up for each year of CALMET data. Model parameters were set to the values specified in the revised modeling protoc ol (Appendix B).
The CALPUFF modeling considered the emission of SO2 , NOx, PM10 (coarse particulate matter, 2.5μ to 10μ), and PM2.5 (fine particulate matter, under 2.5 μ).
The CALPUFF modeling also tracked SO4, NO3, and HNO 3, which are generated by the chemical transformation of the emitted SO2 and NOx. The def ault MESOPUFF II algorithms described the rates of transformation. The MESOPUFF-generated transform ation rates are a function of the background ozone and ammonia concentrations, the former set by observations, the latter using monthly average values provided by MPCA.
The CALPUFF modeling used the receptors for the Bou ndary Water Canoe Area Wilderness and Voyageurs National Park provided by the MPCA in the original subject-to-BART modeling files.


### CALPOST
CALPOST converted the hourly concentration and mont hly average relative humidity files generated by CALPUFF into 24-hour time-averaged extinction coeff icients. These emissions-based extinction coefficients were compared to the 20% best days bac kground extinction coefficients designated in the modeling protocol.

## 2. Visibility Impacts Analysis

As indicated in EPA’s final BART guidance 2 , states are required to consider the degree of vis ibility improvement resulting from the retrofit technology in combination with other factors, such as economic s and technical feasibility, when determining BART fo r an individual source.
The CALPUFF program models how a pollutant contribu tes to visibility impairment with consideration for the background atmospheric ammonia, ozone and m eteorological data. Additionally, the interactions between the visibility impairing pollutants NOx, SO 2 and PM10 can play a large part in predicting impairment. It is therefore important to take a mul ti-pollutant approach when assessing visibility imp acts. 

### Assessing Visibility Impairment
The visibility impairment contribution for differen t emission rate scenarios can be determined using t he CALMET, CALPUFF, and CALPOST modeling templates pro vided by the Minnesota Pollution Control Agency (MPCA). The Minnesota BART modeling protocol 3 describes the CALPUFF model inputs including the meteorological data set and backgroun d atmospheric ammonia and ozone concentrations along with the functions of the CALPOST post proces sing. There are two criteria with which to assess t he expected post-BART visibility improvement: the 98th percentile delta deciview and the number of days on which a source exceeds an impairment threshold.
As defined by federal guidance 4 a source "contributes to visibility impairment” if the 98th percentile of any year’s modeling results meets or exceeds the th reshold of five-tenths of a deciview (dV) at a fede rally protected Class I area receptor. The pre-BART evalu ation of this criterion conducted by the Minnesota Pollution Control Agency identified this facility a s having BART eligible source(s) 5 that could cause or contribute to visibility impairment at Minnesota Cl ass I areas. In addition to establishing whether or not a source contributes to impairment on the 98th percen tile, the severity of the visibility impairment contribution or reasonably attributed visibility im pairment can be gauged by assessing the number of d ays on which a source exceeds 0.5 dV.

2 40 CFR 51, Appendix Y. 3 MPCA, March 2006, Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject-to-Bart in the State of Minnesota. 4 40 CFR 51, Appendix Y. 5 MPCA, March 2006, Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject-to-Bart in the State of Minnesota.

### Predicting 24-Hour Maximum Emission Rates

Pursuant to guidance from MPCA and to be consistentwith use of the highest daily emissions for preBART visibility impacts, the post-BART emissions to be used for the visibility impacts analysis should reflect a maximum 24-hour average basis. There wer e no post-BART scenarios to be modeled.
Table 4-1 describes the pre-BART model input parame ters. There were no post-BART scenarios to be modeled.


### Modeled Results
Visibility impairment was modeled using the meteoro logical data for the years 2002, 2003 and 2004 for the pre-BART emission scenario. Results for the 98t h percentile and number of days above 0.5 dV at Boundary Waters Canoe Area Wilderness (BWCA) and Vo yageurs National Park (VNP) are included in Table 4-2.