Appendix J

Supplemental Modeling Demonstration, William H. Zimmer 

Facility

Introduction

This document supports the redesignation request for the Campbell-Clermont partial 

nonattainment area in the State of Ohio and the Commonwealth of Kentucky. This 

nonattainment area encompasses emissions from the Walter C. Beckjord facility. There 

are no other significant sources of SO2 emissions within the nonattainment area that 

warrant inclusion in the modeling analysis. As can be seen from the inventory included 

in the redesignation request, the SO2 emissions from the point sources comprise 

99.95% of the 2014 SO2 emissions in the entire nonattainment area. Notably, violations 

at this monitor were determined to be caused by emissions from the Walter C. Beckjord 

facility located along the Ohio River in Ohio east of the monitor. On September 1, 

20141, the Walter C. Beckjord facility ceased operations. Ohio EPA was notified of the 

permanent shutdown on October 14, 2014. (Appendix B and I of the redesignation 

request) There are no other significant point sources of SO2 emissions located in the 

nonattainment area. Within the portion of Campbell County, KY that is a part of this area 

there are 11 sources which combined emit less than one ton per year (tpy) of SO2. 

(Appendix C of the redesignation request) There are no other point sources of SO2

emissions in the portion of Clermont County, OH that is a part of this area. 

Located south (and slightly east) of the monitor, but outside of the nonattainment area, 

is the William H. Zimmer facility (see Figure 1). It was determined during the 

nonattainment designation process that emissions from the William H. Zimmer facility 

likely do not impact the violating monitor at question, and therefore, the nonattainment 

area was not expanded to encompass this facility. To support the previous conclusion, 

Ohio EPA performed an extensive meteorology, emissions and back-trajectory analysis 

and has included this analysis as Appendix D of the redesignation request. This 

analysis concludes that it was in fact the Walter C. Beckjord facility that caused the 

violations and not the William H. Zimmer facility.

 

1

The letter contained in Appendix B identifies the permanent shutdown of all units occurred on October 1, 

2014. However, a review of CAMD emissions showed that all the units ceased operation by September 

1, 2014.
Figure 1: Location of monitor 21-037-3002 the William H. Zimmer Station. 

In support of this conclusion, Ohio EPA conducted a supplemental modeling analysis to 

determine the location of maximum impact from emissions originating from the William 

H. Zimmer facility as well as a conservative extrapolation of monitored values to the 

point of maximum impact. The supplemental modeling was performed due to the 

proximity of the William H. Zimmer facility to the nonattainment area and the level of 

emissions from this source. Ohio EPA determined that the significant distance (30 to 35 

km), prevailing winds, and emission reductions from sources located to the west of the 

nonattainment area did not warrant the inclusion of these sources in a supplemental 

modeling analysis. This is consistent with U.S. EPA’s Ohio Area Designations For the 

2010 SO2 Primary National Ambient Air Quality Standard technical support document. 

The analysis presented in this document further demonstrates that emissions from 

William H. Zimmer do not impact the nonattainment area to a significant degree and that 

emissions from William H. Zimmer are not likely to cause exceedances both at the 

monitor location or in the entirety of the nonattainment area. 

Modeling Approach 

Per U.S. EPA’s SO2 nonattainment area SIP guidance, 

“Appendix A of this document contains modeling guidance supplemental to that 

provided in the preamble to the final rulemaking promulgating the 2010 S02 

NAAQS and in 40 CFR part 51, Appendix W. Appendix A of this document has 

also been updated to respond to issues raised during the comment period related 
to the September 2011 draft SO2 Guidance Document. This guidance clarifies 

the EPA's recommendations on how to conduct refined dispersion modeling 

under Appendix W to support the implementation of the 2010 SO2 NAAQS.”

Per the SO2 nonattainment area SIP guidance, five years of National Weather Service 

data is sufficient to represent attainment of the standard. The purpose of this 

demonstration, determining the location of maximum impact of emissions from William 

H. Zimmer and demonstrating that these emissions will not cause exceedances in the 

nonattainment area, necessitates that the limited period of time for which monitor data is 

available after the shutdown of the Walter C. Beckjord facility is replicated by the 

modeling analysis. As such, five years of meteorological data was not used, but a 

limited meteorological dataset from August 30, 2014 to February 28, 2015, inclusive, 

was modeled. This period of time represents the most recent period of time for which 

the Walter C. Beckjord facility is shutdown and data is available. As a full three years of 

data are not available, the modeled form of the standard is expressed as the 99th

percentile of the available 192 maximum daily values. For a time period of 192 days, 

the form of the standard of both monitored and modeled values is represented by the 

second highest maximum daily value. 

The recommended dispersion model for SIP modeling for SO2 is the American 

Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) 

modeling system. There are two input data processors that are regulatory components 

of the AERMOD modeling system: AERMET, a meteorological data preprocessor that 

incorporates air dispersion based on planetary boundary layer turbulence structure and 

scaling concepts, and AERMAP, a terrain data preprocessor that incorporates complex 

terrain using United States Geological Survey (USGS) Digital Elevation Data. 

Additionally, Ohio EPA utilized the AERMINUTE module to incorporate 1-minute ASOS 

meteorological data into the hourly surface input file. Ohio EPA utilized the most up-todate versions of AERMOD and the associated preprocessors available at the time of the 

modeling analyses. These are as follows: AERMOD version 14134, AERMET version 

14134, AERMINUTE version 14237, and AERMAP version 11103.

The intent of this supplemental modeling is to demonstrate that the William H. Zimmer 

facility does not cause or contribute to an exceedance of the standard not only at the 

violating monitor, but across the entirety of the nonattainment area. For this purpose, 

Ohio EPA collected monitor data for the August 30, 2014 through February 28, 2015 

period, when the entirety of the Walter C. Beckjord facility is known to have zero 

emissions. Using this monitor data, Ohio EPA modeled all sources at the William H. 

Zimmer facility at 1 gram per second. Using the modeled impacts at receptors across 

the nonattainment area, as well as the location of the monitor, Ohio EPA scaled the 99th

percentile of monitor data for this period to represent a maximum predicted impacted in 

the nonattainment area as a whole. As described below, this modeling is conservative 

in its treatment of constant emissions, the assumption that a one-to-one ratio between 

monitored concentrations and impacts in the nonattainment area is present, and its 

consideration of only the spatial, and not temporal, relationship between monitor and 

modeled values.
 

Meteorological Data

In order to generate meteorological input data for use with AERMOD, AERMET, along 

with AERMINUTE and AERSURFACE preprocessing for the modeling domain was 

conducted to generate the surface (.sfc) and profile (.pfl). Ohio EPA used the 

AERMINUTE pre-processing module. This module accepts as input 1-minute ASOS 

meteorological surface observations, calculates an hourly average for each hour in the 

modeled time period, and substitutes any missing values from the co-located ISHD 

surface data. Use of AERMINUTE reduces the number of calm hours present in the 

input files, and these enhanced hourly files are therefore considered more 

representative of local meteorological conditions. 

Meteorological data from August 30, 2014 through February 28, 2015 from the 

Cincinnati, OH surface station (Station # 93814) located at the Covington/Greater 

Cincinnati Airport in Kentucky and the Wilmington, OH upper air station (Station # 

13841) located at the Wilmington Airborne Park airport were used in these analyses. 

These sites were determined to be representative of the nonattainment area. 

AERSURFACE was run using twelve sectors and four seasons for the surface station 

location.

Emission Sources

Three emission sources (two egress points) from William H. Zimmer were included in 

the modeling analysis. The relevant release point parameters for the two egress points 

included in the analysis are presented in Table 1, below. As described previously, the 

emission rate of all units was set to 1 gram/second to allow for a straightforward scaling 

of modeled values to monitored concentrations. All emissions sources included in the 

modeling analysis were treated as point sources.

Source 

ID Source Description

Easting 

(X)

Northing 

(Y)

Base 

Elevation

Stack 

Height Temperature

Exit 

Velocity

Stack 

Diameter SO2

(m) (m) (m) (m) (K) (m/s) (m) (g/s)

B006_ZM Main Boiler Unit 1 Stack 740462.3 4305892 155.4 174 328 16.971 12.8 1

AUX_AB Aux Blr AB Comn Stack 740391.7 4305630 155.3 91 604 26.3 3.35 1

Table 1: Modeled SO2 emission sources, William H. Zimmer.

Receptors

A receptor grid of 1000 meter spacing was placed within the boundaries of the 

nonattainment area. Initial screening-level modeling indicated that the maximum impact 

of William H. Zimmer occurs within approximately 1 km of the facility. The center of the 

nonattainment area itself is located approximately 20 km (11.5 km at the closest point)

from the William H. Zimmer emission units, and as such, a fine receptor grid was 

deemed unnecessary to capture significant concentration gradients. Limiting the 

number of receptors was also necessary to maintain reasonable file sizes to conduct 
post-processing and analysis of modeled outputs. In addition to this grid, a single 

receptor was placed in the monitor location. A second modeling grid, using 50 meter 

spacing to 3 km, was performed to determine the location of Zimmer’s maximum 

impact. This finer grid was placed based on screening level modeling analysis.

Results

As stated previously, the modeling analysis was conducted to determine the location of 

maximum impact from emissions originating from the William H. Zimmer facility and to 

conservatively demonstrate, using monitored values, that emissions from William H. 

Zimmer will not cause an exceedance of the standard anywhere within the 

nonattainment area. The 2

nd highest modeled maximum daily value for the time period 

(99th percentile) at the receptor representing the monitor was 0.18731 g/m3. Ohio EPA 

determined that the 2

nd highest maximum modeled value across all receptors in the 

nonattainment area was 0.40866 g/m3, and used this value for the extrapolation 

analysis.

To extrapolate these values based on monitor data, Ohio EPA determined that the 2nd

highest maximum daily value recorded during the August 30, 2014 to February 28, 2015 

period to be 24 ppb. Using the modeled impacts above, Ohio EPA used a simple ratio

to scale this value to the point of maximum impact in the nonattainment area, as follows:

0.18731

24 ppb =

0.40866

X

Using the 2nd highest maximum daily value across all receptors in the nonattainment 

area, 0.40866 g/m3, in the ratio above yields a maximum concentration of 52.4 ppb. 

The conservatively extrapolated value is below the standard.

Ohio EPA considers this demonstration highly conservative for several reasons. Firstly, 

the modeling assumed continuous operation of all units at the William H. Zimmer facility, 

which is not reflective of normal operating conditions, in particular the two auxiliary 

boilers. These units operated only 676 hours in 2013 and 1,167 hours in 2014.

Secondly, the extrapolation implicitly assumes that all ambient SO2 recorded at the 

monitor location originates from William H. Zimmer. Lastly, the temporal relationship 

between the monitor data and modeled data was not considered. By accounting only for 

the spatial relationship between modeled and monitor values, the extrapolation 

assumes that the 99th percentile impacts occur simultaneously across the entirety of 

nonattainment area, including at the monitor location. This provides an additional layer 

of conservatism to the analysis. When modeled values and monitor values are paired in 

time, the first-highest maximum extrapolated impact was determined to be 30 ppb.

An additional extrapolation of modeled impacts was performed based on actual 

emissions data from the William H. Zimmer facility. The highest annual emissions from

years 2010-2014 occurred in 2010, when the William H. Zimmer facility emitted 

19,388.1 tons of SO2. This annual emission rate was converted to an average emission 
rate of 557.73 grams/second. Using this value, and the results of the extrapolation 

demonstration above, Ohio EPA used the following ratio to estimate the impacts of 

emissions from the William H. Zimmer plant at both the receptor location and at the 

point of highest impact in the nonattainment area:

2 grams/second

0.40866 ug/m3

=

557.73 grams/second

X ug/m3

The solution to this equation, 113.96 g/m3(43.56 ppb) is well below the standard of 75 

ppb and indicates that emissions from the William H. Zimmer facility are unlikely to 

cause an exceedance of the standard across the entirety of the nonattainment area. 

Substituting the modeled results at the monitor location, 0.18731 g/m3, into the above 

ratio yields an estimated impact of 52.23 g/m3(19.96 ppb). This extrapolation is 

remarkable in its consistency with the monitor data for periods when the Walter C. 

Beckjord facility was not operational and with the previous extrapolation based on 

monitor data. These results, as well as the consistency of these analyses with monitor 

values, provide strong additional support for Ohio EPA’s contention that the closure of 

the Walter C. Beckjord facility will provide for attainment of the standard in the entirety 

of the nonattainment area and that emissions from William H. Zimmer will not cause or 

contribute to an exceedance of the standard.

Analysis of wind rose data from the Covington/Greater Cincinnati Airport for the first 

highest and second highest maximum daily concentrations recorded at the monitor

during the August 30, 2014 through February 28, 2015 period support the conclusion 

that the analysis conducted by Ohio EPA is highly conservative and indicates that 

emissions from William H. Zimmer are not contributing to elevated monitor readings. 

The first highest maximum daily value recorded during this period was 34 ppb, occurring 

on January 14, 2015 at 9:00 AM. Monitor values remained elevated until 12:00 PM on 

the same day. The second highest maximum daily value of 24 ppb occurred on 

January 6, 2015 at 7:00 PM. Concentrations recorded at the monitor were elevated 

from January 6, 2015 at 5:00 AM until 12:00 AM on January 7, 2015. The wind roses 

for these periods are shown in Figure 2, below.
Figure 2: KCVG wind roses, January 6 and January 14, 2015.
The data shown in Figure 2 indicates that winds were primarily from the West and 

Northwest during the times when the highest and second highest monitored values 

were recorded. This suggests that emissions from William H. Zimmer were not 

impacting the monitor, or the nonattainment area, during these times. An analysis of 

hourly emissions, monitor values, and wind directions, presented in Appendix K of this 

redesignation submittal confirms that when emissions from the Walter C. Beckjord 

facility are eliminated from analysis, the wind directions primarily impacting the monitor 

are from the West and Northwest, and that at no time when the Walter C. Beckjord 

facility was not operating was an hourly monitor value above 34 ppb recorded. Thus, 

the extrapolation analysis performed based on modeled impacts represents a highly 

conservative estimate of the impact of emissions from William H. Zimmer on both the 

monitor and the nonattainment area as a whole. Further, Ohio EPA determined that 

point of maximum impact of emissions from Zimmer during the modeled time period 

was located approximately 1.4 km to the southeast from the largest source at the 

William H. Zimmer facility. From the point of this maximum impact to the point of 

maximum impact within the nonattainment area, there is a decrease in concentration of 

84%. 

These analyses, as well as the analysis presented in Appendix K, further support the 

results of the trajectory analysis presented in Appendix D, and demonstrate that the 

impacts of Zimmer are minimal at both the monitor location and the entirety of the 

nonattainment area. These results are consistent with the predominant winds in the 

area, which originate primarily from the south and southwest. Additional wind rose data 

is presented in Appendix K.