VIA E-MAIL: schrock.bill@epa.gov

May 3, 2012

Mr. Bill Schrock

U.S. Environmental Protection Agency

109 T.W. Alexander Drive (E143-03)

Research Triangle Park, NC 27709

RE: Docket ID No. EPA–HQ–OAR–2007-0544, National Emission Standards for Hazardous Air Pollutants From the 

Pulp and Paper Industry (76 Federal Register 881328, December 27, 2011) – Revisions to Residual Risk 

Assessment Data for the Port Townsend Mill

Dear Mr. Schrock:

Port Townsend Paper Corporation (PTPC) owns and operates a Kraft pulp and paper mill located in Port 

Townsend, Washington (Port Townsend Mill). The US Environmental Protection Agency (EPA) conducted 

residual risk assessment modeling of the Port Townsend Mill (as well as all other major source mills) as part of 

the Risk and Technology Review for the National Emission Standards for Hazardous Air Pollutants From the 

Pulp and Paper Industry (Pulp and Paper NESHAP). Several environmental groups have used the results of 

EPA’s risk assessment to argue that EPA should require greater reductions in emissions through the Pulp and 

Paper NESHAP rulemaking, even though EPA’s residual risk assessment concluded that the modeled risk was 

acceptable. For this reason, it remains critical that EPA’s risk modeling is as accurate as possible. To this end, 

PTPC reviewed the input parameters used by EPA for modeling residual risk from the Port Townsend Mill and 

identified several parameters that require revision. The purpose of this letter is to provide updated information 

specific to the evaluation of modeled risk from the Port Townsend Mill in the form of the National Emissions 

Inventory (NEI) data revisions provided in Attachment 1 and to provide supporting information to document 

the revisions. 

The revisions described in this letter are provided to more accurately characterize the emission sources at the 

Port Townsend mill and are expected to decrease the modeled risk compared to the EPA October 2011 risk 

modeling results, as summarized in Section 5. This letter presents the NEI data revisions in three parts: updates

to source parameters, source locations, and emission rates. The letter also addresses the appropriateness of 

meteorological data and, lastly, summarizes risk modeling results based on the attached revisions.

1. SOURCE PARAMETERS

EPA’s residual risk modeling was conducted using an updated version of the EPA Human Exposure Model (HEM) 

not available to the public. Therefore, Trinity Consultants (Trinity) conducted modeling using the publicallyavailable version, HEM-3. HEM-3 requires two input files to characterize emission sources in the model. The 

first is a source location input file, which lists source parameters for modeled emission sources, including one 

record for each individual source to be modeled. This source location input file provides the location, size, 

height, and configuration of each source. The following sub-sections describe the revisions made to source 

parameters at the mill. 
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Aerated Stabilization Basin (ASB Pond)

Emissions from the ASB Pond were modeled using the U.S. EPA Wastewater Model, WATER9. As indicated by 

the WATER9 model, the vast majority of the air emissions emanate from the inlet zone. Additionally, the mill’s 

2010 sampling required by the clean condensate alternative provisions, supports this model result, because 

three of the four quarters of test data show that the concentration of methanol decreases by over 99% in the 

first zone. As such, the modeled length and width of the basin have been revised to better characterize the 

dimensions of the ASB Pond. The revised X and Y length of the ASB pond volume source are 350 feet and 230 

feet, respectively. 

Additionally, it should be noted that modeling using an area source type likely over predicts the modeled 

concentrations from the ASB pond and thus, modeled risk. The inlet zone of the ASB Pond is at a temperature of 

approximately 110° Fahrenheit, resulting in thermal plume rise, and the aerators and air flow from the fine 

bubble diffusers in this area also cause mechanical plume rise. PTPC has observed this plume rise from the inlet 

zone of the ASB Pond during monitoring (i.e., the plume rises above the pond due to these thermal buoyancy and 

mechanical lift effects). HEM-3 does not consider this thermal or mechanical plume rise effect from area 

sources, and instead assumes modest dispersion only due to meteorological effects. Therefore, this assumption

results in over prediction of the risk impacts from the ASB Pond. 

Recovery Furnace

The revised stack diameter of the Recovery Furnace is 7 feet, resulting in an associated revised exit velocity of 

80.2 feet per second. The previously reported diameter was based on the location where source tests are 

conducted, rather than at the exit to the atmosphere.

2. SOURCE LOCATIONS

Aeration Stabilization Basin (ASB Pond)

The source location input file also provides source locations for modeled emission sources. Section 1 describes 

the revisions made to the X and Y length of the volume source representing the ASB pond. The location of the 

southwest corner of the source is also updated to reflect the inlet zone, where nearly all of the air emissions 

emanate from the ASB pond.

Stack Locations

In 2007, PTPC measured source locations with a GPS system. PTPC measured source location again in 2009, this 

time using Google Map coordinates, which vary slightly from the GPS system. The coordinates of the Lime Kiln, 

Power Boiler 10, Recovery Furnace, and Smelt Dissolving Tank are updated to reflect the Google Map coordinate 

system. It appears that EPA’s modeling used the same location for multiple stacks. Table 1 present the revised 

source locations used in the revised model. 
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Table 1. Revised Emission Source Locations

Emission ID Emission Source

Latitude

(° N)

Longitude

(° W)

M_WK0007 ASB Pond 48.095383 -122.804596

W_LK0004 Lime Kiln 48.093569 -122.797946

W_IC0005, 

W_IC0006 Power Boiler 10 48.093501 -122.797596

W_ND0001, 

W_ND0002 Recovery Furnace 48.093426 -122.796841

W_SK0003 Smelt Dissolving Tank 48.093781 -122.797371

3. EMISSION RATES

The second input file required by HEM-3 is the emissions input file, which lists emission rates for modeled 

emission sources. The emissions file contains one record for each combination of emission source and pollutant. 

The ASB pond emission rate of acetaldehyde is revised based on mill data from 2010 and 2011 and process 

improvements. Lime Kiln, Power Boiler 10, and Smelt Dissolving Tank emission rates for some pollutants are 

revised to reflect the median emission factor in applicable data sets in the National Council for Air and Stream 

Improvement (NCASI) Technical Bulletin (TB) No. 973. Only emission factors from these sources for pollutants 

that contributed significantly to the maximum cancer impact are included in the revision. It is likely that other 

emission rates from other sources and pollutants may also be better represented by the median of the data set; 

however, due to time constraints, this review is limited to the pollutants discussed below. 

Toxic air pollutant emission rates from the Lime Kiln, Power Boiler 10, and Smelt Dissolving Tank are revised 

based on NCASI guidance for selecting representative average emission factors. NCASI recognizes a 

shortcoming of the Kaplan-Meier (K-M) estimation method used throughout TB No. 973, namely that for data 

sets with very few detects, the mean and median using the K-M method may differ quite widely, with the median 

being significantly lower than the mean. As such, NCASI reanalyzed all data sets with a mean to median ratio of 

greater than 5.0 to estimate a more realistic median value. Thus, the median reported in TB No. 973 for data 

sets with very few detects does not require further analysis and may be considered a representative emission 

factor. 

As a general rule of thumb, NCASI recommends that the median be selected over the mean when the data set is 

non-normal or skewed and large.1 The selection of the median over the mean in such cases ensures that the 

population average is not unduly affected by one or two extreme high data values. 2

PTPC has reviewed applicable data sets in NCASI TB No. 973 for pollutants presented in this letter and has 

determined that the median represents better the population average. Most of these data sets are determined to 

be non-normal, because the upper prediction limit is greater than the mean plus 1.645 of the standard 

 1 NCASI TB No. 973. Compilation of ‘Air Toxic’ and Total Hydrocarbon Emissions Data for Pulp and Paper Mill Sources –

A Second Update, Section 11.0, Page 200. February 2010. 2 Each of the emission factors in Table 2, Table 3, and Table 4, revised to be based on the median of the data set, have 

been determined to be based on a non-normal or skewed data set.
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deviation.3 For the two data sets that do not meet this general test (cadmium from lime kilns and arsenic from 

power boilers), these data sets are also determined to be skewed, because they contain one extreme value that is 

over twenty times larger than the mean of the other source tests, which skews the population mean. 

Additionally, the majority of the data sets are determined to be considered large; where the data sets could not 

clearly be considered large, a review of the data showed that these data sets also included one or two extreme 

values that unduly affect the mean.

The following sub-sections identify applicable data sets and their associated medium datum point for each 

emission unit, and provide further explanation for other revisions.

Aerated Stabilization Basin (ASB Pond)

The revised acetaldehyde emission rate of 6.3 tons per year from the ASB Pond is based on the average of the 

2010 and 2011 sampling results and the 23.9 percent volatilization rate of acetaldehyde determined from 

WATER9 modeling. As determined based on the past five years of data for ASB influent, and on process 

improvements associated with the ASB pond and the mill, the two most recent years are more representative of

current and future operation than the 2009 emission rate reported previously. 

Lime Kiln

Table 2 presents the revised emission factors for the Lime Kiln, which are set to the median emission factor in 

NCASI TB No. 973 Table 4.25 and 4.27. 4 Emission factors are revised based on the review described in Section 3

of this letter.

Table 2. Revised Lime Kiln Emission Factors

Pollutant

Revised Emission Factor a

(lb/T CaO)

Revised Emissions

(tpy)

Acetaldehyde b 6.42E-03 0.18

Arsenic compounds 2.80E-06 0.00010

Cadmium compounds b 5.81E-06 0.00019

Naphthalene 4.62E-04 0.013

Nickel compounds b 8.62E-05 0.0028

a The revised emission factor is the median of the data set for that pollutant, as presented in NCASI TB No. 973, Table 

4.25 or Table 4.27.

b Large data set.

 3 NCASI TB No. 973, page 201, states “if the UPL is greater than the mean plus 1.645 * SD (standard deviation), then it 

may be assumed that the data set was found to be non-normal.” The cadmium data set from lime kilns and the arsenic 

data set from power boilers do not meet this general test, but these data sets are also determined to be skewed based 

on containing one extreme high.

4 NCASI Technical Bulletin No. 973, Compilation of ‘Air Toxic’ and Total Hydrocarbon Emissions Data for Pulp and Paper 

Mill Sources – A Second Update. February 2010. Table 4.25, Summary of Non-Metal Air Toxic Emissions from Kraft Lime 

Kilns (in lb/T CaO), provides non-metal air toxic emission factors from Kraft lime kilns. Table 4.27, Summary of Trace 

Metal Emissions from Kraft Lime Kilns with Wet Scrubbers (lb/T CaO), provides metal emission factors from lime kilns 

at Kraft plants. 
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Power Boiler 10

Table 3 presents the revised emission factors for Power Boiler 10, which are set to the median emission factor in

NCASI TB No. 973 Table 7.2.5 Emission factors are revised based on the review described in Section 3 of this 

letter.

Table 3. Revised Power Boiler 10 Emission Factors

Pollutant a

Revised Emission Factor

(lb/106 Btu)

Revised Emissions

(tpy)

Arsenic compounds b 1.84E-06 0.0022

Beryllium compounds 3.41E-07 0.00083

Cadmium compounds b 1.85E-06 0.0019

a The revised emission factor is the median of the data set for that pollutant, as presented in NCASI TB No. 973, Table 

7.2.

b Large data set.

Smelt Dissolving Tank

The emission factors for organic compounds are set to zero to reflect the use of fresh water in the recausticizing 

area, including the Smelt Dissolving Tank scrubber. According to the NCASI SARA handbook, the emission 

factors for organic compounds apply only to those smelt dissolving tanks that do not use fresh water for mud 

washing. The Port Townsend Mill uses fresh water exclusively in the Smelt Dissolving Tank scrubber, and 

primarily in the mud washer.6 Thus, the organic emission factors in NCASI TB No. 973 are not applicable. 

According to NCASI guidance in TB No. 973 discussed in Section 3 of this letter, the median of the arsenic data 

set, as presented in NCASI TB No. 973 Table 4.29, is representative of the population average.

7 Table 4 presents

the revised emission factors for the Smelt Dissolving Tank. 

 5 Table 7.1 in NCASI TB No. 973, Summary of Air Toxic Emissions from Wood-fired Boilers (lb/106 Btu), provides nonmetal air toxic emission factors from wood-fired boilers. Table 7.2, Summary of Trace Metal Emissions from Woodfired Boilers (lb/106 Btu), provides metal emission factors from wood-fired boilers. 6 Evaporation condensate is rarely used for mud washing.

7 Table 4.29, Summary of Trace Metal Emissions from Kraft Smelt Dissolving Tanks (lb/T BLS), provides metal air toxic 

emission factors from Kraft Smelt Dissolving Tanks. 
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Table 4. Revised Smelt Dissolving Tank Emission Factors

Pollutant

Revised Emission Factor

(lb/T BLS)

Revised Emissions

(tpy)

Acetaldehyde b 0 0

Acrolein b 0 0

Arsenic compounds a 9.41E-07 0.00019

Benzene b 0 0

Cresolsb 0 0

Formaldehyde b 0 0

Methanol b 0 0

Naphthalene b 0 0

Phenol b 0 0

POM 71002 b 0 0

Propionaldehyde b 0 0

a The revised emission factor is the median of the data set for that pollutant, as presented in NCASI TB No. 973, Table 

4.29. The arsenic data set is determined to be a large, non-normal data set.

b The emission factors for organic compounds are set to zero.

4. METEOROLOGICAL DATA

HEM-3 includes a library of preprocessed meteorological data from the National Weather Service (NWS) 

observation stations, though user-specific meteorological data may also be used. One year of surface data is 

obtained from the meteorological station at the Seattle-Tacoma International Airport (station ID 24233) for 

1991. Upper air data is obtained from the Quillayute upper air station (upper air ID 94240) for 1991. 

The Port Townsend Mill is located on the Olympic Peninsula near the Puget Sound. Because of the location’s 

proximity to the Olympic Mountains, Puget Sound, and other bodies of water, the Port Townsend area is subject 

to microclimate effects. Additionally, the mill is located in an area of complex terrain with a substantial body of 

water between the mill and the Seattle-Tacoma International Airport. Therefore, the regional airport used in the 

HEM modeling conducted by EPA is not representative of the Port Townsend Mill and may result in over 

prediction of modeled results from the mill. More representative good quality meteorological data are available 

from the Port Townsend station (WMO ID 994025).8

5. SUMMARY OF MODELING RESULTS

This section presents the results of revised HEM-3 risk assessment modeling conducted for the Port Townsend 

Mill by Trinity. The model input parameters were revised from the EPA model only as described in the 

preceding sections. This analysis also includes a “base case” model, which consists of the inputs used in EPA’s 

model, but that is re-run using the publicly available version of HEM-3 (the EPA model was run using a different 

version of HEM). The base case model is run because the results of the revised model are not directly 

comparable to the results of the EPA model. This section compares the results of the revised model to the base 

case model. 

 8 The Port Townsend station is less than three miles from the mill and is also located near the Port Townsend Bay 

coastline. The wind and temperature data are good quality and complete; however, the station does not include cloud 

cover data. Cloud cover data could be supplemented from nearby stations such as Whidbey Islands (KNUW) or 

Everett (KPAE), which are both closer to the mill than the Seattle-Tacoma International Airport.
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Table 5 presents the maximum individual cancer risk (MIR) percentage decrease from the base case for the 

three worst-case receptors for the base case model and the three worst-case receptors for the revised model. 

The table is ordered by base case rank; that is, the worst-case receptor for the base is presented first, followed 

by the second worst-case receptor, and so on. 

Table 5. Results of HEM Modeling

Location Base Case Rank Revised Rank

Percentage Decrease 

From Base Case a

A 1 17 74%

B 2 1 31%

C 3 13 60%

D 5 2 29%

E 7 3 25% a The percentage decrease represents the decrease between the revised scenario and the base case model. 

Based on Trinity’s best efforts to simulate the HEM modeling used by EPA, it is evident that using the revised 

information provided would result in a reduced risk. Our client, PTPC requests that EPA update the residual risk 

assessment to include the attached revisions in order to obtain model results that are more representative of 

current and future operations at the Port Townsend Mill. If you have any questions or comments about the 

information presented in this letter, please do not hesitate to contact me at (253) 867-5600 or Val DeLeo (PTPC) 

at (360) 379-2082. 

Sincerely,

TRINITY CONSULTANTS

Anna Henolson, P.E.

Senior Consultant
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ATTACHMENT 1

NEI Data Revisions

(Electronic file: mact_1626-1_facility_NEI42357.xls)