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MEMORANDUM

TO: Anne Pope, EPA

FROM: Susan Fairchild, Project Lead

DATE: September 16, 2011

SUBJECT: Emissions Data Used in Residual Risk Modeling for Mineral Wool 

Production

The purpose of this memorandum is to provide information on the RTR database used in 

estimating residual risk for the Mineral Wool Production Maximum Achievable Control 

Technology (MACT) source category. 

BACKGROUND 

Section 112 of the Clean Air Act (CAA) establishes a two-stage regulatory process to 

address emissions of hazardous air pollutants (HAPs) from stationary sources. In the first 

stage, section 112(d) requires the Environmental Protection Agency (EPA) to develop 

technology-based standards for categories of industrial sources. In the second stage, 

known as the residual risk stage, section 112(f)(2) requires EPA to assess the health and 

environmental risks that remain after sources come into compliance with MACT. If 

additional risk reductions are necessary to protect public health with an ample margin of 

safety or to prevent adverse environmental effects, EPA must develop standards to 

address these remaining (“residual”) risks. As part of this second stage, data were

gathered to assess the residual risks from the Mineral Wool Production MACT source 

category. 

EMISSIONS DATA USED IN RESIDUAL RISK MODELING

I. Information Collection Request (ICR)

A voluntary ICR was sent out in March 2010 to seven mineral wool production facilities 

currently operating in the US. ICR responses from all the facilities were compiled in the 

project database and included information on facility processes, equipment, control 

devices, costs, and HAP emissions. Facility-specific production rate information was 

also included and was claimed as confidential business information (CBI), which resulted 

in much of the project database being treated as CBI.

II. Emissions Testing

Mineral wool facilities were asked to supply test data on cupolas, curing ovens, and 

collection operations. All facilities supplied existing test data, new test data conducted in 

2010, or a combination of these for one or more emission unit(s). Six of the mineral wool 

production facilities conducted “new” emissions testing in 2010. The one facility that did 
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not conduct any recent (2010) emissions testing was Amerrock Products LP (Amerrock) 

located in Nolanville, TX. The test results were typically presented as an average of 

three test runs and provided in units of mass of pollutant per mass of production (e.g., 

pounds (lbs) of HAP/ton of melt).

Both new and existing test results were used to calculate average emission rates for 

emission sources. The number of data sets varied depending on the pollutant, emission 

source, and the type of product being produced at the facility (one to four datasets were 

used for a pollutant at a specific source).

III. Source-Specific Emissions

Using the production rates that each facility provided in their ICR response and the 

emission rates from the emission testing, annual emissions (tpy) for each pollutant were 

calculated for each emission source. The sources modeled in the risk analysis are listed as 

follows.

o Unbonded lines: Cupolas

o Bonded lines: Cupolas, Curing Ovens, Collection, and Cooling. 

As previously mentioned, the pollutants and emission sources tested by facilities varied. 

For facilities that did not perform testing on a particular pollutant at a specified source, an 

emission rate (lb/ton melt) for each missing pollutant was calculated from a similar 

source at another facility. If there was more than one similar source that had emission rate

data, the average emission rate of all the similar sources was used. This emission rate was

then multiplied by the production rate of the facility with the missing data. Testing 

parameters (velocity, temperature, etc.) of the similar source were also used (or the 

average if there was more than one similar source) to populate the data set for each 

facility. The stack parameters (height, diameter, etc.) were all taken from facility ICR 

responses – none of them were estimated or based on similar sources. 

3a. Cupola Emissions

Pollutants estimated for cupolas include: HAP Metals, Hydrogen Chloride (HCl), 

Hydrogen Fluoride (HF), Hexavalent Chromium (Cr+6), Carbonyl Sulfide (COS), 

Mercury (Hg).

In order to calculate an average emission rates (lb/ton melt) from cupolas for each 

pollutant, the control device had to be taken in account. Cupolas were divided into two

categories:

Cupolas with baghouse control

Cupolas with baghouse and incinerator control
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Therefore, if a cupola that only has baghouse control was not tested for a certain 

pollutant, an average emission rate (lb/ton melt) for that pollutant was calculated using 

test results from other cupolas that also only have baghouse control. 

Amerrock - The Amerrock facility did not do any recent (2010) emissions 

testing and has two cupolas routed to one stack with a scrubber and a 

baghouse (fabric filter) control. Since they are the only facility with that 

configuration and we did not have enough test data to estimate the control 

efficiency of the scrubber for all the pollutants, the average emission rate 

(lb/ton melt) of cupolas with just a baghouse control were conservatively used 

and multiplied by Amerrock’s total plant production capacity (tons of melt) to 

account for emissions from both cupolas. 

Thermafiber - The Thermafiber facility has two cupolas that are not routed 

together; they tested each cupola separately for almost all pollutants. A few 

pollutants were tested at one cupola but not the other. When this was the case, 

the emission rate (lb/ton melt) of the cupola tested was used along with the 

production capacity of the cupola with the missing pollutant to get annual 

emissions. 

3b. Curing Oven, Cooling, and Collection Emissions

Pollutants estimated for Curing/Collection include: Formaldehyde, Phenol, Methanol.

Curing, cooling, and collection stack configurations for each facility that produces 

bonded material (three facilities) are different (some have the exhaust/emissions routed 

together and some do not). The only emissions that had to be estimated under 

Curing/Cooling/Collection were for two pollutants at Thermafiber’s curing oven. 

Thermafiber has curing operations that are routed to an independent stack. Rockwool is 

the only other facility that also has curing operations routed to an stack; therefore, the 

emission rate (lb/ton melt) for Rockwool was used along with Thermafiber’s production 

capacity from the ICR to estimate annual emissions for the missing pollutants. 

IV. Chromium and Mercury Speciation

Consistent with the HAP list in the Clean Air Act, metals such as chromium and mercury 

may be reported in the ICR under different names, including chromium, chromium 

compounds, mercury, and mercury compounds. Facilities that submitted chromium 

emissions data reported it as total chromium and hexavalent chromium emissions. 

Hexavalent chromium emissions were not speciated further and were modeled as 

chromium VI. Total chromium was speciated to Chromium III by subtracting chromium 

VI emissions from total chromium. In some cases chromium VI emissions were larger 

than total chromium. For these circumstances it was assumed that all chromium 

emissions were hexavalent chromium and chromium III emissions were “0”. Facilities 

that submitted mercury data provided it as total mercury; the following table summarizes 

the speciation factors that were applied to mercury emissions. 
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POLLUTANT_CODE POLLUTANT_DESCRIPTION HAP_CATEGORY_NAME % of total

200 Elemental Gaseous Mercury Mercury Compounds 80%

202 Particulate Divalent Mercury Mercury Compounds 10%

201 Gaseous Divalent Mercury Mercury Compounds 10%

V. Emission Process Group Assignment

In order to assign risk results to specific operations within mineral wool facilities, 

Emission Process Groups are assigned to SCCs. There are only three types of emission 

process groups for mineral wool production: 1) cupolas, 2) collection, and 3) curing 

operations. Combinations of these processes were used as emission process groups when 

one or more of these processes shared a common stack. 

VI. QA/QC

Companies were sent aerial views of each plant and asked to label and provide 

coordinates for each stack. They were also asked to review their stack configurations for 

each emission unit. All wool fiberglass facilities answered the request and provided 

labeled aerial views along with coordinates. EPA also conducted an extensive review of 

the locational coordinates for all facilities in the wool fiberglass source category. 

Locations were visually reviewed using Google Earth or ArcExplorer. Adjustments were 

made for coordinates based on these visual evaluations if necessary. 

Emissions data, stack parameters, and facility information was also reviewed for each 

unit and pollutant at a given plant. Production rates for each unit were checked with the 

responses provided in the ICR.

After risk modeling was conducted, it was discovered that one test run submitted by a 

facility was not performed during normal operating conditions and that the production 

rate for another facility was interpreted incorrectly and did not capture production for the 

facility as a whole. The data set file was corrected and risks associated with the changed 

sources were remodeled. 

VII. Allowable Emissions

In order to evaluate the risk associated with the highest allowable emissions for all air 

pollutants from the Mineral Wool Production source category, we estimated the 

allowable emissions based on formaldehyde. Formaldehyde was considered the most 

important HAP emitted from this source category based on our screening level risk 

assessment and the HAP for which we had the most data. To estimate emissions at the 

MACT-allowable level from stacks, we estimated the actual formaldehyde emission rates 

at curing and collection sources for facilities that operate bonded lines. These emission 

rates were compared to the maximum allowed by the existing MACT standard ((i.e., 0.06 

pounds of formaldehyde per ton of melt) from all curing ovens. Based on this analysis, 

we concluded that all facilities are emitting formaldehyde at emission rates lower than 
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allowable. The estimated actual formaldehyde emission rates were approximately 2 times 

lower than allowable emissions. The other facilities producing nonbonded product did not 

report any formaldehyde, phenol, or methanol emissions. 

MACT-allowable emissions were conservatively estimated to be 3 times the actual 

emissions for all pollutants in the Mineral Wool Production category to account for 

control device efficiencies at the different facilities. Therefore, to develop the MACTallowable emissions the actual stack emissions were multiplied by 3 for each Mineral 

Wool Production facility.