1 

February 4, 2011 

MEMORANDUM

TO: Docket No.: EPA-HQ-OAR-2004-0305 

FROM: Sharon Nizich, Project Lead 

Risk and Technology Review - National Emission Standards for Hazardous Air 

Pollutants (NESHAP) for Primary Lead Smelting 

SUBJECT: Developments in Practices, Processes, and Control Technologies 

The purpose of this memorandum is to present the results of an analysis to identify 

developments in practices, processes, and control technologies for hazardous air pollutants 

(HAP) emission sources for the Primary Lead Smelting source category. This analysis is part of 

EPA’s review efforts in accordance with section 112(d)(6) of the Clean Air Act (CAA). 

1.0 BACKGROUND 

1.1 Requirements of Section 112(d)(6) of the CAA 

Section 112 of the CAA requires EPA to establish technology-based standards for 

sources of HAP. These technology-based standards are often referred to as maximum achievable 

control technology, or MACT, standards. Section 112 also contains provisions requiring EPA to 

revisit these standards. Specifically, paragraph 112(d)(6) section states: 

(6) REVIEW AND REVISION. – The Administrator shall review, and revise as 

necessary (taking into account developments in practices, processes, and control 

technologies), emission standards promulgated under this section no less often 

than every 8 years. 

1.2 Description of Primary Lead Smelting Source Category and NESHAP 

Requirements 

The Primary Lead Smelting source category includes all facilities that smelt lead-bearing 

ore concentrates to produce lead metal using pyrometallugical techniques. The source category 

does not include secondary lead smelters, lead remelters, or lead refiners that are not located at a 

primary lead smelting facility. Lead is used to make various construction and consumer products 

such as batteries, paint, glass, piping, and filler. Lead sulfide (PbS) ore concentrates are the main 

feed material to primary lead smelters. The primary lead smelting process consists of PbS 

concentrate storage and handling, sintering of ore concentrates, sinter crushing and handling, 

smelting of sinter to lead metal, drossing (i.e., removing the solid oxide deposits), refining and 

alloying of lead metal, and smelting of the drosses. 
2 

HAP is emitted from primary lead smelting as process emissions, process fugitive 

emissions, and fugitive dust emissions. Process emissions are associated with the exhaust gases 

from sinter machines and blast and dross furnaces. HAP expected in process emissions are 

metals (mostly lead, but also some arsenic, cadmium, and other metals) and also may include 

organic compounds that result from incomplete combustion of coke and natural gas combustion. 

Process fugitive emissions occur at various points during the smelting process (such as during 

charging and tapping of furnaces) and generally include metal HAP. Fugitive dust emissions 

result from the entrainment of dust due to material handling, vehicle traffic, and wind erosion 

from storage piles. All fugitive dust emissions contain metal HAP. The majority of these 

fugitive emissions are related to concentrate handling, sinter transfer, and sintering operations. 

 The NESHAP for Primary Lead Smelting were promulgated on June 4, 1999 (64 FR 

30194) and codified at 40 CFR part 63, subpart TTT. The Primary Lead Smelting MACT 

standard applies to affected sources of HAP at primary lead smelters. Primary lead smelters are 

defined as “...any facility engaged in the production of lead metal from lead sulfide ore 

concentrates through the use of pyrometallurgical techniques.” At the time of promulgation of 

the Primary Lead Smelting MACT rule, there were three operating lead smelters. Today there is 

one operating facility, The Doe Run Resources Corporation (Doe Run) in Herculaneum, 

Missouri, that is subject to the MACT standard. 

 

 The Primary Lead Smelting MACT standard applies to sinter machines, blast furnaces, 

dross furnaces, process fugitive sources, and fugitive dust sources. Process and process fugitive 

emissions of lead compounds from sinter machines, blast furnaces, and dross furnaces are 

limited to 500 grams (g) of lead emissions per mega gram (Mg) of lead produced (i.e., 500 g/Mg 

of lead produced, or 1.0 lb/ton of lead produced). Process fugitive sources that are subject to the 

MACT standard are dross furnace charging, blast furnace and dross furnace tapping, and the 

sinter machine (charging, discharge end, crushing, and sizing). Process fugitive emissions must 

be captured by a hood and ventilated to a baghouse or equivalent control device. In addition, the 

sinter machine area must be enclosed in a building that is ventilated to a baghouse at a rate that 

maintains a positive in-draft through any doorway opening. The MACT standard also requires 

the use of bag leak detection systems for continuous monitoring of baghouses. For fugitive dust 

sources, the MACT standard requires that the owner or operator prepare and operate at all times 

according to a standard operating procedures (SOP) manual that describes in detail the measures 

used to control fugitive dust emissions from plant roadways, material storage and handling areas, 

sinter machine areas, furnace areas, and refining and casting areas. The work practices outlined 

in the SOP manual developed for compliance with a state implementation plan is considered to 

be compliant with the MACT standard with regard to fugitive emissions work practice controls. 

 Other metal HAP emitted from the primary lead smelting processes (arsenic, cadmium, 

cobalt and nickel) are covered by the MACT standard by the regulation of lead, which is a 

surrogate for all other nonvolatile metal HAP. Lead is not a surrogate for mercury. However, 

mercury emissions are not a concern for this source category because the mercury content of the 

lead sulfide ore and other materials that could introduce mercury into the process is below the 

detection limit. Organic HAP are emitted in very small quantities from the incomplete 

combustion of small amounts of coke in the blast furnace and natural gas combustion sources 
3 

such as space heating and generators. Although they were considered in the development of the 

1999 MACT rule, they were not regulated because they are emitted at a rate so low as to be 

unreliable to measure and infeasible to reduce. A more detailed discussion of EPA’s 

consideration of VOC and organic HAP emissions in this review is presented in Attachment 1. 

Acid gas HAP were not identified and, therefore, were not regulated in the original MACT rule. 

More recent emissions data indicate that acid gas HAP are not emitted by the lead smelting 

process. 

2.0 DEVELOPMENTS IN PRACTICES, PROCESSES, AND CONTROL 

TECHNOLOGIES 

For the purposes of this technology review, a “development” was considered to be 

any of the following: 

 Add-on control technology or other equipment that was not identified and 

considered during the development of the NESHAP for the source category; 

 Improvement in add-on control technology or other equipment that was identified 

and considered during NESHAP development for the source category that could 

result in significant additional HAP emissions reductions; 

 Work practice or operational procedure that was not identified and considered 

during NESHAP development for the source category; and 

 Process change or pollution prevention alternative that could be broadly applied 

that was not identified and considered during the development of the NESHAP 

for the source category. 

To identify developments in practices, processes, and control technologies, we 

conducted searches of EPA’s RACT/BACT/LAER clearinghouse and the internet for 

information on primary lead smelting. We also reviewed the state permit, state 

implementation plan (SIP) and the information collection request (ICR) response from 

the one remaining primary lead smelting facility. The search results are summarized 

below. 

At the time of the MACT rule promulgation, HAP emissions from the primary lead 

smelting source category were primarily lead but also included small amounts of arsenic, 

cadmium, cobalt, and nickel, and low levels of combustion related organics. Emissions 

data from a 2010 ICR response from the only remaining primary lead smelter (1) 

confirmed that, with the exception of the level of emissions, the emissions profile for the 

facility has not changed, with lead accounting for about 99 percent of the HAP emissions. 

Therefore, this technology review focused on developments in practices, processes, and 

control technologies applicable to lead emission sources. 

2.1 Clearinghouse and Internet Searches 

RACT/BACT/LAER Clearinghouse

The terms “RACT”, “BACT”, and “LAER” are acronyms for different program 

requirements under EPA’s New Source Review (NSR) program. Under EPA’s New 
4 

Source Review (NSR) program, if a company is planning to build a new plant or modify 

an existing plant such that air pollution emissions will increase, the company must obtain 

an NSR permit. The NSR permit is a construction permit which requires the company to 

minimize air pollution emissions by changing the process to prevent air pollution and/or 

installing air pollution control equipment. RACT, or Reasonable Available Control 

Technology, is required on sources in areas that are not meeting national ambient air 

quality standards (i.e. non-attainment areas). BACT, or Best Available Control 

Technology, is required on major new or modified sources in attainment areas. LAER, or 

Lowest Achievable Emission Rate, is required on major new or modified sources in nonattainment areas. BACT and LAER (and sometimes RACT) are determined on a caseby-case basis, usually by State or local permitting agencies. EPA established the 

RACT/BACT/LAER Clearinghouse, or RBLC, to provided a central database of air 

pollution technology information (including past BACT and LAER decisions contained 

in NSR permits) to promote the sharing of information among permitting agencies and to 

aid in future case-by-case determinations. However, data in the RBLC are not limited to 

sources subject to RACT, BACT, and LAER requirements. Noteworthy prevention and 

control technology decisions and information are included even if they are not related to 

past RACT, BACT, or LAER decisions. 

The RBLC contains over 5,000 air pollution control permit determinations that 

can help indentify appropriate technologies to mitigate most air pollutant emission 

streams. It was designed to help permit applicants and reviewers to make pollution 

prevention and control technology decisions for stationary air pollution sources, and 

includes data submitted by several U.S. territories and all 50 States on over 200 different 

air pollutants and 1,000 industrial processes. 

 The RBLC was searched for facilities that conduct primary lead smelting as well 

as for facilities in other nonferrous manufacturing industries. No facilities were 

identified during the search and no new control technologies or developments in existing 

control technologies were identified to further reduce emissions from primary lead 

smelting facilities. 

Internet Search

 A general search of the internet was conducted for information on new processes 

and control technologies for primary lead smelting. The search identified one new 

technology, a hydrometallurgical process, which could potentially be used in lieu of 

pyrometallurgical smelting to produce lead metal from lead sulfide ore. The 

hydrometallurgical lead processing technology is under development and uses 

electrolysis and electrowinning to produce lead from lead ore. This technology, however, 

is currently only in demonstration project status and not commercially available. 

Therefore, it is not a proven technology and currently cannot be considered a replacement 

technology for primary lead smelting operations. 

2.2 State SIP and ICR 
5 

 Based on our review of The Doe Run Herculaneum Title V permit, the Missouri SIP for 

lead, and information provided in the Section 114 ICR response from The Doe Run Company, 

we have determined that there have been advances in emission control measures since the 1999 

Primary Lead Smelting MACT standard. The following paragraphs discuss these advances and 

improvements. 

 

The 1999 MACT lead emission limit for primary lead smelting was set at 1 lb/ton. The 

limit is a facility-wide emission limit that applies to the aggregation of emissions discharged 

from the air pollution control devices used to control emissions from the following sources: 

 Sinter machine; 

 Blast furnace; 

 Dross furnace; 

 Dross furnace charging location; 

 Blast furnace and dross furnace tapping location; 

 Sinter machine charging location; 

 Sinter machine discharge end; 

 Sinter crushing and sizing equipment; and 

 Sinter machine area. 

A facility-wide limit format was used because it was consistent with SIPs, the 

commingling of exhaust gases from processes to a single stack made it impossible to set limits 

for individual sources, it gave the facilities more flexibility in complying with the standard, and 

it promoted pollution prevention by giving each facility the ability to meet the emission limit 

through any combination of source reduction and control technology options. 

The 1999 MACT lead limit was set using the lead emission limits from the lead SIPs for 

the states in which primary lead smelting sources were operational at the time of the rulemaking. 

EPA took each of the three lead SIP limits, in lb/day, divided them by the corresponding lead 

production capacity, in tons/day, and calculated a lead emission rate in lb/ton. The results were 

as follows: 

ASARCO - Missouri 1.0 lb/ton 

ASARCO - Montana 1.0 lb/ton 

Doe Run - Missouri 0.84 lb/ton 

The values were ranked and the median value (1.0 lb/ton) was selected as representative 

of the MACT floor. 

Since the MACT standard was promulgated, the industry has undergone significant 

changes. Two of the three facilities have shut down. As discussed above, the only remaining 

primary lead smelting facility is the Doe Run smelter at Herculaneum, Missouri. Because the 

Doe Run facility is located in an area designated as non-attainment for the lead National 

Ambient Air Quality Standard (NAAQS), the facility is subject to control requirements under the 

Missouri SIP for lead. In an effort to meet the lead NAAQS, Missouri revised the lead SIP as it 

applied to the Doe Run facility in 2000, 2002 and 2007, requiring numerous emissions reducing 
6 

measures and improvements to add-on control devices, processes, and work practices. SIP 

requirements are also incorporated into Doe Run’s Title V permit. 

The SIP requirements, implemented after the 1999 MACT standard, were considered in 

our technology review. The SIP requirements, summarized below, are described in detail in the 

2007 revision of SIP prepared by the Missouri DNR (available at 

http://www.dnr.mo.gov/ENV/apcp/docs/2007revision.pdf). The SIP addresses process, process 

fugitives, and fugitive lead emissions and requires enhancements of existing emission control 

technology, adding or upgrading enclosures, process changes and limitations, and work 

practices. 

 Under the SIP, fugitive dust emissions are controlled by comprehensive work practices 

including road watering and automatic sprinklers, using regenerative sweepers to remove dust 

from paved surfaces to reduce emissions from traffic, maintaining a minimum water content for 

ore concentrate and for baghouse dust that is loaded into railcars, and inspecting the siding that 

encloses buildings (followed by prompt repairs if needed). 

 

Our review found that the practices implemented under the SIP to control fugitive dust 

emissions have resulted in reductions in these emissions. As a result of the SIP requirements, we 

find that all feasible practices and controls available for control of fugitive dust emissions in this 

industry have already been implemented. Therefore, EPA did not find further applicable 

practices or controls that should be required under the MACT to reduce fugitive emissions. 

 Baghouses are the most common control devices used to control process and process 

fugitive emissions of lead compounds at the Herculaneum facility with the exception of the 

process emissions from the sinter machine, which are controlled by a combination of devices in 

series: electrostatic precipitator, baghouse, and acid plant (for control of sulfur dioxide). The 

buildings that house the blast furnaces, dross furnaces, and refinery kettles are also exhausted to 

a baghouse. Improvements to existing emission controls required by the SIP include the 

installation of pleated filters to lower the air-to-cloth ratio for baghouses, increased ventilation 

and improved ventilation hoods at the blast furnace, and using reverse flow technology for 

baghouse cleaning. SIP-required measures also included the installation of enclosures for 

unloading ore concentrate, sinter storage, and the sides of the sinter machine (which are 

evacuated to a baghouse). 

 

 Process changes implemented in response to the SIP to reduce emissions include a 

process control system for the injection of air through the blast furnace tuyeres located at the 

bottom of the blast furnace, limitations on individual process and overall plant throughputs, and 

limiting specific operations to only certain times of the day when the impact on ambient air 

concentrations is less. Emissions from malfunctions will be reduced by alarms that sound when 

the baghouse fan malfunctions, an interlock system to restrict air flow into the blast furnace 

when the baghouse is not operating properly, and cameras for the dross and refinery kettles to 

detect kettle failure (i.e., when a plume of smoke is detected from the stack, the kettle burner can 

be immediately shut off and the problem corrected). 

Under the SIP, technological improvements have also been made to the refining 

operations at the Doe Run facility. Under the current MACT, refining operations are not subject 
7 

to the lead emission limit because at the time the MACT standards were developed, emissions 

from refining were considered fugitive in nature. In response to the SIP requirements, the Doe 

Run facility has enclosed the refining and casting operations and now exhausts the emission from 

the refining kettles as well as the refining building to baghouses. 

Recent stack tests show that these improvements have resulted in emissions substantially 

lower than are allowed under the current MACT rule. To assess the impacts of the technological 

improvements, lead emissions data from 2008 were compared with emissions data from 2000. 

Data from 2008 was selected because it reflects the many technological improvements that have 

been implemented at the facility since the MACT rule promulgation. Emissions data from earlier 

years would not account for all of the emission reducing changes that have been implemented at 

the Doe Run facility given that some of the improvements were not implemented until 2007 and 

2008. In 2008, lead emissions from the smelter operations sintering, blast furnace and drossing 

(i.e. from the main stack) were 13.31 TPY and emissions from the baghouse controlling 

emissions from the blast furnace and dross plant building (i.e., baghouse 7) were 1.81 TPY for a 

total of approximately 15.1 TPY. At the 2008 lead production rate of 149,500 tons, the emission 

rate at Doe Run was about 0.2 lb/ton, an 80 percent reduction from the current MACT limit of 1 

lb/ton. 

The 2008 emissions of 13.31 TPY from sintering, blast furnace operations, and drossing 

operations, represent nearly 70 percent of total facility-wide lead emissions and reflect the annual 

rate of emissions achievable as a result of the technological improvements that have been made 

since 1999. EPA believes that the level of emissions in 2008 support the lowering of the MACT 

limit to be consistent with the demonstrated level of performance. 

In order to establish an emission limit that would properly reflect the facility 

performance, EPA used the actual 2008 annual emissions from the sintering, blast furnace and 

drossing operations (i.e. 13.31 TPY) and then accounted for variability using the 95 percent 

confidence upper predictive limit (UPL). The 95 percent confidence UPL for the lead emissions 

is 14.8 tons. The use of the UPL to account for variability in emissions and the emissions data 

used in the calculation is discussed in Attachment 2. 

To estimate the plant wide emission limit that EPA is proposing, the technology-based 

emissions level for sintering, blast furnace and dross furnace operations (i.e., 14.8 TPY) was 

added to the other risk-based emission levels established for the other emission sources at the 

facility. The development of the plant wide emission limit is described in the preamble to the 

proposed rule. 

3.0 CONCLUSION 

 This review identified several developments in practices, controls or processes that have 

been implemented in the primary lead smelting source category since the 1999 MACT 

promulgation. The primary lead smelting source category currently includes one operating 

facility compared to three at the time the MACT rule was promulgated. The one remaining 

facility, The Doe Run Resources Corporation, has implemented numerous work practices to 

control fugitive emissions and additional enclosures and improvements to add-on controls to 

address process and process fugitive emissions since the 1999 MACT. Additionally, refinery 
8 

operation emissions, which were formerly fugitive, are now captured and exhausted through a 

baghouse. 

The improvements identified in this review were all requirements imposed on the Doe 

Run facility through the Missouri Lead SIP in order to comply with the lead NAAQS. As a 

result, current emissions data indicate an approximate 80 percent plant wide reduction in lead 

emissions since the MACT was promulgated. Although these lead emission reductions are not 

the result of the MACT requirements, EPA believes that the current demonstrated emission 

levels represent an achievable performance and that a reduction in the standard is warranted to 

bring the standard in line with actual performance. 

To determine the emissions level on which the new emission limit would be based, EPA 

used the 2008 emissions for the facility as reported in the Section 114 ICR response for the main 

stack emission (which includes the sintering, blast furnace, and drossing operations), and 

considered variability based on recent stack tests. EPA calculated that the new emission limit 

should be based on a 14.8 tons per year contribution from the sintering, blast furnace,and 

drossing operations (i.e. the main stack). This 14.8 tons per year should be included in the 

calculation of the facility-wide lead emission limit taking into consideration any other necessary 

emission reductions resulting from the residual risk analysis being conducted under Section 

112(f)(2) for the source category. 

4.0 REFERENCES 

 1. Letter from Curran, D.Y., Stinson Morrison Hecker LLP to S. Nizich, US Environmental 

Protection Agency, Response from The Doe Run Resources Corporation to EPA’s December 4, 

2009, Section 114 Information Collection Request, February 5, 2010. 
9 

ATTACHMENT 1 

VOC and Organic HAP Emissions from the Main Stack

During the original MACT development in 1997, VOC emissions testing was performed 

by the EPA on the uncontrolled blast furnace exhaust at the Doe Run smelter to determine the 

magnitude of organic HAP emissions from primary lead blast furnaces. The emissions data 

obtained indicated low (part per billion) levels of several organic HAP compounds. The five 

compounds with the highest measured emission rates were benzene (62 ppb, 0.29 lb/hr), 

methylene chloride (50 ppb, 0.26 lb/hr), acetaldehyde (60 ppb, 0.15 lb/hr), carbon disulfide (33 

ppb, 0.15 lb/ hr), and formaldehyde (87 ppb, 0.15 lb/ hr). Combined, the measured organic HAP 

emissions totaled 2.3 lb/hr, which is equivalent to an annual emission rate approaching 10 tons 

per year. At the time of the original MACT development, EPA believed these levels of organic 

HAP emissions were not significant enough to warrant regulation and were far below what the 

EPA has historically considered achievable with add-on controls (e.g., thermal oxidizers). The 

EPA generally considers thermal oxidizers capable of achieving a 98 percent emission reduction 

or an outlet concentration of 20 ppm, whichever is greater. As stated above, organic HAP 

concentrations at primary lead smelters range from 33 to 87 ppb, or three orders of magnitude 

less than what the EPA has considered achievable with thermal oxidizers. Therefore, the EPA 

believes that it is technically infeasible to reduce organic HAP emissions from primary lead blast 

furnaces through the use of add-on controls. 

EPA evaluated 2008 VOC and the 2005 NEI organic HAP data to determine whether it 

was feasible to require reductions in organic HAP emissions. Data was analyzed from the Doe 

Run emission inventory (as supplied to the State of Missouri) and the 2005 NEI. VOC data 

reported in Doe Run emission inventories lists total VOC emissions in 2008 of 2.21 TPY. 

Information on individual organic HAP emissions and total VOC from the 2005 NEI lists total 

VOC emissions of 2.56 TPY and organic HAP emissions of about 0.06 TPY, or about 2 percent 

of total VOC. Applying this percentage to the 2008 total VOC emissions results in 2008 organic 

HAP emissions of approximately 0.04 TPY, far below the 10 TPY reported in the original 

MACT. 

Using the 2005 NEI data for the Doe Run facility, VOC emissions are approximately 43 

times the level of organic HAP emissions. Applying this ratio to the concentrations reported in 

the original MACT of 33 to 87 ppb (or 0.033 to 0.087 ppm), we estimate total VOC 

concentrations to be between 1.4 ppm and 3.7 ppm at the Doe Run facility. These VOC 

concentration levels (1.4 to 3.7 ppm) are well below the 4 ppm detection limit of the 

measurement methods currently available for VOC. We believe it is technically and 

economically impracticable to measure VOC’s at these levels. 

Recent information on a thermal oxidizer used to control organic emissions from a 

cement kiln showed that the thermal oxidizer was capable of reducing VOC emissions to 4 ppmv 

(at 7 percent oxygen), a level that is at least three orders of magnitude greater than the organic 

HAP concentrations measured at the Doe Run facility. At higher VOC concentrations, for 

example 15 ppmv and above, a thermal oxidizer will have a removal efficiency of about 98 
10 

percent. At lower VOC concentrations of about 3 ppmv, a thermal oxidizer’s removal efficiency 

is expected to be no better than 50 percent. The estimated VOC concentrations at the Doe Run 

facility are estimated to be 1.4 to 3.7 ppm, thus an even lower removal efficiency is likely. 

Additionally, the use of thermal oxidizers has various significant adverse environmental 

consequences, including increase in emissions of criteria pollutants, and significant extra energy 

utilization, with attendant increases in carbon dioxide (CO2) gas emissions. 

Based on these considerations, EPA has determined that the VOC emissions from this 

facility do not warrant consideration for regulation under the section 112(d)(6) technology 

review. 
11 

ATTACHMENT 2 

Variability and Upper Predictive Limit Calculation

Main Stack Lead Emissions

In assessing sources’ performance, EPA may consider variability both in identifying 

which performers are “best” and in assessing their level of performance. Brick MACT, 479 F. 

3d at 881-82; see also Mossville Envt’l Action Now v. EPA, 370 F.3d 1232, 1241–42 (D.C. Cir 

2004) (EPA must exercise its judgment, based on an evaluation of the relevant factors and 

available data, to determine the level of emissions control that has been achieved by the best 

performing sources considering these sources’ operating variability). 

Variability in lead producers’ performance has a number of causes. For emissions of lead 

compounds that are controlled by baghouses, the variability is chiefly due to variations in 

performance of the control device for which both run-to-run and test-to-test variability must be 

accounted.1 

In determining a plant-wide emission limit, we used annual emissions discharged from 

the air pollution control devices used to control lead emissions from the Doe Run primary lead 

smelter. For this rule, we used the 2008 emissions reported by Doe Run to the State of 

Missouri. Variability was added only to the main stack emissions as the emission levels for the 

other sources had required risk-based emission levels. 

We assessed variability using a statistical formula designed to estimate an emissions level 

that is equivalent to the source’s performance based on future compliance tests. Specifically, the 

calculated limit is an upper prediction limit (UPL) calculated with the Student’s t-test using the 

TINV function in Microsoft Excel®. The Student’s t-test has also been used in other EPA 

rulemakings (e.g., NESHAP for Portland Cement Manufacturing; NSPS for 

Hospital/Medical/Infectious Waste Incinerators; NESHAP for Industrial, Commercial, and 

Institutional Boilers and Process Heaters) in accounting for variability. A prediction interval for 

a future observation is an interval that will, with a specified degree of confidence, contain the 

next (or some other pre-specified) randomly selected observation from a population. In other 

words, the prediction interval estimates what the upper bound of future values will be, based 

upon present or past samples taken. The UPL consequently represents the value which we can 

expect the mean of future observations (3-run average for lead) to fall below within a specified 

level of confidence, based upon the results of an independent sample from the same population. 

In other words, if we were to randomly select a future test condition from any of these sources 

(i.e., average of 3 runs or 30-day average) we can be 95 percent confident that the reported level 

will fall at or below the UPL value. Use of the UPL is appropriate in this rulemaking because it 

sets a limit any single or future source can meet based on the source’s past performance. 

                                                           

1 Run-to-run variability is essentially within-test variability, and encompasses variability in individual runs 

comprising the compliance test, and includes uncertainties in correlation of monitoring parameters and emissions, 

and imprecision of stack test methods and laboratory analysis. 72 FR at 54877 (Sept. 27, 2007). Test-to-test 

variability results from variability in pollution device control efficiencies over time (depending on many factors, 

including for fabric filters the point in the maintenance cycle in which a fabric filter is tested). Test-to-test 

variability can be termed long-term variability. 72 FR at 54878. 
12 

This formula uses a pooled variance (in the s2

 term) that encompasses all the data-point to 

data-point variability. Where variability was calculated using the UPL statistical approach, we 

used the sample standard deviation calculated from the emissions data distributions for lead. The 

standard deviation is the common measure of the dispersion of the data set around an average. 

We note here that the methodology accounts for both short-term and long-term variability and 

encompasses run-to-run and test-to-test variability. 

We adopted a form of the UPL equation that has been used in more recent rulemakings. 

See 75 FR 54970 (September 9, 2010), 75 FR 32020 (June 4, 2010) and 75 FR 31905 (June 4, 

2010). The UPL used in this proposed rule is calculated by: 

Where: 

x ̄ = 2008 annual emissions 

n = the number of test runs 

m = the number of test runs in the compliance average 

s

2

 = observed variance 

t = student t distribution statistic 

This calculation was performed using the following Excel functions: 

95 percent UPL = 2008 annual emissions + [STDEV(Test Runs) x TINV(2 x probability, n-1 

degrees of freedom)*SQRT((1/n)+(1/m))], for a one-tailed t-value, probability 

of 0.05, and sample size of n 

Figure 1 presents the UPL calculation using the recent stack test data for the main stack at the Doe Run 

Herculaneum facility. Figure 2 is a listing of stack test results used in the calculation of the UPL. 
13 

Figure 1 - UPL Calculations for Main Stack Lead Emission

UPL Pooled Variance=

Runs 2001-2008

1 2.28

2 2.35

3 3.15

4 2.85

5 0.47

6 0.58

7 0.39

8 0.43

9 0.40

ni = number test runs = 9

Total Number of sources = 1

n =Total # test runs = 9

8

This step is for QC only:

means 1.4335

1.4335 13.31 Main Stack Pb emissions (tons/yr) ‐ 2008 EI

Mean =

Pooled Variance = 1.42101

m= number future runs = 3 Method 12 test quarterly (3 runs/test)

Term1 0.4444

Term2 0.6316

Squared root Term2 0.7947

t‐statistic = quantile t‐distribution with df degrees of freedom at .95 confidence level = 1.859548033

UPL  POOLED VARIANCE = 14.78779913

Doe Run Main Stack Pb

Emissions, lb/hr

NOTE: the pvalue for the t-statistic is calculated as: 2*alpha, where 1-alpha is desired confidence, so if 99% confidence is desired then alpha=0.01 and 

2*alpha=2*(0.01)

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i ik

i k

x x n  

1

N

i

i

n





N

2

,

1 1 Xt s df p n m

       

2

,

1 1 Xt s df p n m

       
14 

Figure 2 - Doe Run Herculaneum Stack Test Data from Section 114 ICR Response

Source Year of Test Run # 

Emissions 

Tests Results 

for Pb (lb/hr) 

Production 

during 

testing 

(tons Pb/hr) 

Emissions 

rate during 

testing 

(lb Pb/ton 

Pb produced)

Main Stack 2001 1 6.07 

 2 4.95 

 3 3.13 

 2002 1 20.24 8.88 2.28 

 2 20.87 8.88 2.35 

 3 27.99 8.88 3.15 

 2003 1 25.2 8.83 2.85 

 2 11.92 25.38 0.47 

 3 14.62 25.38 0.58 

 2004 1 6.85 17.50 0.39 

 2 7.46 17.50 0.43 

 3 6.99 17.50 0.40 

 2006 1 3.3 

 2 4 

 3 4 

 2008 1 10.81 

 2 17.49 

 3 19.23