PHOSPHORIC ACID MANUFACTURING AND PHOSPHATE 

FERTILIZER PRODUCTION RTR AND STANDARDS OF 

PERFORMANCE FOR PHOSPHATE PROCESSING 

SUMMARY OF PUBLIC COMMENTS AND RESPONSES

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Sector Policies and Programs Division

Research Triangle Park, North Carolina 27711

July 2015
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The primary contact regarding questions or comments on this document is:

Tina Ndoh (919) 541-2750

U.S. Environmental Protection Agency

OAQPS/Sector Policies and Programs Division (D243-02)

Research Triangle Park, North Carolina 27711

Email: Ndoh.Tina@epa.gov
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TABLE OF CONTENTS

Section Page No.

TABLE OF CONTENTS ............................................................................................................iii

1.0 INTRODUCTION ........................................................................................................... 1-1

2.0 LIST OF COMMENTERS .............................................................................................. 2-1

3.0 RISK ASSESSMENT...................................................................................................... 3-1

3.1 Supports Conclusion Of NESHAP Residual Risk Assessment ........................... 3-1

3.2 NESHAP Residual Risk Assessment Approach Needs Update .......................... 3-1

3.3 Lead...................................................................................................................... 3-6

3.4 Whether NESHAP Residual Risk Assessment Consistent with the Key 

Recommendations Contained in the SAB.......................................................... 3-10

3.5 Data Collection From Section 114 Survey And Testing Requests.................... 3-11

3.6 HF Emissions Data Used For NESHAP Residual Risk Assessment Not 

Representative Of Actual HF Emissions ........................................................... 3-11

3.7 Chromium Emission Data Used For NESHAP Residual Risk Assessment Not 

Representative Of Actual Chromium Emissions............................................... 3-13

3.8 Stack Parameters Used For NESHAP Residual Risk Assessment Not 

Representative Of Actual Stack Parameters...................................................... 3-14

3.9 Conservative Assumptions Used In NESHAP Residual Risk Assessment Bias 

Results................................................................................................................ 3-15

3.10 Selection of Meteorological Data In NESHAP Residual Risk Assessment ...... 3-15

3.11 Rationale for Maximum One-Hour Emission Rate In NESHAP Residual Risk 

Assessment......................................................................................................... 3-17

3.12 Ecological Assessment Endpoints In NESHAP Residual Risk Assessment ..... 3-19

3.13 Exposure Modeling Uncertainty In NESHAP Residual Risk Assessment........ 3-20

4.0 NESHAP TECHNOLOGY REVIEWS AND NSPS REVIEWS.................................... 4-1

4.1 Supports Conclusions Of NESHAP Technology Reviews and NSPS Reviews.. 4-1

5.0 STATUTORY AUTHORITY ......................................................................................... 5-1

5.1 No Basis For Other Changes................................................................................ 5-1

6.0 HG LIMIT AND HF WORK PRACTICE STANDARDS FOR CALCINERS ............. 6-1

6.1 Technical Feasibility of Hg Control Devices and Hg BTF Limit........................ 6-1

6.2 Supports Hg BTF Limit ....................................................................................... 6-3

6.3 Set Health-Based Hg Limit.................................................................................. 6-3

6.4 Hg Deposition ...................................................................................................... 6-5

6.5 Hg UPL Calculation............................................................................................. 6-5

6.6 HF Work Practice for Phosphate Rock Calciners................................................ 6-8

7.0 HF WORK PRACTICE STANDARDS FOR GYPSUM DEWATERING STACKS AND 

COOLING PONDS ......................................................................................................... 7-1

7.1 Submergence Of Discharge Pipe ......................................................................... 7-1

7.2 Rim Ditch (Cell) Building Technique.................................................................. 7-1

7.3 Wetting Of The Active Gypsum Stack ................................................................ 7-2

7.4 Application Of Slaked Lime ................................................................................ 7-2

7.5 Soil Caps And Vegetation.................................................................................... 7-3

7.6 Closure Of Gypsum Dewatering Stacks.............................................................. 7-3
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7.7 Other Techniques................................................................................................. 7-4

7.8 Requirement To Use At Least Two Of The Control Measures........................... 7-4

7.9 Gypsum Dewatering Stack Area To Phosphoric Acid Manufacturing Capacity 

Ratio..................................................................................................................... 7-5

7.10 Necessity or Justification of HF Work Practices................................................. 7-7

7.11 HF Work Practice For Gypsum Dewatering Stacks and Cooling Ponds Interfere 

With Other Regulatory Programs ........................................................................ 7-8

7.12 Cooling Pond Considerations For HF Work Practice.......................................... 7-9

8.0 TRANSLATION OF TOTAL FLUORIDE LIMITS TO HF LIMITS ........................... 8-1

8.1 Proposed HF Limits Are More Stringent Than Current Total Fluoride Limits... 8-1

8.2 Reliance On EPA Method 26A HF Emissions Test Data To Establish New 

Standards Is In Error............................................................................................ 8-1

8.3 Total Fluoride Surrogate For HF ......................................................................... 8-3

9.0 MEASUREMENT, MONITORING, AND REPORTING REQUIREMENTS ............. 9-4

9.1 Quantifying HF Emissions From Gypsum and Cooling Waters ......................... 9-4

9.2 EPA Method 320.................................................................................................. 9-5

9.3 EPA Method 26A................................................................................................. 9-6

9.4 FTIR HF CEMS................................................................................................... 9-7

9.5 Pressure Drop Across Absorber........................................................................... 9-8

9.6 Absorber Monitoring Options.............................................................................. 9-9

9.7 Acceptable Range From Baseline Average Value............................................... 9-9

9.8 Operating Range Established From A Previous Test ........................................ 9-10

9.9 Approving Operating Ranges ............................................................................ 9-10

9.10 Maximum Representative Operating Conditions............................................... 9-11

9.11 Performance Test Frequency ............................................................................. 9-12

9.12 Condenser Monitoring ....................................................................................... 9-12

10.0 COMPLIANCE DATES AND FREQUENCY OF PERFORMANCE TESTS ........... 10-1

10.1 Compliance Dates For Newly Regulated Sources............................................. 10-1

10.2 Compliance Dates For Absorber Monitoring .................................................... 10-3

10.3 Compliance Dates For Fabric Filter Monitoring ............................................... 10-3

10.4 Compliance Dates For Stack Testing................................................................. 10-3

11.0 APPLICABILITY, DEFINITIONS, AND TERMINOLOGY...................................... 11-1

11.1 Expanded Scope Of Process Lines .................................................................... 11-1

11.2 Clarification To Oxidation Reactors Included In SPA Process Lines............... 11-1

11.3 Clarifications To Clarifiers And Defluorination Systems Included In WPPA 

Process Lines ..................................................................................................... 11-2

11.4 Clarification To Granular Triple Superphosphate Fertilizer Process Line ........ 11-3

11.5 Clarification To Phosphate Fertilizer Process Line Or Production Plant .......... 11-3

11.6 Clarification To Purified Phosphoric Acid ........................................................ 11-5

11.7 Gypsum Dewatering Stack Definition ............................................................... 11-5

11.8 Closed and Active Gypsum Dewatering Stack Definitions............................... 11-6

11.9 Cooling Pond Definition.................................................................................... 11-7

11.10 Production Capacity Clarification...................................................................... 11-8

11.11 Applicability Clarification - Kiln Process.......................................................... 11-8

11.12 Clarification To Calciners.................................................................................. 11-9

11.13 Clarification To Scrubber Terminology............................................................. 11-9

12.0 ECONOMIC AND EMISSIONS IMPACTS ................................................................ 12-1

12.1 Cost-Effectiveness of Hg Control Devices........................................................ 12-1
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12.2 Gypstack Management Plan Control Measure Impacts..................................... 12-2

12.3 Gypstack Ratio Impacts..................................................................................... 12-3

12.4 Impact from Additional Sources........................................................................ 12-4

12.5 Testing and Monitoring Costs............................................................................ 12-5

12.6 Economic Impacts.............................................................................................. 12-7

12.7 Economic Benefits and Regulatory Planning and Review ................................ 12-9

12.8 Environmental Justice...................................................................................... 12-10

13.0 STARTUP, SHUTDOWN, AND MALFUNCTIONS................................................ 13-12

13.1 Whether EPA Appropriately Removed The Startup, Shutdown, and Malfunction 

Exemption........................................................................................................ 13-12

13.2 Feasibility Of Estimating Emissions During SSM Events .............................. 13-16

13.3 Work Practice Standard In Place Of Emission Limits..................................... 13-17

13.4 Make An Explicit Exemption For Monitoring During SSM ........................... 13-21

14.0 OTHER COMMENTS................................................................................................. 14-24

14.1 Scrubber Water to Cooling Tower Exemption ................................................ 14-24

14.2 Miscellaneous .................................................................................................. 14-26

14.3 Inherently Safer Technology (IST).................................................................. 14-26

14.4 Extension Requests.......................................................................................... 14-29

14.5 Organics Content Subcategory ........................................................................ 14-29
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1.0 INTRODUCTION

On November 7, 2014, the Environmental Protection Agency (EPA) proposed revisions 

to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Phosphoric 

Acid Manufacturing and Phosphate Fertilizer Production source categories and to new source 

performance standards (NSPS) for several phosphate processing categories. Some significant 

comments and responses appear in the preamble to the final rules. This document contains 

summaries of all the public comments that the EPA received on the proposed standards

(comments that are summarized and addressed in the preamble to the proposed rule are also 

provided in this document for completeness). Copies of all comments submitted are available at 

the EPA docket Center Public Reading Room. Comment letters are also available electronically 

through http://www.regulations.gov by searching Docket ID No. EPA-HQ-OAR-2012-0522.
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2.0 LIST OF COMMENTERS

The EPA received 14 comment letters after November 7, 2014 on the proposed revisions 

to the NESHAP for the Phosphoric Acid Manufacturing and Phosphate Fertilizer Production 

source categories and to NSPS for several phosphate processing categories. All comment letters 

are contained in Docket EPA-HQ-OAR-2012-0522. The commenter, affiliation, and item 

number in Docket EPA-HQ-OAR-2012-0522 are listed in Table 2-1. A list of acronyms and 

units of measure used in this document appears after the list of commenters.

Table 2-1. Public Comments Received After the Proposed Rule for Phosphoric Acid 

Manufacturing and Phosphate Fertilizer Production RTR and Standards of Performance 

for Phosphate Processing, Proposed Rule Docket EPA-HQ-OAR-2012-0522

Commenter Identification Code Commenter and Affiliation

EPA-HQ-OAR-2012-0522-0030 Paul DeKok, President, PCS Phosphate Company, Inc.

EPA-HQ-OAR-2012-0522-0031 David Jellerson, Senior Director, Environmental, Mosaic 

Fertilizer, LLC

EPA-HQ-OAR-2012-0522-0035 E. Donald Elliott and Gerald H. Yamada, Covington & 

Burling LLP on behalf of the PCS Phosphate Company, Inc.

EPA-HQ-OAR-2012-0522-0036 Mark Vignovic, Vice President - Safety, Health & 

Environment, JDC Phosphate

EPA-HQ-OAR-2012-0522-0037 PCS Phosphate Company, Inc.; PCS Nitrogen, Inc.; and 

White Springs Agricultural Chemicals, Inc.

EPA-HQ-OAR-2012-0522-0038 Andy O'Hare, The Fertilizer Institute

EPA-HQ-OAR-2012-0522-0039 David Jellerson, Senior Director, Environmental, Mosaic 

Fertilizer, LLC

EPA-HQ-OAR-2012-0522-0041 Sheila Holman, Director, North Carolina Department of 

Environment and Natural Resources, Division of Air Quality 

(NCDAQ)

EPA-HQ-OAR-2012-0522-0042 Emma C. Cheuse, Earthjustice on behalf of Sierra Club

EPA-HQ-OAR-2012-0522-0043 Alan L. Prouty, Vice President, Sustainability and 

Regulatory Affairs, J.R. Simplot Company

EPA-HQ-OAR-2012-0522-0047 Gerald Yamada, Outside Council behalf of PCS Phosphate 

Co.

EPA-HQ-OAR-2012-0522-0054 Reverend Jerry Langley, Zion Grove Church of Christ

EPA-HQ-OAR-2012-0522-0055 Terry L. Baker, Senior Director, Environmental and Mine 

Development, PotashCorp

EPA-HQ-OAR-2012-0522-0056 Gerald Yamada and Casey Bradford, Counsels on behalf of 

PCS Phosphate Company
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List of Acronyms and Abbreviations

Acronyms

ACI Activated carbon injection

AEGL Acute exposure guideline levels

APF Ammonium phosphate fertilizer

ASOS Automated surface observation system

BLDS Baghouse leak detection system

BTF Beyond the floor

CAA Clean Air Act

CEMS Continuous emissions monitoring system

CFR Code of Federal Regulations

CPMS Continuous parameter monitoring system

DAP Diammonium phosphate

EJ Environmental justice

EPA Environmental Protection Agency

F Fluoride

FR Federal Register

FTIR Fourier transform infrared spectroscopy

GMCS Gore Mercury Control System 

HAP Hazardous air pollutants

HF Hydrogen fluoride

Hg Mercury

HON Hazardous Organic NESHAP

HQ Hazard quotient

ICR Information Collection Request

IRIS Integrated Risk Information System

IST Inherently safer technology

LOAEL Lowest-observed-adverse-effect level

MACT Maximum achievable control technology

MAP Monoammonium phosphate

MOA Mode of action

NAAQS National Ambient Air Quality Standards

NACAA National Association of Clean Air Agencies

NAS National Academy of Sciences 

NATA National-Scale Air Toxics Assessment

NEI National emissions inventory

NESHAP National Emissions Standards for Hazardous Air Pollutants

NOAEL No-observed-adverse-effect level

NSPS New source performance standard

OAQPS Office of Air Quality Planning and Standards

ODW Office of Drinking Water

OEHHA Office of Environmental Health Hazard Assessment

OHEA Office of Health and Environmental Assessment

OMB Office of Management and Budget

P2O5 Phosphorus pentoxide

PB-HAP Hazardous air pollutants known to be persistent and bio-accumulative in the 

environment
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PM Particulate matter

PPA Purified phosphoric acid

ppm Parts per million

RCRA Resource Conservation and Recovery Act

RfD Reference doses

RfC Reference concentration

RIA Regulatory impact analysis

RTR Residual risk and technology review

SiF4 Silicon tetrafluoride

SPA Superphosphoric acid

SSM Startup, shutdown, and malfunction

TOSHI Target organ-specific hazard index

tpy Tons per year

μg/dL Microgram per deciliter

UPL Upper prediction limit

WESP Wet electrostatic precipitator

WPPA Wet-process phosphoric acid

WWW World Wide Web
3-1

3.0 RISK ASSESSMENT

3.1 Supports Conclusion Of NESHAP Residual Risk Assessment 

Comment: Two commenters (0039, 0038) supported the EPA's residual risk assessment 

conclusions that the existing National Emissions Standards for Hazardous Air Pollutants

(NESHAP) for the Phosphoric Acid Manufacturing and Phosphate Fertilizer Production source 

categories currently are amply protective of public health and the environment. 

Response to Comment: We acknowledge the commenters’ support for the EPA’s residual 

risk assessment conclusions.

3.2 NESHAP Residual Risk Assessment Approach Needs Update

Comment: One commenter (0042)1stated that the EPA’s residual risk assessment 

underestimates risk. This commenter (0042) argued that the EPA is currently relying on outdated 

risk assessment methods that fail to incorporate the current science on the cumulative impacts of 

environmental exposures and community and individual vulnerability. The commenter urged the 

EPA to perform a full “cumulative risk assessment” as recommended by The National Research 

Council, National Academy of Sciences (NAS), and incorporate the recommendations and 

information from the NAS, other independent scientists, and the example models from California 

EPA’s Office of Environmental Health Hazard Assessment (OEHHA), and take immediate steps 

to better assess cumulative risk and impacts. The commenter cited their 2012 Cumulative Risk 

Assessment Comments and pointed out that these bodies have provided substantial criticism of 

EPA’s approach and urged EPA to follow current science and take more protective approaches 

on important specific major issues.

The commenter suggested that the EPA implement the following as part of their residual 

risk assessment: (1) Account for increased susceptibility by using age-dependent adjustment 

factors for all carcinogens, not just known mutagens; (2) Pre-natal susceptibility: Account for 

increased susceptibility by using a pre-natal adjustment factor for all carcinogens of at least 10X; 

(3) For chronic non-cancer risk, consult and apply child-specific reference values (such as those 

created by California EPA scientists), where available; (4) If child-specific reference values are 

unavailable, consult science on early exposure impacts, and use an additional default factor of at 

 

1 Docket ID No. EPA-HQ-OAR-2012-0522-0040 is a duplicate to Docket ID No. EPA-HQ-OAR-2012-0522-0042.
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least 10X; (5) Account for increased vulnerability resulting from and related to demographic 

factors, as part of the risk assessment; (6) Fully integrate the findings of its environmental justice 

analyses into its risk assessments and rulemakings, and set stronger pollution limits to provide 

environmental justice; (7) Assess and aggregate exposure from multiple pathways – including by 

adding inhalation and non-inhalation-based cancer risks; (8) Include the interaction of multiple 

pollutants; (9) Account for exposure to multiple sources, and until EPA has a specific 

mechanism for estimating total exposures, a default or uncertainty factor of at least 10X should 

be used to provide overburdened communities with the protection they need now; (10) Reduce 

EPA’s benchmark of what it considers acceptable lifetime cancer risk instead of relying on the 

outdated upper limit of 100-in-a-million; (11) Use a Margin of Exposure (MOE) framework for 

non-cancer impacts and adjust the target MOE according to known vulnerability factors; and 

(12) In the face of increasing evidence calling into question the assumption of a safe or 

acceptable level of exposure, EPA should also consider reforming risk assessments to support 

reducing risks to the lowest possible level, to protect public health, rather than suggesting that 

there is a safe or acceptable level.

Response to Comment: We disagree with the comment that we failed to consider or 

account for cumulative risk. The EPA modeled whole-facility risks for both chronic cancer and 

non-cancer impacts to understand the risk contribution of the sources within the Phosphoric Acid 

Manufacturing and Phosphate Fertilizer Production source categories. The individual cancer 

risks for each source category were aggregated for all carcinogens. In assessing noncancer 

hazard from chronic exposures for pollutants that have similar modes of action or (where this 

information is absent) that affect the same target organ, we aggregated the hazard quotients 

(HQ). This process creates, for each target organ, a target organ-specific hazard index (TOSHI), 

defined as the sum of hazard quotients for individual hazardous air pollutants (HAP) that affect 

the same organ or organ system. All TOSHI calculations presented here were based exclusively 

on effects occurring at the “critical dose” (i.e., the lowest dose that produces adverse health 

effects). Whole facility risks were estimated utilizing the 2005 National Emissions Inventory 

(NEI), with updated facility-wide and source category data files developed by the EPA through 

emission data updates from industry, states, and National Association of Clean Air Agencies 

(NACAA). 

We disagree with the general comment that the EPA should adopt the Cal OEHHA childprotective scientific approach on cancer. The EPA has an approach for selecting appropriate 
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health benchmark values and in general, this approach places greater weight on the EPA derived 

health benchmarks than those from other agencies (see 

http://www.epa.gov/ttn/atw/nata1999/99pdfs/healtheffectsinfo.pdf). Notably, this approach 

favoring EPA benchmarks (when they exist) over all others has been endorsed by the Science 

Advisory Board (SAB). Further, the EPA is currently evaluating whether it is appropriate to use 

the Cal OEHHA child- specific reference doses, and we note that because there are currently no 

such values for HAP inhalation, their current utility would be limited to persistent and 

bioaccumulative (PB-HAP), which may be associated with non-negligible ingestion exposures. 

That is, before using these child-specific reference doses (RfDs), the EPA would need to 

evaluate whether they have been appropriately derived.

We also disagree with the comment that the risk assessment for these source categories 

do not consider the groups that may be most at-risk (e.g., pregnant women). When the EPA 

derives exposure reference concentrations and unit risk estimates for metal HAP, it also 

considers the most sensitive populations identified in the available literature, and importantly, 

these are the values used in our risk assessments (see “A review of the reference dose and 

reference concentration processes.” EPA/630/P-02/002F. Risk Assessment Forum, Washington, 

DC. Available online at http://www.epa.gov/raf/publications/pdfs/rfd-final.pdf). With respect to 

maternal exposure in utero specifically, we are unaware of literature that would allow for a 

robust characterization of risk during this stage of development for the HAP we are assessing 

from this source category.

We acknowledge that population subgroups, including children, may have a potential for 

risk that is greater than the general population due to greater relative exposure and/or greater 

susceptibility to the toxicant. As explained in previous actions, including the final Hazardous 

Organic NESHAP (HON) residual risk and technology review (RTR) (71 FR 76610-76611), the 

assessments we undertake to estimate risk account for this potential vulnerability. With respect to 

exposure, the risk assessments we perform implicitly account for this greater potential for 

exposure by assuming lifetime exposure, in which populations are conservatively presumed to be 

exposed to airborne concentrations at their residence continuously, 24 hours per day for a full 

lifetime, including childhood. With regard to children’s potentially greater susceptibility to noncancer toxicants, the assessments rely on EPA (or comparable) hazard identification and doseresponse values which have been developed to be protective for all subgroups of the general 

population, including children.
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For example, a review2of the chronic reference value process concluded that the EPA’s 

reference concentration (RfC) derivation processes adequately considered potential susceptibility 

of different subgroups with specific consideration of children, such that the resultant RfC values 

pertain to the full human population “including sensitive subgroups,” a phrase which is inclusive 

of childhood. With respect to cancer, the EPA uses the age-dependent adjustment factor 

approach referred to by the commenter, but limits the use of those factors only to carcinogenic 

pollutants that are known to act via mutagenic mode of action (MOA), in contrast to the OEHHA 

approach, which uses them across the board for all carcinogens regardless of mode of action. In 

lieu of chemical-specific data on which age or life-stage specific risk estimates or potencies can 

be determined, default age dependent adjustment factors can be applied when assessing cancer 

risk for early-life exposures to chemicals which cause cancer through a mutagenic MOA. The 

estimated risks must also be considered in the context of the full set of assumptions used for this 

risk assessment. For example, we used a health-protective assumption of a 70-year exposure 

duration in our risk estimates; however, using the national average residency time of 12 years

would reduce the estimate of risk by roughly a factor of 6. Our unit risk estimates for HAP are 

considered a plausible upper-bound estimate; actual potency is likely to be lower and some of 

which could be as low as zero. After considering these and other factors, we continue to consider 

the risks based on existing emissions from these source categories to provide an ample margin of 

safety (consistent with the Benzene NESHAP framework).

We are not able to determine the baseline health status of individuals or communities in a 

national rulemaking. Individual privacy issues as they relate to health records and the costs that 

would be associated with such an analysis make the analysis infeasible. As stated in the EPA’s 

May 2015, Guidance on Considering Environmental Justice During the Development of 

Regulatory Actions,

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the agency is encouraging rule writers and policy makers to look at the 

whole range of factors that impact communities and population groups when crafting rules. The 

EPA is continuing to discuss and pilot approaches that are consistent with the agency’s 

responsibilities regarding EJ as outlined in EO 12898. In determining the need for tighter 

residual risk standards, the EPA strives to limit to no higher than 100-in-1 million the estimated 

 

2 U.S. EPA. A Review of the Reference Dose and Reference Concentration Processes. U.S. Environmental 

Protection Agency, Risk Assessment Forum, Washington, DC, EPA/630/P-02/002F, 2002.

3 Guidance on Considering Environmental Justice During the Development of Regulatory Actions. 

http://epa.gov/environmentaljustice/resources/policy/considering-ej-in-rulemaking-guide-final.pdf. May 2015.
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cancer risk for persons living near a plant if exposed to the maximum pollutant concentration for 

70 years and to protect the greatest number of persons to an individual lifetime risk of no higher 

than 1-in-1 million. Considerations are made for all people regardless of racial or socioeconomic 

status, and the EPA does not believe it is necessary to establish a default factor to account for 

socioeconomic and other community-based stressors.

We have combined risk assessment results to the extent that it is appropriate to do so. We 

consider the effect of mixtures of carcinogens and use a TOSHI approach for our chronic 

noncancer assessments. We do not use a TOSHI approach for our acute analyses nor do we 

combine the results of our inhalation and multipathway assessments.

As described in the risk assessment report (available in the docket for this action), we do 

not sum results of the acute noncancer inhalation assessment to create a combined acute risk 

number that would represent the total acute risk for all pollutants that act in a similar way on the 

same organ system or systems (similar to the chronic TOSHI). The acute screen is already a 

conservative scenario. That is, the acute screening scenario assumes worst-case meteorology, 

peak emissions for all emission points occurring concurrently and an individual being located at 

the site of maximum concentration for an hour. Thus, as noted in the residual risk assessment for 

these source categories (Docket ID No. EPA-HQ-OAR-2012-0522-0006), “because of the 

conservative nature of the acute inhalation screening and the variable nature of emissions and 

potential exposures, acute impacts were screened on an individual pollutant basis, not using the 

TOSHI approach.”

We did not combine the inhalation and multipathway risk assessment results for each 

pollutant because it is inappropriate to do so. The multipathway risk assessment conducted for 

proposal was a screening-level assessment (i.e., Tier 1). It used highly conservative assumptions 

designed to ensure that facilities with results below the screening threshold values did not have 

the potential for multipathway impacts of concern. The screening scenario is a hypothetical 

scenario, and due to the theoretical construct of the screening model, exceedances of the 

thresholds are not directly translatable into estimates of risk or hazard quotients for these 

facilities. In situations where we have previously summed the inhalation and multipathway 

assessment results (e.g., secondary lead smelters), it was for two refined assessments, and still 

serves as a conservative overestimate of potential risks given that it is highly unlikely that the 

same receptor has the maximum results in both assessments.
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We also disagree with the commenter’s assertion that additional quantitative assessment 

of risks from sources outside the source categories is required under the statute. The statute 

requires the EPA to provide the quantitative risk information necessary to inform RTR 

regulatory decisions, and to this end, the EPA conducts a comprehensive assessment of the risks 

associated with exposure to the HAP emitted by the source categories and supplements that with 

additional information that is available about other possible concurrent and relevant risks.

We generally draw no bright lines of acceptability regarding cancer or noncancer risks 

from source category HAP emissions. It is always important to consider the specific uncertainties 

of the emissions and health effects information regarding the source category in question when 

deciding exactly what level of cancer and noncancer risk should be considered acceptable. In 

addition, the source category-specific decision of what constitutes an acceptable level of risk 

should be a holistic one; that is, it should simultaneously consider all potential health impacts --

chronic and acute, cancer and noncancer, and multipathway -- along with their uncertainties, 

when determining the acceptable level of source category risk. In other words, we look at the risk 

numbers within the context of uncertainty associated with emissions and health benchmark 

values. The Benzene NESHAP decision framework of 1989 acknowledged this; in today’s 

world, such flexibility is even more imperative, because new information relevant to the question 

of risk acceptability is being developed all the time, and the accuracy and uncertainty of each 

piece of information must be considered in a weight-of- evidence approach for each decision. 

This relevant body of information is growing fast (and will continue to grow even faster), 

necessitating a flexible weight-of-evidence approach that acknowledges both complexity and 

uncertainty in the simplest and most transparent way possible. While this challenge is 

formidable, it is nonetheless the goal of the EPA’s RTR decision-making, and it is the goal of the 

risk assessment to provide the information to support the decision-making process.

3.3 Lead 

Comment: One commenter (0042) argued that by just considering and relying solely on 

the Lead National Ambient Air Quality Standards (NAAQS) in its proposed residual risk 

assessment, EPA has not met the legal standard of section 7412(f)(2), which requires an “ample 

margin of safety to protect public health,” rather than the NAAQS, which requires an “adequate 

margin of safety.” The commenter contented that to fulfill its § 7412(f)(2) obligations, the EPA 

must use the best science on assessing children’s health risk of exposure to lead, rather than 
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considering only the 2008 Lead NAAQS. The commenter stated that the EPA must address and 

incorporate the best currently available information on children’s exposure, including the 

Children’s Health Protection Advisory Committee recommendation of protecting children from 

an ambient concentration of lead of 0.02 μg/m3, rather than assuming that the 2008 NAAQS 

level of 0.15 μg/m3 is protective enough. The commenter asserted that the EPA’s sole reliance 

on the Lead NAAQS is both unlawful and arbitrary, and the EPA has failed to provide a 

reasoned explanation for not setting a standard that assures protection below the level of the 

2008 NAAQS.

The commenter stated that the residual risk assessment ignores current data showing that 

harm, particularly to children, can occur at levels below the lead NAAQS, including: (1) The 

CDC has now recognized that there is no safe level of exposure, and has replaced the nowoutdated 10 microgram per deciliter (μg/dL) standard with a recognition that action is required, 

at least, at the reference level of 5 μg/dL; (2) California’s health benchmark for lead shows EPA 

should look at least at a blood-lead level change of 1.0 μg/dL as the level at which measurable 

neurological harm, illustrated by a correlating loss of 1 IQ point, can occur; (3) As EPA’s 

Children’s Health Protection Advisory Committee recognizes, new research in recent years 

suggests that the loss of 1 IQ point can occur at an even lower blood-lead level: 0.01 μg/dL, and 

requires stronger protection than EPA assumes in this rule based on its use of only the 2008 Lead 

NAAQS; (4) there is strong scientific evidence showing greater harm from combined exposure 

to lead and manganese, which are both emitted here, and must the combined impacts from these 

exposures must be accounted for; and (5) EPA must evaluate evidence showing a link between 

maternal blood-lead levels and low birth weight, released in 2013.

In addition, the commenter stated that the residual risk standards are designed to do more 

than just replicate other statutory protections, such as those provided by the NAAQS. The 

commenter asserted that if Congress had intended EPA simply to replicate the NAAQS, or some 

other different Clean Air Act requirement, in its section 7412(f)(2) residual risk rulemaking, the 

section 7412(f)(2) requirement would become redundant for any hazardous air pollutant that also 

has any relationship to any other regulated pollutant. The commenter argued that if there were 

any ambiguity on this question, statutory construction requires a reading of section 7412(f)(2) 

that preserves its independent value and meaning.

Response to Comment: We disagree with the comment that the use of the lead NAAQS 

does not sufficiently protect children. First, the lead NAAQS primary standard targets protection 
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to the most susceptible group in the human population – children – and is designed to protect 

against adverse effects to children’s most sensitive organ system – the developing neurological 

system. (See 73 FR at 66975, 66976.) Second, the primary NAAQS for lead is specifically 

targeted at those children living near major sources of lead, such as secondary smelters. (See 73 

FR at 67002/3 “in applying the evidence-based framework, we are focused on a subpopulation of 

U.S. children, those living near air sources and more likely to be exposed at the level of the 

standard”; to the same effect see 73 FR 67000/3--“The framework in effect focuses on the 

sensitive subpopulation that is the group of children living near sources and more likely to be 

exposed at the level of the standard. The evidence-based framework estimates a mean air-related 

IQ loss for this subpopulation of children; it does not estimate a mean for all U.S. children”; 73 

FR 67005/1--“the air-related IQ loss framework provides estimates for the mean air-related IQ 

loss of a subset of the population of U.S. children, and there are uncertainties associated with 

those estimates. It provides estimates for that subset of children likely to be exposed to the level 

of the standard, which is generally expected to be the subpopulation of children living near 

sources who are likely to be most highly exposed.”) In addition, in reviewing and sustaining the 

lead primary NAAQS, we note that the D.C. Circuit specifically noted that the rule was targeted 

to protect children living near lead sources: “EPA explained that the scientific evidence showing 

the impact of lead exposure in young children in the United States led it ‘to give greater 

prominence to children as the sensitive subpopulation in this review’ and to focus its revision of 

the lead NAAQS on the ‘sensitive subpopulation that is the group of children living near [lead 

emission] sources and more likely to be exposed at the level of the standard.’ Given the scientific 

evidence on which it relied, the EPA’s decision to base the revised lead NAAQS on protecting 

the subset of children likely to be exposed to airborne lead at the level of the standard was not 

arbitrary or capricious.” Coalition of Battery Recyclers, 604 F. 3d at 618.

Furthermore, as noted in the risk assessment document, there is no RfD or other 

comparable chronic health benchmark value for lead compounds. That is, in 1988, the EPA’s 

Integrated Risk Information System (IRIS) program reviewed the health effects data regarding 

lead and its inorganic compounds and determined that it would be inappropriate to develop an 

RfD for these compounds, saying, “A great deal of information on the health effects of lead has 

been obtained through decades of medical observation and scientific research. This information 

has been assessed in the development of air and water quality criteria by the agency’s Office of 

Health and Environmental Assessment (OHEA) in support of regulatory decision-making by the 
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Office of Air Quality Planning and Standards (OAQPS) and by the Office of Drinking Water 

(ODW). By comparison to most other environmental toxicants, the degree of uncertainty about 

the health effects of lead is quite low. It appears that some of these effects, particularly changes 

in the levels of certain blood enzymes and in aspects of children’s neurobehavioral development, 

may occur at blood lead levels so low as to be essentially without a threshold. The agency’s RfD 

Work Group discussed inorganic lead (and lead compounds) at two meetings (07/08/1985 and 

07/22/1985) and considered it inappropriate to develop an RfD for inorganic lead.” The EPA’s 

IRIS assessment for Lead and compounds (inorganic) (CASRN 7439-92-1), 

http://www.epa.gov/iris/subst/0277.htm.

The commenter also makes the legal argument that the primary NAAQS provides an 

“adequate” margin of safety, but that Clean Air Act (CAA) section 112 (f)(2) requires that a 

residual risk standard provide an “ample” margin of safety, reasoning from this that a NAAQS 

cannot just be substituted as the measure for evaluating acceptability of risk and that some 

greater level of protection is required. We do not accept the commenter’s argument. The EPA is 

considering the primary NAAQS for lead --which incorporates an adequate margin of safety -- in 

determining whether lead risks (taken together with cancer and other non-cancer health risks) 

from air-borne lead from phosphate facilities are acceptable or unacceptable. Thus, to the extent 

the commenter’s argument rests on the difference between ‘adequate’ and ‘ample’ margin of 

safety, the argument is misplaced. 4 Margin-of-safety determinations for this rule are conducted 

separately, in accord with the two-step framework set forth in the Benzene NESHAP and the en 

banc opinion in Vinyl Chloride. See not only Vinyl Chloride, 824 F. 2d at 1165, 1166 but NRDC 

v. EPA, 902 F. 2d 962, 973-74 (D.C. Cir. 1990) (distinguishing the NAAQS process, whereby 

the margin of safety analysis is incorporated as part of the standard without a two-step analysis, 

from residual risk determinations).5 Using that framework, with its consideration of costs, costeffectiveness, technological feasibility, and other factors set out in the Benzene NESHAP, at 

proposal we did not identify any additional controls beyond those that would need to be 

implemented to ensure an acceptable level of risk with an ample margin of safety. The EPA thus 

 

4

Indeed, the EPA’s utilization of a standard which also incorporates an adequate margin of safety to evaluate 

acceptability of risk is an added conservative (i.e. protective) element in its approach here. 

5 The court was referring to the predecessor provision to the current CAA section 112 (f), but its analysis is equally 

applicable to the revised provision. 
3-10

disagrees with the commenter that CAA section 112 (f)(2) standards must be more stringent than 

a primary NAAQS as a matter of law.

3.4 Whether NESHAP Residual Risk Assessment Consistent with the Key 

Recommendations Contained in the SAB

Comment: One commenter (0042) stated that the EPA has no valid basis to state that its 

proposed risk assessment methods are “consistent with the key recommendations contained in 

the [SAB] report.”

Two commenters (0038, 0043) suggested that the EPA provide greater specificity 

regarding how the EPA’s methods used to assess risks in their residual risk assessment are 

consistent with those peer-reviewed by EPA’s SAB in 2009 and described in their peer review 

report issued in 2010, and also are consistent with the key recommendations contained in that 

report. The commenter contended that the residual risk assessment does not appear to fully 

delineate the risk assessment methods, default assumptions, data extrapolations and uncertainties 

for each step of the assessment. The commenter stated that it would help interested parties better 

verify the results and determine for themselves whether the risk assessment provides an accurate 

representation of potential residual risk if the EPA would provide full-fledged documentation in 

the residual risk assessment and its associated appendices regarding decisions for air disposition 

modeling, facility definitions, emissions data manipulation, selection of specific reference, 

toxicity criteria, and use of modeling assumptions. The commenter (0043) provided a detailed 

review of this topic in an appendix to their comment describing the residual risk assessment, 

issues with the methodology and assumptions, and recommendations for changes to make, 

including more transparency. 

Response to Comment: EPA’s SAB has reviewed and supported our residual risk 

program several times over the past 17 years. First, in 1998 they examined our analytical and 

policy approach for assessing residual risk from hazardous air pollutants emitted from stationary 

sources, followed by a second review in 2000 to verify that our application to a specific source 

category was consistent with the approved approach. A third SAB consultation in 2006 focused 

on development of emissions inventories for source categories and updated methods for 

characterizing human exposure and risks. Again in 2009, the SAB reviewed and supported our 

updated and expanded air toxics risk assessment methods, including our multipathway 
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assessment, refinement of acute risk screening, and the methods of assessing potential 

environmental risk. 

Our residual risk assessment report for these source categories, available in the docket for 

this proposed rulemaking, provided a comprehensive discussion of our current methods, models, 

health benchmarks, modeling results, risk characterization, and uncertainties as they have 

evolved over time as a result of these SAB consultations. In addition, the 9 appendices associated 

with this report provided extensive detail on the models and how they were used, the individual 

analyses (inhalation, acute, multipathway), and facility-specific results. To further our 

transparency, the docket for the proposed rulemaking also included all of the model input files 

necessary to recreate our analyses. We believe this fully documents our risk assessment methods, 

default assumptions, data extrapolations and uncertainties and allows interested parties to verify 

our results.

3.5 Data Collection From Section 114 Survey And Testing Requests

Comment: One commenter (0038) stated that the RTRs were supported by the best 

available information from the affected facilities in each source category. However, this 

commenter contended that certain summary passages of the proposed rule might suggest that the 

EPA did not receive adequate information in response to its CAA § 114 requests; and explained 

that in limited instances, responsive information was not available because (1) it does not exist, 

or (2) it was not requested by the EPA. This commenter requested the EPA clarify in the 

rulemaking docket that the responses provided by industry were commensurate with the relevant 

statutory obligations.

Response to Comment: The Agency collected data during two CAA section 114 requests 

(one during 2010 and the other in 2014). The industry provided the majority of requested data 

and follow-up information requested. The Agency acknowledges and appreciates the costs and 

efforts expended by the industry in providing these data.

3.6 HF Emissions Data Used For NESHAP Residual Risk Assessment Not 

Representative Of Actual HF Emissions

Comment: One commenter (0043) argued that fugitive hydrogen fluoride (HF) emissions 

used in the NESHAP residual risk assessment are not representative of actual emissions at their 

facilities, but rather overestimate emissions, and that the subsequent residual risk assessment 

lacks transparency in methodology and has an overtly conservative bias (i.e., overstates risk). 
3-12

The commenter stated that the combination of several assumptions and factors used by the EPA, 

result in a factor of 17 times higher HF emission rate than the facility’s calculations; the 

commenter provided a detailed review of this topic as tables and appendices to their comment 

including HF emissions from their cooling towers and gypsum dewatering stacks. The 

commenter also stated that the EPA assumes that 93% of the total fluoride emitted from cooling 

towers is HF, but the EPA does not explain the basis for this value; the commenter contended 

that the “93%” value does not accurately represent HF emissions from the cooling towers. 

Further, the commenter noted that the EPA uses a multiplication factor of 1 in the acute 

inhalation residual risk assessment for HF emissions from gypsum dewatering stacks, cooling 

ponds, and cooling towers. However, a multiplication factor of 2 was used for the cooling tower 

at the Simplot Don-Pocatello facility; the commenter requested the EPA explain their 

justification.

Response to Comment: The EPA disagrees with the commenter and believes the HF 

emissions are representative for gypsum dewatering stacks and cooling towers. When 

determining emissions from gypsum dewatering stacks, we developed HF emission factors (tons 

per acre per year) based on the available fugitive emissions test data. The gypsum dewatering 

stack test data were from open path tunable diode laser or open path fourier transform infrared 

with radial plume mapping tests performed at four different facilities in the U.S. and Canada. We 

considered this to be a representative sample of the industry. In addition, gypsum dewatering 

stack test data were not available at proposal specifically for the two Simplot facilities the 

commenter references. If specific data were available for these facilities, then it would have been 

considered for the analysis. 

Regarding cooling towers, we believe that assuming 93 percent of the cooling tower 

fluoride emissions are HF is appropriate. The commenter shows two studies where the HF ratio 

was examined, one of these shows that HF constitutes the bulk of the fluoride emissions while 

the other shows a lower HF contribution. We also reviewed another study (see the document 

“LaCosse_Measuring HF Emissions from WPPA Facilities_1993,” available in Docket ID No. 

EPA-HQ-OAR-2012-0522) that shows HF contributing more than 99 percent of the fluoride 

emissions. Therefore, data do support a contribution of 93 percent for HF emissions to total 

fluoride emissions for fugitive sources. The commenter is correct that a multiplication factor of 2 

was used for the cooling tower at Simplot Don-Pocatello. This was based on a review of data that 

showed large variability in cooling tower emissions at this plant, which range up to 175 pounds 
3-13

of total fluoride per year (see Appendix Q11 from Simplot’s “Response to December 10, 2007 

EPA Request for Information, Section 3007 of the Resource Conservation and Recovery Act,”

which is available in the docket for this action). Simplot also acknowledged their cooling tower 

emissions were variable in their comment letter when they state “factors that Simplot has used to 

calculate HF emissions from cooling towers, gypsum stacks and point sources have varied over 

the years for both the Rock Springs and Pocatello plants.” Due to this variability, we determined 

a multiple factor of 2 was appropriate for the Simplot Don-Pocatello cooling tower. 

Because we believe the HF emissions from fugitive sources are representative, we 

disagree that risk was overstated. We are not revising the HF emissions for fugitive sources nor 

re-analyzing the risk assessment for phosphoric acid plants. We determined there was no risk at 

proposal and the risk analysis was not considered when the work practice for gypsum dewatering 

stacks and cooling ponds was developed. Therefore, re-evaluating emissions and risk for fugitive 

sources would not lead to rule revisions.

3.7 Chromium Emission Data Used For NESHAP Residual Risk Assessment Not 

Representative Of Actual Chromium Emissions

Comment: One commenter (0043) argued that the EPA needs to reconsider the 

assumption used in the NESHAP residual risk assessment that all chromium is hexavalent 

chromium. The commenter provided a detailed review of this topic in an appendix to their 

comment concluding that that tests for chromium can easily provide false positive values for 

hexavalent chromium.

Response to Comment: The Agency disagrees with the commenter that all chromium was 

considered hexavalent chromium in the NESHAP residual risk assessment. The Agency used 

reported hexavalent chromium emissions values in the NESHAP residual risk assessment, and 

did not assume that all chromium was hexavalent chromium. The values included in the risk 

modeling file were the reported hexavalent chromium and the estimated trivalent chromium 

values. The Agency assumed that the non-speciated chromium values represented total 

chromium emissions, and subtracted the reported hexavalent chromium emission values from the 

non-speciated total to estimate trivalent chromium. The total non-speciated chromium values 

were not included in the risk modeling file. In the few instances where the reported hexavalent 

chromium value for a process exceeded the reported non-speciated total chromium value, only 

the reported hexavalent chromium value was included in the modeling file. The total non-
3-14

speciated value was not included and the trivalent chromium was not estimated for these 

instances. For the remaining processes that only had total chromium emissions and no hexavalent 

or trivalent chromium emissions were reported, the Agency used speciation profiles to speciate 

the total into hexavalent and trivalent chromium emissions.

3.8 Stack Parameters Used For NESHAP Residual Risk Assessment Not Representative 

Of Actual Stack Parameters

Comment: One commenter (0043) stated that stack parameters used in the analysis are 

not representative of actual stack parameters at their facilities. The commenter stated that the 

stack parameters used for one of their facilities are an average of data provided by PotashCorp 

(PCS) Aurora; the commenter argued that there is no basis given, nor is it appropriate to use PCS 

stack parameters with their facility emission data. The commenter provided a detailed review of 

this topic in a table to their comment. In addition, the commenter contended that the use of 

wrong modeling inputs for the source characteristics further distorted the determination of an 

“acute” concentration of HF in the area near one of their facilities.

Response to Comment: When available, the Agency used actual facility specific stack 

parameters in the NESHAP residual risk assessment; if parameters were not known, the Agency 

used best available data. The Agency asked for stack parameters on Form C-2-e of the 2010 

CAA Section 114 survey; respondents were asked in this portion of the survey to provide 

specific information on emission points including, but not limited to, coordinates, release height, 

diameter, and velocity. For cases where a facility did not provide stack parameters for an 

emission point in their response to the 2010 CAA Section 114 survey, such was the case with the 

facility that the commenter is referring to, the Agency used averages from other facilities to 

estimate the stack parameters. While the use of default stack parameters may have impacted the 

estimated acute HF ambient concentrations, stack height and diameter, and exit gas temperature 

and velocity are not the sole drivers in the development of estimated ambient concentrations.

Therefore, any inaccuracies resulting from this use of average parameters rather than actual 

parameters would be expected to be minimal enough to not be relevant to the final risk 

assessment.
3-15

3.9 Conservative Assumptions Used In NESHAP Residual Risk Assessment Bias 

Results 

Comment: One commenter (0038) asserted that given the highly conservative 

assumptions used by the EPA throughout the risk assessment process, including not only the 

residual risk assessment methodology but also the derivation of dose-response thresholds (e.g., 

IRIS RfC, RfD, AEGLs, MRLs, and CalEPA RELs) against which exposure data were 

compared, the residual risk characterizations in the residual risk assessment are inherently biased 

upwards. The commenter recommended the EPA expressly describe the conclusions drawn there 

from as highly conservative. 

Response to Comment: Uncertainty and the potential for bias are inherent in all risk 

assessments, including those performed for this rulemaking. Although uncertainty exists, we 

believe that our approach, which used conservative tools and assumptions, ensures that our 

decisions are health protective and environmentally protective. A brief discussion of the 

uncertainties in the RTR emissions datasets, dispersion modeling, inhalation exposure estimates 

and dose-response relationships can be found in the proposal for this rulemaking (79 FR 66512). 

A more thorough discussion of these uncertainties is included in the memorandum “Residual 

Risk Assessment for Phosphate Fertilizer Production and Phosphoric Acid Manufacturing Source 

Categories in support of the July 2015 Risk and Technology Review Final Rule,” which is 

available in the docket for this action.

3.10 Selection of Meteorological Data In NESHAP Residual Risk Assessment 

Comment: One commenter (0038) requested clarification regarding the selection of offsite meteorological data used for modeling air-dispersion characteristics and subsequent 

inhalation exposure. The commenter said that the EPA states that five years of modeling data are 

“ideal,” but in the residual risk assessment, only data from 1991 were used. The commenter 

pointed out that Appendix 2 from the residual risk assessment suggests there is an 

incompatibility between meteorological data and the air dispersion modeling, resulting in an 

arbitrary decision to use 1991 as the sole source of meteorological data. The commenter stated 

that some significant improvement could be achieved in air dispersion modeling results by either 

(1) updating the air dispersion model to accept meteorological data after 1991, using data from a 

five-year period before 1992, or (2) selecting a single year that is typical of meteorological 

conditions for the source being characterized. The commenter pointed out that the EPA used 
3-16

2005 National-Scale Air Toxics Assessment (NATA) NEI data updated via the use of CAA § 

114 information requests from all U.S. phosphate fertilizer and phosphoric acid manufacturers 

submitted in 2010 and 2014; and stated that this improvement is important, given that the 

selection of the meteorology dataset translates directly to the estimated exposures and risks, 

resulting in a variance of 17% lower to 84% higher than the estimated values.

Response to Comment: When we began performing RTR risk assessments, we chose 

meteorological data considering the amount of data quality assurance needed and AERMOD run 

times. We restricted our meteorological data to that collected prior to the installation of the 

Automated Surface Observation System (ASOS). The ASOS had been found to omit the ceiling 

height for a large percentage of observations at a number of meteorological stations. Because 

installation and operation of ASOS equipment began in 1992, we selected the year 1991. As 

newer, higher quality ASOS data have become available, we have added newer data and 

additional data site locations to the meteorological data library we use in our risk assessments. 

Currently, all of our meteorological data has been updated and risk assessment modeling uses 

data from the year 2011. However, at the time these source categories were modeled, the update 

of the meteorological data had not occurred. Since the risk were considered acceptable with an 

ample margin of safety and the emissions had not increased since we modeled, we concluded for 

the proposal and re-iterate for the final rulemaking, that it is not necessary to re-model these 

source categories with the updated meteorological data.

Although 5 years of meteorological data is preferred for assessing chronic exposures and 

risks, we use a single year (2011) of meteorological data in our risk assessments because of

AERMOD model run times. Because we frequently run AERMOD for entire source category 

with many individual emissions points and for many receptors, using 5 years of meteorological 

data would increase already significant model run times by a factor of five compared to a single 

year. In a sensitivity analysis of the impact of using a single year of meteorological data 

compared to 5 years, we found that modeled concentrations differed by less than ten percent on 

average and thus, the use of one year of meteorological data is not likely to appreciably affect the 

results of the risk assessment.
3-17

3.11 Rationale for Maximum One-Hour Emission Rate In NESHAP Residual Risk 

Assessment 

Comment: One commenter (0038) requested that the EPA adequately explain its rationale 

for the maximum one-hour emission rate used for determining potential acute exposures. The 

commenter argued that there is no clear rationale for the EPA’s selection of a factor of ten for 

derivation of the highest hourly ambient concentration at off-site locations. The commenter 

asserted that the EPA provides no policy directive or technical evaluation to justify its 

“engineering judgment” other than to state that “EPA uses a multiplier of 10 to predict worst 

case emissions during a process upset or control device malfunction.” The commenter pointed 

out that the EPA presented multiple acute HQ estimates for some HAPs in Appendix 8, Table 1 

with a footnote indicating that a second set of estimates for HF were based on emissions 

estimates representing a factor of two rather than the ten-fold multiplier.

The commenter stated that it is confident that there is no good reason to assume that 

emissions during a process upset or control device malfunction can be reasonably expected to 

result in a highest hourly ambient concentration at any off-site location; therefore, requests that 

the EPA re-examine the selection of a factor of ten to derive the highest hourly ambient 

concentration. The commenter said that at a minimum, the EPA must explain its “engineering 

judgment” on this subject.

Response to Comment: When screening for potentially significant acute exposures, we 

used an estimate of the highest hourly ambient concentration at any off-site location as the 

surrogate for the maximum potential acute exposure concentration for any individual. These 

hourly concentrations are based on hourly emissions. Since information is not usually available 

on short-term emission rates, we generally apply the assumption that the maximum one-hour 

emission rate from any source is ten times the average annual hourly emission rate for that 

source. (The average hourly emissions rate is defined as the total emissions for a year divided by 

the total number of operating hours in the year.) This choice of a factor of ten for acute screening 

was originally based on engineering judgment.

To develop a more robust peak-to-mean emissions factor, and in response to one of the 

key messages from the SAB consultation on our RTR Assessment Plan, we performed an 

analysis using a short-term emissions dataset from a number of sources located in Texas 
3-18

(originally reported on by Allen et al. 2004)6. In that report, the Texas Environmental Research 

Consortium Project compared hourly and annual emissions data for volatile organic compounds

for all facilities in a heavily-industrialized 4-county area (Harris, Galveston, Chambers, and 

Brazoria Counties) over an eleven-month time period in 2001. We obtained the dataset and 

performed our own analysis, focusing on sources which reported emitting high quantities of HAP 

over short periods of time. A discussion of this analysis appeared in Appendix 3 Analysis of data 

on short-term emission rates relative to long-term emission rates of the “Draft Residual Risk 

Assessment for Phosphate Fertilizer Production and Phosphoric Acid Manufacturing” available 

in the docket for the proposed rulemaking and will also appear in the docket for the final 

promulgation (Docket ID No. EPA-HQ-OAR-2012-0522-0006). The results of this analysis 

indicated most peak emission events were less than twice the annual average, and the highest 

was a factor of 74 times the annual average, and the 99th percentile ratio of peak hourly emission 

rate to the annual hourly emission rate was 9. Based on these results, we generally chose the 

factor of ten for all initial screening. This factor is intended to cover all possible hourly peaks 

associated with routinely-variable emissions. While there have been some documented emission 

excursions above this level, our analysis of the data from the Texas Environmental Research 

Consortium suggests that this factor should cover more than 99 percent of the short-term peak 

gaseous or volatile HAP emissions from typical industrial sources. We have no data relating 

specifically to peak short-term emissions of particulate HAP. In the absence of source categoryspecific data, we use this same default approach for particulate emissions as well. 

For phosphate fertilizer production facilities an acute multiplier of 10 (x) the average 1-hr 

emission rates was applied to all sources. For phosphoric acid manufacturing facilities a 

multiplier of 10 (x) was applied for point sources based on the information collection request 

(ICR) data and engineering knowledge of the source category processes, and for emissions from 

fugitive sources (gypsum ponds and cooling ponds) an acute multiplier of 1 was applied (for all 

but one instance; see response to comment in section 3.6 of this document for further detail 

regarding this one instance).

 

6 Allen, D., C. Murphy, Y. Kimura, W. Vizuete, T. Edgar, H. Jeffries, B.-U. Kim, M. Webster, and M. Symons, 

2004. Variable industrial VOC emissions and their impact on ozone formation in the Houston Galveston Area. Final 

Report: Texas Environmental Research Consortium Project H-13. 

http://files.harc.edu/Projects/AirQuality/Projects/H013.2003/H13FinalReport.pdf
3-19

3.12 Ecological Assessment Endpoints In NESHAP Residual Risk Assessment 

Comment: One commenter (0038) requested that the EPA provide clarification regarding 

the selection of ecological assessment endpoints. The commenter pointed out that the EPA 

indicates that these endpoints were selected based on a hierarchy of programmatic, federal 

agency or state agency benchmarks; however, the residual risk assessment indicates that a 

Canadian “LOEL” ecological benchmark was used. The commenter requests a technical and 

legal justification for the EPA’s use of the “Canadian LOEL ecological benchmark,” as well as 

an explanation of that benchmark, so that it can meaningfully review the benchmark for 

applicability to facility-specific ecosystems. The commenter also suggested that the EPA discuss 

its overall use of international ecological benchmarks, and how such benchmarks fit into the 

EPA’s decision-making hierarchy (assuming there is a legal justification for including them in 

the first instance).

Response to Comment: The RTR environmental risk screenings of acid gases are 

conducted using modeled estimates of ambient air concentrations based on emissions from the 

regulated source. Therefore, the benchmark for HF for plants is required to be expressed as an air 

concentration. Currently, the EPA does not have an air concentration-based environmental 

benchmark for HF at either the programmatic level or regional level. In addition, air 

concentration-based environmental benchmarks are not available from other federal agencies. 

However, air concentration-based HF benchmarks have been established by several states, 

including Texas, Kentucky, New York, Washington, and Tennessee, as a part of their ambient air 

quality standards.

The “Draft Residual Risk Assessment for Phosphate Fertilizer Production and Phosphoric 

Acid Manufacturing,” which was available in the docket for this proposed rulemaking, presented 

the environmental risk screen results in Table 3.2-4 (for Phosphate Fertilizer Production) and 

Table 4.2-4 (for Phosphoric Acid Manufacturing). In footnote 3 of these tables we indicated that: 

“For HF, we evaluated two benchmarks, one from Canada and the other from the State 

of Washington. Although, they are both considered to be LOELs - the level between a 

NOAEL and a LOAEL, we have listed the results under the LOAEL column. The results 

presented in the table are the same for both the LOEL from Canada and the LOEL from 

the State of Washington (i.e., no facility showing exceedance of averaged values; 1% of 

area in category showing and exceedance).”

The Environment Canada criteria of 0.4 ug HF/m3 was developed using regression analysis 

of exposure-concentration versus exposure-duration data and is defined as:
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"The level above which there are demonstrated effects on human health and/or the 

environment. It is scientifically based and defines the boundary between the LOAEL and 

the NOAEL. It is considered to be the level of exposure just below that most likely to 

result in a defined and identifiable but minimal effect." (CCME 1999)

The Environment Canada criteria was developed using data from 13 investigations into the 

effects of HF on plants that represented 32 separate effects results. The data set included 18 

effects results from studies using plants of horticultural importance, 10 from studies using 

agricultural species, and 4 from studies of effects on forest (conifer) species. Many of the plant 

species included in these studies are of great importance in the U.S., such as (Canadian 

Environmental Protection Act/Federal Provincial Advisory Committee Working Group on Air 

Quality Objectives and Guidelines, July 1996): corn, wheat, pine trees, potatoes, spruce trees, 

peach, peanut, green beans, strawberries, barley, alfalfa, onion, and beans.

3.13 Exposure Modeling Uncertainty In NESHAP Residual Risk Assessment 

Comment: One commenter (0038) requested that the EPA provide some quantitative or 

qualitative rationale for its characterization of the exposure modeling uncertainty where the EPA 

states that: “Although every effort has been made to identify all the relevant facilities and 

emission points, as well as to develop accurate estimates of the annual emission rates for all 

relevant HAP, the uncertainties in our emission inventory likely dominate the uncertainties in our 

exposure modeling estimates. The chronic exposure modeling uncertainties are considered 

relatively small in comparison, since we are using EPA’s refined local dispersion model with 

site-specific parameters and reasonably representative meteorology.” The commenter stated that 

it finds no basis for the statement that “uncertainties in our emission inventory likely dominate 

the uncertainties in our exposure modeling estimates” given that there are only twelve facilities 

in the phosphoric acid source category and eleven facilities in the phosphate fertilizer source 

category, the availability of NATA NEI data, and the additional data provided through two 

information requests. The commenter added that this is especially true given that selection of the 

meteorology dataset can result in a variance of 17% lower to 84% higher than the estimated 

values.

Response to Comment: Several types of uncertainty are inherent in all risk assessments, 

such as the uncertainty associated with the emissions datasets, dispersion modeling, inhalation 

exposure estimates and dose-response relationships. For all RTR risk assessments the models, 

methods to estimate exposure, and the dose-response values have undergone rigorous peer and/or 
3-21

SAB review. Although the development of the RTR emissions datasets involved quality 

assurance/quality control processes, the accuracy of emissions values will vary depending on the 

source of the data, the degree to which data are incomplete or missing, the degree to which 

assumptions made to complete the datasets are accurate, errors in emission estimates and other 

factors. Therefore, it is reasonable to anticipate that the uncertainties in our emission inventory 

likely dominate the uncertainties in our exposure modeling estimates.
4-1

4.0 NESHAP TECHNOLOGY REVIEWS AND NSPS REVIEWS

4.1 Supports Conclusions Of NESHAP Technology Reviews and NSPS Reviews

Comment: Two commenters (0039, 0038) stated that they agree with the EPA’s 

conclusion that there are no new developments in practices, processes, or control technologies 

that can be applied in either phosphoric acid manufacturing or phosphate fertilizer production 

that would reduce hazardous air pollutants below current levels. One of these commenters (0039)

also stated that the EPA correctly determined that no changes to the new source performance 

standard (NSPS) were warranted.

Response to Comment: We thank the commenters for their support. However, as a point 

of clarification, the EPA determined that there are no new cost-effective developments in 

practices, processes, or control technologies for these source categories. Also, we do want to 

clarify that, as explained in the preamble to the proposed rule, our technology review did reveal 

that superphosphoric acid (SPA) process lines at four different facilities include an oxidation 

reactor to remove organic impurities from the acid. Refer to the preamble of the final rule for 

additional discussion regarding the applicability of oxidation reactors in the final rule.
5-1

5.0 STATUTORY AUTHORITY

5.1 No Basis For Other Changes

Comment: Four commenters (0037, 0039, 0038, 0043) urged the EPA to explain to why 

the proposed standards are revised to be more restrictive even though the EPA’s overarching 

conclusions are that: (1) the phosphoric acid and phosphate fertilizer source categories pose no 

risk to human health or the environment, and (2) no new developments have arisen in practices, 

processes, or control technologies that can be applied. One of these commenters (0038) stated 

that at present, it is not clear that the EPA has the requisite statutory authority or a factual basis 

to change the standards, given that the fundamental RTR conclusions culminating in the 1999 

rulemaking have not changed (based on EPA’s own review and findings during this RTR 

process). This commenter (0038) suggested that the EPA establish and explain this nexus 

between the outcomes of the RTR and EPA’s proposed changes to the substantive rules in 

Subparts AA and BB; otherwise, imposing those changes on phosphoric acid and phosphate 

fertilizer facilities will lack a rational basis. 

One commenter (0037) questioned the EPA’s legal authority to adopt changes to 

applicability definitions and compliance procedures that potentially make the NESHAP broader 

and more stringent than is currently the case (e.g., this commenter pointed out that the proposed 

HF limits are more stringent than the current total fluoride limits); the commenter cited the 

Petroleum Refinery Sector RTR and NSPS, and argued that the EPA has recognized that it does 

not have the authority to issue more stringent standards in these circumstances.

Another commenter (0039) argued that CAA section 112(f) does not provide the EPA 

with any authority to revise the existing NESHAP if the existing standards already provide an 

ample margin of safety, or if cancer risk already is less than one in one million. This commenter 

also asserted that despite the EPA’s conclusions from its review of the NSPS that "no costeffective emission reductions strategies [were] identified" and the EPA did "not see any basis for 

concluding that the 'best system of emissions reduction' has changed,” the EPA proposes to 

"clarify" the NSPS in a manner that will significantly expand the scope of the rule. This 

commenter argued that the EPA’s proposal to modify the definition of "wet-process phosphoric 

acid plant" in NSPS subpart T to include "clarifiers" and "defluorination systems." are 

unwarranted given EPA's conclusions that these sources already present low risks and because 

there have not been developments in technology or changes in practice to justify this change. The 
5-2

commenter stated that the unnecessary nature of EPA's action is perhaps even more pronounced 

in the NSPS context, in which the statute explicitly allows EPA to leave the NSPS in place when, 

like here, current standards are effective. The commenter suggested that the EPA interpret its 

authority consistent with the CAA and in a manner that avoids the imposition of significant costs 

without any benefit.

Two commenters (0039, 0043) pointed out that the additional work practice standards for 

gypsum dewatering stack and cooling ponds, impose millions of dollars in costs and years of 

effort on the part of regulated entities, and potentially increase environmental risks associated 

with process water management, even though the EPA has determined that current standards are 

protective of human health and the environment and that revisions are otherwise unnecessary. 

Further, the commenters stated that the EPA has presented no analysis that these proposed work 

practices would result in any material reduction in emissions. One of these commenters (0039)

claimed that EPA’s justification of the reason to promulgate fugitive HF controls for gypsum 

dewater stacks and cooling ponds is based on two cases that do not support its position (National 

Lime Association v. Environmental Protection Agency, 233 F.3d 625 (D.C. Cir. 2000) and Sierra 

Club v. Environmental Protection Agency, 479 F.3d 875 (D.C. Cir. 2007). They claimed these 

cases are distinguishable from the situation with HF emissions from subpart AA sources because 

there are existing controls for these sources. Also, they claimed that the EPA did not explain how 

the work practice standards are analogous to a maximum achievable control technology (MACT)

floor, in that they provided no information on what emission limitations are achieved by the best 

performing phosphoric acid or phosphate manufacturing sources from gypsum dewatering stacks 

and cooling ponds (because these emissions “cannot be measured”). They also asserted that since 

imposing a MACT floor based on reliable determination of the best performing sources is not 

possible, then the EPA is obliged to adopt standards under CAA section 112(h) that, consistent 

with CAA section 112(d)(2), take into account costs and non-air quality health and 

environmental impacts and energy requirements.

Response to Comment: As stated in the preamble for the proposed rule, the Agency is not 

proposing revisions under the authority of CAA Sections 111(b)(1) (B), 112(d)(6), or 112(f)(2) 

since we did not identify any cost-effective control technologies or practices for emission 

reductions and since the current standards were found to provide an ample margin of safety to 

protect public health. 
5-3

The standards that were proposed to address mercury (Hg) and HF emissions from 

calciners, and HF emissions from fugitive sources are for currently unregulated emission

sources, and proposed under the authority of CAA Section 112(d)(2) and (d)(3). Therefore, we 

disagree with the commenter’s statement that we should allow the residual risk analysis to advise 

whether we address unregulated emission sources. The latter is clearly not designed to inform the 

former, as the residual risk analysis should, in practice, be conducted no later than 8 years after 

the original standard is set. 

The Agency is not adopting the proposed clarifications for defluorination units and 

clarifiers, but is adopting the clarifications for oxidation reactors. Refer to the preamble of the 

final rule for additional discussion regarding the applicability of oxidation reactors in the final 

rule.

The Agency does not agree with the estimated cost for compliance for the gypsum 

dewatering stack management plan. In response to other comments, the Agency has clarified the 

requirements for the management plan. We believe these clarifications will make the covered 

entities, and subsequent costs more clear to facilities. Refer to the preamble of the final rule for 

additional details of the work practice standards for gypsum dewatering stacks and cooling ponds 

included in the final rule. As previously noted, these are also currently unregulated sources. 

Therefore it is not appropriate to use the residual risk analysis to determine whether regulation is 

necessary.

The work practice standards adopted in the final rule represent MACT as they are a 

collection of best practices for emission reduction within the industry.
6-1

6.0 HG LIMIT AND HF WORK PRACTICE STANDARDS FOR 

CALCINERS

6.1 Technical Feasibility of Hg Control Devices and Hg BTF Limit

Comment: Some commenters (0037, 0041) did not support the EPA’s decision to set a 

BTF limit for Hg from phosphate rock calciners because they stated that the emissions do not 

present unacceptable risks nor do the emission limits yield any benefits. The commenters 

asserted that the EPA fails to show that the proposed BTF Hg limit would produce health or 

environmental benefits that justify the costs of achieving the standard as required by CAA 

section 112(d)(2). Commenters (0037, 0041) further claimed that the EPA’s own risk assessment 

shows that the BTF limit is not necessary from a risk standpoint because the NESHAP 

regulation, prior to implementation of the proposed Hg BTF limits, protects human health and 

the environment with an ample margin of safety. The commenters (0037, 0041) maintained that 

under CAA section 112(d)(2), the EPA may set an emission limit that is more stringent than the 

MACT floor only if the Agency determines that the BTF limit is “achievable” based on a 

consideration of the relative costs and benefits. One commenter (0037) cited regulations where 

the EPA did not set BTF limits for a particular pollutant because the benefits were minimal and 

the risk would not be appreciably reduced. Commenters (0037, 0041) supported setting the 

MACT floor as the Hg limit. 

Commenters (0037, 0041) stated the Hg control devices that the EPA evaluated for the 

phosphate rock calciner BTF limit were not technically feasible, but did note two potential 

solutions. Specifically, the commenters stated that use of ACI just prior to the existing WESP or 

after the WESP with a fabric filter is not technically feasible. The commenters (0037, 0041)

explained the exhaust gas downstream of the WESP is completely saturated and contains 

entrained water droplets; this would plug the fabric filter, result in performance degradation of 

the activated carbon, and could lead to plugging of the injection lances and formation of deposits 

on the ducts. The commenters (0037, 0041) further explained that it would not be feasible to 

install heating systems or design engineering control to avoid these problems, due to high costs 

and the technical complexity. The commenters (0037, 0041) noted that installing the ACI just 

prior to the WESP was also not feasible, again due to performance degradation of the activated 

carbon, but also due to the fact that the existing WESPs could not capture the additional 
6-2

particulate load. The commenters (0037, 0041) reported that installing the ACI upstream of the 

existing Venturi scrubber is technically feasible, because the gas upstream of the scrubber is not 

completely saturated. However, the commenters (0037, 0041) noted several design and 

operational modifications that would be necessary; these modifications focused on reducing the 

temperature of the exhaust gas streams to less than 375 degrees Fahrenheit. When installing ACI 

upstream of the existing Venturi scrubber, the ACI vendor used by a commenter (0037)

recommended the use of treated (e.g., halogenated) carbon at an injection rate of 30 lb/MMacf, 

in order to meet the BTF Hg limit. The commenter (0037) said that the carbon injection rate may 

need to be as much as 30 lb/MMacf based on site-specific conditions, such as temperature, Hg 

concentration, moisture, and sulfur content of the phosphate rock calciner exhaust stream. In 

support of a high injection rate, the commenter (0037) also cited a reference from 1994 that 

observed an increased injection rate due to temperature of the exhaust gas stream.

Regarding fixed-bed carbon adsorption, commenters (0037, 0041) stated a traditional 

fixed-bed carbon adsorption system would not be feasible, due to the presence of entrained water 

droplets that would severely degrade sorbent performance and cause plugging within the bed. 

The commenters (0037, 0041) indicated that new Gore Mercury Control System (GMCS) 

technology might be technically feasible because it uses a fixed sorbent structure with a sorbent 

polymer composite material to adsorb Hg; the GMCS polymer composite material might protect 

the sorbent from entrained water droplets and other contaminants in the flue gas. The 

commenters (0037, 0041) stated that to utilize a GMCS fixed-bed carbon adsorption system, 

several adjustments to the calciners would be necessary, as well as a pilot study to confirm the 

feasibility. Another commenter (0043) also reported they were evaluating the use of the GMCS 

system, but were only in preliminary stages as their phosphate rock calciner is not yet operating. 

A commenter (0037) also explained that each phosphate rock calciner would need its own 

controls and a single control system for all phosphate rock calciners would not be feasible due to 

safety and operational concerns. One commenter (0037) provided a detailed review of Hg control 

devices in an attachment to their comment.

Response to Comment: The results of the residual risk analyses are not part of the 

beyond-the-floor MACT determination, and accordingly, the commenter’s concern about not 

considering risk results is not appropriate. Additionally, as a result of the additional information 

provided by the commenters, we agree that it is not technically feasible to use ACI just prior to 

the existing WESP or after the WESP with a fabric filter to control Hg emissions from phosphate 
6-3

rock calciners. We also agree that a traditional fixed-bed carbon adsorption system is not 

technically feasible to control Hg emissions from phosphate rock calciners. Furthermore, we 

agree that use of ACI is technically feasible to control Hg emissions from phosphate rock 

calciners if it is installed upstream of the existing venturi scrubber, where the moisture content is 

lower.

We are not finalizing the proposed BTF Hg limit (i.e., 0.014 mg Hg/dscm @ 3% O2) in 

NESHAP subpart AA for existing phosphate rock calciners due to potential significant economic 

impacts associated with the costs of controls. Instead, we are finalizing a MACT floor Hg limit

for existing phosphate rock calciners. We are finalizing the proposed BTF Hg limit (i.e., 0.14 mg 

Hg/dscm @ 3% O2) in NESHAP subpart AA for new phosphate rock calciners. Refer to the 

preamble of the final rule for additional details.

6.2 Supports Hg BTF Limit

Comment: One commenter (0042) support the EPA’s recognition of the need to set a 

beyond-the-floor limit for Hg from phosphate rock calciners. 

Response to Comment: We acknowledge the commenters’ support for the EPA’s 

proposed rule. However, we are not finalizing the proposed BTF Hg limit (i.e., 0.014 mg 

Hg/dscm @ 3% O2) in NESHAP subpart AA for existing phosphate rock calciners due to 

potential significant economic impacts associated with the costs of controls. Instead, we are 

finalizing a MACT floor Hg limit for existing phosphate rock calciners. We are finalizing the 

proposed BTF Hg limit (i.e., 0.14 mg Hg/dscm @ 3% O2) in NESHAP subpart AA for new 

phosphate rock calciners. Refer to the preamble of the final rule for additional details.

6.3 Set Health-Based Hg Limit

Comment: One commenter (0037) stated that the EPA could set a health-based limit for 

Hg under CAA § 112(d)(4) that is equivalent to the MACT floor for phosphate rock calciners. 

The commenter (0037) maintained that CAA section 112(d)(4) is designed to prevent the 

promulgation of emission limits that are more stringent than necessary to protect human health 

and the environment with an ample margin of safety. The commenter continued that under that 

section, EPA can set health-based limits for certain pollutants based on established health 

thresholds as an alternative to promulgating limits under CAA § 112(d)(2). The commenter 

(0037) stated that emissions test data for the phosphate rock calciners showed that approximately 
6-4

99% of the Hg is elemental Hg, and elemental Hg is eligible for CAA § 112(d)(4) because it is 

classified as a Group D pollutant. 

Response to Comment: After considering the comment, the EPA has decided that it is not 

appropriate to adopt an emissions standard for elemental Hg under EPA’s CAA section 

112(d)(4) authority.

Hg is a persistent, bioaccumulative toxic metal that is typically emitted from industrial 

sources in three forms: gaseous elemental Hg (Hg0), the form primarily released by phosphate 

rock calciners; oxidized Hg compounds (Hg+2); and particle-bound Hg (HgP). Whereas oxidized 

(divalent) and particle-bound Hg will deposit relatively closer to the release source, gaseous 

elemental Hg emitted into the air does not quickly deposit or chemically react in the atmosphere, 

but is transported much further, often becoming part of the global pool, before undergoing 

transformation to inorganic Hg compounds (divalent Hg) and deposited. As a result, deposition 

of Hg to watersheds includes Hg originating from local/regional sources, combined with Hg that 

has been transported regionally and globally from global anthropogenic and natural sources.

Once deposited, inorganic forms of Hg transform to methylmercury, a persistent and 

toxic contaminant that bioaccumulates in fish and is associated with neurodevelopmental effects 

in children. In fact, while Hg exposure and risk can occur through a variety of pathways, the 

dominant human exposure pathway associated with ambient air emissions is through the 

consumption of fish that have bioaccumulated Hg originally deposited to watersheds following 

atmospheric release and transport. EPA previously has established that “there is no evidence for 

a biological threshold observed for critical effect of neurological deficits in children studied in 

the principal studies of the IRIS assessment for MeHg [methylmercury].”7 Thus, the EPA does 

not consider methylmercury to be a threshold pollutant.

The EPA notes that the Agency’s authority under CAA section 112(d)(4) is discretionary. 

That provision states that the EPA ‘‘may’’ consider establishing health thresholds when setting 

emissions standards under CAA section 112(d). By the use of the term ‘‘may,’’ Congress clearly 

intended to allow the EPA to decide not to consider a health threshold even for pollutants which 

have an established threshold, and it is appropriate for the EPA to consider relevant factors, such 

as the ability for a threshold pollutant to undergo chemical transformation to a non-threshold 

 

7 Revised Technical Support Document: National-Scale Assessment of Mercury Risk to Populations with High 

Consumption of Self-caught Freshwater Fish; In Support of the Appropriate and Necessary Finding for Coal-and 

Oil-Fired Electric Generating Units; footnote 17; http://www.epa.gov/ttn/atw/utility/revisedmercurytsd.pdf
6-5

pollutant and the known and potential cumulative public health and environmental effects of 

elemental and methylmercury in the environment when deciding whether to exercise its 

discretion under CAA section 112(d)(4).8

6.4 Hg Deposition

Comment: A commenter (0041) indicated that 97 percent of future Hg deposition in 

North Carolina will come from out-of-state Hg emission sources. Given this finding, the 

commenter (0041) concluded that any additional control measures offer limited environmental 

benefit to further reduce Hg emissions from in-state sources, and as such does not support the 

BTF limit.

Response to Comment: We are not finalizing the proposed BTF Hg limit (i.e., 0.014 mg 

Hg/dscm @ 3% O2) in NESHAP subpart AA for existing phosphate rock calciners due to 

potential significant economic impacts associated with the costs of controls. Instead, we are 

finalizing a MACT floor Hg limit for existing phosphate rock calciners. We are finalizing the 

proposed BTF Hg limit (i.e., 0.14 mg Hg/dscm @ 3% O2) in NESHAP subpart AA for new 

phosphate rock calciners. Refer to the preamble of the final rule for additional details.

6.5 Hg UPL Calculation

Comment: One commenter (0042) disagrees with the EPA’s use of a high variability 

factor in setting the MACT standards for these pollutants as it is unsupported and results in a 

standard that is higher than appropriate. This commenter stated that the EPA’s use of the upper 

prediction limit (UPL) is unlawful and arbitrary. The commenter explained the UPL was 

remanded by the D.C. Circuit in 2013 due to the EPA’s interpretation of “average emissions 

limitation achieved by the best performing 12 percent,” and that the EPA’s new rationale fails to 

clarify this issue. Also, according to the commenter, the Court noted that the UPL produces an 

“apparently illogical result.” The commenter asserts the UPL is the level EPA expects any 

“future” test by any source in the top 12 percent to “fall below” during 99 out of 100 

performance tests and it is the level that a source “would be expected to meet a specified percent 

of the time that the source is operating.” The commenter continued that the UPL is neither the 

required “average” nor even any measure of what units have actually “achieved.” The 

 

8 See September 9, 2010 National Emission Standards for Hazardous Air Pollutants From the Portland Cement 

Manufacturing Industry and Standards of Performance for Portland Cement Plants; Final Rule, at 75 FR 54970.
6-6

commenter further observed the average of the Hg emissions test data is lower than the 

calculated UPL value.

Lastly, the commenter concludes that the EPA is increasing the limit above the average of 

what data in the record show sources have actually achieved and, the resulting emission limits 

the EPA proposes to set are higher and weaker than the statute directs and that communities need 

to protect their health. The commenter concludes that the EPA may not redefine what “average 

emission limitation” means when its meaning is clear nor may it distort the text “achieved” 

beyond its meaning. If the EPA believes test data it is using does not accurately reflect what 

sources have achieved, the commenter states, then it should collect better test data.

Response to Comment: As stated in the memorandum entitled “Use of the Upper 

Prediction Limit for Calculating MACT Floors” (Docket ID No. EPA-HQ-OAR-2010-0522-

0007) (UPL memorandum), “In the context of development of MACT floors, the UPL is a value, 

calculated from a dataset, which identifies the average emissions level that a source or group of 

sources is meeting and would be expected to meet a specified percent of the time that the source 

is operating. That percent of time is based on the confidence level used in the UPL equation, as 

explained in more detail below. For a single best controlled emission source that serves as the 

basis for a new source MACT floor, the 99 percent UPL is the emissions level that the source 

would be predicted to be below during 99 out of 100 performance tests, including emissions tests 

conducted in the past, present, and future, based on the short term stack test data available for 

that source. It is important to note that the UPL does not represent the worst emissions 

performance of the best performing units at any time, but rather the average level expected to 

have been achieved over time, as the first element of the UPL equation is the average of the 

short-term emissions test data from the best performing units. In other words, the 99 percent 

UPL is the level of emissions that we are 99 percent confident is achieved by the average source 

represented in a dataset (in the case of MACT standards, the dataset representing the 

performance of the best performers as specified in the CAA) over a long-term period based on its 

previous, measured performance history as reflected in short-term stack test data.” Contrary to 

the commenter’s assertion, the NACWA court did not find the UPL to be an arbitrary approach, 

but simply asked for a better explanation from the Agency. The UPL memorandum provides the 

explanation of what the UPL represents sought by the NACWA Court. It also explains why the 

UPL is representative of the level of performance achieved by the best performing unit or units. 

The court did not state that the “average emissions limitation achieved by the best performing 
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12 percent” must be equal to the mean of the available data, as suggested by the commenter, and 

in past decisions the Court has upheld that it is appropriate for EPA to account for variability

when establishing numeric MACT standards. See Mossville Environmental Action Now v. EPA, 

370 F.3d 1232, 1241-42 (D.C. Cir. 2004).

We also refer the commenter to the proposal MACT floor memorandum, which is in the 

rulemaking docket. This memorandum provides a detailed discussion of the EPA’s authority to 

consider variability, especially given that MACT and other technology-based standards are 

necessarily derived from short term emissions test data and such data are not representative of 

the range of operating conditions that the best-performing facilities face on a day-to-day basis. In 

statistical terms, each test produces a limited data sample, not a complete enumeration of the 

available data for performance of the unit over a long period of time. The EPA, therefore, often 

needs to adjust the short-term data to account for these varying conditions in order to properly 

estimate these sources’ performance over time. The types of variability that the EPA accounts for 

include variability between and within tests at the same unit as well as between units in the pool 

of “best performing units.” This memo also describes the EPA’s selection of the UPL 

methodology to address such variability. 

In response to the concern over “apparently illogical result,” EPA first notes that 

commenters reference a court decision that addressed MACT standards for a different source 

category, which are not at issue in this rulemaking. Second, the commenter did not assert that the 

methodology resulted in an “apparently illogical result” in this rulemaking as the court pointed 

out in NACWA. Rather, the commenter asserts that the methodology results in limits that are 

less stringent than they believe is required. Finally, the UPL methodology used to establish the 

MACT standards referenced in the comment was not the same UPL methodology used to set the 

standards in today’s action. We note that the “apparently illogical result,” from a different 

rulemaking, resulted from analysis of small datasets and the use of procedures that EPA no 

longer follows. We included in the docket a memo explaining how we adjusted the UPL 

methodology to address situations in which the Agency must establish MACT standards with 

limited data. That memo, entitled Approach for Applying the Upper Predictive Limit to Limited 

Datasets (Docket ID No. EPA-HQ-OAR-2012-0522), provides an analysis of the use of the UPL 

for limited data sets and includes procedures to evaluate whether additional analyses beyond the 

use of the 99 percent UPL are needed. We also note that the “apparently illogical results” 

questioned by the court will no longer occur provided the procedures laid out in our UPL
6-8

memorandum and limited data sets memorandum are followed, as was done in this rule. 

Accordingly, we believe that our use of the UPL, as specified in the above referenced memo, is 

in accordance with recent Court decisions. 

Finally, the EPA is tasked with setting standards using available data and, while we agree 

that more data is desirable, the standards that we proposed are based on a reasonable amount of 

data that, while not perfect, provide sufficient information with which to develop standards that 

reasonably reflect the required levels of performance. EPA must rely on emission test methods 

that are available to the Agency and to sources. As described in the UPL memorandum, our 

standards reflect the average emission limitation achieved by the best source or sources as 

required under the statute.

6.6 HF Work Practice for Phosphate Rock Calciners

Comment: One commenter (0037) supported the HF work practices and stated they are 

consistent with their current phosphate rock calciner operations. Another commenter (0043), 

does not support the implementation of HF work practices, because the emissions were BDL, the 

measured concentrations were questionable, and HF cannot practicably be measured from the 

phosphate rock calciners. This commenter (0043), which is in the process of conducting studies 

on a future calciner, noted that preliminary results indicate a calcination temperature of at least 

2000 degrees Fahrenheit is necessary for their phosphate rock calciner. This commenter (0043) 

also explained they are evaluating a flash calciner, which operates with a much shorter retention 

time than the fluidized bed calciners currently in operation at another facility. 

A commenter (0043) does not agree that wet scrubbers should be required because their 

phosphate rock calciner will be located in a remote area where treatment and disposal options for 

scrubber liquors may not be available. The commenter (0043) has identified potential other 

solutions which can be as effective as wet scrubbers, and therefore recommended the EPA 

should allow for other control technologies with equivalent efficiencies.

A commenter (0042) does not support the use of work practices for HF, and declared the 

EPA should set numeric emission limits for HF from phosphate rock calciners. The commenter 

maintained the EPA has not provided the determination and supporting evidence the Clean Air 

Act requires to set these standards instead of numeric limits, and that the EPA failed to satisfy 

the test it must meet to promulgate work practice standards “in lieu of” numeric emission 

standards set by CAA section 112(h). The commenter (0042) stated that not using the available 
6-9

emissions data to set a floor limit is unlawful and arbitrary, even if the data are below the 

detection limit.

Response to Comments: This comment is addressed in the preamble of the final rule. We 

are not finalizing work practice standards for HF from phosphate rock calciners, as proposed. 

Instead, we are including a total fluoride emission limit for phosphate rock calciners in NESHAP 

subpart AA.
7-1

7.0 HF WORK PRACTICE STANDARDS FOR GYPSUM 

DEWATERING STACKS AND COOLING PONDS

7.1 Submergence Of Discharge Pipe

Comment: Three commenters (0037, 0039, 0043) opposed the use of submerged 

discharge pipes and siphon breaks below the surface of the cooling pond as a fugitive HF 

emissions control technique. They claimed that submerging cooling pond discharge lines for 

above-grade ponds would create a significant risk for a siphon effect to occur when a pumping 

system is shutdown, causing backpressure on the pump seals back down the line, and, thus, 

defeating the purpose of the siphon break. One of these commenters (0037) added that 

submerging siphon breaks will impede the ability of these devices to prevent backflow because 

submersion may interfere with the atmospheric connection needed to make siphon breaks operate 

properly.

Response to comment: We agree with commenters that submerging siphon breaks could 

impede the ability of these devices to prevent backflow; therefore, we are removing this 

requirement from the final rule. Refer to the preamble of the final rule for additional details.

7.2 Rim Ditch (Cell) Building Technique

Comment: Two commenters (0039, 0038) contended it is not feasible to minimize the 

stack surface area of gypsum stack ponds as a work practice to minimize fugitive HF emissions, 

and another commenter (0043) believed the technique is generally implementable.

One commenter (0039) stated that although they use a rim ditch (cell) building technique, 

it is not an appropriate work practice for reducing HF emissions, and mentioned that the EPA 

does not provide data or an explanation of the linkage between minimizing the gypsum 

dewatering stack surface area and reducing emissions. This commenter suggested that the EPA 

define the technique as “a gypsum stack building technique where gypsum slurry is deposited 

along the stack perimeter with flow directed along a ditch before the liquid flow is conveyed to 

the settling compartments.” Another commenter (0038) stated that minimizing the gypsum pond 

surface areas is not feasible in Florida, North Carolina, and Louisiana because gypsum pond 

surface areas are optimized to provide annual evaporative water losses necessary to maintain 

zero water discharge.
7-2

Response to Comment: We believe that using the rim ditch technique over the lifespan of 

a gypsum dewatering stack will reduce the surface area of the gypsum pond and thereby reduce 

fugitive HF emissions. Refer to the preamble of the final rule for additional details.

7.3 Wetting Of The Active Gypsum Stack

Comment: Four commenters (0037, 0039, 0038, 0043) objected to the use of wetting of 

the active gypsum stack as a fugitive HF emissions control technique because the technique may 

be infeasible and counter-productive due to water balance issues at nearly every affected facility.

One commenter (0043) argued that applying fresh water is not feasible (i.e., water trucks are not 

feasible or safe; irrigation in the West is not feasible; pipes are at risk of freezing) and another 

commenter (0037) stated that using recycled water may actually increase fugitive emissions 

because HF resides primarily in residual and make-up waters used to transport the gypsum slurry 

to the gypsum dewatering stack. One commenter (0039) contended that determining hot or dry 

periods is too subjective; therefore, it would be difficult to know when the control technique 

would apply. Another commenter (0043) illustrated the uncertainty of wetting of the active 

gypsum dewatering stack as a fugitive HF emissions control technique by identifying two studies 

with contradicting conclusions (one concluded that most HF is emitted from aqueous surfaces 

and trends with solar radiation, and the other study concluded that drying gypsum is a major 

source of ambient fluoride emissions from gypsum storage areas).

Response to Comment: We are not adopting this proposed control measure in the 

NESHAP subpart AA final rule. Refer to the preamble of the final rule for additional details.

7.4 Application Of Slaked Lime

Comment: One commenter (0039) challenged the EPA’s lack of evidence on the 

effectiveness of applying slaked lime to gypsum dewatering stacks as a fugitive HF emissions 

control technique, and claimed that it would not be feasible, referring to rain as threat to 

eliminate the potential for effectiveness. On the contrary, another commenter (0043) described 

how they apply a lime solution on top of reachable drying gypsum stack areas, and that the 

reaction of fluoride with slaked lime does result in the “tie-up” of volatile F, although they are 

not aware of any studies that have measured or quantified reductions.

Response to Comment: We believe slaked lime can precipitate fluorides from gypsum 

dewatering stacks and cooling ponds, thus reducing the availability of fluorides in solution that 
7-3

could then be released into the air during evaporation. Refer to the preamble of the final rule for 

additional details.

7.5 Soil Caps And Vegetation

Comment: Three commenters (0039, 0038, 0043) contended there is no evidence that 

applying soil caps and vegetation to gypsum dewatering stacks reduce fugitive HF emissions. 

Commenters (0039, 0038) also claimed that enormous costs would be associated with the 

fugitive HF emissions control technique requiring facilities to apply soil caps and vegetation to 

all side slopes of the active gypsum dewatering stack up to 50 feet below the stack top. Some of 

these commenters (0038, 0043) mentioned that there are state rules that require soil caps and side 

vegetation on side slopes for erosion/water impact control, but not for the purpose of fugitive HF 

emissions control.

Response to Comment: We believe that this control measure creates a barrier on the 

surface of the gypsum dewatering stack side slopes that reduces HF emissions; therefore, we 

disagree with commenters’ assertion that applying soil caps and vegetation may not be an 

effective option for fugitive HF emissions control. Refer to the preamble of the final rule for 

additional details.

7.6 Closure Of Gypsum Dewatering Stacks

Comment: Two commenters (0039, 0043) requested that the closure of a gypsum 

dewatering stack not be considered a fugitive HF emissions control technique. One of these 

commenters (0039) contended that the EPA should allow the final cover on a closed stack to 

consist of a synthetic liner, as this would achieve the same purpose as a vegetative liner and may 

be more appropriate in some instances. One commenter (0043) explained that some states and 

the EPA have closure requirements under Resource Conservation and Recovery Act (RCRA), 

including for example: requirements for long term care practices (beyond 20-50 years); shaping 

and configuration of gypsum dewatering stacks; site security. They suggested that due to these 

detailed requirements, it would be best to defer to stack closure requirements within other 

regulations and not have NESHAP requirements that involve or require stack closure.

Response to Comment: We disagree with commenters’ requests to exclude closure from 

the list of measures for controlling fugitive HF emissions from gypsum dewatering stacks. We 

believe that closing a gypsum dewatering stack is one of the best solutions for reducing fugitive 
7-4

HF emissions because it permanently reduces the emissions from the greatest contributing 

source. Refer to the preamble of the final rule for additional details.

7.7 Other Techniques

Comment: Three commenters (0037, 0038, 0055) requested that if the EPA proceeds with 

a final rule that includes work practices for reducing fugitive HF emissions from gypsum 

dewatering stacks or cooling ponds, the work practices should include a flexibility mechanism 

for facilities to use additional practices not codified during this rulemaking. One of these 

commenters (0038) asserted that work practice standards that might commonly be practicable for 

other industries are not universally practicable (or legally permissible) throughout the phosphoric 

acid and phosphate fertilizer industries; and some practices might be appropriate for some 

facilities but not others (depending on location, climate, etc). 

Response to Comment: We are not including an option in the NESHAP subpart AA final 

rule, as commenters requested, that would provide a flexibility mechanism for facilities to use 

additional practices not codified during this rulemaking. This type of flexibility does not provide 

regulatory certainty that is needed for both industry and the EPA.

7.8 Requirement To Use At Least Two Of The Control Measures

Comment: One commenter (0038) requested that the EPA eliminate the “dual practice” 

approach for new sources. The commenter (0038) declared that the requirement to implement “at 

least two of the control techniques” listed for “each regulated gypsum dewatering stack and 

cooling pond” is not possible without a broader list that includes at least two practices for 

cooling ponds. Additionally, with regard to closing an active gypsum dewatering stack as a 

control technique option, the commenter contended that giving an owner of a new gypsum 

dewatering stack the option of closing it in tandem with a mandatory second control technique is 

“nonsensical” because the “new stack would immediately have to be closed to implement the 

practice.” Another commenter (0043) wanted clarification as to whether the lateral expansion of 

an existing gypsum dewatering stack is considered a new stack, and thus would trigger the 

proposed work practice standards related to the size of active gypsum dewatering stacks and 

production ratio. The commenter also sought clarification as to whether at least two of the 

control techniques be used in the gypsum dewatering stack and cooling pond management plan 

for controlling fugitive HF emissions would be required.
7-5

Response to Comment: We agree with the commenter that the proposed requirement for 

new gypsum dewatering stacks and cooling ponds to implement “at least two of the control 

techniques” listed for “each” regulated “gypsum dewatering stack and cooling pond,” would 

make compliance for cooling ponds impossible for new sources without a broader list with at 

least two control measures for cooling ponds. In the final rule, the Agency is using the 

terminology “control measures” in lieu of the proposed terminology “control techniques” 

because it more accurately describes the list of options in the rule and avoids confusion with 

other CAA programs. Refer to the preamble of the final rule for additional details.

7.9 Gypsum Dewatering Stack Area To Phosphoric Acid Manufacturing Capacity Ratio

Comment: Several commenters (0037, 0039, 0038, 0043) requested that the EPA either 

reconsider, withdraw, or eliminate the proposed gypsum dewatering stack area limitation of 80 

acres per 100,000 tpy capacity (in equivalent P2O5 feed). The commenters claimed the use of 

flawed data and assumptions in the EPA’s analysis in the following areas: (1) Ambiguous 

definitions of a “gypsum dewatering stack,” and “new” and “existing” stacks; (2) inaccurate or 

outdated data on acreage of existing stacks and production capacity, stack closures, and plans for 

new stacks; (3) flawed or missing rationale and correlation between the gypsum dewatering stack 

area and phosphoric acid manufacturing capacity; (4) no technical or legal basis for the selection 

of the 80-acre cutoff; (5) no consideration given to site-specific variables that influence the 

acreage of gypsum dewatering stacks; and (6) failure to consider impacts from closing an 

existing stack prior to commissioning a new stack. 

These commenters claimed the term “gypsum dewatering stack” is so broadly and 

ambiguously defined they are unable to determine the scope and impact of the proposed area 

limitation of 80 acres per 100,000 tpy capacity, or how the proposed limitation would be applied 

to facilities. They claimed the EPA’s definition includes a wide array of features that have never 

before been considered part of the gypsum dewatering stack (e.g., pumps, piping, all collection 

and conveyance systems associated with gypsum to the stack and process wastewater return to 

the plant). Commenters argued that the EPA underestimated stack acreage used in the analysis 

and that the estimates should be much larger when the “total system” acreage is used. These 

commenters stated that using the “total system” acreage in the analysis demonstrates that the 

EPA significantly underestimated the number of acres at each facility that would need to be 

closed. One of these commenters (0038) asked whether a vertical expansion of an existing stack 
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would be considered a “new” facility, and how the proposed work practice might be evaluated 

for compliance when surfaces of a “closed” facility might be overlapped by an immediatelyadjacent “new” facility.

Additionally, commenters argued that the EPA’s technical rationale for limiting stack 

area was based on an arbitrary correlation with production capacity. One of these commenters 

(0043) said there is no relationship between gypsum dewatering stack area and phosphoric acid 

manufacturing capacity, and that outliers were removed from the analysis further confirming no 

quantitative relationship between stack area and facility capacity. This commenter also asserted 

that limiting the size of the gypsum dewatering stacks is not proven to limit HF emissions.

Furthermore, two commenters (0038, 0043) claimed the 80-acre limit does not consider

an evaluation of water balance and process water cooling needs for individual facilities. These 

commenters pointed out that a flat area does not require as large of a footprint for its gypsum 

dewatering stacks as compared to an area with large topographic relief. One of these commenters

(0043) provided examples of two gypsum dewatering stacks located in mountainous areas that 

require larger footprints to construct ponds due to longer runs of pipe, roads, and dike.

Finally, one commenter (0038) claimed that an updated acreage-based analysis would 

need to account for the transition period between a stack becoming “inactive” and the point in 

time of “closure” so as not to exceed the acreage limit while constructing a new stack. Another 

commenter (0043) stated that the startup of a gypsum dewatering stack is a lengthy process that 

may take more than a year, and that the “ratio” requirement inaccurately assumes simultaneous 

closure of an old stack with the opening (i.e., new construction) of a new stack. Another 

commenter (0039) also contended that construction and closure take years to complete and occur 

simultaneously, and that closing a gypsum dewatering stack before beginning construction on a 

new stack would require an entire companion production facility to be idled for an extended 

period and impose “enormous direct and lost opportunity costs...such costs and plant idling are 

not justified.”

Response to Comment: We are not adopting the proposed work practice that limits the 

size of active gypsum dewatering stacks, which would have been applicable to facilities when 

new gypsum dewatering stacks are constructed. Refer to the preamble of the final rule for 

additional details.
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7.10 Necessity or Justification of HF Work Practices

Comment: Three commenters (0037, 0038, 0039) claimed that there is insufficient 

technical analysis as to the feasibility and effectiveness of the control techniques that were 

proposed as options (as part of a work practice standard in the form of a management plan) for 

controlling fugitive HF emissions from gypsum dewatering stacks and cooling ponds. One of 

these commenters (0038) supported the EPA’s claim that emissions from gypsum dewatering 

stacks and cooling ponds would inherently constitute fugitive emissions, and that conceptually, a 

work practice standard is a reasonable approach to emissions control; however, they challenged 

the technical basis for the specific control techniques listed in the proposed management plan. 

Commenters (0043) contended that the proposed control techniques have not been demonstrated 

to have an effect on fugitive HF emissions, and stated the EPA did not quantify the expected 

reductions in HF emissions resulting from the proposed work practice standard for gypsum 

dewatering stacks and cooling ponds. A commenter (0043) noted that some of the control 

techniques were derived from their facility’s title V permit and that the EPA needed to recognize 

that (a) it is not clear (with a couple of exceptions) that these control techniques provide any 

significant emission reductions; (b) recent information may not support these control techniques 

providing emission reductions; and (c) there is considerable uncertainty in the emissions 

associated with cooling ponds and gypsum dewatering stacks. Commenters (0037, 0038, 0039)

argued that the EPA must justify the control techniques and show that they are not only 

technically effective, but also cost-effective and achievable within the industry. These 

commenters (0037, 0038, 0039) asserted that only two sources of information were used by the 

EPA in its determination of the control techniques that were proposed as options for controlling 

fugitive HF emissions in the proposed gypsum dewatering stack and cooling pond management 

plan. Commenters also noted that there is a large amount of uncertainty related to which specific 

control techniques are feasible and effective in reducing fugitive HF emissions.

Response to Comment: This comment is addressed in the preamble of the final rule. In 

the preamble of the final rule we explain how each control measure is feasible and effective in 

reducing fugitive HF emissions.
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7.11 HF Work Practice For Gypsum Dewatering Stacks and Cooling Ponds Interfere 

With Other Regulatory Programs 

Comment: One commenter (0037) contended that setting work practice standards for 

gypsum dewatering stacks and cooling ponds under the NESHAP should be deferred until the 

EPA completes efforts under other regulatory programs. This commenter (0037) pointed out the 

EPA’s ongoing efforts to identify appropriate work practices and arrange for their 

implementation in connection with pending enforcement actions under other environmental 

programs. They claimed that the proposed regulation to establish new standards for gypsum 

dewatering stacks and cooling ponds could interfere with those efforts. This commenter stated 

that one of their facilities is planning to build a new gypsum dewatering stack under an 

Administrative Consent Order with EPA Region 4 pursuant to RCRA § 7003(a). This commenter 

stated that the construction of the new gypsum dewatering stack could trigger the EPA’s 

Proposed Area Limitation and it would not be possible for the facility to comply because the 

facility could not transition any portion of its active gypsum dewatering stacks to meet the EPA’s 

proposed definition of a “closed gypsum dewatering stack” before commencing construction of 

the new gypsum stack. Another commenter (0038) suggested that the EPA should provide a 

mechanism for authorizing alternative work practices approved by the local/delegate permitting 

authority; the commenter argued that absent such a flexibility mechanism, the NESHAP could 

conflict with other regulatory requirements and hamstring industry’s ability to adopt the most 

effective measures that work at specific sites.

Response to Comment: We are adopting the proposed work practice standard that 

requires you to prepare, and operate in accordance with, a gypsum dewatering stack and cooling 

pond management plan. However, based on analysis of public comments, we are making some 

changes to the specific control techniques that we proposed as options in the plan for controlling 

fugitive HF emissions in an effort to provide additional clarity to facilities. (In the final rule, the 

Agency is using the terminology “control measures” in lieu of the proposed terminology “control 

techniques” because it more accurately describes the list of options in the rule and avoids 

confusion with other CAA programs.) The Agency is also not adopting the proposed work 

practice that limits the size of active gypsum dewatering stacks which would have been 

applicable to facilities when new gypsum dewatering stacks are constructed; therefore, the 

commenter’s concerns regarding the construction of a new gypsum dewatering stack are not 
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applicable. Refer to the preamble of the final rule for additional details of the work practice 

standards for gypsum dewatering stacks and cooling ponds included in the final rule.

7.12 Cooling Pond Considerations For HF Work Practice

Comment: One commenter (0038) referenced a 1978 EPA document: “Evaluation of 

Emissions and Control Techniques for Reducing Fluoride Emissions from Gypsum Ponds in the 

Phosphoric Acid Industry” and questioned why the EPA proposed work practice standards 

focused solely on gypsum dewatering stacks, while the EPA has in the past studied and 

documented more work practices for controls of cooling pond emissions, which are not discussed 

as alternatives to the proposed rule. Another commenter (0037) requested that if EPA keeps 

cooling ponds as part of the gypsum dewatering stack and cooling pond management plan, then 

EPA should provide more than one work practice that could be implemented at a cooling pond. 

This commenter suggested that EPA add a control measure option (for cooling ponds) that would 

require developing a plan to optimize the size of cooling ponds to address fugitive HF emissions 

(as appropriate based on the conditions at the facility).

In addition, another commenter (0055) suggested other control measure options for 

reducing fugitive HF emissions from cooling ponds. This commenter suggested EPA include an 

option to develop and implement a plan for dredging cooling ponds which helps maintain 

cooling capacity, and, therefore, can reduce fugitive emissions by reducing the vapor pressure of

fluoride in the pond water. This commenter also suggested EPA include an option to implement 

a system for the recovery of fluoride for water that is directed to cooling ponds. The commenter 

pointed out that one of its facilities has the capability to recover fluoride as hydrofluorosilicic 

acid during the phosphoric acid evaporation process. The commenter stated that this recovery 

process is operated as needed to meet the market demand for hydrofluorosilicic acid. Finally, the 

commenter suggested EPA include an option to implement a system for the removal of fluoride 

for water that is directed to cooling ponds (for example, by adding lime to increase the pH).

Response to Comment: We have included additional control measure options for 

reducing fugitive HF emissions from cooling ponds. Refer to the preamble of the final rule for 

additional details.
8-1

8.0 TRANSLATION OF TOTAL FLUORIDE LIMITS TO HF LIMITS

8.1 Proposed HF Limits Are More Stringent Than Current Total Fluoride Limits 

Comment: One commenter (0043) argued that the molecular weight difference between 

total fluoride and HF is 11.1 percent; therefore, the current standards need to be increased by 

11.1 percent to allow the scenario where 100 percent of total fluoride emissions could be HF. 

Similarly, another commenter (0037) pointed out that the proposed HF limits are more stringent 

than the current total fluoride limits.

Response to Comment: In light of the Agency’s decision to remove EPA Method 320 

from NESHAP subparts AA and BB (refer to preamble for final rule for further details), and 

subsequently retain total fluoride limits to the final rule, the calculation that we were to use to 

translate the current total fluoride limit (lb total F/ton P2O5 feed) into an HF limit (lb HF/ ton 

P2O5 feed) is no longer relevant. However, the Agency disagrees with this commenter’s method 

for translating the current total fluoride limit to HF limits. From a practical standpoint, it may 

have been appropriate to stoichiometrically translate the current total fluoride limits (lbs total 

F/ton P2O5 feed) into HF limits (lbs HF/ ton P2O5 feed) since the current standard uses total

fluoride as a surrogate for HF, and as such, the standard allows that 100 percent of all total

fluoride emissions could be HF. However, the 11.1 percent factor suggested by the commenter is 

not correct, but the HF limits could have been derived by multiplying the current total fluoride 

limits by 1.053 which is the HF molar equivalent to fluoride (i.e., for every 20.01 lbmol HF/lb 

HF there is 18.9984 lbmol F/ lb F). Had the Agency decided to use this approach, the HF limit 

would have accounted for the mass of hydrogen (H) that reacts with fluorine (F, or in this case 

total F) to produce HF.

8.2 Reliance On EPA Method 26A HF Emissions Test Data To Establish New 

Standards Is In Error

Comment: One commenter (0038) stated that because the EPA did not upload the EPA 

Method 320 test data into the publicly-available electronic docket for the rulemaking, it assumed 

that the EPA generally relied on the Method 26A data to establish the proposed standards; this 

commenter argued that the inherent upward bias of the Method 26A data shows that it is 

inappropriate for setting new HF standards, and the reliance on HF emissions test data to 

establish new standards is in error. The commenter pointed out that based on the test data that the 
8-2

EPA collected from the CAA § 114 requests, HF emissions measured via Method 26A were 

substantially greater than TF emissions measured (for the same emissions points) via Method 

13B in 21 of 37 cases. The commenter asserted that in light of the fundamental fact that HF 

should only be a fraction of TF emissions, use of the clearly upward-biased HF data to set new 

standards will inherently lead to stricter standards than the current TF standards. In addition, the 

commenter argued that at least 5 facilities likely would be unable to achieve the proposed HF 

standards based on the available data. The commenter asserted that the EPA must provide a 

technical justification for its insistence on using Method 26A to establish standards for Subparts 

AA and BB, as well as its insistence on using Method 320 for purposes of HAP testing by 

regulated sources in the future.

Response to Comment: The Agency disagrees with the commenter that EPA Method 320 

test data is not publicly available in the docket for the rulemaking. All of the responses that the 

Agency received to the 2010 and 2014 CAA Section 114 surveys, including all test results, are 

available under Docket ID No. EPA-HQ-OAR-2012-0522-0032, entitled: “Section 114 Surveys 

on DVD: 2010 Section 114 Requests Sent to Facilities 2010 Section 114 Responses From 

Facilities 2014 Section 114 Requests Sent to Facilities 2014 Section 114 Responses From 

Facilities.” Anyone can request a copy of this DVD from the docket office.

The Agency also disagrees with the commenter that EPA Method 26A data was used to 

establish the proposed HF standards. In 2010, the Agency requested facilities conduct HF 

emissions testing via EPA Method 26A from specific processes included in the Phosphoric Acid 

Manufacturing and Phosphate Fertilizer Production source categories. Facilities submitted results 

of these tests to the EPA in the fall of 2010. The Agency determined that it needed additional 

data to evaluate HF emissions limits, and on January 24, 2014, the EPA issued another CAA 

section 114 survey and testing request to certain facilities in order to gather additional HF 

emissions data from calciners and certain wet-process phosphoric acid (WPPA), SPA and 

Ammonium phosphate fertilizer (APF) lines using EPA Method 320. It was the 2014 test results 

that the Agency used to conclude at proposal that moving to a form of the standard that requires 

HF (the target HAP) to be measured (but retained the same numeric values as the current total

fluoride standards) would be achievable by all facilities. The 2010 and 2014 test results are 

available in the docket for this action. However, in light of information provided by commenters, 

the Agency has determined that EPA Method 320 is not an appropriate test method for 

accurately measuring HF emissions from process lines at these specific source categories due to 
8-3

the complex and often incomplete chemical reactions with silicon compounds in these sources.

Accordingly, the Agency is not adopting the proposed HF standards. As a result of this

determination to not adopt the proposed HF standards, the Agency has retained the current total

fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B as a surrogate 

for the HAP HF, rather than HF emission limits using EPA Method 320. Refer to the preamble 

of the final rule for additional details.

8.3 Total Fluoride Surrogate For HF 

Comment: One commenter (0038) argued that total fluoride should remain the surrogate 

for HF under Subparts AA and BB, as measured by Method 13A or 13B. The commenter pointed 

out that since the EPA already has established a clear correlation between HF and total fluoride 

under Subparts AA and BB in prior rules, the EPA has a particularly high technical burden to 

reverse its position on this issue. The commenter added that the courts “have clearly held that 

‘EPA may use a surrogate to regulate hazardous pollutants if it is reasonable to do so’” based on 

a demonstrable “correlation” between a HAP and its surrogate, which EPA already has 

investigated, found, and established by regulation in current Subparts AA and BB. The 

commenter also asserted that the EPA’s statement in the proposed rule at 79 Fed. Reg. at 66,545 

actually reaffirms the close correlation between total fluoride and HF, and supports the continued 

surrogacy relationship between total fluoride and HF.

The commenter requested the EPA explain its technical basis for abandoning the 

longstanding total fluoride surrogate for HF. The commenter argued that the EPA has established 

similar surrogacy relationships to measure HAPs in other regulated source categories in the past, 

citing the November 25, 2011 Proposed National Emissions Standards for Hazardous Air 

Pollutants: Mineral Wool Production and Wool Fiberglass Manufacturing.

Two commenters (0039, 0038) support the EPA allowing facilities to comply with 

current total fluoride standards using Method 13A or 13B as an alternative to complying with the 

proposed HF standard. In allowing this alternative compliance mechanism, one commenter 

(0039) added that the standard should continue to apply to total fluoride rather than HF. The 

other commenter (0038) requested that the EPA extend this option to Subpart BB.

Response to Comment: The Agency is not adopting the proposed HF standards. As a 

result of this determination to not adopt the proposed HF standards, the Agency has retained the 

current total fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B 
9-4

as a surrogate for the HAP HF, rather than HF emission limits using EPA Method 320. Refer to 

the preamble of the final rule for additional details.

9.0 MEASUREMENT, MONITORING, AND REPORTING 

REQUIREMENTS

9.1 Quantifying HF Emissions From Gypsum and Cooling Waters

Comment: One commenter (0043) stated that the measurement of HF emissions from the 

phosphoric acid process is difficult because the ratio of fluoride to silica has a great influence on 

the concentration of HF present in phosphoric acid process streams, including gypsum and 

cooling waters. The commenter contended that the concentration of HF in gypsum waters is 

expected to be less than 10% for their facilities due to this ratio and provided a detailed review of 

this topic in an appendix to their comment. In addition, the commenter argued that the 

differences in chemistry (such as fluoride to Si ratio) explain why there are such wide 

measurements in fluoride emissions from gypsum ponds in general; the commenter provided a 

review of studies in an appendix to their comment that shows estimates from 0.012 to 18.3 

pounds of fluoride per wetted acre per day. The commenter also argued that the percentage of 

fluoride air emissions that are HF varies depending on such factors as the concentration of HF in 

the process/gypsum water, the season of the year, and whether the gypsum surface is wet or dry. 

The commenter cited a paper by Lee and Koogler that provides an overview of gypsum pond 

fluoride chemistry and also discusses technical issues associated with measuring fluoride 

emissions from such ponds. The commenter stated that the fluoride concentrations in a gypsum 

pond tend to stabilize over time, pond chemistry is also pH dependent, and the volatilization of 

HF is a function of the HF concentration in the gypsum water, the temperature of the gypsum 

water, and wind speed.

Response to Comment: The Agency is not adopting the proposed HF standards. As a 

result of this determination to not adopt the proposed HF standards, the Agency has retained the 

current total fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B 

as a surrogate for the HAP HF, rather than HF emission limits using EPA Method 320. Refer to 

the preamble of the final rule for additional details.
9-5

9.2 EPA Method 320

Comment: Four commenters (0037, 0039, 0038, 0043) opposed the use of EPA Method 

320 to test for HF, and supported the retention of a total fluorides compliance standard and 

associated testing using Method 13A or 13B. These commenters argued that EPA Method 320 

leads to unreliable and unrepresentative results because some reactive fluoride compounds in the 

exhaust may form HF in the sampling train. One of these commenters (0038) contended that 

EPA did not explain anywhere in the docket why EPA Method 320 is achievable, effective, or 

scientifically preferable, nor why EPA plans to deviate from using TF as a surrogate, and EPA 

Method 13A or13B.

One commenter (0038) explained that complex reactions leading to fluoride emissions 

occur not only in the processing units located at Phosphoric Acid Manufacturing and Phosphate 

Fertilizer Production source categories, but also in the scrubber systems designed to remove 

fluorides from the stack gases. The commenter (0038) stated that these reactions result in a mix 

of gaseous, aerosol, and particle bound fluorides (all three phases) in the stack gas, in the form of 

compounds like SiF4, various fluorosilicate aerosols and/or droplets, ammonium fluoride, 

ammonium bifluoride, and/or ammonium fluorosilicate. This commenter (0038) argued that 

these compounds have the potential to be captured in a Method 320 sampling train, biasing or 

interfering with the results of the sampling. The commenter cited technical feedback on this topic 

that it had already provided the EPA (and also provided in an attachment to their comment).

Another commenter (0039) submitted information explaining how it is not only impossible to 

eliminate interactions using EPA Method 320 to test for HF, but it is also expected to be 

extremely difficult to accurately and repeatedly quantify those interactions. Two commenters 

(0038, 0043) stated that the sampling conducted in response to the EPA’s information requests 

demonstrated that SiF4 readily reacts with water vapor in the stack gas producing HF and silicon 

hydroxide; and one of these commenters (0038) provided information showing that this reaction 

is dependent on temperature, moisture, and residence time in the sampling system.

Two commenters (0038, 0043) listed technical issues that they encountered during EPA 

Method 320 sampling that they conducted in response to EPA’s information requests, including, 

but not limited to: short shelf life and high expense of HF calibration gases, measuring HF at low 

concentrations, HF spike gas would rapidly corroded sample tube materials, sample pump 

clogging, transporting a representative sample of stack gas containing only native HF (i.e., the 

HF actually present in the stack gas and not artifact HF created by the decomposition or 
9-6

conversion of other fluoride species), crane/platform construction to hold heavy equipment, and 

obtaining accurate quality assurance spike results; one of these commenters (0038) argued that 

these problems, and others would persist if EPA Method 320 becomes a mandatory or optional 

approach for testing. One of these commenters (0043) suggested putting a NaOH scrubber 

solution just upstream of the sample pump to prevent deterioration in performance of the sample 

pump. The other commenter (0038) recommended certain procedures be followed when 

conducting EPA Method 320 at Phosphoric Acid Manufacturing and Phosphate Fertilizer 

Production source categories; however, also cautioned that their recommendations would not 

resolve all of the inherent problems with the sampling and analysis process. 

Response to Comment: The Agency is not adopting the proposed HF standards. As a 

result of this determination to not adopt the proposed HF standards, the Agency has retained the 

current total fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B 

as a surrogate for the HAP HF, rather than HF emission limits using EPA Method 320. Refer to 

the preamble of the final rule for additional details.

9.3 EPA Method 26A

Comment: One commenter (0038) argued that EPA Method 26A is fundamentally flawed 

for purposes of evaluating possible HF emissions from Subpart AA and BB regulated sources; 

the commenter explained why test limitations and interference render HF data collected via 

Method 26A unreliable. The commenter cited technical feedback on this topic that it had already 

provided the EPA (and also provided in an attachment to their comment).

Response to Comment: The Agency disagrees with the commenter that the 2010 EPA 

Method 26A test results were used to evaluate HF emissions from the Phosphoric Acid 

Manufacturing and Phosphate Fertilizer Production source categories. In 2010, the Agency 

requested facilities conduct HF emissions testing via EPA Method 26A from specific processes

included in the Phosphoric Acid Manufacturing and Phosphate Fertilizer Production source 

categories. Facilities submitted results of these tests to the EPA in the fall of 2010. The Agency 

determined that it needed additional data to evaluate HF emissions limits, and on January 24, 

2014, the EPA issued another CAA section 114 survey and testing request to certain facilities in 

order to gather additional HF emissions data from calciners and certain WPPA, SPA and APF 

lines using EPA Method 320. It was the 2014 test results that the Agency used to conclude at 

proposal that moving to a form of the standard that requires HF (the target HAP) to be measured 
9-7

(but retain the same numeric values as the current total fluoride standards) would be achievable 

by all facilities. The 2010 and 2014 test results are available in the docket for this action.

However, in light of information provided by commenters, the Agency has determined that EPA 

Method 320 is not an appropriate test method for accurately measuring HF emissions from 

process lines at these specific source categories due to the complex and often incomplete 

chemical reactions with silicon compounds in these sources. Accordingly, the Agency is not 

adopting the proposed HF standards. As a result of this determination to not adopt the proposed 

HF standards, the Agency has retained the current total fluoride limits (lb total F/ton P2O5 feed) 

measured using EPA Method 13A or 13B as a surrogate for the HAP HF, rather than HF 

emission limits using EPA Method 320. Refer to the preamble of the final rule for additional 

details.

9.4 FTIR HF CEMS

Comment: Three commenters (0037, 0038, 0043) oppose the option to use fourier 

transform infrared spectroscopy (FTIR) HF continuous emissions monitoring system (CEMS) as 

a continuous monitoring compliance approach for HF at Subpart AA and BB affected sources. 

These commenters cited EPA’s technical memorandum “Approach for Hydrogen Fluoride 

Continuous Emission Monitoring and Compliance Determination with EPA Method 320,” and 

argued that the option to use FTIR HF CEMS exceeds the capabilities of existing technology, 

there are no details on the required methods to implement such a system, there are no known 

field demonstrations of this type of system, and the option has not been proven. One of these 

commenters (0037) stated that while FTIR HF CEMS may have the capability to reliably 

perform to PS-18 specifications, the cost of demonstration will be significant and lengthy. This 

commenter (0037) pointed out that it took two to four years for the National Institute of 

Standards and Technology to generate reliable HCl calibration standards. Another of these 

commenters (0038) stated that their primary concern with FTIR HF CEMS as a continuous 

monitoring compliance approach for HF at Subpart AA and BB affected sources is the chemistry 

of the gas matrix in the proposed affected sources; the chemistry renders HF CEMS impractical, 

if not impossible. Citing the major problems encountered in the EPA Method 320 sampling 

undertaken to respond to EPA’s 2014 information request, this commenter (0038) argued that the 

technical challenges to accurately measure HF continuously cannot be addressed by any 

available EPA method nor certified by any EPA performance specification. This commenter 
9-8

(0038) provided additional details describing the known and predicted limitations of measuring 

HF emissions using HF CEMS for the affected sources.

A commenters (0042) contended that the EPA must consider requiring continuous HF 

emission monitoring before finalizing the proposal. The commenter (0042) pointed out that there 

is a HF sensor (suitable for 0-10 parts per million (ppm) monitoring range and a 0.1 ppm 

resolution) available for the Ultima X Series Gas Monitors. 

Response to Comment: The Agency is not adopting the proposed HF standards. As a 

result of this determination to not adopt the proposed HF standards, the Agency has retained the 

current total fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B 

as a surrogate for the HAP HF, rather than HF emission limits using EPA Method 320. Refer to 

the preamble of the final rule for additional details.

9.5 Pressure Drop Across Absorber

Comment: Three commenters (0039, 0038, 0043) requested the EPA delete the 

requirement that pressure drop across an absorber must be greater than 5 inches of water in order 

to use the option of measuring pressure drop as an operating parameter. These commenters 

contended that the EPA has not articulated any basis for the requirement. These commenters 

provided data demonstrating that units operate in compliance with the emission standards when 

the pressure drop across an absorber is less than 5 inches of water. One of these commenters 

(0043) expressed safety concerns associated with when operating scrubbers at higher range 

pressure drop settings, citing one of its facilities has experienced the entrainment of moisture 

within the absorbing tower when operating at pressure drops in excess of 8 inches of water, and 

another of its facilities experienced the buildup of excessive fumes on the digester floor when 

operating the digester scrubber as high as 6 inches of water. 

Response to Comment: We are not revising the final rule based on this comment. The 

Agency maintains its determination that pressure drop is not an appropriate monitoring 

parameter for absorbers that do not use the energy from the inlet gas to increase contact between 

the gas and liquid in the absorber. However, the Agency has made several changes to the

absorber monitoring requirements in the final rule. Refer to the preamble of the final rule for 

additional details.
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9.6 Absorber Monitoring Options

Comment: Three commenters (0039, 0038, 0043) called attention to the options of either 

measuring (1) the temperature at the wet scrubber gas stream outlet and pressure at the liquid 

inlet of the absorber, or (2) the temperature at the scrubber gas stream outlet and scrubber gas 

stream inlet. One of these commenters (0043) said that they do not believe monitoring gas 

temperature in locations of large ambient temperature ranges would provide accurate monitoring 

of the absorbers performance. The commenter argued that temperature and pressure probes 

would be very susceptible to scaling issues. In addition, this commenter (0043) contended that 

liquid inlet pressure does not provide any additional monitoring of the absorber performance, 

since the inlet liquid flow rate is already measured and monitored. Another commenter (0039)

contended that the EPA has not provided any data or analysis to show that there is a correlation 

between temperature and emissions; the commenter stated that they were not aware of any data 

suggesting a relationship between exit temperature and emissions, or that monitoring temperature 

difference across an absorber would be effective. One of these commenters (0038) argued that 

they were not in a position to evaluate the difficulties associated with performing the associated 

monitoring and establishing the requisite operating ranges.

Response to Comment: The Agency has made several changes to the absorber monitoring 

requirements in the final rule based on this comment. Refer to the preamble of the final rule for 

additional details.

9.7 Acceptable Range From Baseline Average Value 

Comment: One commenter (0039) requested that the EPA revise §63.625(d)(1)(ii)(B) to 

have similar wording to §63.625(d)(1)(ii)(A), in which the allowable parametric limits may 

encompass up to +/- 20% of the of the baseline average values for the series of tests used under 

this option; that is, the parametric limit may extend -20% below the lowest baseline average and 

up to +20% above the highest baseline average from the series of performance tests used for this 

option.

Response to Comment: The Agency determined that it is not necessary to revise 

§63.625(d)(1)(ii)(B) to allow for a ±20 percent operating margin, as this commenter requests, 

because this provision already allows for a source to establish an operating limit range for a 

control device without having to apply an operating margin, such as ±20 percent. Refer to the 

preamble of the final rule for additional details.
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9.8 Operating Range Established From A Previous Test

Comment: One commenter (0043) stated that §63.607(a) and §63.627(a) is somewhat 

ambiguous, tending to suggest that affected facilities would be immediately required to 

implement new equipment operating ranges following a source test, even if operating conditions 

from previous source tests demonstrated compliance with fluoride emission standards. The 

commenter argued that there is no reason that a new performance test at a new operating range 

should invalidate a previous performance test at a different operating range.

Response to Comment: The Agency has clarified this provision in the final rule at 

§63.607(a) and §63.627(a) that during the most recent performance test, if owners or operators

demonstrate compliance with the emission limit while operating their control device outside the 

previously established operating limit, owners or operators must establish a new operating limit 

based on that most recent performance test and notify the Administrator that the operating limit 

changed based on data collected during the most recent performance test. Refer to the preamble 

of the final rule for additional details.

9.9 Approving Operating Ranges 

Comment: Three commenters (0037, 0038, 0039) support the EPA’s proposal to 

eliminate the requirement that facilities may not implement new operating parameter ranges until 

the Administrator has approved them, or 30 days have passed since submission of the 

performance test results. However, two of these commenters (0039, 0038) pointed out that the 

EPA did not make the same allowance in §63.625(d)(1)(ii)(B), where a series of tests (potentially 

including historical tests) are used to establish an operating range. The commenter (0038)

pointed out that §63.605(d)(1)(iii)(B) and §63.625(d)(1)(ii)(B), as proposed, do not provide the 

30-day default period for the effectiveness of the new ranges if the EPA Administrator does not 

act; therefore, as currently set forth in the proposed rule, sources will be left in limbo waiting for 

the EPA Administrator to respond before they can implement new ranges. The commenter 

(0038) suggested that the EPA revise the proposed regulatory language to require submission of 

the new ranges to EPA, but delete the requirement to request and obtain EPA’s approval of the 

new ranges. Similarly, another commenter (0043) requested the EPA clarify the process for 

establishing new equipment operating ranges following source performance testing. This 

commenter contended that facilities should have the ability to update operating parameters if 
9-11

they desire based on source testing, and the facility should be required to submit the new ranges, 

but not be required to obtain EPA’s approval of the new ranges.

In addition, the commenter (0038) requested that the EPA clarify how revising the 

proposed regulatory language to require submission of the new ranges to the EPA, but deleting 

the requirement to request and obtain EPA’s approval of the new ranges, will affect possible 

obligations to undertake permit modifications of Title V permits under 40 C.F.R. Part 70. This 

commenter stated that such administrative processes are not fully anticipated in the proposed 

rule.

Response to Comment: The requirements at §63.605(d)(1)(iii)(B) and 

§63.625(d)(1)(ii)(B) have been revised in the final rule, as the commenter requests, to remove 

the requirement that facilities must request and obtain approval of the Administrator for 

changing operating limits. Refer to the preamble of the final rule for additional details.

9.10 Maximum Representative Operating Conditions

Comment: One commenter (0043) requested the EPA clarify §63.606(d) and §63.626(d) 

as to whether “maximum representative operating conditions” apply solely to the pollution 

control equipment or includes the manufacturing process equipment. The commenter also 

requested EPA clarify whether these conditions only pertain to items within the operator’s

control such as temperature, fan speed, etc. or whether it would also include conditions inherent 

to the manufacturing process such as variation in quality of feed stock materials. The commenter 

pointed out that the “maximum representative operating conditions” would not generate “normal 

operating ranges” required for administrator approval in §63.607(a) and §63.627(a). The 

commenter suggested that the EPA consider replacing the maximum representative operating 

conditions with language similar to Idaho air rule for “worst-case normal conditions” at IDAPA 

58.01.01.157.2(a).

Another commenter (0037) noted the changes in the language establishing the operational 

requirements for stack testing; this commenter identified these changes as non-substantive with 

regard to current testing protocols.

Response to Comment: In an effort to address the commenter’s request to clarify what we 

mean by “maximum representative operating conditions,” the Agency has revised the 

terminology in the final rule at §63.606(d) and §63.626(d) to align with the Clean Air Act 

National Stack Testing Guidance that was issued on April 27, 2009. In this guidance, EPA 
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clarified that performance tests should be performed under those representative (normal) 

conditions that: (1) represent the range of combined process and control measure conditions 

under which the facility expects to operate (regardless of the frequency of the conditions); and 

(2) are likely to most challenge the emissions control measures of the facility with regard to 

meeting the applicable emission standards, but without creating an unsafe condition. 

Furthermore, EPA stated in the guidance that “the test plan should generally include use of fuel, 

raw materials, and other process/control equipment that the facility expects to use during future 

operations that would present the greatest challenge in meeting applicable emissions standards. 

To demonstrate the facility’s ability to meet concentration standards and emissions rate 

standards, for example, the facility generally should use the fuel or raw materials that it expects 

to use and that have the highest emissions potential for the regulated pollutant(s) being tested.” 

Because of this guidance, the Agency has determined that it is not necessary to use language 

similar to the Idaho air rule as suggested by the commenter.

9.11 Performance Test Frequency

Comment: One commenter (0039) stated that the EPA changed the frequency of 

performance testing in the proposed §63.606 and §63.626(b) from the current standard of "once 

per annum" (i.e., once per calendar year) to "annual" and "no more than 13 months after the date 

the previous performance test was conducted." The commenter argued that this change could 

create significant scheduling difficulties where a unit is shutdown for maintenance for other 

reasons within the proposed test window. The commenter requested that the EPA maintain the 

existing annual testing schedule, and argued that the EPA has not provided a reasonable 

justification to change it.

Response to Comment: The Agency agrees with the commenter to retain the existing 

annual testing schedule, and has revised §63.606(b) and §63.626(b) in the final rule. However, 

instead of using the phrase “once per annum” in the final rule, as the commenter suggests, the 

Agency has used the phrase “once per calendar year” for clarity.

9.12 Condenser Monitoring

Comment: One commenter (0039) stated that the rule does not define the term 

“condensers” but Table 3 of the proposed Subpart AA requires the installation of a continuous 

parameter monitoring system (CPMS) to measure stack exit gas temperatures for "condensers." 
9-13

Commenter requested meaningful opportunity to comment due to lack of understanding of the 

EPA’s intent regarding condensers. 

Response to Comment: The Agency is not adopting the proposed monitoring 

requirements for condensers in Table 3 and 4 of Subpart AA; therefore, we are not defining the 

term “condenser” in the final rule. After further review, we determined that condensers are not 

used as control devices in the phosphoric acid manufacturing source category.
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10.0 COMPLIANCE DATES AND FREQUENCY OF PERFORMANCE 

TESTS

10.1 Compliance Dates For Newly Regulated Sources

Comment: Two commenters (0037, 0038) requested additional time for facilities to come 

into compliance with the expanded scope of the NESHAP which will capture newly regulated 

sources. One commenter (0038) stated that there is no time allotted for industry to design, 

procure, and install equipment to ensure emissions from these newly regulated sources are within 

the proscribed standards. One commenter (0037) requested a three-year period for newly covered 

equipment to be controlled and tested. The commenter argued that current emission limits were 

established without considering emissions from newly covered equipment. The commenter 

specifically refers to the PCS Phosphate Aurora facility and the cost of new control devices 

installed at this location. The commenter alleged that failure to consider newly covered 

equipment into the proposed rule brings the validity of the MACT floor into question. This 

commenter also asserted that the proposed one-year compliance period to prepare, and operate in 

accordance with, a management plan for each existing gypsum dewatering stack or cooling pond, 

at 40 C.F.R. § 63.602(d), does not allow enough time to evaluate, select, plan for, and implement

the appropriate practice(s). The commenter requested existing facilities be given at least two 

years to comply with these proposed work practice standards.

Additionally, one of these commenters (0038) requested the EPA provide a clear time 

period to phase in the effect of emission limits at oxidation reactors, as well as other components 

of process lines for which EPA has proposed definitional changes. The commenter stated that it

would not be possible to meet total fluoride limits at all oxidation reactors at the moment the 

EPA publishes the rule. The commenter argued that facilities either would have to shutdown to 

avoid immediate non-compliance (and thereby incur the costs of production downtime and 

restart), or place themselves in non-compliance by continuing to operate (and potentially incur 

costs, or worse, subject themselves to enforcement proceedings by EPA or other agencies)). 

Similarly, another commenter (0043) said it may need two years or more to comply with the 

proposed definition for WPPA and SPA plants that includes clarifiers and deflourination 

systems.
10-2

Response to Comment: We disagree with the commenter that a one-year compliance 

period to prepare, and operate in accordance with a management plan for each existing gypsum 

dewatering stack or cooling pond, does not allow enough time to evaluate, select, plan for, and 

implement the appropriate practice(s). As we explain in the preamble to the final rule, we believe 

the list of control measure options is exhaustive enough that a facility has a number of options 

for selecting a control measure that would be feasible for their particular operations. We assume 

that facilities would choose the lowest cost option, and that all facilities are using at least one of 

the control measure options already. In addition, we’ve revised the management plan in response 

to comments, and believe this list to represent best practices known to industry and the Agency. 

The Agency has made considerable effort9before and after proposal in identifying a list of 

control measure options that encompass enough variety that at least one control measure option 

is feasible for at least one of each facility’s existing gypsum dewatering stacks and/or cooling 

ponds. In fact, we are not aware of any facilities that do not use a rim ditch (cell) building 

technique.

Also, we are not including clarifiers and defluorination processes in the WPPA process 

line definition of the final rule (refer to the preamble of the final rule for additional details); 

therefore, the commenters’ request to include additional time for facilities to come into 

compliance with these proposed changes are not applicable. However, we are adopting the 

proposed superphosphoric acid process line definition in the final rule to include oxidation 

reactors (refer to the preamble of the final rule for additional details), and we do agree that it 

would not be possible to meet total fluoride limits at all oxidation reactors at the moment the 

EPA publishes the rule. As we explain in the preamble to the final rule, based on the information 

we received, with the exception of possibly one facility, we determined that it would not be 

necessary for facilities to upgrade existing control systems, or to install a control system, to 

comply with the emission limit. Therefore, we believe a one year lead time is adequate and are 

including a requirement in the final rule that facilities must include emissions from oxidation 

 

9 See the following documents which are all available in Docket ID No. EPA-HQ-OAR-2012-0522): “USEPA 

Meeting with The Fertilizer Institute, July 24, 2013”; “TFI meeting with USEPA to discuss RTR for Phosphoric 

Acid and Phosphate Fertilizer NESHAPs, September 11, 2014”; “EPA Meeting Minutes for TFI Discussion March 

12, 2015”; “Summary of Potential Costs for Implementing Phosphate NESHAPs/Recommendations for 

Phosphogypsum Stack Work Practices, May 5, 2015”; “Notes from Meeting with Florida DEP Regarding Gypsum 

Dewatering Stack and Cooling Pond Management Plan, March 4, 2015”; and “Site Visits to Mosaic Plant City and 

Mosaic New Wales, March 4, 2015.” 
10-3

reactors, when determining compliance with the total fluoride limits for superphosphoric acid 

process lines, no later than one year after the effective date of the rule.

10.2 Compliance Dates For Absorber Monitoring

Comment: One commenter (0043) stated it would need a minimum of 16 months to 

comply with the proposed monitoring options for absorbers that are not allowed, by the proposed 

rule, to use the option of measuring pressure drop as an operating parameter (since the pressure 

drop across an absorber must be greater than 5 inches of water). The commenter stated that it 

currently does not have the equipment installed to monitor absorber liquid and gas flow, gas 

stream inlet/outlet pressure, gas stream inlet/outlet temperature, or liquid inlet pressure.

Response to Comment: The Agency has made changes to the monitoring options for 

absorbers since proposal based on comments received (refer to the preamble of the final rule for 

additional details). Based on the changes made since proposal, the Agency believes the cost to 

implement these finalized monitoring requirements is minimal for facilities. For low-energy 

absorbers, we are allowing the gas stream be measured by either measuring the gas stream flow 

at the absorber inlet; or using the design blower capacity, with appropriate adjustments for 

pressure drop. Therefore, facilities would not need to purchase new equipment to measure gas 

flow at the inlet of the absorber since they may choose to use design blower capacity. 

Furthermore, we are not requiring any new monitoring for high-energy absorbers; therefore, 

these facilities are already equipped to monitor as required in the final rule.

10.3 Compliance Dates For Fabric Filter Monitoring

Comment: One commenter (0043) stated it would need a minimum of one year to comply 

with the proposed requirement that a fabric filter must be equipped with a bag leak detection 

system installed, calibrated, and maintained. The commenter stated that it currently does not 

have a bag leak detection system installed.

Response to Comment: Agency agrees with the commenter, and has revised the final rule 

to allow one year for owners and operators to comply with the requirement to install, calibrate, 

and maintain a bag leak detection system on a fabric filter.

10.4 Compliance Dates For Stack Testing

Comment: One commenter (0043) stated for one of its facilities, it would need a 

minimum of 16 months to comply with the proposed requirements at 40 C.F.R. 63.606(a) and 
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63.626(a) that you must stack test and demonstrate compliance within 1 year of publication. The 

commenter stated that if the rule requires facility modification, 1 year may not be adequate to 

meet requirement. Similarly, the commenter pointed out that it may need 2 years or more to 

comply with the testing because one of its facilities would need to install equipment to segregate 

emissions to determine emissions compliance.

Response to Comment: The Agency is not adopting the proposed HF standards. As a 

result of this determination to not adopt the proposed HF standards, the Agency has retained the 

current total fluoride limits (lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B 

as a surrogate for the HAP HF, rather than HF emission limits using EPA Method 320.

Therefore, the commenters’ request to include additional time for facilities to come into 

compliance with the proposed performance testing is not applicable. Refer to the preamble of the 

final rule for additional details.
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11.0 APPLICABILITY, DEFINITIONS, AND TERMINOLOGY

11.1 Expanded Scope Of Process Lines

Comment: One commenter (0038) stated that the EPA has introduced ambiguity and 

vagueness with its definition of a generic “process line” that includes “all equipment associated 

with the production of any grade or purity of a phosphoric acid product including emission 

control equipment.” The commenter asserted that under this expansive definition, every 

hypothetical fugitive emission source would have to be accounted for in determining 

compliance. The commenter explained that the EPA has not collected emission data from “all 

equipment” nor provided guidance on estimating emissions for such sources in order to allow 

entities with process lines to demonstrate compliance. The commenter stressed the “process line” 

definition, as it currently stands, could include a wash plant that prepares phosphate ore or 

product storage tanks due to these sources being considered “associated” with production and 

thus subject to the proposed NESHAP.

Response to Comment: This comment is addressed in the preamble of the final rule. The 

Agency agrees with the commenter that it is not necessary to include the generic “process line” 

definition, and has removed it from the NESHAP subpart AA final rule. This definition did not 

provide additional clarity to facilities, and it was not our intent to include emissions from “all 

equipment” that is “associated” with phosphoric acid production for compliance determinations. 

Specific definitions are provided for WPPA process line, SPA process line, and PPA process line 

and, therefore, enough specificity is already provided in the rule.

11.2 Clarification To Oxidation Reactors Included In SPA Process Lines

Comment: Three commenters (0037, 0038, 0043) remarked that the proposed definition 

phosphoric acid process lines to include oxidation reactors is problematic and goes beyond 

clarification. These three commenters requested that EPA develop much more specific language 

or provide a clear technical basis under the CAA because any equipment that was not expressly 

included in EPA’s MACT floor calculations should not be included in the proposed definition. 

Two commenters (0037, 0038) mentioned that the Applicability Clarifications Memo 

captured four facilities, but it was not clear whether the PCS Aurora facility was included in the 

count. The commenters stated that the oxidation step at this facility is carried out in agitated 

tanks that do not have any emissions control, and the emissions from the oxidation step are not 
11-2

included in their annual performance testing (when demonstrating compliance with the current 

total fluoride limits). The commenters said that it was not clear whether this oxidation step 

involves an “oxidation reactor” as proposed; and if it does, the commenters argued that the EPA 

has not considered additional costs imposed by including “any equipment that uses an oxidizing 

agent to treat phosphoric acid” within the scope of the NESHAP at 40 CFR Part 63, Subpart AA.

Response to comment: The Agency is adopting clarifications for oxidation reactors in 

NESHAP subpart AA. Refer to the preamble of the final rule for additional discussion regarding 

the applicability of oxidation reactors in the final rule.

11.3 Clarifications To Clarifiers And Defluorination Systems Included In WPPA Process 

Lines

Comment: Four commenters (0037, 0039, 0038, 0043) oppose the proposed expanded 

definition of "wet-process phosphoric acid line" to include "clarifiers" and "defluorination 

processes." These commenters stated that the proposed revisions have the potential to pull in 

several “defluorination processes” and “clarifiers” that are not subject to the current rule (e.g., 

animal feed phosphate production operations that have traditionally been outside the scope of 

this subpart). These commenters argued that any unit operation that conducts evaporation or 

concentrates phosphoric acid will have the effect of defluorinating to some extent. One of these 

commenters (0037) stated that they have a desulfation process at one of their facilities that 

reduces fluorides; the commenter also said that this facility’s WPPA process line has several 

filter product / evaporator feed tanks and evaporator product tanks that could potentially be 

deemed clarifiers, and thus be pulled into the proposed rule. Another of these commenters (0039)

argued that it is not logical to include clarifier and defluorination systems in the definition 

because they operate independently of process lines, and are often operated when feed is not put 

into process lines (and so are not a process line manufacturing phosphoric acid by reacting 

phosphate rock and acid). This commenter (0039) added that clarifiers often operate more like 

tanks than process equipment and are not routinely emptied; and emissions from clarifiers are not 

a function of phosphate feed material to the reactor. The commenter (0039) stated that the 

addition of clarifiers will require significant facility modifications to accommodate emissions 

testing because although some clarifiers are evacuated to WPPA scrubbers, others are not; and 

even though some clarifiers have independent evacuation and scrubbing systems, other clarifiers 

have no evacuation and scrubbing systems. The commenter (0043) also stated that one of their 
11-3

facilities contains clarifiers that are not source tested or vented to a web scrubber. This

commenter (0043) also stated that it was not possible for one of their facilities to determine 

whether they meet the proposed standard for a WPPA process line that includes defluorination 

processes because their defluorination units are not only integrated with their WPPA process, but 

also with processes that do not meet the definition of WPPA lines. The commenter (0039) added 

that defluorination processes and clarifiers are often subject to separate emissions control 

requirements in their Title V permits.

Two commenters (0039, 0038) stated that since the original rule was adopted, the 

definition of “wet-process phosphoric line” has not been interpreted to extend or apply to 

clarifiers or defluorination processes. One of these commenters (0039) claimed that the only 

rationale the EPA provides is that the rules were "initially intended" to cover these sources, but 

argued that neither the original proposal, nor the original final rule mention the term "clarifier" or 

"defluorination process." The commenters insisted that the EPA conduct CAA § 112(d)(2) or 

112(d)(3) analyses for these new affected units. If the EPA conducts these analyses, and decide 

to expand the definition of "wet-process phosphoric acid line" to include "clarifiers" and 

"defluorination processes,” the commenter (0038) suggested that the definition exclude units that 

partially clarify or defluorinate an in-process stream incidentally.

Response to comment: This comment is addressed in the preamble of the final rule. The 

Agency is not adopting the proposed clarifications for defluorination units and clarifiers.

11.4 Clarification To Granular Triple Superphosphate Fertilizer Process Line

Comment: One commenter (0043) clarified that based on the current proposed definition 

of granular triple superphosphate fertilized process line in §63.621 they do not manufacture 

“granular triple superphosphate” and are thus not subject to Subpart BB requirements for their 0-

45-0 product. The commenter elaborated that the production of their 0-45-0 granular fertilizer 

does not involve reacting phosphoric acid with phosphate rock and does not require a multi-day 

curing phase.

Response to comment: We thank the commenter for this clarification.

11.5 Clarification To Phosphate Fertilizer Process Line Or Production Plant

Comment: Four commenters (0037, 0039, 0038, 0043) disapproved of the proposed 

expansion of the applicability provision for diammonium process lines (DAP) and 
11-4

monoammonium process lines (MAP) in 40 CFR §63.620(b)(1) to include “any process line that 

produces a reaction product of ammonia and phosphoric acid.” One commenter (0037) asserted 

that the expanded language could include production of non-granular products that were in 

existence since the original NESHAP but not regulated by it and EPA provided no basis for 

expansion of applicability to bring in these processes now. Commenters (0039, 0038) reiterated 

that the proposed applicability provision for DAP and MAP process lines was vague and 

overbroad and would inadvertently regulate any process that combines ammonia and phosphoric 

acid regardless of the end-product or purpose of facility. One commenter (0043) recommended a 

change in the definition to clarify that Subpart BB applies specifically to solid, granulated 

phosphate products to avoid inclusion of liquid fertilizer products in the proposed rule.

Additionally, the commenter (0039) pointed out that the definition of DAP and MAP 

process lines as proposed in Section 63.621 is being expanded to include cooling towers and 

requests that cooling towers be excluded from the rule. The commenter asserted that cooling 

towers are not considered point sources subject to emissions testing and emissions cannot be 

effectively measured. The commenter added that cooling towers may be used to ancillary 

operations like air conditioning systems that would not have emissions.

Response to comment: We are revising the definitions of “phosphate fertilizer process 

line” and “phosphate fertilizer production plant” in the final rule at §63.621 to reference granular 

phosphate fertilizer. Also, the definitions of phosphate fertilizer process line and phosphate 

fertilizer production plant were defined together at proposal (phosphate fertilizer process line or 

production plant), but are defined separately in the finalized rule for clarity. Refer to the 

preamble of the final rule for additional discussion about the applicability provision for DAP and 

MAP process lines.

Furthermore, we agree with the commenter that the definition of DAP and MAP process 

lines in §63.621 should not be expanded to include cooling towers. We proposed this change to 

correspond with the proposed condition in NESHAP subpart BB that excludes the use of 

evaporative cooling towers for any liquid effluent from any wet scrubbing device installed to 

control HF emissions from process equipment. In lieu of the proposed definition of DAP and 

MAP process lines to include evaporative cooling towers, we are finalizing an applicability 

provision in §63.620(b)(1) to include “evaporative cooling tower” as an affected source at a 

phosphate fertilizer production plant, and added a definition of “evaporative cooling tower” to 

§63.621 that reflects the same definition used in NESHAP subpart AA. For the same reasons, we 
11-5

also removed “cooling towers” from the definition of “granular triple superphosphate process 

line” in §63.621.

11.6 Clarification To Purified Phosphoric Acid

Comment: One commenter (0043) requested that the proposed definition of a purified 

phosphoric acid (PPA) plant in 40 CFR 63.601 be modified to contain clarification regarding 

solvent extraction. The commenter elaborated that they operate a PPA process which does not 

use solvent extraction or any equipment associated with solvent extraction, but rather a 

proprietary processes which utilizes physical methods to remove impurities. The commenter 

alleged that therefore the PPA process at their facility does not meet the definition of a PPA line 

and is not subject to requirements in §63.602 (b) or associated requirements in Subpart AA 

(§63.600 through 611). The commenter requested that a sentence be added at the end of the PPA 

plant definition in 40 CFR 63.601 to specifically state PPA process lines that do not use a HAP 

as a solvent in the separation of impurities do not meet the proposed definition. 

Response to comment: The Agency has determined that a change to the proposed 

definition of a PPA plant at §63.601 is unwarranted and disagrees with the commenter that it be

modified to contain clarification regarding solvent extraction. The Agency has determined that 

the proposed definition is sufficient at excluding PPA process lines that do not use a HAP as a 

solvent in the separation of impurities because the final rule definition says that a purified 

phosphoric acid process line is a process line “...that uses a HAP as a solvent....”

11.7 Gypsum Dewatering Stack Definition

Comment: Commenters (0037, 0038, 0043) stated that the definition of gypsum 

dewatering stack was too broad and obscured its true meaning. They claimed the EPA’s 

definition includes a wide array of features that have never before been considered part of the 

stack (e.g., pumps, piping, all collection and conveyance systems associated with 

phosphogypsum to the stack and process wastewater return to the plant). Commenters (0037, 

0038, 0039) also stated that they were concerned that cooling ponds not connected to gypsum 

stacks were included in the definition.

One commenter (0037) proposed that the stack should be considered “just the area where 

phosphogypsum is deposited” including the base of the stack, the rim ditch, and the surface in 

the center of the stack where the final gypsum settles out. Two commenters (0038, 0043)

recommended the EPA create a plain definition that focuses on the “footprint” of the stack, 
11-6

including the drying phosphogypsum slurry and ponds inside the perimeter of the gypsum 

dewatering stack’s base. Two commenters (0037, 0038) suggested the definition should not 

include the return ditch or any cooling pond that is physically separate from the active stack. 

Another commenter (0039) recommended that the EPA use the definition of “phosphogypsum 

stack” from Florida regulations, “any defined geographic area associated with a phosphoric acid 

production facility in which phosphogypsum is disposed of or stored, other than within a fully 

enclosed building, container or tank" (FAC § 62-673.200).

A commenter (0038) argued the individual gypsum cells within a stack could be 

considered as separate gypsum dewatering stacks, due to the unclear definition. 

Response to Comment: This comment is addressed in the preamble of the final rule. In 

the final rule, we are revising the definition of “gypsum dewatering stack.”

11.8 Closed and Active Gypsum Dewatering Stack Definitions

Comment: Commenters (0037, 0038, 0039) stated that they were concerned about the 

distinction between closed and active gypsum dewatering stacks. They stated the point or 

transition period between “active” status and final “closure” status should be clear. Commenters 

noted it takes several years to close a gypsum dewatering stack, and this period is not considered 

in either the definition of active or closed. Therefore, stacks that are inactive and in the closure 

process would still be considered active.

Commenters (0037, 0038) stated the term closed gypsum dewatering stack could also 

include stacks that have temporarily stopped receiving phosphogypsum and have received any 

form of a “cover.” The commenter continued that the definition must not have the intent of 

deeming an active gypsum dewatering stack closed the moment the stack is no longer receiving 

phosphogypsum and has some sort of cover. One commenter (0037) rotates their three gypsum 

dewatering stacks and was concerned that when a stack is not receiving phosphogypsum during 

this cycle, that it may be considered closed.

Three commenters (0037, 0038, 0039) recommended the definition of closed gypsum 

dewatering relate to the end of its production life and when no further routine additions of 

phosphogypsum will be made to the stack. These commenters also stated the “final cover” 

requirements should not be include in the definition, and were more appropriate as part of the 

work practice standard.
11-7

A commenter (0038) observed that 40 CFR, part 61, subpart R defines an active gypsum 

dewatering stack as one that continues to receive gypsum or process water, and stated the subpart 

AA definition should correspond to the one in subpart R. 

One commenter (0039) requested the EPA clarify that a lined pond on top of a closed 

gypsum stack does not render an otherwise closed stack "active." 

Two commenters (0039, 0043) stated that including a soil cover, rather than simply 

vegetative cover, in the definition of closed gypsum dewatering stack is not necessary. The 

commenters noted that soil cover is not required to sustain vegetation. A commenter (0039) also 

argued the requirement for drought resistant vegetative cover is ambiguous and nonsensical; 

drought resistant cover may actually be less hardy and viable than other types of vegetative 

cover. Another commenter (0043) noted that sustaining vegetation is difficult. The commenter 

(0039) requested that initial grassing and subsequent vegetative ecosystems that may develop 

after initial grassing satisfy the definition of an appropriate cover.

Response to Comment: This comment is addressed in the preamble of the final rule. In 

the final rule, we are removing the definition of “closed gypsum dewatering stack,” revising the

definition of “active gypsum dewatering stack,” and revising the definitions for when a gypsum 

dewatering stack is considered “new” or “existing.” In addition, in the final rule, we are

removing the proposed work practice that limits the size of active gypsum dewatering stacks.

11.9 Cooling Pond Definition

Comment: A commenter (0039) requested that the EPA revise the definition of cooling 

pond to exclude ponds that are not used primarily for cooling the phosphoric acid production 

process.

Response to Comment: The Agency has determined that a change to the “cooling pond” 

definition at §63.601 is unwarranted and disagrees with the commenter. The Agency has 

determined that the proposed definition is sufficient at excluding ponds that are not used 

primarily for cooling the phosphoric acid production process, such as reservoirs not intrinsic to 

the normal cooling pond loop because the definition explicitly uses the term “primarily” to 

describe how a cooling pond must be used to be considered an affected source.
11-8

11.10 Production Capacity Clarification

Comment: One commenter (Simplot) requested the EPA clarify whether “annual 

phosphoric acid manufacturing capacity” in the ratio limit refers to the production capacity of the 

entire facility or the capacity of P2O5 feed to the facility.

Response to Comment: The Agency is not adopting the proposed work practice that 

limits the size of active gypsum dewatering stacks (refer to the preamble of the final rule for 

additional details); therefore, the commenters’ request for clarification on what is meant by 

“annual phosphoric acid manufacturing capacity” is no longer applicable.

11.11 Applicability Clarification - Kiln Process

Comment: A commenter (0036) stated they produce a high purity phosphoric acid using 

the Improved Hard Process (IHP), which they call Kiln Produced Phosphoric Acid (KPPA). The 

commenter requested that the EPA clarify that the IHP process, regardless of facility size or the 

potential to emit HAP, will not be subject to part 63, subpart AA or part 60, subparts T and U for 

phosphoric acid facilities. The commenter continued that the IHP process and KPPA production 

is fundamentally different than WPPA production. IHP is a thermal process that uses a ported 

rotary kiln for the direct conversion of phosphate rock to 70% phosphoric acid. The commenter 

stated that phosphate rock, sand, clay, and petroleum coke are dried, milled, formed into pellets, 

and fired in a rotary kiln for induration. The indurated pellets are then fired in a ported rotary 

kiln, phosphorus and carbon monoxide evolve, and P4O10 gas forms. The gas is cooled and 

absorbed in water to produce 70% phosphoric acid.

Response to Comment: Based on the information provided by the commenter, the EPA 

agrees that KPPA produced using the IHP process is not subject to 40 CFR 63, subpart AA or 40 

CFR 60, subparts T and U. The definitions for wet-process phosphoric acid process line (in 40 

CFR 63, subpart AA) and wet-process phosphoric acid plant (in 40 CFR 60, subpart T) 

specifically state that phosphoric acid be manufactured by reacting phosphate rock and acid. 

Because acid is not used with the IHP, the IHP is not applicable to the wet-process phosphoric 

acid process. Moreover, the IHP would not be considered a superphosphoric acid plant under 40 

CFR 60, subpart U because the IHP does not concentrate phosphoric acid that was manufactured 

using the wet-process. The EPA is not including specific revisions in rule language to address 

this comment because enough specificity is already included in the definitions sections of these 

rules.
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11.12 Clarification To Calciners

Comment: One commenter (0043) requested clarification on the applicability of §63.600 

to calciners that are not located at the same location of a phosphoric acid manufacturing plant. 

The commenter noted that the proposed rule language in §63.600(b) requires calciners to be 

physically located where the phosphoric acid manufacturing plant is located. The commenter 

thus asserted that a calciner not located at a phosphoric acid manufacturing plant is not 

applicable to 40 CFR 63 Subpart AA. 

The commenter additionally requested that the discrepancies in the definition of calciner 

in 40 CFR 60.400 and 40 CFR 63.600 be addressed. The commenter recommended a consistent 

definition for a calciner used to remove water and organics from phosphate rock (ore) be used in 

an effort to clarify how Clean Air Act requirements apply to phosphate rock calciners. 

Response to comment: The Agency agrees with the commenter that according to the final 

rule at §63.600(b), the requirements of 40 CFR 63, subpart AA apply to a phosphate rock 

calciner that is located at a phosphoric acid manufacturing plant. In addition, the Agency is not 

revising the definitions of a calciner at 40 CFR 60, subpart NN and 40 CFR 63, subpart AA. The 

commenter did not provide support for their request, and the Agency is unable to understand the 

need to clarify these definitions. 

11.13 Clarification To Scrubber Terminology

Comment: Once commenter (0039) requested that the EPA be consistent in the 

terminology that it uses citing the term “wet scrubbing device” is used in Section 63.602(c) 

instead of “absorber.”

Response to Comment: The Agency agrees with the commenter, and has revised the final 

rule at §63.602(c) and §63.622(c) so that the terminology is consistent with the use of “absorber” 

instead of “wet scrubbing device.”
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12.0 ECONOMIC AND EMISSIONS IMPACTS

12.1 Cost-Effectiveness of Hg Control Devices

Comment: Several commenters (0037, 0041, 0043) argued that ACI and fixed-bed carbon 

adsorption were not cost effective for controlling Hg emissions from phosphate rock calciners. 

Two commenters (0037, 0041) reported a site-specific cost estimate for installing GMCS fixedbed carbon adsorption downstream of the existing WESP, with capital costs of $32 million and 

annual costs of $5.8 million; the resulting cost-effectiveness was approximately $40,000 per 

pound of Hg. The commenters noted the GMCS cost-effectiveness ($40,000/lb Hg) was much 

higher than the cost-effectiveness the EPA presented in the proposed rule ($8,000/lb Hg) for a 

traditional fixed-bed carbon adsorption system. Commenters also reported a site-specific cost 

estimate for installing ACI upstream of the existing Venturi scrubbers, with capital costs of $21.1 

million and annual costs of $9.1 million; this resulted in a cost-effectiveness of approximately 

$63,000 per pound of Hg. The commenters noted this ACI cost-effectiveness ($63,000/lb Hg) 

was much higher than the cost-effectiveness the EPA presented in the proposed rule ($12,100/lb 

Hg). The commenters (0037, 0041) stated that because their costs for ACI and GMCS fixed-bed 

carbon adsorption were site-specific, they are much more representative than the costs developed 

by the EPA for the proposed rule. Finally, one commenter (0037) stressed that the site-specific 

Hg control cost-effectiveness numbers were well above the cost-effectiveness for other rules 

where the EPA implemented BTF Hg controls. Another commenter (0043) noted that 

preliminary information for installing Hg controls resulted in estimates of $17.5 million in 

capital costs and $10 million for annual costs. A commenter (0037) provided a detailed review of 

Hg control devices in an attachment to their comment.

Response to Comment: We are not finalizing the proposed BTF Hg limit (i.e., 0.014 mg 

Hg/dscm @ 3% O2) in NESHAP subpart AA for existing phosphate rock calciners due to 

potential significant economic impacts associated with the costs of controls. Instead, we are 

finalizing a MACT floor Hg limit for existing phosphate rock calciners and do not anticipate that 

any facilities will need to install a new control device to meet the existing phosphate rock 

calciner Hg limit. 

We are finalizing the proposed BTF Hg limit (i.e., 0.14 mg Hg/dscm @ 3% O2) in 

NESHAP subpart AA for new phosphate rock calciners. We are finalizing costs for the BTF Hg 
12-2

limit for new phosphate rock calciners based on the application of ACI installed upstream of the 

existing venturi scrubber. Refer to the preamble of the final rule for additional details.

12.2 Gypstack Management Plan Control Measure Impacts

Comment: One commenter (0038) stated that implementing HF work practices for the 

gypsum dewatering stack and cooling pond management plan may be the most expensive aspect 

of the rulemaking. The commenter (0038) also remarked that the EPA did not quantify the costs 

to implement work practices, but it was crucial that EPA study and explain the economic costs of 

this rulemaking in thorough, concrete terms.

Two commenters (0038, 0043) provided cost estimates for closure of side slopes. Closing 

side slopes was estimated at $4.8 million per bench, according to a commenter (0038). The 

commenter stated that installing seepage collection drains to manage drainage from a stack can 

take more than a year to construct, and cost from $80,000 to $100,000 per acre. Another 

commenter (0043) indicated that closure costs were approximately $25,000 per acre, for 

applying soil and seeding. One commenter (0038) estimated that closing the side slopes of 

gypsum dewatering stacks would reduce the useful life of a 400 acre stack by approximately 

36%.

Two commenters (0038, 0043) provided cost estimates for slaked lime application. One 

commenter (0038) declared that applying slaked lime to a 400 acre gypsum dewatering stack 

would cost $3.0 million, for a one-time application. A separate commenter (0043) explained that 

additional equipment and infrastructure were necessary for lime application, with a cost of $1.09 

million, and lime spraying equipment was an additional $100,000. The commenter (0043) stated 

that annual costs for applying slaked lime to 30 acres of their gypsum dewatering stack range 

from $23,000 to $36,000. 

Response to Comment: The Agency thanks the commenters for the cost details provided. 

However, we disagree with commenters that the gypsum dewatering stack and cooling pond 

management plan would be cost-prohibitive. We believe the list of control measure options is 

exhaustive enough that if a facility does not want to use a certain control measure that is listed in 

the final rule, then they can select a different one that would be more feasible and cost-effective 

for their particular operations. We also assume that the option most economically feasible for a 
12-3

facility will be chosen. In addition, we made considerable effort10 before and after proposal in 

identifying a list of control measure options that encompass enough variety that at least one 

control measure option is feasible for at least one of each facility’s existing gypsum dewatering 

stacks and/or cooling ponds. Refer to the preamble of the final rule for additional details of the 

work practice standards for gypsum dewatering stacks and cooling ponds included in the final 

rule.

12.3 Gypstack Ratio Impacts

Comment: One commenter (0043) observed that the EPA did not estimate costs for 

complying with the ratio of gypsum dewatering stack area to annual phosphoric acid 

manufacturing capacity, because the EPA was not aware of any new gypsum dewatering stack 

projects. However, the commenter (0043) stated they are planning to build a gypsum dewatering 

stack. The commenter (0043) provided an example cost estimate for a 200 acre gypsum 

dewatering stack expansion, where 407 acres would be required to be closed. The commenter 

(0043) applied a closure cost of $25,000 per acre, which resulted in an estimate of $10,175,000 

to comply with the ratio. The commenter (0043) also remarked that this analysis did not include 

costs associated with managing water balance. Including water management, the commenter 

(0043) estimated it would cost more than $100,000 per acre with annual water management costs 

of $4,275,000. Another commenter (0037) reported they are already planning on closing a large 

portion of their existing gypsum dewatering stacks, but the ratio may force the process to occur 

sooner than planned, with estimated costs of more than $105 million at $163,000 per acre. 

Response to Comment: The Agency thanks the commenters for the cost details provided. 

However, we are not adopting the proposed work practice in NESHAP subpart AA that limits the 

size of active gypsum dewatering stacks (which would have been applicable to facilities when 

new gypsum dewatering stacks are constructed), and therefore these costs are not applicable to 

the economic analysis of the final rule. Refer to the preamble of the final rule for a discussion of 

 

10 See the following documents which are all available in Docket ID No. EPA-HQ-OAR-2012-0522): “USEPA 

Meeting with The Fertilizer Institute, July 24, 2013”; “TFI meeting with USEPA to discuss RTR for Phosphoric 

Acid and Phosphate Fertilizer NESHAPs, September 11, 2014”; “EPA Meeting Minutes for TFI Discussion March 

12, 2015”; “Summary of Potential Costs for Implementing Phosphate NESHAPs/Recommendations for 

Phosphogypsum Stack Work Practices, May 5, 2015”; “Notes from Meeting with Florida DEP Regarding Gypsum 

Dewatering Stack and Cooling Pond Management Plan, March 4, 2015”; and “Site Visits to Mosaic Plant City and 

Mosaic New Wales, March 4, 2015.” 
12-4

why we are not adopting the proposed work practice that limits the size of active gypsum 

dewatering stacks.

12.4 Impact from Additional Sources

Comment: Four commenters (0037, 0039, 0038, 0043) stated that the EPA failed to 

properly characterize the additional costs that would be incurred due to inclusion of clarifiers, 

defluorination units, and oxidation reactors. One commenter (0043) noted the emissions from 

one of their defluorination units are not captured as part of their WPPA process line, but rather 

are controlled with their phosphate fertilizer process. The commenter continued they would need 

to construct a new stack and modify existing air permit requirements, estimated at $455,000, in 

order to comply. The commenter (0043) also explained they operate a second defluorination unit 

with their SPA process line, and new equipment would need to be installed to separate the 

process, which was estimated to cost $7,500,000. A commenter (0043) reported that controlling 

all clarifiers would require the installation of a scrubber, ducting and piping, and instrumentation 

with an estimated cost of $10,994,000. 

Two commenters (0039, 0038) stated that attempting to comply with the expanded 

definition of WPPA process lines that includes clarifiers and defluorination units would cost tens 

of millions of dollars. One of these commenters (0039) said that facility modifications to 

incorporate full emission capture, control, and testing for their clarifiers were estimated to cost 

$15 million collectively at two facilities. Another commenter (0037) projected that installing two 

new emission control devices on evaporator hotwells and oxidation reactors, along with 

enhancing clarifier emission controls would cost approximately $500,000 for their facility to 

achieve compliance. This commenter also provided supplemental cost information outside of the 

comment period, which elaborated on oxidation reactor and clarifier control costs (see Docket ID 

No. EPA-HQ-OAR-2012-0522-0051). The commenter estimated that controlling clarifiers would 

cost approximately $396,500 and controlling their oxidation reactor would cost approximately 

$270,500.

A commenter (0039) also contended the EPA did not adequately justify including 

clarifiers within the definition, taking into account the inconsequential emissions reductions. The 

commenter explained that clarifier emissions at one facility were estimated at 51.7 pounds per 

year total fluoride or 0.009 tons HF (assuming HF is one-third of the total fluoride emissions). 
12-5

The commenter (0039) estimated that for this facility it will cost approximately $6 million to 

install controls (covers and scrubbers). With operating and maintenance expenses, the annual 

cost was estimated at more than $30 million per ton of HF emissions reduced. At a separate 

facility, the commenter (0039) reported that annual emissions from three clarifiers will be less 

than 0.38 tons total fluoride or 0.13 tons of HF (assuming HF is one-third of the total fluoride 

emissions). The commenter then stated that using EPA's low estimate of $8,000 in incremental 

costs for Method 320 testing per stack, the additional annual testing costs alone amounted to over 

$190,000 per ton of HF emissions from these three sources. The commenter (0039) stated these 

costs are not reasonable considering that these emissions are insignificant and EPA's own risk 

analysis supports the conclusion that existing practices are amply protective.

Response to Comment: We are not including clarifiers and defluorination processes in the 

WPPA process line definition of the final rule (refer to the preamble of the final rule for 

additional details); therefore, we did not estimate costs for these sources, and the industry will 

not incur any costs for these sources. However, we are adopting the proposed superphosphoric 

acid process line definition in the final rule to include oxidation reactors; refer to the preamble of 

the final rule for additional discussion regarding the applicability and cost impacts of oxidation 

reactors.

12.5 Testing and Monitoring Costs

Comment: One commenter (0037) stated the EPA underestimated costs to measure Hg 

emissions with Method 30B. The commenter explained that due to site-specific conditions, such 

as access and safety training, $20,000 per stack test is more appropriate.

Four commenters (0037, 0038, 0039, 0043) expressed concern over the increase in 

testing costs from using Method 320 instead of Method 13A or 13B. One commenter (0043) 

stated the incremental cost to conduct Method 320 was $9,000 per test, which was similar to the 

EPA’s estimate of $8,000 per test. However, the commenter noted this was about a 3 fold 

increase in testing costs. Another commenter (0038) stated they expect costs to increase at least 

3.5 to 4 times when using Method 320 instead of 13B. Separate commenters (0037, 0038)

contended that Method 320 testing is not routine and is dependent upon site-specific factors, and 

that the EPA cost does not account for this. The commenters (0037, 0038) noted that HF 

calibration gases are approximately $4,000, by themselves. Commenters (0037, 0038) also stated 
12-6

that costs increase if Method 301 validations are necessary. The commenters (0037, 0038)

contended the EPA needed to consider the one-time cost to adjust sample ports and the recurring 

cost to procure a crane to lift Method 320 testing equipment to the sampling point.

One commenter (0043) stated that baghouse leak detection instrumentation and 

installation costs were $113,000, with annual costs for preventive maintenance of $5,760. The 

commenter (0043) also noted they would realize a one-time cost of $220,000 for additional 

parametric monitoring equipment for five scrubbers, with annual costs for cleaning and routine 

maintenance of $13,500. The commenter remarked that these costs may not be included in the 

proposed rule cost estimate.

A commenter (0043) also remarked that the EPA needed to determine how the additional 

scrubber controls would impact water use, including the water balance, and energy costs.

Response to Comment: The Agency disagrees with the commenter that access and safety 

training would lead to more than double the costs for Method 30B. Method 30B is required for 

phosphate rock calciners, which must also conduct particulate matter (PM) compliance tests 

using Method 5. These two test methods are similar; an access point in the stack would already 

be available and we would expect minimal differences in safety training for using Method 30B 

versus Method 5. While the Method 30B cost used at proposal was an estimate for a general 

facility, we believe that more than doubling the cost of Method 30B due to access and safety 

training concerns is not appropriate. The commenter did not provide a detailed discussion with 

specifics to illustrate why increased stack test costs were appropriate. Based on the limited 

information provided, and our knowledge of the testing costs, we do not agree with their cited 

cost of $20,000 per stack test. The Method 30B estimate of $6,400 was based on a 20 percent 

reduction from the full cost of $8,000; a 20 percent reduction is appropriate when multiple stack 

tests are conducted, which is the case for phosphate rock calciners. However, in light of the 

commenter’s concerns, we have removed the 20 percent reduction and applied the full Method 

30B cost estimate of $8,000 per stack test. 

The Agency is not adopting the proposed HF standards. As a result of this determination

to not adopt the proposed HF standards, the Agency has retained the current total fluoride limits 

(lb total F/ton P2O5 feed) measured using EPA Method 13A or 13B as a surrogate for the HAP 

HF, rather than HF emission limits using EPA Method 320. Therefore, the commenter’s concern 
12-7

over the increase in testing costs from using EPA Method 320 instead of EPA Method 13A or 

13B is no longer applicable. Refer to the preamble of the final rule for additional details.

The Agency agrees that costs for a baghouse leak detection system (BLDS) should have 

been included in the proposed rule. For the final rule, we are including BLDS capital and annual 

costs using data from previous rulemakings; capital costs equal approximately $25,200 and 

annual costs are approximately $9,900 per fabric filter. In the technology review it was noted 

that three facilities employ fabric filters on their phosphate fertilizer process lines. The final rule 

includes BLDS costs for these three facilities; refer to the memorandum “Control Costs and 

Emissions Reductions for Phosphoric Acid and Phosphate Fertilizer Production Source 

Categories - Final Rule,” which is available in the docket for this rule, for additional cost details. 

The Agency agrees that costs for the proposed additional absorber monitoring options 

should have been included in the proposed rule. However, due to certain absorber monitoring 

revisions that we made in the final rule, costs associated with absorber monitoring is assumed to 

be zero for the final rule. Refer to the preamble of the final rule for discussion regarding the 

changes made to absorber parametric monitoring and the costs related to these changes.

12.6 Economic Impacts

Comment: Several commenters (0037, 0038, 0043) were concerned about the overall 

economic impact the proposed rules would have on the industry. Each commenter (0037, 0038, 

0043) cited concerns about individual costs associated with proposed requirements (e.g., BTF Hg 

limits, the gypsum dewatering stack and cooling pond management plan, testing and monitoring 

costs, costs associated with rule clarifications), and believed that cumulatively these 

requirements would impose a substantial economic impact. Commenters (0037, 0038) estimated 

the costs would be well above $100 million. Commenters (0037, 0043) also noted the phosphoric 

acid industry is global and that costly requirements make domestic producers less competitive 

and put their operations at risk. A commenter (0043) mentioned that the EPA needed to consider 

the total cost of capital for the proposed rule. The commenter explained that the total cost of 

capital reflects the capital that could have been re-invested back into domestic production. The 

commenter (0043) stated that such reinvestment is crucial for the domestic industry to stay 

competitive with the international competition, which often does not have the same level of 

environmental protection costs as in the United States. One commenter (0037) warned that 
12-8

increased regulatory burden has been cited as a factor in recent phosphoric acid plant closures. A 

commenter (0038) also declared the EPA should address the issues raised in all comments to the 

proposed rule, and then submit a full economic analysis for public review.

Response to Comment: The Agency agrees with commenters that the proposed rule did 

have a substantial economic impact to one facility, PCS Aurora, due to the proposed BTF Hg 

limit for phosphate rock calciners. 

All comments were reviewed and addressed, and as a result, certain changes were 

incorporated into the final rule. The cost for the final rule is well below $100 million. 

Commenters stated that particularly high costs would be incurred by the industry as a result of 

the gypsum dewatering stack and cooling pond management plan (where industry estimated 

closure costs) and applicability clarifications to include clarifiers and defluorination units in the 

definition of WPPA process line. These requirements were removed or revised for clarity, which 

eases most of the cost burden that industry was concerned with (refer to the preamble of the final 

rule for further details). 

The other major cost in the proposed rule that commenters were concerned about was 

complying with the BTF Hg limit for phosphate rock calciners. However, we are not finalizing 

the proposed BTF Hg limit (i.e., 0.014 mg Hg/dscm @ 3% O2) in NESHAP subpart AA for 

existing phosphate rock calciners. Instead, we are finalizing a MACT floor Hg limit for existing 

phosphate rock calciners and do not anticipate that any facilities will need to install a new control 

device to meet the existing phosphate rock calciner Hg limit. The Agency determined there 

would be a significant economic impact to PCS Aurora due to the BTF Hg limit for existing 

phosphate rock calciners, and as such, it is not being finalized.

We are finalizing the proposed BTF Hg limit (i.e., 0.14 mg Hg/dscm @ 3% O2) in 

NESHAP subpart AA for new phosphate rock calciners. The Agency determined that a BTF Hg 

limit for new phosphate rock calciners is appropriate and cost-effective. See the preamble to the 

final rule and the memorandum “Control Costs and Emissions Reductions for Phosphoric Acid 

and Phosphate Fertilizer Production Source Categories - Final Rule,” which is available in the 

docket for this rule, for additional cost details and discussion.
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12.7 Economic Benefits and Regulatory Planning and Review

Comment: Commenters (0038, 0043) were concerned the EPA did not fully evaluate the 

benefits of the proposed rule. They stated that because costs were potentially much higher than 

the EPA originally calculated, examining the benefits were necessary. The commenters (0037, 

0038) provided a detailed review of the economics and benefits of the proposed rule in an 

attachment to their comments. A commenter (0037) reported that the potential costs associated 

with the Hg limit outweigh the benefits. The commenter (0037) maintained that the EPA 

justified Hg controls in other rules by focusing on the benefits of reductions in PM, ozone, and 

CO2 emissions that would occur with the installation of Hg controls (co-benefits). The 

commenter (0037) then noted the co-benefits of the proposed phosphate rock calciner Hg limits 

would be minimal because existing venturing scrubbers and WESPs control emissions of PM 

and SO2. The commenter (0037) reported that the analysis they conducted showed the Hg limit 

fails the benefit-cost test, and can be expected to decrease societal well-being. 

Commenters also believed the rule to be subject to Executive Order 12866 due to their 

projected costs. Two commenters (0037, 0038) stated the rule is economically significant and 

should be submitted to Office of Management and Budget (OMB) for review, according to 

Executive Order 12866. Both commenters mentioned the proposed rule would have an economic 

impact greater than $100 million, and recommended the EPA conduct a full Regulatory Impact 

Analysis. A commenter (0038) further contended that even if the economic impact was less than 

$100 million, an economic analysis was necessary because there are relatively few entities that 

produce phosphoric acid and phosphate fertilizer products in the United States. The commenter 

(0038) continued that the EPA must evaluate how the proposed rule could “adversely affect in a 

material way . . . a sector of the economy” and this sector-based analysis is an independent and 

sufficient condition to undertake a required economic analysis under Executive Order 12866.

Response to Comment: The Agency did not conduct a full Regulatory Impact Analysis 

(RIA) for the proposed rule due to our determination that this rule is not economically 

significant. We have evaluated the costs presented by industry, and determined the costs for the 

rule are much less than those cited. As a result, we still believe the rule to not be economically 

significant, and accordingly, not subject to an RIA. All comments were reviewed and addressed, 

and as a result, certain changes were incorporated into the final rule. Commenters stated that 

particularly high costs would be incurred by the industry as a result of the gypsum dewatering 
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stack and cooling pond management plan (where industry estimated closure costs) and 

applicability clarifications to include clarifiers and defluorination units in the definition of 

WPPA process line. These requirements were removed or revised for clarity, which eases most 

of the cost burden that industry was concerned with. 

The other major cost in the proposed rule that commenters were concerned about was 

complying with the BTF Hg limit for phosphate rock calciners. However, we are not finalizing 

the proposed BTF Hg limit (i.e., 0.014 mg Hg/dscm @ 3% O2) in NESHAP subpart AA for 

existing phosphate rock calciners. Instead, we are finalizing a MACT floor Hg limit for existing 

phosphate rock calciners and do not anticipate that any facilities will need to install a new control 

device to meet the existing phosphate rock calciner Hg limit. The Agency determined there 

would be a significant economic impact to PCS Aurora due to the BTF Hg limit for existing 

phosphate rock calciners, and as such, it is not being finalized. 

We are finalizing the proposed BTF Hg limit (i.e., 0.14 mg Hg/dscm @ 3% O2) in 

NESHAP subpart AA for new phosphate rock calciners. The Agency determined that a BTF Hg 

limit for new phosphate rock calciners is appropriate and cost-effective. See the preamble to the 

final rule and the memorandum “Control Costs and Emissions Reductions for Phosphoric Acid 

and Phosphate Fertilizer Production Source Categories - Final Rule,” which is available in the 

docket for this rule, for additional cost details and discussion.

12.8 Environmental Justice

Comment: Several commenters (0035, 0037, 0047, 0054) contended that the EPA did not 

adequately address the environmental justice impacts (including any substantive analysis of the 

economic impacts and effects, as well as cumulative impacts and effects) the proposed rule may 

have on minority and low-income populations in and around PCS Aurora’s plant. Two of these

commenters (0035, 0037) noted that the EPA concluded “we found the risks from these source 

categories to be acceptable for all populations.” However, the commenters maintained that the 

EPA is only considering “risks” from pollution, which it found to be negligible, while ignoring 

the economic and employment effects on minority and low income communities from setting the 

NESHAP “below the floor” even where not necessary to do so for health reasons. Demographics 

on PCS Aurora employees were provided by the commenters, which show African Americans 

exceed the national average of 13%. In addition, commenters (0035, 0037) observed that 20.6% 
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of the population around the PCS Aurora facility lives below the poverty line, exceeding the 

national average of 14.9%. The commenters contested that any workforce reductions caused by 

the proposed rule at this facility would disproportionately affect low-income and African 

American populations. The commenters (0035, 0037) also reported that between 2011 and 2014, 

the workforce associated with the PCS Aurora facility dropped from 1,910 to 1,159 employees, 

and were concerned the proposed rule could further increase the reductions in workforce. The 

commenters also explained that many of the facility’s contractors are small businesses, which 

should also be analyzed because the methodology is flexible so that environmental justice 

impacts can be assessed without being limited by demographics. One commenter (0035) 

requested that the EPA issue a Notice of Data Availability (NODA) to remedy this deficiency. 

Another commenter (0047) requested that EPA defer any action on the beyond the floor limit 

until the economic impacts can be assessed consistent with EPA's environmental justice 

guidance. The commenter argued that CAA Section 112(d)(2) must be read to require that EPA 

comply with the functional equivalent of the National Environmental Policy Act (NEPA)

requirements including assessing environmental justice impacts. This commenter also argued 

that Executive Orders 12866 and 13563, under which the Office of Information and Regulatory 

Affairs (OIRA) reviews draft regulations, call for EPA to conduct an environmental justice 

assessment. This commenter further argued that based on EPA’s Environmental Justice Toolkit 

at p.24, the economic model that must be used to assess the environmental justice economic 

impacts would not be the same one used to pass OIRA scrutiny, but rather those economic 

indicators that are most important to minority and low income communities such as lost wages 

and reduced property values. A commenter (0056) also provided a copy of a news article that 

discussed economics and the increasing poverty in Beaufort County. 

Response to Comment: The EPA continues to make environmental justice an agency 

priority and appreciates the comments provided and suggestions on how the agency can move 

forward in the areas of environmental justice analysis and economic analysis. Environmental 

justice assessments inclusive of economic considerations are an evolving area where guidance, 

such as the referenced toolkit, are currently being evaluated and balanced against availability of 

data, resources and statutory authority considerations. The EPA does not collect information on 

those employed in the immediate surrounding areas of affected facilities. In the case of the 

Phosphoric Acid Manufacturing NESHAP and NSPS reviews, based on information provided by 
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commenters during (and after) the proposal period, the EPA concludes that there would be a 

significant economic impact to PCS Aurora given that estimated costs to comply with the 

proposed BTF Hg limit for phosphate rock calciners are a significant percentage of revenues. 

However, an employment analysis was not conducted. We are not finalizing the proposed BTF 

Hg limit (i.e., 0.014 mg Hg/dscm @ 3% O2) in NESHAP subpart AA for existing phosphate rock 

calciners. Instead, we are finalizing a MACT floor Hg limit for existing phosphate rock 

calciners. Refer to the preamble of the final rule for additional details

13.0 STARTUP, SHUTDOWN, AND MALFUNCTIONS

13.1 Whether EPA Appropriately Removed The Startup, Shutdown, and Malfunction 

Exemption

Comment: Two commenters (0037, 0038) requested that the EPA withdraw the proposal 

to end the SSM exemptions for Subparts AA and BB, or further explain the EPA’s reasoning for 

ending the exemption in the context of these two industries. These commenters (0037, 0038)

argued that the EPA had failed to adequately explain why subparts AA and BB cannot retain the 

current SSM exemptions and the use of the “affirmative defense” for malfunctions based on 

statutory law and recent court decisions, and why they need to be removed from the two 

subparts. The commenters asserted that the EPA had failed to explain why the SSM provisions 

are no longer necessary. The commenters cited comments submitted by the SSM Coalition on 

the EPA’s Proposed Petroleum Refinery Sector Risk and Technology Review and New Source 

Performance Standards, Docket ID No. EPA¬HQ-OAR-2010-0682, which argued that 1) EPA’s 

approach “fails to account adequately for emissions that occur during SSM periods,” 2) is based 

“on an incorrect reading of the D.C. Circuit’s Sierra Club v. EPA decision,” and 3) changes 

“regulations that have been in place for many years and whose SSM provisions were never 

challenged in court, without any justification of its authority to do so and without any apparent 

factual analysis of the statutory criteria for standard-setting.”

One commenter (0038) requested that the EPA’s rationale for removing the current SSM 

and affirmative defense provisions is based on a misinterpretation of recent case law and the 

statute. The commenter argued that the case on which the EPA relies for removing the 

affirmative defense provisions, NRDC v. EPA, is irrelevant to using SSM exemptions and to 

maintaining the affirmative defense for malfunctions, and that the EPA conceded as much with 
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respect to the removal of affirmative defense in the preamble to the proposed rule in footnote 29 

(79 FR 66542). 

The commenter (0038) speculated that the EPA, in arguing that an affirmative defense is 

not “necessary,” appears to be relying either on (1) the rationale that the EPA may use its caseby-case enforcement discretion to provide flexibility if a source cannot comply as a result of a 

malfunction, or (2) a rationale that penalties for violations caused by malfunctions in 

administrative proceedings and judicial proceedings should be consistent, as put forth by the 

EPA in the preamble to the proposed rule. (See 79 FR 66541)

The commenter (0038) argued that the affirmative defense provisions would not prohibit 

the EPA from still using case-by-case enforcement discretion to provide flexibility, and the 

commenter noted that the affirmative defense is still subject to rebuttal by the EPA in 

enforcement actions.

The commenter (0038) suggested that the EPA is relying on the need for consistency as 

the basis for removing the affirmative defense provisions by citing CAA section 113(e) 

[identified as 113(h) by the commenter]. The commenter noted that the EPA already has 

acknowledged that the holding in NRDC v. EPA made a distinction between “judicial” defenses 

(which only Article III courts may regulate), versus “administrative” defenses, such as the one 

provided in the two subparts, and that applying the criteria in CAA Section 113(e) does not mean 

that penalties in judicial and administrative proceedings need to be consistent. Therefore, the 

need for consistency also does not support removing the affirmative defense provisions, 

according to the commenter.

The same commenter noted that the EPA has argued in the preamble to the proposed rule 

that the affirmative defense is no longer “necessary” because of the removal of the exemption for 

SSM excess emissions. The commenter noted that the EPA refers to an earlier discussion in the 

preamble in support of this rationale (see 79 FR 66542, footnote 29), but asserted that this 

supporting discussion is not apparent earlier in the preamble.

Response to Comment: Sierra Club v. EPA, 551 F.3d 1019 (D.C. Cir. 2008), the United 

States Court of Appeals for the District of Columbia Circuit vacated the startup, shutdown, and 

malfunction (SSM) exemption contained in section 63.6(f)(1) and (h)(1) of the Part 63 General 

Provisions. When incorporated into CAA section 112(d) regulations for specific source 

categories, the exemption in these two provisions exempted sources from the requirement to 
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comply with the otherwise applicable CAA section 112(d) emission standard during periods of 

SSM. In Sierra Club, the court explained that under section 302(k) of the CAA, emissions 

standards or limitations must be continuous in nature. The court then held that the SSM 

exemption violates the CAA's requirement that some section 112 standard apply continuously.

To ensure that some CAA section 112 standard applies at all times, we are specifying that 

the SSM exemption in the 40 CFR part 63 General Provisions does not apply to subparts AA and 

BB, adopting a work practice standard that applies in lieu of the HAP emission limits during 

periods of startup and shutdown, and clarifying that the emission limits apply at all other times, 

including during periods of malfunction. The work practice requires that control devices be 

operated normally during periods of startup and shutdown. As we explained in the proposal 

preamble at 79 FR 66540, the work practice standard applies because it is not feasible to 

prescribe or enforce an emissions standard during startup and shutdown. As we explain in the 

preamble to the final rule, we are clarifying that to comply with the work practice, facilities must 

monitor the same control device operating parameters and comply with the same operating limits 

that are established to otherwise comply with the emission limits.

Regarding periods of malfunction, the Clean Air Act does not allow EPA to provide 

“affirmative defense” provisions into NESHAP. In the Portland cement decision issued April 18, 

2014 (NRDC v. EPA), the D.C. Circuit vacated a regulatory provision establishing an 

affirmative defense to civil penalties for violations of emission standards caused by unavoidable 

malfunctions. The court found that the authority under the CAA to determine penalty amounts 

lies exclusively with federal District Courts.

In light of NRDC, EPA is no longer including regulatory affirmative defense provisions 

in its rules. However, if a source is unable to comply with an emission standard as a result of a 

malfunction, the EPA may use its case-by-case enforcement discretion to provide flexibility in 

deciding if a penalty is appropriate. Further, in an EPA or citizen enforcement action, the court 

has the discretion to consider any defense raised and determine whether penalties are 

appropriate. As explained further in the proposal preamble at 79 FR 99543, the rule can 

reasonably be applied during unanticipated malfunctions and encourages practices that will avoid 

malfunctions.

Comment: Two comments (0037, 0038) argued that the EPA’s proposed alternative to 

the SSM exemptions and the affirmative defense for malfunctions, relying on case-by-case 
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enforcement discretion for every malfunction that causes excess emissions, would ignore the 

realities of the production process and would create uncertainty regarding compliance. One 

commenter (0038) argued that the courts have also recognized the need for flexibility and cited 

as an example, Essex Chem. Corp. v. Ruckelshaus, 486 F.2d 427, 432-33 (D.C. Cir. 1973), cert. 

denied,416 U.S. 969 (1974), in which the commenters said that the court remanded a “never to 

be exceeded” standard because SSM provisions are inherently “necessary to preserve the 

reasonableness of the standards as a whole,” and that the court further explained that “nowhere in 

the record has there been a showing that the [normal] standards can be equaled during periods of 

less than normal operation, when plant efficiency and consequently pollution emissions vary 

significantly from the norm.” 

One commenter (0038) argued that it would be inappropriate and arbitrary for the EPA to 

deem all exceedances of a standard to be a violation, and that the proposed approach would 

unfairly subject companies to enforcement action for malfunctions that the EPA acknowledges in 

the proposal preamble are “not reasonably preventable.” (See 79 FR 66541.) The commenters 

argued that the EPA has acknowledged in prior actions that malfunctions beyond the control of 

the operators should not be a basis for imposing penalties when they result in exceedance of a 

standard. In support, the commenters cited 40 CFR 63.7(e), which specifies conditions for the 

conduct or performance tests, and also language at 40 CFR 63.600(e) and 63.620(e), and also the 

current definition of “malfunction” at 40 CFR 63.2.

Response to Comment: As we previously explained in our response to the comment 

immediately above, the final rule is consistent with the requirements of the Clean Air Act and 

provides reasonable flexibility to comply with the standards at all times, including periods of 

SSM. All exceedances to standards are violations. If EPA determines that an exceedance was 

outside the control of the source, then EPA has discretion to determine an appropriate response.

In the event that a source fails to comply with the applicable CAA section 112 standards 

as a result of a malfunction event, the EPA would determine an appropriate response based on, 

among other things, the good faith efforts of the source to minimize emissions during 

malfunction periods, including preventative and corrective actions, as well as root cause analyses 

to ascertain and rectify excess emissions. The EPA would also consider whether the source’s 

failure to comply with the CAA section 112 standard was, in fact, ‘‘sudden, infrequent, not 

reasonably preventable’’ and was not instead ‘‘caused in part by poor maintenance or careless 
13-16

operation.’’ See 40 CFR 63.2 (definition of malfunction). If the EPA determines in a particular 

case that enforcement action against a source for violation of an emission standard is warranted, 

the source can raise any and all defenses in that enforcement action and the federal district court 

will determine what, if any, relief is appropriate. The same is true for citizen enforcement 

actions.

13.2 Feasibility Of Estimating Emissions During SSM Events

Comment: Two commenters (0037, 0043) argued that compliance with the EPA proposal 

at 40 CFR 63.607(b) and 63.627(b) to require affected facilities to develop and maintain records 

of an estimate of the volume of each regulated pollutant emitted over the applicable standard and 

a description of the method used to estimate emissions” was difficult, if not impossible. The 

commenters argued that it would be difficult to estimate excess emissions for the same reasons it 

would be difficult to apply numeric emission limits to malfunction emissions. The commenters 

asserted that because malfunctions are unpredictable in their occurrence and duration, can be 

caused by unknown factors, and may cause rapid changes in emissions, it is difficult to estimate 

emissions with any reasonable degree of uncertainty. The commenters argued that these 

estimates should not be required, and if required, they should not be held against facilities during 

the exercise of case-by-case enforcement discretion.

One commenter (0043) noted that they do not have a scientific basis to estimate 

emissions during SSM periods because source testing is not performed during such periods of 

unstable air emissions.

The same commenter (0043) asserted that determining excess emissions during 

malfunction events is even more challenging as the root cause of these events is likely to be quite 

variable and will have differing effects on the concentration of air pollutants. The commenter 

requested that the EPA maintain the record keeping requirements associated with 40 CFR 

63.10(b)(2)(i) and (ii) and remove the record keeping requirements associated with the proposed 

rule at 40 CFR 63.607(b) and 63.627(b), or simply remove the requirement to quantify excess 

emissions during periods of shutdown, startup or malfunction.

Response to Comment: We are retaining the requirement as proposed to report an 

estimate of the quantity of each regulated pollutant emitted over any emission limit and a 

description of the method used to estimate the emissions in situations where the duration of an 
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exceedance of an emissions limit, work practice standard, or operating limit is 1 percent of the 

total operating time for the reporting period or greater, including periods of SSM. This 

requirement will ensure that there is adequate information to allow the EPA to determine the 

severity of the failure to meet an applicable standard and to provide data that may document how 

the source met the general duty to minimize emissions during an exceedance event. 

We disagree with the commenter that it is not possible to estimate emissions during SSM. 

The rule provides facilities the flexibility to select the most appropriate method to estimate 

emissions based on process knowledge and the circumstances of each situation. Examples of 

such methods would include product-loss calculations, mass balance calculations, measurements 

when available, or engineering judgment based on known process parameters.

13.3 Work Practice Standard In Place Of Emission Limits

Comment: One commenter (0038) agreed that the creation of work practice standards for 

periods of startup or shutdown would qualify as “standards” to the ruling in Sierra Club v. EPA

that case’s ruling that CAA § 302(k)210 requires that some standard apply “on a continuous 

basis,” in lieu of not providing any standards whatsoever. (See 551 F.3d at 1021-22, 1027-28.) 

The same commenter noted that the Sierra Club court stated that the EPA had “not purported to 

act under CAA section 112(h), providing that a standard may be relaxed ‘if it is not feasible’ . . . 

based on either a (1) design or (2) source specific basis” under the facts of that case. (Id. at 

1028.) Instead, according to the commenter, the Sierra Club court reserved the EPA’s authority 

under the CAA to create flexibility or different standards for periods of SSM, including when it 

was “not feasible” to prescribe a numeric emission limit at all times of operation. The commenter 

concluded that the EPA has the authority to use work practice standards to regulate SSM periods 

under Subparts AA and BB in lieu of imposing numeric standards and operating parameters 

during those periods.

Response to Comment: We concur with the commenter that the CAA section 112(h) 

provides for EPA to establish work practice standards in situations where it is not feasible to 

prescribe or enforce an emission limit. In the final rule, we are retaining the proposed 

requirement for a work practice for periods of startup and shutdown. See preamble discussion of 

the proposed rule at 79 FR 66541 and 66551 for our rationale under CAA section 112(h) for 

establishing the work practice standard for subparts AA and BB, respectively.
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Comment: One commenter (0043) asked whether the proposed requirements in 40 CFR 

63.602(h) and 63.622(d) to operate emission control equipment during periods of startup and 

shutdown as a means to “demonstrate compliance” with emission limits specified in the rule is 

intended to negate the requirement to calculate and record estimated excess emissions during 

these periods as proposed in 40 CFR 63.607(b) and 63.627(b).

Response to Comment: The work practice that applies during startup and shutdown does 

not negate any other applicable recordkeeping or reporting requirement in the rule. The 

requirement to calculate and report excess emissions during startup and shutdown is triggered 

only if the following criterion are both met: (1) the facility does not comply with the work 

practice standard during these periods; for example, if the control device is not operated 

continuously during startup or shutdown periods or if the control device is not operated within 

the applicable operating limits (refer to the response to comment 13.4 in this document for 

further details); and (2) the duration of an exceedance of the work practice standard or operating 

limit is 1 percent of the total operating time for the reporting period or greater. The emissions 

calculation would take into account any emission reductions achieved by the control equipment.

Comment: Several commenters (0037, 0038, 0043) argued that the EPA’s proposed work 

practice standard for periods of startup and shutdown failed to account for how equipment in the 

phosphoric acid industry works. In order to comply with the proposed startup and shutdown 

requirements, the operator must begin operation of any control device(s) being used at the 

affected source prior to introducing any feed into the affected source and continue operation of 

the control device(s) through the shutdown period until all feed material has been processed 

through the affected source. The commenters noted that it is not feasible to process all feed 

material from a process prior to shutting down most equipment at a facility. For example, the 

phosphoric acid reactors and beds in the calciners may not be able to process all the feed material 

in them prior to shutdown and there would always still be feed material left in the equipment 

even after it is shutdown. The same would be true for nearly all process units in the industry. The 

commenters requested that the EPA revise 40 CFR 63.602(h) to require compliance with the 

work practice standard only up to the point in time when no more feed or in-process materials 

are being introduced into the production unit.

Two commenters (0038, 0039) agreed with the other commenters that it is not feasible to 

base the conclusion of a “shutdown” on the point at which all feed has “been processed.” Instead, 
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they suggested that the EPA should clarify the work practice standard of keeping all emission 

control equipment active during shutdowns. The commenters reported that facilities in the 

industry consider the commencement of “shutdown” as the moment at which the plant ceases 

adding feed to the affected process, rather than basing shutdown on when all feed materials have 

been processed through the process. The commenters recommended that the EPA should define 

“shutdown” to begin when the facility ceases adding feed to an affected process line, and to 

conclude when the affected process line equipment is deactivated, even though some feed or 

residues may still be present within particular parts of the process.

One of the commenters (0039) also noted that it is common practice to have short-term 

shutdown of process inputs for temporary maintenance work (including work on emission 

control equipment) where the entire system is not emptied. In these cases, feed phosphoric acid 

and ammonia to the process is suspended as is flow from the reactor to the granulator. The 

commenter argued that because the source of fluoride to the system has ceased and dust 

generating material flows are suspended, there should be no significant source of emissions to 

control, and it is not necessary to require the utilization of control devices until all feed material 

has been processed. Instead, the commenter recommended that an affected entity should be 

allowed to turn off control devices when reactor and granulator feeds have been stopped, unless 

the system is being emptied, in which case control devices should be required as long as the 

material handling system is in operation.

Response to Comment: This comment is addressed in the preamble of the final rule. We 

agree with the commenter that the rule needs to have a more precise definition of startup and 

shutdown that more clearly and reasonably establishes the time periods when the work practice 

applies and when the emission limits apply.

Comment: One commenter (0038) argued that the EPA should specify that the proposed 

work practices for plant startup and shutdown periods apply “in lieu of” any other emission 

standards, and that such periods should not be counted for testing, monitoring, or operating 

parameter requirements. The commenter noted that the proposed rules at 40 CFR 63.602(h) and 

63.622(d) require the use of work practices “to demonstrate compliance with any emission 

limits” during periods of startup and shutdown. The commenter agrees with the EPA’s 

conclusion that it is not feasible to apply numeric limits to startup and shutdown because certain 

variables required to calculate emissions would be zero during such periods. The commenter also 
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agreed with the EPA that existing emission control devices would still be effective during 

periods of startup or shutdown, if activated. However, the commenter recommended that the rule 

should clarify that startup and shutdown events should not be required to comply with the 

monitoring and operating parameter requirements because startup and shutdown events generally 

are not representative operating conditions for other compliance purposes, such as emissions 

testing. Instead, the commenter (0038), as well as a second commenter (0043), recommended 

that, because the startup and shutdown periods are not representative, the rule should only 

require that (1) all emission control devices be kept active, and (2) owners and operators follow 

the general duty to control emissions, and owners and operators should not be required to 

monitor operating parameters during startup and shutdown periods.

The commenter (0038) argued that the approach in the proposed rules at 40 CFR 

63.602(h) and 63.622(d) to require the use of work practices “to demonstrate compliance with 

any emission limits” during periods of startup and shutdown is “directly inconsistent” with the 

approach that the EPA has applied to other source categories, where such practices clearly were 

prescribed “in lieu of” numeric emission limits that would otherwise apply. (The commenter 

cites, for example, 78 FR 10015, February 12, 2013.) According to the commenter, the EPA 

made it clear in other industries’ rules that such work practice standards apply “in place of” or 

“in lieu of” numeric standards, including with respect to monitoring and recordkeeping 

requirements. (See id. at 10013 and 10015.) The commenter argues that according to the 

preamble language cited for those other industries, “there will no longer be a numerical emission 

standard applicable during startup and shutdown,” and the EPA recognizes that “the 

recordkeeping requirement must change to reflect the content of the work practice standard”(Id. 

at 10014). 

Therefore, the commenter (0038) recommended that the EPA should clearly explain that 

work practices are not applied to “demonstrate compliance” with numeric limits under Subparts 

AA and BB, which the EPA acknowledges are “not feasible” for startup and shutdown periods, 

and instead, the work practices should be written to apply “in lieu of” the numeric limits during 

those periods. The commenter argues that without this clarification, it will appear that both the 

numeric standards and the work practice standards would apply during startup and shutdown. 

The commenter suggests that this can be corrected in the rule by using the “in lieu of” language 

used for other industries.
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Response to Comment: This comment is addressed in the preamble of the final rule. The 

commenter is correct that our intention at proposal was that the numeric emission limits would 

not apply during periods of startup and shutdown, but that facilities would comply with the work 

practice instead.

Comment: One commenter (0042) asserted that, with respect to the EPA proposal to set 

work practice standards, instead of setting numeric standards, to reduce HF from phosphate rock 

calciners during normal operations and during startup and shutdown periods, the EPA has not 

provided the determination and supporting evidence the Clean Air Act requires to set these 

standards instead of numeric limits. The commenters argued that the EPA failed to meet the test 

to promulgate work practice standards “in lieu of” numeric emission standards set by CAA 

section 112(h).

Response to Comment: For reasons that are described in the preamble to the final rule, 

we are not publishing the proposed HF work practice for phosphate rock calciners, but instead 

have adopted a numeric emission limit for total fluorides. The preamble to the final rule further 

explains that the total fluorides emission limit does not apply during periods of startup and 

shutdown and that facilities must comply with the work practice of §63.602(h) instead. The 

preamble provides the CAA section 112(h) justification for adopting a work practice standard in 

lieu of an emission limit.

13.4 Make An Explicit Exemption For Monitoring During SSM

Two commenters (0037, 0038) recommended that the EPA amend the rule to make clear 

that the work practice standards for startup and shutdown also apply in lieu of the parametric 

monitoring requirements set forth in Subparts AA and BB and make explicit that parametric 

operating requirements do not apply during times of startup and shutdown.

One commenter (0038) argued that when the EPA established the flow rate and pressure 

drop parametric monitoring requirements in its 1999 final rule, the EPA concluded that requiring 

continuous monitoring of these parameters “help[ed] assure continuous compliance with the 

emission limit” (64 FR 31365, June 10, 1999). The commenter (0038) also asserted that the rules 

specify that “[t]he emission limitations and operating parameter requirements of this subpart do 

not apply during periods of startup, shutdown, or malfunction . . . .” (40 CFR 63.600(e) and 

63.620(e)). The commenter argued that this was a reasonable action because the operating 
13-22

parameter ranges are established during annual performance tests, and these tests cannot be 

performed during startup and shutdown conditions.

The commenter (0038) suggested that in the proposed rule, the EPA exempt compliance 

with the emission limits during startup and shutdown periods, impose work practice standards in 

lieu thereof, and retain the prohibition on conducting a performance test during periods of startup 

or shutdown (79 FR 66570 (proposed 40 CFR 63.606(d)), and 79 FR 66582 (proposed 40 CFR 

63.626(d)). The commenter suggested that the proposed rule is silent on the applicability of the 

parametric monitoring requirements during startup and shutdown. The commenter asserted that 

because the parametric monitoring provisions provide an inference of compliance with the 

emission limits (64 FR 31365, June 10, 1999), and these emission limits do not apply during 

startup and shutdown, the commenter concluded that the parametric monitoring provisions 

similarly should not apply during startups and shutdowns.

The commenters (0037, 0038) pointed to two recent EPA NESHAP rulemakings to 

support their conclusion. First, the commenters argued that in its industrial, commercial and 

institutional boilers and process heaters NESHAP reconsideration proposal (hereinafter, the 

“Boiler NESHAP”), the EPA, responding to a comment soliciting clarification “that the 

operating limits and opacity limits do not apply during periods of startup and shutdown,” stated 

that with the finalization of work practice standards, “EPA agrees that the requested clarification 

is what was intended in the final rule” (76 FR 80598 and 80615, December 23, 2011). The 

commenters asserted that to this end, in its response to the reconsideration, the EPA made clear 

that affected sources must comply with “all applicable emissions and operating limits at all times 

the unit is operating except for periods that meet the definitions of startup and shutdown in this 

subpart, during which times you must comply with these work practices” (78 FR 7138 and 7142, 

January 31, 2013). The commenters noted that in the Boiler NESHAP regulations, the EPA 

required the implementation of work practice standards in lieu of compliance with the operating 

parameter requirements during startup and shutdown by (1) excluding periods of startup and 

shutdown from the averaging period (Id. at 7187, 40 CFR 63.7575, the definition of a 30-day 

rolling average” excludes “hours during startup and shutdown”), and (2) expressly stating that 

the “standards” (the emission limits and operating requirements) do not apply during periods of 

startup or shutdown. (Id. at 7163, 40 CFR 63.7500(f), entitled “What emission limitations, work 

practice standards, and operating limits must I meet?” applies “at all times the affected unit is 
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operating, except during periods of startup and shutdown during which time you must comply 

only with Table 3 of this subpart.”)

Second, the commenters (0037, 0038) argued that in its Portland Cement NESHAP, the 

EPA specified an operating limit for kilns, identified as a temperature limit established during a 

performance test, and that the temperature limit applied at all times the raw mill is operating, 

“except during periods of startup and shutdown” (78 FR 10039, February 12, 2013, 40 CFR 

63.1346(a)(1)). Further, for the continuous monitoring requirements, including operating limits, 

the Portland Cement NESHAP required operating of the monitoring system at all times the 

affected source is operating, “[e]xcept for periods of startup and shutdown” (Id. at 10041, 40 

CFR 63.1348(b)(1)(ii)).

The commenters (0037, 0038) argued that given the EPA’s conclusion in the proposed 

rule that the emission limits should not apply during startup and shutdown, and because the 

parametric monitoring requirements are established during a performance test (which cannot be 

performed during a startup or a shutdown) and used to infer compliance with the emission limits, 

the EPA should make clear in the final rule that the operating parameters requirements do not 

apply during a startup or a shutdown. The commenter recommended that the EPA should make 

this explicit (1) in the operating and monitoring requirement sections of Subparts AA and BB 

(proposed 40 CFR 63.605 and 63.625), and (2) by defining the averaging period (currently daily) 

as excluding periods of startup and shutdown (proposed 40 CFR Part 63, Subpart AA, Table 4 

and Subpart BB, Table 4). As an alternative, the commenters recommended that if the EPA 

continues to require compliance with the parametric monitoring requirements during startup and 

shutdown periods, then the EPA should adopt a longer averaging period, from daily to 30 days, 

to allow for the effects of startups and shutdowns to be reduced by a longer period of steady-state 

operations. The commenter noted that the Boiler NESHAP has a 30-day averaging period for 

pressure drop and liquid flow rate, and excludes periods of startup and shutdown from the 

averaging period (40 CFR 63.7575, definition of “30-day rolling average”) and 40 CFR Part 63, 

Subpart DDDDD, Table 4). The commenter suggested that their suggested alternate would be 

substantially more stringent than the Boiler NESHAP approach since it would include periods of 

startup and shutdown in the 30-day averaging period, while at the same time avoid misleading 

“exceedances” caused by the inclusion of periods of startup and shutdown compared to daily 

average parametric limits.
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Response to Comment: This comment is addressed in the preamble of the final rule. We 

disagree with the commenters about the applicability of the operating limits. Based on these 

comments, we have clarified in the final rule that to comply with the work practice during 

periods of startup and shutdown, facilities must monitor the operating parameters specified in 

Table 3 to subpart AA or subpart BB and comply with the operating limits specified in Table 4 

of subpart AA or subpart BB.

14.0 OTHER COMMENTS

14.1 Scrubber Water to Cooling Tower Exemption

Comment: Two commenters (0038, 0043) stated that they were concerned about the 

requirement that scrubber water may not be sent to evaporative cooling towers. The commenters 

noted these concerns go back to the 1999 rulemaking for subpart AA, and with similar language 

proposed for subpart BB, clarification was necessary to fully understand the requirement. The 

commenters (0038, 0043) stated their interpretation of the rule was that while scrubber water 

may not be sent to evaporative cooling towers, it may be discharged to cooling ponds or gypsum 

dewatering stack ponds. The commenters (0038, 0043) stated that they were concerned about 

another interpretation, that when facilities have evaporative cooling towers, no scrubber water 

may reenter the process water system (i.e., scrubber water could not be sent to ponds either, as 

that water would eventually go through evaporative cooling towers). The commenters (0038, 

0043) continued that if this is the EPA’s interpretation of the requirement, then the costs and 

effects on water balance would be significant and they must be evaluated. Commenters (0038, 

0043) also stated the EPA did not determine the benefits from implementing the prohibition in 

the 1999 rulemaking nor the proposed rule, such as the advantage of or difference in emissions 

resulting from sending scrubber water to ponds instead of evaporative cooling towers. 

Commenters (0038, 0043) stressed this topic because cooling ponds were a significant source of 

HF as well. Commenters also observed that there was not necessarily a directly relationship 

between fluoride in the water and HF emissions from evaporative cooling towers. The 

commenters (0038, 0043) recommended that the EPA revise §63.602(c) and §63.622(c) to 

include the word “directly,” in order to resolve this issue: 
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(c) You must not directly introduce into any existing or new evaporative cooling tower any 

liquid effluent from any wet scrubbing device installed to control emissions from process 

equipment.

The commenters (0038, 0043) noted this revision will avoid creating a burdensome “indirect” 

prohibition on using any water from ponds in an evaporative cooling tower, to the extent that the 

pond water might have contacted or received any amount of beneficially reused scrubber water.

Response to Comment: We disagree with the commenters statement that there is 

ambiguity in the requirements prohibiting the introduction of scrubbing water into cooling 

towers. In supplemental information provided by one commenter (refer to the March 6, 2007 

letter addressed to Terry T. Uhling of J.R. Simplot Company which can be found in Appendix I 

of Docket ID No. EPA-HQ-OAR-2012-0522-0043), the EPA Region 10 Office of Compliance 

and Enforcement noted that: “Subpart AA Prohibits Sending Scrubber Water to Cooling Towers, 

Even Indirectly.” We agree with that statement; the language of the prohibition is not ambiguous. 

It prohibits sending "into any evaporative cooling tower any liquid effluent from any wet 

scrubbing device installed to control emissions from process equipment" (40 C.F.R. § 63.602(e) 

(emphasis added)). Additionally, in an applicability determination made by the Agency on April 

29, 2005, we clearly state that even if “scrubber liquid effluent at the facility is being diluted 

with other process waste waters” it is still subject to the rule, and a violation to reintroduce those 

liquids to the cooling tower. (http://www.epa.gov/oecaadix/pdf/adi-mact-m050025.pdf). 

Therefore, we are not amending the proposed regulatory text to clarify applicability, as we 

believe that the intent is abundantly clear. 

In addition, we are not revising the provision to only include ‘direct’ introduction of 

scrubber liquid effluent as this is contrary to the clearly expressed intent of the rule. The 

arguments raised in this action by the commenters regarding benefit and cost were previously 

raised and rejected during the initial rulemaking process for 40 CFR part 63, subpart AA. The 

EPA promulgated 40 CFR part 63, subpart AA on June 10, 1999 (64 FR 31358). In the preamble 

to the June 10, 1999 final rule, EPA noted that a commenter argued the Agency had not 

considered the benefits or the compliance costs of the proposed work standard (i.e., to forbid the 

introduction of liquids containing the effluent from air pollution control devices into any 

evaporative cooling tower) and § 63.602(e) should be deleted; however, other commenters 

supported the Agency’s proposed requirement. In response to these comments, the Agency 
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elected to base NESHAP upon the floor level of control (i.e., the least stringent option permitted 

by the Act), and stated that any consideration of costs would be of significance only for 

consideration of options for control levels exceeding the floor level of stringency. With regard to 

the commenters statement about advantage of or difference in emissions resulting from sending 

scrubber water to cooling ponds instead of evaporative cooling towers, even if fluoride emissions 

from cooling ponds are in fact higher than EPA understood them to be in 1999, EPA’s implicit 

determination in 1999, that routing scrubber water (even indirectly) to cooling towers results in 

higher fluoride emissions to the ambient air than routing scrubber water to cooling ponds or 

gypsum ponds, remains a valid determination. Furthermore, as stated in the preamble to the June 

10, 1999 final rule, it does not make sense to scrub HF (and other HAPs) from potential emission 

points and then allow these HAPs to evaporate when the scrubber water is routed to evaporative 

cooling towers.

14.2 Miscellaneous

Comment: Two commenters (0039, 0043) stated that the requirements for control 

techniques for “fugitive dust” should be removed because subpart AA is for the control of HAPs 

(not fugitive dust) and state environmental agencies regulate fugitive dust. 

Response to Comment: We agree with the commenters that the phrase “fugitive dust” 

should be removed from NESHAP subpart AA because the rule is for the control of HAPs and 

not fugitive dust. We have removed the phrase “fugitive dust” from the final rule at §63.602.

14.3 Inherently Safer Technology (IST)

Comment: A commenter (0042) advocated that the EPA must address safety concerns 

from catastrophic incidents and resulting air pollution releases at fertilizer facilities during this 

rulemaking process. The commenter’s main recommendation is that the rulemaking should 

require and incentivize preventative measures within the chemical and fertilizer industries 

through the use of Inherently Safer Technology (IST). The commenter presented the following 

arguments in favor of its position:

 Health studies. One in three U.S. school children goes to school within a vulnerability 

zone of a hazardous chemical facility, and they cite a report by Center for Effective 

Government: at http://www.foreffectivegov.org/files/kids-in-danger-zones-report.pdf. 

They also contended that the public supports the use of inherently safer, alternatives to 
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current technologies, and they cite a national poll by Lake Research that showed that a 

strong majority of likely voters from both parties support new requirements to use of 

safer cost-effective alternatives. http://preventchemicaldisasters.org/113-2.

 Executive Order. President Obama signed an Executive Order on August 1, 2013 

recognizing that “additional measures can be taken by executive departments and 

agencies with regulatory authority to further improve chemical facility safety and security 

coordination with owners and operators. The commenter suggested that the EPA should 

use its CAA regulatory authority in 42 U.S.C. §7412(d), (f), and (r) to fulfill these 

objectives.

 Routine and catastrophic releases are preventable. Findings by the U.S. Chemical Safety 

Board (CSB) documented that several recent tragedies from refinery and other chemical 

plant disasters are often preventable, and made recommendations for preventative 

measures. The commenter claimed that the Board’s recommendation would also prevent 

release of HF. They provide two examples of fertilizer plant explosions/releases from 

facilities “similar” to those covered by the EPA’s rule (i.e., April 2013 fertilizer 

storage/distribution plant in West Texas, and January 2010 release of phosgene at facility 

in Belle, WV), and refer to “at least six” major instances of HF releases from refineries in 

recent years. Also, the commenter cites the State of California’s response to the Chevron 

Richmond fire in 2012 that included recommendations to prevent similar incidents, which 

the commenter claimed are applicable to chemical and fertilizer plants.

 Inherently Safer Technology (IST), also known as Inherently Safer Design (ISD). The 

commenter suggested that the EPA must apply recommendations from experts in 

chemical plant safety for the use of IST/ISD, and do so under its §7412(d) and (f) 

authorities. They provided a list of currently available ISTs, and compelled the EPA to 

require the application of these ISTs to be used at chemical and fertilizer plants:

o Requirement for anonymous near-miss and other types of anonymous safety and 

maintenance reporting. The commenter claimed this has been implemented at the 

Belle, WV plant (DuPont), and quoted Bureau of Safety and Environmental 

Enforcement Director Brian Salerno as committing to make this tool available to 

(the offshore oil and gas) industry “soon.”
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o Requirement for back-up power to prevent toxic emission spikes. The commenter 

claimed that such systems represent a “development” within §7412(d)(6), which 

the EPA must update the §7412(d) standards to reflect.

o Leak detection and repair requirements which can prevent leaks from turning into 

catastrophes. The commenter argued that EPA has not addressed leak detection 

and repair in this rulemaking, but the EPA should do so to satisfy its obligations 

under §7412(d) and (f), and to assure safety.

Response to Comment: Section 112(r) of the CAA was added in 1990 to address 

catastrophic releases. EPA’s regulations on catastrophic releases appear in 40 CFR part 68. We 

currently have a petition for rulemaking to address IST under CAA section 112(r) and part 68. 

Also, pursuant to Executive Order 13650, EPA has issued a “Request for Information” soliciting 

public views on the appropriateness of IST regulations and is considering pursuing rulemaking 

as part of the regulation, standard and guidance modernization effort called for by the Executive 

Order.

Historically, EPA’s authority to address catastrophic releases under the NESHAP 

program was questioned under the pre 1990 CAA (see House Energy & Commerce, Rep. 101-

490, at 157(1990) (House Report); see also Senate Print 103-38, A Legislative History of the 

Clean Air Act Amendments of 1990, volume II, at 2743 (remarks of Representative Richardson, 

sponsor of House amendment on accidental releases adopted in House bill) (“Nothing in current 

law requires chemical or other industrial facilities handling toxic chemicals to take steps to avoid 

the accidental release of dangerous chemicals into the air”). To promote specific programs to 

address the risks associated with accidental releases, Congress added CAA section 112(r) (see, 

e.g., House Report at 157); Senate Environment & Public Works, Rep. 101-228, at 205 – 07 

(1989).

In light of the extensive history and efforts of the agency on IST specifically and 

catastrophic accidents generally under the section 112(r) program, and in light of the statutory 

structure of CAA section 112, we view the request to enact IST provisions in this rule to be 

outside the scope of CAA section 112(d)(2), section 112(f)(2) and section 112(d)(6). Therefore,

this comment is outside the scope of the current rulemaking.
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14.4 Extension Requests

Comment: Two commenters (0030, 0031) requested an extension to the comment period 

for the proposed rule. The commenters presented various reasons for this request, including, 

among others, the need to determine how the proposed changes (the addition of entirely new 

limits for HF and mercury emissions, new work practice standards for several processes, and a 

number of new monitoring and reporting requirements) would impact specific facilities.

Response to Comment: OAQPS/ SPPD

The EPA extended the deadline for written comments on the proposed amendments by 

30 days to January 21, 2015 in order to afford additional time for review.

14.5 Organics Content Subcategory

Comment: One commenter (PCS, 5/1/15) recommended that the EPA create a new 

subcategory for WPPA processes that use phosphate rock with organics content greater than 0.9 

percent. The commenter stated the phosphate rock used by PCS Aurora is the only phosphate 

rock that exceeds this organics content threshold, and is thus unique for the industry. The 

commenter (PCS, 5/1/15) provided a table comparing the organics content of various phosphate 

rocks used by the industry and noted their phosphate rock organics content is more than twice the 

next highest phosphate rock. They claimed the high organic content requires them to calcine the 

rock to remove organics. The commenter (PCS, 5/1/15) continued that with the creation of this 

new subcategory, the Hg limit for phosphate rock calciners should be set at the MACT floor 

level and not at the beyond-the-floor level. 

Response to Comment: The EPA does acknowledge that the commenter has provided 

information to demonstrate the need for calcination at this facility. One option that was discussed 

with this commenter at a previous meeting (see the memorandum “Summary of August 14, 2012 

US EPA Meeting with PCS Phosphate,” which is available in the docket for this action) was 

removal of calciner units to reduce mercury emissions. The commenter demonstrated that 

calcination was required due to the nature of raw materials used at this facility and the required 

specifications from some of the products. 

However, the EPA does not agree with the commenter’s statements that a subcategory for 

WPPA process that use phosphate rock with organics content greater than 0.9 percent is 

appropriate. The CAA allows for subcategories based on class, type, and size of sources within a 
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category or subcategory (CAA § 112(d)(1)). The reason to develop subcategories is that typically 

different subcategories have different emissions characteristics, and using emissions data from 

processes that are inherently different to develop an emissions limit is sometimes not 

appropriate. However, that is not the case here. All the data used to evaluate potential emissions 

from calciners came from this one facility and the commenter provided no data to indicate that 

the remainder of the process is different from other phosphoric acid process, only that, at this 

particular facility, additional pretreatment of the raw material is necessary. Therefore there is no 

basis or reason to develop different subcategories based on the presence of calciners and the EPA 

will not accept the suggested subcategory strategy.