Mandatory Greenhouse Gas 

Reporting Rule: EPA’s 

Response to Public Comments 

Subpart DD: Electric Transmission 

and Distribution Equipment Use 
 

November 8, 2010 Subpart DD—Response to Comment Document 2 

FOREWORD 

This document provides responses to public comments on the U.S. Environmental Protection Agency’s 

(EPA’s) Proposed Mandatory Greenhouse Gas Reporting Rule: Additional Sources of Fluorinated GHGs: 

Subpart DD, Electric Transmission and Distribution Equipment Use. EPA published a Notice of Proposed 

Rulemaking in the Federal Register (FR) on April 12, 2010 (75 FR 18652). EPA received comments on 

this proposed rule via mail, e-mail, and at a public hearing held in Washington D.C. on April 20, 2010. 

Copies of all comments submitted are available at the EPA Docket Center Public Reading Room. 

Comments letters and transcripts of the public hearings are also available electronically through 

http://www.regulations.gov by searching Docket ID EPA-HQ-OAR-2009-0927. 

EPA prepared this document in multiple sections, with each section focusing on a different broad 

category of comments on the rule. In light of the large number of comments received and the significant 

overlap between many comments, this document does not respond to each comment individually. Rather, 

EPA summarized and provided a single response to each significant argument, assertion, and question 

contained within the totality of comments. Within each comment summary, EPA provides in parentheses 

one or more lists of Docket ID numbers for commenters who raised particular issues; however, these lists 

are not meant to be exhaustive, and EPA does not individually identify each and every commenter who 

made a certain point in all instances, particularly in cases where multiple commenters expressed 

essentially identical arguments. 

EPA’s responses to comments are generally provided immediately following each comment summary. In 

some cases, EPA provided responses to specific comments or groups of similar comments in the 

preamble to the final rulemaking. Rather than repeating those responses in this document, EPA has 

referenced the preamble. 

Comments were assigned to specific section of this document based on an assessment of the principal 

subject of the comment; however, some comments inevitably overlap multiple subject areas. 
 

November 8, 2010 Subpart DD—Response to Comment Document 3 

Table of Contents 

1. Definition of the Source Category......................................................................................... 4 

1.1 Definition of a Facility—Track 1..................................................................................... 4 

1.2 Definition of a Facility—Track 2..................................................................................... 4 

1.3 All-in Provision and Boundary between Electricity Generation Facility and T&D 

Facility—Track 1 .................................................................................................................... 10 

1.4 All-in Provision and Boundary between Electricity Generation Facility and T&D 

Facility—Track 2 .................................................................................................................... 11 

1.5 Installation of Electrical Equipment at Electric Power Systems—Track 2 ................... 13 

1.6 De Minimis Exemption for Sealed-pressure Equipment—Track 1............................... 13 

1.7 De Minimis Exemption for Sealed-pressure Equipment—Track 2............................... 14 

1.8 Other (Definition of Source Category) ......................................................................... 16 

2. Reporting Threshold ........................................................................................................... 17 

2.1 Threshold Analysis—Track 1....................................................................................... 17 

2.2 Other (Reporting Threshold)........................................................................................ 18 

3. GHGs to Report—Track 1 .................................................................................................. 19 

4. Detailed GHG Emission Calculation Procedures/Equations............................................... 20 

5. Monitoring and QA/QC Requirements ................................................................................ 21 

5.1 Frequency of Weighing Cylinders—Track 1 ................................................................ 21 

5.2 Frequency of Weighing Cylinders—Track 2 ................................................................ 22 

5.3 Accuracy and Precision of Scales—Track 1................................................................ 23 

5.4 Accuracy and Precision of Scales—Track 2................................................................ 24 

5.5 Frequency of Scale Calibration ................................................................................... 25 

5.6 Other (Monitoring and QA/QC Requirements)—Track 1............................................. 25 

6. Data Reporting Requirements—Track 1............................................................................. 26 

7. Other Subpart DD Comments – Track 1............................................................................. 28 

8. Other Subpart DD Comments – Track 2............................................................................. 29 

Appendix A – List of Commenters Sorted by Submission Number............................................ 30 
 

November 8, 2010 Subpart DD—Response to Comment Document 4 

1. Definition of the Source Category 

1.1 Definition of a Facility—Track 1 

Relevant Bin Number 4.1.1 

Comment Summary 1.1-a: Two commenters (0407 and 0639) supported the concept of a reporting 

facility as an entire transmission and distribution system rather than an individual building, such as a gasinsulated substation. 

Response 1.1-a: EPA appreciates the commenters’ support of the proposed definition of a facility. 

Comment Summary 1.1-b: One commenter (0608) sought clarification on how to determine the 

boundary of a facility if numerous electric power retail companies have a common owner. The 

commenter asked if the common owner should be considered one facility, or whether each individual 

electric power retail company should be considered a separate facility. 

Response 1.1-b: The final rule clarifies that the facility boundary is based on a physical collection of 

equipment that functions as an integrated unit between two specified points: (1) the point(s) at which 

electric energy is obtained by the facility from an electricity generating unit or a different electric power 

transmission or distribution entity that does not have a common owner and (2) the point(s) at which the 

customer(s) or another electric power transmission or distribution entity that does not have a common 

owner receives the electric energy. Therefore, numerous electric power retail companies would only be 

considered one reporting facility if they are electrically linked through transmission and distribution lines 

in a continuous manner without being separated by electric power entities with a different owner. 

It should also be noted that for purposes of the reporting threshold, if distinct facilities have a common 

owner and the total nameplate capacity of all the facilities with the common owner exceeds 17,820 

pounds, then each facility must report emissions even if the nameplate capacity of an individual facility is 

less than 17,820 pounds. 

Comment Summary 1.1-c: Commenters 0624, 1021, and 1080 stated that reporting should be 

corporate-level to ensure that the largest potential emitters of SF6 are covered by the rule as well as to 

ensure accurate reporting. The commenters argued that corporate-level reporting will minimize the 

burden among owners and operators of electric power systems in determining what collections of 

electrical equipment constitute each electric power system. 

Response 1.1-c: See the Subpart DD Final Preamble, Section III, “Summary of Comments and 

Responses” for EPA’s response on corporate-level reporting. 

 

1.2 Definition of a Facility—Track 2 

Relevant Bin Number 4.1.1 

Comment Summary 1.2-a: EPA requested comment on whether it would be appropriate to use the 

Regional Greenhouse Gas Initiative (RGGI) definition of a transmission and/or distribution entity for 

assistance in defining an electric power system facility. RGGI defines a transmission and/or distribution 

entity as ‘‘the assets and equipment used to transmit and distribute electricity from an electric generator 

to the electrical load of a customer. Includes all related assets and equipment located within the service 

territory of the entity, defined as the service territory of a load-servicing entity specified by the applicable 

state regulatory agency.” Commenters 0075, 0086, 0088, 0109, and 0133 did not think the RGGI 

definition is appropriate for use in the definition of a facility for Subpart DD. Commenter 0075 considered 

the EPA definition more “specific and definitive.” Commenter 0088 considered EPA’s proposed definition 

to be generally more consistent with national industry standards than the RGGI definition. 
 

November 8, 2010 Subpart DD—Response to Comment Document 5 

Response 1.2-a: EPA appreciates the comments regarding the appropriateness of the RGGI definition of 

a transmission and/or distribution entity. EPA did not incorporate the RGGI definition into the definition of 

a facility for this subpart due to the ambiguity involved with the definition and the lack of support of the 

RGGI definition among commenters. 

Comment Summary 1.2-b: Six commenters (0075, 0088, 0097, 0098, 0115, 0128) generally agreed 

with the system-wide facility concept contained in EPA’s proposed definition of an electric power system 

facility. Commenter 0075 noted that it is reflective of the way the commenter has reported emissions 

under EPA’s SF6 Emission Reduction Partnership for Electric Power Systems. 

Response 1.2-b: EPA has retained the system-wide facility concept as part of the facility definition for 

this subpart. 

Comment Summary 1.2-c: EPA proposed the following as part of the language relating to the definition 

of a facility: “Reporting by the electric power system would comprise all gas-insulated equipment located 

between the point of generation and the point at which the ultimate customer receives the electricity.” 

Commenters 0075 and 0088 requested that the reference to “ultimate” customer be removed from the 

language since many utilities and electric power providers do not provide electric power directly to the 

ultimate consumer, but rather to a different utility or electric power provider. Commenter 0075 explained 

that removing the word “ultimate” from the physical description of an electric power system would clarify 

that there might be numerous distinct facilities from the point at which electric power is generated to the 

point at which electric power is provided to the ultimate consumer. 

Response 1.2-c: EPA acknowledges that the proposed language would not be appropriate for cases in 

which an electric power entity provides electricity to another electric power entity rather than the ultimate 

retail customer. EPA has removed reference to the “ultimate customer” in the final rule and has clarified 

that the downstream boundary of the facility is “the point(s) at which the customer(s) or another electric 

power transmission or distribution entity that does not have a common owner receives the electric 

energy.” 

Comment Summary 1.2-d: Commenter 0083 stated that the proposed language describing electric 

power systems as equipment “operated as an integrated unit by one electric power entity or several 

entities that have a single owner" could be interpreted to mean that one parent company would have to 

report emissions for all its subsidiaries, which would not be desirable for the commenter given its 

ownership structure. The commenter explained that it is a subsidiary company with its own board of 

directors that is distinct from its parent company’s other subsidiaries, and thereby thought each 

subsidiary should be allowed to report separately. 

Response 1.2-d: : The final rule clarifies that the facility boundary is based on a physical collection of 

equipment that functions as an integrated unit between two specified points: (1) the point(s) at which 

electric energy is obtained by the facility from an electricity generating unit or a different electric power 

transmission or distribution entity that does not have a common owner and (2) the point(s) at which the 

customer(s) or another electric power transmission or distribution entity that does not have a common 

owner receives the electric energy. Therefore, numerous subsidiaries would only be considered one 

reporting facility if they are electrically linked through transmission and distribution lines in a continuous 

manner without being separated by electric power entities with a different owner. 

. See Subpart DD Final Preamble, Section III, “Summary of Comments and Responses” for EPA’s 

additional discussion of the final Definition of a Facility language. 

Comment Summary 1.2-e: Seven commenters (0083, 0087, 0097, 0098, 0101, 0127, 0133) argued that 

reporting should be based on the ownership of equipment (frequently referred to in comments as 

corporate-level reporting) to ensure accurate reporting, reduce ambiguity regarding what collections of 

equipment constitute facilities, and reduce the overall burden of reporting. Commenters 0083, 0087, and 
 

November 8, 2010 Subpart DD—Response to Comment Document 6 

0133 considered the term “operated as” in the proposed definition of a facility to be ambiguous since the 

operation of electrical equipment can mean many different things. Commenter 0083 thought that 

“operated as” could be interpreted to mean the performance of maintenance activities and argued that 

the entity responsible for performing maintenance activities on equipment should not be responsible for 

reporting emissions from that equipment since the entity has no power to make decisions regarding the 

purchase or replacement of the equipment. 

Commenter 0087 acknowledged that corporate-level reporting can lead to ambiguities if there are 

multiple owners of equipment. To avoid this potential ambiguity in multiple-owner situations, commenters 

0087 and 0101 suggested that reporting be based on whichever owner is responsible for the 

maintenance of the equipment. 

Commenter 0133 stated that “corporate reporting would allow an entity to determine quickly and 

accurately what equipment should be counted toward the reporting threshold (that which it owns) and 

then report fully the emissions related to that equipment (based on service and maintenance records). It 

also would eliminate any confusion that may be caused by introducing operational relationships into the 

definition of ‘electric power system’.” 

Commenter 0133 agreed with EPA that the entity responsible for equipment service and maintenance 

activities is most capable of accurate data collection and compiling, but the commenter argued this notion 

supports reporting based on ownership since the owners have the obligation to service and maintain their 

equipment. 

Response 1.2-e: See the Subpart DD Final Preamble, Section III, “Summary of Comments and 

Responses” for EPA’s response on corporate-level reporting. To avoid confusion, EPA has removed the 

term “operated as” from the definition of facility. The definition of facility in the final rule refers to 

equipment that “is owned, serviced, or maintained by a single electric power transmission of distribution 

entity (or multiple entities with a common owner).” The phrase “owned, serviced, or maintained” as used 

in the definition of facility is not intended to allow or suggest segmenting portions of a system for the 

purpose of avoiding General Provisions (40 CFR 98.2 - 98.4), the reporting requirements that are 

applicable to all owners and operators associated with the facility.

Comment Summary 1.2f: Commenters 0127 and 0133 interpreted the definition of a facility proposed by 

EPA to mean that a single facility constitutes all generation, transmission, or distribution assets that are 

operated as an integrated unit even if different companies are responsible for the generation, 

transmission, and distribution of the electricity. The commenters expressed concern that the proposed 

facility definition will lead to confusion and inaccurate emission reports if numerous companies have to 

share data in order to calculate emissions. 

Response 1.2-f: To avoid confusion, EPA has removed the term “operated as” from the definition of 

facility. Instead, the definition refers to equipment that “functions as” an integrated unit, and that is 

owned, serviced, or maintained by a single electric power transmission or distribution entity. The final 

rule clarifies that the facility boundary is based on a physical collection of equipment that functions as an 

integrated unit, that is owned, serviced or maintained by a single electric power transmission or 

distribution entity (or multiple entities with a common owner), and that is located between two specified 

points: (1) the point(s) at which electric energy is obtained by the facility from an electricity generating 

unit or a different electric power transmission or distribution entity that does not have a common owner 

and (2) the point(s) at which the customer(s) or another electric power transmission or distribution entity 

that does not have a common owner receives the electric energy. Therefore, numerous electric power 

retail companies would only be considered one reporting facility if they are electrically linked through 

transmission and distribution lines in a continuous manner without being separated by electric power 

entities with a different owner. 

Comment Summary 1.2-g: Commenter 0096 requested that reporting be required by whichever entity 

directly owns and operates a collection of equipment. The commenter elaborated as follows, “For 

example, at a power plant where most of the switchyard is owned by a local distribution company (LDG), 

the LDG would report on the equipment that it operates as part of its overall T&D system SF6 reporting. 
 

November 8, 2010 Subpart DD—Response to Comment Document 7 

To the extent that the power plant operator manages any SF6 containing equipment at the same power 

plant, the power plant operator would report SF6 emissions from any equipment that it manages at the 

facility as part of its power plant facility-level reporting. However, the power plant operator would only 

report SF6 emissions for equipment it owns as part of its facility report if the facility would otherwise 

exceed the 25,000 tonne Mandatory Reporting Rule (MRR) reporting threshold for the facility.”

Response 1.2-g: The commenter’s proposal may be suitable for certain ownership and operational 

relationships. However, the definition of a facility for this subpart must be applicable to scenarios in which 

there are multiple owners or complex ownership and operational relationships involved with specific 

pieces equipment. EPA’s final definition of a facility is based on a physical collection of equipment 

located between two specified points, where the equipment is owned, serviced, or maintained by a single 

electric power entity (or multiple entities with a common owner). Per the General Provisions (40 CFR 

98.2 - 98.4), the reporting requirements are applicable to all owners and operators associated with the 

facility. See Subpart DD Final Preamble, Section III, “Summary of Comments and Responses” for 

additional discussion of the final Definition of a Facility language. 

Comment Summary 1.2-h: Commenter 0098 recommended the following edits to EPA’s proposed 

facility definition: 

EPA proposes to define the facility as follows: For purposes of this subpart, “facility” means an 

electric power system. Electric power system means the collection of SF6- and PFC-insulated 

equipment linked through electric power transmission or distribution lines and operated as an 

integrated unit by one electric power entity or several entities that have a single owner.

The commenter did not indicate why this edit should be made. 

Response 1.2-h: One of EPA’s intentions of the proposed language was to avoid situations where a 

parent company divides several subsidiary companies into separate facilities even though the subsidiary 

companies are located next to each other and operate electrical equipment that is interconnected by 

lines. Therefore, EPA used language to clarify that in this scenario, the electrical equipment throughout 

the subsidiary companies would be considered as part of a single facility. See Subpart DD Final 

Preamble, Section III, “Summary of Comments and Responses” for additional discussion of the final 

Definition of a Facility language. 

Comment Summary 1.2-i: Commenter 0101 indicated that EPA assumed a single electric power 

company always owns and operates all transmission and distribution equipment from the point of 

generation to the point at which customers ultimately receive electricity. The commenter noted that in 

some cases the owner of a piece of equipment is different from the operator of that piece of equipment, 

and the commenter is concerned that under the proposed definition of a facility, double-counting of 

emissions might occur from both the owners and operators of a piece of equipment reporting SF6

emissions from the equipment. 

Response 1.2-i: EPA acknowledges that the transmission and distribution equipment from the point of 

generation to the point at which customers ultimately receive electricity is not always owned and 

operated by a single electric power entity. EPA has clarified the boundaries of a Subpart DD facility in the 

final rule, and notes that there may be more than one distinct electric power system facility located from 

the point at which electricity is generated to the point at which the ultimate customer receives the 

electricity. See Subpart DD Final Preamble, Section III, “Summary of Comments and Responses” for 

additional discussion of the final Definition of a Facility language and clarification of reporting obligations. 

Comment Summary 1.2-j: Commenter 0101 argued that the following activities listed in the Monitoring 

and QA/QC requirements of 40 CFR §98.304 are not possible for an owner that does not operate or 

maintain a substation to conduct: (1) Ensure purchases from bulk gas distributors, Original Equipment 

Manufacturers, and off-site recycling are accounted for, (2) Ensure all cylinders are consistently weighed 

on certified scales, and (3) Provide proof that all scales are certified using NIST-traceable standards. 
 

November 8, 2010 Subpart DD—Response to Comment Document 8 

Response 1.2-j: Per the General Provisions (40 CFR 98.2 - 98.4), the reporting requirements are 

applicable to all owners and operators of a facility, but is up to the owners and operators to designate a 

representative who will be responsible for certifying, signing, and submitting GHG reports to EPA. This 

means that the owner, operator, or some combination of the two can conduct the monitoring and QA/QC 

measures listed in 40 CFR §98.304 for the facility. 

Comment Summary 1.2-k: Commenter 0109 supported the “operation” differentiation between electric 

power systems in the definition of a facility proposed by EPA and noted that it will be reporting on an 

“operation basis” under other subparts of the rule. 

Response 1.2-k: EPA appreciates the commenter’s support of the proposed definition of a facility. EPA 

did propose defining the facility boundaries on the basis of operation. However, due to the myriad 

relationships and operational structures among owners and operators of electric power systems as well 

as other issues raised by commenters, it was necessary to revise the facility definition to no longer 

differentiate facility boundaries solely on the basis of equipment operation. The definition now refers to 

equipment that is “owned, serviced, or maintained by” a single entity. To avoid confusion, EPA has 

removed the term “operated as” from the definition of facility. The definition of facility in the final rule 

refers to equipment that “is owned, serviced, or maintained by a single electric power transmission of 

distribution entity (or multiple entities with a common owner).” The phrase “owned, serviced, or 

maintained” as used in the definition of facility is not intended to allow or suggest segmenting portions of 

a system for the purpose of avoiding General Provisions (40 CFR 98.2 - 98.4), the reporting requirements 

that are applicable to all owners and operators associated with the facility. See Subpart DD Final 

Preamble, Section III, “Summary of Comments and Responses” for additional discussion of the final 

Definition of a Facility language. 

Comment Summary 1.2-l: Commenter 0115 requested flexibility in the EPA proposed definition of a 

facility “with respect to ownership, geographic service territories and business structure.” The commenter 

explained that there are multiple transmission assets located geographically within the boundaries of its 

service territories that it operates and maintains but does not own. The commenter would like the 

definition to “allow for segregation of assets by ownership or by operating entity in the event future 

operating practices and agreements with these third parties provide for a mechanism to segregate the 

affects these third-party assets have on [the commenter’s] overall emissions.” 

Response 1.2-l: EPA acknowledges that flexibility in the definition of an electric power system facility to 

segregate electrical equipment based on either ownership or operational control might provide 

convenience to certain SF6 equipment users under certain conditions. However, it is essential that the 

definition of a facility for this subpart clearly identify which collections of equipment constitute a facility 

and the points at which a facility begins and ends. This is essential because given the complex owner 

and operator relationships in the industry, allowing flexibility to define a facility differently depending on 

the situation encountered would greatly increase the risk of double-counting, underreporting, and/or 

confusion regarding the boundaries of a facility. To avoid confusion, EPA has removed the term 

“operated as” from the definition of facility. The definition of facility in the final rule refers to equipment 

that “is owned, serviced, or maintained by a single electric power transmission of distribution entity (or 

multiple entities with a common owner).” The phrase “owned, serviced, or maintained” as used in the 

definition of facility is not intended to allow or suggest segmenting portions of a system for the purpose of 

avoiding General Provisions (40 CFR 98.2 - 98.4), the reporting requirements that are applicable to all 

owners and operators associated with the facility. See Subpart DD Final Preamble, Section III, 

“Summary of Comments and Responses” for additional discussion of the final Definition of a Facility 

language. 

Comment Summary 1.2-m: Commenter 0119 suggested that “EPA clarify the applicability of the rule to 

clarify that ‘electric power systems’ are owned by electric distribution companies and that these 

companies would be responsible for reporting any emissions.” 
 

November 8, 2010 Subpart DD—Response to Comment Document 9 

Response 1.2-m: Per the General Provisions (40 CFR 98.2 - 98.4), the reporting requirements are 

applicable to all owners and operators of a facility, and it is up to the owners and operators to designate a 

representative who will be responsible for certifying, signing, and submitting GHG reports to EPA. 

Furthermore, the owners of electric power system facilities are not limited to electric distribution 

companies; there are myriad types of entities that can own an electric power system facility. For more 

information on the types of entities that can be considered owners of electric power system facilities as 

well as which entities are responsible for reporting emissions, please see Subpart DD Final Preamble, 

Section III, “Summary of Comments and Responses.” 

Comment Summary 1.2-n: Commenter 0120 suggested that the system boundary in the final rule 

include all equipment operated by a single owner, regardless of whether or not the equipment is 

electrically linked through lines. The commenter noted that it currently has a single unified information 

collection protocol for the three “affiliates” it operates even though the “affiliates” are not linked through 

lines. The commenter stated that having to report emissions for the three affiliates separately would be 

an incremental burden since it would necessitate establishing multiple information collection systems. 

Response 1.2-n: EPA acknowledges that in certain cases, it may be more convenient for affiliate 

companies to compile a single set of emission estimates and submit one report to EPA through a 

common owner. However, EPA examined a variety of reporting levels for Subpart DD and concluded that 

the facility definition must be based on a physical collection of equipment to avoid issues associated with 

corporate-level reporting (or reporting based solely on a common ownership). These issues include the 

complexity of corporate ownership structures, the potential for double-counting emissions when there are 

multiple owners associated with an electric power system, and the challenges of tracking and monitoring 

emissions for a facility over time if there are changes in the ownership. For more information on the 

EPA’s examination of options for defining a facility for Subpart DD, see Subpart DD Final Preamble, 

Section III, “Summary of Comments and Responses” as well as the TSD, located here: 

www.epa.gov/climatechange/emissins/ghgrulemaking.html 

Comment Summary 1.2-o: Commenter 0133 argued that the joint obligation for reporting between 

owners and operators in §98.3 will be confusing in practice if applied to Subpart DD since owners and 

operates are not equally capable of measuring emissions or defining clear facility boundaries for the 

source category. The commenter stated that in order to avoid confusion and inaccurate emission reports, 

EPA needs to clarify “how this joint reporting obligation would be structured.” 

Response 1.2-o: The details of the joint reporting obligation between owners and operators are provided 

in the General Provisions (40 CFR 98.2 - 98.4). According to the General Provisions, the reporting 

requirements are applicable to all owners and operators of a facility. But it is up to the owners and 

operators to designate a representative who will be responsible for certifying, signing, and submitting 

GHG reports to EPA. Therefore, the owners and operators of a facility can coordinate in measuring 

emissions and confirming the facility boundary if they are indeed “not equally capable of measuring 

emissions from a facility or defining clear facility boundaries.” 

Comment Summary 1.2-p: Commenter 0088 was supportive of how EPA’s proposed definition of a 

facility recognized the physical interconnection and operational interdependence of system components, 

but was concerned about EPA’s assertion that “regardless of the role that operation or ownership plays in 

the final source category definition, the obligation to report will apply to both owners and operators.” The 

commenter thought this could lead to double-counting of emissions. Commenter TRANS-DC-04 (2010) 

also expressed concern that holding both owners and operators of electric power systems responsible for 

SF6 may lead to double-counting of emissions.” 

Response 1.2-p: The details of the joint reporting obligation between owners and operators are provided 

in the General Provisions (40 CFR 98.2 - 98.4). According to the General Provisions, the reporting 

requirements are applicable to all owners and operators of a facility. But it is up to the owners and 

operators to designate a representative who will be responsible for certifying, signing, and submitting 

GHG reports to EPA. Since the designated representative is selected by an agreement binding on all the 
 

November 8, 2010 Subpart DD—Response to Comment Document 10 

owners and operators of the facility, then the designated representative should be fully capable of 

ensuring that the facility emissions were measured properly and that emissions were not double-counted.

Comment Summary 1.2-q: Commenter TRANS-DC-04 (2010) thought that in certain cases, the myriad 

of ownership and operational relationships for electric power systems across regions and companies 

might not be “amenable” to reporting at the system-wide level. 

Response 1.2-q: The mass-balance monitoring methods for subpart DD, which are based on the IPCC 

Tier 3 method of measuring emissions from electric power systems, require monitoring of emissions for 

an entire electric power system and are not conducive for measuring emissions for a specific piece of 

equipment or single substation within a larger electric power system. Given the myriad ownership and 

operational relationships in the electric power system industry, EPA acknowledges that coordination 

might be required among distinct owners and operators in order to ensure that emissions are measured 

accurately and reliably. For more information on EPA’s rationale for system-wide reporting, please see 

the TSD located here: www.epa.gov/climatechange/emissins/ghgrulemaking.html 

1.3 All-in Provision and Boundary between Electricity Generation Facility and T&D 

Facility—Track 1 

Relevant Bin Number 4.1.1.1 

Comment Summary 1.3-a: Twelve commenters (0407, 0455, 0584, 0597, 0618, 0624, 0661, 0725, 

1021, 1080, 1566, 1741) requested clarification and/or expressed concern over the general reporting 

requirement located in §98.2(a)(2) that any subpart D electric generating unit facility above the reporting 

threshold would be required to report emissions for all source categories that are located at the facility, 

including SF6 emissions under subpart DD. 

Five commenters (0407, 0584, 1021, 1080, 1741) stated that including SF6 emissions from electric 

equipment in subpart D facility emission reports could lead to double-counting of emissions since 

facilities in subpart DD might encompass electrical equipment that is located at a subpart D facility. 

Response 1.3-a: Based on the concerns expressed by commenters, EPA has made alterations to the 

Reporting Threshold language in §98.301 so that a subpart D electric generating unit facility would only 

be required to report emissions associated with the Electrical Transmission and Distribution Equipment 

Use source category if the amount of SF6 and PFC-insulated equipment within the subpart D facility 

exceeds the reporting threshold for subpart DD, which is 17,820 lbs of SF6 and PFC nameplate capacity. 

EPA expects that in general, the subpart D facility will not independently meet this threshold and thus is 

unlikely to incur the reporting obligation and the risk of double-counting emissions. For more information, 

please see the Subpart DD Final Preamble, Section III, “Summary of Comments and Responses.” 

Comment Summary 1.3-b: Seven commenters (0407, 0455, 0597, 0624, 1021, 1080, 1741) argued that 

it would be very difficult to accurately measure SF6 emissions from only electrical equipment at a electric 

generating unit that is part of an integrated utility since the SF6 stocks that services this equipment are 

often stored and tracked in a central storage area for the integrated utility. In this scenario, the SF6 stored 

at the central storage areas would be used to service equipment throughout the integrated transmission 

and distribution system, not just a single electric generating unit. These commenters noted that the massbalance is only an efficient and effective method for measuring emissions at the system-level and not for 

a single physical location such as an electric generating unit facility. 

Response 1.3-b: As explained in section §98.301-Reporting Threshold of the final rule, Subpart DD 

emissions occurring at an electric generating unit (EGU) facility would only need to be reported if the 

nameplate capacity of the SF6 and PFC insulated equipment at the facility exceeds the subpart DD 

threshold of 17,820 pounds of nameplate capacity. EPA does not expect that many EGU facilities will 

have this much SF6 and PFC-insulated equipment. If an EGU does exceed the subpart DD threshold, 
 

November 8, 2010 Subpart DD—Response to Comment Document 11 

then conducting mass-balance emissions monitoring at this facility, as required by subpart DD, should be 

a similar process and similar burden as conducting the mass-balance monitoring methods for non-EGU 

facilities. For more information, please see the Subpart DD Final Preamble, Section III, “Summary of 

Comments and Responses.” 

Comment Summary 1.3-c: Commenters 0624, 1021, and 1741 specifically requested clarification on 

reporting responsibilities between different owners in certain cases where substations are “co-located” 

with electricity generation facilities. As explained by commenter 0624, “If co-located substations and 

other supporting infrastructure included SF6-containing equipment owned by the same electric generating 

facility owner, then it appears that the proposed rule would require any SF6 emissions to be included in 

the reporting by the generating facility owner. However, if the substation and other supporting 

infrastructure is owned by another entity (i.e., not the owner of the generating facility), it is unclear who 

would be responsible for reporting any SF6 emissions emanating from the co-located substations and 

other supporting structure, the owner of the generating facility or the owner of the SF6 -containing 

equipment.” 

Response 1.3-c: According to the General Provisions (40 CFR 98.2 - 98.4), the reporting requirements 

are applicable to all owners and operators of a facility (although the actual emission report is certified, 

signed, and submitted to EPA by the representative designated by the owners and operators of the 

facility). If the SF6 insulated equipment co-located at an electricity generating unit is part of a subpart DD 

electric power system facility, then the owners and operators of the electric power system facility would 

report emissions for that equipment. In the case of an electricity generating unit that must report subpart 

DD emissions for SF6 -insulated equipment co-located at the facility (note that this would only be required 

if the EGU had more than 17,820 pounds of SF6 and PFC insulating equipment located within its facility), 

the emissions report for the EGU facility would need to include emissions for any SF6 insulated 

equipment located within the facility, regardless of whether the owners and operators of the EGU are the 

same as the owners and operators of the SF6-insulated equipment. See subpart A §98.2-98.4 and 

subpart D §98.301 for more information. 

Comment Summary 1.3-d: Commenters 0624, 0479, and 0547 sought clarification on whether a 

Subpart DD facility that falls above the threshold would be required to report emissions from a source 

category that is located at the same site as the Subpart DD facility. Commenters 0624 and 0479 asked 

whether a Subpart DD facility would be required to report emissions from combustion sources on site if 

under the same ownership control and, if so, whether there would be any emissions or heat input size 

threshold for determining applicability. Commenters 0624, 0479, and 0547 recommended that portable 

equipment or generating units designated as emergency generators should be exempted from Subpart 

DD facility emission reports. 

Response 1.3-d: The facility definition for subpart DD (see 40 CFR §98.307) is unique from the definition 

of a facility used in other subparts (see General Provisions, 40 CFR 98.2 - 98.4) in that the electric power 

system facility only encompasses electric transmission and distribution equipment and servicing 

inventory insulated with or containing SF6 or PFCs. The electric power system facility does not include 

co-located emission sources. However, per General Provisions 40 CFR 98.2 - 98.4, the facility must 

report for all applicable source categories listed in Table A—3 and Table A—4 of subpart A that are 

triggered by the facility.. 

1.4 All-in Provision and Boundary between Electricity Generation Facility and T&D 

Facility—Track 2 

Relevant Bin Number 4.1.1.1 

Comment Summary 1.4-a: Seven commenters (0088, 0096, 0097, 0126, 0127, 0133, TRANS-DC-04 

(2010)) requested clarification and/or expressed concern over the general reporting requirement located 

in § 98.2(a)(2) that any subpart D electric generating unit facility above the reporting threshold would be 
 

November 8, 2010 Subpart DD—Response to Comment Document 12 

required to report emissions for all source categories that are located at the facility, including SF6

emissions under Subpart DD. The commenters argued that this would lead to ambiguities in reporting 

responsibilities and impose an unreasonable burden while only capturing a relatively small amount of 

emissions. 

Commenters 0096 and 0126 requested a de minimis exception for SF6 -insulated equipment for electric 

generating unit emission reports. Commenter 0096 stated “in the case of power plants, that a de minimis 

exemption from SF6 reporting should be explicitly allowed for the power plant facility since the vast 

majority of SF6 is typically used in T&O applications that will be reported on by LOCs as part of their 

system-wide reporting of SF6. As an alternative, simplified engineering estimation techniques should be 

allowed at facilities with de minimis SF6 emissions. Overall, in the context of the magnitude of CO2

emissions from power plants, SF6 emissions are negligible. As an example, we estimate that SF6

emissions at the largest fossil plant operated by [the commenter] that SF6 emissions were less than 0.1% 

of the facility's total GHG emissions in 2008.” Commenter 0126 recommended either a complete de 

minimis exception or a separate threshold of 17,820 lbs of SF6 nameplate capacity at the electric 

generating facility to trigger SF6 emissions reporting. 

Commenter 0097 cited the complexity of electric generation and electricity transmission ownership 

structures as a major impediment to accounting for SF6 emissions from switchyards at electricity 

generation facilities and recommends the following: “1. Require transmission and distribution entities to 

report SF6 emissions for the equipment that it owns within the switchyard, and 2. Require electric 

generation facility entities to report SF6 emissions for the equipment that it owns within the switchyard. 

However, EPA should identify SF6 emissions as de minimis compared to stationary combustion 

greenhouse gas emissions on site, and permit the use of alternative calculation methodologies (such as 

engineering calculations) to estimate the emissions of SF6 containing equipment rather than the mass 

balance methodology.”

Commenter 0098 supported the general recommendations from commenter 0097, but offered slightly 

different recommendations: “1. Require transmission/distribution and electric generating entities to 

separately report SF6 emissions for the equipment that they own within the switchyard, and 2. Allow 

electric generation facility entities to report SF6 emissions for the equipment that it owns within the 

switchyard/contiguous power block with utilization of alternative calculation methodologies (such as 

engineering calculations) to estimate the emissions of SF6 containing equipment rather than the mass 

balance methodology. EPA should identify SF6 emissions as de minimis compared to stationary 

combustion greenhouse gas emissions on-site. (Also, keep the 17,820 pound minimum by reporting 

entity.) Reporters should be allowed the option to report per mass balance where the incoming inventory 

and the returning bottles are weight certified by the suppliers/recyclers. Suppliers of equipment or bottles 

must supply certified gas weight to the purchaser 3. Electric generation facilities and T&D entities that are 

owned by the same parent company but operated as distinct companies should be allowed to report at 

the distinct company level.” 

Response 1.4-a: EPA agrees that reporting subpart DD emissions as part of subpart D facility emission 

reports would, in most cases, only capture emissions that are minor and/or already captured as part of a 

subpart DD facility emission report. However, in some cases there might be considerable SF6 emissions 

that occur at an EGU facility that would not be accounted for if subpart D facilities were not required to 

report any subpart DD emissions that occur. To balance the risk of unaccounted emissions with the 

burden associated with reporting subpart DD emissions for distinct EGU facilities, EPA is only requiring 

that subpart D facilities include subpart DD emissions in their emission reports if the total nameplate 

capacity of SF6 and PFC containing equipment located within that facility exceeds 17,820 pounds. 

In terms of the reporting responsibility for SF6 -insulated equipment located at an EGU facility, the 

General Provisions (40 CFR 98.2 - 98.4) dictate that the reporting requirements are applicable to all 

owners and operators of a facility (although the actual emission report is certified, signed, and submitted 

to EPA by the representative designated by the owners and operators of the facility). If the SF6 insulated 

equipment co-located at an electricity generating unit is part of a subpart DD electric power system 

facility, then the owners and operators of the electric power system facility would report emissions for that 

equipment. In the case of an electricity generating unit that must report subpart DD emissions for SF6 -
 

November 8, 2010 Subpart DD—Response to Comment Document 13 

insulated equipment co-located at the facility (i.e., an EGU with more than 17,820 pounds of SF6 and 

PFC insulating equipment located within its facility), the emissions report for the EGU facility would need 

to include emissions for any SF6 insulated equipment located within the facility, regardless of whether the 

owners and operators of the EGU are the same as the owners and operators of the SF6 -insulated 

equipment. See subpart A §98.2-98.4 and subpart D §98.301 for more information. 

1.5 Installation of Electrical Equipment at Electric Power Systems—Track 2 

Relevant Bin Number 4.1.3 

Comment Summary 1.5-a: Five commenters (0081, 0094, 0096, 0097, 0125) recommended that a 

Subpart DD facility should not be responsible for emissions from new equipment being installed at the 

Subpart DD facility until the equipment has been transferred to the equipment user by the electrical 

equipment manufacturer. Commenter 0081 recommended that the point of transfer be when the 

equipment has been “received, inspected, and accepted by the utility and the title has been transferred.” 

Commenter 0096 stated that “regarding GIS equipment assembled on-site by a manufacturer, [the 

commenter] requests that the manufacturer be responsible for any SF6 reporting up until the point in time 

that the end user takes final acceptance of the equipment (i.e., at the point in time when the end user 

confirms that all contract agreements have been met and takes ''final delivery" of the completed GIS 

equipment). For shipped, pre-assembled GIS equipment, the end user should take responsibility for SF6

reporting at the point in time at which the title for the equipment transfers to the end user.” Commenter 

0125 recommends the point of transfer be defined as “the point when the equipment warranty is activated 

or when the title is transferred or another such point described in the contract between the customer and 

the equipment manufacturer or third party.” 

Response 1.5-a: EPA has confirmed that some equipment is not installed by the purchaser of the 

equipment. For example gas insulated substations are typically assembled by the manufacturer onsite 

and it can take several months to complete assembly, inspection, and final acceptance and 

commissioning. For this reason, gas accounting is best done by the entity that is commissioning the 

equipment and handling the gas that will be installed into the equipment.EPA agrees with the 

commenters that the Subpart DD facilities should not be responsible for reporting emissions from new 

equipment being installed (or from the installation process itself) at the Subpart DD facility until the title to 

the equipment has been transferred to the equipment user by the electrical equipment manufacturer. 

EPA has included the following language in Subpart DD §98.302—GHGs to report: “For acquisitions of 

equipment containing or insulated with SF6 or PFCs, you must report emissions from the equipment after 

the title to the equipment is transferred to the electric power transmission or distribution entity.” 

 

1.6 De Minimis Exemption for Sealed-pressure Equipment—Track 1 

Relevant Bin Number 4.1.4 

Comment Summary 1.6-a: Eight commenters (0407, 0479, 0547, 0624, 1021, 1080, 1569, 1741) 

requested clarification on whether there is a de minimis exception for hermetically sealed-pressure 

equipment that is not intended to be serviced during its lifetime. Seven commenters (0407, 0479, 0547, 

0624, 1021, 1080, 1741) specifically argued for a de minimis exception in the context of the Data 

Reporting Requirement Nameplate capacity of equipment containing SF6. Commenters 0407 and 1741 

noted that a de minimis exception only for the total system-wide nameplate capacity reporting 

requirement would not exclude hermetically sealed-pressure equipment from being captured in the massbalance emissions monitoring method since the system-wide nameplate capacity is not an input to the 

mass-balance equation. 

Commenter 1569 argued for a general de minimis exception throughout Subpart DD. In addition to 

arguing for a de minimis exception for hermetically sealed-pressure equipment, commenter 1569 also 

argued that any equipment with less than 15 pounds of nameplate capacity should be exempted from all 

Subpart DD inventory and emission reporting requirements. 

Commenter 1741 suggested that if there is no de minimis exception for hermetically sealed-pressure 

equipment, there should be an option for facilities to estimate the internal volume for a typical piece of 
 

November 8, 2010 Subpart DD—Response to Comment Document 14 

sealed-pressure equipment within different equipment categories, and then use the internal volumes to 

assume a maximum nameplate capacity amount for equipment within each category. 

Response 1.6-a: EPA concurs that the burden associated with performing a bottom-up assessment to 

determine the nameplate capacity of each piece of sealed-pressure equipment within an electric power 

transmission and distribution facility is high when compared to the benefits of performing such an 

assessment. As a result, EPA has excluded sealed-pressure equipment from the data reporting 

requirement for total facility-wide nameplate capacity existing as of the beginning of the year. However, 

the potential for emissions from sealed-pressure equipment due to catastrophic events or equipment 

disposal still makes it important to document emissions from sealed-pressure equipment, especially for 

facilities that specialize in electricity distribution. EPA has clarified that SF6 arriving inside newly acquired 

sealed-pressure equipment must still be included as part of the SF6 acquisitions input of the massbalance equation, and sealed-pressure equipment that is new or retired must still be considered as a 

change to the nameplate capacity in the mass-balance equation. 

For the purpose of determining which equipment must be included in the overall nameplate capacity 

threshold, EPA considers it more appropriate to distinguish equipment based on whether it is hermetically 

sealed rather than whether it is above or below a specified nameplate capacity threshold (such as 15 

pounds as suggested by commenter 1569). This is because it can be burdensome to obtain the exact 

nameplate capacity of relatively small distribution equipment whereas it is generally straightforward to 

determine whether the equipment is sealed-pressure equipment. Distinguishing equipment based on 

whether it is sealed-pressure or closed-pressure reduces the potential error associated with determining 

whether a piece of equipment should be included in the system-wide nameplate capacity estimate. 

Sealed pressure equipment generally contains anywhere from a few ounces to 15 pounds of SF6. 

1.7 De Minimis Exemption for Sealed-pressure Equipment—Track 2 

Relevant Bin Number 4.1.4 

Comment Summary 1.7-a: Ten commenters (0075, 0083, 0086, 0096, 0097, 0098, 0109, 0120, 0126, 

0133) recommended a de minimis exception for hermetically sealed-pressure equipment in the Subpart 

DD source category. Commenters 0075 and 0083 noted that emissions from this type of equipment are 

very low—except in the case of catastrophic failure—and that the equipment does not typically require 

servicing or recharging of SF6 over its operational lifetime. 

Commenter 0075 asserted that “including this equipment in the definition of a ‘facility’ simply complicates 

reporting and verification with essentially no added benefit or value to the reporting rule or the 

compilation of total SF6 emissions.” 

Since hermetically sealed-pressure equipment is non-serviceable, Commenter 0083 recommended 

excluding the equipment by using the following language in §98.302—GHGs to Report: “You must report 

total SF6 and PFC emissions (including emissions from fugitive equipment leaks, installation, servicing, 

equipment decommissioning and disposal, and from storage cylinders) from the following types of 

serviceable equipment: (a) Gas-insulated substations (b) Circuit breakers (c) Switchgear (d) Gasinsulated lines (e) Electrical transformers.” 

Commenter 0086 recommended three options for reducing the burden associated with inventorying 

hermetically sealed-pressure equipment for the §98.302 Data Reporting Requirement for system-wide 

nameplate capacity of equipment containing SF6. The three recommended options provided by 

commenter 0086 were as follows: “(1) establish a de-minimus capacity for specific equipment below 

which the equipment would be exempt from the inventory requirements, (2) clarify that, after an initial 

inventory, smaller pieces of equipment do not need to be included in annual inventories, or (3) for smaller 

equipment, such as switches, allow affected entities the option of estimating the volume of small 

equipment and assuming a maximum nameplate amount of SF6 for each one.” 

Commenters 0094 and 0096 recommended excluding “small distribution equipment, containing less than 

35 pounds of SF6” from reporting. Commenter 0094 did not think that tracking small equipment is 
 

November 8, 2010 Subpart DD—Response to Comment Document 15 

efficient, and notes that while approximately 43% of its circuit breakers have less than 35 lbs of SF6, 

distribution equipment accounts for only 2% of its total SF6 emissions. 

Commenter 0120 recommended a de minimis exception for equipment containing less than 15 pounds, 

or a complete reporting exception for all distribution equipment. Commenter 0133 recommended a de 

minimis exception for sealed-pressure equipment in the context of the §98.302 Data Reporting 

Requirement for system-wide nameplate capacity of equipment containing SF6, and noted that this would 

not exclude hermetically sealed-pressure equipment from being captured in the mass-balance emissions 

monitoring method since the system-wide nameplate capacity is not an input to the mass-balance 

equation. 

Response 1.7-a: Comments regarding the inclusion of sealed-pressure equipment in reporting 

requirements that were received after EPA’s second Subpart DD proposal in 2010 were very similar to 

the comments received in EPA’s first Subpart DD proposal from 2009. Please see Response 1.6-a or 

Subpart DD Final Preamble, Section III, “Summary of Comments and Responses” for EPA’s response. 

Comment Summary 1.7-b: Commenter 0096 thought that tracking of SF6 from hermetically sealedpressure equipment “would be better performed by upstream reporting of SF6 by original equipment 

manufacturers (OEMs) where it would be much easier for OEMs to report a complete picture of small 

sealed equipment sold in the United States.” Commenter 0097 supports this notion by stating that 

hermetically sealed-pressure equipment is a case where “upstream regulation of SF6 is more effective, 

specifically at the original equipment manufacturer.” 

Response 1.7-b: Under Subpart SS—Electrical Equipment Manufacture and Refurbishment and 

Manufacturing of Electrical Components, OEMs must monitor emissions that occur from the manufacture 

of sealed-pressure as well as include sealed-pressure equipment in their data reporting requirements. 

However, this does not render the inclusion of sealed-pressure equipment in subpart DD reporting 

requirements unnecessary. The potential for emissions from sealed-pressure equipment due to 

catastrophic events or equipment disposal still makes it important for electrical equipment users to 

document emissions from sealed-pressure equipment, especially for Subpart DD facilities that are highly 

involved in electricity distribution. While emissions from sealed-pressure equipment must be monitored 

by Subpart DD facilities, EPA has removed the requirement for including sealed-pressure equipment as 

part of the data reporting requirement for total facility-wide nameplate capacity existing as of the 

beginning of the year. 

Comment Summary 1.7-c: Commenter 0109 provided separate recommendations for three different 

types of sealed pressure equipment: transmission, distribution—SF6 gas insulated, and distribution—SF6

gas insulated/interrupting. The commenter thought it was reasonable for sealed-pressure transmission 

equipment to be included in reporting since the typical mass of SF6 in each piece is between 5 and 18 

pounds, and “there are facilities with a good quantity of devices (typically identified as circuit switchers) 

yielding significant nameplate capacity.” The commenter stated that the “interrupting type” used in 

distribution applications has not been available in the U.S. for many years, and should only be included in 

reporting if this type of equipment represents more than 0.5% of total nameplate capacity. Lastly, the 

commenter stated that reporting on “distribution equipment with SF6 as an insulating gas at very low 

pressure (typically less than 1 atmosphere)” would be a significant issue since this equipment holds such 

small amounts of SF6 and the “administrative burden of estimating the nameplate capacity and tracking 

this distributed distribution equipment is extremely high.” 

Response 1.7-c: EPA appreciates the commenter’s detailed delineation of the various types of sealedpressure equipment as well as the commenter’s thoughts on the appropriateness of including each type 

of sealed-pressure equipment in the Subpart DD reporting requirements. Due to the need for simplicity in 

knowing when to include a piece of equipment in the reporting requirements as well as the potential for 

emissions from sealed-pressure equipment used for electricity distribution, EPA is requiring that SF6

arriving inside all types of newly acquired sealed-pressure equipment must still be considered as part of 

the SF6 acquisitions input of the mass-balance equation, and all types of sealed-pressure equipment that 

is new or retired must be considered as a change to the nameplate capacity in the mass-balance 

equation. But in an effort to reduce the overall burden for affected entities, EPA has excluded all types of 
 

November 8, 2010 Subpart DD—Response to Comment Document 16 

sealed-pressure equipment from the data reporting requirement for total facility-wide nameplate capacity 

existing as of the beginning of the year. 

1.8 Other (Definition of Source Category) 

Relevant Bin Number: 4.1 

Track 1 

Comment Summary 1.8-a: Two commenters (0612, 1741) requested clarification on exactly what 

equipment is included in the Subpart DD source category. Commenter 0612 specifically requested 

clarification on whether scientific research equipment that contains SF6 would be included in the electrical 

equipment regulated in Subpart DD. Commenter 1741 sought clarification on whether processes that use 

SF6 as a testing gas would be regulated in Subpart DD. 

Response 1.8-a: The Subpart DD source category includes all SF6 and PFC insulated equipment and 

servicing inventory that is used within an electric power system. For a definition of the electric power 

system facility, see Subpart DD §98.307-Definitions. If the SF6-insulated equipment and servicing 

inventory discussed by the commenters are used within an electric power system, then the equipment 

and servicing inventory would be covered under Subpart DD even if the equipment is not listed in 

§98.307-Definition of the Source Category. 

The subpart A General Provisions (40 CFR 98.2 - 98.4) do exclude research and development activities 

from being covered by the source categories provided in the rule. Research and development activities 

are defined in subpart A as those activities conducted in process units or at laboratory bench-scale 

settings whose purpose is to conduct research and development for new processes, technologies, or 

products and whose purpose is not for the manufacture of products for commercial sale, except in a de 

minimis manner. 

Track 2 

Comment Summary 1.8-b: Commenter 0109 explained that the use of SF6 in transformers is not 

widespread due to largely unsuccessful experimental trials using SF6 insulated transformers. The 

commenter recommended that due to the high administrative burden for tracking and reporting this nonswitchgear equipment, EPA establish “a minimum threshold on quantity to trigger reporting (i.e. 2 or more 

transformers).” 

Response 1.8-b: Although the use of SF6 in electric power transformers might not be as widespread as 

SF6 use in other types of electrical equipment, there is still the potential for SF6 emissions from SF6-

insulated transformers that are actively in use in the United States today. Furthermore, SF6-insulated 

transformers are marketed to electrical equipment users in the United States, and it is unclear how much 

of this equipment will be utilized in the future. Due to the potential for emissions from electric power 

transformers currently in use as well as the potential for an increase in the use of these transformers, 

EPA is not providing reporting exceptions for SF6-insulated transformers in the Subpart DD source 

category.
 

November 8, 2010 Subpart DD—Response to Comment Document 17 

2. Reporting Threshold 

Relevant Bin Number 4.2 

Track 1 

Comment Summary 2-a: Commenter 0413 questioned why EPA “appears to be requiring reporting of 

very minor SF6 gas emissions when nameplate capacity exceeds 17,820 pounds, while a larger emission 

from electrical equipment with lower SF6 nameplate capacity equipment will be unreported.” 

Response 2-a: The 17,820 pound threshold was developed as a nameplate-based approximate of the 

25,000 metric tons of CO2 equivalent threshold. The nameplate capacity equivalent to a 25,000 metric 

ton of CO2 equivalent was estimated using data reported by Partners in EPA’s SF6 Emission Reduction 

Partnership for Electric Power Systems. EPA’s threshold analysis showed that the 17,820 pound 

nameplate capacity threshold would cover a small percentage of the total electric utilities in the United 

States (approximately 10%) while covering a large percentage of annual SF6 emissions from electric 

power systems in the United States (approximately 83 percent). A nameplate capacity-based threshold 

was chosen because it allows potential sources to determine whether they are above or below the 

threshold much quicker than if the sources had to measuring emissions for this determination, thereby 

reducing the burden for the industry as a whole. While it is possible that a facility with less than 17,820 

pounds of nameplate capacity has greater SF6 emissions than a facility with greater than 17,820 pounds 

of nameplate capacity, EPA’s analysis concluded that nameplate capacity is strongly correlated with SF6

emissions, more so than other parameters like high-voltage transmission miles. For more information on 

EPA’s threshold analysis, please see the TSD located here: 

www.epa.gov/climatechange/emissins/ghgrulemaking.html 

Comment Summary 2-b: Commenters 0551, 0479, and 0547 agreed with the 17,820 pounds of SF6

nameplate capacity threshold proposed by EPA for subpart DD. Commenters 0479 and 0547 noted that it 

allows potential sources to quickly determine whether they are covered. 

Response 2-b: EPA appreciates the commenters’ support of the reporting threshold. 

2.1 Threshold Analysis—Track 1

Relevant Bin Number 4.2.1 

Comment Summary 2.1-a: Commenter 0413 stated that “no peer review scientific evidence exists to link 

nameplate capacity with actual SF6 gas emissions or leakage.” The commenter disagreed with EPA’s 

method for calculating the 17,280 pounds of SF6 nameplate capacity threshold for subpart DD. 

Specifically, the commenter considered the use of 1999 weighted utility leak rates of SF6 to be inaccurate 

since utilities currently emit SF6 at lower rates than they did in 1999. The commenter thought a “more 

rational assumption would be leakage rates well below 1% annually.” 

Response 2.1-a: The relationship between nameplate capacity (how much SF6 equipment contains 

when full) and the amount of SF6 emissions that occur from equipment is not perfect; other factors such 

as equipment age and geographic location can have an impact on emissions. Nonetheless, EPA’s 

analysis showed that nameplate capacity is a strong correlate to SF6 emissions and stronger than other 

potential correlates such as high-voltage transmission miles. EPA used 1999 weighted leak rates from 42 

Partners of EPA’s SF6 Emission Reduction Partnership for Electric Power Systems (1999 was the first 

year that the Partnership received data) because it is assumed that utilities who have not participated in 

the Partnership activities have not achieved the emission reductions from 1999-2008 that have been 

achieved by Partners, and it was essential that a non-emissions based threshold be conservative enough 

to ensure that sources emitting more than 25,000 metric tons of CO2 equivalent were covered by the 

threshold. EPA does not consider the leakage rates of “well below 1% annually” to be a rational 

assumption since the average Partnership leak rates have never been below 4% since the inception of 

the Partnership. 
 

November 8, 2010 Subpart DD—Response to Comment Document 18 

2.2 Other (Reporting Threshold) 

Relevant Bin Number 4.2.2 

Track 1 

Comment Summary 2.2-a: Commenter 0547 stated that “EPA should recognize that nameplate 

capacity inventory of in-service power systems is achievable for distinct facilities such as substation sites 

but would be virtually impossible for most power systems in the transmission and distribution lines 

system.” 

Response 2.2-a: EPA is assuming the commenter is stating that it would be virtually impossible for an 

entity that transmits and distributes electricity to determine the entire system-wide nameplate capacity of 

all equipment within its electric transmission and distribution system. Contrary to the opinion of the 

commenter, many electric power entities in EPA’s SF6 Emission Reduction Partnership for Electric Power 

Systems have provided system-wide nameplate capacity estimates to EPA for all SF6-insulated 

equipment within the system except sealed-pressure equipment used for electricity distribution. 

Comment Summary 2.2-b: Commenter 1569 remarked that “There are some pieces of electrical 

equipment that do not list the capacity of SF6 in pounds on the nameplate, but rather give the pressure of 

SF6 in the system in pounds per square inch (psig). It is our recommendation that the EPA establish a set 

protocol to use to calculate the weight of SF6 in the equipment based on a set pressure and temperature 

when the weight is not explicitly listed on the nameplate.” 

Response 2.2-b: EPA understands that in some cases the capacity of a piece of equipment is not clearly 

affixed to the equipment itself. In these cases, EPA recommends contacting the original manufacturer of 

the equipment, who should be able to provide the nameplate capacity of the equipment. 

Track 2 

Comment Summary 2.2-c: Commenter 0126 stated that “EPA is proposing to add electric power 

systems to the list of "all-in" source categories in 40 CFR 98.2(a)(1). The reason for EPA's proposal is 

that electric power systems have a production capacity or gas consumption threshold rather than a CO2e 

emission threshold. Sources in the "all-in" category must report emissions from all source categories for 

which calculation methodologies are provided in any subpart of the rule.” The commenter questions why 

EPA would abandon the concept of a CO2e emission threshold for SF6 and PFC that existed in 2009 (for 

the initial proposal) and instead “consider in its current proposal a production capacity or a gas 

consumption threshold.” 

Response 2.2-c: The 17,820 pound nameplate capacity threshold for Subpart DD proposed in 2010 was 

the same threshold as proposed in 2009. The reason EPA is listing Subpart DD as an “all-in” category is 

because the threshold for Subpart DD is capacity-based rather than a CO2e emission threshold. EPA 

notes that if a facility contains either an “all-in” source category listed in §98.2(a)(1) or a source category 

listed in §98.2(a)(2) that triggers the 25,000 metric ton of CO2e threshold, the facility must report for all 

applicable source categories listed in Table A—3 and Table A—4 of subpart A that are triggered by the 

facility. But EPA also notes that an electric power system facility (as specifically defined in subpart DD) 

only encompasses electric transmission and distribution equipment and servicing inventory insulated with 

or containing SF6 or PFCs; as such, the electric power system facility boundaries do not extend to 

emission sources other than the electric transmission and distribution equipment and servicing inventory. 
 

November 8, 2010 Subpart DD—Response to Comment Document 19 

3. GHGs to Report—Track 1 

Relevant Bin Number 4.3 

Comment Summary 3-a: Commenter 0661 asked “EPA to clarify whether PFCs are based on 

nameplates or whether mass balances can be used to assess PFC emissions.” 

Response 3-a: PFC emissions must be measured in the exact same manner as SF6 emissions using the 

mass balance monitoring methods provided in §98.302. 

Comment Summary 3-b: Commenter 1569 noted that sometimes SF6 is emitted or destroyed due to a 

lightning strike or fire, and recommended that EPA exempt emissions of SF6 from a force majeure event, 

or at least establish a separate reporting section for those cases. 

Response 3-b: Emissions of SF6 that occur from a force majeure event are not exempted from the 

Subpart DD reporting requirements. The mass-balance monitoring methods required for Subpart DD are 

designed for a system-wide emissions measurement and are not conducive for use in measuring 

emissions occurring from specific events affecting specific pieces of equipment. The commenter should 

note that the purpose of the Mandatory Reporting Rule is to collect emissions data; the rule does not 

penalize facilities based on the quantity of their emissions. 
 

November 8, 2010 Subpart DD—Response to Comment Document 20 

4. Detailed GHG Emission Calculation Procedures/Equations

Relevant Bin Number 4.4 

Track 1 

Comment Summary 4-a: Commenter 0096 requested that EPA allow for flexibility for “higher quality, 

direct measurement data when available” in place of the proposed mass-balance method. The 

commenter stated that the objective of EPA’s proposed regulation can be “best accomplished by looking 

at the amount of SF6 added to equipment which would equate to loss of SF6 as emissions. For example, 

a company may have the actual weight of SF6 added to equipment during the year based on actual SF6

use which is a far better measure that simply looking at a mass balance for that year. The use of SF6

may be determined by the weight difference between the amount SF6 purchased (full bottle) and the 

remaining amount of SF6 in an empty bottle of SF6. In other cases a company may actually weigh the 

amount of SF6 gas added to each piece of equipment.” 

Response 4-a: The monitoring methods required by Subpart DD to measure SF6 emissions are based 

on the IPCC Tier 3 method provided in the peer-reviewed 2006 IPCC Guidelines for National 

Greenhouse Gas Inventories. The Tier 3 mass balance method is considered by IPCC to be the most 

accurate method for measuring SF6 emissions from electric power systems. Observing the amount of SF6

that is charged into leaky equipment might be a useful tool for estimating emissions from a specific piece 

of equipment, but this direct measurement completely overlooks potential emissions that can occur 

elsewhere within an electric power system. For example, if a circuit breaker is decommissioned from the 

electric power system and the SF6 within the breakers is vented into the atmosphere, the direct 

measurement method described by the commenter would not capture these emissions. Another example 

of emissions that would not be captured using the commenter’s method would be emissions that occur 

from a faulty cylinder valve. 

Track 2 

Comment Summary 4-b: Commenter 0096 argued that the mass-balance formula should not include 

annual nameplate capacity changes since these changes have “no bearing on the amount of SF6 used 

during the year.” The commenter stated that instead of using the annual change in nameplate capacity, 

“a single system capacity value, such as the start of the year capacity, should be used in the SF6 leak 

rate formula.” 

Response 4-b: The annual nameplate capacity change is essential to include in the mass-balance 

monitoring methods for Subpart DD in order to measure emissions accurately. The mass-balance 

method works by systematically accounting for all SF6 uses within the system. The amount of SF6 that 

cannot be accounted for by the electric power system is equal to the emissions during the year since the 

unaccounted for SF6 was not recorded as being used in a non-emissions context (such as the SF6 being 

sent offsite for recycling or added to the storage inventory). Assessing the changes in nameplate capacity 

plays an integral role in accounting for SF6 gas uses. For example, if new equipment is purchased during 

the year and the equipment is filled with SF6 stocks from the user’s storage inventory, then the nameplate 

capacity of the new equipment must be used to reconcile the amount of SF6 that was withdrawn from 

inventory, otherwise the amount of gas withdrawn from the storage inventory would register as an 

emission. 
 

November 8, 2010 Subpart DD—Response to Comment Document 21 

5. Monitoring and QA/QC Requirements 

Relevant Bin Numbers: Section 4.5 

Track 1 

Comment Summary 5-a: Commenter 0608 stated that it is very difficult to weigh the amount of SF6 in 

gas carts with on board storage vessels to an accuracy of 1 percent. This commenter’s current practice is 

to estimate the weight of gas carts with onboard storage vessels using engineering calculations. 

Commenter 0608 noted that the “weighing method is based on a pivoting table single point measuring 

system and removal of individual cylinders from the gas carts is difficult.” The commenter also explained 

that large carts are also used that have non-removable tanks on trailers; the proposed rule would require 

the weighing of the entire trailer, which would not yield an accurate measurement of gas because of 

“other materials such as compressor fluid and filter material which vary overtime.” The commenter 

requested “a more pragmatic approach that tracks its current business practice: (1) cylinders should be 

weighed at the beginning and end of each reporting period; 2) the weight of SF6 in gas carts with onboard 

storage vessels may be calculated using the current methodology; and (3) the manufactured supplied 

and installed weighing system in gas carts with onboard SF6 cylinders should be permitted. By allowing 

[the commenter] to continue its current practices, US EPA would reduce the reporting burden and still 

achieve its aim of gathering emissions data.” Commenter 0608 also explained that this approach is 

consistent with methods provided for under the Climate Registry Protocol for reporting SF6 emissions 

from Electricity Transmission and Distribution systems. 

Response 5-a: After assessing concerns among numerous reporters about the proposed scale accuracy 

requirements, EPA eased the scale accuracy requirement from a relative requirement of 1% of true 

weight to an absolute requirement of +/- 2 pounds of true weight. In addition, EPA has removed the 

proposed requirement in §98.306 (b)(2) for weighing storage cylinders as they enter and leave the 

storage inventory and clarified that the QA/QC requirements for scale accuracy and calibration apply only 

to cylinders returned to the gas supplier and cylinders weighed at the beginning and end of each year for 

the beginning and end-of-year storage inventory. EPA also examined the use of engineering calculations 

and alternative techniques other than scale weighing for determining SF6 weight. Due to the unreliability 

of the most commonly used engineering calculations for weighing gas, such as using temperature and 

pressure readings, EPA determined that such methods are not suitable for the Subpart DD mass-balance 

monitoring methods, which rely on highly accurate inputs. For more information on the potential issues 

with using engineering calculations to determine the weight of SF6, see comment response 5.1-b. For 

more information on the necessity for highly accurate mass-balance inputs, see comment response 5.2-

a.

5.1 Frequency of Weighing Cylinders—Track 1 

Relevant Bin Numbers: Section 4.5, 4.5.1, and 4.5.3 

Comment Summary 5.1-a: Ten commenters (0455, 1021, 0608, 0624, 0618, 1566, 0902, 0479, 0547, 

1645) disfavored EPA’s proposed requirement of weighing gas cylinders each time they leave and enter 

storage. Commenter 1021 noted that EPA does not explain what purpose weighing cylinders leaving and 

entering storage in addition to the weighing of cylinders at the beginning and the end of every year would 

serve.

Commenter 0455 asserted that “weighing cylinders twice each time they are used, ‘as they are leaving 

and entering storage,’ would result in a significant increase in worker hours.” Commenters 0455, 0624, 

0618, and 1566 suggested that SF6 cylinders could be monitored by taking initial measurement of SF6

stored in containers, combined with the submission of records tracking subsequent SF6. This approach, 

they stated, would be less costly than monitoring requirement proposed in §98.304(b)(2). 

Commenters 0479 and 0547 are concerned about the potential administrative burden and health and 

safety issues associated with frequent cylinder weighing by substation personnel, and preferred a 

standardized approach that relies on SF6 vendors and recyclers to provide weighing services of the 

delivered cylinders and residual gas upon return of the cylinder. These commenters believed that SF6
 

November 8, 2010 Subpart DD—Response to Comment Document 22 

vendors and recyclers are better prepared to report this information, as they already employ procedures 

to weigh cylinders using scales that are routinely maintained and calibrated. 

Commenter 0902 noted that the “rule as written will require employees to manually lift and weigh each 

tank of SF6 in order to gather the information needed in the reporting process. Because a full tank of SF6

weighs over 200 lbs., increased handling of cylinders could increase risk of worker injury.” Commenter 

0902 favored the use of alternate methods of information gathering, stating that, “although current 

technology requires weighing gas cylinders to obtain an accurate measurement of SF6 usage, future 

reporting need not be limited to this inherently unsafe method of information gathering. An alternate 

method of data collection that meets the stated accuracy requirements will allow reporting methods to 

keep pace with advances in technology.” 

Commenters 1645 and 0608 favored the approach used under the existing voluntary program between 

electric power systems and EPA. Commenter 1645 noted that, “although the interim weighing of cylinders 

as they are used, handled, and relocated may have internal inventory value to the user, this information 

is not necessary for accurate annual reporting, and can add significantly and unnecessarily to an 

organization’s labor burden and book keeping requirements, if mandated by the reporting rule.” 

Commenter 0608 asserted that individual cylinder weighing is impractical and questionably cost effective 

given that at each facility, cylinders may leave and enter storage 20 times per year. 

Response 5.1-a: EPA agrees that the benefit of weighing SF6 gas cylinders as they enter and leave 

inventory does not justify the costs of performing this activity. EPA has removed this requirement from § 

98.306 (b)(2) and clarified that the QA/QC requirements for scale accuracy and calibration apply to 

cylinders returned to the gas supplier and cylinders weighed at the beginning and end of each year for 

the beginning and end-of-year storage inventory.

Comment Summary 5.1-b: Commenter 1566 suggested that instead of weighing cylinders to track the 

quantity of contained SF6, the pressure of the gas could be measured using a standard pressure gauge 

and the mass calculated using the ideal gas law. Commenter 1566 noted, “considering the relatively de 

minimis greenhouse gas emissions resulting from use and handling of SF6, this method of tracking the 

SF6 content in cylinders in lieu of weighing cylinders should be sufficient.” 

Response 5.1-b: Measuring the amount of SF6 in cylinders using temperature and pressure calculations 

is not an adequate method for weighing SF6 cylinders in the context of mandatory reporting since SF6 in 

a cylinder can be in both a gaseous and liquefied state, thereby making pressure readings unreliable. For 

example, in cases where gas extraction from the cylinder has cooled the temperature of SF6 liquid in the 

cylinder to the point where it will no longer vaporize, a zero PSIG pressure reading could be read from 

the cylinder when there is still SF6 remaining as a heel in the cylinder. 

5.2 Frequency of Weighing Cylinders—Track 2 

Relevant Bin Numbers: Section 4.5, 4.5.1, and 4.5.3 

Comment Summary 5.2-a: Four commenters (0133, 0097, 0098, 0083) disfavored EPA’s proposed 

requirement of weighing gas cylinders each time they leave and enter storage. Commenters 0133 noted 

that EPA does not explain what purpose weighing cylinders leaving and entering storage in addition to 

the weighing of cylinders at the beginning and the end of every year would serve.

Commenters 0097 and 0098 were concerned about the potential administrative burden and health and 

safety issues associated with frequent cylinder weighing by substation personnel, and preferred a 

standardized approach that relies on SF6 vendors and recyclers to provide weighing services of the 

delivered cylinders and residual gas upon return of the cylinder. These commenters believed that SF6

vendors and recyclers are better prepared to report this information, as they already employ procedures 

to weigh cylinders using scales that are routinely maintained and calibrated. 

In regards to administrative burden, Commenter 0083 explained that while a spreadsheet maintained by 

one person may be appropriate for smaller or densely developed utilities, it is not feasible for a company 
 

November 8, 2010 Subpart DD—Response to Comment Document 23 

with transmission operations spanning large geographic areas, which would instead require expensive 

software upgrades that can take months or years to install. 

Response 5.2-a: EPA agrees that the benefit of weighing SF6 gas cylinders as they enter and leave 

inventory does not justify the costs of performing this activity. EPA has removed this requirement from § 

98.306 (b)(2) and clarified that the QA/QC requirements for scale accuracy and calibration apply to 

cylinders returned to the gas supplier and cylinders weighed at the beginning and end of each year for 

the beginning and end-of-year storage inventory.

Comment Summary 5.2-b: Commenters 0097 and 0098 were in favor of EPA permitting the use of best 

available estimation methodologies in the first reporting year to limit the administrative burden on industry 

to weigh each SF6 cylinder, which would allow facilities flexibility in reporting using a combination of 

internal engineering calculations and/or purchase records. 

Response 5.2-b: EPA understands that it might be difficult for some entities to employ the monitoring, 

data reporting, and QA/QC requirements by the beginning of 2011. Therefore, facilities may use best 

available monitoring methods during 2011 to the extent provided in §98.3(d)(1) through (d)(2), with the 

date changes specified in the final rule. For more information, see §98.303(a) of the final rule. 

5.3 Accuracy and Precision of Scales—Track 1 

Relevant Bin Numbers: Section 4.5.2 

Comment Summary 5.3-a: Six commenters (0902, 1021, 0618, 0624, 1566, 0608) disagreed with the 

proposed scale accuracy language at §98.304(b)(l), that states, "cylinders returned to the gas supplier 

are consistently weighed on a scale that is certified to be accurate and precise to within 1 percent of the 

true weight", and "If the gas supplier weighs the residual gas, obtain from the gas supplier a detailed 

monthly accounting, within 1 percent, of residual gas amounts in the cylinders returned to the gas 

supplier" and at §98.304(b)(2), that states, "Cylinders shall be weighed on a scale that is certified to be 

accurate within 1 percent of the true weight." 

Commenters were concerned about the cost of scales requiring this level of accuracy and the need to 

purchase several of them for each site where cylinders are stored. Commenter 0902 stated that they will 

have to purchase multiple scales at each location, which span thousands of transmission miles. This 

commenter was concerned about the cost of a scale of this accuracy, which is around $1,200 and the 

need for several scales, which would result in the expenditure of thousands of dollars.” 

Commenter 1012 remarked that given the expense of highly accurate scales and the associated workerhours with repeated weighing and scale recalibration, EPA should explain “why its chosen 

methodology—the mass balance approach—does not provide sufficient information for reporting 

purposes such that the additional burden of frequent, highly accurate weighing is justified.” 

Commenters 0618, 0624, and 1566 were also concerned about the need to purchase and maintain 

numerous high-accuracy scales at each facility storing SF6 cylinders, which is costly for monitoring “what 

translates to ‘de minimis’ quantities of GHG emissions.” 

Commenter 0902 appreciated the necessity for accurate reporting but believed that a one percent 

accuracy requirement is arbitrary and unnecessarily burdensome on the industry. Commenter 0902 

explained that a one percent requirement will vary greatly within the reporting process. “A scale that is 

one percent accurate for a full 220 pound tank of SF6 will not be one percent accurate for a tank 

containing only a couple pounds of residual gas being returned to the supplier.” Commenter 0902 

suggested a maximum variance in pounds rather than a percentage of the true weight. “A requirement 

that scales be accurate within two pounds, which is one percent of a full SF6 tank, will reduce the 

financial burden on affected companies while still providing accurate reporting.” This commenter 

explained that “designating a variance in terms of pounds establishes a clearly defined limit, and will 

result in more consistent and accurate reporting.” 

Response 5.3-a: The 1 percent accuracy requirement was proposed by EPA because the mass-balance 

method for measuring emissions requires accurate inputs, and the overall uncertainty of the emission 
 

November 8, 2010 Subpart DD—Response to Comment Document 24 

estimate rises significantly as the potential inaccuracy of each input increases. However, EPA also 

recognizes that the price of scales does increase as the accuracy of the scale increases and that many 

electric power entities do not currently use scales that are accurate to within 1 percent of the true weight. 

In order to balance the reporting burden with the need for accurate mass-balance inputs, this Final Rule 

requires the accuracy and precision of scales used to weigh cylinders to be based on pounds, within +/- 2 

pounds of true weight. 

EPA deemed the +/- 2 pound accuracy requirement to be an appropriate accuracy level based on a 

sensitivity analysis using mass-balance emission estimate data from four different size Partners from 

EPA’s SF6 Emission Reduction Partnership for Electric Power Systems. The sensitivity analysis involved 

testing the effect of five different scale accuracies on the relative uncertainty of the emissions estimates 

(on a 95% confidence interval). The five scale accuracies tested included: 1% (relative), 2% (relative), 1 

pound (absolute), 2 pounds (absolute), and 1% of full scale at 330 pounds (absolute). Assuming 2% 

uncertainty in the nameplate capacity parameters of the mass-balance formula (which are not measured 

using scales), the 2 pound scale accuracy requirement resulted in a range of relative uncertainties 

among Partners between 1% and 4.4%. The analysis also showed that the 1% relative scale accuracy 

resulted in a range of relative uncertainties between 0.5% and 4.1%, and the 5% relative scale accuracy 

resulted in a range of relative uncertainties between 2.6% and 6.5%. The complete sensitivity analysis 

can be found here: www.epa.gov/climatechange/emissins/ghgrulemaking.html

5.4 Accuracy and Precision of Scales—Track 2 

Relevant Bin Numbers: Section 4.5.2 

Comment summary 5.4-a: Commenter 0083 stated that they will have to purchase multiple scales at 

each location, which span thousands of transmission miles. This commenter was concerned about the 

cost of a scale of this accuracy, which is around $2,000 and the need for several scales, which would 

result in the expenditure of thousands of dollars. The commenter appreciated the necessity for accurate 

reporting but believed that a one percent accuracy requirement is arbitrary and unnecessarily 

burdensome on the industry. Commenter 0083 recommended amending §98.304(b)(1) and (2) as 

follows: 

“(1) Ensure that cylinders returned to the gas supplier are consistently measured by a method certified to 

be accurate and precise within 2 pounds, and are recalibrated per the manufacturer's specifications. 

Either measure residual gas (the amount of gas remaining in returned cylinders) or have the gas supplier 

measure it. If the gas supplier measures the residual gas, obtain from the gas supplier a detailed monthly 

accounting, within 2 pounds, of residual gas amounts in each cylinder returned to the gas supplier. 

(2) Ensure that procedures are in place to measure all cylinders as they are leaving and entering the 

electric power system. Cylinders shall be measured by a method certified to be accurate and precise 

within 2 pounds and shall be recalibrated at the frequency specified by the manufacturer.” 

Commenter 0902 explained that a one percent requirement will vary greatly within the reporting process. 

“A scale that is one percent accurate for a full 220 pound tank of SF6 will not be one percent accurate for 

a tank containing only a couple pounds of residual gas being returned to the supplier.” Commenter 0902 

suggests a maximum variance in pounds rather than a percentage of the true weight. “A requirement that 

scales be accurate within two pounds, which is one percent of a full SF6 tank, will reduce the financial 

burden on affected companies while still providing accurate reporting.” This commenter explains that 

“designating a variance in terms of pounds establishes a clearly defined limit, and will result in more 

consistent and accurate reporting.” 

Commenter 0133 remarked that given the expense of highly accurate scales and the associated workerhours with repeated weighing and scale recalibration, EPA should explain “why its chosen 

methodology—the mass balance approach—does not provide sufficient information for reporting 

purposes such that the additional burden of frequent, highly accurate weighing is justified.” 

Response 5.4-a: Please see Response 5.3a for EPA’s response to this comment. 
 

November 8, 2010 Subpart DD—Response to Comment Document 25 

5.5 Frequency of Scale Calibration 

Relevant Bin Numbers: Section 4.5.1 and 4.5.2

Track 1 

Comment Summary 5.5-a: Three commenters (0568, Email-034-1, and 1645) did not support a 

calibration frequency that requires annual recalibration or the minimum frequency specified by the 

manufacturer, whichever is more frequent. Commenter 0568 advocated removing the phrase, 

“whichever is more frequent” found at § 98.304(b)(2) because removing this phrase “will allow for the 

purchase of a higher quality scale that may not require recalibration as often as once a year, and will not 

provide an incentive for the regulated entity to purchase a lower quality scale and replace it yearly.” This 

commenter stated that “the current wording of the Proposal encourages this practice because the cost of 

replacement for scales can be less than the cost in time and money of recalibrating scales.” Commenter 

Email-034-1 recommended this change because the calibration cycle of the scales they intend to 

purchase is every 3 years. 

Response 5.5-a: EPA agrees that scale recalibration in accordance with manufacturer specifications is 

sufficient and that the incremental costs associated with annual recalibration (when the manufacturer’s 

specified calibration is less frequent) are not justified. EPA has retained the requirement that recalibration 

occur in accordance with manufacturer specifications but removed the requirement for a minimum of 

annual recalibration. 

 

Track 2 

Comment Summary 5.5-b: Three commenters (0083, 0109, 0115) did not support a calibration 

frequency that requires annual recalibration or the minimum frequency specified by the manufacturer, 

whichever is more frequent because of cost and logistical reasons. Commenter 0083 stated that “the 

manufacturer of the scale is better equipped than the EPA to determine the minimum maintenance 

requirements for their own product. Annual certification is costly, time consuming, and most notably 

unnecessary.” 

Response 5.5-b: Please see Response 5.5-a for EPA’s response to this comment.

5.6 Other (Monitoring and QA/QC Requirements)—Track 1 

Relevant Bin Numbers: Section 4.5.3

Comment Summary 5.6-a: Commenter 1062 “supports the Tier 3 mass-balance protocol as being 

adequate as long as good QA/QC procedures are utilized. It is important that reporting methods and 

verification be consistent nationally.” 

Response 5.6-a: EPA appreciates the support of the commenter. §98.303 and §98.305 of Subpart DD 

provide numerous QA/QC and data reporting requirements to ensure that data reported to EPA is 

accurate and complete.
 

November 8, 2010 Subpart DD—Response to Comment Document 26 

6. Data Reporting Requirements—Track 1 

Relevant Bin Numbers: Section 4.7

Comment Summary 6-a: Commenter 0413 said that “EPA is seeking excessively detailed and 

redundant information regarding electrical equipment containing SF6 gas.” The commenter states that 

“the amount of information sought creates a reporting requirement for use of SF6 gas not its emissions 

into the atmosphere. This new regulation of ‘use’ is unauthorized and unnecessary as EPA's data 

showing significant reduction in SF6 emissions from 1990 to 2007. Congress only authorized reporting of 

SF6 gas emission and did not authorize a complex regulatory system for regulating the use of SF6 gas.” 

Response 6-a: The system-level mass-balance monitoring methods required by Subpart DD are 

considered the most accurate and complete method for measuring SF6 emissions for an electric power 

system because the method captures emissions that occur anywhere within the system by tracking 

system-level SF6 use. This comprehensive monitoring method is important because an electric power 

system can span thousands of miles, and emissions can occur from a wide variety of causes throughout 

the electric power system including improper gas handling, leaky equipment, and faulty cylinder valves. 

While facilities are required to track and document SF6 gas use within the system to yield accurate inputs 

for the mass-balance formula, EPA is not regulating how or when SF6 can be used by the facility. For 

more information on the selection of monitoring methods for Subpart DD, please see the TSD located 

here: www.epa.gov/climatechange/emissins/ghgrulemaking.html For a further detailed response on the 

amount of information required to be reported on U.S. greenhouse gas emissions, please see the 2009 

Response to Comments Volume 13 – Content of the Annual Report document, comment EPA-HQ-OAR2008-0508-0604.1 excerpt 5 (p. 1-2).

Comment Summary 6-b: Commenter 0413 stated that due to the amount of data reporting requirements 

required for Subpart DD, “EPA is seeking to create a significant amount of paperwork for utilities, which 

have successfully and significantly reduced SF6 emissions” from 1990 to 2007. 

Response 6-b: Through the mandatory reporting rule, EPA is seeking to collect accurate and 

comprehensive greenhouse gas emissions data to inform policymaking. EPA values the progress made 

under the Partnership in reducing emissions, but this does not obviate the need for mandatory reporting. 

There are large electric power systems that have not participated in the voluntary Partnership, and the 

emissions estimated through the voluntary Partnership have not undergone the QA/QC requirements 

necessary to ensure they are reliable enough to inform policymaking. While compiling and reporting 

emission data does involve a burden to affected entities, EPA has attempted to minimize the burden as 

much as possible while still insuring that emissions data is accurate, complete, and verifiable. 

Comment Summary 6-c: Commenter 0413 stated that the reporting requirement for total system-wide 

nameplate capacity is excessively detailed because “there should be no need to report if the equipment 

is no longer in service.” 

Response 6-c: The data reporting requirements for Subpart DD require reporting the nameplate capacity 

of equipment containing SF6 and the nameplate capacity of equipment containing PFC existing at the 

beginning of the year (not including hermetically sealed-pressure switchgear). For purposes of compiling 

the system-wide nameplate capacity value, facilities should only include equipment that is energized. 

Equipment that is not in service but still contains SF6 should be treated as a part of the storage inventory. 

Comment Summary 6-d: Commenters 0902 and 0568 requested clarification on whether the SF6 inside 

partially-filled electrical equipment that has been purchased but not yet installed should be considered as 

part of the mass-balance input §98.306(h) "SF6 with or inside new equipment purchased in the year" or 

the input §98.306(g) "SF6 stored in containers at the beginning and end of the year.” Commenter 0568 

also requested clarification regarding whether the nameplate capacity of this equipment should be 

recorded as new nameplate capacity acquired during the year (if the equipment is not yet installed at the 

end of the year). 
 

November 8, 2010 Subpart DD—Response to Comment Document 27 

Response 6-d: SF6 that is inside partially-filled electrical equipment that has been purchased by the 

facility (i.e., the title has been transferred to the facility) but is not yet installed should be counted as part 

of the mass balance input §98.306(h) "SF6 with or inside new equipment purchased in the year" as well 

as the mass-balance input §98.306(g) "SF6 stored in containers at the beginning and end of the year” 

(assuming the equipment still has not been installed by the end of the year). 

Comment Summary 6-e: Commenter 1645 argued that the number of transmission miles for a facility, 

as requested in the data reporting requirements of Subpart DD, is not a good metric for correlating with 

nameplate capacity and SF6 emissions. The commenter thought a better metric for evaluating “SF6

emission intensity” would be the number of SF6 breakers within an electric power system facility. The 

commenter noted that the amount of SF6 emissions associated with transmission miles is largely 

dependent on the geographic region of the country and whether the transmission miles are located in 

rural or urban areas within specific geographic regions. 

Response 6-e: EPA acknowledges that the amount of SF6 used per transmission mile varies depending 

on the geographic region where the transmission lines occur. However, EPA’s analysis indicated that 

transmission miles still correlates strongly with nameplate capacity and SF6 emissions, albeit not as 

strongly as the correlation between nameplate capacity and SF6 emissions, and therefore EPA is 

requiring transmission miles as a data reporting requirement. (For more information on EPA’s threshold 

analysis, please see the TSD located here: www.epa.gov/climatechange/emissins/ghgrulemaking.html.) 

The number of SF6 breakers within an electric power system facility could also provide useful information. 

However, due to the wide-variety of circuit breaker sizes and vintages, which can hold drastically different 

amounts of SF6, there is limited usefulness to simply knowing the total number of breakers within an 

electric power system facility. Therefore, EPA is not requiring this value as a data reporting requirement. 

 
 

November 8, 2010 Subpart DD—Response to Comment Document 28 

7. Other Subpart DD Comments – Track 1 

Relevant Bin Numbers: Section 4.10

Comment Summary 7-a: Commenter 0212 stated that the nameplate capacity approach for Subpart DD 

does allow utilities to quickly determine whether they must report, but does not allow utilities to get credit 

for reduced emissions, which may be possible even as nameplate capacity increases. The commenter 

asked whether EPA has a mechanism to address this going forward. Commenter 0902 suggested that 

“EPA adopt an incentive program to encourage continued emission reductions and to offset the additional 

reporting costs under the mandatory reporting rule. Utilization of tax or other financial incentives will 

provide a business case for companies to aggressively pursue reduction of SF6 emissions.” 

Response 7-a: The purpose of the Mandatory Reporting Rule is to collect accurate and comprehensive 

data on the amount of greenhouse gases emissions from various sources to help inform policymaking. 

EPA does not have a mechanism for providing financial incentives for greenhouse gas emission 

reductions through the Mandatory Reporting Rule because such incentives would be outside the scope of 

the rule.

Comment Summary 7-b: Commenter 0555, after reviewing the mechanisms for the use of SF6 in 

electrical equipment, “applaud[s] EPA for a substantial document, and agree that the general 

methodology for SF6 emissions from electric power systems is feasible.” 

Response 7-b: EPA appreciates the support from the commenter. 

Comment Summary 7-c: Commenter 1569 agreed that greenhouse gas emission reports for Subpart 

DD should be submitted on an annual basis since more frequent reporting using the mass-balance 

emission measurement methods could result in errors. 

Response 7-c: EPA appreciates commenter’s support of annual reporting. 
 

November 8, 2010 Subpart DD—Response to Comment Document 29 

8. Other Subpart DD Comments – Track 2 

Relevant Bin Numbers: Section 4.10

Comment Summary 8-a: Commenter 0075 noted that “the proposed rule does not address the small 

quantities of SF6 used as a tracer for leak detection in pressurized systems, such as nuclear power plant 

boiler tubes.” 

Response 8-a: EPA appreciates the commenter’s concern about other uses of SF6 that are not covered 

by the rule. The purpose of the Mandatory Reporting Rule is to collect greenhouse gas emissions data 

from significant sources without subjecting small sources to a reporting burden. EPA is not currently 

aware of significant SF6 emissions occurring from its use as a tracer gas for leak detection in pressurized 

systems, but will continue to examine whether significant greenhouse gas emissions occur from sources 

not currently covered by the Mandatory Reporting Rule. 

Comment Summary 8-b: Commenter 0128 supported EPA’s inclusion of fluorinated greenhouse gas 

reporting provisions for electric transmission and distribution use and thought it will enhance the overall 

accuracy of EPA’s greenhouse gas reporting rule and help the agency move towards a “truly 

comprehensive inventory of national GHG emissions.” 

Response 8-b: EPA appreciates the support from the commenter. 
 

November 8, 2010 Subpart DD—Response to Comment Document 30 

Appendix A – List of Commenters Sorted by Submission Number 

Submission No. Commenter Organization 

EPA-HQ-OAR-2009-0927-0075 Kenneth Boyd Southern Company 

EPA-HQ-OAR-2009-0927-0081 Kenneth Boyd Southern Company 

EPA-HQ-OAR-2009-0927-0083 Deborah Boyle Oncor 

EPA-HQ-OAR-2009-0927-0086 Pamela F. Faggert 

Dominion Resource 

Services, Inc. 

EPA-HQ-OAR-2009-0927-0087 Holly Propst 

Western Business 

Roundtable 

EPA-HQ-OAR-2009-0927-0088 Carol Whitman 

National Rural Electric 

Cooperative Association 

EPA-HQ-OAR-2009-0927-0094 Alexander G. Taft National Grid 

EPA-HQ-OAR-2009-0927-0096 Bruce D. Alexander Exelon Corporation 

EPA-HQ-OAR-2009-0927-0097 Michael Bradley The Clean Energy Group 

EPA-HQ-OAR-2009-0927-0098 Rayburn L. Butts Nextera Energy, Inc. 

EPA-HQ-OAR-2009-0927-0101 Scott Davis Arizona Public Service 

EPA-HQ-OAR-2009-0927-0109 McCabe American Electric Power 

EPA-HQ-OAR-2009-0927-0115 Michael B. McNulty ITC Holdings 

EPA-HQ-OAR-2009-0927-0119 Rob Rouse 

The Dow Chemical 

Company 

EPA-HQ-OAR-2009-0927-0120 Ruthanne Calabrese Northeast Utilities 

EPA-HQ-OAR-2009-0927-0125 Eric Hsieh 

National Electric Managers 

Association 

EPA-HQ-OAR-2009-0927-0126 Wesley McNealy Pepco Holdings, Inc. 

EPA-HQ-OAR-2009-0927-0127 Gregory Ryan DTE, Energy 

EPA-HQ-OAR-2009-0927-0128 Pamela Campos 

Environmental Defense 

Fund 

EPA-HQ-OAR-2009-0927-0133 Quinlan Shea Edison Electric Institute 

EPA-HQ-OAR-2008-0508-0212 Emily Fisher Edison Electric Institute 

EPA-HQ-OAR-2008-0508-0407 Michael Stroben Duke Energy Corporation, 

EPA-HQ-OAR-2008-0508-0413 

Environmental Task Force 

of the Northwest Public 

Power Association 

EPA-HQ-OAR-2008-0508-0455 Debra Jezouit 

Class of '85 Regulatory 

Response Group 

EPA-HQ-OAR-2008-0508-0479 Michael Bradley The Clean Energy Group 

EPA-HQ-OAR-2008-0508-0547 Wesley McNealy Pepco Holdings, Inc. 

EPA-HQ-OAR-2008-0508-0551 Delaine Shane 

Metropolitan Water District 

of Southern California, 

EPA-HQ-OAR-2008-0508-0555 Kyle Pistor NEMA 

EPA-HQ-OAR-2008-0508-0568 Rita Hayen 

American Transmission 

Company LLC 

EPA-HQ-OAR-2008-0508-0584 Nicole McIntosh Consumers Energy 

EPA-HQ-OAR-2008-0508-0597 Angila Retherford Vectren 

EPA-HQ-OAR-2008-0508-0608 Linda Sullivan National Grid 

EPA-HQ-OAR-2008-0508-0612 Andrew Lawrence Department of Energy 

EPA-HQ-OAR-2008-0508-0618 Vincent Brisini RRI Energy, Inc. 

EPA-HQ-OAR-2008-0508-0624 Joseph Miakisz FPL Group 

EPA-HQ-OAR-2008-0508-0639 Scott Davis 

Arizona Public Service 

Company 

EPA-HQ-OAR-2008-0508-0661 J.P. Blackford American Public Power 
 

November 8, 2010 Subpart DD—Response to Comment Document 31 

Submission No. Commenter Organization 

Association 

EPA-HQ-OAR-2008-0508-0685 Helen A. Howes Exelon Corporation 

EPA-HQ-OAR-2008-0508-0725 John McManus American Electric Power 

EPA-HQ-OAR-2008-0508-0902 Deborah Boyle Oncor Electric Delivery 

EPA-HQ-OAR-2008-0508-1021 Quinlan Shea Edison Electric Institute 

EPA-HQ-OAR-2008-0508-1062 Matthew Frank State of Wisconsin 

EPA-HQ-OAR-2008-0508-1080 Kelly Carmichael NiSource 

EPA-HQ-OAR-2008-0508-1566 Robbie LaBorde Cleco Corporation 

EPA-HQ-OAR-2008-0508-1569 Patricia Meehan New York Power Authority 

EPA-HQ-OAR-2008-0508-1645 Southern Company 

EPA-HQ-OAR-2008-0508-1741 Pamela Faggert Dominion 

EMAIL-034 Steve Lowder 

Bonneville Power 

Administration 

Trans-DC-04 Dan Chartier Edison Electric Institute