# TECHNICAL SUPPORT DOCUMENT FOR PROCESS EMISSIONS OF SULFUR HEXAFLUORIDE (SF 6 

# ) AND PFCs FROM ELETRIC POWER SYSTEMS:

PROPOSED RULE FOR MANDATORY REPORTING OF GREENHOUSE GASES

Revised November 2010

Office of Air and Radiation U.S. Environmental Protection AgencyC ontents 1. Source Description

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a. Total U.S. Emissions

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b. Emissions to be Reported

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c. Facility Definition Characterization ................................................................................................................1
2. Options for Reporting Threshold

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9 3. Options for Monitoring Methods

......................................................................................................................... 4. Procedures for Estimating Missing Data

.............................................................................................................. 5. QA/QC Requirements

............................................................................................................................... ........... 6. Reporting Procedures

............................................................................................................................... ............ 7. References

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### Source Description The largest use of SF 6 , both in the United States and internationally, is as an electrical insulator and interrupter in equipment that transmits and distributes electricity (RAND 2004). The gas has been employed by the electric power industry in the United States since the 1950s because of its dielectric strength and arc- quenching characteristics. It is used in gas-insulated substations, circuit breakers, other switchgear, and in gas-insulated lines. Sulfur hexafluoride has replaced flammable insulating oils in many applications and allows for more compact substations in dense urban areas. Currently, there are no available substitutes for SF 6 in high voltage applications. Fugitive emissions of SF 6 can escape from gas-insulated substations an d switch gear through seals, especially from older equipment. The gas can also be released during equipment manufacturing, installation, servicing, and disposal.
PFCs are sometimes used as dielectrics and heat transfer fluids in power tr ansformers. PFCs are also used for retrofitting CFC-113 cooled transformers. One PFC used in this application is perfluorohexane (C 6 F 14 ). In terms of both absolute and carbon-weighted emissions, PFC emissions from electrical equipment are generally believed to be much smaller than SF 6 emissions from electrical equipment; however, there may be some exceptions to this pattern (IPCC, 2006).

a. Total U.S. Emissions
Emissions of SF 6 from an estimated 1,364 electric power system utilities 1 were estimated to be 12.4 Tg CO 2 Eq. in 2006 (EPA 2008). EPA does not have an estimate of PFC emissions from electric power system utilities.

b. Emissions to be Reported EPA is requiring electric power systems to report all SF 6 and PFC emissions, including those from equipment installation (once the title of equipment has been transferre d to the equipment user), equipment use, and equipment decommissioning and disposal.

c. Facility Definition Characterization The General Provisions for the Mandatory Reporting Rule, 40 CFR Part 98 Subpart A, define a facility as “any physical property, plant, building, structure, source, or stationary equipment located on one or more contiguous or adjacent properties in actual physical contact or separated solely by a public roadway or other public right-of-way and under common ownership or common control, that emits or may emit any greenhouse gas.” But this definition is not suitable for an electric power syst em since the electrical equipment that comprises an electric power system is typically at numerous substations that are not contiguous to each other but are instead connected by electrical lines. Using the Subpart A definition of a facility could lead to an electric power system being subdivided into many different facilities due to equipment that is geographically separated from other equipment even if the equipment is connected by electrical lines. This c ould introduce confusion in calculating whether a fac ility exceeds the reporting threshold and in determining the boundary between facilities. Therefore, the Subpart A de finition is not considered an appropriate definition for this source category. To identify an appropriate definition of a facility, EPA first considered the followi ng levels of reporting: per piece of equipment, per substation or switchyard, and corporate-le vel. Reporting per piece of equipment or per substation was deemed costly and highly impracti cal for reporters, primarily due to th e high number of substations and pieces of equipment that are operated by a utility. A large utility can have thousands of substations that each include many pieces of SF 6 -insulated equipment. Reporting SF 6 emissions from each piece of equipment would not only involve a significant labor burden, but could also overlook emissions that occur during SF 6 handling. Reporting emissions by

1 The estimated total number of electric power system (EPS) utilities includes all companies participating in the SF 6 Emission Reduction Partnership for Electric Power Systems and the num ber includes non-partner utilities with non-zero transmission miles. The estimated total number of EPS utilities that emit SF 6 likely underestimates the population, as some utilities may own high-voltage equipment yet not own transmission miles. However, the estimated number is consistent with the U.S. inventory methodology, in which only non-partner utilities with non-zero transmission miles and partner utilities are assumed to emit SF 6 .

November 2010 1substation would require setting up a separate mass-bala nce accounting system for each substation, which would involve a significant labor burden and does not reflect the way that utilities handle bulk gas across substations (gas is usually purchased and stored in a centralized fashion for use in numerous substations). Corporate-level reporting can raise issues because the ownership structure in the el ectric power industry can be very complex. In addition, utilities in the electric power industry are owned and opera ted by numerous types of public and private entities, which can include an investor -owned company, an electric cooperative, a public electric supply corporation, a federal government agency, a municipally owned electric depart ment, an electric public utility district (PUD), and a jointly owned electric supply project (EIA 2007). These myriad and potentially complex ownership structures could introduce the potential for under reporting, double-counting, or other reporting issues if reporting is required on a corporate-level. EPA also considered electric power sy stem level reporting, under which the electric power system would be considered an aggregation of equipmen t that is interconnected and shares a common owner or operator. Several advantages exist with this type of system level reporting. For example, system level reporting is consistent with the way that most utilities track their SF 6 use and is conducive for using IPCC’s Tier 3 utility-level mass-balance approach to emissions monitoring. The Tier 3 utility-level mass balance approach has been proven to be a practical and reasonable approach for the more than 80 utilities that currently participate in EPA’s SF 6 Emission Reduction Partnership for Electric Power Systems. Reporting emissi ons from the aggregation of electrically connected equipment also reduces the ambiguity associated with defining the boundary of the system by not making the boundary dependent on the different types of corporate or operational structures, which can be very complex. A variety of definitions were reviewed to identify a definition for an electric power system that best captures this aggregation of interconnected equipment in the context of mandatory reporting. As summarized in Table 1 , EPA reviewed current definitions from the Federal Energy Regulatory Commis sion (FERC), North American Energy Reliability Corporation (NERC), California Air Resources Board (CARB), the Regional Greenhouse Gas Initiative (RGGI), and the Energy Information Administration of the Department of Energy (EIA). EPA also consulted with members of industry (U.S. Electric Power Utility Representa tives, 2009) in addition to re viewing current regulations relevant to industry. Table 1: Alternative Options for Facility Definition
Source Term Definition

Transmission “Moving bulk energy products from where they are produced or generated to distribution lines that carry the energy products to consumers.” (FERC 2010)

Distribution “For natural gas - the act of distributing gas from the city gate or plant to the customer. For electric - the act of distributing electric power using low voltage transmission lines that deliver power to retail customers.” (FERC 2010) FERC a

Facility “A set of electrical equipment th at operates as a single Bulk Electric System Element (e.g., a line, a generator, a shunt compensator, transformer, etc.).” (FERC 2010)

Distribution Provider “Provides and operates the “wires” between the transmission system and the end-use customer. For those end-use customers who are serv ed at transmission voltages, the Transmission Owners also serves as the Distribution Provider. Thus, the Distribution Provider is not defined by a specific voltage, but rather as performing the Distribution function at any voltage.” (NERC 2010) NERC

Transmission “An interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to cu stomers or is delivered to other electric systems.” (NERC 2010)

CARB Electrical Power System “means the combination of electrical generators (i.e., power plants), transmission and distribution lines, equipment, circuits, and transformers used to generate and transport

November 2010 2electricity from the generator to consumption areas or to adjacent electrical power systems.” (CARB 2007)

RGGI Transmission and/or distribution entity “The assets and equipment used to transmit and distribute electricity from an el ectric 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-serving entity specified by the applicable state regulatory agency.” (RGGI 2008)

EIA Electrical Power System “An individual electric power entity--a company; an electric cooperative; a public electric supply corporation as the Tennessee Valley authority; a similar Federal department or agency such as the Bonneville Power Administration; the Bureau of Reclamation or the Corps of Engineers; a municipally owned electric department offering service to the public; or an electric public utility district (a “PUD”); also a jointly owned electric supply project such as the Keystone.” (EIA 2007)

a FERC does not define electric power sy stem; but rather, their glossary defers to the EIA energy glossary for this term. The alternative definitions listed in Table 1 do provide lang uage that is inclusive of different types of electrical utilities as well as different types of transmission and dist ribution equipment. However, the alternative definitions lack the level of specificity and completeness required to be used on their own to define electric power systems for mandatory reporting. Specific issues regarding the alternative definitions and their applicability to mandatory reporting are as follows:

• FERC: fragmented between transmission and distribution; unclear boundaries between systems.

• NERC: fragmented between transmission and distribution; unclear boundaries between systems.

• CARB: unclear boundari es between systems..

• RGGI: based on the service territory of the load-serving entity, but some SF 6 insulated electrical equipment is used by owners/operators who do not have a service territory (i.e., transmission-only companies).

• EIA: outlines different entities that can be consid ered electric power systems, but unclear about boundaries between systems as well as the physical assets that constitute an electric power system.

After a thorough review of these alternative definitions, it became clear that an approp riate definition should address the need for clear boundaries, broad applicability, inclusiveness, and monitoring efficiency. In order to achieve these goals, EPA developed the following definition of an electric power system facility: [an electric power system is comprised of] all elect ric transmission and distribution equipment insulated with or containing SF 6 or PFCs that is linked through electric power transmission or distribution lines and 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: (1) the point(s) at which electric ener gy is obtained 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 any customer or another electric po wer transmission or distribution entity that does not have a common owner receives the electric energy. The facility also in cludes servicing inventory for such equipment that contains SF 6 or PFCs. In this facility definition, the term “electric power transm ission or distribution entity” is introduced. To maintain clarity, EPA developed a separate definition of “electric pow er transmission or distribution entity” largely based on the EIA definition shown in Table 1. The definition provided for “electric power transmission or distribution entity” is as follows.

November 2010 3any entity that transmits, distributes, or supplies elect ricity to a consumer or other user, including any company, electric cooperativ e, public electric supply corporation, a similar Federal department (including the Bureau of Reclamation or the Corps of Engineers), a municipally owned electric department offering service to the public, an electric public utility di strict, or a jointly owned electric supply project.

2. 

### Options for Reporting Threshold EPA evaluated a range of threshold options for electric power systems. These included em ission threshold options of 1,000, 10,000, 25,000, and 100,000 metric tons CO 2 e, and nameplate capacity thresholds equivalent to these (713; 7,128; 17, 820; and 71,280 lbs of SF 6 ). These equivalencies were developed using historical (1999) data from utilities that participate in EPA’s SF 6 Emission Reduction Partnership for Elect ric Power Systems (Partnership). To determine the nameplate capacity threshold level, the emissions threshold was converted to pounds of SF 6 and divided by the 1999 weighted average annual leak rate (as a fraction of nameplate capacity) of the Partnership. This leak rate was developed by dividing the 1999 SF 6 emissions reported by 42 partner utilities by the nameplate capacity reported by these partners. 2 Partners with extraordinarily high or low leak rates (outliers) were excluded from the analysis. The Partners included in the analysis represented approximately 24 percent of U.S. transmission miles in 2000. Based on information from the Partnership and from the UDI database, EPA estimates that the 17,820 lbs of SF 6 nameplate capacity threshold covers only a small percentage (10 percent or 141 utilities) of total utilities, while covering the majority (approximately 83 percent) of annual emissions. A capacity-based threshold permits sources to quickly dete rmine whether they are covere d. There have been many mergers and acquisitions in the electric power industry, which could complicate e fforts to estimate recent emissions. In contrast, nameplate capacity is generally a known variable. A summary of these threshold options, the total national SF 6 emissions, the total number of facilities, and th e number of facilities and emissions falling above each threshold is presented in Table 2

.

2 EPA used 1999 weighted leak rates under the assumption that ut ilities who have not participated in the Partnership activities have not achieved the emission reductions fro m 1999-2008 that have been achieved by Pa rtners who have taken voluntary actions to reduce emissions, In addition, it was e ssential that a non-emissions based threshold be conserva tive enough to ensure that sources emitting more than 25,000 metric tons of CO 2 equivalent were cove red by the threshold.

November 2010 4Table 2: Options for Emissions and Capacity -Based Thresholds for Electric Power Systems Emissions Covered Facilities Covered

Emission Threshold Level (mtCO 2 e) Total National SF 6 Emissions (million mtCO2e) Total Number of Facilities Million mtCO 2 e Percent Facilities Percent 1,000 12.4 1364 12.2 98.3 564 41.3 10,000 12.4 1364 10.87 87.6 158 11.6 25,000 12.4 1364 10.11 81.5 111 8.1 100,000 12.4 1364 5.84 47.1 27 2
Nameplate Capacity Threshold (lbs SF 6 )
713 12.4 1364 12.19 98.3 578 42.4 7,128 12.4 1364 10.96 88.3 183 13.4 17,820 12.4 1364 10.32 83.2 141 10.3 71,280 12.4 1364 5.95 48.0 35 2.6
Transmission-Mile Threshold (miles)
47 12.4 1364 12.20 98.3 584 42.8
475 12.4 1364 10.86 87.5 186 13.6 1,186 12.4 1364 8.74 70.4 140 10.3 4,745 12.4 1364 4.53 36.5 34 2.5
EPA also evaluated a threshold based on the length of the transmission lines, defined as the miles of lines carrying voltages above 34.5 kV, owned by electric power systems. Like the nameplate capacity threshold, the transmission mile threshold was developed by dividing the emissions threshold by an emission factor, this one expressing emissions in terms of transmission miles. The emission factor was developed using the 1999 SF 6 emissions reported by 43 partner utilities (representing approximately 24 perc ent of U.S. transmission miles in 2000), and 2000 transmission mileage data obtained from the 2001 UDI Di rectory of Electric Power Pr oducers and Distributors (UDI 2001). The transmission-mile threshold equivalent to 25,000 mtCO 2 e is 1,186 miles. The relationship between emissions and transmission miles, while strong, is not as strong as that between emissions and nameplate capacity. On the one hand, some utilities have far larger nameplate capacities and emissions than would be expected based on their transmission miles. This is the case for some urban utilities that have large volumes of SF 6 in gas-insulated switchgear (GIS). On the other hand, some utilities have lower nameplate capacities and emissions than would be expected based on their transmission miles, because most of their transmission lines use lower voltages and typically use less SF 6 .

a. 

### Equipment under common ownership and c ontrol located outs ide the facility EPA considered that the definition of the electric power sy stem facility could under certain circumstances result in a company dividing its assets into more th an one facility that each fa ll below the threshold. Fo r example, if a company owns two electric power systems as subsidiary compan ies and each subsidiary company owns and operates collections of SF 6 insulated equipment that are in the same geogra phic vicinity but not electrically connected, then the two collections of equipment [owned by the subsidiary companies] would be considered separate reporting facilities. EPA considered whether or not in situations where the nameplat e capacities for each of the subsidiary companies were below the reporting threshold of 17,820 pounds, these facilities wo uld be required to report emissions if their combined nameplate capacities were above 17,820 pounds.

November 2010 5Given that the purpose of the reporting threshold is to ca pture the largest quantity of emissions while minimizing the burden to industry, allowing subsidiary companies in the example mentioned above to avoid reporting emissions when their combined nameplate capacities would fall above the threshold would be counter to the purpose of the threshold. Monitoring equipment such as cylinder scales, as well as recordkeeping technologies and procedures, are often shared among subsidiary companies to reduce the overall expense to the parent company. If numerous subsidiary companies with a single pa rent company are all separated as di stinct facilities (because they are not connected electrically), then each c ould fall below the reporting threshold resulting in significant emissions going unreported to EPA even though much of the reporting burden could be shared among the subsidiary companies or absorbed by the parent company. To avoid this situation, it is necessary that electric power system facilities add their nameplate capacities to the nameplate capacities of other electric power transmission or distribution facilities with a common owner when determining whether they fall above or below the 17,820 pound nameplate capacity threshold. If facilities with a common owner collectively fall above the reporting threshold, then the emissions for each distinct facility must still be monitored and reported separately to EPA.

b. 

### Reporting emissions from SF 6 

### and PFC insulated equipment located at electricity generating units (EGUs) Electricity generating units (EGUs) that report under Su bpart D of the Mandatory Reporting Rule often contain relatively small amounts of SF 6 and PFC insulated equipment. Under subpart A general provisions, EGU facilities that are required to report subpart D emissions must also report other sour ce category emissions that occur at the facility location, including subpart DD emissions. In some cases, calculating emissions from SF 6 and PFC insulated equipment lo cated at EGU sites would be straightforward. However, in other cas es where integrated utilities operate generation facilities as well as electrical equipment that transmits and distributes electricity from the generation facilities, it could be difficult to estimate emissions from equipment at the EGU sites separately from equipment outside of the EGU sites that are serviced by the same centralized SF 6 stocks. Furthermore, there is a risk of double-counting emissions if EGUs include subpart DD emissions in their subpart D facility emission reports since those emissions might also be included in subpart DD electric power transmission or distribution facility reports. Since th ere are generally small amounts of SF 6 and PFC insulated equipment located at EGUs relative to electric power transmission or distribution systems, the benefit of reporting emissions from equipment located at EGUs usually does not outweigh the potential issues cited above. The exception would be if there was a large amount of SF 6 or PFC insulated equipment located at the EGU that could result in a large amount of emissions. Therefore, the final rule specifies that EGUs only need to include subpart DD emissions in their facility reports if the amount of SF 6 or PFC containing equipment located within the subpart D facility exceeds a threshol d of 17,820 pounds of nameplate cap acity, which is the same reporting threshold applied to subpart DD electric power transmission or distribution system facilities.

3. 

### Options for Monitoring Methods
EPA reviewed the 2006 IPCC Guidelines , the SF 6 Emission Reduction Partnership for Electric Power Systems, the Inventory of U.S. Greenhouse Gas Emissions and Sinks , the Technical Guidelines fo r the Voluntary Reporting of Greenhouse Gases (1605(b)) Program, EPA’ s Climate Leaders Program, and The C limate Registry for this analysis.
These methods coalesce around the thre e options presented in the 2006 IPCC Gu idelines. These include a Tier 1 approach that estimates emissions by multiplying equipmen t nameplate capacity by defau lt emission factors, a Tier 2 approach that estimates emissions by multiplying equipment nameplate capacity by national emission factors, and a Tier 3 mass-balance approach that estimates emissions based on facility-specific data on SF 6 consumption and nameplate capacity changes. Although the Tier 1 method is simple, the default emission factors have large uncertainty due to variability associated with handling and management practices, age of equipment, mix of equipment, and other similar factors. Utilities participating in EPA’s Partnership have reduced their emission factors to less than the Tier 1 default values. Less than 10 percent of U.S. utilities participate in this program, however, these utilities represent over 40% of the transmission miles in the U.S.

November 2010 6Tier 2 methods use country-specific emi ssion factors, but the Partner utilities have demonstrated through calculating their own utility-level emission factors that there is large variability (less than one percent to greater than 35%) in utility-level emission factors across the nation. The Tier 3 approach is a utility-level mass-balance appr oach. This method is the approach used in EPA’s SF 6 Emission Reduction Partnership for Electric Power Systems. The mass-balance approach works by tracking and systematically accounting for all utility uses of SF 6 during the reporting year. The quantity of SF 6 that cannot be accounted for is assumed to have been emitted to the atmosphere. The following equation describes the mass-balance approach.

User Emissions = Decrease in SF 6 Inventory + Acquisitions of SF 6 – Disbursements of SF 6 – Net Increase in Total Nameplate Capacity of Equipment where,
Decrease in SF 6 Inventory is SF 6 stored in containers (but not in equipment) at the beginning of the year – SF 6 stored in containers (but not in equipment) at the end of the year. Acquisitions of SF 6 is SF 6 purchased from chemical producers or distributors in bulk + SF 6 purchased from equipment manufacturers or distributors with or inside of equipment + SF 6 returned to site after off-site recycling. Disbursements of SF 6 is SF 6 in bulk and contained in equipment that is sold to other entities + SF 6 returned to suppliers + SF 6 sent off-site for recycling + SF 6 sent to destruction facilities. Net Increase in Total Nameplate Capacity of Equipment is the nameplate capacity of new equipment – nameplate capacity of retiring equipment. (Note that nameplate capacity refers to the full and proper charge of equipment rather than to the actual charge, which may reflect leakage.) This method can also be applied to emissions of PFCs from power transformers.

4. 

### Procedures for Estimating Missing Data To be accurate, the mass-balance approach requires measured values for all inputs. Partner utilities missing inputs to the mass-balance approach have estimated emissions using other methods, such as assuming that all purchased SF 6 is emitted. However, this method over-estimates emi ssions. Should the utility be missing records for a given input, it may be possible that the gas or equipment supplier has information in their records for the utility. Alternatively, values from previous years could be applie d to the current year, but this approach introduces large uncertainties because emission rates va ry from year to year.

5. 

### QA/QC Requirements QA/QC methods for reviewing completeness and accuracy of reporting include the following.

• Review inputs to the mass balance equation to ensure inputs and outputs to the facility’s system are all accounted for in all appropriate sections.

• Ensure no negative inputs are entered and negative emissions are not calculated. However, the change in storage inventory and nameplate capacity may be calculated as negative numbers.

• Ensure that beginning of year inventory matches end of year inventory from previous year.

• Ensure that in addition to SF 6 purchased from bulk gas distributors, SF 6 purchased from Original Equipment Manufacturers (OEM) and SF 6 returned to the facility from off-site recycling are also accounted for among the total additions. QA/QC methods should be employed throughout the year. Important checks/procedures include the following.

• Ensure that cylinders returned to the vendor are weighed in a consistent manner on a scale that is certified to be accurate and precise to within 2 pounds of true weight and is periodically recalibrated per the manufacturer’s specifications.

o Gas suppliers measure the amount of gas remaining in cylinders/tanks returned (residual gas).

November 2010 7o Gas suppliers can provide a detailed monthly spreadsheet with exact residual gas amounts returned.

• Ensure all substations have provided information to the person responsible for compiling the emissions report (if it is not already handled through an electronic inventory system).

a. Analysis to determine scale accuracy requirements
A ±1 percent relative accuracy requirement for scales wa s originally proposed; howev er, based on comments EPA received during the public comment period indicating that the proposed requirement was t oo stringent, EPA reassessed the appropriate level of accuracy and precision for scales us ed to weigh cylinders. The first steps undertaken by EPA to reassess scale accuracy requirements were to research scale manufacturer Web sites and to contact scale manufacturers and electrical equipment users to better understand what scales are available on the market and the typical specifications of scales designed to weigh cylinders. 3 Additional discussion with industry occurred at EPA’s SF 6 Partnership for Electric Powe r Systems Partner Meeting, from May 13-14, 2010, where Partners discussed what types of scales they currently use, the price of various types of scales, and recommendations on scale accuracy requirem ents. The recommendations varied among Partners, with some Partners recommending rela tive accuracy requirements in the ± 3-5% range and at least one Partner recommending an absolute accuracy requirement of ± 2 pounds of true weight (EPA Partner Meeting, 2010), EPA also contacted two representatives from the Partnership in follow up to these conversations (BPA, 2010; Oncor, 2010). After consulting directly with industry and reviewing p ublic comments, EPA performed a sensitivity analysis using a variety of scale accuracies to analyze what effect changes in scale accuracies would have on the relative uncertainty of emission estimates. The analysis was performed using 2008 reported data from four various sized Partners of EPA’s SF 6 Emission Reduction Partnership for Electric Powe r Systems. Since the price of scales tends to increase as scale accuracy increases (all else being e qual), EPA’s goal was to determine which scale accuracy requirement would result in the least cost burden while still providing emission estimates with reasonable uncertainty levels. The summary re sults from the sensitivity analysis are provided in Table 3 below. 4
Table 3: Relative Uncertainties of Emission Estimates fo r Various Scale Accuracies (95% Confidence Interval) Level of accuracy applied to mass-balance inputs a Partner 1 Partner 2 Partner 3 Partner 4 Average

± 1% (relative) 2.6% 4.1% 0.5% 2.6% 2.5%
± 5% (relative) 9.8% 6.5% 2.6% 2.8% 5.4%
± 1 pound (absolute) 2.5% 4.1% 0.5% 2.6% 2.4%
± 2 pound (absolute) 4.1% 4.4% 1% 2.6% 3%
± 1% of full scale (absolute) b 6.5% 5% 1.7% 2.6% 4%

a The level of accuracy was applied to all inputs except for new an d retiring nameplate capacities, which are not measured using scales and were assumed to have 2% relative uncertainty. Calc ulations also were performed using relative uncertainties of 1% and 5% for new and retiring nameplate capaci ties; the entire analys is and corresponding results can be found in the public dock et (Docket ID No. EPA-HQ-OAR-2009-0927). b Assuming full scale is equivalent to a scale capacity of 330 pounds.
After reviewing the results of the sensitivity analysis as well as public comments submitted by electrical equipment users, EPA determined that a ±2 pound absolute accuracy requirement offered the best balance between the accuracy of emission estimates and the burden incurred by electric po wer system facilities. Therefore, the final rule requires scales to be accurate within ±2 pounds of true weight. This absolute accuracy requirement is less stringent than the ±1 percent relative accuracy requirement that was original ly proposed. Scales with accuracy less than ±2 pounds absolute were associated with emission estimate uncertaintie s of greater than 5%, which is too high for yielding data

3 Documentation of the internet research and correspondence with scale ma nufacturers can be found in the docket for this rule (Docket ID No. EPA-HQ-OAR-2009-0927). 4 The analysis in its entirety is pr ovided in the docket for this rule (Docket ID No. EPA-HQ-OAR-2009-0927).

November 2010 8that is useful to policymaking. In addition, numerous commenters recommended an absolute scale accuracy requirement of ±2 pounds as a way to reduce the financial burden to equipment users. 5

6. 

### Reporting Procedures The following supplemental data would be useful for confirming emissions calculations and/or calculating emission rates that could be compared across facilities for quality control purposes:

• Nameplate capacity:

o Existing at the beginning of the year.

o New during the year.

o Retired during the year.

• Transmission miles (length of lines carrying voltages above 35 kV).

• Distribution miles (length of lines carrying voltages at or below 35 kV).

• SF 6 and PFC stored in containers, but not in ener gized equipment, at the beginning of the year.

• SF 6 and PFC stored in containers, but not in en ergized equipment, at the end of the year.

• SF 6 and PFC purchased in bulk from chemical producers or distributors

• SF 6 and PFC purchased from equipment manufacturers or distributors with or inside equipment

• SF 6 and PFC returned to facility after off-site recycling.

• SF 6 and PFC in bulk and contained in equipment sold to other entities.

• SF 6 and PFC returned to suppliers.

• SF 6 and PFC sent off-site for recycling.

• SF 6 and PFC sent off-site for destruction.

7. 

### References BPA (2010). Personal correspondence between Steve Lowd er of Bonneville Power Administration (BPA) and Paul Stewart of ICF International, June 30, 2010. Available in EPA docket EPA-HQ-OAR-2009-0927. CARB (2007) Proposed Regulation Order Division 3. AIR RESOURCES Chapter 1. AIR RESOURCES BOARD Subchapter 10. Climate Change Article 4. Regulations to Achieve Greenhouse Gas Emission Reductions Subarticle 3.1. Regulation for Reducing Sulfur Hexafluoride Emissions from Gas Insulated Switchgear. June 21, 2007. Available at: http://www.arb.ca.gov/regact/2010/sf6elec/appa.pdf FERC (2010) Glossary. Federal Energy Regulatory Commission, Washington, DC. Available at: http://www.ferc.gov/ help/glossary.asp EIA (2007) Electric Power Industry Overview. Energy Information Administration, Washington, DC. Available at: http://www.eia.doe.gov/cneaf/electricity/page/prim2/toc2.html EPA (2008) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006. U.S. Environmental Protection Agency, Washington, DC. Available at: http://www.epa.gov/climatechange/emissions/downloads/08_CR.pdf EPA Partner Meeting (2010). EPA’s SF 6 Emission Reduction Partnership fo r Electric Power Systems Partner Meeting. Dallas, TX. May 13 and 14, 2010. Meeting notes available in EPA docket EPA-HQ-OAR-2009-0927. NERC (2010) Glossary of Terms Used in Reliability Standards. North American Electric Reliability Corporation, Washington, DC. Available at: http://www.nerc.com/docs/standards/rs/Glossary_2009April20.pdf

5 For a summary of public comme nts relating to scale accuracy , see the response-to-comment document for subpart DD in the docket for this rule (Docket ID No. EPA-HQ-OAR-2009-0927).

November 2010 9November 2010 10 Oncor (2010). Personal correspondence among Ray Averitt, Deborah Boyle, and Lauren Casey of Oncor and Paul Stewart of ICF International. June 30, 2010. Available in EPA docket EPA-HQ-OAR-2009-0927.. IPCC (2006) 2006 IPCC Guidelines for National Greenhouse Gas Inventories . The National Greenhouse Gas Inventories Programme, The Intergovernmental Panel on Climate Change, H.S. Eggleston, L. Buendia, K. Miwa, T Ngara, and K. Tanabe (eds.). Hayama, Kana gawa, Japan. Available at: http://www.ipccnggip.iges.or.jp/public/2006gl/index.html. RGGI (2008) Regional Gr eenhouse Gas Initiative Model Rule. Revi sed December 31, 2008. Available at: http://www.rggi.org/docs/Model%20R ule%20Revised%2012.31.08.pdf. RAND (2004) RAND Enviro nmental Science and Policy Center, “Trends in SF 6 Sales and End-Use Applications: 1961-2003,” Katie D. Smythe. International Conference on SF 6 and the Environment: Emission Reduction Strategies . Scottsdale, AZ. December 1-3, 2004. Ava ilable at: http://www.epa.gov/electricpowersf6/documents/conf04_smythe.pdf. UDI (2001) 2001 UDI Directory of Electric Power Producers and Distributors, 109 th Edition , Platts. Available for purchase at: http://www.platts.com/Pro ducts/electricpowerproducerdirectory U.S. Electric Power Utility Representatives (2009) Personal communication betw een Deborah Harris, ICF International and representatives from companies that are Partners in EPA’s SF 6 Emission Reduction Partnership to Electric Power Systems. October 2009. Available in EPA docket EPA-HQ-OAR-2009-0927.