UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF

 AIR AND RADIATION 

Technical Revisions to Subpart W of the Greenhouse Gas Reporting Rule 

Docket: EPA-HQ-OAR-2011-0512 

Title: Transmission Distribution (T-D) Transfer Station Survey Plan Optional Methodology 

Summary: This memo provides a discussion on the option for natural gas distribution facilities 

to conduct monitoring at their T-D transfer stations over a multiple year cycle, not exceeding five 

years. The memo provides the general rationale behind the option provided in this rule and also 

lays out the steps needed to determine emissions from above grade metering-regulating stations. 

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Transmission Distribution (T-D) Transfer Station Survey Plan Optional Methodology 

This memorandum provides a background on amendments to the relevant data calculation 

methodologies and the associated data reporting requirements for local distribution companies 

reporting under the natural gas distribution industry segment of Subpart W of the Greenhouse 

Gas Reporting Program (GHGRP). 

Background 

In November 2010, EPA finalized requirements including provisions for natural gas 

distribution facilities to survey leaks at custody transfer city gate stations (see Mandatory 

Reporting of Greenhouse Gases from Petroleum and Natural Gas Systems – Subpart W, 75 FR 

74458). EPA received requests from industry to clarify the terms “custody transfer” and “city 

gate” which reporters stated were unclear and resulted in confusion as to which stations were 

covered under the rule and further, which stations would require leak surveys. In order to 

address the concerns raised by industry, and to clarify EPA’s intent on which stations were 

covered by the final rule and which stations would require leak surveys, EPA proposed (see 

Technical Revisions and Clarifications to Subpart A, Subpart I, and Subpart W, 76 FR 56010) a 

new definition, transmission-distribution (T-D) transfer station, which clarified which stations 

would require leak surveys under the rule. In addition, EPA proposed a new definition, meteringregulating station, to generally define the types of stations covered under the rule, of which 

transmission-distribution transfer stations are a subset. 

In response to the proposed definitions, commenters were generally in support of the 

definitions. Specifically, commenters stated support for the definition for the T-D transfer 

stations. (see Mandatory Reporting of Greenhouse Gases – Technical Revisions to the Petroleum 

and Natural Gas Systems Category of the Greenhouse Gas Reporting Rule: EPA’s Response to 

Public Comments” docket EPA-HQ-OAR-2011-0512). However, commenters stated that this 

definition would require reporters to conduct leak surveys at above grade metering-regulating 

stations that were not included under what they understood the term “custody transfer station” to 

mean. Commenters further noted that the number of new stations included would increase the 

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burden associated with conformance to the annual leak survey requirement in 40 CFR 98.233(q) 

for natural gas distribution reporters. 

Analysis of Multiple Year Survey Plan for Fulfilling of Leak Survey Requirements in 40 

CFR 98.233(q) 

The November 2010 Final Rule required natural gas distribution reporters to conduct leak 

detection at “custody transfer” stations. Under that rule, EPA estimated that approximately 9,500 

“custody transfer” stations would be monitored nationally. EPA’s analysis was based on the best 

available data and accounted for the monitoring cost of these stations and was based on activity 

data derived from the EPA/GRI Study –Methane Emissions from the Natural Gas Industry 

(1996). In response to confusion about what constitutes a “custody transfer” station, EPA 

proposed in the September 2011 technical corrections rule to require monitoring of 

“transmission-distribution transfer stations.” One commenter, trade association, surveyed 42 of 

their “larger member” natural gas distribution companies. The commenter noted that those 42 

natural gas distribution companies appeared to have 20,781 T-D transfer stations based on the 

proposed definition. 

In a separate analysis conducted under the November 2010 final rule, EPA determined 

that 24 of the largest natural gas distribution company reporters for Subpart W account for about 

50 percent of the total miles of mains from all reporters. It is possible that the number of TD 

transfer stations may have increased based on comments EPA received on the September 9, 2011 

proposal. Therefore, EPA has finalized an amendment in the December 2011 final rule that 

allows natural gas distribution reporters to spread their monitoring of TD transfer stations over a 

maximum period of five years as opposed to the requirement in the November 2010 final rule 

which required all covered stations to be surveyed annually. Based on the analysis EPA 

conducted in the November 2010 final rule (see EIA docket EPA-HQ-OAR-2009-0923) EPA 

estimated that 9,500 number of stations would be surveyed annually, while in this final rule, EPA 

is estimating that on an annual basis less than 9,500 stations will need to be monitored. 

Therefore, the cost estimate for the November 2010 final rule (based on 9,500 stations per year) 

provides a conservative estimate of the annual monitoring required under the December 2011 

final rule (less than 9,500 stations per year). 

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Addition of Equation W-30B for Natural Gas Distribution Industry Segment Reporters 

To reduce the burden, EPA is allowing reporters to complete a leak survey of all of their 

T-D transfer stations over a set number of years (referred to as cycle in 40 CFR Subpart W). A 

cycle can span a maximum of 5 years and an equal number of T-D transfer stations must be 

surveyed during each year of the cycle. For example, if a reporter chooses to complete the survey 

in 4 years, 25 % of the total number of T-D transfer stations must be surveyed each year. The 

emission factor that reporters are required to determine in Equation W-32, uses data from 

surveys in the preceding year of the cycle. 

Steps to estimate emissions from all above grade metering-regulating stations, including TD transfer stations at each facility. 

Step 1: Conduct leak detection at above grade T-D transfer stations. 

Natural gas distribution facilities must conduct leak detection at all their T-D transfer stations 

over a multiple year cycle, not exceeding 5 years. At each T-D transfer station the facility must 

identify a count of equipment leaks by component type. Then the emissions for each component 

type must be added for the number of years that constitute one cycle over the entire facility. For 

the first few years the total will be for whichever years the data is available. This must be done 

using Equation W-30B of this rule as below. 

E = GHG * 

t x (EF *T )	 (Eq. W-30B) s,i i ∑ ∑ p,q 

q=t−n+1 p=1 

Es,i = Annual total volumetric GHG emissions at standard conditions from each 

component type in cubic feet, as specified in (q)(1) through (q)(8) of section 

98.233. 

x = Total number of each component type. 

EF = Leaker emission factor for specific component types listed in Table W-2 through 

Table W-7 of 98.238. 

GHGi = For natural gas distribution, GHGi equals 1 for CH4 and 1.1×10-2 CO2. 

t = Calendar year of reporting. 

n = The number of years over which one complete cycle of leak detection is 

conducted over all the T-D transfer stations in a natural gas distribution facility; 0 

< n ≤ 5. For the first (n-1) calendar years of reporting the summation in Equation 

W-30B should be for years that the data is available. 

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Tp,q = The total time the component, p, was found leaking and operational, in hours, in 

year q. If one leak detection survey is conducted, assume the component was 

leaking for the entire period n. If multiple leak detection surveys are conducted, 

assume that the component found to be leaking has been leaking since the 

previous survey (if not found to be leaking in the previous survey) or the 

beginning of the calendar year (if it was found to be leaking in the previous 

survey). For the last leak detection survey in the cycle, assume that all leaking 

components continue to leak until the end of the cycle. 

Step 2: Develop and emission factor per component type and meter/regulator run 

Facilities must use the total emissions per component type developed in Equation W-30B and 

develop an emission factor per component type and meter/regulator run by dividing this total 

emission by the count of meter/regulator runs at all T-D transfer stations that were monitored in 

the cycle. This must be done using Equation W-32 of this rule as below. 

E ÷ 8760 s,i EF =	 (Eq. W-32) Count 

EF = Facility emission factor for a meter/regulator run per component type at above 

grade metering-regulating for GHGi in cubic feet per meter/regulator run per 

hour. 

Es,i = Annual volumetric GHG i emissions, CO2 or CH4 at standard condition from each 

component type at all above grade TD transfer stations, from Equation W-30B. 

Count = Total number of meter/regulator runs at all TD transfer stations that were 

monitored over the years that constitute one complete cycle as per (q)(8)(i) of 

98.233. 

8760 = Conversion to hourly emissions 

Step 3: Estimate emissions from all above grade meter-regulating stations 

Facilities must use the emission factor per component type and meter/regulator run developed in 

Step 2 and multiply it by the number of meter/regulator runs in the entire facility to estimate 

emissions. This must be done using Equation W-31 of this rule as below. 

Es,i =Counts *EFs *GHGi *Ts	 (Eq. W-31) 

Es,i = Annual volumetric GHG emissions at standard conditions from each component 

type in cubic feet. 

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Counts = Total number of this type of emission source at the facility. Natural gas 

distribution shall count the meter/regulator runs as described in paragraph (r)(6) 

of 98.233. 

EF = Population emission factor for the specific component type, as listed in Table 

W-1A and Tables W-3 through Table W-7 of this subpart. EF for 

meter/regulator runs at above grade metering-regulating stations is determined 

in Equation W-32. 

GHGi = For natural gas distribution, GHGi equals 1 for CH4 and 1.1×10-2 CO2. 

Ts = Average estimated time that each component type associated with the 

equipment leak emission was operational in the calendar year, in hours, using 

engineering estimate based on best available data. 

Conclusion 

EPA is amending 40 CFR 98.233(q)(8) by allowing each above grade T-D transfer station the 

option to conduct a leak detection survey at least once in any five consecutive calendar years, 

with a minimum of 20 percent of their total number of stations being leak surveyed annually. 

EPA evaluated Department of Transportation (DOT) regulations for comparison in the context of 

monitoring frequency. As provided in the November 2010 docket memorandum “Understanding 

the Substance of DOT Regulations and Comparing them to the Subpart W Requirements,” DOT 

requires leak detection surveys annually for more populated areas and every five years for less 

populated locations. Although the DOT regulations cover various stations are not duplicative of 

EPA regulations under the Greenhouse Gas Reporting Program, providing the option to align the 

survey frequencies for both requirements may reduce burden for some reporters. EPA added the 

five consecutive year leak detection period to potentially coincide with reporters’ leak inspection 

requirement under DOT regulations in order to give reporters the opportunity to fulfill Subpart 

W requirements during the regular DOT survey or maintenance visit. Thus the annual burden is 

not increased and the necessary data is collected over a longer period of time and EPA concludes 

that the new requirements do not place additional burden in terms of visitation frequency on 

natural gas distribution reporters1

. 

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 For further details on DOT requirements, please see the November 2010 docket memorandum “Understanding the 

Substance of DOT Regulations and Comparing them to the Subpart W Requirements” and Section II.D of the 

preamble to this final rule: Technical Revisions to Subpart W of the Greenhouse Gas Reporting Rule . 

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