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 be hind the option provided in this rule and also lays out the steps needed to de termine emissions from above gr ade metering-regulating stations.

1Transmission Distribution (T-D) Transfer Station Survey Plan Optional Methodology

This memorandum provides a background on amendm ents to the relevant data calculation methodologies and the associated data reporting requirements for local distribution companies reporting under the natural gas distribution indu stry segment of Subpart W of the Greenhouse Gas Reporting Program (GHGRP).

Background In November 2010, EPA finalized requirement s including provisions for natural gas distribution facilities to survey leaks at custody transfer city gate stations (see Mandatory Reporting of Greenhouse Gases from Petroleum a nd Natural Gas Systems – Subpart W, 75 FR 74458). EPA received requests from industry to clarify the terms “custo dy transfer” and “city gate” which reporters stated were unclear and resulted in confusi on as to which stations were
covered under the rule and furthe r, 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 w ould require leak surveys, EPA proposed (see
Technical Revisions and Clarific ations to Subpart A, Subpart I, and Subpart W, 76 FR 56010) a new definition, transmission-distribution (T-D) tran sfer station, which clar ified which stations would require leak surveys under the rule. In a ddition, 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, comm enters were generally in support of the definitions. Specifically, commenters stated supp ort 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 Green house 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

2burden associated with conformance to the annu al leak survey require ment 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 natura l gas distribution repor ters to conduct leak detection at “custody transfer” st ations. Under that ru le, EPA estimated that approximately 9,500 “custody transfer” stations would be monitored nationally. EPA’s an alysis 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 tr ansfer” station, EPA proposed in the September 2011 technical corr ections rule to require monitoring of
“transmission-distribution transfer stations.” On e commenter, trade association, surveyed 42 of their “larger member” natural ga s 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 co nducted 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 re porters. 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 th e requirement in the November 2010 final rule which required all covered stations to be su rveyed annually. Based on the analysis EPA
conducted in the November 2010 final rule (see EIA docket EP A-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 th an 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 a nnual monitoring required under the December 2011 final rule (less than 9,50 0 stations per year).

3Addition of Equation W-30B for Natural Ga s 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 eq ual number of T-D transfer stations must be surveyed during each year of the cycle. For exampl e, if a reporter chooses to complete the survey in 4 years, 25 % of the total number of T-D tran sfer 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 gr ade metering-regulating stations, including T

D 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 al l their T-D transfer stations over a multiple year cycle, not exceeding 5 years. At each T-D transfer sta tion 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

E s,i = Annual total volumetric GHG emissions at standard conditions from each component type in cubic feet, as specif ied 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.
GHG i = For natural gas distribution, GHG i equals 1 for CH 4 and 1.1×10 -2 CO 2 . t = Calendar year of reporting.

n = The number of years over which one co mplete cycle of leak detection is conducted over all the T-D transfer stations in a natural gas di stribution 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.

4T p,q = The total time the component, p, was f ound 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 l eaking 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 surv ey 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 co mponent 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/regulat or runs at all T-D transfer st ations 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 GHG i in cubic feet per me ter/regulator run per hour.
E s,i = Annual volumetric GHG i emissions, CO 2 or CH 4 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 a ll above grade meter-regulating stations
Facilities must use the emission factor per com ponent type and meter/regu lator run developed in Step 2 and multiply it by the number of meter/regul ator runs in the entire facility to estimate emissions. This must be done using E quation W-31 of this rule as below.



### E

s , i 

### = Count
s 

### * EF
s 

### * GHG i 

### * T
s (Eq. W-31)

E s,i = Annual volumetric GHG emissions at standard conditions from each component type in cubic feet.

5Count s = Total number of this type of emission source at the facility. Natural gas distribution shall count the meter/regulato r runs as described in paragraph (r)(6) of 98.233.
EF = Population emission factor for the sp ecific 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 mete ring-regulating stations is determined in Equation W-32.
GHG i = For natural gas distribution, GHG i equals 1 for CH 4 and 1.1×10 -2 CO 2 . T s = Average estimated time that each co mponent 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 detecti on 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 compar ison in the context of monitoring frequency. As provided in the November 2010 docket memorandum “Understanding the Substance of DOT Regulati ons and Comparing them to th e Subpart W Requirements,” DOT requires leak detection surveys annually for mo re populated areas and ev ery five years for less populated locations. Although the DOT regulations c over various stations ar e not duplicative of EPA regulations under the Greenhouse Gas Reporti ng 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 detec tion period to potentially coincide with reporters’ leak inspection requirement under DOT regulations in order to give reporters th e opportunity to fulfill Subpart W requirements during the regular DOT survey or maintenance visit. Th us the annual burden is not increased and the necessary data is collecte d over a longer period of time and EPA concludes that the new requirements do not place additional burden in te rms of visitation frequency on natural gas distribution reporters 1

.

1 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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