1 MEMORANDUM

TO: Docket # EPA-HQ-OAR-2011-0512

FROM: Alexis McKittrick and Mark DeFigueiredo, EPA/CCD

DATE : February 20, 2014

SUBJECT : Greenhouse Gas Reporting Rule: Te chnical Support for Revisions and Confidentiality Determinations for Petr oleum and Natural Gas Systems; Proposed
Rule

The EPA is proposing revisions a nd other clarifications to 40 CFR part 98, subpart W (hereafter referred to as “subpart W”). This memora ndum provides background information on certain proposed revisions relating to the following emission sources or specific provisions 1 :

1. Well venting for liquids unloading

2. Gas well venting during completions and workovers with hydraulic fracturing

3. Blowdown vent stacks

4. Dump valves not closing properly at onshore production storage tanks

5. Associated gas venting and flar ing from produced hydrocarbons

6. Reciprocating and centrifugal compressor venting

7. Best available monitoring methods (BAMM).

1 WELL VENTING FOR LIQUIDS UNLOADING

The EPA is proposing to revise the calc ulation and reporting requirements for well venting from liquids unloading to allow for annualiz ing venting data for faci lities that calculate emissions using a recording flow meter (Cal culation Method 1). This proposed amendment would address reporter concer ns and simplify reporting.

Some reporters have expresse d difficulty in collecting well venting data using a recording flow meter for the exact period of January 1 to December 31, because they contend that it would require them to be physically present at each recording flow meter on December 31. These reporters described that the ac tivity data gathered for liquids unloading associated with well venting events are often recorded locally at the well site. They asserted that the data are not

1 For background information related to other proposed revisions, please refer to documents contained in Docket No. EPA-HQ-OAR-2011-0512.2 transmitted to a centralized location and must be collected by a technician visiting each well site. As a result, they asserted that it is logistically difficult for some reporters with multiple wells in this configuration to collect data from all we lls on exactly December 31st or January 1st. They suggested that it would be more practical for these reporters to collect the data over a period of several weeks, depending on the number of wells and the distance between wells.

Options to address this issu e of allowing reporters to use time periods other than exactly January 1 to December 31 (e.g., a period that may cover 300 to 400 days, instead of exactly 365) include: (1) allow the use of an average estima ted time that venting occurs in a year, using engineering estimates based on be st available data; or (2) a llow reporters to compute an

annualized estimate based on data that are coll ected over at least 300 days of the reporting period. The first option increases information collection flexibility and requires minimal revisions to the current regulat ory language. However, the option potentially compromises data quality due to use of inconsistent methods amon g reporters to perform th e engineering estimates. The second option increases information collection flexibility as well, while still requiring the collection of venting data and avoiding both th e need to use engineering estimates and to

establish criteria for “best available data.” A dditionally, the same procedure would be used across all reporters, resulting in a consistent emissions calculation method. Although the collected data may or may not represent the exact reporting year, if each monitoring period begins immediately following the last, then all venting events w ould be captured in one of two consecutive reporting years. For example, if a re porter chose to collect data for the period from January 1, 2014 to December 1, 2014 for the 2014 repor ting year, then the da ta collection for the 2015 reporting year would start on December 2, 2014 as opposed to January 1, 2015.

The EPA is proposing to revise Calculation Method 1 (40 CFR 98.233(f)(1)) such that reporters may use an annualized value to determine the cumulative amount of time of venting (“Tp” in Equation W-7A and W-7B) if data ar e not available for the specific time period January 1 to December 31. The EPA is specifying that if an annualized value is used, the monitoring period must begin before February 1 and must not end before December 1 of the reporting year, and that a minimum of 300 cons ecutive days must be used by reporters to

determine the annualized vent time. The EPA is al so proposing that the date of the end of one monitoring period must be the start of the next monitoring period for the next reporting year, and that all days must be monitored and all venti ng accounted for. The EPA is proposing that if a reporter uses a monitoring period other than a full calendar year for any we ll, they must report the percentage of wells for which a monitoring period other than a full calendar year is used.

The EPA is also proposing an additional ch ange to Calculation Method 1 at 40 CFR 98.233(f)(1) to separate the calculation and reporti ng of emissions from wells that have plunger lifts and wells that do not have plunger lifts. The calculation and reporti ng of emissions from these sources separately would allow the EPA and the public to better analyze the reported emissions and activity data. A clarification is also proposed for Calculation Method 2 at 40 CFR 98.233(f)(2) to clarify that this method is used for wells without plunger lifts.3 The EPA also proposes to amend the definition of the term “SP p ” in Equation W-8 (40 CFR 98.233(f)(2)) to clarify that if casing pressure is not availabl e for each well, reporters may determine the casing pressure usi ng a ratio of the casing pressure to tubing pressure from a well in the same sub-basin where the casing pressu re is known. This amendment would improve the consistency of the calculation method used to determine casing pressure across reporters.

2 GAS WELL VENTING DURING COMPLETIONS AND WORKOVERS WITH

HYDRAULIC FRACTURING

The EPA is proposing to amend 40 CFR 98.238 to add definitions for “reduced emissions completion” and “reduced emissions workover.” Currently, reduced emissions completions and

reduced emission workovers are mentioned in the relevant calculation method as equipment that separates natural gas from the backflow and sends this natural gas to a flow-line. However, the rule currently has no defined terms for reducedemissions completions and reduced emissions workovers. Since the time that subpart W wa s promulgated, the EPA promulgated new source performance standards for the o il and natural gas sector under 40 CFR part 60, subpart OOOO, that requires the use of a reduced emissions comp letion (following fracturing or re-fracturing) in specified circumstances.

The EPA is proposing to add a definition for “reduced emissions completion” to subpart

W that would be consistent with the description of that term in the new source performance standard (see 76 FR 52757-8, August 23, 2011). Speci fically, the EPA is proposing to amend 40
CFR 98.238 to define a “redu ced emissions completion” as a well completion following fracturing where gas flowback that is otherwise vented is captur ed, cleaned, and routed to the flow line or collection system, re-injected into th e well or another well, used as an on-site fuel source, or used for other useful purpose that a pur chased fuel or raw material would serve, with no direct release to the atmosphere. We ar e proposing to amend 40 CFR 98.238 to define a

“reduced emissions workover” as a well workover with hydraulic fr acturing (i.e., re-fracturing) where gas flowback that is otherwise vented is captured, cleaned, and routed to the flow line or collection system, re-injected into the well or anothe r well, used as an on-site fuel source, or used for other useful purpose that a purchased fuel or raw material would serve, with no direct release to the atmosphere.

The EPA is also proposing to amend the de finition of “well completions” in 40 CFR 98.6

to delete the term “re-fracture” because this te rm applies to an already producing well and a “refracturing” is considered a well workover, not a well completion, for the purposes of Part 98. This amendment is intended to avoid potential confusion concerning whet her a re-fracture is a completion or workover in the context of subpart W. This change would also better align the existing definition of “well completions” with the new proposed definition of a “reduced emissions completion” by clarif ying that a reduced emission completion applies to only new fractures and that re-fractures are potentiall y covered under the new definition of “reduced

emission workover.” The definition of “well wo rkover” in 40 CFR 98.6 already refers to refractures, so no clarifying change is needed for that definition.4 The EPA is also proposing to revise re porting requirements for completions and workovers to differentiate between completi ons and workovers with different well type combinations in each sub-basin category. A well type combination is being proposed as a unique combination of the following factors: vertical or horizontal (i.e., directiona l drilling), with flaring or without flaring, and reduced emission co mpletion/workover or not reduced emission completion/workover. Specifically, for well completions and workovers with hydraulic fracturing, the EPA is proposing to require separa te counts and separate reporting of emissions for the different well type combinations. These revisions would improve data quality for emissions from wells with hydraulic fracturi ng. The EPA is also proposing revisions to Equation W-10A that would add clarity and increas e the accuracy of emissions calculations for gas well completions and workovers with hydraulic fracturing. In the final subpart W rule, the measurement or calculation for determining the ratio of flowback during well completions and workovers to 30-day production rate in Equation W-10A (40 CFR 98.233(g)) begins immediately upon initiating flowback of a well. Some reporters have asserted that the flowback characteristics of a well following hydraulic fractu ring do not enable measurement or calculation to begin immediately upon initiating flowback due to a lack of sufficient gas being present, and

the calculation needs to be revised to account fo r this fact. Therefore, the EPA is proposing to modify the calculation to require the measuremen t of flow rate only when sufficient gas is present to enable flow rate measurement. In addition, some reporters have asserted that the accuracy of emissions calculati ons could be affected by the co mbined use of sales gas volume and approximations on flow rates for non-measured wells. To resolve this apparent issue, the time variable “Tp” in Equation W-10A and W-10B is being modified. Time that the gas is routed to production would no longer be included, so it would no longer be necessary to subtract the volume of gas being sent to sales.

The EPA is also proposing changes to 40 CFR 98.233(g) and (h) to support the separate

calculation of emissions from completions and workovers that are vented, flared, or use equipment that separates natural gas from the back flow and sends this natural gas to a flow-line (i.e., reduced emissions completions or reduced emissions workovers). Reporters currently calculate emissions from all completion and workover activities, but the equations do not facilitate the classification of the activity need ed for separate reporting. The EPA is proposing to revise Equation W-13 in 40 CFR 98.233(h) to se parate the calculation of emissions from workovers from the calculation of completions in to two equations. The EPA is also proposing to clarify that reporters must calc ulate the annual volumetric natura l gas emissions from each gas well venting during workovers without hydrauli c fracturing using Equation W-13A and from each gas well venting from completions wit hout hydraulic fracturing using new Equation W13B. The proposed methodology also requi res the addition of parameter “E s,p ” for Equation W13B to specify the annual volumet ric natural gas emissions in st andard cubic feet from well completions. We are also proposing to revise 40 CFR 98.233(g)(1) to cl arify the number of

measurements or calculations that must be take n to estimate the average ratio of flowback rate (FRM).5 3 BLOWDOWN VENT STACKS

During implementation of the final subpart W rule, some reporters requested that the EPA allow the use of a factor to adjust for co mpressibility when calculating emissions from

blowdown vents. The calculation method for blow down vents included in the existing subpart W rule assumes natural gas is an ideal gas with a compressibility factor of 1, and does not include an adjustment for compressibility in the calculation.

The compressibility of methane at standardconditions is close to 1. However, the compressibility of methane at low temperatures and high pressures is sign ificantly different, as illustrated in Table 3.1. The natural gas pro cessing and transmission compression segments covered by subpart W can operate systems at pressures higher than 25 atmospheres. 2

Table 3.1. Compressibility of Natural Gas at Sample Temperatures and Pressures 3

Temperature (deg K) 1 atm 5 atm 10 atm 40 atm

150 0.9854 0.9225 0.8275 0.1411

200 0.9936 0.9676 0.9339 0.6784

250 0.9965 0.9838 0.9680 0.8682

350 0.9991 0.9954 0.9911 0.9662

Although the EPA had previously considered including the compressibi lity term (76 FR 56010, September 9, 2011), the EPA ultimately did not propose including the factor. The EPA concluded at that time that including a compressi bility adjustment coul d create a degree of uncertainty among reporters when trying to compare their reported blowdown values on a

volume basis. The EPA noted at that time th at although the compressibility of pure light hydrocarbon substances is well known, the compressi bility of hydrocarbon mi xtures is less well known and the composition of natural gas throughout the segments covered by subpart W can be variable. At that time, we determined that ideal gas law calculations we re adequate for reporting purposes under Part 98.

The EPA notes that the circumstances surround ing this issue are now different, because the EPA is proposing the option of using site-spe cific data for gas compositions, if available. Therefore, the original concern regarding the variation in the compos ition of natural gas at subpart W facilities and its eff ect on compressibility would be addressed through data collection on actual gas composition. The EPA has determined that at high pressures and low temperatures, the accuracy of the emission estimate would be improved if a compressibility factor were

included in the calculation.

2 Natural gas transmission compressor station components and main line pressures are in the range of 500 to 1000 psi (34 to 68 atmospheres). See page 6-32, American Petroleum Institute (August 2009), Compendium of Greenhouse Gas Emission Methodologies for the Oil and Natural Gas Industry

. 3 Values derived from Table 3-172 of Perry, R. H. (1984). Perry's Chemical Engineers' Handbook, Sixth Edition. New York, New York: McGraw-Hill Book Company.6 Options to address the compressibility factor include: (1) include the compressibility term “z” into Equations W-14A and W-14B with the requi rement that “z” can be assumed to be “1” if the temperature is above -10 degr ees Fahrenheit and pressure is below 5 atmospheres (or if the compressibility factor at the actual temperature and pressure is 0.98 or greater) or (2) allow the compressibility to be used at the reporter’s discretion. The EPA is proposing the first option above to ensure clarity and consistency with any variations in the compre ssibility term from “1” are applied among reporters.

The EPA is proposing to remove the currentreporting requirement s for blowdown vents in the rule related to “unique physical volumes,” but would retain the requirement to calculate and keep records for blowdown vent stack emissions from each unique volume. Examples of the proposed equipment types that would replace th e requirement in 40 CF R 98.233(i) to track and report by unique volume are identified as follows:

 Station piping

 Pipeline venting (inside the co mpressor station fence line)

 Compressors

 Scrubbers/Strainers

 Pig launchers and receivers

 Emergency shutdowns

 All other blowdowns greater than or equal to 50 cubic feet.

These equipment categories cover all blowdow n venting from equipment or event types associated with the three (3 ) source categories (i.e., onshore natural gas processing, onshore natural gas transmission compression, and lique fied natural gas (LNG) import and export equipment). With this proposed option, the repo rting burden would be reduced and detailed information on equipment type would provide the EPA with sufficient detail to determine the

source of emissions.

The EPA is not proposing a change to the “unique volume” calculation methods, because

an accurate estimate of emissions can be obtaine d only by either estimating the actual volume of equipment vented, or by directly measuring th e emissions. The calculation methods in 40 CFR 98.233(i)(2) (i.e., Equations W-14A and W-14B) would not need to be revised, because all reporters would still need to determine annua l venting emissions for each unique volume.

It is possible that some facilities are currently using (or would prefer to use) a flow meter

on some of their blowdown vents. If a flow me ter were used, Equation W-14A or W-14B would not be necessary for calculating the annual volum etric amount of natural gas vented. This option would allow reporters to use an ex isting flow meter, or to install a flow meter in locations where

emissions are a routine occurrence rather than calculating indivi dual volumes. The accuracy of flow meter measurements is equal to or gr eater than the curren t unique volume method. Therefore, the EPA is also proposing an op tional calculation method for blowdown emissions7 where a flow meter is in place to measure the emissions directly. If a bl owdown vent is equipped with a flow meter, there would not be an advant age to calculating the em issions using the unique volume, temperature, and pressure conditions of the equipment instead of the directly measured flow rate. The EPA is proposing this alternat ive calculation method in 40 CFR 98.233(i), along with associated reporting requirements in 40 CFR 98.236.

4 DUMP VALVES NOT CLOSING PROP ERLY AT ONSHORE PRODUCTION

STORAGE TANKS

Currently, subpart W reporters must calcula te annual emissions from onshore production storage tanks, including emi ssions during periods when the liquid dump valve on gas-liquid separators does not close pr operly (40 CFR 98.233(j)(8)).

Some reporters have asserted that the curren t requirements for calculating emissions from separator dump valves that ar e not closing properly requires a high effort to monitor and document that separator dump va lves are closing properly. They have also asserted that the current equations require them to keep unnece ssarily large amounts of records to document periods when the valves are closing prope rly, as well as not closing properly.

According to these reporters, onshore produc tion companies typically have equipment maintenance and monitoring programs in place to maintain the integrity of their equipment and to minimize losses of natural gas from various ty pes of equipment leaks, including dump valves that are not closing properly on gas liquid separators on ons hore production storage tanks.

Large companies may be responsible for se veral thousand dump valves and some may use remote monitoring to determine whether or not the dump valves are operating properly, while other companies may rely on technicians vi siting a well site to test the equipment and ensure it is working properly. Companies thatuse remote monitoring can determine if a dump valve is not closing properly, as indicated by a drop in pressu re, a low level in a gas/liquid separator, a decrease in gas production rates, or a sudden increase in the level of a storage tank. Reporters have asserted that field technicians usually undert ake corrective actions within 24 hours of when companies detect abnormal operations at remotely monitored wells.

Other companies may rely on field technicians alone to ensure that equipment such as dump valves are operating correc tly. Field technicians will take corrective actions when they detect faulty equipment. Reporters have assert ed that the frequency with which a technician visits a well will depend on the company’s standa rd operating procedures, but it will range from once every few days to no more than once every two weeks.

In the case of either remote monitoring or field monitoring of equi pment, some reporters further asserted that they should not need to record information documen ting the occurrences of dump valves that are closing properly and should, instead, reco rd only those times when the dump valves are not closing prope rly. They asserted that because dump valves operate properly the vast majority of the time and because many companies are responsible for large numbers of8 dump valves that are monitored continuously or visited frequently, doc umenting that they are operating properly entails making and keeping large amounts of records that can become

burdensome.

Equation W-16 in the current rule also does notcalculate separately emissions for those periods when the dump valves are not closing pr operly. Instead, the current equation calculates total annual emissions from each storage tank, and combines emissions during normal dump valve operation with emissions when dump valves are not closing properl y. Under the current equation, the data do not distingui sh emissions that occur when dump valves are not closing properly from the total emissions from the sepa rator on the storage tank. Therefore, the EPA is proposing to simplify Equation W-16 to calculate emissions for only pe riods when the dump valve is not closing properly. Th e EPA is clarifying that the revi sed equation calculates only the

additional emissions that result when th e dump valve is not closing properly.

Because the revised Equation W-16 would calcu late only the additional emissions from dump valves not closing properly, it was necessary to adjust the co rrection factors (CFn) in order to simplify the equation. The EPA is proposing to decrease the correcti on factors for crude oil production and gas condensate production by “1” to reflect emissions originating only from the dump valve not closing properly.

5 ASSOCIATED GAS VENTING AND FLARING FROM PRODUCED

HYDROCARBONS

Subpart W reporters must calculate annual emi ssions from associated natural gas venting and flaring (40 CFR 98.233(m)).

Some reporters have requeste d that a term be added to Equation W-18 to account for situations where a portion of the natural gas is going to the sales line and a portion of the natural gas is flared. These reporters described situa tions in which new well production could exceed the capacity of the sales line until the downstream op erator makes adjustments, or where temporary equipment problems limit the sales line capacity. In these situations, some of the natural gas production from a well may be flared while some of the production goes to sales. In this case, these reporters assert that the associated ga s emissions calculation method, found in Equation W18, would overestimate the associated gas emissi ons, because the equation estimates emissions based on the gas to oil ratio (GOR) and volume of oil produced during th e flaring period. The GOR is based on total gas from the well, which means all the gas would be reported as flared, despite some of the gas going to the sales line.

Three options to address these re porters’ concerns are: (1) a llow the use of an “adjusted” gas to oil ratio, where reporters would use engineer ing estimates to revise the gas to oil ratio to account for average amount of gas sent to sales; (2) require re porters to meter the amount of associated gas vented or flared; or (3) add a defi nition of “Associated gas venting or flaring” to clarify what is covered by this term and add term s to Equation W-18 to exclude gas sent to sales

and emissions that are calculated an d reported elsewhere under subpart W.9 Allowing reporters to use engineering estimates in the first option to revise the gas to oil ratio to account for average amount of gas sent to sales could provide flex ibility, but would result in inconsistent data collection among reporters and could potentially compromise data quality. The second option to require reporters to meter th e amount of associated gas vented or flared would result in greater data quality but could potentially increase burden on reporters.

The EPA is proposing the third option of addi ng a definition of “Associated gas venting or flaring” and adding terms to Equation W-18 to subtract the volume of associated gas sent to sales from the annual volumetric natural gas emi ssions from associated gas venting. The EPA is also proposing to include in the equation a term for emissions that are calculated and reported in other sections of subpart W. These proposed ch anges would minimize the risk of over-estimating emissions, clarify the emissions to be reported, an d are not expected to significantly increase the reporting burden.

6 RECIPROCATING AND CENTRIFUGAL COMPRESSOR VENTING

To address the issue of measuring compre ssors every 3 years in the not-operatingdepressurized-mode, options include: (1) allo w measurement in not-operating-depressurizedmode to be taken at the next scheduled depr essurized compressor shutdown (for reciprocating compressors, this measurement can be taken during the next scheduled shutdown when the compressor rod packing is replaced); and (2) allo w measurement in not-operating-depressurizedmode to be taken every 5 years (instead of on ce every 3 years). The option to allow measurement in not-operating-depressurized-mode to be taken at the next scheduled depressurized compressor shutdown would require minimal revisions to regula tory text, allow report ers flexibility, provide consistent data collection among re porters, and facilities would notpotentially have to shut down a compressor every 3 years for the sole purpose of measuring that compressor in not-operatingdepressurized-mode. The option to allow measur ement in not-operating-depressurized-mode to be taken every 5 years would result in minimal re visions to regulatory te xt, and would eliminate facilities having to shut down a compressor prio r to every 5 years for the sole purpose of measuring in not-operating-depressurized-mode. However, this option may not provide enough flexibility for reporters who do not shut down their compressor(s) within a 5-year period. Therefore, the EPA is proposing to revise the requirement to measure each compressor in the not-operating-depressurized-mode at least on ce every 3 years. In place of the current requirements, the EPA is proposing that each compressor must be measured in not-operatingdepressurized-mode at least once in any 3 consecu tive calendar years, provided the measurement can be taken during a scheduled shutdown. If there is no scheduled shutdown within 3 consecutive calendar years, then a measurement w ould have to be made at the next scheduled depressurized compressor shutdown. For reciproca ting compressors, this measurement could be taken during the next scheduled depressurized shutdown when the compressor rod packing is replaced.

Some reporters have contended that it is notpractical to require a measurement from each individual compressor for groups of compressors th at are routed to a co mmon vent manifold (or10 flare header), because this would require the en tire group of compressors that are connected to the common manifold (or flare header) to be shutdown, blown down, and purged in order to safely install meters (or ports for temporary meters) and enable individual measurements. The reporters stated that it is extr emely rare that entire groups of compressors are shutdown at the same time. In the November 2010 response to public comments on the subpart W final rule (Docket ID No. EPA-HQ-OAR-200 9-0923), the EPA noted that comm enters requested that the

EPA allow direct measurements of common manifo lded vent lines on compressors. At least one

commenter stated that if conti nuous measurement of manifolded vent lines and aggregate annual emissions reporting were allowed as an option for measuring compressors, they would be able to safely collect and report to th e EPA continuously measured data . The EPA did not include this option in the 2010 final subpart W rule because it was not clear whether measurements at a common vent outlet could be used to correctly characterize annual emissions from individual

compressors.

To address the issue of having to measure individual compressors that are manifolded to a single vent, options include requiring reporters to take either one, two, or three measurements per year on the common vent (or flare) stack that is associated with the manifolded group of compressor sources (before emissions are co mingled with other non-compressor emission sources). The option to require one or two annual m easurements from a single point in the manifold would likely reduce overall burden on re porters. However, the process variation in a manifold fed by several sources over the year could be high enough that overall data quality

could be reduced if one or two measurements are not representative of the entire year’s operations. The option to require three annual meas urements from a single point in a manifold would likely reduce overall burden on reporters, wh ile ensuring a more representative data set and better data quality than collecting one or tw o data points. Any of these options to require annual measurements would resolve the reporter’s concerns about the techni cal and safety issues with installing and utilizing samp ling ports in manifolded lines. The accuracy of these options would vary with the number of annual m easurements that would be required.

For compressors that are manifolded to a common vent (or flare header), the EPA is proposing to require measurements to be taken at least three times per year at a single point in the manifold, downstream of all compressor inputs. These measurements would need to be taken where emissions cannot be comingled with othe r non-compressor emission sources. This option

would maintain accurate characterization of annua l emissions from compressors at the facility.

Annual volumetric emissions would be determin ed for each manifolded group of compressors combined for all operating conditions (mode-source combinations). Reporters would still be required to report activity data for any individu ally measured sources (i.e., non-manifolded sources) at the compressor level. However, th e EPA proposes that operators that choose to conduct continuous measurements at a single point in the manifold downstream of all compressor inputs would report emissions at the manifold level. Activity data reported would include information about the individual compresso rs included in the manifolded vent. This proposed measurement option would allow the EPA to correctly characteri ze and analyze total11 compressor emissions at individual facilities in the petroleum and natu ral gas source category while reducing burden to the industry.

Currently, for most emission sources (incl uding compressors), subpart W requires that flare emissions be calculated separately for each source type, backed out of the total flare emissions, and reported with each source type sepa rately. For other emission sources that do not have a requirement to report as a specific source type emission, the remaining flare emissions are reported in the flare source type. To address the issue of having to measure each compressor when it is routed to an operati onal flare, facilities c ould calculate and report emissions with other

flare emissions. This would addre ss reporters’ safety concerns, pr ovide reporters flexibility, and would reduce burden by not requirin g reporters to sample compresso rs individually to calculate the portion combusted in the flare.

The EPA is proposing to allow operators to calculate and repo rt emissions from compressors that are routed to a flare with ot her flare emissions (in lieu of backing these

emissions out of the total flare emissions and reporting them as compressor emissions).

7 BEST AVAILABLE MONITORING METHODS (BAMM)

In order to provide facilities with time to adju st to the requirements of the rule, subpart W has provisions allowing the optional use of BAMM for unique or unusual circumstances. Where a facility uses BAMM, it is required to follow em ission calculations specified by the EPA, but is

allowed to use alternative methods for determini ng inputs to calculate em issions. Inputs are the values used by facilities to calculate equation outputs. Examples of BAMM include: Monitoring methods used by the facility that do not meet th e specifications of subpart W, supplier data, engineering calculations, and other company records. Faciliti es are required to receive approval from the EPA prior to using BAMM and these fa cilities are required to specify in their GHG annual reports when BAMM is used for an emission source.

The EPA has previously noted that the Agen cy intended to “approve the use of BAMM beyond 2011 only in cases that are unique or unusual” (76 FR 59538). Furthermore, the EPA limited the approvals of BAMM to one reporting year in k eeping with the intent to allow use of BAMM as a transitional provision until facilities co me into compliance with the final rule. While the EPA occasionally uses BAMM for targeted, short-term monitoring flexibilities (i.e., provision for reporters who become subject to Pa rt 98 from the recent GWP changes to subpart

A to have automatic BAMM for the first three months of reporting), no industry-specific subpart
within Part 98 continues to use the BAMM flexibility ex cept subpart W.

The EPA has proposed several revisions to the subpart W calculation methods and reporting requirements addressing technical feasib ility. Table 7.1 summarizes examples of such proposed revisions to the rule, by emission sour ce type. The proposed changes would modify the subpart W data collection and calculation requirements, reso lving the need for the BAMM flexibility beyond the effective date of the final rule.12 Table 7.1. Examples of Proposed Revisions.

Emission Source Type Issue Proposed Revisions Centrifugal and reciprocating

compressors Compressor emissions are manifolded together and individual compressor vents are not accessible or practical to measure. Language was added to subpart W to
allow emission measurement at the manifold vent outlet, rather than at each individual compressor.Reporting emissions for notoperating-depressurized-mode. Measurements in the not-operatingdepressurized-mode should be taken during scheduled depressurized compressor shutdowns. If there is no scheduled depressurized shutdown within three consecutive calendar years, then the
measurement must be taken at the next
scheduled shutdown. For reciprocating compressors, reporters can take these measurements during the
next scheduled shutdown when the compressor rod packing is replaced. Compressor emissions routed to flares must be sampled individually and reported separately as a portion
of the flare emissions. Allow reporters to calculate and report compressor emissions sent to an operating flare in combination with other flare emissions. Reporters would still report compressor-related activity data. Onshore production storage
tanks Reporting of emissions from dump valves that are not closing properly. Facilities must still report emissions from dump valves that are not closing properly. Equation W-16 was revised to calculate emissions that result from only the dump valves that are not closing properly. Recordkeeping revised to keep records only for the dump valves that are not closing properly; removed the need to keep records for properly closing dump
valves. Blowdown vent stacks Method of reporting data by unique physical volume is not consistent with industry practices. Blowdown emissions may be grouped by equipment type for reporting, but
emissions must still be calculated for each unique physical volume. Alternatively, facilities may use a flow

meter. Well venting for liquids unloading Not feasible to gather vent hours or number of unloadings from all controllers on one day, i.e. January 1
or December 31. Language was revised to allow facilities to use an annualized value and gather data for monitoring periods with start/end dates between December 1 and January 31 that are at least 300 days. Parameters such as well depth and casing or tubing in ternal diameter
are not available. No change in rule because facilities have been able to use existing BAMM periods
to collect needed data. Uncertainty regarding definition of shut-in pressure in Equation W-8. Shut-in pressure definition was revised to clarify when it should be determined.
Definition was also revised to describe how to estimate casing pressure for a well if it is not known, using data from
other wells in the same sub-basin.13 Emission Source Type Issue Proposed Revisions Completions and workovers Uncertainty regarding the point in time when a completion or workover begins. Equations W-10A and W-10B were revised for clarity regarding start times to require the measurement of flow rate only when sufficient gas is present to
enable flow rate measurement.
Parameter “FRM
s ” in Equation W10A is not well-specific. “FRM
s ” was modified to be specific to each sub-basin and well type
combination. Flowback measurement equipment may not be available to meet
demand. No change in rule because facilities have been able to use existing BAMM periods to address equipment availability issues.

The EPA is proposing to remove all provi sions in 40 CFR 98.234(f) for BAMM. The removal of BAMM would improve data quality by requiring consistent reporting for each segment in subpart W. The EPA is proposing to remove the BAMM provisions, because it is expected that facilities would be able to comply with the monitoring and QA/QC methods required under subpart W if the proposed amendments are finalized. It has been the EPA’s intent throughout implementation of subpart W that BAMM be available as a limited, transitional program to serve as a bridge to full compliance with the rule for cases where reporters faced reasonable impediments to using the monitoring methods in the rule. The proposed amendments are in keeping with the EPA’s stated intent to transition to re porting without BAMM.