 Change Agents:
Making Sense of the Subpart W Revisions
White Paper
 Enviance
 Change Agents: Making Sense of the Subpart W Revisions
Change Agents:
Making Sense of
the Subpart W
Revisions
White Paper
On December 23, 2011, the Environmental
Protection Agency issued a final rule that
amends Subparts A and more significantly,
Subpart W of the EPA Greenhouse Gas
Mandatory Reporting Rule (GHG MRR).
The revisions were intended to correct errors
and address issues identified by reporters.
Given the significance of the changes, many
companies are wondering how the revisions
affect their reporting requirements. Are there
additional errors in the subpart revisions?
Enviance has created this white paper to
answer these questions and help companies
navigate the most significant and relevant
changes in Subpart W.
Definitions
EPA made clarifications regarding several
Subpart A and Subpart W definitions of
source category. For example, it was clarified
that the terms “Owner” and “Operator” used
in Subpart A have the same definition as
defined in Subpart W 98.238. This is an
important clarification because a different
definition was originally provided in Subpart
 Page 2
A. In essence, it refers to the permit holder or
person who pays taxes on the well pad or
location, or operator of the facility.
EPA also clarified the meaning of
Continuous
and
Intermittent
Bleed
Pneumatic Devices in Subpart. In Subpart W
98.230, Onshore Petroleum and Natural Gas
Production was clarified to include
dehydrators and vessels on well pads or
associated with a single well page. In
addition, Enhanced Oil Recovery operations
that use CO2 are included. The recovery of
separated gases is not required in Onshore
Natural Gas Processing, and the included
processes are identified in generic terms. The
25 MM scf/day threshold applies to plants
that do not fractionate. Relating to Onshore
Natural Gas Transmission Compression,
“transmission pipeline” is now defined at
98.238 to be consistent with the intent used
at 98.230. In addition, the revisions clarify
what Transmission Compression facility
includes, and removed the term “natural gas
dehydration.”
Under Natural Gas Distribution, EPA
replaced “city gate station” with “meteringregulating station.” This is an important
improvement as Enviance found many
reporting clients couldn’t understand what
“city gate” was meant to be. Both “meteringregulating
station”
and
“distribution
pipeline” at 98.238 are defined in the
revisions to be consistent with the intent at
98.230. In addition, the Local Distribution
Company description was made consistent
 Change Agents: Making Sense of the Subpart W Revisions
with Subparts NN, essentially meaning
suppliers of fuels.
EPA also provided definitions for specific
terms in Subpart W 98.238. “Associated with
single well pad” was newly added for
consistency with its source category
definition. In addition, “Facility for Onshore
Petroleum and Natural Gas Production” was
revised for clarification, reflecting the single
well pad approach. “Facility for Onshore
Petroleum and Natural Gas Distribution” was
revised to clarify that all distribution
pipelines operated by an LDC in a single
state are included.
Additional Subpart W definition changes
include:
“Farm taps” has been revised to
eliminate the reference to city gate.
“Flare” at the ground level or
elevated is newly added, and energy
recovery is not required. The broad
definition brings in almost any
combustion that’s not heat recovery
or furnace.
“Forced extraction of natural gas
liquids” is newly added and describes
the removal of C2+ hydrocarbons.
The definition excludes dehydration
and other water removal activities.
“Gas well” has been removed and is
now addressed in the “sub-basin”
category definition.
“Natural gas” is newly added and
includes field quality, pipeline quality
or process gas.
“Oil well” has been removed and is
now addressed in the “sub-basin”
definition.
“Pressure groups” is newly added and
used in revised calculations for Well
Venting for Liquids Unloading.
“Tubing diameter groups” is newly
added and used in revised
calculations for Well Venting for
Liquids Unloading.
“Sub-basin category” is newly added,
changing from measurements at the
field level to the sub-basin level. This
category has county overlay in this
definition.
“Transmission-distribution
(T-D)
transfer station” is newly added,
defining what was previously termed
“custody transfer.” This has been
added for consistency with the
definition of distribution facility.
“Transmission pipeline” has been
revised, clarifying the definition to be
consistent with FERC or state rateregulated pipelines, or those covered
by the Hinshaw Exemption of 1994
Natural Gas Act.
“Horizontal well” is newly added and
used in calculations for well
completions and workovers.
“Vertical well” is newly added and
used in calculations for well
completions and workovers.
“Well testing venting and flaring” is
newly added, defined as occurring at
the time the production rate is
 Page 3
 Change Agents: Making Sense of the Subpart W Revisions
determined. If the production rate is
determine upon completion, then that
activity would be part of completions
and workovers, as opposed to using
the different calculation for well
testing and flaring.
Calculations
In the December 23, 2011 revisions to
Subparts A and W, there were 58 separate
changes to calculation definitions or the
terms used in the calculations. As most of the
changes are clarifications and technical
improvements, this white paper covers the
most significant changes.
One key change is that the standard
temperature was defined as 60o F. Many of
the changes made to the emission factors are
due to the standard temperature and pressure
(STP) change. For example, in Table 1A
(onshore production), most of the new
factors are lower and the pneumatic devices
are now different for the Eastern and Western
United States. The Western U.S. appears to
be changed due to the STP shift, while the
Eastern changes are perhaps due to new
information. In either case, the emission
factors are reduced.
In Tables 2 (natural gas processing), Table 3
(transmission compression), Table 4
(underground storage), Tables 5 and 6 (LNG
storage and import/export), and Table 7
(natural gas distribution), all changes are due
to the change in STP.
 Page 4
There have also been significant actions
taken in the calculations changes. For
pneumatic devices and pneumatic pumps,
Equations W-1 and W-2 now use Tt (average
estimated number of operational hours). The
default is now 8760 hours, which is a change
EPA made at the request of industry to allow
people with data on their operating time to
have a lower value to go from hourly
emissions to yearly emissions.
In addition, both equations use correct
factors to convert scf to CO2e:
•
•
CH4: 0.000403 metric tons CO2e per
scf CH4 at 60F
CO2: 0.00005262 metric tons CO2e
per scf CO2 at 60F
Acid gas removal calculations, Equations W4A and W-4B, were added in place of W-4 to
clarify inlet vs. outlet measurement
approaches. Previously, reporters had to make
their own decision with single equation 4.
The well venting for liquids unloading
calculation now uses the tubing diameter and
pressure group combination approach in
Equation W-7. Those two factors go into the
flow rate (FR) factor below, for a unique
combination of tubing diameter and pressure
group.
 Change Agents: Making Sense of the Subpart W Revisions
For gas well venting completions/workovers
with hydraulic fracturing, reporters now need
to aggregate measurements at the sub-basin
level. In addition, Equations W-10A and W10B have been added in place of W-10 to
reflect whether the backflow (synonymous
with the term flowback used in the industry)
is measured with a meter. Use Eq. W-10A if
flowback is calculated or measured. Use Eq.
W-10B if flowback is measured or vent gas
flow rate is measured.
Blowdown vent stacks are now applicable to
only manually activated operations and use
the “unique physical volume” concept.
Equation W-14A is used when temperature
and pressure are the same for all blowdowns
or a group of blowdown events.
Equation W-14B is used when temperature
and pressure vary for each event, and is the
sum of all individual blowdowns.
Equations have been renamed and Equation
W-11C has been added to determine if the
flow is sonic. If the value of R in Eq. W11C is equal to or greater than 2, then flow is
sonic and Eq. W-11B should be used to
calculate FR (which is subsequently used in
defining FRM in Eq. W-12). If flow is not
sonic, use Eq. W-11A to calculate FR.
Equation W-12 now defines FRM, the ratio
of backflow rate to average production rate.
FRM is then used in other calculations.
For onshore production storage tanks, EPA
clarified that the 10bpd threshold is based on
annual average daily throughput. Equation
W-15 was corrected to add the factor of
1,000 that was missing. [Please note,
however, that e-CFR did not display the
factor of 1,000 in W-15 as of May 18, 2012.]
Equation W-16 was revised to reflect yearly
emissions rather than hourly.
EPA replaced well testing venting and flaring
Equation W-17 with W-17A for oil well and
W-17B for gas well. Eq. W-17A uses the gas
to oil ration method, which helpful as a
substitute for storage tank counts. The gas to
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 Change Agents: Making Sense of the Subpart W Revisions
oil ratio for materials multiplied by the
throughput provides the potential maximum
gas emissions for that. For gas wells, an
estimate is provided by calculating
production rate multiplied by daily flow.
Eq. W-17A is also useful as an easy means of
calculating emissions from separators, tanks,
and combinations of the two. As stated
above, it assumes that all gas in the oil is
emitted. This may overstate the emissions
somewhat, but this conservative approach
may be well worth it, since it is much simpler
than using E&P Tanks or other more
complex emissions estimating applications.
For flare stack emissions at 98.233(n), EPA
made a clarification that onshore natural gas
processing plants that solely fractionate a
liquid stream use GHG mole percent in feed
natural gas liquid for all streams. In addition,
the Tier 4 (CEMS) method is allowed if
CEMS is present.
For leak detection and leaker emission
factors in 98.233(q), Equations W-30A and
W-30B were added in place of W-30. W-30A
should be used for natural gas processing,
transmission compression, underground
storage and LNG storage and import/export.
W-30B is used for natural gas distribution.
 Page 6
For underground storage and transmission
compression GHGi, use 0.975 for CH4 and
0.011 for CO2. For LNG storage and
import/export GHGi, use 1.0 for CH4 and 0
for CO2. For natural gas distribution GHGi,
use 1.0 for CH4 and 0.011 for CO2 [the CO2
value, however, is likely a mistake since the
total should not exceed 1.0.] In addition,
monitoring for leaks can be done over a
period of up to 5 years.
In population count and emission factors
(98.233r), “meter/regulator runs” at above
grade “metering-regulating stations” term is
used instead of “non-custody transfer city
gate.” In equation W-31, underground
storage and transmission compression GHGi
uses 0.975 for CH4 and 0.011 for CO2. LNG
storage and import/export GHGi uses 1.0 for
CH4 and 0 for CO2. Natural gas distribution
GHGi uses 1.0 for CH4 and 0.011 for CO2,
which could possibly be a mistake. Equation
W-32 now yields an emission factor with a
unit of measure of scf per meter-regulator run
per hour. There may also be a potential
mistake in the combined use of W-30B and
W-32 to produce the emission factor in W31, which results in the double use of GHGi.
Since the GHG factor is present in each one,
it actually creates a much lower than
intended emissions factor.
 Change Agents: Making Sense of the Subpart W Revisions
For volumetric emissions in 98.233t, the
standard temperature was set at 60 degrees F
and standard pressure was retained at 14.7
psia.
In GHG volumetric emission in 98.233u, the
mole fraction (Mi) should be an annual
average value when measuring. The default
mole fraction was set at 0.95 for CH4. Please
note the inconsistency with 98.233q for these
values. It may take some work to unify how
fugitive emissions vs. process emissions and
their default values are being handled.
•
Segment
•
98.233(u)
• 98.233(q)
•
TC
•
0.95
• 0.975
•
Und.
Storage
•
0.95
• 0.975
•
LNGs
•
0.95
• 1.0
•
Distribution
•
0.95
• 1.0
For GHG mass emissions in 98.233v, ρ I is
the density of GHGi. Use 0.0526 kg/ft3 for
CO2and N2O, and 0.0422 kg/ft3 for CH4at
60 °F and 14.7 psia.
numerous other calculations. There is a
significant error in that this equation takes
the volume of individual gas and multiplies it
by density and global warming potential to
come up with the equivalent amount of
CO2e. However, the CH4 density factor is
incorrect (correct value noted above.) The
mistake is a factor of 2.2, so do not apply it
as it will more than double the amount of
emissions.
After notifying EPA on January 13, 2012 that
the CH4 density value is incorrect in Eq. W36, Enviance received response that “if the
EPA decides to issue guidance on this topic,
it
will
be
posted
here:
http://www.epa.gov/climatechange/emissions
/subpart/w.html.
For onshore production and distribution
combustion in 98.233(z), EPA clarified that
external fuel combustion sources with a rated
heat capacity equal to or less than 5
mmBtu/hour are exempt. In addition, internal
fuel combustion sources that are not
compressor drivers and with a rated heat
capacity equal to or less than 1 mmBtu/hour
are exempt. EPA also clarified that Subpart C
methods should be used in the following
cases:
•
•
Please note that the density of CH4 provided
by EPA is incorrect. The correct value is
0.01919 kg/ft3. Another note of caution is
that Equation W-36 is applied to results from
•
•
Fuel is listed in Table C-1 or blend
thereof
Fuel is pipeline quality natural gas
with minimum HHV of 950 Btu/scf
Can use any tier of Subpart C
Reporting as required in Subpart W 98.236(c)(19)
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 Change Agents: Making Sense of the Subpart W Revisions
Subpart W methods should be used in the
following cases:
•
•
•
Field gas, process vent gas or blend
thereof, or not pipeline quality
Use
calculation
method
at
98.233(z)(2) – carbon content
approach
Reporting as required in Subpart W 98.236(c)(19)
In essence, if an organization’s fuel meets
qualities shown in Table C-1 from Subpart C,
then use Subpart C methods. Otherwise, use
the Subpart W method, which is a carbon
counting method.
Reporting
A reporting rollup by equipment/component
type is common. The population emission
factor reporting had a significant rollup
change. The original rule required rollup by
equipment type. The revisions now ask for it
by component type, which significantly
changes the way calculations are put together
and assembled after basic calculations are
done.
For gas sent to a flare, companies now need
to report the amount to unlit flare and to lit
flare. Emissions are reported under the
equipment source type, not at the flare.
Companies need to back those emissions out
when doing their flare calculations so as not
to double report.
A unique name or ID is now required for
blowdown vents for all segments (unique
 Page 8
blowdown volume), acid gas recovery units
in onshore processing segment, dehydrators
in onshore processing segment, flares in
onshore processing segment, and storage
vessels
in
transmission
compression
segment.
Reporting changes for well venting for
liquids unloading for each tubing diameter
group and pressure group combination in
each sub-basin category include: count of
wells vented to the atmosphere for liquids
unloading – which is a fairly significant
change, count of plunger lifts, whether the
selected well from the tubing diameter and
pressure group combination had a plunger
lift, cumulative number of unloading vented
to the atmosphere, and average flow rate of
the measured well venting in cubic feet per
hour.
Additional reporting changes are internal
casing or tubing diameter and well depth of
each well in that tubing size and pressure
combination, casing pressure in that tubing
size group and pressure group combination
that does not have a plunger lift, tubing
pressure in a tubing size group and pressure
group combination that has a plunger lift, and
annual CO2 and CH4 emissions, expressed
in metric tons of COe for each gas.
Reporting by sub-basin category is also
applied to workovers and completions,
storage tanks for onshore production, and
enhanced oil recovery. For each oil sub-basin
category, EPA has also added a requirement
that companies report their best estimate of
 Change Agents: Making Sense of the Subpart W Revisions
API gravity, gas to oil ratio, and average low
pressure separator pressure.
Conclusion
EPA made many revisions and additions in
its December 2011 revisions rule – some
minor and some significant. It can be
overwhelming to understand how the
changes affect your organization and how
changes in calculations and reporting,
combined with some of the errors, could
affect the outcome for your company.
This white paper has provided a high-level
overview of some of the more significant and
relevant revisions. But if you’re in need of
further detail on the Subpart W revisions,
organized by subject matter, Enviance has
created a 200+ page, detailed guide to the
revisions. The content and expert advice is
easy to read and use, and provides a step-bystep guide to implementation.
Contact John at 760-496-0200, x215 to
receive your copy of Enviance’s 200+ page
Guide to Subpart W revisions!
About Enviance
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Fertilizer, Los Angeles World Airports,
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California, Midway Products, NV Energy,
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Physics Laboratory, Roquette America,
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Industry leaders have used Enviance to
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For more information: www.enviance.com
 Page 9