than 60 days, while other agencies specified that the request should be
submitted within 30 days from the initial exceedance.
    Industry representatives from private and publicly owned landfills
as well as waste industry consultants opposed the requirement to submit
a request for an alternative corrective action timeline within 15 days.
The commenters were concerned that 15 days is not enough time to assess
the appropriate solution across miles of interconnected piping. In
addition, the commenters were concerned that a 15-day time period would
increase the paperwork for both the landfill and the reviewing
regulatory agency. One commenter indicated that while many repairs can
be completed within 60 days, some repairs, especially in cold weather
climates, may take longer. One industry commenter suggested that a
timeframe of 90 days to complete any adjustments or repairs is
appropriate. If the corrections could not be made within 90 days, the
commenter stated that the landfill would be prepared to have the system
expanded within 120 days.
    Industry commenters raised the issue that the timeline for
corrective action for surface exceedances in the current subpart WWW
regulations, 40 CFR 60.755(c)(4)(v), allow 120 days to install a new
well or other collection device or submit an alternative timeline for
another corrective action. These commenters also indicated that the
1998 NSPS amendments modified the corrective action for wellhead
parameter exceedances to be consistent with the timeframe allowed for
correcting surface exceedances (63 FR 32748, June 16, 1998). The
commenters also noted that the 1998 amendments recognized that
installation of a new well may not always be the appropriate corrective
action for remedying a wellhead exceedance.
    Despite the 1998 rule amendments, several of these industry
commenters note that interpretation and implementation of the 1998
amendments to 40 CFR 60.755(a)(3) have been inconsistent, with some
agencies only requiring the landfill owner or operator to submit
requests if the corrective action will take longer than 120 days. Other
states have taken the position that any exceedances that cannot be
resolved within 15 days must automatically result in a requirement to
expand the GCCS. One commenter referenced determinations that required
landfills to submit an alternative timeline request within 15 days. One
commenter indicated that the original rule never anticipated
notification and a request for an alternative compliance timeline
within 15 days, while another commenter indicated that the state of
Texas requires landfills to submit alternative timelines only if the
corrective action requires more than 120 days to complete.
    In consideration of the 1998 final rule notice, industry
commenters, recommended that EPA require landfill owners or operators
to submit an alternative timeline request for approval as soon as
practicable and only in circumstances in which a system expansion or
alternative corrective action will require more than 120 days to
complete. One of the commenters suggested that this approach was
consistent with the Petroleum Refineries NSPS (40 CFR part 60, subpart
Ja). The commenter noted that while the Landfills NSPS requires special
approval to avoid the default corrective action of expanding the GCCS,
the Refineries NSPS requires a root cause analysis to identify the
appropriate corrective action, without specifying a default approach.
The Refineries NSPS requires a root cause analysis and a corrective
action analysis for exceedances and requires the facility to implement
the corrective action within

45 days. If the corrective action cannot be completed in 45 days, the
refinery must document and record all corrective actions completed to
date. For actions not fully completed by day 45, they must develop an
implementation schedule, as soon as practicable, for beginning and
completing all corrective action.
    One commenter provided some ideas for landfills to demonstrate good
faith effort to comply with the 120-day corrective action schedule.
They suggested the rules clarify that the landfill owner or operator is
required to submit a notification to the agency that identifies and
describes the diagnosis performed, the results of the diagnosis,
identifies the corrective measure or alternative remedy to be
implemented and reason(s) why system expansion is not appropriate to
correct the exceedance. Under such an approach, corrective measures
other than expansion that take 0-60 days to complete from the initial
exceedance would not require any notification or approval but they
would be documented in the annual compliance report. For corrective
actions other than expansion that take longer than 60 days but less
than 120 days to complete, the landfill owner or operator would notify
the regulatory agency by day 75 from the date of the initial
exceedance. This would allow 45 days for the agency to review and
comment, and such notification would not require agency approval so as
not to delay the site from proceeding with and completing the
corrective action, as long as the corrective actions are completed
within the 120-day timeframe.
    Industry commenters indicated that the timeline for corrective
action is affected by other regulations. Two of these commenters noted
that any corrective action that involves disturbing the final landfill
cover could delay diagnosing the problem. All of these commenters noted
that a 60-day timeframe is problematic for landfills affected by the
Asbestos NESHAP (40 CFR part 61, subpart M), which requires a 45-day
notification prior to disturbing areas that may have asbestos
containing material.
    Response: The EPA is retaining the corrective action requirements
for temperature in addition to negative pressure. The EPA recognizes
the importance of temperature as a critical indicator of landfill fires
and its effect on methanogens. Further, removal of the corrective
action requirements for temperature could have the unintended
consequence of improper operation of a GCCS, which could lead to a
subsurface fire. Due to the important of this parameter, e-reporting
requirements for excessive temperatures have also been established to
better assess landfill fires.\39\
---------------------------------------------------------------------------

    \39\ The need to rely on temperature in addition to pressure is
also illustrated in the report titled Subsurface Heating Events at
Solid Waste and Construction and Demolition Debris Landfills: Best
Management Practices at http://www.epa.ohio.gov/portals/34/document/guidance/subsurface%20heating%20events.1009.pdf.
---------------------------------------------------------------------------

    After carefully considering the comments received and evaluating
the available data, the EPA is finalizing corrective action
requirements that generally give owners or operators 60 days to
investigate and determine the appropriate corrective action and then
implement that action. The EPA has retained the requirements for
temperature and positive pressure, in that if positive pressure or
temperature exceedances exist, action must be initiated to correct the
exceedances within 5 calendar days. This requirement has been retained
to ensure the landfill takes prompt action to ensure the GCCS remains
well-operated. The EPA recognizes, however, that the appropriate
corrective action, as well as a schedule to implement it, is site-
specific and depends on the reason for the exceedance. Therefore, for
corrective action that takes longer than 60 days after the initial
exceedance to implement, the EPA is providing flexibility for the
landfill to determine the appropriate course of action based on a root
cause analysis. Specifically, if the owner or operator cannot achieve
negative pressure or temperature of 55 degrees Celsius (131 degrees
Fahrenheit) at the GCCS wellhead within 15 days, then the owner or
operator must conduct a root cause analysis and correct the exceedance
as soon as practicable, but no later than 60 days after positive
pressure or temperature above 55 degrees Celsius (131 degrees
Fahrenheit) was first measured. An implementation schedule is required
for exceedances that take longer than 60 days to correct. A root cause
analysis is an assessment conducted through a process of investigation
to determine the primary cause(s), and any other contributing cause(s),
of positive pressure at a wellhead or temperature above 55 degrees
Celsius (131 degrees Fahrenheit). The root cause analysis and
documentation of the corrective action taken to restore negative
pressure or temperature of 55 degrees Celsius (131 degrees Fahrenheit)
must be kept on site as a record, but they do not have to be submitted
or approved.
    If negative pressure or temperature of 55 degrees Celsius (131
degrees Fahrenheit) cannot be achieved within 60 days, then the owner
or operator must develop an implementation schedule to complete the
corrective action(s) as soon as practicable, but no more than 120 days
following the positive pressure or temperature reading. The
implementation schedule, root cause analysis, and documentation of the
corrective action taken to restore negative pressure or temperature of
55 degrees Celsius (131 degrees Fahrenheit) must be submitted in the
facility's next annual report, but these items do not have to be
approved.
    If the exceedance cannot be corrected (or is not expected to be
corrected) within 120 days, then the owner or operator must submit the
root cause analysis, plan for corrective action to restore negative
pressure or temperature of 55 degrees Celsius (131 degrees Fahrenheit),
and the corresponding implementation timeline to the Administrator. The
Administrator must approve the plan for corrective action and the
corresponding timeline. The owner or operator must submit the proposed
corrective action and timeline to the Administrator for approval as
soon as practicable but no later than 75 days after the initial
exceedance. Requiring approval by the regulatory agency for corrective
action timelines that extend beyond 120 days is consistent with the
corrective action timeline for surface emissions in 40 CFR
60.765(c)(4)(v). This approach also prevents the landfill owner or
operator from delaying submittals for corrective action requests until
day 120. Once the negative pressure has been restored, the facility
must document the corrective actions taken in the facility's next
annual report.
    For the corrective action required to address positive pressure,
the owner or operator must keep a record of the root cause analysis
conducted, including a description of the recommended corrective
action(s); the date for corrective action(s) already completed
following the positive pressure reading; and for action(s) not already
completed within 60 days of the initial positive pressure reading, a
schedule for implementation, including proposed commencement and
completion dates. For corrective actions taking longer than 60 days to
correct the exceedance, the owner or operator would also include in the
annual report the root cause analysis, recommended corrective
action(s), date corrective actions were completed, and schedule for
implementing corrective actions. The owner or operator must also notify
the Administrator within 75 days. For corrective actions that take
longer than 120 days to correct the exceedance, the

owner or operator would include, in a separate notification submitted
to the Administrator for approval as soon as practicable, but no later
than 75 days after the initial positive pressure reading, the root
cause analysis, recommended corrective action(s), date corrective
actions taken to date were completed, and proposed schedule for
implementing corrective actions.
3. Landfills Recirculating Leachate or Adding Other Liquids
    In the 2014 ANPRM and 2015 proposed Emission Guidelines, the EPA
solicited input on whether additional action should be taken to address
emissions from wet landfills (i.e., landfills that recirculate leachate
or add liquids). Commenters differed on whether the EPA should require
separate thresholds or different lag times for landfills that
recirculate leachate or add liquids. (The lag time is the time period
between when the landfill exceeds the emission rate threshold and when
controls are required to be installed and started up.) Commenters
supported more environmentally protective requirements for wet
landfills and asserted that wet landfills produce more methane but
actually collect less. Commenters stated that the EPA should shorten
the lag time for installing controls. Other commenters opposed separate
requirements for wet landfills and contended that additional
requirements for wet landfills would achieve minimal emission
reductions and would result in a significant additional burden for
landfills that recirculate leachate. One commenter said that the EPA
should focus on potential emission reductions at landfills that
recirculate leachate.
    Commenters also differed on what methane generation rate (k-value)
should be used in the landfills NSPS for wet landfills. One commenter
indicated that they have previously provided several studies on k-
values for wet landfills to EPA and urged the EPA to update the
emission factors for wet landfills based on this literature prior to
adjusting the control requirements at landfills recirculating leachate
or adding other liquids. Another commenter asked the EPA to use higher,
more representative k-values, or perhaps a sensitivity analysis for a
range of k-values to estimate the impacts of controlling emissions from
wet landfills in the landfills NSPS.
    Based on the diverse nature of the feedback provided and several
other outstanding EPA actions affecting the control requirements and
emission factors for wet landfills, the EPA is not creating separate
emission threshold or lag time requirements for wet landfills in this
action. Instead, the EPA believes it is appropriate to further assess
emissions from wet landfills prior to taking additional action on
control requirements or changes to the k-values. As a result, the EPA
is finalizing additional electronic reporting requirements for wet
landfills with a design capacity of 2.5 million Mg or greater to inform
potential future action on wet landfills. The final rule is limiting
reporting of this additional data to wet landfills that meet the
current size threshold of 2.5 million Mg of design capacity to be
consistent with the universe of landfills that are affected by the
rule.
    Specifically, the final NSPS requires annual electronic reporting
of the volume of leachate recirculated (gallons per year) and the
volume of other liquids added (gallons per year), as well as the
surface area over which the leachate is recirculated (or sprayed), and
the surface area (acres) over which any leachate or liquids are
applied. The quantity of leachate recirculated or liquids added should
be based on company records or engineering estimates. The initial
report will collect historical data for the 10 years preceding the
initial annual reporting year, to the extent the data are available in
on-site records, along with data corresponding to the initial reporting
year. After the initial report, the other annual electronic reports
will include only the quantities of leachate recirculated and/or added
liquid and their corresponding surface areas for each the subsequent
reporting year. The EPA believes many landfills, especially those
operating with a Research, Development, and Demonstration (RD&D)
permit, already keep records and may submit reports containing
quantities of liquids added. So, the effort to track these additional
data is expected to be minimal. RD&D permits are issued through
Resource Conservation and Recovery Act (RCRA) subtitle D part 258
regulations for MSW landfills. The EPA is also aware of some state
rules that require reporting of leachate or added liquids outside of
the Clean Air Act reporting requirements. Consolidating these data in
an electronic format in a central repository can help inform how
leachate or added liquids affect LFG generation and collection whether
air emission standards should be adjusted for wet landfills.
    The EPA is also requiring the landfill to report the total waste
disposed (Mg) in the area with recirculated leachate and/or added
liquids, as well as the annual waste acceptance rates (Mg/yr) in those
same areas. Recognizing that the waste quantities may be tracked at the
scale house entry to the landfill and not the specific cell where the
liquids are added, the EPA is allowing the landfill to report data
based on on-site records or engineering estimates.
    The EPA is allowing owners or operators of landfills to discontinue
annual reporting of the wet landfill report after the landfill has
submitted its closure report recognizing that this information would be
difficult to obtain after the landfill closed, these landfills are
unlikely to still be adding liquids if closed, and also because the gas
generation from these landfills are on the downward side of their gas
generation curve.
    The EPA is also aware of annual LFG collected and annual LFG
generation data electronically reported to 40 CFR part 98, subpart HH
of the GHGRP and therefore the EPA is not requesting reporting of these
data in this rule to avoid duplicative requests. However, the EPA may
link the wet landfill practices data collected under the landfills NSPS
with the annual gas collected data under subpart HH in order to inform
how liquids addition affects LFG emissions. Similarly, the EPA
understands that precipitation may affect gas generation. However,
since precipitation data are readily available through the National
Weather Service, the EPA is not requiring reporting of this parameter.
Instead, the EPA will use existing electronic data already available to
link up with data collected under this final rule. These additional
data will be used to assess the appropriateness of potential future
action on wet areas of landfills.
    The Paperwork Reduction Act (PRA) requires each federal agency to
obtain OMB approval before undertaking a collection of information
directed to 10 or more people. The PRA applies whether a ``collection
of information is mandatory, voluntary, or required to obtain or retain
a benefit.'' The EPA believes the additional data on wet landfills will
be beneficial for evaluating whether separate thresholds for wet
landfills are appropriate when revising future MSW landfill standards.
Because the EPA understands that many of the data elements in the wet
landfill report, including quantities of leachate or other liquids
added and the surface areas over which those liquids are added are
tracked at a state level as part of a leachate management or RD&D
permit, the EPA does not anticipate these data. Additionally, the EPA
is allowing landfill owners or operators to report the data elements in
the wet landfill

monitoring report using either engineering estimates or on-site records
to minimize the burden on respondents, depending on the types of
records the landfill owner/operator may keep.
    This is a new rule and a new collections submitted to OMB under EPA
ICR number 2498.03. This collection is similar to collections for
subpart WWW. Thus, many of the line item burden estimates in this ICR
estimate are the same as the burdens submitted to OMB under ICR number
1557.09 for the most recent ICR renewal for subpart WWW.
4. Portable Analyzers
    Commenters on the proposed NSPS (79 FR 41796) requested that the
EPA specify that portable gas composition analyzers are an acceptable
alternative to Methods 3A or 3C, and noted that these devices are
commonly used in practice to measure wellhead parameters and are
calibrated according to the manufacturer's specifications. Currently,
approvals of these analyzers are done on a case-by-case basis.
Therefore, in the preamble for the proposed revisions of the Emission
Guidelines (80 FR 52141), the EPA requested data or information on
using a portable gas composition analyzer according to Method 3A for
wellhead monitoring. The EPA also requested data on other reference
methods used for calibrating these analyzers.
    Comment: Many commenters supported the use of portable gas
composition analyzers and requested that the EPA specify that these
analyzers may be used as an approved alternative monitoring method for
well monitoring. Three state agencies indicated the use of the portable
analyzers is common practice. One of these agencies stated that Method
3A and Method 3C are designed to be used in ``quasi-CEMS'' and/or
``laboratory benchtop'' situations and most landfill operators are not
using this type of equipment to test wellhead LFG; instead, landfill
operators are using handheld-size portable analyzers. Another state
agency stated that portable gas composition analyzers (e.g., Landtec
GEM 2000) are a standard for conducting MSW landfill well monitoring
and the analyzers provide additional information on gas composition
than what the current Emission Guidelines require, which provides
operators with a better understanding of the condition of the landfill.
This commenter said that a primary advantage of portable gas
composition analyzers, for both landfills and regulators, is that these
devices take and record the monitored readings (as well as other
information on gas composition that is not required to be monitored in
the Emission Guidelines), which can then be downloaded into a
spreadsheet and prevent landfills from making data collection mistakes.
The commenter suggested that the EPA and state air pollution control
agencies would benefit if the EPA were to require landfills to submit,
in their semi-annual reports, all of the monitoring data recorded by
portable gas composition analyzers.
    One commenter stated that most portable gas composition analyzers
can be used to measure the oxygen level at the wellhead and can be
calibrated according to Method 3A, but are unlikely to be calibrated
according to Method 3C (to measure oxygen or nitrogen levels) because
such calibration requires the use of gas chromatograph equipment with a
thermal conductivity detector and integrator. The commenter said that
Method 3A is straightforward and does not specify a particular
technology. Several commenters specifically referenced the comments
from an equipment manufacturer, which provided specific details on how
its Landtec GEM Series portable analyzers are able to comply with each
specific requirement in Method 3A, including the calibration
requirements. Two of these commenters said that portable gas
composition analyzers should be allowed in both the Emissions
Guidelines and NSPS. Another of these commenters requested that the EPA
add language to the rule to recognize that balance gas is commonly used
as a surrogate for nitrogen.
    With regard to the EPA's request for data on other reference
methods used for calibrating portable gas composition analyzers, one
commenter suggested that the EPA allow ASTM D6522 as an alternative to
Method 3A because an analyzer can easily be calibrated for oxygen alone
following ASTM D6522. The commenter stated that although the QA/QC
procedures in ASTM D6522 are different from Method 3A, they are just as
rigorous as Method 3A. The commenter stated that it has extensive data
available showing portable gas composition analyzers are routinely
calibrated according to ASTM Method D6522 for measuring NOx, CO, and
oxygen during engine testing. This commenter also stated that any
analyzer or device must be calibrated according to an EPA approved
method and not just manufacturer's specifications.
    Response: The EPA appreciates the commenters providing information
regarding the use of portable gas composition analyzers for landfill
monitoring. Commenters provided data showing that their portable gas
composition analyzers are used to monitor the oxygen level at a
wellhead and are capable of meeting the calibration requirements in
Method 3A. Therefore, in today's action, we are clarifying the use of
portable gas composition analyzers with Method 3A. A portable gas
composition analyzer may be used to monitor the oxygen level at a
wellhead provided that the portable analyzer is calibrated and meets
all QA/QC according to Method 3A. Although we did not receive enough
information regarding calibration methods that could be used on a
portable gas composition analyzer to monitor the nitrogen level at a
wellhead, any portable combustion monitor analyzer that uses gas
chromatography and thermal conductivity technology may be used with
Method 3C. Other technologies for the measurement of nitrogen may be
used in lieu of Method 3C through the administrative alternative test
method process outlined in 40 CFR 60.8(b)(2).
    Regarding the suggestion to allow ASTM D6522-11 as an alternative
to Method 3A, the EPA thanks the commenter for their perspective. As
long as all the quality assurance is conducted as required by ASTM
D6522-11, then ASTM D6522-11 may be used as an alternative to Method 3A
for wellhead monitoring (prior to combustion). Examples of quality
assurance required by ASTM D6522-11 include, but are not limited to:
Analyzers must have a linearity check, interference check, bias check
using mid-level gases, stability check, and be calibrated before a
test; and a calibration error check and the interference verification
must be conducted after the testing has occurred. Due to a different
sample matrix typically found in post-combustion gas streams as stated
in the applicability of ASTM D6522-11, the interference check must be
done on the oxygen measurement with the appropriate gases (e.g., carbon
dioxide, VOC mixture, and methane) and concentration ranges. The ASTM
D6522-11 method also has calibrations before and calibration checks
after testing. According to Methods 3A, 3C, and ASTM D6522-11, the data
are valid only when they pass the bias check or zero and upscale
calibration error check. The EPA does not believe manufacturers'
specifications are rigorous enough to ensure data are of a proper
quality.
5. More Precise Location Data
    The EPA proposed more specific requirements for reporting the
locations where measured methane surface emissions are 500 ppm above

background in the 2015 proposed Emission Guidelines (80 FR 52124).
Specifically, the EPA proposed to require landfills to report the
latitude and longitude coordinates of each surface emissions monitoring
(SEM) exceedance using an instrument with an accuracy of at least 3
meters. This includes surface methane readings above 500 ppm for
landfills conducting quarterly SEM with GCCS in place, as well as
landfills that are conducting Tier 4 SEM to determine the timing of
GCCS installation.
    Comments: Several commenters support and several commenters oppose
the EPA's proposed requirement to report the latitude and longitude
coordinates of each methane surface emissions exceedance using an
instrument with an accuracy of at least 3 meters.
    Of those commenters that support the requirement, one said that
making global positioning system (GPS) coordinates of each exceedance
available will assist owners or operators in determining the location
and timing of exceedances relative to the GCCS components and would
also assist in inspections and enforcement. This commenter added that
these requirements provide important compliance monitoring assurances
as well as important information to landfill owners or operators
regarding their GCCS effectiveness. Other supportive commenters argued
that all SEM data and GPS coordinates should be recorded, no matter
whether there is an exceedance. One of these commenters, a state
agency, said that the NSPS and Emission Guidelines have historically
required retention of only exceedance data, but GPS data correlated
with SEM readings would be an invaluable addition to the monitoring
procedure. Another commenter said recording all SEM data (rather than
only exceedances) is necessary to show compliance with the monitoring
requirement; and by linking the methane readings with positioning data,
the time required to process the data will be reduced. Commenters said
that by correlating the SEM readings directly with the location of the
reading, facilities and their regulators can easily gain a clear
picture of how the LFG collection system was functioning and anticipate
problems before they arise by tracking trends in the data.
    Of the commenters that oppose the requirement that owners or
operators of landfills report the latitude and longitude coordinates of
each exceedance using an instrument with an accuracy of at least 3
meters, one said it is unclear why coordinate information must be
reported, given that it merely adds burden for sites to collect and
report as well as for agencies to review. Two of these commenters
argued that the added expense to purchase an instrument (i.e., a GPS
device), use that GPS device in the field, and then plot the GPS data
on a map, may provide no additional value to the operator compared to
marking exceedances with marker flags. One of these commenters stated
that 3 meters is too much of an error range such that the use of GPS
alone may not allow the operator to return the exact spot of the
exceedance, and may still necessitate the use of a marker flag. Another
of these commenters added that the existing approach of marking
exceedances at their exact physical location with a marker flag is
actually more accurate because it does not rely on a technology with
accuracy limitations.
    Some of the commenters that oppose the requirement said that it is
unclear from the docket materials (e.g., the Regulatory Impact
Analysis) whether the EPA evaluated: (1) If GPS equipment can achieve
an accuracy of at least 3 meters; (2) the cost to purchase or rent GPS
equipment; and/or (3) the size and weight of the GPS equipment with
regard to requiring a technician to carry another field monitoring
instrument. One of these commenters added that because GPS equipment is
not typically integrated into other monitoring devices, monitoring
technicians will be required to carry the GPS equipment in addition to
the monitoring equipment, which could be difficult and present a safety
concern.
    Response: The EPA is finalizing a requirement for landfills to
report the latitude and longitude coordinates of each surface emissions
exceedance, as proposed in the 2015 Emission Guidelines, except the
instrument accuracy must be at least 4 meters instead of 3 meters. GPS
technology is readily available and is currently in use at landfills in
California and other landfills employing electronic LFG data management
systems. These GPS devices have the ability to identify latitude and
longitude coordinates in decimal degrees with at least five decimal
places. This level of accuracy and precision is consistent with the
requirements finalized in the Petroleum Refinery Sector Risk and
Technology Review and New Source Performance Standards (80 FR 75250).
The EPA is aware of one device that is already in use by some landfills
in California to conduct surface emissions monitoring and to create a
more comprehensive understanding of the GCCS. The instrument,
containing a flame ionization detector (FID), is linked by Bluetooth
wireless technology to a GPS-enabled handheld field instrument. This
instrument has an accuracy of 2-4 meters.
    When reviewing site records on the location of the traversed path
and where surface emission leaks were identified, inspectors will be
able to identify areas of the landfill where surface monitoring
activities may be incomplete, which may assist with targeting
inspections to problem areas of the landfill. In addition, more precise
location data will allow the landfill owner or operator to overlay the
coordinates of surface exceedances against maps of the GCCS to
determine spatial and temporal patterns of exceedances relative to GCCS
components. Both the landfill owner or operator and regulators can use
locational data to gain perspective on how the LFG collection system is
functioning over time and will allow the landfill to track trends in
GCCS performance and cover practices.
    Using GPS locational data will provide a more robust and long-term
record of GCCS performance compared to the short-term practice of
simply marking an exceedance location with a marker flag. Owners or
operators may continue the practice of marking exceedances with a flag,
but GPS data will allow the landfill owner or operator to return
readily to the location of the exceedance to not only take the required
corrective action, but also to track and inform long-term performance
of the GCCS to minimize emissions.
    The EPA included the rental price of a Trimble Integrated Landfill
Gas Solution device, which combines a FID linked by Bluetooth wireless
technology to a GPS-enabled handheld field instrument, in the revised
testing and monitoring cost analysis for both the final NSPS and final
Emission Guidelines. The GPS location is recorded in real time as the
technician traverses the path so the labor involved in gathering and
recording the data with GPS coordinates is expected to be minimal. In
fact, the recording of each surface reading and the corresponding
locational data is automatic, in contrast to the older technology,
which may have involved handwriting an exceedance in a notebook and
then transposing the data to a computer after returning from the field.
Eliminating transposing the data could reduce data entry errors and
improve data accuracy and credibility. The GPS device is already in use
by landfills that maintain an electronic LFG data management system to
map long-term trends in GCCS performance. The GPS device weighs
approximately 21 ounces (including

battery weight) and can be clipped to a belt or attached to a backpack
to allow the technician to complete the monitoring safely.
6. Update and Approval of Design Plan
    The EPA proposed three criteria for when a design plan must be
submitted for approval: (1) Within 90 days of expanding operations to
an area not covered by the previously approved design plan; (2) before
installing or expanding the gas collection system in a way that is not
consistent with the previous design plan; and (3) prior to implementing
an approved alternative operating parameter value for temperature,
nitrogen, or oxygen, if the owner or operator has requested alternative
operating parameter values. Further, the EPA proposed to maintain the
same site-specific design plan review and approval procedures while
soliciting comment on ways to streamline the design plan submission and
approval procedures. Similarly, the August 2015 proposed Emission
Guidelines included the first two criteria but omitted the third
criteria to submit an updated design plan prior to implementing an
approved alternative operating parameter value for temperature,
nitrogen, or oxygen.
    Comment: Commenters opposed the requirement to update the design
plan prior to implementing an approved alternative operating parameter
value for temperature, nitrogen, or oxygen because the requirement to
obtain approval of the updated design plan creates a duplicative
approval process for these alternative values. Commenters stated that
the EPA has removed operational flexibility and placed additional
burden on the regulatory agencies by requiring this update and approval
process for design plans. Several commenters noted that there is no
approval timeline, which leaves landfills in limbo regarding their
operations, even when alternative operating values have already been
approved for the landfill.
    Response: As discussed in Section VI.A.1 of this preamble, the EPA
is finalizing the removal of operational standards for nitrogen/oxygen
levels at the wellhead. High temperature values will be reported
electronically on an annual basis. Thus, the EPA has also removed the
criterion to update the design plan for alternative operational
standards. The EPA did not finalize this criterion, in order to
minimize additional burden on approving agencies and landfill owners or
operators. See the Response to Comments document located in the docket
for this final rule for additional discussion related to updates and
approval of the design plan.

B. Tier 4

    The proposed subpart XXX included three different tiers that are
available to an affected landfill to estimate whether or not the
landfill exceeds the NMOC emission threshold, thus requiring collection
and controls. The EPA requested comment on whether to include an
additional tier, ``Tier 4'', which would allow the use of site-specific
measurements of surface methane emissions to determine if installation
of a GCCS is required.
    Further, in the Emission Guidelines, the EPA proposed Tier 4 as an
alternative site-specific emission threshold determination for when a
landfill must install and operate a GCCS (80 FR 52112). Under the
proposed Tier 4, landfills could demonstrate that surface methane
emissions are below 500 ppm for four consecutive quarters based on the
results of quarterly site-specific methane emissions monitoring of the
perimeter of the landfill and entire surface of the landfill along a
pattern that traverses the landfill at 30-meter (98-ft) intervals, in
addition to where visual observations may indicate elevated
concentrations of LFG, such as distressed vegetation and cracks or
seeps in the cover and all cover penetrations. Once a landfill opts to
use Tier 4, any reading of 500 ppm or greater would require the
installation and operation of a GCCS within 30 months of the Tier 2
exceedance. For both Tier 4 SEM for determining the timing for GCCS
installation and SEM to ensure a well-operated GCCS, the EPA considered
limiting SEM during windy conditions. Specifically, in the Emission
Guidelines, the EPA proposed that SEM must be terminated when the
average wind speed exceeds 5 mph or the instantaneous wind speed
exceeds 10 mph. However, the EPA also proposed that the Administrator
may approve alternatives to this wind speed SEM termination for
landfills consistently having measured winds in excess of these
specified limits.
    The EPA received several comments on both the general request for
comment on a Tier 4 provision in the 2014 NSPS proposal as well as more
specific comments on the proposed Tier 4 provision included in the 2015
Emission Guidelines proposal. These comments are summarized below.
    Comment: Many commenters, representing industry, state regulatory
agencies, and environmental interests, supported the Tier 4 SEM
approach for determining when a GCCS must be installed. In addition,
the Environmental Defense Fund (EDF) presented the idea of a surface
concentration threshold as one of many potential alternatives to
further reduce emissions from landfills in its January 2013
whitepaper.\40\ Commenters stated that the option to conduct site-
specific measurements using SEM is a more accurate indication of when
gas collection is necessary to reduce emissions, compared to modeled
emission rates. SEM is a data-driven approach that is better able to
adjust for differentials in gas generation that may be a result of
climate differences, waste acceptance rates, and cover soil materials
that vary between landfills in different regions of the United States.
One of these commenters claims that modeling can also cause landfills
to install GCCS prematurely, incurring a financial burden that is not
warranted.
---------------------------------------------------------------------------

    \40\ Environmental Defense Fund. Recommendations and
Considerations for EPA's Forthcoming Revisions to Section 111
Standards for MSW Landfills. January 2, 2013. See EPA-HQ-OAR-2003-
0215-0050.
---------------------------------------------------------------------------

    One commenter disagreed with using Tier 4 to determine the timing
of GCCS installation and suggested that the approach provides landfills
another option to delay installation of controls. This commenter
suggested either removing the provision or making Tier 4 much more
stringent. Other commenters expressed concern about state agencies'
lack of experience with SEM and time to determine whether Tier 4
monitoring requires a GCCS to be installed. These commenters also
requested guidance for Tier 4 implementation procedures.
    Commenters disagreed on the potential benefits of a Tier 4 option.
Commenters representing both industry and environmental interests
asserted the SEM option would encourage landfill owners or operators to
implement methane reduction practices, such as the use of oxidative
landfill covers, organic waste diversion, and interim gas control
measures (horizontal gas collectors, connecting a leachate collection
recovery system into a GCCS), noting that such practices could be
implemented more quickly and more cost-effectively than a GCCS
installed in accordance with the design plan requirements of the
current NSPS. One commenter indicated that the use of SEM in
determining the need to install a GCCS would reduce costs and energy
consumption for landfills otherwise required to install controls. The
commenter also asserted that landfills would not generate a sufficient
amount of gas to support a collection system but would remain below
surface emission thresholds based on site-specific

measurements. Two commenters disagreed that Tier 4 would encourage
organics diversion at landfills. One of these commenters agreed that
Tier 4 would encourage the use of other methane reduction practices
such as oxidative covers and interim gas controls, but these practices
would be done at the expense of more effective installation of active
GCCS.
    Commenters made several specific suggestions regarding details of
how Tier 4 should be implemented, including which landfills should
qualify for Tier 4, the areas subject to SEM under Tier 4, the surface
emission concentration to identify exceedances and how many exceedances
would be needed to trigger GCCS installation under Tier 4, the ordering
of Tiers 1-3 relative to Tier 4, and meteorological conditions
necessary to achieve robust results. A summary of each of these
implementation comments is presented below.
    Which landfills should qualify. Some commenters believe that the
EPA should limit the types of landfills that qualify for Tier 4. One
commenter opposed the inclusion of a Tier 4 option for new landfills,
stating that it allows a subset of new landfills to delay methane
capture requirements when these landfills will be required to install a
GCCS in the future and should have a GCCS designed and installed during
landfill construction. One commenter encouraged the EPA to ban Tier 4
for landfills with a voluntary (non-regulatory) GCCS because it is
possible that GCCS design, monitoring, recordkeeping, and reporting
requirements could be avoided indefinitely through the use of a non-
regulatory GCCS that may not provide the same level of control as
required by the EPA landfills regulations. Another commenter thinks
that Tier 4 could be conducted at landfills with a GCCS installed, but
that the GCCS should follow typical operational conditions during the
Tier 4 test. In other words, if portions of the site are typically
offline due to decreased gas flow, the commenter thinks those portions
must remain offline during Tier 4. Further, one commenter believes that
no means of gas control whatsoever should be employed during the Tier 4
exemption.
    Which areas. Commenters also recommended certain Tier 4 procedures
for GCCS installation. They recommended conducting Tier 4 over the
parts of the landfill that are required to install a GCCS, following
the SEM methods currently established in 40 CFR part 60, subpart WWW.
If no exceedances of 500 ppm over background concentration occur, then
GCCS installation would not be required. Quarterly SEM would be
conducted thereafter until the landfill or area of the landfill is
closed. Closed areas would also be reviewed using the SEM approach, but
if no exceedances occur, those closed areas would no longer be required
to be tested.
    Surface exceedances and corrective action. Regarding how many
surface exceedances identified using Tier 4 should trigger GCCS
installation requirements, commenters generally supported some form of
corrective action allowance. Some commenters recommended that if an
exceedance occurred during Tier 4 SEM testing, then landfill owners or
operators should follow the same procedures and timelines for
remediation and re-monitoring as outlined in 40 CFR part 60, subpart
WWW. These commenters further suggested that if an exceedance could not
be remediated under the existing subpart WWW procedures, then the
landfill would be required to prepare a GCCS design plan within 1 year
of the initial exceedance and install a GCCS within the monitored area
within 30 months of the initial exceedance. One commenter claimed that
a lack of corrective action would cause facilities to avoid using Tier
4, causing it to seldom be used. Another commenter recommended some
level of corrective action, because a single exceedance would not mean
that LFG emissions were sufficient to necessitate GCCS installation.
One commenter recommended providing a short period of time for
corrective action and re-testing before GCCS installation. Other
commenters recommend that Tier 4 SEM be modified to allow for a single,
10-day corrective action period for each exceedance of the 500 ppm
threshold. Another commenter agreed to allow 10 days to correct the
first exceedance, but also recommended allowing 10 days to correct the
second exceedance, 1 year from the third exceedance to prepare the GCCS
design plan, and 30 months from the initial exceedance to install the
GCCS.
    Order of tiers. In regards to moving through the tiers, commenters
presented one of two opinions. Some commenters suggested that Tier 4 be
available for use in place of or in addition to performing a Tier 1 or
Tier 2 analysis. Several commenters suggested that Tier 4 could be
employed at any point following a Tier 1 or Tier 2 test where the
calculated NMOC emission rate was greater than the NMOC threshold for
installing a GCCS. On the other hand, another commenter suggested that
Tier 4 become the new Tier 3.
    Threshold concentration. Commenters disagreed on the appropriate
surface threshold concentration. Several commenters did not support a
threshold below 500 ppm. Other commenters supported the adoption of a
200 ppm threshold for Tier 4 consistent with the CA Landfill Methane
Rule (LMR) and incorporating an integrated limit of 25 ppm for Tier 4.
    Frequency. There were a variety of opinions on how often SEM should
be conducted for Tier 4. One commenter (suggested the SEM should be
done annually instead of quarterly. Two other commenters were concerned
with reducing the frequency to semi-annually unless the landfill no
longer accepted waste. One of these commenters noted that if a landfill
has already crossed the 34 Mg/yr NMOC threshold and the facility
continues to receive solid waste, then the expected gas generation will
continue to increase.
    Wind restrictions. In the 2015 Emission Guidelines, the EPA
proposed Tier 4 as an alternative site-specific emission threshold for
determining when a landfill must install and operate a GCCS. For both
Tier 4 SEM for determining the timing for GCCS installation and SEM to
ensure a well-operated GCCS, the EPA considered limiting SEM during
windy conditions. Specifically, in the 2015 Emission Guidelines, the
EPA proposed that SEM must be terminated when the average wind speed
exceeds 5 mph or the instantaneous wind speed exceeds 10 mph. However,
the EPA also proposed that the Administrator may approve alternatives
to this wind speed surface monitoring termination for landfills
consistently having measured winds in excess of these specified limits.
    Many commenters, including many state agencies, opposed limiting
surface monitoring during windy conditions, stating that the wind
restrictions would be a significant inhibitor to completing the
required monitoring in many regions of the country due to typical windy
conditions. Commenters also stated that it would be difficult to
schedule and reschedule dedicated sampling crews.
    Commenters claimed that climate conditions across the United States
are too variable, that monitoring the wind using an anemometer is not
representative of wind conditions where the surface monitoring is
required (5-10 cm of surface), and that it is difficult to assemble
monitoring teams and schedule monitoring events if they may be
cancelled due to wind. One commenter supports the development of a Tier
4 SEM methodology that is functional during windy conditions.

Other commenters support the removal of the wind speed criteria and
replacement with a requirement that surface monitoring be performed
during typical meteorological conditions. Lastly, one commenter pointed
out that the Tier 4 proposal is inconsistent with the ongoing quarterly
SEM requirements since Tier 4 has wind restrictions and the ongoing
quarterly SEM does not.
    One commenter noted that EPA recognized wind speed can skew the
results of SEM. Another commenter did not submit comments specific to
the wind speed limitations; however, this commenter supported the SEM
approach in the CA LMR, which does include wind speed restrictions.
    Traverse pattern. One commenter recommended that EPA require
enhanced SEM as part of Tier 4 demonstrations, including tighter
walking patterns, consistent with the CA LMR.
    Recordkeeping and reporting requirement. Some commenters believed
the requirement to maintain all data was burdensome and that landfills
should only be required to document exceedances of the 500 ppm
threshold. These same commenters supported the notification
requirement; however, one commenter believes landfills should not be
required to reschedule monitoring events based on the availability of
regulatory authorities. Furthermore, two commenters thought the
notification requirement was acceptable but with the existing wind
requirements, coordination with regulators could become even more
challenging. Another commenter did not support the notification
requirement because Tier 4 is voluntary.
    Response: After considering public comments and input from small
entity outreach, the EPA is finalizing Tier 4 SEM procedures for
determining when a landfill must install a GCCS. Tier 4 provides
operational flexibility and allows owners or operators of landfills
that have exceeded the modeled NMOC emission rate threshold to
demonstrate that site-specific surface methane emissions are below a
specific threshold.
    The EPA agrees with commenters that the Tier 4 SEM option will
encourage landfill owners or operators to implement methane reduction
practices, such as the use of oxidative landfill covers, organic waste
diversion, and interim gas control measures and that such practices can
be implemented more quickly and more cost-effectively than an NSPS-
compliant GCCS. Such measures can directly affect surface emissions and
when employed would help a landfill ensure that surface emissions are
low. The EPA expects that delaying installation of a regulatory GCCS
will not have a significant negative impact on public health or the
environment, if the surface emissions can be demonstrated to be kept
below the threshold with early control or voluntary control measures.
In fact, the EPA expects that alternative methane reduction operational
practices employed by landfill owners or operators who are interested
in Tier 4 will reduce near-term emissions of LFG from the surface of
the landfill.
    Under Tier 4, the landfill owner or operator would continue to
calculate the NMOC emission rate using Tiers 1, 2, or 3, and report
results in the annual report to demonstrate that NMOC emissions are
less than 50 Mg/yr. However, a landfill that can demonstrate that
surface emissions are below 500 ppm over the entire perimeter of the
landfill and along a pattern that traverses the landfill at 30-meter
intervals for four consecutive quarters will not trigger the
requirement to install a GCCS even if Tier 1, 2, or 3 calculations
indicate that the 34 Mg/yr threshold has been exceeded. Regarding
frequency of monitoring, the EPA is finalizing an approach where
quarterly SEM is required for Tier 4 indefinitely unless the landfill
is closed. Closed landfills would be able to reduce the frequency of
surface emission monitoring to annually after four quarters of no
surface exceedances of 500 ppm methane or greater. Landfills that are
closed are on the downside of their gas generation profile.
    Tier 4 is allowed only if the landfill owner or operator can
demonstrate that NMOC emissions are greater than or equal to 34 Mg/yr
but less than 50 Mg/yr using Tier 1 or Tier 2. Tier 3 was not required
because tiers 1 and 2 are more commonly used. If both Tier 1 and Tier 2
indicate NMOC emissions of 50 Mg/yr or greater, then Tier 4 cannot be
used. This change avoids a potential conflict between what is required
under the Emission Guidelines and what is required by the landfills
NESHAP for landfills with modeled NMOC emissions greater than 50 Mg/yr.
It also ensures that landfills with modeled NMOC emissions at 50 Mg/yr
or more continue to be required to install controls at an NMOC level
and on a schedule that is at least as stringent as the current NSPS (40
CFR part 60, subpart WWW). To demonstrate that NMOC emissions are less
than 50 Mg/yr according to Tier 1 and Tier 2, landfill owners or
operators will continue to calculate the NMOC emission rate and report
results annually.
    If the landfill opts to use Tier 4 for its emission threshold
determination and there is any measured concentration of methane of 500
ppm or greater from the surface of the landfill, the owner or operator
must install a GCCS, and the landfill cannot go back to using Tiers 1,
2, or 3. Once there is any measured concentration of methane of 500 ppm
or greater from the surface of the landfill, the EPA is requiring a
GCCS to be installed and operated within 30 months of the most recent
NMOC emission rate report with a calculated NMOC emission rate of 34
Mg/yr or greater according to Tier 2. Starting the 30 months from the
most recent NMOC emission rate report ensures that a GCCS is installed
in a timely manner. The EPA believes that if a landfill owner or
operator chooses to use Tier 4 SEM, it is appropriate to require the
installation and operation of a GCCS when any reading of 500 ppm or
greater is detected during the quarterly SEM event. Since Tier 4 is
allowed only if the landfill owner or operator can demonstrate that
NMOC emissions are greater than or equal to 34 Mg/yr NMOC, but less
than 50 Mg/yr using Tier 1 or Tier 2, we would expect the methane
emissions at the landfill to be below the 500 ppm threshold. If an
exceedance of the threshold is detected, it would be indicative of
higher emissions than would normally be expected at a landfill.
    The EPA is requiring installation of a GCCS upon any measured
concentration of methane of 500 ppm or greater from the surface of the
landfill--without any corrective action, to ensure that landfills
employ operational practices that minimize emissions. A reading of 500
ppm methane for a landfill that has modeled NMOC emissions greater than
or equal to 34 Mg/yr NMOC would indicate that the landfill conditions
warrant installation of a GCCS.
    The EPA selected a 500 ppm threshold for Tier 4 because 500 ppm is
consistent with the level the EPA determined to be appropriate to
demonstrate that a GCCS is well-designed and well-operated. In other
words, when conducted properly, SEM is a good indicator of how well a
GCCS is operating overall. For landfills without a GCCS (including
those that may be using other LFG mitigation strategies), the level of
500 ppm methane will demonstrate that site-specific surface methane
emissions are as low as those allowed at a landfill with a well-
operated and well-designed GCCS in place. (See the docketed memorandum
``Establishing a Site-Specific Emission Threshold Alternative for MSW
Landfills, 2015.'') Therefore,

the EPA believes this alternative site-specific concentration threshold
will achieve the goal of minimizing methane emissions to the
atmosphere. In addition, this approach is consistent with the surface
concentration threshold approach in the CA LMR.
    In response to public comments concerned with implementation of
Tier 4 with wind speed restrictions, the EPA is retaining a wind speed
limitation but allowing the use of a wind barrier when onsite wind
speed exceeds the limits in the regulation. The EPA is also providing
additional clarifications about probe placement (as described in
section IV.A.2 of this preamble) for Tier 4 SEM. In the proposed NSPS
(80 FR 52136), the EPA acknowledged concerns about the accuracy of SEM
under windy conditions. The EPA is including the wind speed
restriction, because air movement can affect whether the monitor is
accurately reading the methane concentration during surface monitoring.
Because Tier 4 is an optional emission threshold methodology, the EPA
believes that wind speed restrictions and the use of wind barriers are
appropriate to ensure the reliability of the results, which in turn
determine the timing of GCCS installation. We also refined the wind
speed criteria to account for gusts up to 10 mph and clarified that
measurements must be terminated if the average wind speed exceeds 25
mph.
    Regarding landfills equipped with a non-regulatory GCCS, the EPA is
allowing the non-regulatory GCCS to be in operation during the Tier 4
SEM demonstration, but only if the non-regulatory GCCS has operated for
at least 75 percent of the hours during the 12 months leading up to the
Tier 4 SEM demonstration (6,570 hours), as discussed below. The EPA
recognizes that many landfills have acted early to control their
emissions and installed a GCCS before surpassing the size and NMOC
emission thresholds in the landfills regulations in order to recover
and utilize LFG methane for beneficial use, flare for carbon credits,
control odors, or meet state-specific regulations that may be more
stringent than the federal NSPS standards. Thus, during the SEM
demonstration, the non-regulatory GCCS must continue to operate as it
normally would to collect and control as much LFG as possible. Although
these landfills do not operate their GCCS under the landfills NSPS,
they employ the same technology that would be applied to comply with
the landfills NSPS. Many of these non-regulatory GCCSs are located at
sites that are likely to eventually exceed the NSPS size and NMOC
emissions thresholds and thus if no exceedances are identified during a
Tier 4 SEM, the system is operating at a level consistent with the
landfills NSPS collection and control requirements and operational
standards at a point in time earlier than when federal regulations
would require. These near-term methane reductions from non-regulatory
GCCS are beneficial to the environment and the goal of achieving short-
term emission reductions of methane, a potent greenhouse gas. In
addition, landfill owners or operators have incentive to operate the
GCCS as efficiently as possible to collect and control LFG to avoid
surface exceedances, as it would reduce paperwork requirements
associated with the compliance provisions of the landfills NSPS. The
non-regulatory GCCS would have to be robust to keep readings below 500
ppm methane during an SEM demonstration.
    To not allow the Tier 4 demonstration while a non-regulatory GCCS
is in operation under these circumstances would create a disincentive
for landfill owners or operators to install control systems voluntarily
before emissions reach the regulatory threshold for review. The
requirement to operate the GCCS at least 75 percent of the hours during
the 12 months leading up to the Tier 4 SEM demonstration (described
below) will ensure that the non-regulatory GCCS is in regular use and
thus represents accurate operation of the facility.
    The landfill owner or operator is allowed to operate the non-
regulatory GCCS during the Tier 4 demonstration, but only if the non-
regulatory GCCS has operated for at least 75 percent of the hours
during the 12 months leading up to the Tier 4 SEM demonstration (6,570
of 8,760 hours). To demonstrate that the non-regulatory GCCS operated
at least 75 percent of the hours during the 12 months leading up to the
Tier 4 SEM demonstration, landfill owners or operators must keep
records of the total operating hours of the gas collection system as
measured for each destruction device (i.e., at the flare, engine, or
other destruction device), as well as the annual operating hours where
active gas flow was sent to each destruction device. If the non-
regulatory GCCS has not operated at least 75 percent of the hours
during the 12 months leading up to the Tier 4 SEM demonstration, then
the landfill is not eligible for Tier 4. The EPA seeks to encourage use
of voluntary non-regulatory GCCS systems for early gas collection
before emissions reach the regulatory threshold for review, while still
allowing landfill owners and operators to use Tier 4 surface emissions
monitoring approach to determine if a GCCS is required. We believe that
requiring the operation of the non-regulatory GCCS at least 75 percent
of the hours during the 12 months leading up to the Tier 4 SEM
demonstration (described below) will ensure that the non-regulatory
GCCS is in regular use and thus results would be representative of the
operation of the landfill.
    Regarding other recordkeeping and reporting requirements associated
with Tier 4, the EPA is finalizing the requirement to retain all
surface data readings, including calibration data and traverse path and
sampling location data based on GPS coordinates up to 5 decimal places.
This approach will improve transparency of Tier 4 results, and make
them readily available to any inspector coming to the landfill.
Further, many sites already use data loggers to collect and store SEM
readings and evaluate geospatial surface emission trends over time and
the EPA disagrees that it would be overly burdensome to record these
data and maintain them on-site. While the final rule is specifically
requiring an electronic record of the latitude and longitude
coordinates of each surface measurement, the EPA is not specifying a
file extension for storing a record of an actual digital map file
because each landfill or each regulatory agency may employ different
GIS mapping or data management software programs. Instead, the EPA
believes the electronic record of latitude and longitude coordinates
associated with each surface emission sample will be more appropriate
to withstand variation in technology versions over time or across
different agencies, while still providing for a record format that can
be easily converted into a map. The records will also include wind
speed data, a timestamp (to the nearest second) of when the sample
collection begins, and a log of the length of time each sample was
taken (e.g., the time the probe was held over the surface for each
sample). The EPA is also finalizing a recordkeeping requirement to take
and store digital photographs of the instrument setup. The photographs
must be time and date-stamped and taken at the first sampling location
prior to sampling and at the last sampling location after sampling at
the end of each sampling day, for the duration of the Tier 4 monitoring
demonstration. The EPA believes these records will help provide
credibility to the Tier 4 sampling results.
    The EPA is also finalizing a requirement to notify delegated
authorities 30 days prior to the Tier 4 test so that officials can be
present to observe the SEM. This notification is

consistent with other notification requirements for stack testing. This
notification requirement will also mitigate concerns that the SEM is
being conducted incorrectly and ensure transparency of results achieved
during the SEM approach. In the event the Tier 4 SEM is postponed due
to weather conditions or other unforeseen events, the EPA is requiring
the owner or operator to notify the delegated authority to arrange a
rescheduled Tier 4 SEM date.
    Emerging Measurement Technologies. Today's rulemaking provides
certain MSW landfill owners or operators the option of using either
modeling or the Tier 4 SEM approach to determine whether controls are
required to be installed at specific landfills. Current modeling
approaches, which rely on the decomposition rate of different waste
streams buried in a landfill, are prone to uncertainties due to
inaccuracies in input data and often unverifiable assumptions. Current
surface emission measurement methodologies can also have associated
uncertainties.
    New methane emissions measurement methodologies are emerging that
are anticipated to provide landfill methane emission rates (mass per
unit time) over time, thereby reducing significantly the uncertainty
associated with current modeling and emission measurements approaches.
Two promising examples of new methane measurement methodologies being
used by research groups to quantify landfill methane emissions are
mobile tracer correlation (TC) 41 42 43 44 and discrete area
source eddy covariance (DASEC).\45\
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    \41\ Development of a mobile tracer correlation method for
assessment of air emissions from landfills and other area sources,
Foster-Wittig, T.A.; Thoma, E.D.; Green, R.B.; Hater, G.R.; Swan,
N.D.; Chanton, J.P. Atmos. Environ. 2015, 102 (0), 323-330.
    \42\ Quantification of methane emissions from 15 Danish
landfills using the mobile tracer dispersion method, M[oslash]nster,
J.; Samuelsson, J.; Kjeldsen, P.; Scheutz, C. Waste Manage. 2015, 35
(0), 177-186.
    \43\ Methane Emissions Measured at Two California Landfills by
OTM-10 and an Acetylene Tracer Method, Green, R.B., Hater, G.R.,
Thoma, E.D., DeWees, J., Rella, C.W., Crosson, E.R., Goldsmith,
C.D., Swan, N., Proceedings of the Global Waste Management
Symposium, San Antonio, TX, October 3-6, 2010.
    \44\ Development of Mobile Measurement Method Series OTM 33;
Thoma, E.D.; Brantley, H.L.; Squier, B.; DeWees, J.; Segall, R.;
Merrill, R.; Proceedings of the Air and Waste Management Conference
and Exhibition, Raleigh, NC, June 22-25, 2015.
    \45\ Using Eddy Covariance to Quantify Methane Emissions from a
Dynamic Heterogeneous Area, Xu, L., Lin, X., Amen, J., Welding, K.
and McDermitt, D. Impact of changes in barometric pressure on
landfill methane emission. Global Biogeochemical Cycles 2014, 28(7),
pp. 679-695.

    1. Mobile tracer correlation. This methodology provides a
``snap-shot in time'' assessment of whole facility methane emissions
using on-site release of atmospheric tracer gases. It provides a
total mass emission rate of methane (or other gas) per unit of time.
An instrumented vehicle driving 1 km to 4 km downwind of the
landfill simultaneously measures the emitted landfill methane plume
along with the superimposed tracer gas release. The landfill methane
emission rate is determined through a simple ratio to the known
tracer gas release rate. The technique has been demonstrated using a
variety of tracer gases and instruments by a number of groups to
investigate emissions from landfills and other sources. The mobile
tracer correlation approach is under development by the EPA as a
Category C ``other test method (OTM)'' with potential posting in
2017 (https://www3.epa.gov/ttnemc01/prelim.html).
    2. Eddy covariance (EC). This micrometeorological method
estimates the source emission rate from the vertical wind speed and
gas concentration above the emitting surface. This technique
measures the emissions flux in mass of methane (or other gas) per
unit area. The technique is well-established for measurement of
emission fluxes from spatially-extended homogenous sources, such as
very large, flat fields. Discrete area source eddy covariance
(DASEC) is an application of EC to finite, heterogeneous area
sources. This application of EC has been recently demonstrated on
landfills, although method development questions on the effects of
topography and variable observational foot print remain. DASEC
provides the potential for long term (near continuous) measurements
of discrete sections of a landfill using solar-powered on-site
instrumentation. Development of this type of long term measurement
capability is critical to better understand and track changes in
landfill emissions overtime that may be caused by both site
management and atmospheric factors.

    In sum, as noted above, these techniques are still being
investigated and additional work will be needed before the EPA can deem
them ready for use in this application. Once additional research is
completed, we believe that DASEC used in combination with mobile TC
will provide a characterization of methane landfill emissions with
significantly reduced uncertainty over current models or measurement
techniques.

C. Changes To Address Closed or Non-Productive Areas

    The EPA proposed criteria that allow a landfill owner or operator
to cap or remove the GCCS from certain areas of the landfill where gas
generation is expected to be diminished. Specifically, the 2014
proposed NSPS allowed GCCS removal when the landfill is closed, the
GCCS has been operated for a minimum of 15 years, and the NMOC gas
produced by the landfill is calculated below 40 Mg/yr for three
consecutive quarters.
    Comment: Commenters opposed the 15-year criteria for GCCS
equipment, stating that the requirement is arbitrary and does not
account for the site-specific conditions. One commenter added that the
15-year criteria presents significant compliance challenges and costs
for a facility and the NSPS presents few options to address low flow
and gas quality conditions. Another commenter contended that the length
of time a GCCS has been operating in a portion of a landfill is
unrelated to the productivity of that area and that the age of the
waste is more relevant. Other commenters believe that regardless of how
long a GCCS system has actually been in operation, closed landfills
should be able to discontinue operations based on site-specific
emission levels. One commenter believes that a closed MSW landfill
should be able to remove NSPS control requirements once the site
demonstrates that it emits less than the emissions threshold based on
actual LFG flow and site-specific NMOC concentration in accordance with
40 CFR 60.764(b) regardless of the age of the GCCS or how long it has
operated.
    Several commenters noted that the provision provided in the 2015
Emission Guidelines to allow landfills to demonstrate the GCCS could
not be operated for 15 years due to declining flow was vague, and more
guidance was needed to provide instructions to landfills on how to
demonstrate this to regulators.
    Response: After considering public comments, the EPA is finalizing
criteria for capping, removing, or decommissioning the GCCS that are
similar to the criteria in 40 CFR part 60, subpart WWW, but have been
adjusted to reflect the NMOC emission threshold in the final rule and
to provide flexibility on the requirement to operate the GCCS for 15
years. The final criteria are: (1) The landfill is closed, (2) the GCCS
has been in operation for 15 years or the landfill owner or operator
demonstrates that the GCCS will be unable to operate for 15 years due
to declining gas flow, and (3) three successive tests for NMOC
emissions are below the NMOC emission threshold of 34 Mg/yr.
    The EPA is requiring that NMOC emission rate of the landfill must
be less than 34 Mg/yr on three successive test dates. This makes the
threshold for removing a GCCS consistent with the threshold for
installing a GCCS. In addition, the EPA is retaining the requirement to
operate the GCCS for 15 years, but is providing flexibility to address
declining gas flow in areas where the GCCS has not operated for 15

years. If the landfill is closed and the NMOC emission rate is less
than 34 Mg/yr, but the GCCS has not operated for 15 years, the landfill
owner or operator can demonstrate that the GCCS will be unable to
operate for 15 years due to declining gas flows. The EPA is providing
this flexibility to address areas of declining gas flows due to the age
of the waste, arid climate, or low organic content. Given that there
are unique situations that could cause low gas flow, or low gas quality
which would cause a GCCS to be unable to operate for 15 years, the EPA
is not providing prescriptive criteria for how a landfill owner or
operator can demonstrate that a GCCS could not operate for 15 years and
will proceed with a site-specific approach for handling these unique
cases. Some examples of data elements that could be used to demonstrate
a GCCS is unable to operate may include supplemental fuel use at the
flare to sustain operations or LFG quality sample measurements showing
methane content lower than what is viable for combustion in the
destruction device.

D. Startup, Shutdown, and Malfunction Provisions

    In July 2014, the EPA proposed that the standards in subpart XXX
apply at all times, including periods of startup or shutdown, and
periods of malfunction. In addition, the proposed NSPS included
recordkeeping and reporting requirements for all landfill owners or
operators to estimate emissions during such periods.
    Similarly, the EPA proposed standards that apply at all times in
the August 2015 proposed Emission Guidelines. However, the EPA
considered how the landfill emissions differ from those generated by
industrial or manufacturing sources. Specifically, the EPA noted that
landfill emissions are produced by a continuous biological process that
cannot be stopped or restarted. Therefore, the primary concern related
to SSM is with malfunction of the landfill GCCS and associated
monitoring equipment, not with the startup or shutdown of the entire
source. SSM periods that we have determined should be covered by the
work practice standard are those periods when the landfill GCCS and
associated monitoring equipment are not operating.
    To address these SSM periods, the EPA proposed in the 2015 Emission
Guidelines that in the event the collection or control system is not
operating the gas mover system must be shut down and all valves in the
GCCS contributing to venting of gas to the atmosphere must be closed
within 1 hour of the collection or control system not operating. This
provision is consistent with 40 CFR part 60, subpart WWW. Additionally,
the EPA proposed recordkeeping of combustion temperature, bypass flow,
and periods when the flare flame or the flare pilot flame is out. The
EPA received numerous comments on the 2014 proposed changes to the NSPS
and the additional proposed edits made in the 2015 Emission Guidelines.
A summary of these comments is presented below.
    Sierra Club v. EPA, 551 F.3d 1019 (D.C. Cir. 2008). Many commenters
stated that the Sierra Club decision, which addressed SSM conditions in
EPA rules, applies only to rules with numerical emission limits and not
to rules that are specified as a work practice. One of these commenters
elaborated that Sierra Club applies to section 111 of the Clean Air
Act. Therefore, the commenter concluded that landfills subject to the
NSPS are not bound by the findings of Sierra Club and instead they are
legally allowed to develop a clear and achievable landfill rule by
considering the unique circumstances that a landfill is a biological
process that cannot be stopped or restarted and that the gas collection
and control systems must periodically be shut down for maintenance,
repair, and expansion.
    Retain the 5 day/1-hour exemption for SSM events. Many commenters,
including affected industry commenters and some state agencies,
disagreed with removing the provisions in 40 CFR part 60, subpart WWW
which allow for a 5-day exemption period for collection systems and 1-
hour exemption period for treatment or control devices. These
commenters indicated that by removing this provision, state and local
agencies could misconstrue the rule to require that a landfill must
operate the gas collection system at all times, even during SSM,
including periods of collection system construction, expansion, and
repair. These commenters suggested instead of removing the exemption
provision during periods of SSM, compliance can be maintained as long
as the landfill owner or operator minimizes emissions of LFG by
following the applicable work practices and restores the system to
operation as expeditiously as practicable.
    One of the state agency commenters, suggested that the 5-day and 1-
hour time limitations in subpart WWW are appropriate for most
situations and instead of removing these exemptions, the new subpart
XXX could provide a mechanism for the facility to apply to the
Administration for an extension of those timeframes. On the contrary,
one state agency commenter and an NGO agreed with the standards
applying at all times, including periods of SSM.
    If the 5 day/1-hour exemption is not retained, the EPA should add a
work practice standard for SSM events. One commenter was concerned that
the preamble language for the 2014 proposed Emission Guidelines does
not clarify how a landfill can demonstrate compliance with the standard
during SSM events, stating that ``compliance with proposed 40 CFR
60.34f(e) does not constitute compliance with the applicable standards
in proposed 40 CFR 60.36f'' and that ``by shutting down flow to the
flare or other control devices a source is unlikely to be in violation
of the 98 percent emission reduction requirements since there will be
no gas flowing to the control device'' (emphasis added, see 80 FR
52134-52135). This commenter stated that the EPA must clarify this
confusion and specify a clear set of work practices (e.g., shut down of
the gas mover system and prevention of venting) that constitute
compliance during SSM periods when the collection or control system is
not operated. Several other industry commenters and the U.S. Small
Business Administration also asked that the rule specifically
accommodate periods when the collection system is not operating during
activities associated with construction, expansion, repair,
replacement, testing, upgrades, or other maintenance of the system or
its components.
    Reporting requirement to estimate NMOC emissions whenever the
collection system or control system is not operating. Two commenters
representing a state agency and an NGO supported reporting NMOC
emissions during SSM periods. Several industry commenters provided
numerous technical arguments to explain the infeasibility of accurately
estimating NMOC emissions during the short periods of SSM. For example,
methods to estimate LFG emissions are based on site-specific variables
that estimate LFG generation over the life of the landfill, typically
on an annual basis, and cannot be used to estimate hourly or daily
emissions. Accordingly, the commenters contended that it is technically
and practically inappropriate to require landfill owners/operators to
make this estimate for the time periods that the gas collection or
control systems are not operated, given the substantial technical
uncertainties involved in estimating these emissions over discrete,
short-term time periods. Further, other commenters noted that emissions
during SSM are expected to be very low,

reporting SSM emissions is an onerous and meaningless exercise and is
likely to overestimate emissions.
    Two commenters asked that if the reporting requirement is retained,
the EPA should limit the reporting to periods when the flare is free
venting because these are the only emissions that can be estimated
accurately. Several commenters asked EPA to develop guidance on how to
estimate emissions during SSM if this requirement is retained in the
final rule.
    Several commenters stated that because there should be no deviation
from the rule when the work practices of the rule are followed, there
are no excess emissions, and the reported emissions are not relevant to
determining compliance. Commenters are concerned that if estimated NMOC
emissions are reported, states will deem the reported emissions to be
``excess emissions,'' which could be treated as a serious violation.
Therefore, reporting these emissions poses the risk of state or citizen
suits for enforcement, even when a landfill is following all
requirements of the rule.
    Other Comments. Several commenters added that because SSM
provisions apply to numerical emission limitations and a numerical
limitation applies only to the control device (not the collection
devices), commenters stated that SSM provisions should address only
operation of the control devices during periods when LFG is routed from
the collection system.
    Several commenters indicated that the EPA must retain an allowance
of 5 days/1 hour for downtime events so that states do not file
enforcement actions for downtime events that are shorter than the
previously allowed 5 days/1-hour allowance. These commenters also asked
the EPA to clarify that the 1-hour allowance for shutting vents allows
for free venting for 1 hour such that venting during this time period
does not constitute ``excess emissions'' that can be deemed a serious
violation.
    Response: The EPA recognizes that landfills are not typical
affected sources that can be started up or shut down. Landfill
emissions are produced by a continuous biological process that cannot
be stopped or shut down. The EPA also recognizes that the primary
concern is with malfunction of the LFG collection and control system
and associated monitoring equipment, not with the startup, shutdown, or
malfunction of the entire source. The EPA received extensive comments
on the proposed requirements applicable to landfills during SSM events,
as summarized above. Consistent with the recent Court decision that
vacated the exemption in 40 CFR 63.6(f)(1) and (h)(1) for SSM (Sierra
Club v. EPA, 551 F.3d 1019), the EPA has established standards in this
rule that apply at all times.
    The general provisions in 40 CFR part 60 provide that emissions in
excess of the level of the applicable emissions limit during periods of
SSM shall not be considered a violation of the applicable emission
limit unless otherwise specified in the applicable standard (see 40 CFR
60.8(c)) (emphasis added). As reflected in the italicized language, an
individual subpart can supersede this provision.
    The EPA is finalizing a requirement in 40 CFR 60.465(e) whereby the
standards apply at all times, including periods of SSM. However, the
final rule reaffirms the work practice during periods of SSM (40 CFR
60.763(e)). During these SSM events, owners or operators must shut down
the gas mover system and close within 1 hour all valves in the GCCS
contributing to venting of the gas to the atmosphere. This provision is
consistent with 40 CFR part 60, subpart WWW. The landfill owner or
operator must also keep records and submit reports of all periods when
the collection and control device is not operating. The EPA, however,
is not reinstating the 5-day exemption for SSM periods because the
provision provides an exemption from compliance with the standard
during SSM periods, which the EPA does not have the authority to do
under the reasoning of the Sierra Club decision.

E. Definitions of Treated Landfill Gas and Treatment System

    The EPA proposed clarifications related to LFG treatment in the
proposal. Specifically, the EPA proposed to clarify that the use of
treated LFG is not limited to use as a fuel for a stationary combustion
device but also allows other beneficial uses such as vehicle fuel,
production or high-Btu gas for pipeline injection, and use as a raw
material in a chemical manufacturing process. The EPA also proposed to
clarify what constitutes LFG treatment by updating the definition to
include specific numerical values for filtration and dewatering in
order to provide long-term protection of the combustion equipment.
Specifically, the 2014 proposed NSPS included a treatment definition
that required the water dew point of LFG to be reduced to at least 45
degrees Fahrenheit, rather than lowered by at least 20 [deg]F, and
specified a location for the temperature monitoring device that would
demonstrate continuous compliance with the 45 degrees Fahrenheit
requirement. As an alternative to these numerical values, the EPA also
requested comment on an alternative definition for treatment system as
a system that filers, de-waters, and compresses LFG. Additionally, the
EPA requested comment on the use of treatment system monitoring plans
to document procedures to ensure that the LFG has been adequately
treated for the intended use.
    Similarly, the 2015 proposal to revise the Emission Guidelines for
existing landfills included the clarification that the use of treated
LFG is not limited to use as a fuel for a stationary combustion device
and proposed a definition for LFG treatment. Specifically, the Emission
Guidelines proposed a definition of treatment system as a system that
filters, de-waters, and compresses LFG for sale or beneficial use. This
definition did not include specific numerical values in order to allow
tailoring of the level of treatment to the type and design of the
specific combustion or other equipment for other beneficial uses in
which LFG is used.
    Further, the Emission Guidelines included a proposed requirement
for owners or operators to develop a site-specific treatment system
monitoring plan that would include monitoring parameters addressing all
three elements of treatment (filtration, de-watering, and compression)
to ensure the treatment system is operating properly for the intended
end use of the treated LFG. Additional records that demonstrate that
such parameters effectively monitor filtration, de-watering, and
compression system performance were also proposed.
    Consistent with public comments received on previous landfills
documents (67 FR 36475, May 23, 2002; 71 FR 53271, September 8, 2006;
79 FR 41796, July 17, 2014; 79 FR 41772, July 17, 2014), as well as
input from participants in small entity outreach, the EPA is finalizing
a definition of treatment system as a system that filters, de-waters,
and compresses LFG to levels determined by the landfill owner or
operators based on the beneficial end use of the gas. The EPA agrees
with commenters that the extent of filtration, de-watering, and
compression can be site-specific and equipment-dependent, and that
different levels of LFG treatment are required for the protection of
combustion devices that use treated LFG as a fuel.
    Many commenters on the proposed NSPS opposed basing LFG treatment
on specific numerical values for filtration and de-watering because
this ``one-size-fits-all'' approach was not appropriate, and provided
no emission reductions.

One commenter specifically noted the impact of the costs of these
requirements on small entities. Additional discussion of the concerns
related to costs can be found in the Response to Comments document
located in the docket for this rulemaking.
    Commenters also supported the use of a site-specific treatment
system monitoring plan in place of the proposed numeric values and
continuous monitoring and recordkeeping requirements. However, these
commenters opposed submission of these monitoring plans for approval
from the Administrator. Specifically, the commenters stated that LFG
treatment systems are closed loop systems that process LFG for
beneficial use and are not control devices that are subject to emission
limits. Two commenters cited specific examples from recent rulemaking
actions that have similar operation, maintenance, and monitoring plans
that are prepared, followed, maintained, and made available to the
Administrator for review upon request. For example, the greenhouse gas
reporting program (GHGRP) rules require each reporting facility to
prepare, follow, and maintain a monitoring plan which is made available
to an inspector upon request. Another example cited included the
Operation, Maintenance and Monitoring Plan required in the NESHAP for
Brick and Structural Clay Products Manufacturing and the NESHAP for
Clay Ceramics Manufacturing which were finalized on September 24, 2015.
    In consideration of these comments, the EPA is finalizing a
requirement that owners or operators must develop a site-specific
treatment system monitoring plan that includes monitoring parameters
that address filtration, de-watering, and compression to ensure the LFG
treatment system is properly operating for the intended end use of the
treated LFG. The EPA is also finalizing a requirement that landfills
owners or operators seeking to demonstrate compliance using a LFG
treatment system must maintain and operate all monitoring systems in
accordance with the site-specific treatment system monitoring plan and
maintain records of parameters that ensure the treatment is operating
properly for the intended use of the gas. The EPA is not finalizing the
requirement that these monitoring plans obtain Administrator approval
because the treatment system monitoring plan must be submitted as part
of the landfill's Title V air pollution control permit application and
these monitoring parameters would be integrated into the permit as
enforceable conditions (i.e., the landfill monitors the treatment
system monitoring parameters and maintains them in the specified
range).
    The EPA is also finalizing revisions to 40 CFR 60.762(b)(2)(iii)(C)
to clarify that if treated LFG cannot be beneficially used for reasons
such as end-user capacity limitations, market conditions for gas sales,
or unforeseeable shutdowns of the beneficial use equipment, then the
treated gas must be controlled in a flare. The flare requirements apply
to any gas routed to flares, regardless of whether the LFG is treated.
The intent is to require all gas not used for beneficial use to be
controlled in either a non-enclosed flare or a control system designed
to reduce NMOC by 98 weight-percent to an outlet NMOC concentration of
less than 20 ppm, in accordance with 40 CFR 60.762(b)(A) or (B).

F. Other Corrections and Clarifications

1. Test Methods
    In the 2014 proposed NSPS, the EPA did not include EPA Method 18 or
EPA Method 25A. In the 2015 proposed Emissions Guidelines, the EPA
proposed to include Method 25A based on public comments received on the
2014 proposed NSPS and the EPA's recognition that the use of Method 25A
is necessary for measuring outlet concentrations less than 50 ppm NMOC.
However, the EPA did not propose to include Method 18 (80 FR 52112)
because the EPA had determined that Method 18 was not appropriate or
cost effective for testing the large number of NMOCs found in landfill
samples. Specifically, 40 target analytes are listed in the current
landfills section of AP-42 and 160 analytes are listed in the draft
landfills section AP-42. The EPA determined that the extensive quality
assurance required by the method makes the method technically and
economically prohibitive for all the potential target analytes.
    Comment: Commenters (requested that the EPA retain both Methods 18
and 25A in the final rule and cited a number of reasons that the EPA
should retain them, including both technical and legal reasons.
Commenters stated that landfill owners or operators have relied on
these test methods to demonstrate compliance for performance testing of
enclosed flares as a part of EPA policy for over a decade under 40 CFR
60.764 [60.754]. One commenter emphasized the importance of Method 25A
because its use is required for many sources with an outlet
concentration of less than 50 ppmv NMOC as carbon.
    The commenters noted that the majority of LFG destruction devices
show NMOC concentrations below 50 ppmv as carbon. Due to issues with
Methods 25/25C in measuring NMOC content under this level, commenters
observed that the proposed NSPS rule change effectively removes the
ability to accurately measure compliance with the 20 ppmv outlet
standard for a large class of enclosed combustors. Commenter believes
that Method 25A is the superior testing methodology for certain
circumstances and is more commonly used in practice. Commenters cited
limitations of Method 25, including sensitivity of the test method to
water and carbon dioxide and the inability to measure NMOC content
below 50 ppmv as carbon.
    Commenters also contended that the EPA did not provide any
justification for removing these methods. Commenters stated that the
EPA did not provide any factual data, methodology, or any legal or
policy justification for its proposed exclusion of Method 25A or Method
18; thus commenters claimed that the EPA did not satisfy the notice-
and-comment requirements of the CAA.
    Response: After considering public comments, the EPA is including
both EPA Method 25A and EPA Method 18 in the final landfills
regulations (40 CFR part 60, subparts Cf and XXX).
    After reviewing the comments received on the NSPS for new landfills
proposed on July 17, 2014, the EPA recognizes that the use of Method
25A is necessary for measuring outlet concentrations less than 50 ppm
NMOC. EPA Method 25A determines total gaseous organic concentration of
vapor (total organic compounds). Because the rule regulates NMOC, EPA
Method 18 or Method 3C is needed to determine the concentration of
methane in the gas stream. Method 25A, in conjunction with Methods 18
or 3C (for methane), can be used to determine NMOC for the outlet
concentrations less than 50 ppm NMOC as carbon. Note that Method 25A
flame ionization detectors are insensitive to formaldehyde.
    While Method 18 may be used in conjunction with Method 25A for
methane or specific compounds of interest, there are limitations on the
number of analytes that can be reasonably quantified in measuring the
sum of all NMOCs. With the possibility of 40 target analytes listed in
the current landfill section of AP-42 (160 analytes in the draft
landfill AP-42), Method 18 is not an appropriate or cost effective
method to test all NMOCs found in landfill samples. The extensive QA
required by the method makes the method technically and economically

prohibitive for all the potential target analytes.
2. Tier 2 Sampling Procedure
    The EPA continues to believe that the number of samples required
per hectare is appropriate for Tier 2. As described in 40 CFR 60.764,
the EPA is reaffirming that the two samples are required per hectare
and if additional samples are taken, all samples must be used in
determining the site-specific NMOC concentration. Landfill owners or
operators must also ensure that the probes are evenly distributed over
the landfill surface. The EPA explored a number of methods, including a
statistical approach, when establishing requirements for the number and
location of Tier 2 samples for the original rule. Public commenters
raised significant concerns with approaches based on equations. As
such, the EPA determined that a simplified method (2 samples per
hectare) was best and received no public comments to the contrary.
3. Specifications for Active GCCS
    The EPA received a comment saying that proposed 40 CFR 60.769(a)(1)
referenced the term ``perimeter areas'' and noted that this term was
not well defined or explained. The EPA has removed this phrase to avoid
confusion. The intent is that all wells installed in the boundary of
the waste mass that are connected to the active GCCS should be operated
according to 40 CFR 60.769. The final rule language is clearer on this
point.
    The EPA also added a phrase to 40 CFR 60.769(a)(1) based on public
comment to ensure that GCCS design allows for the ability to isolate a
well or section and still be able to operate the remainder of the
active collection system.
4. Wellhead Pressure Monitoring
    In response to public comments, we are clarifying the location and
type of pressure required to be measured monthly at each wellhead to
demonstrate whether the requirement to maintain negative pressure is
being met.
5. Definition of Modification
    In the 2014 proposed NSPS, the EPA included ``mass or volume'' in
the definition of modification. Based on public comments, which
correctly point out that mass can change based on the density of the
waste received, we are finalizing the definition of modification
consistent with the definition in subpart WWW, which is based on volume
only. We also changed the reference to ``horizontal'' to ``lateral''
within the modification definition to be consistent with the defined
term ``lateral expansion''.
6. Definition of Sludge and Solid Waste
    We are updating the definitions of sludge and solid waste to
reference the terms as defined in 40 CFR 258.2 for consistency with the
terms as defined in RCRA.
7. Non-degradable Waste
    The EPA is reaffirming that all the waste must be included in
calculating the design capacity. Non-degradable waste cannot be
subtracted from the permitted landfill design capacity. However, non-
degradable waste can be subtracted from the mass of solid waste when
calculating the NMOC emission rate because such waste would not produce
NMOC emissions. Non-degradable waste is defined as waste that does not
break down through chemical or microbiological activity. Examples
include concrete, municipal waste combustor ash, and metals. Petroleum
contaminated soils (PCS) and paper mill sludges likely contain organics
that could be emitted as MSW LFG emissions. Therefore, emissions from
PCS and sludges would need to be accounted for in the emission estimate
only. The EPA is also reaffirming that documentation of the nature and
amount of non-degradable waste needs to be maintained when subtracting
the mass of non-degradable waste from the total mass of waste for NMOC
emission rate calculations.

VII. Impacts of This Final Rule

    For most NSPS, impacts are expressed 5 years after the effective
date of the rule. However, for the landfills NSPS, impacts are
expressed 10 years after the effective date (year 2025) because the
landfills regulations require controls at a given landfill only after
the NMOC emission rate reaches the level of the regulatory threshold,
which may take a number of years. Further, once the NMOC emission rate
is exceeded, the reporting and control timeframe allows 3 months to
submit the first NMOC emission report and then 30 months after
exceeding the NMOC emission threshold before the GCCS is required to be
installed. Additionally, the regulations allow the collection and
control devices to be capped or removed at each landfill after certain
criteria are met, which includes having the GCCS operate a minimum of
15 years. Controls would not be required over the same time period for
all landfills. The impacts are a direct result of control; therefore,
the annualized impacts change from year to year. By 2025, over 80
percent of the greenfield landfills and modified landfills affected by
the NSPS are expected to have installed controls and thus, the EPA
considered the impacts of the final rule relative to the baseline in
2025.
    The landfills dataset used for estimating the impacts of the NSPS
is discussed in detail in the August 27, 2015 supplemental proposal for
the NSPS (80 FR 52163). The EPA made several significant edits to the
dataset since the August 2015 supplemental proposal, based on public
comments received; new data made available from the landfills reporting
2014 emissions to 40 CFR part 98, subpart HH of the GHGRP; and
consultations with EPA regional offices, and state and local
authorities to identify additional landfills expected to undergo a
modification within the next 5 years. After incorporating all of the
updates to the inventory and adding the landfills expected to modify,
the revised dataset to analyze the impacts of the final rule now has
137 landfills that commenced construction, reconstruction, or
modification after July 17, 2014.\46\ A detailed discussion of updates
made to the dataset is in the docketed memorandum, ``Summary of Updated
Landfill Dataset Used in the Cost and Emission Reduction Analysis of
Landfills Regulations, 2016.''
---------------------------------------------------------------------------

    \46\ July 17, 2014, is the proposed date of the revised NSPS for
MSW landfills in 40 CFR part 60, subpart XXX. A landfill opening or
commencing construction on its modification after this date would
become subject to this new subpart and would not be subject to the
revised emission guidelines. The EPA cannot predict the exact month
a model landfill will open so the analysis uses a cutoff year of
2014.
---------------------------------------------------------------------------

    The methodology used for estimating the impacts of the NSPS is
discussed in detail in the August 27, 2015 supplemental proposal to the
NSPS (80 FR 52163). The EPA made several significant edits to the
dataset since the August 2015 supplemental proposal based on public
comments and comments on a separate peer review of the EPA Landfill Gas
Energy Cost (LFGcost) model.\47\ Notably, the EPA adjusted its
assumption of gas collection efficiency to an average of 85 percent.
The impacts analysis at the proposal or supplemental proposal did not
apply a collection efficiency assumption. However, in consideration of
public comments received and EPA assumptions in subpart HH of the
GHGRP, and analyses performed for marginal abatement cost curves, the
EPA has included an 85 percent average

gas collection efficiency factor to reflect a more realistic indicator
of GCCS performance.\48\ In addition, Chapter 2.4 of the EPA AP-42 for
MSW landfills cites a range of collection efficiencies for LFG between
60 and 85 percent, with an average of 75 percent. The EPA also adjusted
electricity purchase price and anticipated revenue estimates using
forecasted commercial retail electricity rate data and forecasted
electricity generation price data for different Energy Information
Administration (EIA) Electricity Market Module regions.49 50
---------------------------------------------------------------------------

    \47\ See the docketed 2016 RIA for additional discussion of
changes made on the methodology for estimating impacts as a result
of the LFGcost peer review.
    \48\ USEPA. Global Mitigation of Non-CO2 Greenhouse
Gases: 2010-2030. EPA-430-R-13-011.
    \49\ See the docketed 2016 RIA for additional discussion of
changes made to electricity pricing assumptions.
    \50\ To map existing landfill sites to EIA's Electricity Market
Module regions, the sites' geospatial coordinates were overlayed on
a map of the EMM regions. The AEO Electricity Market Module regions
are commensurate with the eGRID2012 primary regions for which a
shapefile is available at https://www.epa.gov/energy/download-egrid2012-shapefiles. For expected new landfills within a state the
specific location is unknown, therefore the landfill is located at
the state's centroid for purposes of mapping the site to an EMM
region.
---------------------------------------------------------------------------

    A detailed discussion of the methodology and equations used to
estimate the impacts of the final rule are available in the docketed
memorandum ``Updated Methodology for Estimating Cost and Emission
Impacts of MSW Landfill Regulations, 2016.'' The results of applying
this methodology to the population of new or modified landfills
potentially subject to the final rule are in the docketed memorandum
``Revised Cost and Emission Impacts Resulting from the Landfill NSPS
Review, 2016.'' Table 2 of this preamble summarizes the emission
reductions and costs associated with the final rule.

                                                 Table 2--Emission Reductions and Costs for Final Rule in Year 2025 at New or Modified Landfills
                                                                                [2012$]
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                No. of
                                                                   No. of                 landfills     Annual     Annual      Annual      Annual
                                                                 landfills     No. of     reporting    net cost     NMOC       methane      CO2e       NMOC cost     Methane cost    CO2e cost
                             Option                               affected   landfills     but not     (million  reductions  reductions  reductions  effectiveness  effectiveness  effectiveness
                                                                    \b\     controlling  controlling    $2012)     (Mg/yr)    (million    (million       ($/Mg)         ($/Mg)       ($/mt) \d\
                                                                                \c\                               Mg/yr)    mt/yr) \d\
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Baseline (2.5 million Mg design capacity/50 Mg/yr NMOC)........        128         103           25        90.4      10,520         1.7        41.4        8,600           54.6            2.2
Option (2.5 million Mg design capacity/34 Mg/yr NMOC)..........          0          12          -13     6.0 \e\         281         .04         1.1       21,470            136            5.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Options in this table show the impacts of reducing the NMOC emission threshold below baseline levels for all landfills.
\b\ Landfills are affected by the landfills NSPS based on design capacity. Once affected, they calculate and report emissions until they exceed the NMOC threshold, which triggers control
  requirements. Since we are not changing the size threshold, there are no incremental landfills affected.
\c\ Since the number of landfills affected remains the same as the baseline, the number of landfills reporting NMOC (but not controlling) decreases since more landfills will control emissions
  under the final rule.
\d\ Results do not include secondary CO2 impacts.
\e\ The annualized costs represent the costs compared to no changes to the current NSPS (i.e., baseline) and include $11 million to install and operate a GCCS, as well as $0.08 million to
  complete the corresponding testing and monitoring. These control costs are offset by $5.1 million in revenue from electricity sales, which is incorporated into the net control costs for
  certain landfills that are expected to generate revenue by using the LFG to produce electricity.

A. What are the air quality impacts?

    The EPA estimates that the final rule will achieve nearly an
additional 3 percent reduction in NMOC from new, reconstructed, or
modified landfills, or 281 Mg/yr, when compared to the baseline, as
shown in Table 2 of this preamble. The final rule would also achieve
44,300 Mg/yr of methane reductions (1.1 million mtCO2e/yr). These
reductions are achieved by reducing the NMOC threshold from 50 Mg/yr to
34 Mg/yr.

B. What are the water quality and solid waste impacts?

    Leachate is the liquid that passes through the landfilled waste and
strips contaminants from the waste as the leachate percolates.
Precipitation generates the vast majority of leachate volume.
Installation of a gas collection system will generate additional
liquid, in the form of gas condensate, and it will be routed to the
same leachate treatment mechanisms in place for controlling
precipitation-based leachate. Collected leachate can be treated on site
or transported off site to wastewater treatment facilities. Some
landfills have received permits allowing for recirculation of leachate
in the landfill, which may further reduce the volume of leachate
requiring treatment. Additional liquid generated from gas condensate is
not expected to be significant and insufficient data are available to
estimate the increases in leachate resulting from expanded gas
collection and control requirements.
    The additional gas collection and control components required by
this final rule have finite lifetimes (approximately 15 years) and
these pipes and wells will be capped or disposed of at the end of their
useful life. There are insufficient data to quantify the solid waste
resulting from disposal of this control infrastructure.
    Further, the incremental costs of control for the final rule of
$6.0 million in 2025 (7 percent discount, 2012$) are not expected to
have an appreciable market effect on the waste disposal costs, tipping
fees, or the amount of solid waste disposed in landfills because the
costs for gas collection represent a small portion of the overall costs
to design, construct, and operate a landfill. The handling of waste by
the private companies in the industry was estimated to generate $55
billion of revenue in 2011, of which landfilling contributed $13
billion, while a more recent estimate shows the U.S. non-hazardous
solid waste services industry generated about $60 billion in annual
revenues in 2015. These revenue estimates do not include activity
related to publicly owned landfills. For more information, see the
``Regulatory Impact Analysis for the Final Revisions to the Emission
Guidelines for Existing Sources and the New Source Performance
Standards in the Municipal Solid Waste Landfills Sector'' (hereafter
``2016 RIA'') included in the docket. There is also insufficient
information to quantify the effect increased gas control costs might
have on the amount of solid waste disposed in landfills versus other
disposal mechanisms such as recycling, waste-to-energy, or composting.
Note that elements of this final rule--notably lowering the NMOC
threshold to 34 Mg/yr--provide additional incentives to separate waste.

C. What are the secondary air impacts?

    Secondary air impacts may include grid emissions from purchasing
electricity to operate the GCCS

components, by-product emissions from combustion of LFG in flares or
energy recovery devices, and offsets to conventional grid emissions
from new LFG energy supply.
    The secondary air impacts are presented as net impacts, considering
both the energy demand and energy supply resulting from the final rule.
The methodology used to prepare the estimated secondary impacts for
this preamble is discussed in the docketed memorandum ``Revised
Estimates of Secondary Impacts of the Landfills NSPS Review, 2016.''
    While we do expect NOX and sulfur dioxide
(SO2) emission changes as a result of these guidelines, we
expect these changes to be small and these changes have not been
estimated. The net impacts were computed for CO2e. After
considering the offsets from LFG electricity, the impacts of the final
rule are expected to reduce CO2 emissions by 26,000 metric
tons per year. These CO2 emission reductions are in addition
to the methane emission reductions achieved from the direct destruction
of methane in flares or engines presented in Table 2 of this preamble.

D. What are the energy impacts?

    The final rule is expected to have a very minimal impact on energy
supply and consumption. Active gas collection systems require energy to
operate the blowers and pumps and the final rule will increase the
volume of LFG collected. When the least cost control is a flare, energy
may be purchased from the grid to operate the blowers of the LFG
collection system. However, when the least cost control option is an
engine, the engine may provide this energy to the gas control system
and then sell the excess to the grid. Considering the balance of energy
generated and demanded from the estimated least cost controls, the
final rule is estimated to supply 0.07 million megawatt hours (MWh) of
additional energy per year.

E. What are the cost impacts?

    To meet the final rule emission thresholds, a landfill is expected
to install the least cost control for combusting the LFG. The cost
estimates evaluated each landfill to determine whether a gas collection
and flare or a gas collection with flare and engine equipment would be
least cost, after considering local power buyback rates and whether the
quantity of LFG was sufficient to generate electricity. The control
costs include the costs to install and operate gas collection
infrastructure such as wells, header pipes, blowers, and an enclosed
flare. For landfills for which the least cost control option is an
engine, the costs also include the cost to install and operate one or
more reciprocating internal combustion engines to convert the LFG into
electricity. Revenue from electricity sales was incorporated into the
net control costs using forecasted electricity generation price data
from EIA Electricity Market Module regions. Testing and monitoring
costs at controlled landfills include the cost to conduct initial
performance tests on the enclosed flare or engine control equipment,
quarterly surface monitoring, continuous combustion monitoring, and
monthly wellhead monitoring. At uncontrolled landfills, the testing and
monitoring costs include calculation and reporting of NMOC emission
rates.
    The nationwide incremental annualized net cost for the final rule
is $6 million, when using a 7 percent discount rate (2012$). The
annualized costs represent the costs compared to no changes to the
current NSPS (i.e., baseline) and include $11 million to install and
operate a GCCS, as well as $0.08 million to complete the corresponding
testing and monitoring. These control costs are offset by $5.1 million
in revenue from electricity sales, which is incorporated into the net
control costs for certain landfills that are expected to generate
revenue by using the LFG to produce electricity.

F. What are the economic impacts?

    Because of the relatively low net cost of the final rule compared
to the overall size of the MSW industry, as well as the lack of
appropriate economic parameters or model, the EPA is unable to estimate
the impacts on the supply and demand for MSW landfill services.
However, because of the relatively low incremental costs, the EPA does
not believe the final rule would lead to substantial changes in supply
and demand for landfill services or waste disposal costs, tipping fees,
or the amount of waste disposed in landfills. Hence, the overall
economic impact of the final rule should be minimal on the affected
industries and their consumers.

G. What are the benefits?

    This final action is expected to result in significant emissions
reductions from new, reconstructed, or modified MSW landfills. By
lowering the NMOC emissions threshold to 34 Mg/yr, the final NSPS would
achieve reductions of 281 Mg/yr NMOC and 44,300 Mg/yr methane (1.1
million metric tons CO2-Eq./yr). In addition, the final
rulemaking is expected to result in the net reduction of 26,000 metric
tons CO2, due to reduced demand for electricity from the
grid as landfills generate electricity from LFG.
    This rule is expected to result in significant health and welfare
benefits resulting from the climate benefits due to anticipated methane
and CO2 reductions. Methane is a potent GHG that, once
emitted into the atmosphere, absorbs terrestrial infrared radiation
that contributes to increased global warming and continuing climate
change. Methane reacts in the atmosphere to form tropospheric ozone and
stratospheric water vapor, both of which also contribute to global
warming. When accounting for the impacts of changing methane,
tropospheric ozone, and stratospheric water vapor concentrations, the
Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report
(2013) found that historical emissions of methane accounted for about
30 percent of the total current warming influence (radiative forcing)
due to historical emissions of greenhouse gases. Methane is therefore a
major contributor to the climate change impacts described in section
III.B of this preamble. The remainder of this section discusses the
methane reductions expected from this proposed rule and the associated
monetized benefits.
    As discussed in section IV of this preamble, this rulemaking
includes several changes to the NSPS for MSW landfills that will
decrease methane emissions from this sector. Specifically, the final
NSPS are expected to reduce methane emissions from all landfills
annually by about 44,300 metric tons of methane.
    We calculated the global social benefits of these methane emission
reductions using estimates of the social cost of methane (SC-
CH4), a metric that estimates the monetary value of impacts
associated with marginal changes in methane emissions in a given year.
The SC-CH4 estimates applied in this analysis were developed
by Marten et al. (2014) and are discussed in greater detail below.
    A similar metric, the social cost of CO2 (SC-
CO2), provides important context for understanding the
Marten et al. SC-CH4 estimates.\51\ The SC-CO2 is
a metric that estimates the monetary value of impacts associated with
marginal changes in CO2 emissions in a given year. It
includes a wide range of

anticipated climate impacts, such as net changes in agricultural
productivity and human health, property damage from increased flood
risk, and changes in energy system costs, such as reduced costs for
heating and increased costs for air conditioning. Estimates of the SC-
CO2 have been used by the EPA and other federal agencies to
value the impacts of CO2 emissions changes in benefit cost
analysis for GHG-related rulemakings since 2008.
---------------------------------------------------------------------------

    \51\ Previous analyses have commonly referred to the social cost
of carbon dioxide emissions as the social cost of carbon or SCC. To
more easily facilitate the inclusion of non-CO2 GHGs in
the discussion and analysis the more specific SC-CO2
nomenclature is used to refer to the social cost of CO2
emissions.
---------------------------------------------------------------------------

    The SC-CO2 estimates were developed over many years,
using the best science available, and with input from the public.
Specifically, an interagency working group (IWG) that included the EPA
and other executive branch agencies and offices used three integrated
assessment models (IAMs) to develop the SC-CO2 estimates and
recommended four global values for use in regulatory analyses. The SC-
CO2 estimates were first released in February 2010 and
updated in 2013 using new versions of each IAM.
    The 2010 SC-CO2 Technical Support Document (TSD)
provides a complete discussion of the methods used to develop these
estimates and the current SC-CO2 TSD presents and discusses
the 2013 update (including recent minor technical corrections to the
estimates).\52\
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    \52\ Both the 2010 SC-CO2 TSD and the current TSD are
available at: https://www.whitehouse.gov/omb/oira/social-cost-of-carbon.
---------------------------------------------------------------------------

    The SC-CO2 TSDs discuss a number of limitations to the
SC-CO2 analysis, including the incomplete way in which the
IAMs capture catastrophic and non-catastrophic impacts, their
incomplete treatment of adaptation and technological change,
uncertainty in the extrapolation of damages to high temperatures, and
assumptions regarding risk aversion. Currently, IAMs do not assign
value to all of the important physical, ecological, and economic
impacts of climate change recognized in the climate change literature
due to a lack of precise information on the nature of damages and
because the science incorporated into these models understandably lags
behind the most recent research. Nonetheless, these estimates and the
discussion of their limitations represent the best available
information about the social benefits of CO2 reductions to
inform benefit-cost analysis. The EPA and other agencies continue to
engage in research on modeling and valuation of climate impacts with
the goal to improve these estimates, and continue to consider feedback
on the SC-CO2 estimates from stakeholders through a range of
channels, including public comments received on Agency rulemakings, a
separate Office of Management and Budget (OMB) public comment
solicitation, and through regular interactions with stakeholders and
research analysts implementing the SC-CO2 methodology. See
the docketed 2016 RIA for additional details.
    A challenge particularly relevant to this rule is that the IWG did
not estimate the social costs of non-CO2 GHG emissions at
the time the SC-CO2 estimates were developed. In addition,
the directly modeled estimates of the social costs of non-
CO2 GHG emissions previously found in the published
literature were few in number and varied considerably in terms of the
models and input assumptions they employed.\53\ In the past, EPA has
sought to understand the potential importance of monetizing non-
CO2 GHG emissions changes through sensitivity analysis using
an estimate of the GWP of methane to convert emission impacts to
CO2 equivalents, which can then be valued using the SC-
CO2 estimates. This approach approximates the social cost of
methane (SC-CH4) using estimates of the SC-CO2
and the GWP of methane.
---------------------------------------------------------------------------

    \53\ U.S. EPA. 2012. Regulatory Impact Analysis Final New Source
Performance Standards and Amendments to the National Emissions
Standards for Hazardous Air Pollutants for the Oil and Natural Gas
Industry. Office of Air Quality Planning and Standards, Health and
Environmental Impacts Division. April. http://www.epa.gov/ttn/ecas/regdata/RIAs/oil_natural_gas_final_neshap_nsps_ria.pdf. Accessed
April 7, 2016.
---------------------------------------------------------------------------

    The published literature documents a variety of reasons that
directly modeled estimates of SC-CH4 are an analytical
improvement over the estimates from the GWP approximation approach.
Specifically, several recent studies found that GWP-weighted benefit
estimates for CH4 are likely to be lower than the estimates
derived using directly modeled social cost estimates for these
gases.\54\ The GWP reflects only the relative integrated radiative
forcing of a gas over 100 years in comparison to CO2. The
directly modeled social cost estimates differ from the GWP-scaled SC-
CO2 because the relative differences in timing and magnitude
of the warming between gases are explicitly modeled, the non-linear
effects of temperature change on economic damages are included, and
rather than treating all impacts over a hundred years equally, the
modeled damages over the time horizon considered (300 years in this
case) are discounted to present value terms. A detailed discussion of
the limitations of the GWP approach can be found in the RIA.
---------------------------------------------------------------------------

    \54\ See Waldhoff et al (2011); Marten and Newbold (2012); and
Marten et al. (2014).
---------------------------------------------------------------------------

    In general, the commenters on previous rulemakings strongly
encouraged the EPA to incorporate the monetized value of non-
CO2 GHG impacts into the benefit cost analysis. However,
they noted the challenges associated with the GWP approach, as
discussed above, and encouraged the use of directly modeled estimates
of the SC-CH4 to overcome those challenges.
    Since then, a paper by Marten et al. (2014) has provided the first
set of published SC-CH4 estimates in the peer-reviewed
literature that are consistent with the modeling assumptions underlying
the SC-CO2 estimates.55 56 Specifically, the
estimation approach of Marten et al. used the same set of three IAMs,
five socioeconomic-emissions scenarios, equilibrium climate sensitivity
distribution, three constant discount rates, and aggregation approach
used by the IWG to develop the SC-CO2 estimates.
---------------------------------------------------------------------------

    \55\ Marten et al. (2014) also provided the first set of SC-
N2O estimates that are consistent with the assumptions
underlying the IWG SC-CO2 estimates.
    \56\ Marten, A.L., E.A. Kopits, C.W. Griffiths, S.C. Newbold &
A. Wolverton (2014). Incremental CH4 and N2O
mitigation benefits consistent with the U.S. Government's SC-
CO2 estimates, Climate Policy, DOI: 10.1080/
14693062.2014.912981.
---------------------------------------------------------------------------

    The SC-CH4 estimates from Marten, et al. (2014) are
presented in Table 3 of this preamble. More detailed discussion of the
methodology, results, and a comparison to other published estimates can
be found in the RIA and in Marten, et al.

                                    Table 3--Social Cost of CH4, 2012-2050 a
                           [In 2012$ per metric ton (Source: Marten et al., 2014 \b\)]
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                                                                              SC-CH4
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