November 13, 2014 1 

Discussion Paper on Potential Implementation of Alternative Monitoring 

under the GHGRP 

I. Overview 

In October 2009, the Environmental Protection Agency (EPA) created the Greenhouse Gas 

Reporting Program (GHGRP) by issuing the Greenhouse Gas Reporting Rule (40 CFR Part 98). 

The GHGRP requires facility-level annual reporting of greenhouse gases for large direct emitters 

and suppliers in over 40 industrial sectors in the United States. The program includes specific 

monitoring methods for processes and process equipment in order for facilities to calculate 

greenhouse gas (GHG) emissions in a consistent manner. In certain cases, the program allows 

the use of alternative methods. 

During implementation of the GHGRP, the EPA has received requests to allow additional 

flexibility to accommodate the optional use of novel monitoring methods. For example, several 

environmental groups petitioned the EPA for advanced, innovative monitoring methods to be 

allowed under subpart W, which covers Petroleum and Natural Gas Systems.1

 These requests 

stem from advances in technology that could improve the quality of the data submitted and 

potentially reduce the burden on regulated facilities who are using these advanced methods. 

With regard to subpart W, as oil and gas operations seek to capitalize on advances in 

measurement and monitoring technology in optimizing process operations and reducing fugitive 

emissions from process equipment leaks, opportunities could arise for facilities to use innovative 

technologies to gather emissions data. 

The EPA is assessing the potential opportunities for the optional use of innovative measurement 

or monitoring technologies to calculate emissions from affected sources under subpart W and 

other areas of the GHGRP. The EPA’s goal for this assessment is to determine if the optional use 

of such technologies could be applied to the GHGRP to improve the overall accuracy and 

transparency of reported data in a cost-effective way while still meeting the overall objectives of 

Part 98. The EPA is requesting comment on the feasibility, possible regulatory approaches and 

provisions necessary to allow the optional use of advanced measurement or monitoring methods 

in the GHGRP, and methods to ensure compliance with those provisions in an efficient manner. 

In particular, as described in Section IV of this document, the EPA is soliciting data and case 

studies that could provide information regarding the benefits, costs, and other potential 

considerations. 

This paper discusses approved uses of alternative methods under the GHGRP and considerations 

for expanding voluntary use of advanced monitoring methods (described in this document as 

“alternative monitoring”) to subpart W and other subparts of the program. 

The EPA is soliciting input on the ideas in this discussion paper. Following review of the 

comments received, the EPA may propose amendments related to the use of alternative 

innovative technologies in GHGRP monitoring in a future rulemaking. 

 

1

 Petition for Rulemaking and Interpretive Guidance Ensuring Comprehensive Coverage of Methane Sources under 

Subpart W of the Greenhouse Gas Reporting Rule – Petroleum and Natural Gas Systems. March 19, 2013. 

(http://www2.epa.gov/sites/production/files/documents/ghgrp_petition_0.pdf) 
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II. Background 

In the GHGRP, each subpart specifies the monitoring requirements for the specific types of 

processes and units used in that industry. These monitoring requirements can include direct 

emissions measurement, facility-specific engineering calculations, and emission factors derived 

from direct measurement. Monitoring in the GHGRP generally includes requirements regarding 

which parameters to monitor, the type of monitoring device(s) that can be used, the precision and 

accuracy requirements for the monitoring device, the calibration requirements to be conducted 

periodically, the frequency of monitoring, and the reference test method to be used. 

For a few subparts, the EPA has already incorporated the option to use alternative monitoring. In 

particular, in 2009, the Greenhouse Gas Reporting Rule was written to mainly allow alternative 

monitoring for subpart E (Adipic Acid Production) and subpart V (Nitric Acid Production) to 

allow for use of continuous emissions monitoring systems (CEMS) for N2O emissions. At that 

time the EPA was aware of a few facilities that were using CEMS to monitor N2O emissions; 

however, unlike CEMS for CO2, there was no standard test method for certifying a CEMS for 

N2O emissions that the rule could reference. In order to allow these facilities to comply with the 

rule while using a non-standard monitoring system, the GHGRP has provided a way to apply and 

receive approval for its use. 

For subparts E and V, facilities must apply for approval to use alternative monitoring by January 

30th of the applicable reporting year (RY) using a standardized application form. The application 

requires the facility to include details on the facility, the unit name and type, the alternative 

method to be used, a justification for using the alternative method, as well as some additional 

supplemental information. Once the applications are received, they go through a standardized 

technical review. 

Under subpart E, one facility has requested an alternative monitoring method for each year of the 

GHGRP (RY2010 through RY2014). Under subpart V, there have been varying numbers of 

applications per reporting year. Four reporters applied for RY2014. All applications submitted 

for subpart E and subpart V thus far have been approved. 

The provisions of subpart I (Electronics Manufacturing) allow reporters to request approval to 

use an alternative stack test method or to use an alternative method to determine abatement 

system destruction or removal efficiency (DRE). For subpart I, an alternative method is 

described as “any method of sampling and analyzing for a fluorinated GHG or N2O, for the 

determination of parameters other than concentration, for example, flow measurements, that is 

not a method specified in this subpart and that has been demonstrated to the Administrator’s 

satisfaction, using Method 301 in appendix A of part 63, to produce results adequate for the 

Administrator’s determination that it may be used in place of a method specified elsewhere in 

this subpart”. In order to use an alternative method for subpart I, reporters must notify the EPA 

Administrator (or authorized representative) of the intent to use an alternative method. The 

notification must include information on a test plan, the validation of the method using EPA 

Method 301, and the rationale for not using the method specified in the GHGRP. 

If the EPA approves the alternative method test plan for subpart I and the reporter completes the 

test plan, the reporter must then report the results of the alternative method test plan to the 

Administrator for review and approval. The Administrator may then either dispute the results of 

the test plan or approve the alternative method for use in Subpart I. Once an alternative method 

has been approved in subpart I, that same method may be used at any other facility for the same 
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fluorinated GHGs and types of stack or abatement systems, as applicable, provided that approved 

conditions in the test plan also apply to the facility in question. 

These provisions went into effect January 1, 2014. As of July 2014, no alternative method 

applications had been submitted or approved for subpart I. 

There are other EPA programs that also allow for the use of alternative monitoring and/or 

alternative test methods including other Clean Air Act and Clean Water Act programs. See 

Appendix A for additional details on alternative monitoring provisions in some other EPA 

programs. 

In general, the alternative monitoring allowed under these other programs requires one or more 

of the following elements: 

• Detailed applications; 

• Demonstration that the results of the alternative monitoring approach are comparable in 

quality to the methods in the specific rule subparts; and 

• Specific approval from the EPA for a facility to use the method. 

III. Examples of Alternative Monitoring that Could Potentially Be Allowed 

under Subpart W

The issue of alternative monitoring was revisited in March 2013 when, as mentioned in Section 

I, a group of environmental organizations submitted a petition for rulemaking related to methane 

emissions from subpart W (Petroleum and Natural Gas Systems). This petition asserts that new 

and innovative technologies exist today that are being employed by select companies or facilities 

in the oil and natural gas sector and that the data from these technologies may provide enhanced 

or more accurate data than current GHGRP methods. According to the petitioners, real-time 

continuous emissions monitoring technologies are evolving and, by including advanced 

innovative monitoring methods, the GHGRP could accelerate the development and use of these 

technologies, especially with respect to methane emissions. 

Several advanced technologies could potentially be applied to petroleum and natural gas 

systems. A few examples are briefly described below. 

Greenhouse gases like CO2 and methane each absorb a unique and characteristic near-infrared 

wavelength. Tunable diode lasers and laser absorption spectroscopy exploit this property by 

using laser light tuned to a specific mid-infrared wavelength to measure the concentration of a 

specific gas like methane in ambient air. Cavity ring-down spectroscopy (CRDS) is a tunable 

diode laser absorption spectroscopy technique that simultaneously detects gas emissions and 

measures the concentration. A single frequency laser is aimed into a cavity created by two or 

more high reflectivity mirrors. Laser light bounces between the mirrors thousands of times, the 

laser is turned off and the light intensity inside the cavity steadily decays to zero (the “ring 

down”). If a gas is present in the cavity that absorbs the frequency of the laser light, the ring 

down time accelerates due to absorption by the gas. CRDS achieves sensitivity by creating a very 
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long path length for the laser light, significantly enhancing the signal and reducing noise.2, 3 

Cavity ring-down spectroscopy could be used in oil and gas applications and is applicable to 

both fixed continuous emissions monitoring and to mobile monitoring applications. 

Recent advances in optical remote sensing (ORS) technology offer the capability to provide 

measurements of methane and other gases in ambient air.4 An example of one such advanced 

ORS system is differential absorption lidar (DIAL), an open path ORS technology that uses an 

active laser source tuned for a target gas such as methane or CO2, and detects the differential 

signal returned when the laser light is absorbed by the target gas in the atmosphere. DIAL 

systems can quickly scan a vertical plane downwind of an emission source and rapidly generate a 

profile of gas concentration as a function of height and distance. Instantaneous meteorological 

data can be incorporated with the emissions for real time computation of mass emissions flux. 

Detection limits for methane are sensitive to atmospheric conditions and path length but are in 

the range of parts per billion.5, 6

 

For certain subpart W sources, emissions are calculated using emission factors or engineering 

calculations. For example, subpart W emissions from natural gas pneumatic devices are 

calculated using emission factors. The number of pneumatic devices in each facility are counted 

according to type - low continuous bleed, high continuous bleed, and intermittent bleed - and the 

device count is multiplied by a published subpart W emission factor identified for pneumatic 

devices for each particular natural gas industry segment. Innovative monitoring approaches 

could be applied to provide direct measurement or to develop facility-specific emission factors in 

cases where industry segment emission factors are provided by the rule. In the pneumatic device 

example, an operator might directly measure emissions from pneumatic devices. 

It is important to note that alternative monitoring, as discussed in this paper, is not the same as 

provisions for “best available monitoring methods,” or BAMM, which were included in the 

GHGRP in 2009 but have since been removed from the GHGRP except for select, short-term 

monitoring provisions. While Part 98 allowed the use of BAMM in the early stages of 

implementation of the GHGRP for all reporters and for several years for certain subparts, the use 

of BAMM has been phased out for all industry-specific subparts, and the EPA does not intend to 

reintroduce this concept as part of this alternative monitoring discussion. 

BAMM was meant as a temporary allowance for those facilities that could not immediately 

implement the subpart-specific monitoring required, either due to equipment availability or 

technical installation issues that required additional time to resolve. While BAMM was intended 

to include monitoring that may have been less stringent than the GHGRP requirements, the 

purpose of alternative monitoring is to allow for advanced monitoring, flexibility, and innovation 

while improving data quality. 

 

 

2

 Wheeler, M. D., S. M. Newman, et al., 1998, Cavity ring-down spectroscopy. J. Chem. Soc., Faraday Trans. 94(3): 337-351. 

3 Cavity Ring Down Spectroscopy (CRDS); www.picarro.com/technology/cavity_ring_down_spectroscopy

4

 Allen, D.T. et al. Measurements of methane emissions at natural gas production sites in the United States, Proceedings of the 

National Academy of Sciences of the United States of America, 110(44): 17768–17773, 2013. 

5 Whetstone, J., Maxwell , S.E., and others, Differential Absorption LIDAR for Greenhouse Gas Measurements, presentation at 

Council for Optical Radiation Measurements Annual Technical Conference, May 30 – June 1, 2012, Ottawa, Canada.

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Jones, D., The Application of Differential Absorption Lidar (DIAL) for Methane Monitoring, National Physics Laboratory, 

U.K., presentation, September 4, 2014, www.npl.co.uk
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IV. Request for Input 

The EPA is seeking input on the ideas and content of this discussion paper, including whether 

the EPA should allow the use of alternative monitoring in the GHGRP. If so, the Agency seeks 

input on whether the current approaches used in the GHGRP are appropriate and could be 

applied more broadly or if there are other programs that might serve as an appropriate model. 

The EPA also seeks input on what criteria should be considered as part of the Agency’s 

evaluation. In evaluating whether and how to incorporate voluntary use of alternative methods, 

there could be several considerations including: 

• Impact on emissions reporting and quality of data; 

• Impact on the EPA’s ability to effectively verify and evaluate data received; 

• Impact on the public’s ability to analyze data across facilities; 

• Impact on facility and/or EPA burden; 

• Ease of implementation; 

• Extent to which opportunities are created and innovation encouraged; 

• Consistency, equity of treatment among reporters in a subpart or across subparts; and 

• Comparability of data between reporting years; 

In addition to the criteria the EPA should consider, the EPA seeks input on several 

implementation questions that are likely to be raised if the EPA proposes to allow alternative 

monitoring. There are several approaches the EPA could consider that raise multi-faceted 

implementation questions including, but not limited to, the following: 

• How should a facility let EPA know they want to use alternative monitoring? What 

information should be provided? Should this notification be required annually? How 

should EPA provide notification of approval or disapproval? 

• Who could use alternative monitoring? Should only certain subparts be allowed to use it? 

Should there be an emissions threshold? 

• For which parameters could alternative monitoring be used? Should every monitoring 

change be allowed or only significant changes? Should changes to emission calculations 

be allowed? 

• Should a facility be required to prove that its alternative monitoring approach results in 

higher data quality? If yes, how should this be accomplished? 

• Should EPA maintain a list of approved alternative monitoring methods? Should an 

alternative monitoring method approved for use at one facility be eligible for application 

at another facility in the subpart or across other subparts? 

Feedback on these questions will help the EPA consider possible options for designing 

alternative monitoring approaches. 

Appendix B outlines three illustrative examples of how the use of alternative monitoring could 

be applied to the GHGRP. The first example approach is a detailed annual request for use of 

alternative monitoring which could be possible for any parameter in any subpart. The second 
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example approach entails a one-time detailed request which could be limited to only certain 

subparts. In the third example approach, the EPA could publish a list of monitoring technologies 

that are considered alternative and innovative. A facility could submit a one-time indication to 

use this technology for an applicable subpart. These examples are for illustrative purposes only, 

the EPA welcomes comments on whether these or other approaches would be appropriate. 

Following review of the comments received on this discussion paper, the EPA may propose 

amendments related to the use of alternative innovative technologies in reporting to the GHGRP 

in a future rulemaking. 

 
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Appendix A 

Alternative Monitoring in Other EPA Programs

A. Clean Air Act New Source Performance Standards and National Emission 

Standards for Hazardous Air Pollutants 

The EPA’s Office of Air Quality Planning and Standards (OAQPS) allows the use of alternative 

monitoring and/or alternative performance testing under the New Source Performance Standards 

(Title 40, Part 60) and the National Emissions Standards for Hazardous Air Pollutants (Title 40, 

Part 61 and Part 63) of the Clean Air Act. Review and approval of requests are run through the 

EPA’s Emission Measurement Center (EMC). 

Approval of alternative monitoring must allow the Administrator to make adequate 

determination of compliance. In addition, new approvals should be consistent with prior 

approvals. Examples of approvable alternative monitoring are included in §§60.13(l), 61.14(g), 

and 63.8(f). 

For alternative test methods, approval requires that the test method produce results adequate for 

the Administrator’s determination of compliance and that it has been demonstrated to the 

Administrator’s satisfaction using Method 301 of Appendix A, Title 40 Part 63. 

More detailed information about the EMC including links to methods and monitoring for NSPS 

and NESHAP may be found at www.epa.gov/ttn/emc/index.html. 

B. Clean Water Act Alternative Test Procedure Program 

The Clean Water Act (CWA) offers flexibility to modify methods under 40 CFR Part 136. The 

Clean Water Act Alternate Test Procedure (ATP) allows a method developer to ask for review 

(not approval) of the following: 

• Method using a determinative technique (e.g., a pollutant detector) different from that in 

an existing Part 136 method, or 

• Modification to a Part 136 method that falls outside the scope of the modification 

flexibility described in the Part 136 method, or at 40 CFR 136.6. 

The language at 40 CFR 136.6 offers flexibility to modify approved methods without EPA 

review. The applicants must establish equivalent performance as defined in 136.6(b)(2)(i) and 

must document the modified method in a write-up or addendum as described in 136.6(b)(2)(ii). 

A method developer may apply for review of a method modification or a new method through 

the ATP program. 

More detailed information on the ATP may be found at water.epa.gov/scitech/methods/cwa/atp. 
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Appendix B 

Example Approaches for the Alternative Monitoring Mechanism 

In this Appendix we describe three example approaches that could be used to define the 

boundaries and requirements of an alternative monitoring mechanism. These are for illustrative 

purposes only and are intended to help generate comments and ideas on approaches the EPA 

could consider. 

Example Approach A: Detailed Annual Request 

In this example approach, in order to use alternative monitoring, a facility could submit an 

annual detailed request describing the monitoring approach that it wishes to use. An alternative 

method could be eligible for use for any monitoring parameter in any subpart, if it is approved. 

In this approach, each type of monitoring change could be grouped into a major or minor 

category and those monitoring changes considered to be minor would not need a detailed request 

to use alternative monitoring. Under the GHGRP, a major change could include adoption of 

newer monitoring technologies or application of existing technologies to new types of source 

categories or process units. Smaller changes, such as more frequent monitoring, could be 

considered minor changes and need less or no notification. More attention and review could be 

given to alternative monitoring that is considered to be a major change. For example, a facility 

could engage in a trial period of several months to a full reporting year during which they could 

provide data for both the monitoring methods prescribed in the rule and the alternative 

monitoring approach so that a direct comparison may be performed to ensure data quality. 

An internal list of implemented or approved alternative monitoring approaches by subpart could 

be maintained under this example approach. An alternative monitoring approach accepted for 

one facility within a subpart would be acceptable for another facility within the subpart as long 

as data quality is improved for that subpart. 

Considerations: 

- What could be the limits or criteria for ensuring data quality? 

- What could be the length of the trial period for major changes? 

- How could major and minor changes be defined? 

- What justification could a reporter provide to prove applicability and accuracy of the 

alternative method (e.g., EPA Method 301)? 

Example Approach B: One-Time Detailed Request 

In this example approach, a facility could submit a one-time detailed description of the 

alternative monitoring approach that it wishes to use for approval. Approval for the use of this 

alternative monitoring approach could then be in effect for the duration of the use of that 

approach. A facility would only need to submit additional information for further approval if 

any changes are to be made to that approach in future reporting years. 
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For this example approach, the applicability of alternative monitoring could be limited to only 

certain subparts. For example, the alternative monitoring approach could be applicable to only 

direct emitter subparts, only supplier subparts, or only those subparts where facilities have 

requested alternative monitoring in the past. Any monitoring parameter within the determined 

subparts could be eligible for an alternative method to be used, if approved, however that 

parameter would need to fit into the rule-specified calculation equations. No alternative 

calculation equations could be approved. 

All facilities that wish to use alternative monitoring could submit the same initial detailed request 

regardless of whether the change is minor or major.

A public list of approved alternative monitoring approaches by subpart could be maintained. An 

alternative monitoring approach accepted for one facility within a subpart could be acceptable 

for another facility within the subpart as long as data quality is improved. 

Considerations: 

- For which subparts could a facility request to use alternative monitoring? 

- What could be limits or criteria for ensuring data quality? 

- What justification could a reporter provide to prove applicability and accuracy of the 

alternative method (e.g., EPA Method 301)? 

Example Approach C: Public List of Possible Alternative Monitoring Technologies 

In this example approach, a list of monitoring technologies that are considered advanced and 

innovative could be made available. A facility could submit a one-time indication to use this 

technology. The list could include the parameters to be monitored, the specific GHG to be 

measured, the frequency of measurement, the calculation methods for emissions, and other 

details. No official or formal approval would be needed. 

For this example approach, use of alternative monitoring could be limited to certain subparts to 

which the specific technologies apply. The types of monitoring approved could be maintained 

by subpart. Alternative monitoring approaches could not automatically be applied to other 

similar facilities or process units unless listed. 

Considerations: 

- What could be the specific criteria for an alternative monitoring technology? 

- How could information on advanced and innovative technologies be solicited so they could be 

included on the prescribed list? Could a technology be added to the list at a later time, and if 

so, how? 

- How could a technology be assessed to determine that it is appropriate for a particular subpart?