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MEMORANDUM

To: Swarupa Ganguli, U.S. EPA, OAP, Climate Change Division

Docket EPA-HQ-OAR-2014-0451

From: Eastern Research Group

Date: July 2015

Subject: Establishing a Site-Specific Emission Threshold Alt ernative for MSW Landfills

The purpose of this memorandum is to document compo nents of the Tier 4 approach in the proposed revisions to the Municipal Solid Waste (MSW) Landfi lls Emission Guidelines and discuss how EPA selected the surface emission thresholds for the pr oposal.



### 1.0 Current Rule Framework Under the current Emission Guidelines (EG) and New Source Performance Standards (NSPS) for MSW Landfills, the timing of when a gas collection and control system (GCCS) must be installed is based on an emission rate threshold for nonmethane organic comp ounds (NMOC). The landfill has three methods for calculating whether its modeled emissions exceed th e NMOC threshold.
Installation Triggers:
Table 1. NMOC Emission Threshold Determinations for GCCS Installation in Current Rule Framework

Tier 1: Use NMOC emission rate equation to calculate

NMOC emissions and compare to 50 megagrams per year (Mg/yr) threshold (i.e., LandGEM approach). If fail Tier 1, then install GCCS OR go to Tier 2: Use Method 25 or 25C to determine site-specific NMOC concentration and re-calculate NMOC emissions and compare to 50 Mg/yr threshold. If fail Tier 2, then install GCCS OR go to Tier 3: Use Method 2E to determine site-specific k value 1 and re-calculate NMOC emissions and compare to

50 Mg/yr threshold. If fail Tier 3, then install GCCS.

1 A k-value is the methane generation rate constant, expressed in units of year -1

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The timing of when a GCCS can be removed is also ba sed on the NMOC emission rate.
Removal Triggers:
The following three criteria must all be met:
1. The landfill is closed AND 2. The GCCS must have been in operation a minimum of 1 5 years AND 3. The calculated NMOC emission rate at the landfill i s less than 50 Mg/yr. The emission rate is based on actual measured flow rates and average NMO C concentrations in the landfill gas (LFG). 

### 2.0 Background on a Surface Emission-Based Emission Threshold The idea to measure site-specific surface emissions to determine timing of when a GCCS should be installed was received by the Small Business Advoca cy Review (SBAR) Panel from small entity representatives (SERs) when EPA was conducting outr each to small entities during its review of the Landfills NSPS and EG in December 2013. The SERs re commended adding a new method to test direct surface emissions to demonstrate that site-specific emissions are low prior to GCCS installation. 2 In follow-up outreach with the SERs in April 2015, the SERs provided additional feedback on more detailed features of a site-specific surface emission based threshold. 3 In addition, in its January 2013 white paper outlining policy recommendations for the NSPS/EG, t he Environmental Defense Fund (EDF) presented the idea that a surface concentration threshold all ows “a monitoring-based applicability prong that provides built-in incentives for landfill operators to adopt one or more innovative methane avoidance or mitigation strategies, including organic waste dive rsion, oxidative landfill covers, and early LFG con trol measures.” EDF noted that landfill experts state a surface methane concentration of 200 parts per million (ppm) provides further empirical confirmati on that a landfill is ready for installation of a f ull gas capture system. 4 EDF also pointed to the use of a surface concentra tion threshold in the California Landfill Methane Rule (CA LMR). 5
In the July 17, 2014 notices for the proposed NSPS and the Advanced Notice of Proposed Rulemaking (ANPRM) for existing landfills, the EPA solicited c omments on a new Tier 4 surface emission monitoring (SEM) demonstration to allow increased flexibility for landfills that exceed modeled NMOC emission rates if they can demonstrate that measured site-sp ecific surface methane emissions are low. The EPA sought general feedback on the implementation and a ppropriateness of this alternative and specifically sought comment on: (1) which areas of the landfill would be subject to SEM requirements because these areas would no longer be limited to areas with GCCS installed; (2) what number of exceedances over a specified time period would require GCCS installati on; (3) what frequency of SEM demonstration is appropriate (e.g., quarterly monitoring for landfil ls accepting waste, annual monitoring for closed landfills); (4) what exceedance level is appropriat e for determining if a GCCS must be installed (200 ppm or some other level); and (5) what landfills should qualify for using a Tier 4 option. The EPA receive d numerous comments in support of a Tier 4 alternativ e for both the installation and removal of a GCCS.

2 See Docket ID No. EPA-HQ-OAR-2003-0215-005 and EPA -HQ-OAR-2014-0451

3 See Final Report of the Small Business Advocacy Re view Panel on EPA’s Planned Proposed Rule Emission Guidelines and Compliance Times for MSW La ndfills. 2015.

4 See Docket ID No. EPA-HQ-OAR-2014-0451-0008

5 http://www.arb.ca.gov/cc/landfills/landfills.htm3

The EPA also received comments on specific implemen tation concerns, as discussed in the preamble for the proposed revisions to the Emission Guidelines. 

### 3.0 Proposed Tier 4 Approach Based on public comments and feedback from SERs and other stakeholders, EPA has proposed regulatory text for a Tier 4 approach. Under the pr oposed Tier 4 option:

• Area monitored: The SEM demonstration would be cond ucted around the entire perimeter of the landfill and along a traverse pattern at interv als no greater than 30 meters (98 feet), although EPA is requesting comment on whether to re duce the traverse pattern intervals to 25 feet. All surface penetrations and areas where visu al observations indicate elevated concentrations of methane must also be monitored.

• Exceedances: The landfill owner or operator would b e required to submit a design plan within 90 days of the first measured concentration of 500 ppm or greater and would be required to install and begin operating a GCCS within 30 months of the first measured concentration of 500 ppm or greater. Once the 500 ppm or greater thresho ld is exceeded, the owner/operator must install the GCCS within the specified time frame an d cannot delay its installation by taking action to correct the measured exceedance.

• Frequency of monitoring: Monitoring would be requir ed quarterly. After four consecutive quarters, the frequency can be reduced to semi-annu ally at active landfill areas and annually at closed landfills or closed areas of active landfill s if no exceedances were found.

• Threshold: A surface concentration of 500 ppm was p roposed.

• Qualifying landfills: Any landfill exceeding the de sign capacity threshold can opt to use the Tier 4 alternative after failing a Tier 1, Tier 2, or Tier 3 test. Once a landfill fails a Tier 4 test, a GCC S must be installed.
Revised Installation Triggers:
Table 2. NMOC Emission Threshold Determinations for GCCS Installation in Proposed Rule Framework

Tier 1: Use NMOC emission rate equation to calculate NMOC emissions and compare to 34 Mg/yr threshold (i.e., LandGEM approach). If fail Tier 1, then install GCCS OR go to Tier 2 or Tier 4: Tier 2: Use Method 25 or 25C to determine sitespecific NMOC concentration and re-calculate NMOC emissions and compare to 34 Mg/yr threshold.

Tier 4: Use SEM to demonstrate surface methane emissions <500 ppm. If fail Tier 4, then install GC CS. If fail Tier 2, then install GCCS OR go to Tier 3 or Tier 4: Tier 3: Use Method 2E to determine site-specific k value and re-calculate NMOC emissions and compare to 34 Mg/yr threshold.

Tier 4: Use SEM to demonstrate surface methane emissions <500 ppm. If fail Tier 4, then install GC CS.4

If fail Tier 3, then install GCCS OR go to Tier 4. Tier 4: Use SEM to demonstrate surface methane emissions <500 ppm. If fail Tier 4, then install GC CS.

Revised Removal or Decommissioning Triggers:
The following criteria must be met in the proposal:

1. The landfill is closed or an area of an open landfi ll is closed AND 2. The GCCS must have been in operation a minimum of 1 5 years or landfill owner/operator must demonstrate that the GCCS will be unable to operate for 15 years due to declining gas flow AND

3a. The calculated NMOC emission rate at the landfi ll is less than 34 Mg/yr. 6

OR

3b. The landfill or closed area of the landfill dem onstrates for four consecutive quarters that there are no surface methane emissions at or above 500 pp m.


### 4.0 Selection of a Surface Concentration Threshold 4.1 Are the Proposed NMOC Emission Rate Threshold a nd Surface Emission-based Approach Equivalent? When examining options presented under Tiers 1 thro ugh 4, it is important to note that an SEM methane concentration and an NMOC emission rate are two different types of emission limits which are not directly comparable due to their inherent diffe rences in measurement and estimation. An SEM reading in parts per million (ppm) is a concentrati on of methane (limit under Tier 4 option in proposa l is 500 ppm methane) in ambient air at a specific point at the landfill surface at a particular point in time. On the other hand, a modeled NMOC emission ra te (limit in proposal is 34 megagrams/year) represents the estimated amount of NMOC emitted fro m an entire landfill over an entire year based on either default and/or site-specific modeling parame ters and a first-order decay equation used to model emissions over time.
Unlike most emission sources, uncontrolled landfill s emit gas through their entire surface area, not f rom a stack or exhaust vent. The amount of gas emitted from the surface of a landfill is site-specific and varies spatially and temporally at any given landfi ll depending on several factors, including waste ty pe and composition, waste age, waste moisture, waste t emperature, cover practices, other avenues of gas extraction or venting, air temperature, and baromet ric pressure. An SEM concentration measures the methane in the ambient air 5-10 centimeters above t he surface of the landfill at one location and not across the entire landfill. At a typical point sour ce (e.g., manufacturing facility), you would measur e a pollutant concentration and apply it to the volumet ric gas flow rate (e.g., standard cubic feet per mi nute (scfm)) of a uniform and well-defined waste stream to obtain an estimated mass emission rate (e.g., Mg/yr). Because of the differences in how LFG emiss ions are released over time and space, correlating a surface methane concentration to a modeled NMOC mas s emission rate is not practical for landfills.
Commenters representing both industry and environme ntal groups noted the Tier 4 SEM option would encourage landfill owners and operators to implemen t alternative methane reduction practices such as oxidative covers, interim gas control measures, and organic waste diversion. The EPA agrees that such

6 For landfills in the closed landfill subcategory, this third criterion remains less than 50 Mg/yr.5

measures can directly affect surface methane emissi ons and would help a landfill owner/operator ensure that surface emissions are low, enabling the landfill to delay the regulatory requirement to in stall a GCCS. Commenters also expressed concern that a mo deled emissions approach can overestimate emissions, particularly in arid areas. The EPA reco gnizes that modeling uncertainties can in some case s overestimate emissions and a surface-based approach can provide a more relevant and reasonable trigger for installing controls than modeling condu cted under current emission threshold determination s (Tiers 1, 2, and 3).
4.2 What Surface Concentration is Environmentally P rotective? Due to the inability to correlate the modeled NMOC mass emission rate with a specific surface methane concentration, the EPA needed to select a surface c oncentration threshold for Tier 4 that is environmentally protective in order to make the Tie r 4 approach viable. The Best System of Emission Reduction (BSER) for LFG emissions has been defined as a well-designed and well-operated GCCS. Once a GCCS has been installed and put in operation as r equired by the NSPS/EG regulations, the landfill owner/operator must conduct quarterly SEM and corre ct for exceedances of 500 ppm or greater in order to minimize surface emissions to the atmosphe re. This level was selected in the original 1996 ru le based on EPA’s evaluation of available information, including commenter feedback, to indicate proper operation of the GCCS. 7 The EPA believes that it is appropriate to use thi s same threshold for determining when to install a GCCS in the first ins tance. As long as a landfill’s surface emissions of methane remain below 500 ppm, the landfill’s emissi ons are consistent with the potential emissions of a landfill with a GCCS already in place and operating . Further, in addition to being environmentally protective, using the same 500 ppm threshold for de termining when a GCCS is required to be installed under the EG, is consistent with the idea that volu ntary systems installed or actions taken ahead of regulatory requirements must be well-designed and w ell-operated in order to be effective in minimizing surface emissions to the atmosphere.
The EPA reviewed other standards containing surface emission thresholds. The CA LMR retains the 500 ppm level as an appropriate level for instantaneous SEM readings for areas already controlled by a GCCS. California ARB initially proposed a 200 ppm S EM threshold for both GCCS installation and for GCCS operation in its regulation, but finalized 500 ppm for GCCS operation because a lower threshold could cause an operator to overdraw the vacuum on t he GCCS (to avoid a surface exceedance), which in turn could draw in too much oxygen and possibly cau se fires. 8 The EPA recognizes the concerns with setting the threshold too low, which may cause oper ators of voluntary GCCS to overdraw the vacuum on the GCCS, and has proposed a level of 500 ppm consi dering both environmental protection and safety.
With respect to removal of GCCS, while the proposed rule allows for GCCS removal based on a surface emission-based approach, in practice a GCCS is rare ly removed. Landfills would continue to operate the GCCS for safety and LFG migration as part of their 30-year post-closure care obligations under the

7 See Section 1.2.2.6 of Background Information Docum ent at 1-43. Air Emissions from Municipal Solid Waste Landfills-Background Information for Final St andards and Guidelines, U.S. EPA (EPA-453/R-94- 021), accessed at http://www.epa.gov/ttn/atw/landfill/bidfl.pdf

. 8 See Final Statement of Reasons. Page 30-31. http://www.arb.ca.gov/regact/2009/landfills09/landf ills09.htm

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Resource Conservation and Recovery Act (RCRA) regul ations. However, once the GCCS requirements of the EG have passed, the GCCS may run more intermitt ently as gas flows build up enough to support combustion in a flare or other device. A surface em ission-based approach would provide an incentive fo r landfills to maintain tight covers or install earli er final covers in order to keep the landfill’s emi ssion below the threshold, thereby reducing SEM, recordke eping, and reporting burdens associated with the EG requirements for landfills required to operate a GCCS under the rule. A 500 ppm threshold for removal would provide a consistent surface threshol d to ensure that surface emissions venting to the atmosphere were minimized.