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MEMORANDUM

To: Hillary Ward, U.S. EPA, OAQPS, Sector Policies and Programs Division 

 Docket EPA-HQ-OAR-2014-0451 

 

From: Eastern Research Group 

Date: July 2015

Subject: Analysis of Surface Exceedances from California Landfills under the New Source 

Performance Standards and the California Landfill Methane Rule 

1.0 Introduction 

This memorandum summarizes data that the EPA received related to enhanced surface emissions 

monitoring under the California Landfill Methane Rule (CA LMR) in order to assess the environmental 

benefits of modifying the surface emission monitoring (SEM) requirements in the MSW Landfills New 

Source Performance Standards (NSPS) and Emission Guidelines (40 CFR part 60, subparts XXX and Cf). 

The current NSPS and Emission Guidelines SEM provisions require a traverse of the landfill at 30 meter

(98 ft.) intervals; reporting of methane concentrations over 500 ppmv (exceedances), and monitoring 

during typical meteorological conditions. 

The CA LMR requires a tighter traverse pattern of 25 ft.; reporting of instantaneous methane 

concentrations over 500 ppmv or greater; reporting of integrated methane concentrations of 25 ppmv 

or greater within 50,000 sq. ft. grids; and restrictions on monitoring when wind speed exceeds 5 mph 

average and 10 mph instantaneous or within 72 hours of measurable precipitation unless a variance is 

provided. In the July 2014 proposed NSPS revisions (40 CFR part 60 subpart XXX) and the Advanced 

Notice of Proposed Rulemaking for revisions to the MSW Landfills Emission Guidelines, the EPA 

requested comment for additional information on the emission reductions and costs associated with 

enhanced monitoring approaches. 

The current NSPS/ Emission Guidelines and CA LMR require corrective action for exceedances. When a 

landfill shows an exceedance, the landfill must make repairs or adjustments and recheck at 10 days and

30 days to confirm no exceedances continue to occur. If an exceedance cannot be corrected with a 

repair or adjustment, the gas collection and control system (GCCS) must be expanded. 

2.0 Summary of Available Data 

The EPA received a report that compares the current NSPS SEM approach to the CA LMR approach, 

hereinafter referred to as the 2014 Surface Monitoring Report.

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The 2014 Surface Monitoring Report 

focuses on overall number of exceedances per acre (expressed as a percentage), comparing surface 

monitoring results under the CA LMR to the MSW Landfills NSPS or Emission Guidelines. The report does 

 

1

 SCS Engineers. A Comparison of Monitoring Results for California Landfills Under the New Source Performance 

Standards and the California Landfill Methane Rule. October 2014. See Appendix A of this memo for a copy of the 

report.
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not provide data to determine the magnitude of emission reductions that might result from the greater 

exceedances. 

Because the 2014 Surface Monitoring Report focuses on overall exceedances across a pool of landfills, 

the EPA requested background data used to develop the summary analysis in the report. Waste 

Management provided the background data to EPA in February 2015, hereinafter referred to Supporting 

Data Tables for 2014 SEM Report, and the data are included in Appendix B to this memorandum. These 

data were analyzed, as discussed below to determine whether enhanced SEM under the CA LMR 

identified more landfills with exceedances compared to the NSPS SEM. Although compliance monitoring 

reports of both the current and enhanced approaches were available to compare for certain landfills, 

the reports represent different time periods.2 

3.0 Findings and Analysis 

The conclusions of the 2014 Surface Monitoring Report rely largely on a low percentage of overall 

exceedances across a group of landfills, with emphasis on the even smaller percentage of exceedances 

resulting in gas collection and control system (GCCS) expansion after 120 days, to support why the EPA

should not adopt a tighter surface emissions monitoring (SEM) program. 

This section summarizes the analysis of three components of the enhanced SEM in the CA LMR 

compared to the SEM requirements in the current NSPS on a landfill-by-landfill basis as compared to an

aggregate basis of a group of landfills. The spreadsheets used to generate these summaries are available 

in Appendix C of this report. 

3.1 Impact of a Tighter Traverse Pattern (98-foot vs. 25-foot) 

The 2014 Surface Monitoring Report indicates 1.6% exceedances under the current approach (based on 

212 reports and 27,140 acres monitored) and 4.4% exceedances under the enhanced approach (from 

357 reports with 44,607 acres monitored). The report indicates 42 landfills were subject to the NSPS 

SEM monitoring requirements. 

The Supporting Data Tables for 2014 SEM Report show 29 of the 42 NSPS landfills had monitoring 

reports based on both the current and the CA LMR approach. Data indicate over 60% of these landfills 

show exceedances only under the CA approach or greater exceedances with the CA approach. 

Specifically: 

• Seven landfills show exceedances only under the CA approach3; 

• 10 show greater exceedances under CA approach; 

• Four show lower exceedances under the CA approach; and 

• Eight show no exceedances under either approach. 

Further, for those landfills with greater exceedances under the CA LMR, exceedances were on average 

180% more frequent, as shown in Table 1. While the data do provide evidence of greater exceedances, 

we were not able to determine the magnitude of emission reductions that might result from the CA LMR 

approach. 

 

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 Current approach based on reports covering 8 quarters (3rd quarter 2009 through mid-2011); Enhanced 

approach based on reports 10 quarters (mid-2011 through end of 2013). 

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 All of these landfills are located in arid areas (25 inches or less of annual rainfall). All of these landfills have a 

waste-in-place amount over 2.5 million tons. 
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Table 1. Average Traverse Exceedances per Report, by Report Type 

Landfill ID 

Average # of 

Exceedances 

per NSPS 

Report* 

Average # of 

Exceedances 

per LMR 

Report * 

Exceedance 

% Diff** 

Landfill 39 14.7 5.6 -62% 

Landfill 50 14.5 32.5 124%

Landfill 19 4.0 20.3 408%

Landfill 30 8.8 5.6 -36% 

Landfill 66 8.3 28.9 247%

Landfill 02 5.3 6.9 29% 

Landfill 57 7.5 10.1 35% 

Landfill 24 2.7 17.6 558%

Landfill 47 2.3 6.1 163%

Landfill 43 4.0 7.0 75% 

Landfill 69 1.5 1.2 -20% 

Landfill 04 2.0 1.8 -13% 

Landfill 37 2.0 5.0 150%

Landfill 60 1.0 1.3 25% 

* For monitoring reports with >0 exceedances. 

** Negatives indicate more exceedances per report for NSPS than LMR. 

Notes: 

• Exceedances from surface penetrations were extracted from the total exceedances in order to 

get the number of exceedances attributed to the traverse pattern alone.

• Bold text shows landfills having more than double the average number of exceedances per 

report for LMR when compared to NSPS. 

The environmental benefits of locating additional exceedances under a tighter traverse pattern could 

not be quantified based on available data. The 2014 Surface Monitoring Report identified 0.3% of the 

total acres monitored required GCCS expansions. However, it is noted that since all leaks require 

corrective action, even if a GCCS is not required to be expanded, a landfill owner/operator’s response to 

a surface leak would be a combination of: 1) surface repairs (specialized clay to seal cracks or bases of 

wells) and/or 2) adjustments to GCCS, for example increasing the vacuum to pull more gas through the 

GCCS or repairing a blockage in the GCCS to avoid leaks to the surface. Both of these corrective actions 

will result in an environmental benefit, even if the GCCS does not have to be expanded. 

3.2 Effect of Adding an Integrated Reading to Exceedance Criteria (at or above 25 ppmv) 

The Supporting Data Tables for the 2014 Surface Monitoring Report indicate that 703 out of 32,946 grids 

monitored at NSPS landfills (2.1% of grids) had an exceedance of the 25 ppmv limit. 
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• 201 of the 703 grids (28.6%) also had an exceedance of the 500 ppmv instantaneous criteria, 

indicating significant overlap in how the instantaneous and integrated readings identify 

locations with surface emission leaks. 

Of the 29 landfills that monitored under both the current and the CA approach, the data indicate: 

• One landfill shows an exceedance of only the integrated reading 

• Three landfills show no exceedances under current NSPS approach, but show exceedances 

under both the integrated reading and the instantaneous reading under the CA approach 

• Seven landfills show exceedances under both the integrated reading and instantaneous readings 

under both the current NSPS and CA approaches.4

These findings suggest that adding an integrated reading to exceedance criteria (at or above 25 ppmv) 

identified minimal additional exceedances.

3.3 Effect of Wind Speed Limitations During SEM 

Because the CA approach restricts monitoring to occur below specified wind speeds, landfills may 

request approval for alternatives to these restrictions when winds in excess of the specified limits are 

consistently being measured at the surface of the landfill. 

• 2014 Surface Monitoring Report indicates 72.6% of the landfills evaluated required a permanent 

alternative for wind speed due to conditions at the site. 

• Of the 29 landfills that monitored both the current and the CA approach, 76% of the landfills 

(22/29) required an alternative approach for wind speed under the CA approach. 

These findings suggest that a large majority of landfills could not consistently find monitoring periods 

that met the wind speed restrictions in the CA LMR rule. 

 

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 All but one of these seven landfills are located in arid areas (25 inches or less of annual rainfall).