A Comparison of Monitoring Results

For California Landfills under the

New Source Performance Standards

and the California Landfill Methane Rule

Prepared by:

S C S E N G I N E E R S

3900 Kilroy Airport Way, Suite 100

Long Beach, California

(562) 426-9544

October 2014

Offices Nationwide

www.scsengineers.com
N S P S a n d C A L M R C o m p a r a t i v e D a t a

A Comparison of Monitoring Results

for California Landfills under the

New Source Performance Standards

and the California Landfill Methane Rule

Prepared by:

S C S E N G I N E E R S

3900 Kilroy Airport Way, Suite 100

Long Beach, California

(562) 426-9544

October 2014
N S P S a n d C A L M R C o m p a r a t i v e D a t a

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T a b l e o f C o n t e n t s

Section Page

1.0 INTRODUCTION & PURPOSE.............................................................................................................. 1

2.0 BACKGROUND ...................................................................................................................................... 1

2.1 NSPS Monitoring Requirements.................................................................................................1

2.2 California Landfill Methane Rule Monitoring Requirements ................................................2

2.2.1 Instantaneous SEM..................................................................................................2

2.2.2 Integrated SEM.......................................................................................................3

2.3 Side-By-Side Comparison of Monitoring Requirements .......................................................4

3.0 SUMMARY OF THE DATA SET USED FOR COMPARATIVE ANALYSIS......................................... 6

4.0 RESULTS................................................................................................................................................... 7

4.1 NSPS Results Prior to Implementing CA LMR ..........................................................................7

4.2 CA LMR Results for NSPS and LMR-Only Sites.......................................................................8

4.2.1 Instantaneous SEM Results.....................................................................................8

4.2.2 Integrated SEM Results..........................................................................................9

4.3 CA LMR Results for NSPS Sites Only.....................................................................................10

4.3.1 Instantaneous SEM Results for NSPS sites.......................................................10

4.3.2 Integrated SEM Results......................................................................................11

4.4 CA LMR Results for LMR-Only Sites.......................................................................................12

4.4.1 Instantaneous SEM Results..................................................................................12

4.4.2 Integrated SEM Results.......................................................................................12

5.0 COMPARATIVE COST OF NSPS AND LMR MONITORING.........................................................13

6.0 CONCLUSIONS....................................................................................................................................14

6.1 NSPS Landfills Subject to CA LMR.........................................................................................14

6.1.1 Instantaneous SEM...............................................................................................14

 Surface Traverse.................................................................................................14

 Cover Penetrations.............................................................................................15

 Exceedances Requiring GCCS Expansion ......................................................15

6.1.2 Integrated SEM....................................................................................................16

6.2 New Landfills Subject to CA LMR...........................................................................................17
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L i s t o f T a b l e s

No.

1 Comparison of NSPS and CA LMR Monitoring Requirements

2 Landfills Categorized by Applicable Regulation

3 Landfills Categorized by Climate Type

4 Landfills Categorized by Operational Status

5 Landfills Categorized by Type of Ownership

6 Landfills Categorized by Waste-In-Place

7 NSPS Instantaneous SEM Results

8 CA LMR Instantaneous SEM Results

9 CA LMR Integrated SEM Results

10 CA LMR SEM Results for the 42 NSPS sites

11 CA LMR SEM Results for the 30 LMR-only Sites

12 Comparison of Instantaneous SEM Results under NSPS and CA LMR Requirements 
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1.0 INTRODUCTION & PURPOSE

SCS Engineers (SCS) conducted a comparative analysis of the results of Surface Emissions 

Monitoring (SEM) conducted to comply with the requirements of the California Landfill 

Methane Rule (CA LMR) under §95460 to 95476 of Title 17, California Code of Regulations 

(CCR), and the federal monitoring requirements in 40 Code of Federal Regulations (CFR) Part 

60, Subpart WWW (“New Source Performance Standards” or “NSPS”) for municipal solid waste 

(MSW) landfills. This paper reviews data from California landfills that have implemented the 

requirements of NSPS, LMR or both regulations, and summarizes the monitoring results and 

level of effort required for their implementation. 

2.0 BACKGROUND

2.1 NS P S MONI T OR I N G R EQ U I R EM EN TS

The NSPS requires Instantaneous Surface Emissions Monitoring (Instantaneous SEM) on a 

quarterly basis to ensure that the landfill gas (LFG) collection and control system is operating 

properly and that the methane concentration is less than 500 parts per million (ppmv) above 

background at the surface of the landfill. On a quarterly basis, the regulation requires the landfill 

owner or operator to monitor surface concentrations of methane along the entire perimeter of the 

collection area, along a pattern that traverses the landfill at 30 meter (98 foot) spacing intervals 

between the walking paths for each LFG collection area. Additionally, the landfill owner must 

monitor penetrations of the landfill cover where visual observations indicate elevated 

concentrations of LFG, such as distressed vegetation, cracks, or seeps in the cover. The SEM 

monitoring equipment (FID meter) is designed to continuously read methane concentrations and 

record readings at or above 500 ppmv as monitoring personnel traverse the path throughout the 

collection area. Instantaneous SEM is only required for landfill areas required to have gas 

collection and control under the NSPS. The owner or operator may establish an alternative 

traversing pattern that ensures equivalent coverage. Each landfill must develop a surface 

monitoring design plan that includes a topographical map marked with the monitoring route and 

provide an explanation for any site-specific deviations from the 30-meter intervals. Areas with 

steep slopes or other dangerous areas (e.g., where heavy equipment is operating) may be 

excluded from the surface testing to protect personnel safety.

Any reading of 500 ppmv or more at a location is recorded as an exceedance. Typically, cover 

maintenance or adjustments to the collection system are undertaken to remediate the exceedance, 

and the location re-monitored within 10 calendar days of the initial measurement. If remonitoring shows a second exceedance, additional corrective action is undertaken, and the 

location is monitored again within 10 days of the second measurement. If re-monitoring shows a 

third exceedance for the same location in the same quarter, a new well or other collection device 

must be installed within 120 calendar days of the initial exceedance. The United States 

Environmental Protection Agency (EPA), or its delegated state agency, may also approve an 

alternative timeline for remediation or an alternative remedy, such as upgrading the blower, 

header pipes or control device, after receiving a request for approval. Locations that initially 

show an exceedance, but have measured methane concentrations of less than 500 ppmv methane 
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at the first or second 10-day re-monitoring event must be re-monitored one month after the initial 

exceedance was detected to ensure the remedy was successful.

A closed or inactive MSW landfill that has no exceedances after four consecutive monitoring 

periods may be monitored annually. If an exceedance is detected during an annual event, the 

landfill must return to quarterly monitoring. 

The results of the quarterly (or annual) Instantaneous SEM events are reported to the EPA 

Administrator on a semi-annual basis.

2.2 C A LI FOR NI A LA N D F I L L M E TH A NE R U L E MO NI TOR I NG 

R EQ U I R EM EN TS

The CA LMR monitoring approach is similar to the NSPS in many respects, but has additional 

requirements. As discussed below, the Instantaneous SEM monitoring requires the technician to 

follow a tighter, more prescriptive walking pattern. The CA LMR also requires Integrated 

Surface Emissions Monitoring (Integrated SEM), which is not required under the NSPS. 

2 . 2 . 1 I n s t a n t a n e o u s S E M

As with the NSPS, the CA LMR requires sites to conduct Instantaneous SEM of the entire 

landfill surface on a quarterly basis. This requirement, as well as several other requirements of 

the CA LMR, are more stringent, however. The CA LMR requires each landfill owner/operator 

to divide the entire landfill surface, regardless of age of waste, into 50,000 square foot grids

(slightly larger than one acre) and establish a walking pattern that traverses each grid with no 

more than a 25-foot (7.6 meter) spacing interval between the walking paths. As with the NSPS 

monitoring regime, the handheld monitoring device continuously reads methane concentrations 

and, for the CA LMR, records readings at 200 ppmv and above. Moreover, all cover 

penetrations of the landfill surface must be monitored, whether or not they exhibit indications of 

elevated concentrations of LFG. Also, surface testing cannot be performed when the average 

wind speed exceeds five miles per hour (mph), the instantaneous wind speed exceeds 10 mph, or

if there has been measurable precipitation in the preceding 72 hours. In these situations, 

monitoring must be delayed, unless the owner or operator requests and receives approval from 

the California Air Resources Board (CARB) (or delegated air district) for an alternative 

approach. Any reading greater than 500 ppmv methane is considered an exceedance and must be 

recorded. In addition, Instantaneous SEM readings between 200 and 500 ppmv, while not 

considered exceedances, must also be recorded. The location of each exceedance must be 

recorded and marked on a map, and the following data reported:

 Location (or affected grid)

 Concentration in ppmv

 Date and time of measurement

 Corrective action taken to repair the exceedance

 Date of repair

 Results of any required re-monitoring

 Wind speed during surface sampling
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Similar to the NSPS, if an exceedance is detected, the owner/operator must undertake corrective 

action (e.g., cover maintenance/repair or well vacuum adjustments), and the location must be remonitored within 10 calendar days of the initial measurement. If re-monitoring shows an 

exceedance, additional corrective action must be taken, and the location must be re-monitored no 

later than 10 calendar days after the second measurement. If re-monitoring shows a third 

exceedance within the same quarter, a new or replacement well must be installed and compliance 

with the 500 ppmv limit achieved within 120 calendar days. However unlike the NSPS, there is 

no requirement for monthly follow-up monitoring once an exceedance has been corrected.

Closed or inactive MSW landfills, as well as closed or inactive areas on an active MSW landfill, 

that have no exceedances after four consecutive monitoring periods may transition to annual 

monitoring. However, any exceedances during annual monitoring that cannot be remediated 

within 10 calendar days must return to quarterly monitoring. 

The results of the quarterly (or annual) monitoring events are reported to the Executive Officer 

for CARB (or delegated air district) on an annual basis.

2 . 2 . 2 I n t e g r a t e d S E M

Under the CA LMR, Integrated SEM is required in addition to Instantaneous SEM. Under 

Integrated SEM, all methane readings within each 50,000 square foot grid are averaged. An 

averaged reading of 25 ppmv or greater within a grid is considered an exceedance and must be 

remediated. The same grids used to conduct Instantaneous SEM are used for Integrated SEM,

and the walking pattern must be no more than a 25-foot spacing (7.6 meter) interval within each 

grid. As with the Instantaneous SEM, wind and precipitation limitations apply, and the 

owner/operator must record the location of the grid on a map.

If an Integrated SEM exceedance is recorded for a grid, corrective action must be taken (e.g., 

cover maintenance or repair, or well vacuum adjustments), and the grid must be re-monitored 

within 10 calendar days of the initial measurement. If re-monitoring shows a second 

exceedance, additional corrective action must be taken, and the grid must be re-monitored again 

no later than 10 calendar days after the second measurement. If the re-monitoring shows a third 

exceedance, a new or replacement well must be installed and compliance with the integrated 

limit achieved within 120 calendar days of the third measurement.

The owner or operator must report the following information for any Integrated SEM 

exceedance:

 The affected grid

 Average concentration in ppmv

 Date and time of measurement

 Corrective action taken to remediate the exceedance

 Date of the corrective action

 Results of any required re-monitoring

 Wind speed during re-monitoring

Any closed or inactive MSW landfill, as well as any closed or inactive areas on an active MSW 

landfill, that has no exceedances after four consecutive monitoring periods may monitor 
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annually. Any exceedances during the annual monitoring that cannot be remediated within 10 

calendar days will result in a return to quarterly monitoring.

The results of the quarterly (or annual) monitoring events are reported to the Executive Officer 

of CARB (or delegated air district) on an annual basis. 

Sites that do not have any exceedances under both Instantaneous or Integrated SEM for four 

consecutive quarters can increase the grid walking pattern spacing to a 100-foot interval. 

However, similar to the trigger for lower frequency of monitoring, any exceedance that cannot be 

corrected within 10 days will result in a return to 25-foot spacing.

2.3 S I D E - B Y - S I D E C O MP A R I S O N O F M O NI TOR I N G 

R EQ U I R EM EN TS

Table 1 below compares key elements of the NSPS and CA LMR SEM requirements. 
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Table 1. Comparison of NSPS and CA LMR Monitoring Requirements

SEM Requirement NSPS CA LMR

Instantaneous SEM

Area of landfill 

subject to 

Instantaneous SEM

Areas where LFG collection system 

is required to be installed

Entire landfill surface, except 

working face

Path Requirements 98-foot spacing (30 meters) 25-foot spacing (7.6 meters)

Data Recorded Any reading 500 ppmv methane or 

greater above background

Any reading 200 ppmv or greater 

above background

Exceedance 

Threshold Any methane reading ≥ 500 ppmv

Any methane reading >500

ppmv*

Exceedance

Corrective Action 

Requirements

Following exceedance detection, 

perform correction action and remonitor within 10 days; if a second 

exceedance is detected, perform 

additional corrective action and remonitor within 10 days of the 2nd

event; if a 3rd exceedance is detected, 

expand the GCCS or implement an 

approved alternative remedy

Same as NSPS

Integrated SEM N/A

Collect methane readings 

continuously within 50,000 

square-foot grids. Average of 

readings within a grid ≥25 ppmv 

trigger corrective action. 

Cover Penetration 

Monitoring

Monitor penetrations quarterly where 

visual observation indicates elevated 

concentrations of landfill gas (i.e., 

distressed vegetation) 

Monitor all penetrations 

quarterly

Weather Conditions 

(wind, precipitation)

Perform during typical 

meteorological conditions

Wind: Cease SEM if average 

wind speed exceeds 5 mph or 

instantaneous exceeds 10 mph.

Precipitation: Cease SEM if any 

measurable precipitation within 

last 72 hours. 

*Due to similarities in thresholds, some air districts have been enforcing the CA LMR >500 ppmv threshold using 

the NSPS ≥500 ppmv threshold.
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3.0 SUMMARY OF THE DATA SET USED FOR 

COMPARATIVE ANALYSIS

SCS analyzed data from 72 California landfills regulated under the CA LMR, which took effect 

in mid-2011. Because CA LMR requirements are more stringent than the NSPS, after mid2011, the NSPS landfills in the dataset implemented LMR requirements and reported the relevant 

data to the State of California and EPA, as appropriate. SCS obtained the aggregate NSPS 

monitoring results through review of quarterly monitoring reports developed from up to two 

years (8 quarters) prior to implementation of the CA LMR (3

rd quarter 2009 through mid-2011). 

The CA LMR dataset was compiled from monitoring reports beginning with the date of 

implementation (mid-2011) through the end of 2013. Thus, aggregate CA LMR monitoring 

results from NSPS sites and CA LMR only sites (i.e.., sites never subject to the NSPS) were 

obtained from quarterly monitoring reports developed during from July 2011 through December 

2013. 

Table 2 through Table 6 provide additional descriptive information on the landfills in the dataset.

Table 2. Landfills Categorized by Applicable Regulation

No. of Landfills

NSPS & CA LMR CA LMR Only

42 30

Table 3. Landfills Categorized by Climate Type

No. of Landfills

Arid*

(< 25 inches 

precipitation/year)

Non-Arid* 

(>25 inches 

precipitation/year)

60 12

 *Definition of “arid” taken from CA LMR and 40 CFR Part 98

Table 4. Landfills Categorized by Operational Status 

No. of Landfills

Closed Active

27 45

Table 5. Landfills Categorized by Type of Ownership

No. of Landfills

Public Private

41 31

Table 6. Landfills Categorized by Waste-In-Place

No. of Landfills

0-450,000 tons 450,000-2.5 million 

tons >2.5 million tons

0 26 46
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Each quarter of available monitoring data was assessed individually. The data were then 

aggregated to develop summary statistics. SCS collected and compiled the following data for 

each landfill, as available:

 Report type (NSPS/CA LMR), area (acreage/grids) monitored, total number of 

penetrations monitored;

 Number of Instantaneous SEM exceedances identified following the NSPS and/or the CA 

LMR monitoring requirements;

 Number of Instantaneous SEM exceedances from penetrations following the NSPS and 

CA LMR requirements;

 Number of Instantaneous SEM exceedances triggering the 120-day period for expansion 

of the GCCS, or an approved alternative remedy;

 Number of Integrated SEM exceedances (grids with average methane readings > 25 

ppmv) for the landfills regulated under the CA LMR;

 Number of Integrated SEM exceedances triggering the 120-day period for expansion of 

the GCCS or an approved alternative remedy; and

 Comparison of the locations of Instantaneous versus Integrated SEM exceedances.

4.0 RESULTS

This section summarizes the results of the assessment of monitoring conducted under the NSPS 

and CA LMR rules. The discussion is presented in four parts: (1) NSPS monitoring results for 

42 landfills prior to implementation of the CA LMR; (2) CA LMR monitoring results for 72 

landfills, including both the 42 NSPS landfills, and 30 “LMR-only” landfills; (3) comparative 

NSPS and CA LMR monitoring results for the 42 NSPS landfills; (4) CA LMR monitoring 

results for the “LMR-only” landfills. 

4.1 NS P S R ES U L TS P R I OR TO I MP L EM E N TI N G C A L MR

SCS reviewed 212 reports of monitoring conducted using the NSPS regime at 42 California 

landfills subject to the NSPS requirements. A total of 1,147 exceedances (instantaneous SEM 

readings of 500 ppmv methane or greater) were recorded. Of the total, 446 (38.9%) were 

detected by traversing the specified serpentine path, and the remaining 701 (61.1%) were 

detected at penetrations in the landfill surface with visible indicators of elevated concentrations 

of LFG (e.g., distressed vegetation, or cracks or seeps in cover). 

 Exceedances detected traversing the prescribed path: A total of 27,140 acres were 

monitored. Exceedances were detected at 1.6% of the acres monitored. 

 Exceedances detected at targeted penetrations: A total of 26,231 penetrations were 

monitored following the NSPS requirement to target penetrations with visible signs of 

elevated LFG concentrations. Exceedances were detected at 2.7% of the penetrations 

monitored. 

 Exceedances triggering 120-Day GCCS Expansion: Only 1.2% of all exceedances

were unable to be remedied by simple cover repair or collection system adjustments

within the first 20 days, thus triggering the 120-day GCCS expansion requirement. All 
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of these exceedances occurred at one landfill. None of the remaining 41 NSPS landfills 

in the dataset triggered GCCS expansion as a result of instantaneous SEM exceedances. 

Table 7 provides a summary of the NSPS instantaneous SEM results. 

Table 7. NSPS Instantaneous SEM Monitoring Results

Traversing the Prescribed Path (500 ppmv threshold)

NSPS

Landfills

Exceedances as a percentage of acres monitored 1.6%

Targeted Penetration Monitoring

Exceedances as a percentage of penetrations monitored 2.7%

Total

Percentage of exceedances which resulted in GCCS expansion 1.2%

4.2 C A LMR R ES U LTS FOR NS P S A ND LMR -O NLY S I TE S

4 . 2 . 1 I n s t a n t a n e o u s S E M R e s u l t s

SCS reviewed 521 monitoring reports for 72 California landfills subject to the CA LMR, 

including the 42 NSPS described previously. As the rule requires, each landfill was divided into 

50,000-square-foot grids, for a total of 49,790 grids (equivalent to 57,151 acres) subject to 

Instantaneous SEM monitoring across the 72 sites.

1

 The monitoring reports identified a total of 

3,211 recorded exceedances (e.g., methane readings higher than 500 ppmv). Of these, 2,141

exceedances (66.7%) were detected by traversing the specified serpentine path, and the

remaining 1,070 (33.3%) occurred at penetrations in the landfill surface. 

 Exceedances Detected Traversing the Prescribed Path: Of the 57, 151 acres 

monitored, exceedances were detected at 3.7% of the acres monitored.

 Exceedances Detected at Penetrations: A total of 70,529 penetrations were monitored 

at the landfills in the dataset, following the requirements of the CA LMR to monitor 

every penetration during every monitoring event. Exceedances were detected at 1.5% of 

all penetrations monitored. 

 Exceedances Triggering GCCS Expansion: Under the CA LMR, 4.7 % of all 

exceedances triggered the 120-day requirement for GCCS expansion. These exceedances 

occurred at five of the 72 landfills in the dataset, two of which obtained an approved 

alternative remedy other than expanding the GCCS. The remaining three landfills were 

required to undertake a GCCS expansion. It should be noted that the two sites with the 

alternative remedies each had only one exceedance. Sixty-seven (67) of the sites in the 

dataset did not trigger GCCS expansion as a result of Instantaneous SEM exceedances. 

 

1

For comparative purposes, CA LMR monitoring grids have been converted to acres in order to normalize for 

comparison to NSPS. Each 50,000-square-foot-grid is equivalent to 1.148 acres.
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 Requests for Monitoring Variances: The CA LMR includes specific wind and 

precipitation limits for conducting SEM monitoring. Review of the data set indicates that 

these requirements can be difficult to meet. Of the 72 sites evaluated, 53 (or 72.6%) 

required a permanent alternative for wind speed due to conditions at the site. 

Table 8 summarizes the Instantaneous SEM monitoring results under CA LMR.

Table 8. CA LMR Instantaneous SEM Monitoring Results

Traversing the Prescribed Path (500 ppmv threshold)

LMR

Landfills

Exceedances as a percentage of acres monitored 3.7%

Penetration Monitoring

Exceedances as a percentage of penetrations monitored 1.5%

Total

Percentage of exceedances which resulted in GCCS expansion 4.7%

4 . 2 . 2 I n t e g r a t e d S E M R e s u l t s

The monitoring reports reviewed by SCS also provided the results of the Integrated SEM for the 

72 sites. As with Instantaneous SEM, each landfill was divided into 50,000-square-foot grids,

for a total of 41,363 grids subject to Integrated SEM monitoring (equivalent to 47,479 acres).

2

Integrated SEM exceedances (e.g., an integrated grid reading greater than 25 ppmv methane)

were detected in 1.8% of the grids (or 1.5% of the acres monitored).

Only 0.5% of all grids monitored had exceedances which triggered the 120-day requirement to 

expand the GCCS. These exceedances occurred at six of the 72 landfills in the dataset, one of 

which obtained an approved alternative remedy other than expanding the GCCS. The remaining 

five landfills, representing 0.4% of the grids, were required to undertake a GCCS expansion. 

Sixty-six (66) sites in the dataset did not trigger GCCS expansion as a result of Integrated SEM 

exceedances. 

Three of the five landfills (60%) that triggered GCCS expansion due to Integrated SEM results 

also triggered GCCS expansion due to Instantaneous SEM results. 

Table 9 provides a summary of the Integrated SEM results.

 

2 The number of Integrated grids monitored is different than the number of instantaneous grids monitored due to 

allowance under CA LMR for a reduction of monitoring frequency.
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Table 9. CA LMR Integrated SEM Results

Monitoring Grids (>25 ppmv threshold)

LMR

Landfills

Exceedances detected as a percentage of grids monitored (>25 

ppmv) 1.8%

Percentage of exceedances per grids monitored triggering 120-day 

expansion 0.5%

Percentage of exceedances per grid monitored which resulted in 

GCCS expansion 0.4%

4.3 C A LMR R ES U LTS FOR NS P S S I TE S O NLY

This section describes the CA LMR monitoring results for the 42 landfills previously 

implementing the NSPS monitoring regime. Focusing only on the NSPS landfills in this section 

enables us to highlight differences in the two monitoring regimes (NSPS vs. LMR) as applied to 

the same landfills. This “apples to apples” comparison provides more conservative results than 

including landfills never subject to the NSPS and only newly subject to any monitoring regime. 

Comparing the results of the 42 NSPS landfills to the entire data set would result in even smaller

percentage exceedances in all aspects, thus further decreasing cost-effectiveness. 

4 . 3 . 1 I n s t a n t a n e o u s S E M R e s u l t s f o r N S P S s i t e s

NSPS sites represented 58% of the landfills in the dataset, 68% of the monitoring reports, 78% of 

the acres monitored, and over 90% of the instantaneous exceedances detected. 

Exceedances Detected Walking the Prescribed Path

The tighter walking pattern of the CA LMR monitoring regime resulted in detection of more 

exceedances while traversing the monitoring path. NSPS monitoring reports for the “before 

LMR” period documented exceedances at 1.6% of the acres monitored, while the “after LMR” 

results of the same NSPS landfills recorded exceedances at 4.4% of the acres monitored. 

However, the analysis also found that the vast majority of identified exceedances were easily 

remedied with repairs to cover materials and did not require installation or expansion of GCCS. 

Under both the NSPS and the CA LMR, the requirement and timing to expand the GCCS system 

(or obtain approval for an alternative remedy) is the same. In the two years “before LMR,” one 

landfill triggered the 120-day expansion requirement and subsequently expanded its GCCS. In

30 months of CA LMR monitoring at these same NSPS landfills, five landfills triggered the 120-

day expansion, although only three of them were required to expand the GCCS. The 

exceedances that resulted in GCCS expansions at the three landfills represent 0.3% of the total 

acres monitored.

The analysis does not indicate whether these exceedances would have also been identified under 

the NSPS procedures, or whether the CA LMR regime was solely responsible for their 

identification. Furthermore, we do not know if the fundamental decision to expand the GCCS 

was driven by the CA LMR, or whether the GCCS expansions were planned or required by 

NSPS timelines. While CARB promulgated the rule believing that it would result in more 

frequent and earlier LFG collection system installations and expansions, the analysis does not 
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support this conclusion. Even with a much more intensive (and costly) walking pattern, only 

two additional NSPS landfills were required to expand their GCCS under the CA LMR.

Exceedances Detected by Penetration Monitoring

NSPS landfills implementing the Federal NSPS monitoring regime monitored penetrations using 

the standard industry practice of sampling penetrations with visual or other signs indicative of 

elevated concentrations of LFG. The LMR, by contrast, explicitly requires monitoring of every 

penetration to the landfill cover.

Following the NSPS approach, NSPS landfills monitored 26,231 penetrations and detected 

exceedances at 2.7% of penetrations monitored. Under the LMR, the number of penetrations 

monitored increased by 84%, but the percentage of exceedances detected declined to 2.0%. This 

result occurred because exceedances were only detected at 1.1% of the additional penetrations 

monitored . Thus, it appears that the effort expended to monitor every penetration at a landfill is

less effective in finding exceedances than the more targeted NSPS approach of monitoring 

penetrations when there is an indication of an actual problem. 

4 . 3 . 2 I n t e g r a t e d S E M R e s u l t s

Because the current NSPS/EG does not require integrated monitoring, it is not possible to 

conduct a before- and after-LMR implementation comparison. However, available data for the 

42 NSPS sites indicate that integrated exceedances were detected in 2.1% of the grids monitored, 

and GCCS expansion was required for 0.5% of grids monitored. In all, six landfills triggered 

the 120-day expansion requirement, and five of these landfills expanded. Three of these five 

landfills had previously been identified through instantaneous monitoring, which implies that the 

incremental benefit of integrated monitoring may have been the identified need for GCCS 

expansion at two additional landfills. We could not determine from the reports reviewed 

whether the fundamental reason for expansion was solely the CA LMR integrated monitoring 

results, or whether the landfills already planned for GCCS expansions.

Table 10 presents a summary of the results for the 42 NSPS sites subject to CA LMR.
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Table 10. CA LMR SEM Results for 42 NSPS sites

Instantaneous exceedances detected via surface traverse per CA 

LMR requirements, as a percentage of acres monitored 4.4%

Exceedances detected via surface traverse which resulted in GCCS 

expansion, as a percentage of acres monitored 0.3%

Exceedances detected at penetrations monitored per CA LMR

requirements, as a percentage of penetrations monitored 2.0%

Percentage increase in number of penetrations monitored under 

the LMR 84%

Percentage of exceedances detected at the additional 

penetrations monitored under the LMR3 1.1%

Integrated Exceedances detected as a percentage of grids

monitored (>25 ppmv) 2.1%

Percentage of integrated exceedances per grids monitored which 

resulted in GCCS expansion 0.5%

4.4 C A LMR R ES U LTS FOR L MR -O N LY S I T ES

Thirty landfills in the dataset subject to the CA LMR are exempt from the NSPS or EG due to 

their age, design capacity and/or NMOC emissions potential. This section evaluates the results 

of monitoring these “LMR-only” landfills.

4 . 4 . 1 I n s t a n t a n e o u s S E M R e s u l t s

Under the CA LMR, all regulated landfills must follow the requirements for instantaneous and 

integrated surface emissions monitoring. Our review of the instantaneous monitoring results for 

“LMR-only” landfills found that these 30 landfills (42% of the landfills in the dataset), were 

responsible for less than 10% of the exceedances recorded. Approximately 59% of exceedances 

were detected via traversing the monitoring path, and the remaining 41% were detected through 

penetration monitoring. Exceedances were detected via surface traverse in 1.4% of the acres 

monitored, and at 0.6% of the penetrations monitored. 

All of these exceedances were remediated within 20 days with cover repair and/or GCCS 

adjustments. Over the first 30 months of CA LMR implementation, not a single LMR-only 

(non-NSPS) landfill in the dataset had an exceedance that triggered the LMR requirement to 

expand the GCCS. This result is particularly significant because it is the GCCS expansions that 

are primarily responsible for the methane and NMOC reductions associated with this rule. 

4 . 4 . 2 I n t e g r a t e d S E M R e s u l t s

The integrated monitoring results for the 30 landfills in the dataset found that there were no 

exceedances (>25 ppmv) detected in any grid during the first 30-months of LMR 

 

3 Calculated as the incremental increase in exceedances between the NSPS and CA LMR monitoring (for NSPS 

landfills) divided by the incremental difference in the number of penetrations monitored under both cases.
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implementation. As a result, none of these landfills was required to expand its GCCS due to 

integrated monitoring results. 

Table 11 presents a summary of the results for the 30 non-NSPS sites subject to CA LMR. 

Table 11. CA LMR SEM Results for 30 LMR-Only Sites

Instantaneous exceedances detected via surface traverse as a 

percentage of acres monitored 1.4%

Percentage of instantaneous exceedances detected via surface 

traverse which resulted in GCCS expansion 0%

Instantaneous exceedances detected as a percentage of 

penetrations monitored 0.6%

Integrated Exceedances detected as a percentage of grids

monitored (>25 ppmv) 0%

Percentage of integrated exceedances per grids monitored which 

resulted in GCCS expansion 0%

5.0 COMPARATIVE COST OF NSPS AND LMR 

MONITORING

While both the CA LMR and the NSPS require personnel to travel to regulated landfill sites and 

walk the surface of the landfill, there are important differences in the requirements and burden of 

the two approaches. The CA LMR monitoring path has much tighter spacing intervals than the 

NSPS (7.6 vs. 30 meters, or 25 vs. 98 feet), which translates directly into more personnel time 

required in the field and higher implementation costs. In addition, the CA LMR requires 

monitoring of every cover penetration on the landfill, whereas the NSPS requires monitoring 

where there is evidence of a potential surface emission issue. Finally, the CA LMR requires 

Integrated SEM monitoring in addition to instantaneous monitoring, which results in additional 

time and costs, even when performed along with the Instantaneous SEM monitoring.

Instantaneous Monitoring: Conducting instantaneous SEM under the CA LMR is significantly 

more labor-intensive and costly than the monitoring required under the NSPS. Available cost 

data indicate that monitoring at a 25-foot interval and within defined grids greatly increases staff 

hours required to complete the work. This additional cost is driven primarily by the tighter 

walking pattern, which takes proportionately more time to complete. In many cases, the LMR 

requirement to work within a grid creates additional inefficiencies. Overall, this review indicates 

that the time required to perform the CA LMR monitoring is 4 to 5 times greater than that for the 

NSPS, reflecting the need for 4 times more walking due to the spacing decrease and the

additional inefficiencies resulting from the use of grids. This labor time does not include 

compilation and review of the monitoring data, mobilization to/from the site or delay in 

monitoring due to meterological conditions. It also does not include labor time associated with 

cover repair and re-monitoring. 

Penetration Monitoring: The CA LMR requirement to monitor all cover penetrations increases

labor time because walking to and monitoring additional penetrations takes time. The 
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comparison of NSPS and CA LMR requirements for 42 NSPS landfills (described in section 

4.3.2) found the CA LMR requirement to monitor every penetration resulted in an 84% increase 

in the number of penetrations monitored. Because labor costs are the primary driver of 

penetration monitoring costs, this finding implies that the costs of penetration monitoring 

increased by a similar percentage. 

Integrated Monitoring: The Integrated SEM requirements under the CA LMR are estimated to 

increase field time by 25% to 75%, depending on whether the landfill does separate or combined

Instantaneous and Integrated SEM, and the methodology used to develop the integrated 

emissions estimate. Landfills that conduct Instantaneous and Integrated SEM separately must 

undertake two separate traverses of the entire landfill, which doubles the time required to 

conduct the monitoring. Moreover, even at the landfills that perform both requirements at the 

same time, additional time is required to conduct the monitoring. 

EPA’s cost analysis (see Table 5, 79 Fed. Reg. 41823) indicates that adopting the CA LMR 

approach in the proposed NSPS would increase monitoring costs by more than seven times (from 

a total annual cost of $42,300 to $362,900). However, the results of this analysis found that the 

additional effort and resources only detected exceedances at an additional 1.3% of grids

monitored, while increasing gas collection at only one of 72 landfills. 

6.0 CONCLUSIONS

This section summarizes conclusions drawn from the analysis described in this report. The 

conclusions are presented in two sections. The first compares results of surface emissions 

monitoring of NSPS landfills under the NSPS requirements (before the CA LMR) and the CA 

LMR requirements (beginning in mid-2011). The second focuses on the results of surface 

monitoring conduted as required by the CA LMR at non-NSPS landfills (e.g., not previously 

regulated under the NSPS).

6.1 NS P S LA ND F I L LS S U B JE C T T O C A L MR

Insights gained by this analysis are provided for both instantaneous and integrated surface 

emissions monitoring. 

6 . 1 . 1 I n s t a n t a n e o u s S E M

Surface Traverse

The key difference between the NSPS and the CA LMR Instantaneous SEM regimes is the 

increased intensity of site-level monitoring. The density of the CA LMR walking path is 

approximately 4 times greater than that of the NSPS regime (spacing of 25 vs. 98 feet, 

respectively, between walking paths). A review of monitoring results under both programs 

indicates that the CA LMR regime results in the detection of additional exceedances as compared 

to NSPS monitoring, but not at a level commensurate with the additional burden and cost. 

Under the NSPS requirements, exceedances were detected at 1.6% of the total acres monitored. 

Under the CA LMR requirements, such exceedances were detected at 3.7% of the acres 

monitored. Thus, the CA LMR requirements resulted in the detection of exceedances at an 
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additional 2.1% of acres monitored. This slight increase in additional exceedances detected 

suggests that the CA LMR requirements are not cost-effective as they increase costs by more 

than seven times (according to EPA’s cost analysis). 

Cover Penetrations

Under the CA LMR monitoring regime, the number of penetrations monitored was 84% higher 

than under the NSPS requirements. Under the NSPS program, which directs monitoring at 

penetrations exhibiting some obvious sign of elevated methane, exceedances were identified at

2.7% of total penetrations monitored. By comparison, under the CA LMR regime, exceedances 

were identified at 2.0% of total penetrations monitored at the 42 NSPS sites. This suggests that 

the targeted monitoring approach under the NSPS rule is far more cost-effective in identifying

penetration leaks. 

The increased benefit of the CA LMR is even lower, however, because all of the exceedances 

detected under the NSPS requirements were also detected by the CA LMR. In fact, for those 

penetrations monitored solely due to the CA LMR, the percentage difference in the detection of 

exceedances is 1.1%, which is less than half that of the NSPS program. 

As with surface traverse monitoring, cover penetrations are monitored by field personnel 

walking to the penetration at the landfill. By significantly increasing the number of penetrations 

monitored, the CA LMR increases labor costs by nearly a factor of two, while detecting a much 

smaller percentage of exceedances. 

Exceedances Requiring GCCS Expansion 

Under both the NSPS and CA LMR monitoring programs, the percentage of exceedances that 

could not be quickly remedied with cover repairs or GCCS adjustments was low: only 1.2% for 

the NSPS and 5.2% for the CA LMR. This finding indicates that, a preponderance of the 

exceedances identified using instantaneous monitoring (98% for NSPS and 93% for CA LMR)

can be remedied quickly with cover repairs or minor adjustments to the gas collection system. 

In addition, under both rules, only a few landfills were required to expand their GCCS . Under 

the NSPS monitoring regime, exceedances requiring expansion occurred at one landfill (0.1% of 

acres monitored of the NSPS sites in the data set), and three landfills (0.3% of acres monitored of 

the NSPS sites) were required to expand under the CA LMR monitoring approach. Thus, the 

additional intensity of the CA LMR monitoring regime resulted in GCCS expansion at two 

additional NSPS landfills out of the 42 NSPS in the database (or 0.2% of acres monitored at the 

NSPS landfills in the data set). 

Instantaneous surface monitoring under the CA LMR is significantly more expensive than the 

NSPS requirement, and the results of this more intensive monitoring do not justify the increased 

monitoring cost. The vast majority of the exceedances detected under both programs were 

easily remedied, and the CA LMR did not identify a significant number of landfills with 

problems severe enough to require expansion of the GCCS system, which is the main way to 

establish that methane emissions are being reduced.

Table 12 presents a summary of the information for NSPS Landfills subject to the CA LMR.
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Table 12. Comparison of Instantaneous SEM Results 

under NSPS and CA LMR Requirements

Surface Traverse

Under

NSPS

Under

CA LMR

Exceedances detected as percentage of acres monitored 1.6% 3.7%

Incremental exceedances detected under the CA LMR as a 

percentage of acres monitored -- 2.1%

Number of Landfills required to expand GCCS based on surface

traverse monitoring 1 3

Penetration Monitoring

Exceedances detected as a percentage of penetrations monitored 2.7% 1.5%

Total

Exceedances that required GCCS expansion, as a percentage of 

acres monitored 0.1% 0.3%

6 . 1 . 2 I n t e g r a t e d S E M

Integrated SEM monitoring detected exceedances in 2.1% of the grids monitored at NSPS 

landfills following the CA LMR requirements. Only 0.5% of these grids, located at five

landfills, resulted in GCCS expansion. 

In addition, comparison of grid-level monitoring results under the Instantaneous and Integrated 

SEM approaches indicates that 29% of the grids detected using integrated monitoring were also 

detected by instantaneous monitoring. Similarly, three of the five landfills that triggered GCCS 

expansion for integrated monitoring also triggered the expansion requirement due to 

instantaneous monitoring results. Thus, only two landfills were required to expand the GCCS 

due to integrated monitoring. 

Integrated monitoring can require significant additional effort and cost, depending on whether a 

landfill does separate or combined Instantaneous and Integrated SEM. Landfills that conduct 

Instantaneous and Integrated SEM separately must undertake two separate traverses of the entire 

landfill, which doubles the time required to conduct monitoring. Landfills that undertake 

combined monitoring also face increased costs because of the additional time to perform both 

SEM approaches during a single pass of the landfill. Additional costs are also incurred

depending on the method used to develop the integrated emissions estimates. 

The result of the integrated monitoring was to identify two additional landfills for GCCS 

expansion, out of 72 landfills in the data set. Given the significant overlap in monitoring results 

and the additional cost associated with integrated monitoring, integrated monitoring does not 

appear cost-effective.

As discussed in Section 4.2.2, the majority of the landfills that were required to expand the 

GCCS due to Instantaneous SEM monitoring were also identified under the Integrated SEM 

monitoring. This finding indicates that the Instantaneous SEM requirements are effectively 

detecting landfills with collection system problems and potential compliance issues. 
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6.2 N E W LA ND FI L LS S U B JEC T T O C A L MR

As discussed in section 3.0, 30 of the 72 landfills in the CA LMR data set (41% of landfills) 

were not NSPS sites prior to implementation of the CA LMR. These landfills were brought into 

the CA LMR under either the capacity requirement of greater than 450,000 tons in place (for 

active landfills), or the heat rate input capacity requirement of 3.0 million British Thermal Units 

per hour (mmBtu/hr) for closed landfills with both a GCCS that operated after January 1, 1977 

and more than 450,000 tons of waste in place.

For these landfills, Instantaneous SEM data indicate that the intensive monitoring required under 

the CA LMR resulted in detection of a lower percentage of exceedances per acre monitored than 

was found for NSPS landfills monitoring under NSPS requirements prior to implementation of 

the CA LMR. Instantaneous SEM exceedances were detected at only 1.4% of acres monitored 

at non-NSPS landfills under the CA LMR, which is comparable to the detection of exceedances 

at 1.6% of acres monitored at NSPS sites following the NSPS requirements. This is a surprising 

finding, given that the CA LMR requires monitoring of the surface of the landfill on a 25-foot 

pattern, while the NSPS arequires a less-intensive 98-foot pattern.

The effectiveness of penetration monitoring at LMR-only landfills was also much lower. 

Exceedances were detected at only 0.6% of the non-NSPS landfills monitored under the CA 

LMR. This result is significantly lower than exceedance percentages for NSPS landfills under 

the NSPS requirements (2.7% of penetrations) or the CA LMR regime (1.5% of penetrations). 

In addition, none of the Instantaneous SEM exceedances triggered either the 120-day expansion 

requirement or the GCCS expansion requirement. Further, none of the non-NSPS landfills 

covered under the CA LMR detected any integrated SEM exceedances. As a result, not a single 

non-LMR landfills in the data set was required to undertake GCCS expansion.

These monitoring results demonstrate that non-NSPS landfills are too small and/or too old to 

warrant intensive monitoring or regulation. Despite monitoring four times more intensively, 

these landfills detected a smaller percentage of exceedances. With no evidence of significant 

LFG control issues, the cost of this level of monitoring is too high and the impact of monitoring 

on methane emission levels minimal.