1 

MEMORANDUM

TO: Hillary Ward, EPA 

FROM: ERG 

 

DATE: April 2014 

SUBJECT: Estimating Secondary Impacts of the Landfills NSPS Review

The EPA is reviewing the new source performance standards (NSPS) for air emissions from municipal 

solid waste landfills (40 CFR part 60, subpart WWW). This memo presents the assumptions and 

equations used to calculate the secondary impacts that would result from the proposed new subpart XXX 

in 40 CFR part 60. 

The proposed new subpart would affect the nation’s energy supply and is expected to generate a net 

increase in the nation’s energy supply. The combustion of landfill gas (LFG) also creates secondary air 

impacts in the form of by-product emissions, additional energy demand required to operate the control 

system, and avoided emissions from the national electrical grid as a result of new LFG energy supply. 

The secondary impacts are computed for the year 2023, which is 10 years after the NSPS is proposed. 

This is consistent with the presentation of the costs and emission impacts in the preamble. The 

methodologies for estimating costs and emission reductions are presented in the cost and emission 

impacts methodology memorandum1

. The secondary impacts are computed on an incremental basis 

relative to the current NSPS requirements (baseline). 

1. Distribution of Methane to Flares and Engines

The gas curve models (that were used to estimate costs and emission reductions) compute the total 

amount of methane destroyed, as well as the total revenue generated from the sale of electricity to the 

grid, by the current NSPS and the proposed 40 CFR part 60, subpart XXX. Using these values, it is 

possible to back calculate the amount of methane destroyed by the engines vs. the flares. Equations 1, 2, 

and 3 are used to determine the annual electricity produced (in megawatt hours per year or MWh/yr), the 

annual methane sent to engines (metric tons/yr), and the annual methane sent to flares (in cubic feet per 

year or ft3

/yr) in 2023. These amounts are then used to compute the secondary impacts using equations 

described in Sections 2 and 3 of this memorandum. 

Equation 1: Quantity of Electricity Produced 

Elec_Produced = Eng_Revenue ÷ Electricity_Price ÷ 1,000 

Where: 

Elec_Produced = Electricity produced (2023), MWh/yr 

Eng_Revenue = $/yr (computed using equations in the cost and emission impacts 

methodology memorandum)

 

1

 ERG. 2014. Methodology for Estimating Cost and Emission Impacts of Proposed MSW Landfill Regulations. 
2 

Electricity_Price = Average electricity price, $0.06297 per kWh 

1,000 = Conversion factor, kW per MW 

Equation 2: Quantity of Methane Sent to Engines 

CH4Engines = Elec_Produced × 11,100 × 1,000 ÷ 1,012 × 0.0423 ÷ 2,000 × 0.9072 

Where: 

CH4Engines = Methane sent to engines (2023), metric ton/yr 

Elec_Produced = Electricity produced, MWh/yr, from Eqn. 1 

11,100 = Engine heat rate, 11,100 Btu/kWh 

1,000 = Conversion factor, kW per MW 

1,012 = Heating value of methane, Btu/ ft3 CH4

0.0423 = Density of CH4, lb/ ft3 

2,000 = Conversion factor, lb/ton 

0.9072 = Conversion factor, metric ton per short ton 

Equation 3: Quantity of Methane Flared 

CH4flared = (CH4Total - CH4Engines) × 2,000 ÷ 0.9072 ÷ 0.0423 

Where: 

CH4flared = Methane sent to flares (2023), ft3

/yr 

CH4Total = Methane destroyed, (2023), (computed using equations in cost and 

emission impacts methodology memorandum, metric ton/yr) 

CH4Engines = Methane sent to engines, from Eqn. 2 

2,000 = Conversion factor, lb/ton 

0.9072 = Conversion factor, metric ton per short ton 

0.0423 = Density of CH4, lb/ ft3 

2. Energy Impacts

As discussed in the cost and emission impacts methodology memorandum,2

 the regulatory options 

analysis assumes that landfills with sufficient gas to support an LFG engine that are located in areas with 

favorable electricity prices will install LFG engines as a least cost control alternative. 

The energy impacts of the proposed 40 CFR part 60, subpart XXX are two-fold: 

1. Energy demand to operate the blowers of the LFG collection system. This energy is expected to 

be purchased from the grid for landfills that do not have LFG electricity projects installed. For 

landfills with LFG engines installed, the engines are expected to provide this energy to the LFG 

collection system. 

2. Energy supply from the LFG engines. Additional energy generated above what is required to 

operate the LFG collection system is expected to be sold to the local grid. 

 

2

 ERG. 2014. Methodology for Estimating Cost and Emission Impacts of Proposed MSW Landfill Regulations. 
3 

The net energy impacts can be estimated using the following equations: 

Equation 4: Energy Demand 

E_demand = CH4_flared × 0.002 × 2 ÷ 1,000 

Where: 

E_demand = Energy demand (2023), MWh 

CH4_flared = Quantity of methane flared in each option, ft3

/yr, from Eqn. 3 

0.002 = Energy demand of LFG collection system, kWh/ft3

LFG (see cost and 

emission impacts methodology memorandum) 

2 = Multiplier, methane in LFG, assuming 50% methane 

1,000 = Conversion factor kW/MW 

Equation 5: Net Energy Impact 

 E_Impact = Elec_Produced – E_demand 

Where: 

 Elec_Produced = Electricity produced (2023), MWh, from Eqn. 1 

 E_demand = Energy demand 2023, MWh, from Eqn. 4 

Table 1 summarizes the energy impacts of the proposed 40 CFR part 60, subpart XXX. The proposed 

subpart XXX is expected to generate a net increase in the nation’s energy supply. The energy revenue 

provided from new LFG engine energy supply was estimated as part of the cost analysis; as described in 

the cost and emission impacts methodology memorandum.3

 Applying an average national electricity price 

of $0.0629/kWh to the net energy impact, the energy supply is also summarized in Table 1 for the 

proposed subpart XXX. Appendix A shows the detailed calculations of the energy impacts for all of the 

regulatory options presented in the preamble. 

Table 1 Summary of Incremental Energy Impacts of Proposed Subpart XXX in 2023 Above the 

Current NSPS 

Option

Incremental 

Energy Demand 

(MWh)

Incremental 

Energy Supply 

(MWh)

Incremental Net 

Energy Impact 

(MWh)

Incremental 

Value of Net 

Energy Supply 

(2012$)

Proposed subpart to 

reduce NMOC 

threshold to 40 

Mg/yr

674 42,421 42,421 $2,671 

3. Secondary Air Impacts		

In addition to the reduction of methane and NMOC emissions, the proposed subpart has secondary air 

impacts, which are expected to incur in three main components: 

 

3

 ERG. 2014. Methodology for Estimating Cost and Emission Impacts of Proposed MSW Landfill Regulations. 
4 

1. By-product emissions created from the combustion of LFG in flares or engines 

2. Emissions created from purchasing energy from the grid to operate the blowers on the LFG 

collection system. 

3. Avoiding or offsetting emissions from grid electricity by supplying new energy from LFG 

engines. 

By-product Emissions from Flares or Engines

When LFG is controlled using engines or flares, combustion by-product emissions such as SO2 and NOx 

are generated. In addition, trace amounts of LFG constituents, such as mercury (Hg), can be emitted in the 

engine or flare exhaust gas. Equations 6a and 6b and 7a and 7b along with emission factors from Chapter 

2 of EPA’s AP-424

 were used to estimate the secondary air impacts resulting from the combustion of 

LFG. 

Equation 6a: NOx Emissions from Flares 

NOxflare = EFNOxflare × CH4_flared ÷ 2,000 

Where: 

NOxflare = NOx emitted from flared LFG (2023), tpy 

EFNOxflare = NOx emission factor, 40lb/ 106

 dscf methane, from AP-42 

CH4_flared = Quantity of methane flared (2023), dscf/yr 

2,000 = Conversion factor lb/ton 

Equation 6b: NOx Emissions from Engines 

NOxengine = EFNOxengine ÷ 1,012 × 11,100 × 1,000 × Elec_Produced ÷ 2,000 

Where: 

NOxengine = NOx emitted from LFG engines (2023), tpy 

EFNOxengines = NOx emission factor, 250 lb/ 106

 dscf methane, from AP-42 

 1,012 = Methane heating value, Btu/scf 

11,100 = Engine heat rate, Btu/kWh 

1,000 = Conversion factor kW/MW 

Elec_Produced = Electricity produced 2023, MWh, from Eqn 1 

2,000 = Conversion factor lb/ton 

SO2 emissions from the flare and engines vary depending on the sulfur content of the LFG. This analysis 

assumes all sulfur compounds in LFG are converted to SO2 during combustion and uses the AP-42 default 

sulfur content for raw LFG rather than using landfill-specific data. 

Equation 7a: SO2 or Hg Emissions from Flares 

Pollflare = PconcLFG ÷ 106

 × MWpoll ÷ LFGstd ×2 × CH4_flared ÷ 2000 

Where: 

Pollflare = Pollutant emitted from flared LFG (2023), tpy 

 

4

 USEPA. 1998. AP-42 Vol. I. Chapter 2.4. Municipal Solid Waste Landfills. Available on-line at: 

http://www.epa.gov/ttn/chief/ap42/ch02/final/c02s04.pdf. 
5 

PconcLFG = Pollutant concentration of LFG5, ppmv 

MWPoll = Molecular weight of SO2 (64.06) or Hg (200.61), lb/lb-mol 

LFGstd = LFG at standard conditions, 385.5 scf/lb-mol 

2 = Multiplier, ratio of LFG to methane, assuming 50% methane 

CH4_flared = Quantity of methane flared, (2023), dscf/yr, from Eqn 3 

2,000 = Conversion factor lb/ton 

Equation 7b: SO2 or Hg Emissions from Engines 

Polleng = PconcLFG ÷ 106

 × MWpoll ÷ LFGstd *2 ÷ 1,012 × 1,000 × 11,100 × Elec_Produced ÷ 2,000 

Where: 

Polleng = Pollutant emitted from LFG engines (2023), tpy 

PconcLFG = Pollutant concentration of LFG6

MWPoll = Molecular weight of SO2 (64.06) or Hg (200.61), lb/lb-mol 

LFGstd = LFG at standard conditions, 385.5, scf/lb-mol 

2 = Multiplier, ratio of LFG to CH4, assuming 50% methane 

1,012 = Methane heating value, Btu/scf 

1,000 = Conversion factor kW/MW 

11,100 = Engine heat rate, 11,100, Btu/kWh 

Elec_Produced = Electricity produced (2023), MWh, from Eqn. 1 

2,000 = Conversion factor lb/ton 

Emissions from Purchased Electricity

In addition to the emissions resulting directly from the combustion of LFG, there are also emissions 

associated with the energy demand to operate the LFG control system. The energy demand is quantified 

using Equation 2, and emission factors from EPA eGRID (9th edition)7

 can be applied to estimate the 

emissions associated with this purchased electricity. While cap and trade mechanisms in place for SO2

and NOx emissions in the electricity sector prevent quantifying emissions resulting from purchased 

electricity, the eGRID factors can be used to estimate the increase in CO2 and Hg emissions from 

purchased electricity. However, eGRID data are unavailable to estimate the impacts on CO or PM from 

purchased electricity. 

The eGRID factors are presented as lb/MWh output and the data are available for an overall national 

average grid factor as well as an average of only fossil-fuel based electricity. For this analysis, the overall 

national grid average factors were chosen to estimate emissions because on average the purchased 

electricity would reflect the overall national average and not just electricity from fossil sources. The grid 

factors used in this analysis are documented in Table 2. The most recent version of eGRID data does not 

include a factor for mercury, so the 2007 eGRID data set was used to estimate mercury emissions. 

Equation 8: CO2 or Hg Emissions from Grid Purchased Electricity 

Pollgrid = 0.002 × CH4_flared × 2 × EFgrid ÷ 2,000 ÷ 1,000 

Where: 

 

5

 Sulfur concentration is 46.9 ppmv, from AP-42 page 2.4-8; Hg concentration is 2.92E-04 ppmv from Table 2.4-1. 

6

 Sulfur concentration is 46.9 ppmv, from AP-42 page 2.4-8; Hg concentration is 2.92E-04 ppmv from Table 2.4-1. 

7

 USEPA. eGRID 9th Edition (2010 data). February 24, 2014. http://www.epa.gov/cleanenergy/energyresources/egrid/index.html. 
6 

Pollgrid = Pollutant emitted from grid purchased electricity in 2023, tpy 

EFgrid = Emission factor from grid purchased electricity, lb/MWh from Table 2 

0.002 = Electricity consumption by LFG collection blowers, kWh/ft3 LFG 

CH4_flared = Quantity of CH4 flared(2023), dscf/yr, from Eqn. 3 

2 = Multiplier, ratio of LFG to CH4, assuming 50% methane 

1,000 = Conversion factor kWh/MWh 

2,000 = Conversion factor lb/ton 

Table 2. eGRID Emission Factors Used in Impacts Analysis 

Pollutant Factor (lb/MWh) Source

Hg 27.2 eGRID2007 V1.1, national average, all sources 

CO2 1216.18 eGRID 9th Edition (2010 Data) V1.0, national average, all 

sources

Avoided Emissions from Excess Energy Supply

The third component affecting overall secondary air impacts are the emissions avoided as a result of 

increased LFG energy production expected to occur as a result of the new subpart. LFG electricity sold to 

the grid is expected to offset the demand of purchased electricity from the national grid. The eGRID 

factors from Table 2 were used with Equation 9 to estimate the avoided air impacts. 

Equation 9: Avoided CO2 and Hg Emissions from LFG Energy Supply 

Pollavoided = Elec_Produced × EFgrid ÷ 2,000 

Where: 

Pollavoided = Pollutant avoided from grid electricity (2023), tpy 

EFgrid = Emission factor from avoided grid electricity, lb/MWh from Table 2 

Elec_Produced = Average annual electricity produced (2023), MWh, from Eqn. 1 

2,000 = Conversion factor lb/ton 

Net Emissions Impact 

Considering the three sources of emissions impacts from the proposed subpart, a net impact on emissions 

can be computed according to Equation 10 for each pollutant that was estimated using Equations 6 

through 9 above. 

Equation 10: Net Secondary Emissions Impact 

Net Emissions = Polleng + Pollflare + Pollgrid - Pollavoided 

Where: 

Net Emissions = Net emissions (2023), tpy 

Polleng = Pollutant emitted from LFG engines (2023), tpy 

Pollflare = Pollutant emitted from flared LFG (2023), tpy 

Pollgrid = Pollutant emitted from grid purchased electricity (2023), tpy 

Pollavoided = Pollutant avoided from grid electricity (2023), tpy 
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Table 3 summarizes the secondary air impacts of the proposed subpart compared to the current NSPS 

requirements. The CO2 emission reductions presented in this table are in addition to the CO2e emission 

reductions achieved from the direct destruction of methane in flares or engines. Appendix B shows the 

detailed calculations of the secondary air impacts for all of the regulatory options considered. 

Table 3. Summary of Incremental Secondary Air Impacts for Proposed Subpart XXX in 2023 

Pollutant

Emissions Created 

(LFG Flares and 

Engines) (tpy)

Emissions Avoided 

(tpy) Net Emissions (tpy)

SO2 5 Cannot compute Cannot compute 

Hg 9 586 -577 

NOx 62 Cannot compute Cannot compute 

CO2 415 26,554 -26,139