1 

MEMORANDUM

TO: Hillary Ward, EPA 

FROM: ERG 

 

DATE: June 2015 

SUBJECT: Estimating Secondary Impacts of the Emission Guidelines for MSW Landfills

The EPA issued is proposing a review of the emission guidelines for air emissions from existing 

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

equations used to calculate the secondary impacts that would result from the proposed new subpart Cf 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 2025. 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 emission guidelines 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/emission guidelines and the proposed 40 CFR part 60, subpart Cf. 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 2025. 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 (2025), MWh/yr 

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

methodology memorandum)

 

1 ERG. 2015. Updated Methodology for Estimating Cost and Emission Impacts of MSW Landfill Regulations. 
2 

Electricity_Price = Average electricity price, $0.0655 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 (2025), 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 (2025), ft3/yr 

CH4Total = Methane destroyed, (2025), (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 Cf 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. 2015. Updated Methodology for Estimating Cost and Emission Impacts of 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 (2025), MWh 

CH4_flared = Quantity of methane flared in each option, ft3/yr, from Eqn. 3 

0.002 = Energy demand of LFG collection system, kWh/ft3LFG (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 (2025), MWh, from Eqn. 1 

 E_demand = Energy demand 2025, MWh, from Eqn. 4 

Appendix A summarizes the energy impacts of the proposed 40 CFR part 60, subpart Cf. The proposed 

subpart Cf 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 $0.0655/kWh to the net energy supply, the value of the energy supply is also estimated in Appendix A 

for the proposed subpart Cf. 

 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: 

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. These emissions are expected to be relatively small and were not estimated. 

Emissions from Purchased Electricity 

 

3 ERG. 2015. Updated Methodology for Estimating Cost and Emission Impacts of MSW Landfill Regulations. 
4 

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 4, and emission factors from EPA eGRID (9th edition)4 can be applied to estimate the CO2

emissions associated with this purchased electricity. Purchased electricity is also expected to yield 

emissions such as SO2 and NOx and trace amounts of mercury (Hg). These emissions are expected to be 

relatively small and were not estimated. 

Equation 6: CO2 Emissions from Grid Purchased Electricity 

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

Where: 

Pollgrid = Pollutant emitted from grid purchased electricity in 2025, tpy 

EFgrid = Emission factor from grid purchased electricity, lb/MWh from Table 1 

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

CH4_flared = Quantity of CH4 flared(2025), 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 1. eGRID Emission Factors Used in Impacts Analysis 

Pollutant Factor (lb/MWh) Source

CO2 1232.35 eGRID 9

th 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 1 were used with Equation 7 to estimate the avoided air impacts. 

Equation 7: Avoided CO2 Emissions from LFG Energy Supply 

Pollavoided = Elec_Produced × EFgrid ÷ 2,000 

Where: 

Pollavoided = Pollutant avoided from grid electricity (2025), tpy 

EFgrid = Emission factor from avoided grid electricity, lb/MWh from Table 1 

Elec_Produced = Average annual electricity produced (2025), MWh, from Eqn. 1 

2,000 = Conversion factor lb/ton 

Net Emissions Impact 

 

4 USEPA. eGRID 9th Edition (2010 data). February 24, 2014. http://www.epa.gov/cleanenergy/energyresources/egrid/index.html. 
5 

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

can be computed according to Equation 8 for each pollutant that was estimated using Equations 6 and 7 

above. 

Equation 8: Net Secondary Emissions Impact 

Net Emissions = Polleng + Pollflare + Pollgrid - Pollavoided 

Where: 

Net Emissions = Net emissions (2025), tpy 

Polleng = Pollutant emitted from LFG engines (2025), tpy 

Pollflare = Pollutant emitted from flared LFG (2025), tpy 

Pollgrid = Pollutant emitted from grid purchased electricity (2025), tpy 

Pollavoided = Pollutant avoided from grid electricity (2025), tpy 

Appendix B shows the detailed calculations of the secondary air impacts for the proposed option. 
Appendix A: Annual Energy Impacts 2025: 6/30/15

CH4 Flared (ft3/yr)

Energy Needed to Operate Blowers on GCCS (MWh)

MWh generated from Engines

Net Energy Impacts (MWh)

Value of energy supply ($/yr)

Energy Demand to Operate GCCS (MWh)

Energ(MWh

1 802,559 19,579,049 200,639,654,854 18,776,490 $1,229,860

Proposal 2.5/34 13 197,387,162,254 789,549 19,991,327 19,201,778 $1,257,716 (13,010) 

Current NSPS requirements (40 CFR 

part 60 subpart WWW)

2.5/50

Total Impacts Incre

Option
Appendix B: Annual Secondary Air Impacts (2025): 6/30/15

Flare + Energy Total Net Emissions

Emissions Created

Emissions Avoided

Emissions Created

CO2 from Purchased Electricity for Blowers (tpy) CO2 Avoided CO2 CO2 (tpy) 

1 200,639,654,854 19,579,049 494,516 12,064,097 494,516 (11,569,5

Proposal 2.5/34 13 197,387,162,254 486,499 19,991,327 12,318,132 486,499 (11,831,6

Flaring LFG Electricity 

Current NSPS 

requirements (40 CFR 

part 60 subpart 

WWW)

(2.5/50)

MWh 

generated 

Option CH4 Flared (ft3/yr) from Engines