Date: September 10, 2010

To: Rachel Schmeltz, U.S. EPA

From: Jeff Coburn, RTI International

Subject: Modified Bulk MSW Option

Purpose

This memorandum provides background information on the bulk waste model parameters developed for 

the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 (U.S. EPA, 2005) and presents 

parameters for a modified “bulk MSW” option to afford landfill owners and operators to develop sitespecific model parameters without a fully characterizing waste composition following the waste 

categories included in the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for 

National Greenhouse Gas Inventories (IPCC, 2006) . 

Background on Bulk Waste Model Parameters

The key element in developing estimates of the parameters for the first order decay (FOD) model 

is a database of landfills that is reasonably representative of landfills nationwide with sitespecific measurements of landfill gas recovery rates and annual waste acceptance rates (or total 

waste in place). Ideally, the database would have the following characteristics:

 • contain types of wastes representative of landfills nationwide, 

 • include a range of sizes, waste age, and geographical regions (especially if the effect of 

precipitation is to be evaluated),

 • have measurements of the landfill gas collection rate and percent methane (although a 

default value of 50 percent methane probably would not introduce significant error),

 • have measurements of annual waste acceptance rates or total waste in place and year the 

landfill opened (i.e., the waste in place or average annual acceptance rate for the area of 

the landfill under the influence of the collection system),

 • include site-specific estimates of percent recovery (based on design and operational 

characteristics or other information), and

 • include annual average precipitation (if this effect is to be evaluated).

The database used to develop U.S.-specific FOD model parameters was obtained from two 

sources: (1) a database compiled by EPA’s Landfill Methane Outreach Program (LMOP) that 

consists of landfill gas-to-energy (LFGTE) projects and (2) a public access database maintained 
2

by the Energy Information Administration (EIA) consisting of landfills that recover landfill gas 

(both for LFGTE and flares). To develop a refined database, landfills that were reported in both 

the LMOP and EIA databases were extracted. The waste in place (WIP) was compared, and 

landfills with discrepancies between the two databases were identified and eliminated. The final 

refined database contained just over 50 landfills for which there were sufficient waste disposal 

information and methane generation rate data to calculate FOD model parameters.

The next step in the analysis was to develop a best fit estimate of the methane generation 

potential (L0) and decay rate constants (k). To do this, L0 and k were both varied and 

simultaneously estimated directly from Equation 1 using PROC NLIN from SAS®. This 

procedure uses a nonlinear regression that evaluates model parameters in an iterative fashion 

(algorithm) to find the best estimate based on the smallest sum of squared errors. The best fit 

estimate of L0 for the data set from PROC NLIN was 99 m3/Mg of waste. As this result agreed 

well with other values reported in the literature (Peer, Thorneloe, and Epperson, 1993; SWANA, 

1998; U.S. EPA, 1998, a value of 100 m3/Mg was selected and used for the first time in 

developing the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003 (U.S. EPA, 

2005). Subsequent to the issuance of the 2006 IPCC Guidelines (IPCC, 2006), this L0 of 

100 m3/Mg was converted to a degradable organic carbon (DOC) content of 0.20 using the 

default values for other parameters included in the IPCC Waste Model used to help implement 

the 2006 IPCC Guidelines (IPCC, 2006). 

Modified Bulk MSW Model Parameters

In response to EPA’s Mandatory Reporting of Greenhouse Gases: Final Rule (74 FR 56260) and 

proposed technical amendments (75 FR 33950), several questions and comments were received 

about excluding construction and demolition (C&D) wastes and/or other “inert” materials from 

the bulk waste quantities used to estimate methane generation from municipal solid waste 

(MSW) landfills. However, the bulk waste DOC value of 0.20 was derived considering all of the 

waste materials disposed of at these landfills. That is, the bulk waste DOC value is expected to 

already account for the fact that there are some low DOC-containing waste streams, such as 

C&D wastes, that may be co-disposed with MSW within an MSW landfill. To confirm this, a 

review was made of the waste materials accepted at the landfills used to develop the default bulk 

DOC value. The 2004 Chartwell Municipal Solid Waste Facility Directory included listings of 

the types of waste materials accepted by individual landfill for 43 of the landfills in the original 

database. Nearly all of these landfills accepted C&D waste along with MSW and other types of 

waste. Therefore, it can be concluded that the bulk waste DOC value is likely to be 

representative of landfills that accept bulk MSW, C&D waste, as well as other types of wastes, 

and that it is inappropriate to apply this bulk waste DOC value only to MSW portion and apply a 

lower or zero DOC for C&D or inert waste materials.

We do note that there is significant variability in the methane generation potential observed for 

individual landfills within the original database of landfills and in the reported literature. L0 for 

individual landfills typically ranges from 50 to 160 m3/Mg (Peer et al. 1993; SAWANA, 1998; 

SCS Engineers, 2003), which equates to a DOC range of 0.1 to 0.32. In order for facilities to 

develop more landfill-specific methane generation estimates, specific waste composition model 

defaults were provided in the final mandatory greenhouse gas (GHG) reporting rule. However, 

industry representatives argue that the landfills have no way to track the composition of waste 
3

using these detailed categories. It certainly makes sense that a facility’s methane generation 

potential will be correlated with the relative amount of high-DOC and low-DOC waste materials 

disposed of in the landfill. Thus, an alternative approach was sought to provide a means to 

develop an alternative “bulk MSW” DOC value that would allow emissions from landfills to be 

estimated based on limited categories of wastes that are more commonly tracked by landfill 

owners and operators.

Three waste types were envisioned: bulk MSW (not including C&D and inert wastes), C&D 

wastes, and inert wastes. Data were compiled from the Municipal Solid Waste in the United 

States: 1999 and 2007 Facts and Figures (U.S. EPA, 2001 and 2008) to establish a typical waste 

composition for bulk MSW between 1990 and 2007. Table 1 provides a summary of the waste 

composition data. Using the IPCC default values for the various waste types, a weighted average 

DOC for bulk MSW (not including C&D and inert wastes) of 0.31 was determined for the time 

period. This value agrees well with the upper range value of methane generation observed at 

certain MSW landfills. In a separate evaluation, a DOC value of 0.08 was developed for C&D 

waste (Bronstein and Coburn, 2010). Inert waste materials, such as metal, glass, plastics, and 

concrete, have no methane generation potential (DOC = 0.0). Using these three waste categories 

is expected to provide more accurate methane generation estimates for landfills that accept only 

high DOC content waste materials (bulk MSW) and for landfills that accept a significant quantity 

of C&D waste or inert waste materials. 

Table 1. Waste Composition Data for Bulk MSW

Percent of Total Waste Landfilled in Disposal Year2

Waste Type

Default 

DOC1 1990 1995 2000 2005 2006 2007

Paper and paperboard 0.4 30.5 31.3 29.6 25.1 24.1 22.3

Food and garden waste 0.175 30.0 26.7 24.1 24.4 24.8 25.1

Textiles 0.24 3.0 4.2 4.8 5.6 5.8 5.9

Wood 0.43 7.0 6.4 7.0 7.5 7.4 7.6

Rubber and Leather 0.39 3.2 3.5 3.5 3.7 3.7 3.8

Inert s 0.00 26.3 28.0 31.2 34.0 34.1 35.1

Weighted Average DOC 

for Bulk MSW, excluding 

inerts 0.304 0.310 0.313 0.307 0.304 0.301

Long-term Average DOC for Bulk MSW (excluding inerts) 0.31

1

 Default DOC values from IPCC (2006)

2

 Waste composition data from U.S. EPA (2001 and 2008, Table 3)
4

References

Bronstein, K. and J. Coburn (2010). Memorandum for Kate Bronstein and Jeff Coburn, RTI 

International, to Rachel Schmeltz, U.S EPA. “GHG inventory improvement –

construction & demolition waste DOC and Lo value.” April 15.

IPCC. 2006. 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National 

Greenhouse Gas Inventories. Volume 5, Waste; Chapters 2 and 3. Available at: 

http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol5.html. 

Peer, R., S. Thorneloe, and D. Epperson (1993), “A Comparison of Methods for Estimating 

Global Methane Emissions from Landfills,” Chemosphere, 26(1-4): 387-400.

SCS Engineers (2003). Stege, G., and D. Murray. User=s Manual, Mexico Landfill Gas Model, 

Version 1.0. Prepared by SCS Engineers for SEDESOL IIE CONAE. November. 

Solid Waste Association of North America (SWANA) (1998), “Comparison of Models for 

Predicting Landfill Methane Recovery,” Publication No. GR-LG 0075, March.

U.S. Environmental Protection Agency. 2001. Municipal Solid Waste in the United States: 

1999 Facts and Figures. EPA-530-R-01-014. Office of Solid Waste, Washington, DC. 

July.

U.S. Environmental Protection Agency. 2005. Inventory of U.S. Greenhouse Gas Emissions 

and Sinks: 1990-2003. EPA-430-R-05-003. Office of Atmospheric Programs, 

Washington, DC. April 15.

U.S. Environmental Protection Agency. 2008. Municipal Solid Waste in the United States: 

2007 Facts and Figures. EPA-530-R-08-010. Office of Solid Waste, Washington, DC. 

November.