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. Gre enhouse 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 site

specific model parameters without a fully characterizing waste composition followin g 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 parame ters for the first order decay (FOD) model is a database of landfills that is reasonably representative of landfills nationwide with site

specific measurements of landfill gas recovery rates and annual waste acceptance rates (or total waste in place). Ide ally, 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 precipi tation 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 ra tes 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 p ercent 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 tw o 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 maintained2 by the Energy Information Administration (EIA) consisting of landfill s 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 tw o 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 ana lysis was to develop a best fit estimate of the methane generation potential ( L 0 ) and decay rate constants (k). To do this, L 0 and k were both varied and simultaneously estimated directly from Equation 1 using PROC NLIN from SAS ® . This procedure uses a n onlinear 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 L 0 for the data set from PROC NLIN was 99 m 3 /Mg of waste. As this resu lt agreed well with other values reported in the literature (Peer, Thorneloe, and Epperson, 1993; SWANA, 1998; U.S. EPA, 1998, a value of 100 m 3 /Mg was selected and used for the first time in developing the Inventory of U.S. Greenhouse Gas Emissions and Si nks : 1990

- 2003 (U.S. EPA, 2005). Subsequent to the issuance of the 2006 IPCC Guidelines (IPCC, 2006), this L 0 of 100 m 3 /Mg was converted to a degradable organic carbon (DOC) content of 0.20 using the default values for other parameters included in the IPC C 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), severa l 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 was tes, 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 incl uded 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. L 0 for individual landfills typica lly ranges from 50 to 160 m 3 /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 de faults 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 waste3 using these detailed categories. It certainly makes sense that a fac ility’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 valu e 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 va lue 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 gene ration 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 quan tity of C&D waste or inert waste materials.

Table 1. Waste Composition Data for Bulk MSW

Percent of Total Waste Landfilled in Disposal Year 2 Waste Type Default DOC 1 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 3 1

. 2 34.0 34.1 35.1

Weighted Average DOC for Bulk MSW, excluding inerts 0.304 0.310 0.31 3 0.30 7 0.30 4 0.301 Long

- term Average DOC for Bulk MSW ( ex c luding inerts ) 0.31

1 Default DOC values from IPCC (2006)
2 Waste composition data from U.S. EPA ( 2001 and 2008 , Table 3)4 R eferen ces

Bronstei n, K. and J. Coburn (2010). Memorandum for Kate Bronstein and Jeff Coburn, RTI International, to Rachel Schmeltz, U.S EPA. “GHG i nventory i mprovement

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. Peer, R., S. Thorneloe, and D. Epperson (1993), “A Comparison of Methods for Estimating Global Methane Emissions from Landfills,” Chemosphere , 26(1

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