To:	Melissa Weitz, EPA

From:	Jeff Coburn, RTI

Date:	April 15, 2008

Subject:  	Correlations with Landfill Methane Generation and Actual
Emissions

Linear correlations were made with waste in-place (WIP) quantities with
the 2006 methane generation and the predicted actual emissions
(accounting for soil oxidation and landfill gas recovery (at 75 percent
recovery efficiency) for landfills projected to be subject to the NSPS
or Emission Guidelines for landfills).  A series of different periods of
waste disposal were evaluated.  Although landfill capacity is not
expected to correlate well with emissions, this correlation was also
evaluated.    Table 1 summarizes the results, showing the correlation
coefficient (R2) of the linear regression.  As seen in Table 1, the
30-year WIP demonstrated the best correlation with the total 2006
methane generation and the predicted net emissions.  Based on the model
estimates, WIP is expected to be a much better indicator of methane
generation and emissions than landfill capacity.

Note that the correlation with actual landfill specific data is expected
to be much poorer than those shown here since the emission estimates
were made using the landfill waste model and assumed a fixed average DOC
value for all landfills.  Specific landfills may have widely different
DOC values which would cause greater variability of the WIP with
emissions.  Nonetheless, the correlation coefficients are quite high and
suggest that a 30-year waste in-place value provides a reasonable method
of projecting landfill emissions.  

Table 1.  Correlations of Methane Generation and Methane Emissions with
Waste-in-Place (WIP)

Parameter	Years*	Linear Regression Correlation Coefficient (R2)



Methane Generation (tCO2eq)	Methane Emissions (tCO2eq)

5-yr WIP	2001 to 2005	0.8133	0.8030

10-yr WIP	1996 to 2005	0.8708	0.8617

20-yr WIP	1986 to 2005	0.9165	0.9086

25-yr WIP	1981 to 2005	0.9168	0.9092

30-yr WIP	1976 to 2005	0.9170	0.9097

40-yr WIP	1966 to 2005	0.9106	0.9038

Landfill Capacity	N/A	0.6313	0.6256

*Years are inclusive.  Ended with 2005 because 2006 waste does not
contribute to 2006 emissions given the 6 month delay time.

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