AREA A/B ENGINEERING REPORT - Waste Management

Geosyntec Consultants
conversion of C&H in landfills occurs relatively rapidly, typically over the course of a few
decades. However, although C&H will decompose anaerobically to methane and CO2, the
complete decomposition of C&H within a landfill is not expected. In addition, many common
components of the waste mass are wood-based, which contains lignin. Lignin is highly recalcitrant
to anaerobic biodegradation under landfill conditions, and will not undergo any significant
decomposition (Barlaz, 2006). This limited biodegradability, coupled with the fact that modern
landfill designs isolate wastes from the environment using engineered containment systems (which
further restrict anaerobic digestion from proceeding) and are required to capture and control
methane, means that landfills are significantly increasing the net amount of organic carbon
(measured as CO2) that is permanently sequestered as biomass (Barlaz, et al, 2007).
Clearly, accounting for carbon storage in landfills can significantly offset GHG emissions from
landfills. The Intergovernmental Panel on Climate Change (IPCC), USEPA, Oregon Climate Trust,
and California Air Resources Board (CARB) all recognize that carbon storage in a landfill should
be considered a sink when calculating potential carbon emissions. These organizations recognize
that when biogenic waste is disposed in landfills and does not completely decompose, the carbon
that remains is effectively removed from the global carbon cycle. For example, SWICS (2009)
states:
“…the USEPA has published reports that evaluate carbon flows through landfills to estimate their net
GHG emissions. The methodology the USEPA employed recognizes carbon storage in landfills. In
these studies of MSW landfilling, the USEPA summed the GHG emissions from methane generation
and transportation-related carbon dioxide emissions, and then subtracted carbon sequestration
(treated as negative emissions).
Furthermore, the 2006 GHG emissions inventory published by the California Energy Commission
(CEC) indicated that landfill disposal of urban wood waste and yard trimmings is a GHG sink. The
report included only the categories of yard trimming and wood waste, and neglected sequestration
from paper, boxes, yard waste, lumber, textiles, diapers, demolition, medical waste, sludge, and
manure. In California, urban wood waste and yard trimmings represent only 16.4% of the total
California waste stream and only 46% of sequestered carbon within landfills; therefore, restricting
estimates of carbon storage to only these waste types produces an extremely low value of overall
carbon storage for the total amount of waste disposed. Landfill sequestration estimate includes
sequestration from paper, boxes, yard waste, lumber, textiles, diapers, demolition, medical waste,
sludge, and manure.
CARB estimates the total carbon sequestration in landfill to be 4.94 million MTCE in 2005, which is
17.2 million metric tonnes carbon dioxide equivalent (MMTCO2E). CARB estimates that GHG
emissions from landfills were 5.62 MMTCO2E in 2004, much less than the value of the carbon stored
in the landfill.”
In summary of the above, carbon sequestration should be a part of the inventory of potential
GHG emissions from landfills. Since carbon sequestration factors are typically not considered for
landfills, the potential methane emissions from landfills are likely overestimated.
MD10186.doc 137 29 March 2009