Hi Bruce ~
I am glad to hear that you are doing this evaluation. We came across this issue when we were doing our food recovery study for our county solid waste program. We were concerned that the removal of the food from the landfill would negatively impact the revenue from the sale of electricity ($400,000 a year) that we get from our methane recovery system at our landfill, but after doing some research and talking to some landfill gas engineers and our solid waste manager, our conclusion was that the food decomposed so quickly that the methane recovery system wasn't capturing much of this gas anyway. The way that our gas recovery system is constructed is that the extraction wells are only slotted near the lower part of the well to prevent drawing oxygen into the landfill and the recovery system. This means that most of the gas generated in the upper layers probably does not get captured. It also, of course, means that most of this gas will escape into the atmosphere, contributing to global climate change.
The data that we found on rates of decomposition of material in a landfill vary greatly. At a February 1988 solid waste conference here at the University of Wisconsin-Madison, Professor Bob Ham gave the following for the expected half-life for the decomposition of various materials in a landfill:
Rapidly decomposable (food, garden debris): 1/2 year to 1.5 years
Moderatedly decomposable (paper, wood) 5 years to 25
There is a reference to work by Pacey & Altmann, but no specific reference is provided.
In contrast to these data, a December 2000 report from Norway (Miljøkostnader ved avfallsbehandling (Environmental Costs from Solid Waste Management), by the organization ECON for the Norwegian Environmental Protection Department) reported the following half-life for various materials (page 74):
Wet organic 2.8 years
Paper 8.4 years
Wood 10.5 years
Textiles 10.5 years
Plastic 50 years
The source is given as a 1996 report by the Norwegian Pollution Control Authority (SFT). Unfortunately, one of the reports in the bibliography with this date has the same data, but no reference source.
The December 2000 report from Norway goes a step further and assigns an enconomic cost to the environmental impacts of landfills in Norway. Neglecting any potential long term failure of a liner or cover, they conclude that there is a $17 a ton environmental impact, of which about $13.50 a ton is from the emissions of methane.
As we did our food recovery study, we also talked to some university researchers and others on the national level about the fate of methane from food and nobody seemed to have investigated this issue or was aware of any published articles. However, they agreed that the scenario we described on rapid decomposition and the majority of the gas going to the atmosphere was logical.
I hope that this helps and that you will share what you find with others. This seems to be an issue overlooked by state and federal regulators and by others in the landfill industry.
Dane County, WI