Methane emissions from sanitary landfills

Calculations for methane emissions from US landfills based on vertical soil gas concentration gradients at humid and semiarid field sites yield rates ranging from a minimum of 6.10 {times} 10{sup {minus}10} to a maximum of 2.18 {times} 10{sup {minus}6} g cm{sup {minus}2} s{sup {minus}1}. The lower value is for well-vegetated silty clay cover with low relief and soil moisture approaching saturation at a site in northeastern Illinois; the higher value is for nonvegetated sandy silty cover at a sloped site with low soil moisture in southern California. Rates vary seasonally at individual sites, depending on soil moisture and other variables. A comparison of methane emission rates at the California site to estimated methane generation rates suggests that, in the absence of gas collection systems, most of the methane is vented through the cover. Saturation of cover materials induces lateral gas migration. Total methane emissions from US landfills are estimated by two methods: (1) methane generation rates applied to the total mass of landfilled refuse and (2) measured methane flux rates applied to the total US landfill area. This study focuses on measured methane flux rates. 55 refs., 4 figs., 3 tabs.