The purpose of the study was to determine whether some contaminants, known to exist in landfills licensed to receive industrial wastes (Class I sites), were also found at landfills that receive ordinary trash (Class II sites). The District's Technical Services staff conducted a series of tests at 20 Class II sites beginning in 1984, and concluded that, although significant levels of vinyl chloride and benzene were found at many of those sites, the offsite ambient concentrations for vinyl chloride were well below the State ambient air quality standard at five of them which were chosen for ambient testing. The study discusses a known action that takes place in landfills, whereby buried materials undergo bacterial decomposition and generate gases for decades after closure. Although that is a known phenomenon, what is still not known is how vinyl chloride was generated in these Class II landfills. The report also states that migrating methane could be a problem if this gas migrates beyond the landfill property line and becomes trapped in enclosed spaces, presenting a potential explosive hazard.