Persistence of vinyl chloride in ground water at the Woodlawn landfill Superfund site,northeastern Maryland,USA

Since landfill operations ceased in the early 1980s at the Woodlawn landfill Superfund site in northeastern Maryland, USA, the carcinogen vinyl chloride monomer (VCM) has persisted in the site ground water at concentrations in places greater than 100 ppb. Investigations of VCM concentrations from monitoring well data from 1981 through 1991, which were published in 2001, concluded that concentrations were cyclic and were not dissipating. Data from 1991 to 2000 confirm VCM persistence, showing concentration peaks as late as 1997 in the eastern part of the site. These values are significantly above both drinking water standards (>MCL of 2 ppb) and lifetime excess cancer risk (E-6 risk level) from exposure since birth (>0.024 ppb). Sources for VCM are landfill wastes (PVC-sludge) and effluent from an on-site transfer station. In addition to direct release of VCM from wastes, other chlorinated hydrocarbons, trichloroethene and perchloroethene (TCE and PCE) are also present in the ground water, and these compounds can degrade into VCM. Persistence of VCM concentrations is the result of leachate generation, mostly from multi-source wastes in the vadose zone, with subsequent infiltration into the regional aquifer. Increases in VCM concentrations (new leachate generation) alternated with decreases in VCM concentrations (infiltration without leachate) in a cyclic fashion, during this 20-year period.