Re: another question - Vinyl Chloride in Landfill gas

[Alan Watson <alanwatson@gn.apc.org>]

  Alex wrote:
  
  >The proposition that PVC degrades to vinyl chloride in landfills
  >in the absence of both heat and UV and that this 
  >would be the principle source of the chlorinated
  >content of landfill gas....  I really find that
  >hard to accept as being significant at all as 
  >a source.   But if you have research showing 
  >that is the case rather than shear supposition, 
  >please tell us where it can be found.
  >
  >If chlorinated compounds are
  >present in landfill gas I find it much more likely
  >that the sources will be PCB materials disposed
  >in landfills that evaporate, chlorinated solvents 
  >contained in consumer products (i.e. freon, 
  >methylene chloride, paint related solvents, etc.), 
  >small quantity industrial waste disposal or 
  >older surrepticious industrial waste solvent 
  >disposal.
  
  Perhpas so - but the report below from ENDS (Environmental Data Services) 
  indicates high levels of vinyl chloride in landfill gas which need 
  explaining.  It is very likely that they would generate significant 
  levels of dioxin if burned in some of the flares I have seen operating in 
  the UK:
  
  
  ENDS Report: 	228	January 1994
  
  Landfill gas migration study highlights vinyl chloride risk
  
  A study by the British Geological Survey (BGS) has raised new concerns 
  about
  the hazards of landfill gas.  The research showed that volatile 
  carcinogenic
  compounds such as vinyl chloride and benzene migrating from landfill 
  sites can
  build up in soils to levels close to or above safety limits.
  
  Until now concern about the hazards of landfill gas has focussed on 
  migration of methane
  and carbon dioxide, although limited studies have also been carried out 
  on trace gases
  emitted directly from landfills, gas vents and flares.
  
  The BGS study, sponsored by the Department of the Environment, was aimed 
  at finding
  ways to distinguish landfill gas from other underground methane sources 
  such as coal
  seams, marsh gas and mains leakage.
  
  Established methods of differentiating between methane sources include 
  measuring the
  ratio of methane to other gases present or measuring the methane carbon 
  isotope ratio
  13C/12C.  Both can be misleading as bacteria in the soil oxidise methane 
  to carbon
  dioxide.  The organisms tend to preferentially degrade the lighter 12C 
  atoms which diffuse
  more rapidly, reducing the methane 13C/12C ratio.
  
  As a study site, the researchers chose Foxhall landfill in Suffolk.  This 
  was filled with
  municipal waste between 1983 and 1988 before being capped with a polythene
  membrane and fitted with a passive venting system to minimise gas 
  migration.  Despite
  this, the site was producing a plume of gas, affecting crops in an 
  adjacent field.
  Soil gas sampling probes showed that the plume extended some 70 metres 
  northwards
  from the site boundary below a depth of two metres.  Levels of methane in 
  the soil
  declined and levels of carbon dioxide increased with distance, due to 
  methane oxidation
  by soil bacteria.
  
  The researchers used gas chromatography-mass spectrometry to analyse for 
  trace
  organic compounds in the soil gas and in gas from the site's venting 
  system.  Some 77
  compounds were identified, including hydrocarbons, chlorocarbons and 
  aromatics.  The
  distribution of compounds depended upon their boiling point and tendency 
  to be
  absorbed by the soil, but chlorinated hydrocarbons were generally the 
  most mobile.
  Levels of benzene, vinyl chloride and dichlorofluoromethane (CFC 21) 
  approached or
  exceeded the long-term exposure limits for worker safety.  Vinyl chloride 
  levels of up to
  10ppmv were measured in the soil gas and up to 24ppmv in vent gas.  Both 
  exceeded the
  long-term exposure limit of 7ppmv.
  
  Levels of benzene and CFC 21 in the soil gas approached but did not 
  exceed long-term
  exposure limits.  The highest levels measured were 3.3ppmv for benzene, 
  compared to an
  exposure limit of 5ppmv, and 7.0ppmv for CFC 21, compared with a limit of 
  10ppmv.
  Vinyl chloride and CFC 21 were highly mobile in the landfill gas plume, 
  with maximum
  levels of both compounds occurring 50 metres from the site.  Why 
  concentrations were
  lower closer to the landfill could not be explained, but may be a result 
  of past
  management of the site.
  
  The researchers concluded that vinyl chloride was a useful identifier for 
  landfill gas as it is unlikely to be present in other sources of methane.
  
  However, the study also raises the issue of toxicity in cases where 
  buildings close to
  landfills may be affected by gas migration.  Although vinyl chloride and 
  other gases may
  reach toxic levels in small volumes of soil gas, it is uncertain whether 
  this would occur in
  spaces such as cellars or underfloor voids because of the small flows of 
  landfill gas
  involved.  However, the researchers believe that the design of 
  construction projects
  should take full account of the potential toxicity of landfill gas.
  
  ........................................................
         _\\|//_                Alan Watson C.Eng                  
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