Near surface soil vapor clusters for monitoring emissions of volatile organic compounds from soils

The overall objective of this research was to develop and test a method of determining emission rates of volatile organic compounds (VOCs) and other g ases from soil surfaces. Soil vapor clusters (SVCs) were designed as a low dead volume, robust sampling system to obtain vertically resolved profiles of sail gas contaminant concentrations in the near surface zone. The concen tration profiles, when combined with a mathematical model of porous media m ass transport, were used to calculate the contaminant flux from the soil su rface. Initial experiments were conducted using a mesoscale soil remediatio n system under a range of experimental conditions. Helium was used as a tra cer and trichloroethene was used as a model VOC. Flux estimations using the SVCs were within 25% of independent surface flux estimates and were compar able to measurements made using a surface isolation flux chamber (SIFC). In addition, method detection limits for the SVC were an order of magnitude l ower than detection limits with the SIFC. Field trials, conducted with the SVCs at a bioventing site, indicated that the SVC method could be easily us ed in the field to estimate fugitive VOC emission rates. Major advantages o f the SVC method were its low detection limits, lack of required auxiliary equipment, and ability to obtain realtime estimates of fugitive VOC emissio n rates.