Climatic Effects on Vapor Flow and Behavior in the Vadose Zone

Abstract

The concentrations and transport of volatile organic compounds (VOCs) and other vapors in the vadose zone may exhibit some degree of temporal variability due to the effect of various climatic factors, including (1) Air temperature; (2) Barometric pressure; (3) Surface winds; and (4) Soil moisture, including the effects of any water infiltration and/or changes in groundwater level. These variables may directly affect the rates of gas transport through the vadose zone or may indirectly affect transport by changing the soil-gas concentrations at a given location and depth. To understand the potential effect of these factors due to climate change, it is first necessary to understand their effect over typical time periods of one to several days, seasonally, and annually. In this paper, the effects of the above variables over various time periods are presented and the long-term effects due to climate change are discussed. Standard approaches for soil-gas measurement attempt to account for these variables, either to negate their potential influence or to capture data under reasonably worst-case conditions. The appropriateness and adequacy of typical soil vapor measurement approaches are discussed.