PNNL

Abstract

Methods are developed to use data collected during cyclic operation of soil vapor extraction (SVE) systems to help characterize the magnitudes and timescales of mass flux associated with vadose zone contaminant sources. Operational data collected at the Department of Energy’s Hanford site are used to illustrate the use of such data. An analysis was conducted of carbon tetrachloride vapor concentrations collected during and between SVE operations. The objective of the analysis was to evaluate changes in concentrations measured during periods of operation and non-operation of SVE, with a focus on quantifying temporal dynamics of the vadose zone contaminant mass flux, and associated source strength. Three mass-flux terms, representing mass flux during the initial period of a SVE cycle, during the asymptotic period of a cycle, and representing mass flux during the rebound periods, were calculated and compared. It was shown that it is possible to use the rebound data to estimate time frames for effective operation of an SVE system if a sufficient set of historical cyclic operational data exists. This information could then be used to help evaluate changes in SVE operations, including system closure.