Quantifying volatile organic compounds in porous media: effects of sampling method attributes, contaminant characteristics and environmental conditions.

Understanding how sampling methods can impact the accuracy of volatile organic compound (VOC) measurements in samples of soil and subsurface porous media is often critical to sound decision making during characterization and remediation of VOC contaminated sites. In this study, the accuracy of VOC measurements was investigated using an experimental apparatus packed with sandy porous media and contaminated with known levels of VOCs, which could be sampled using different methods under variable, but controlled, conditions. Five sampling methods were examined representing different degrees of porous media disaggregation and duration of atmospheric exposure (MDE) that can occur during sample acquisition and preservation in the field. Three pervasive VOCs were studied (1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene) at low and high concentration levels. Five porous media temperatures were examined ranging from 5 to 80 degrees C to represent ambient or thermal remediation conditions and two water saturation levels were used to mimic vadose zone and groundwater zone conditions. The results of this research demonstrated that sampling method attributes can impact the accuracy of VOC measurements in porous media by causing negative bias in VOC concentration data ranging from near 0 to 90% or more. The magnitude of the negative bias is dependent on the attributes of the sampling method used (i.e., level of MDE) and interactions with key contaminant properties and environmental conditions (i.e., VOC KH, porous media temperature, water saturation level).