Soil Gas Sampling for 1,4-Dioxane during Heated Soil Vapor Extraction

Soil gas sampling for 1,4-dioxane at elevated soil temperatures, such as those experienced during in-situ thermal treatment, has the potential to yield low results due to condensation of water vapor in the ambient temperature sampling vessel and the partitioning of 1,4-dioxane into that condensate. A simple vapor/condensate sampling apparatus was developed to collect both condensate and vapor samples to allow for determination of a reconstituted effective soil gas concentration for 1,4-dioxane. Results using the vapor/condensate sampling apparatus during a heated air injection SVE field demonstration are presented, along with those of a comparable laboratory system. Substantial 1,4-dioxane mass was found in the condensate in both the lab and field (as high as ~50% in field). As soil temperatures increased, less 1,4-dioxane mass was detected in field condensate samples than expected based on laboratory experiments. Extraction well effluent sampling at the wellhead by direct vapor canister sampling provided erratic results (several biased low by a factor of 5 or more) compared to those of the vapor/condensate apparatus. Direct vapor canister sampling of extraction well effluent after the air-water separator, however, provided results reasonably comparable (within 35%) to those using the vapor/condensate apparatus at the wellhead. Soil gas sampling at elevated temperatures using the vapor/condensate apparatus alleviates potential low sampling bias due to condensation.