Soil gas measurements are often used for risk assessment in vapor intrusion investigations. In the case of petroleum-contaminated sites, total petroleum hydrocarbon (TPH) characterization may be required to effectively measure the associated risk. One of the common strategies employed to characterize TPH for risk assessment includes the quantitation of indicator compounds of significant toxicological effects as well as the quantitation of hydrocarbon fractions of similar toxicity and mobility characteristics. While EPA Compendium Method TO-15 is commonly used to assess gasoline-impacted sites, heavier fuel types may not be effectively characterized using whole air collection methods. The low vapor pressures associated with fuels such as diesel and other middle distillates may result in poor recovery and precision using Method TO-15 canister methodology due to condensation effects in the canister.
An alternative sorbent-based method based on EPA Compendium Method TO-17' is evaluated for TPH soil gas measurements, specifically at sites contaminated with middle distillate fuels. A sorbent-based approach offers the inherent advantage of trapping the compounds before condensation occurs. Various adsorbent materials are evaluated for retention of fuel-related target compounds. Results between soil gas measurements from co-located TO-15 canisters and TO-17 sorbent tubes are compared for several fuel types.
Evaluation of Sorbent Methodology for Petroleum-Impacted Site Investigations