You are here:
Final Project Report for the Development of an Active Soil Gas Sampling Method
Citation:
SCHUMACHER, B. A., J. H. ZIMMERMAN, J. ELLIOT, D. SPRINGER, B. HARTMAN, AND G. SWANSON. Final Project Report for the Development of an Active Soil Gas Sampling Method. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-07/076 (NTIS PB2007-112084), 2007.
Impact/Purpose:
Tetra Tech EM, Inc. was contracted by the U.S. Environmental Protection Agency (EPA) to quantitatively assess the effect of sampling procedures on soil gas sample results. Specifically, this investigation was designed to assess the effect of purge rate, purge volume, and sample volume (the principal parameters) on soil gas results and to develop technically defensible values or ranges of values for these parameters that can be incorporated into active soil gas sampling guidance. A number of research groups and local, state, and federal agencies have developed guidance concerning sampling and analytical protocols for active soil gas measurements with the overall objective of facilitating a technically correct approach for site investigations. However, the various guidance documents often omit prescribed ranges for the principal parameters, or if prescribed, lack a quantitative basis for the recommended parameter settings. This investigation was designed to evaluate the principal parameters over the range of values commonly cited in guidance documents and provide defensible recommendations for parameter settings. The experiments were conducted at Installation Restoration Program (IRP) Site 15 on Vandenberg Air Force Base (AFB). To provide data for this investigation, an array of 15 soil vapor sampling probes was deployed at IRP Site 15 above the larger of two plumes of trichloroethylene (TCE) in the groundwater. Three experiments were conducted for this investigation. The first consisted of collecting soil gas samples using purge rates ranging from 100 to 2,000 milliliters per minute (ml/min) while holding the purge volume and sample volume constant at 3 system volumes and 60 ml, respectively. The second consisted of collecting soil gas samples after purging 1 to 100 system volumes from the probes, while holding the purge rate and sample volume constant at 200 ml/min and 60 ml. The third experiment consisted of collecting samples with volumes ranging from 25 to 6,000 ml, while holding the purge rate constant at 200 ml/min. The results of the purge rate experiment show a pronounced increase in the measured TCE concentration at purge rates of 100 ml/min to 200 ml/min followed by a modest trend of increasing measured concentrations with increasing purge rate. However, the observed variability in measured volatile organic compound (VOC) concentrations would not generally be considered significant from a site characterization or vapor intrusion perspective. Based on the data from this investigation, it appears that purge rates of 200 to 500 ml/min should be recommended. The results from the purge volume experiment indicate there was a statistically significant positive correlation between the measured TCE concentrations and purge volume, with concentrations typically more than doubling over the range of purge volumes tested. The effect of purge volume on the measured VOC concentrations was more pronounced than the effect of purge rate; however, this variability may not be significant in terms of site characterization. The data indicate that varying purge volume from 1 to 5 system volumes has relatively little effect on the sample results; however, increasing purge volume above 5 system volumes appears to result in somewhat higher measured TCE concentrations. These experimental data suggest that purge volumes of 2 to 5 system volumes are most appropriate. Measured TCE concentrations were observed to increase with increasing sample volume from 25 to 1,000 ml, but then drop off in the 6,000 ml samples. This observation is significant as the 6,000 ml sample size is commonly used to achieve very low detection levels with EPA method TO-15; however, the drop in measured TCE concentrations at a 6,000 ml sample volume suggests that the low detection levels achievable with large sample size may need to be balanced against the risk of over-purging. Based on the data obtained from this investigation, it
Description:
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the nation's natural resources. Under the mandate of national environmental laws, the EPA strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this mandate, the EPA's Office of Research and Development (ORD) provides data and scientific support that can be used to solve environmental problems, build the scientific knowledge base needed to manage ecological resources wisely, understand how pollutants affect public health, and prevent or reduce environmental risks. The National Exposure Research Laboratory (NERL) is the Agency's center for investigation of technical and management approaches for identifying and quantifying risks to human health and the environment. Goals of the laboratory's research program are to (1) develop and evaluate methods and technologies for characterizing and monitoring air, soil, and water; (2) support regulatory and policy decisions; and (3) provide the scientific support needed to ensure effective implementation of environmental regulations and strategies. Tetra Tech EM Inc. prepared this Project Report for NERL to document the results of an investigation into the effects of purge rate, purge volume, and sample volume on soil gas sample results. Field work for this investigation was conducted during October 2006 at Vandenberg Air Force Base (AFB)Installation Restoration Program (IRP) Site 15. Vandenberg AFB is home to the U.S. Air Force Western Missile Test Range and is headquarters for the 30th Space Wing, which manages Department of Defense space and missile testing, and placing satellites into polar orbit from the West Coast. The Vandenberg AFB IRP, overseen by Mr. Michael McElligott, supported this project by providing access to IRP Site 15 to conduct the testing, facilitating and expediting dig permit reviews, and providing logistical support during the field sampling activities.