Advanced Passive Soil Gas Sampling  Increases Accuracy in Vapor Intrusion Investigations
James E. Whetzel, W. L. Gore and Associates, Inc., Elkton, MD
Hilary Trethewey,W. L. Gore and Associates, Inc., Elkton, MD 
Jay Hodny, W. L. Gore and Associates, Inc., Elkton, MD

Advanced Passive Soil Gas Sampling  Increases Accuracy in Vapor Intrusion Investigations

James E. Whetzel, W. L. Gore & Associates, Inc., 100 Chesapeake Boulevard, Elkton, MD 21921, Tel: 410-392-7600, Fax: 410-506-4780, Email: jwhetzel@wlgore.com
Hilary Trethewey, W.L. Gore& Associates, Inc., 100 Chesapeake Boulevard, Elkton, MD 21921, Tel: 410-392-7600, Fax: 410-506-4780, Email: htrethew@wlgore.com
Jay Hodny, W.L. Gore& Associates, Inc., 100 Chesapeake Boulevard, Elkton, MD 21921, Tel: 410-392-7600, Fax: 410-506-4780, Email: jhodny@wlgore.com

Investigating a contaminated site requires obtaining enough data of sufficient quality to achieve an understanding of all routes of potential exposure. Vapors emanating from subsurface contamination can be a risk to human health. Therefore, consideration of the potential for vapor intrusion into buildings is an essential part of any site investigation. Soil gas sampling directly measures contaminants in the vapor phase fluxing from a source to the surface and is one of the preferred means to assess the vapor risk. To assess the potential of a vapor risk adequately, soil gas samples must be taken at locations that will reflect the true risk to current or future occupants.

Since soil is usually heterogeneous in distribution, typically multiple soil gas samples are required to make risk decisions. The more samples collected, the higher the certainty in the decisions being made. Budget constraints require that the number of samples be minimized. Thus an uncomfortable polarity exists between costs and need for certainty. 

Performing a soil gas screening survey using a passive sampler is a cost effective means to obtain a rich data set. Using calculated soil gas concentrations can provide not only an accurate picture of subsurface conditions, but data can also be used to differentiate areas of little to no concern from areas of significant VI concern.

This presentation will describe the process used to calculate concentration values from passive vapor results, and show comparative results between one passive soil gas sampling and several active sampling techniques. Passive soil gas sampling increases the accuracy of a site investigation while reducing investigative costs.

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