The permeable-membrane method of passive soil-gas collection

An inexpensive passive soil-gas survey technique was developed to examine the distribution of petroleum-related volatile organic compounds in the shallow ground water at a petroleum tank farm in Hanahan, South Carolina. The technique consisted of enclosing empty, open test tubes in sealable polyethylene bags, thus creating a permeable membrane over the open end of the tube. The tubes were buried, open-end downward, in an array encompassing areas of interest at the site. The tubes remained buried for several days. Upon recovery of each tube, the trapped vapor was collected by syringe through the membrane (bag) and immediately analyzed in the field using a portable gas chromatograph. Comparison of the results to concentrations of VOCs in ground water and to the distribution of toluene obtained by using passive soil-gas samplers containing activated carbon indicated that the permeable-membrane method can be an effective, cost-efficient tool in locating ground-water contamination. The use of 40-mL VOC vials that can be capped upon recovery instead of the test tubes enhances the versatility by allowing the vapors to be analyzed either upon recovery or days later