Abstract: A reusable modified helium shroud soil vapor sampling system with an in-line helium detector includes a reusable, portable, sampling platform including a chimney attachable to a well head. The sampling platform includes an area for placement of at least one disposable three-way valve, at least one flow controller, at least one sampling can, an ambient helium detector, a line coupled to a helium tracer source, at least one vapor sampling line coupled to a soil vapor sampling well at a predetermined depth, and at least one purge line coupled to at least one purge source. An in-line helium detector is coupled between the at least one purge line and the at least one purge source, and a flexible collapsible shroud cover is configured to optimally seal a volume of helium between the shroud cover and the sampling platform.