Abstract: In an in-ground vapor monitoring device for use with a conventional, hollow stemmed drill rig including a novel swivel assembly which attaches to a drill rod and which has a central passage formed therethrough. A fluid outlet port and an outlet channel joining the outlet port and central passage are formed in the swivel assembly. The device further includes an auger having an inlet port formed on its operational end which is connected by an inlet channel to a central passage. A vapor filter is disposed in the inlet channel. By applying an external vacuum source, vapor from a borehole is drawn off through the inlet port and filtered by the vapor filter. A gas chromatograph or other vapor analyzer is connected to the outlet port to analyze the drawn off vapors. The novel features of the auger portion of the device may be provided in the form of an auger plug engageable with a conventional auger.