Delineation of Near-Surface Preferential Pathways of Contaminant Transport within the Unsaturated Zone Using Soil-Gas: A New Method for Hydrogeological Site Characterization and Evaluation

Abstract

Abstract. Preferential pathways for contaminant transport between the ground surface and the underlying watertable have been identified by injecting a gaseous-phase tracer and subsequently sampling for the tracer in numerous locations. Zones of anomalously higher tracer concentrations constitute zones in which preferential gaseous transport occurs from a deeper injection well to a sampling point located directly below the surface of the ground. Sulfur hexafluoride constitutes the gaseous tracer. Injection and subsequent sampling were accomplished with Paradise Creek Industries Soil-Gas Probes. Samples were analyzed on-site with an SRI 8610 gas chromatograph equipped with an electron capture detector. The results of the test identify two preferential pathways for gaseous transport that connect the ground surface of the site to the underlying aquifer. The presence of both pathways was confirmed by drilling.