Vapor intrusion investigations often struggle to pinpoint the true subsurface source, especially in urban environments where access is limited by infrastructure and multiple neighboring establishments have engaged in operations that make them a potential suspect. At a state government office where gasoline vapors were making workers ill, Aestus was brought in after direct push borings and a vapor recovery trench failed to identify the origin of the vapors or adequately mitigate the problem.
Aestus utilized their GeoTrax SurveyTM high-resolution electrical resistivity imaging across the site to identify hollow stem auger drilling targets beneath a caliche zone at the depth of direct push refusal (see second two graphics below). The drilling targets confirmed the presence of fugitive LNAPL “blobs” below the direct push refusal zone and identified a previously unknown fuel storage tank source near an adjacent maintenance building. The pathways of vapor migration were mapped and the updated Conceptual Site Model (CSM) provided a defensible, data-supported explanation for observed indoor air impacts.
A major advantage of GeoTrax SurveyTM was the ability to collect data in tight corridors between buildings (field conditions pictured below), providing datasets in key areas that would have been infeasible to obtain with other methods. The results eliminated guesswork, reduced unnecessary sub-slab testing, and helped the client move toward regulatory closure.
