Field determination of geological/chemical properties of an aquifer by cone penetrometry and headspace analysis.
1992
Chiang C.Y. | Loos K.R. | Klopp R.A.
The cone penetrometer with pore pressure measurements was first introduced in 1975. It is generally regarded in the geotechnical community as one of the most efficient tools for stratigraphic logging of soft soils. Recently, the conventional cone penetrometer has been coupled with a porous probe ground-water sampler for environmental applications. This coupled system was used to perform soil logging, collect ground-water samples, and evaluate hydraulic conductivity in an effort to determine the extent and preferential flow pathway(s) of a soluble hydrocarbon plume in a Texas aquifer. Ground-water samples collected by a porous probe sampler were analyzed for hydrocarbon content by a portable gas chromatograph with a photoionization detector (GC/PID) to characterize the extent of the soluble organic plume and provide a field evaluation of ground-water quality. Aqueous concentrations of hydrocarbons calculated from vapor headspace measurements by this technique were in good agreement with direct concentration measurements obtained in the laboratory using standard EPA ground-water analytical procedures. This field procedure makes it possible to efficiently use cone penetrometry equipment in less characterized areas allowing rapid delineation of volatile organic plumes by the headspace analysis. Interpretation of the cone penetrometer test data located a buried channel on the site aligned in an east-west depositional direction. To the north and south of the channel, the soils exhibited reduced hydraulic conductivity due to their respective soil type or depositional density. Analyses of ground-water samples collected from the area confirmed that soluble hydrocarbon migration was following the more permeable channel. In addition, depth selective ground-water sampling recorded sharp changes in the vertical concentration profiles indicating that macroscopic vertical dispersion may be negligible at this site.
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