1887

Abstract

A controlled injection of perchloroethylene (PCE) into a sandy aquifer was undertaken to investigate the<br>effectiveness of ground penetrating radar (GPR) and time domain reflectometry (TDR) for monitoring and<br>detecting the subsurface migration of organic solvents.<br>Surveys were performed at regular intervals during the 70 hour injection and for 38 days following the<br>injection. Background (pre-injection) surveys were conducted to assist in the discrimination between features<br>caused by PCE and those due to natural geologic variability.<br>PCE was chosen because it is a typical member of a class of groundwater contaminants known as dense<br>non-aqueous phase liquids or DNAPLs. Similar to other DNAPLs, PCE has a low dielectric permittivity relative<br>to pore water, therefore PCE saturated soils can be expected to have higher radar velocities.<br>Time domain reflectometry probes were used to measure vertical profiles of in situ dielectric permittiiity.<br>Decreases in dielectric permittiiity of up to 50% were observed where PCE had pooled on low permeability<br>lenses.<br>Initially, GPR reflection events were detected from pooling of the DNAPL on low permeability horizons at 1 m<br>depth. At later times pools were observed on successively deeper horizons. Velocity pullup of the underlying<br>aquitard event was also observed.<br>GPR and TDR provide effective methods for monitoring the progress of PCE migration in a saturated sandy<br>aquifer. Reflections and dielectric contrasts from PCE pools are of such a high magnitude that they may<br>often be distinguishable from geology without the benefii of background data. Wiih background data, zones<br>of residual level PCE saturations are resolvable with GPR and TDR.

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/content/papers/10.3997/2214-4609-pdb.210.1992_037
1992-04-26
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.210.1992_037
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