Using Integrated Radar/Seismic Datasets To Detect and Characterize DNAPLsEPA Grant Number: U915913
Title: Using Integrated Radar/Seismic Datasets To Detect and Characterize DNAPLs
Investigators: Franklin, Jonathan B.
Institution: Stanford University
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $102,000
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Geology , Academic Fellowships , Ecological Indicators/Assessment/Restoration
Dense nonaqueous phase liquids (DNAPLs) are a common class of industrial contaminants including a host of toxic halogenated compounds (trichloroethylene [TCE], tetrachloroethylene [PCE]). Although direct sampling methods for quantifying dissolved DNAPLs in groundwater are well established, the remote detection of free-phase DNAPL bodies is a challenging task for current geophysical techniques. Ground-penetrating radar (GPR) has been used successfully in the field to image the spatial evolution of PCE bodies in a sandy aquifer. However, dielectric constant is not a unique indicator of the presence of DNAPLs, making quantitative estimation of contaminant saturation using only GPR difficult.
The objective of this research project is to explore the feasibility of detecting and characterizing free-phase DNAPLs using a combination of GPR and seismic methods. The integration of radar data with borehole and surface seismic surveys may provide a way to resolve contaminant signature uniqueness. The project consists of experimental and theoretical work on the dielectric/acoustic properties of DNAPL saturated sands, numerical studies including examination of predictive modeling and integrated seismic/radar tomography, and the analysis of field data collected at the former Department of Energy’s Pinellas site with the objective of successfully imaging a known region of DNAPL contamination. The Pinellas data set includes multiple crosswell seismic/radar transects with cone penetrometer testing (CPT) data and extensive core samples to constrain lithology.
I have performed laboratory experiments to confirm and quantify the dielectric and acoustic signatures of DNAPLs in unconsolidated sediments. Two synthetic sands and four natural aquifer samples from Pinellas were used to test existing constituitive relationships. TCE was used as the saturating fluid. Preliminary experimental results suggest that the joint seismic/dielectric signature of TCE can be described by a combination of Gassman fluid substitution (for seismic properties) and a three-phase complex refractive index method relationship (for radar properties). Continuing research will focus on integrating the results from the core-scale measurements with the site-wide crosswell tomography and logging datasets collected previously.