Summary
Attributes analysis is a commonly used data processing and interpretation technique in seismic exploration. The purpose of this study, attribute analysis is proposed, developed and implemented for GPR data to reveal detailed information in detecting the presence of hydrocarbon contaminants. One known hydrocarbon contaminated sites were investigated in order to verify its feasibility. GPR profiles acquired from field, in conjunction with actual field sampling along with the interpretation of attributes are demonstrated in this study. Finally, a conceptual site model of LNAPL contamination is illustrated to explain the observation from attributes. This study gives a good example that thin beds caused by floating LNAPL could be a useful signature for detecting hydrocarbon contamination.
Introduction
Hydrocarbons whose density is lighter than water (~1 g/cm3) would be considered as LNAPLs (Light Non Aqueous Phase Liquids). Once LNAPL is released into subsurface, it will gently migrate downward until reaching a relative low permeability layer. In most cases, the accumulation, concentration and the migration of the LNAPL occurs on top of the groundwater table or within the capillary fringe where the density of the pore fluid (groundwater) is larger than LNAPL.
Traditionally, environmental site investigation relies heavily on reconnaissance and the observations from limited sampling points to determine the spatial distribution of the possible contaminated area. Without densely sampled, it is usually unable to provide a clear range of the contaminated area. The important issue is how to maintain a good balance among the investigation purpose, field operation quality control and budget. Quality and efficiency of the investigation will largely affect upcoming contamination control programs and remediation processes. Application of geophysical methods to detect.
hydrocarbon contaminant started from early 1990s (Daniels et al., 1995; Campbell et al., 1996 and Orlando, 2002). Olhoeft (1992) pointed out that the weak geophysical contrast of contaminants against background soil and rock impose a potential difficulty to discriminate the contaminated area from uncontaminated one. And the more serious concern is that the hazardous concentration of the contaminant for human is always very low (from ppm to ppb). Even through geophysical methods, such as seismic and electromagnetic methods, can detect the contaminant, however, the detection limit may not be sufficient enough for direct identification, especially for rapid site investigation purpose.
