Near-surface seismic reflection investigations at a groundwater contamination site
Levander, Alan R.
Doctor of Philosophy
A 3-D seismic reflection survey was conducted at a groundwater contamination site to adequately image the near surface (<20m) at a level of detail to enhance ongoing remediation activities at the site. The site, Operable Unit 2 (OU2), located at Hill Air Force Base in Ogden, Utah has been the subject of a continuing effort to remove dense nonaqueous phase liquids (DNAPLs), solvents and degreasers, which had been dumped into trenches at the site for eight years. Subsurface maps of the near surface geology, based solely on data from the over 200 monitoring wells drilled at the site, do not provide sufficient detail of subsurface features that trap these contaminants to conduct site remediation in a cost-effective manner. The target geologic feature for remediation, a paleochannel complex, under a surface layer of unconsolidated sands, silts and gravels, cut into a thick layer of clay. The paleochannel traps both groundwater and contaminants. The paleochannel was the focus of an earlier 2-D survey, demonstrating the viability of the site for seismic methods. Successfully imaging the channel profile in three places, results from the 2-D survey served as a testbed for planning for the 3-D survey. The 3-D reflection survey covered an area of 37 x 95m centered over the paleochannel. After data processing, the resulting seismic volume shows a paleochannel complex with two channels from the north merging into a single channel that spreads out across the southern portion of the survey. Intersecting the channel are two displacement surfaces, origins unknown, disrupting channel flow and altering the pattern of erosion and deposition. The resulting map shows the channel complex with depth to base clay varying from 6 to 18.33m. Vertical resolution of the depth-to-clay map is 1.25m (lambda/2). Stratigraphic analysis of the sedimentary package above the interpreted clay surface confirms the seismic interpretation. Comparison with results from a tomographic study (Azaria, 2003) and a VSP study (Gao et al., 2003) at the site confirm the reflection survey results.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation).
Geology; Geophysics; Environmental science; Environmental engineering