No abstract

Recent advances in seismic reflection amplitude analysis (e.g., amplitude versus offset-AVO, bright spot mapping) technology to directly detect the presence of subsurface DNAPL (e.g., CCl4) were applied to 216-Z-9 crib, 200 West Area, DOE Hanford Site, Washington. Modeling to determine what type of anomaly might be present was performed. Model results were incorporated in the interpretation of the seismic data to determine the location of any seismic amplitude anomalies associated with the presence of high concentrations of CCl4. Seismic reflection profiles were collected and analyzed for the presence of DNAPL. Structure contour maps of the contact between the Hanford fine unit and the Plio/Pleistocene unit and between the Plio/Pleistocene unit and the caliche layer were interpreted to determine potential DNAPL flow direction. Models indicate that the contact between the Plio/Pleistocene unit and the caliche should have a positive reflection coefficient. When high concentrations of CCl4 are present, the reflection coefficient of this interface displays a noticeable positive increase in the seismic amplitude (i.e., bright spot). Amplitude data contoured on the Plio/Pleistocene-caliche boundary display high values indicating the presence of DNAPL to the north and east of the crib area. The seismic data agree well with the well control in areas of high concentrations of CCl4.

No abstract

No abstract

Field experiments were conducted to determine the location and distribution of subsurface DNAPL contamination at two DOE sites by use of two-dimensional, high-resolution seismic reflection surveys and borehole geophysical data. These studies make use of seismic reflection amplitude versus offset (AVO) technology to directly detect the presence of subsurface free-phase DNAPL.The research was conducted at Savannah River Site, SC and Hanford Site, WA. At each of these sites research consisted of site evaluation, seismic model studies, seismic acquisition, processing, and interpretation. The seismic model studies were undertaken prior to field acquisition to determine the likelihood of an AVO response from the DNAPL. The full Zoeppritz equations were used to create the model responses.At M-Area, Savannah River Site the model data show that at the base of the DNAPL plume the seismic amplitude should flip polarity on the far offsets (Class 2 AVO). The 2D seismic reflection field data processed into near and far offset stacks indicate such anomalies occur at the depth where the known DNAPL occurs. At the 200 West Area, Hanford Site the DNAPL is suspected to pool at two different stratigraphic intervals. The model data show that at the upper interval, the Hanford Fine/Plio-Pleistocene boundary, amplitude should decrease along the boundary if DNAPL is present (Class 1 AVO anomaly dim-out). At the lower boundary the models show that, if DNAPL is present, the seismic amplitude should become very negative (Class 3 AVO bright spot). A series of 2D seismic lines were acquired and processed. In the areas where DNAPL was suspected to occur (high concentrations measured in wells) seismic amplitude was found to decrease dramatically along the Hanford Fine/Plio-Pleistocene contact and along the Plio-Pleistocene/caliche contact the seismic amplitudes became even more negative consistent with the model study.