A borehole geophysical method for detection and quantification of dense, non-aqueous phase liquids (DNAPL) in saturated soils

To test the method, a field site was selected that is known to be heavily contaminated with DNAPL, principally trichloroethylene (TCE). The site is on a large barrier island complex in the southeastern US. The site stratigraphy consists of about 15 m of sands, silts and minor clay, with silt content generally increasing with depth. Boundaries of finer-grained soils delineated by cross plots of CPT variables are present at elevations of − 2.4, − 5.5, − 8.9, and − 9.8 m. Calculated fractional DNAPL, the DNAPL volume over total volume, shows peaks at elevations of − 2.4, − 5.5, − 9.1, and − 9.8 m, near the tops of the finer-grained units. Fractional DNAPL volume averages about 0.12, with maximum values of about 0.25. Porosity ranges from about 0.3 to 0.55, averaging 0.44. DNAPL saturation is the DNAPL volume divided by pore volume, and is a measure of the volume of available pore space occupied by DNAPL. The highest DNAPL saturation values are near the tops of the finer-grained layers. DNAPL saturation averages about 0.25 in the contaminated zone, with maximum values of about 0.45. The method shows significant promise for quantifying DNAPL volume and saturation using cone-penetrometer testing, making it very suitable for saturated, unconsolidated soils contaminated with residual DNAPL.