MAPPING OF DNAPLs FREE PRODUCT (undissolved phase)

A FLUTe technique, developed in concert with the Savannah River Site, is a color reactive liner that changes color dramatically in the presence of a variety of DNAPL substances. The mechanism is described at NAPL FLUTe. The color reactive cover on the outside of a carrier liner (i.e., a blank liner) can be emplaced in an open borehole or via the interior of several push rods or driven casing methods. The "trick" of this method is that the liner is removed by inversion(peeling) of the liner, with the stained cover, from the wall of the hole. The cover is thereby carried to the inside of the inverting liner where it is protected from any other contact with the hole wall as the liner rises to the surface. The stain pattern on the cover provides the exact location of the undissolved DNAPL in the hole.

This technique has been used at many sites in many States. The installation into core holes is particularly easy. The dye which is used has been changed from the toxic Sudan IV to a non-toxic substance of equal performance. Since the cover is hydrophobic, the contaminant is wicked into the cover, transporting the telltale dye with it.

In some cases, the free product does not mobilize the dye, but is still wicked into the cover and provides a dark stain and strong odor for ease of "reading" the cover.

Wicking of gasoline is dramatic, but because of the wicking process, the liner stain is not a particularly good indication of the thickness of thin layers of gasoline.

Most situations yielding strong results are conductive sands overlying clay or silt layers that cause the DNAPL to pond on the fine grain layer. Over spectacular results have been obtained in fractured rock where the DNAPL is lying in the fracture.

The color reactive material has been used alone as an indicator of DNAPL distribution in core by laying the core on top of the reactive material as the core is extruded from the core barrel. However, if the core is exposed to the air, many solvents are immediately lost and may not reach the reactive material. A much more successful use has been to sandwich a strip of the reactive cover in the center of a split core sample. Even more successful is using a tubular bag of the cover material to surround a sonic core sample as it is extruded from the core barrel. Sonic Core NAPL FLUTe Procedure (pdf)

Note, this technique is not intended to indicate the presence of the dissolved phase.

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