ABSORBER INSTALLATIONS ON A LINER

The liner shown in the basic mechanism can be covered with an absorbent material. As the liner is everted into place, the absorber rolls out against the hole wall. The absorber is pressed firmly against the hole wall by the interior pressure of the liner. (Note that only 1 psi of excess pressure in the liner produces the same force/area against the hole wall as about 2 inches of lead lying on a table.). The flexible liner and absorber conform very well to the hole wall. By pressing the absorber so firmly against the hole wall, the absorber can wick up pore fluids from a medium of relatively high capillary tension. In fact, a very dry absorber can have a capillary tension of many bars.

The drawing shows how a continuous absorbent covering on the liner is rolled out against the hole wall. A variety of absorbent coverings have been used. Some were only short annular surrounds on the liner, attached to the liner with buttons. Others were patches of absorbent material. The most common is a continuous covering with wicking barriers of coarse nonabsorbent material dividing the tubular absorber into short pieces. The wicking barriers prevent the absorber from transporting contaminants very far along the hole. In that way, each section is a local sample of the available pore liquids.

In many cases, the absorbers become quite wet. As the liner is inverted from the hole, the absorbent material is rolled to the interior of the inverting liner. This prevents the absorber from contacting the hole wall at any other location than where it was initially placed. The absorber travels to the hole collar, well protected inside the inverted liner.

At the surface, the liner is often everted into a long, flat tubular sleeve of plastic film. The absorber is disconnected from the end of the liner. The liner is then inverted from out of the absorber. The absorbent covering is left flat in the tubular film, with little or no contact with the air. Elastic bands can then be wrapped on the tubular plastic to form "sausage link-like sections" of absorber sealed in plastic for analysis. If the contaminant was colored, it can be easily seen staining the white absorber. If the contaminant is radioactive, it can be scanned for a profile of the activity in the hole. The NAPL FLUTe system of color reactive mapping of NAPLs is a special kind of absorber.

The absorbent covering is most easily emplaced in the vadose zone in a stable hole. Air or water can be used as the pressurizing fluid. If a liquid is used, it should be tagged with a tracer/dye to assure that if any is absorbed in the cover, it is not mistaken for a pore liquid. As with other everting liners, absorber liners can be everted into passages in any direction, even vertically upward and around bends. Absorber FLUTe systems have been installed, using the duet technique, in a hole already sealed and supported by another liner (e.g., a 4 in. absorber liner into a hole sealed by a 6 in. liner). In most cases, the first larger liner was a Vadose FLUTe in use for gas sampling.

The absorber collection of vadose pore liquids has been done the most by Lawrence Livermore National Laboratory since 1991. Carl Keller and Brian Travis wrote a paper on the utility of absorber collection of vadose fluids. Comparisons of laboratory measurements were made with vadose flow model calculations for a variety of saturations and materials. That paper is in the proceedings of the NGWA 7th Outdoor Action Conference in Las Vegas, 1993. With the use of well-characterized absorbers, the weight gain of the absorber can be an indirect measure of the capillary tension of the formation.

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