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MINI FLUTe™
The purpose for this system is to obtain multi level water or pore gas samples from the inexpensive cone penetrometer or Geoprobe hole. The characteristics are:
- Installed through the interior of driven casing or rods
- Seals the hole with a pressurized liner (usually water filled)
- Provides up to three sampling elevations in the skinny hole
- Removable by inversion of the liner from the hole
The in-place screen/liner geometry is shown in the drawing. The liner contains several sealed sleeves with perforations through the liner from the sleeve interior to the formation
The liner is installed in much the same manner as the NAPL FLUTe system (see Emplacement of liners via push rods). ). The liner is dilated in the hole as the rod is withdrawn. The trick is to dilate the liner in the hole, supporting the hole wall, without dilating the liner in the rod, which would cause prohibitive friction. Once the rod is removed and the water filled liner is in position, the mini wells (1/2" flush joint casing with screen at the bottom) are inserted into the sleeves. This allows the mini wells to be pushed into the sleeves to the depth of the perforations. Once in place, a ball is dropped into the mini well to serve as a check valve at the top end of the screen. A central tube is then lowered into the mini well. The mini well can be pumped by applying air pressure to the interior of the mini well to force the water up the central tube. When the pressure is dropped, the mini well refills from the formation via the perforations and the screen. The screen is surrounded by a permeable mesh to allow water to flow into the sleeve and enter the screen slots along the entire circumference of the mini well. The formation water is not in contact with the water that fills and pressurizes the liner.
The completed well system (without the surface vault) is shown in the photo. The water level can be tagged in each mini well. The wellhead assembly is typically encased in a subsurface vault built around the liner.
To remove the Mini FLUTe system, the mini wells are removed from the sleeves, and the central tube is pulled from the liner, which causes the liner to invert and to be peeled from the hole.
In the limited situations where the mini well screen has matched the screen of a normal water well nearby (5 ft distant), the mini well produced the higher level of carbon tetrachloride. An advantage of this approach is that the hole produced by the push rod is sealed with a continuous pressurized liner. This is a more reliable seal than that obtained by trying to fill the slender annulus in such a small hole with a pumped fill material. Heaving sands are prevented from flowing upward into the rod by the water in the rod and by the dilating liner. Since the liner dilates as the rod is being pulled, the hole wall is supported against slough. In some installations, the liner is later filled with a Bentonite slurry via the central tube that is used for water injection in the emplacement procedure (see NAPL FLUTe for the emplacement procedure for the liner). The Bentonite fill provides the same excess head as the water fill to seal the liner against the hole wall.
A paper describing this installation procedure and the nearby water quality test results from other wells is available at Publications.
A Single well version, which uses the same emplacement procedure is available. The single well system is complete as installed in the rod and the installation is finished when the rod is pulled. The single well system is fully removable by simply pulling up on the central tube which peels the liner from the hole by inversion.
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