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Application of the GFV-System on the job
The measuring equipment is carried to each individual site by a transporter. It includes any tools and instruments required for measurement as well as the electricity supply, if
not provided by the customer. The work is carried out by a project engineer and a technical engineer.After setting up the measuring system, the probe is installed at the defined depth and fixed with
packers. Meanwhile, the screens in the monitoring well are sifted through and the well casing junctions or transitions are located (fig. 1 and 2). This ensures the positioning of the measuring sections in clean parts of
the screens. Particulary dirty segments which are not suitable for measuring are shown on computer pictures. The instalment is followed by a calming phase in order to re-establish the natural hydraulic
conditions and temperatures. Subsequently, the first measuring series starts. One series consists of a permanent flow measurement in a fixed depth over any desired time period. By simultaneously taking measurements in
two independent sections of the probe, the data are statistically secured. Video pictures show the groundwater particles in suspension (fig. 3). The pictures are transferred to a computer. A special programme calculates
and updates the data of the current in the screen in one-second-intervals. The data are shown in graphics.
Fig.: realtime results shown in graphics during the measuring phase
Duration of measurement:
The application, including mounting and dismounting, takes at least 2.5 hours per monitoring well, dependent on the flow conditions and the
number of measuring series per monitoring well. With very instationary flow conditions or very low velocities it might be necessary to extend the measurement period in order to obtain valid evidence on flow direction
and velocity.The Measuring Probe:
The GFV measuring system registers the current in the center of the screen and thus along the median stream line within the well. The
measurement is carried out in two open measuring sections of the GFV-Probe. The sections are kept in a distance of about one metre separated by a packer (fig. 5), i.e. the measurements are taken in two
different places at same time. Thus, the data guarantees the quality of the figures and allows to draw conclusions on diverse influencing factors as described above.
In addition, a radial camera integrated in the probe enables to check the filter screens prior to measurement in order to stay away from dirty well casing junctions while measuring.
Fig.: equipment, staff, and control-unit in action
Preconditions:
The GFV measuring system is usable in 4- and 5-inch monitoring wells.
Other gauge diameters on request.
The well screens and the well casing junctions must be clean.
The parts of the screen where the measuring sections of the probe will be
installed are to be examined and documented in advance. In dirty parts of the screen no measurements are carried out, for the flow conditions would be affected and consequently the measuring data, the
specifications of the monitoring wells are to be provided in advance.Since the GFV measuring system works without adding artificial flow markers, an official permit for the application is not required.
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