C. Analysis of temperature variations among the 30 thermistors allows determination of flow rate and direction in three dimensions. The velocity meter is permanently installed in saturated, porous, unconsolidated media at the point where the ground water flow is to be determined. This is currently accomplished using a hollow-stem auger drilling process. Natural backfill must collapse around the probe as the augers are removed to insure intimate contact between the formation and probe. A 2.5 cm diameter PVC conduit which connects to the device and extends to the surface protects power and data wiring.
Orientation is accomplished through alignment of the data wiring conduit with an a known azimuth.
Above-ground support for the velocity meter includes power supply and data acquisition equipment. Power requirements for the probe depend upon aquifer characteristics and typically range from 60 to 120 watts. Data acquisition equipment is manufactured by Campbell Scientific Inc. and includes a CR-10 datalogger, an AM416 4x16 relay multiplexer, a data storage module, and a MD9 serial interface module. Once installed, the heater within the probe is turned on to stabilize the temperature of the surrounding aquifer. Temperature data from the time period between 0.5 and 3.5 hours after initial heater start-up is used to produce a calibration file that adjusts for the influence of the thermal properties of media surrounding the probe.