mGCW Technology for Remediation of Groundwater Containing Chlorinated Hydrocarbons and Heavy Metals:
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In addition to establishment of differences in potentiometric head via function of the mGCW, it is important to document the direction of vertical and horizontal groundwater movement. It is equally important to measure the in situ velocity of groundwater movement in order to validate numerical calculations of groundwater circulation time.

Perhaps the most timely, accurate, and cost-efficient means of generating these data in the field employs the use of in situ groundwater velocity sensors (ISGV). As described by Ballard (1996) and Pacific Northwest National Laboratory (1996), these in situ probes use a thermal perturbation technique to directly measure the three-dimensional groundwater flow direction and velocity inunconsolidated, saturated, porous media. The probe consists of a cylindrical heater about 30-inches long by 2-inches in diameter with an array of 30 calibrated temperature sensors located on their surface. The probes are buried in the ground and surrounded by the natural formation. Once positioned, a heater is activated and the sediment and groundwater surrounding the probe are warmed 20 to 30C above ambient groundwater temperature. In the absence of groundwater flow past the sensors, the temperature distribution on the probe's surface is independent of azimuth and symmetric about the vertical midpoint of the probe. When there is flow past the probe, the temperature distribution is perturbed as the heat emanating from the probe is advected by the moving fluid. Sensors monitor continuously and record to a central data acquisition system. PC-based software converts the measured probe surface temperature distribution into flow velocity i.e., three-dimensional magnitude and direction.

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