Development and application of flow meter system with single well for velocity and direction of groundwater flow

For the confirmation of safetyness for the land disposal of radioactive wastes, recently, it becomes more important to evaluate the groundwater flow in detail. We have developed a groundwater flow meter to measure simultaneously the velocity and direction of groundwater flow by means of detecting the electric potential difference between the groundwater to be measured and the distilled water as a tracer in a single well. In surveying the groundwater flow by tracking the tracer movement, it is important to clarify the influences of a borehole to the groundwater flow field inside and outside the hole bored in surveyed underground. In this paper, we introduce the outline of the groundwater flow meter system developed by us and describe the laboratory test results for the basic measuring accuracy in relation with the structure of measured well. On the other hand, the laboratory tests for the tracer transport with groundwater flow across a cylindrical borehole in the homogeneous porous media and analyses for the groundwater flow and fracer dispersion were performed. From the comparison between the observed and analyzed results, the good accuracy of this measuring system was identified and that the remarkable differences of groundwater flow velocity between inside and outside of the well could be quantitatively represented. Furthermore, we apply this groundwater flow meter system to the several types of in-situ surveys such as shallow underground, fractured rocks and so on, so it is made clear that this system can be practically used to measure the groundwater flow direction and velocity as low as order of 1x10-6 - 10-7 cm/sec. (author)