Packing the Experiment

The piezometers consist of 1/8 inch O.D. tubes which are passed through the plexiglass wall of the tank. The hole is created in the plexiglass with a drill and is sealed after the tube is passed through with silicon glue. On the exterior of the tank, the 1/8 inch tube is unioned with 1/4 inch O.D. tube which can be run either to a manometer board or to a high precision pressure transducer. It is estimated that the precision of water level measurements is approximately 0.5 mm on the manometer board (using new tubing), but that this precision decays with time as biological growth changes the inner surface properties of the tube (thereby influencing surface tension and observed water level in the manometer). Using a high precision pressure transducer, we can measure head with a precision of approximately 0.1 mm, but must be careful of electrical and instrument drift both with time a temperature. The impact of temperature is reduced by placing the entire experiment in a climate controlled chamber.




One concern is always the impact of the tube on the flow field. This figure shows the interior wall of the tank with all piezometer tubes installed. Each tube extend for approximately 5 mm into the tank. Our initial analysis of this density indicates that these tubes do not significantly influence the flow field. Close agreement between the heads measured in these tubes and the heads predicted using MODFLOW support this conclusion.

Also included for this experiment are over 300 pairs of platinum wires. Once again installed through the wall of the tank, these wire pairs allow estimation of the concentration of ionic species such as chloride. Calibration of these "electrodes" is performed in situ.