In September/October 2000 the equipment for the control measurement of the high-pH fluid injection in the dipole flow field were assembled and tested. Consequently, some modifications to the measurement units had to be made before the final experiments could start. The preparations for the mixing of the injection fluid were carried out in early March 2001 and the final dipole was established.

The layout of the experimental site can be seen below.

A series of tracer tests has been carried out at the HPF site to characterise changes to the properties of the shear zone. This has involved injection of radioactive (¹³¹I, ²⁴Na, ⁸²Br) and non-radioactive (uranine dye) tracers in parallel with injection of a high pH solution which aims to represent a "young" cement fluid. These tests have greatly improved the understanding of the shear zone and have provided raw data for input into modelling codes. In conjunction with the tracer measurements, on-line monitoring of Eh, pH, EC and temperature are also carried out. Furthermore, sampling of all intervals, with focus on the shear zone intervals are carried out every two to three months for hydrochemical and tracer analysis.

Chemistry box inflow. Records Eh, pH and EC

These tests have also led to developments at the HPF site as it is a technical challenge to keep these operations running due to problems caused by the corrosion of equipment and clogging of injection extraction lines by the high pH fluid.

The HPF site at the GTS was upgraded in preparation for the final tracer test. This included new data acquisition systems and replacement of pumps, valves and tubing.