TRACER TEST AT EL BERROCAL SITE

Tracer tests provide highly valuable information about the transport p roperties of saturated rocks which is essential to the characterizatio n of a potential radioactive waste repository site. In the frame of El Berrocal project, a set of tracer tests was performed in a complex ge ometry of inclined boreholes, combined with highly fractured transmiss ive zones. The aims of the tracer test programme were to gain experien ce, knowledge and insight into field transport experiments. To achieve this a detailed programme of new instrumentation design, site charact erization and laboratory tasks was developed. For field monitoring a n ew electronic system was developed. The system is able to measure up t o 256 parameters per borehole, with surface equipment to control pumpi ng rates and physical and chemical parameters at both injection and ex traction boreholes. The experiments progressed from single borehole di lution tests under both natural flow and forced gradient conditions to convergent flow tracer tests. Dilution tests helped to discriminate t he most suitable borehole sections at which to inject tracers. The tra cers were selected by the results of the laboratory programme. Uranine (fluorescein), DTPA-gadolinium (diethylenetriaminopentacetic acid, ga dolinium (III)), and deuterium were injected simultaneously in one bor ehole section and recovered at another borehole 20 m away, pumping at a flowrate of 0.1 1 min(-1). First results showed a thickness porosity of 1.2 X 10(-3) m and a longitudinal dispersivity of 17.0 m using ura nine data acquired over a period of 4 d, at which point the recovery c oncentration had reached a maximum. However, gadolinium and deuterium appeared to travel faster, arriving at peak values after only 2 d of i njection. (C) 1997 Elsevier Science B.V.