Dye Tracing Survey at Poitiers Experimental Hydrogeological Site
Dye Tracing Survey at the Experimental Hydrogeological Site (SEH) at Poitiers
Introduction
Within the framework of the “Karsto’gen” Dye Tracing Survey project, led by CPGF Horizon and in partnership with the University of Poitiers and Valeport Water, the following objectives have been defined:
- To verify and confirm the quality of in-situ borehole measurements using Hyperion fluorometers developed by Valeport Water.
- To verify the transfers of water masses between the various karst horizons developed within the Aalenian and Bajocian limestones on the Le Deffend experimental platform (France).
Protocol
To verify the points mentioned in the introduction, a research methodology was defined at the University of Poitiers’s Le Deffend site, where 42 boreholes, drilled from 2002, have allowed two Poitou regional tables to be studied. This protocol includes the completion of a convergent radial tracing campaign with a total of six field fluorometers. The convergent radial tracing technique involves constant pumping within a central well with a parallel injection of the tracer, in this case, uranine, into a piezometer. Valeport Water’s Hyperion fluorometers were then installed at various depths within the piezometers between the injection and pumping stages.
Upstream from the dye tracing sites temperature, conductivity and flow, directly within the boreholes were logged in each piezometer. These data helped assess the scale of the flows between the lower karst and the upper karst levels and so allowed hypotheses to be drawn regarding the transfer of water masses; this in turn helped refine the tracer dye injection and fluorometer positioning for future investigations.
Conclusion
CPGF HORIZON, with the assistance of the University of Poitiers and Valeport Water, has established a research and development programme. The data acquired using Hyperion fluorometers allow these karst exchanges to be described. The knowledge acquired during this study is designed to facilitate future searches for drinking water on the Poitou threshold from an operational point of view.
The protocol for this and future surveys were extended to include a calibration process for all the fluorometers used, using the same water samples collected from the survey site. In this way, the specific qualities of the water can be taken into consideration. pH was thought to be of particular importance.