Considerations on the hydrogeological functioning and on the vulnerability of groundwater to contamination in Sierra de las Nieves (Málaga) during a dry-period tracer test

A tracer test during low-flow conditions was carried out in the karstic aquifer of Sierra de las Nieves (Málaga) in order to assess its hydrogeological functioning and vulnerability to contamination. Two kilogrammes of Eosine were injected in an active siphon located in the Sima del Aire cave shaft (-640 m) at the end of August 2003. The springs were sampled until November 2003. For more than 50 days, the tracer was not detected at any of the springs. After several rainfall events in October 2003, a signal was observed in the two Río Grande springs. The first arrival of Eosine appears before the increase of spring discharge and the dilution effect of the most important rainfalls (86 mm, October 25th). The calculated groundwater velocities (below 4 m/hour) are not representative of the dry period because rainfall forced the Eosine transport. However, they give an idea about the long residence time if a contamination event occurs during low-flow condition