Stefano Palpacelli

A DNA tracer used in column tests for hydrogeology applications

Tracing techniques are commonly used to investigate groundwater quality and dynamics, as well as to measure the hydrogeological parameters of aquifers. The last decade has seen a growing interest in environmentally friendly tracers, including single-stranded DNA molecules. In this study, an electrolytic tracer and a synthetic DNA tracer are comparatively evaluated in laboratory scale tests to assess their potential application in field studies aimed at investigating groundwater environments. A real-time quantitative Polymerase Chain Reaction assay was developed and optimized to detect and quantify the DNA tracer, while tracer column tests were performed to investigate the DNA tracer behavior and to compare it to the electrolytic tracer. The results show that the DNA tracer has an almost pure convective flow, while the KCl tracer experiences dispersive behavior. The tracing method proposed can be applied in hydrogeological field studies involving calcareous fractured rock systems, with the DNA tracer particularly suitable in tracing karst systems, which are often characterized by several conduits of flow. To test the DNA tracer in operation, a preliminary test was conducted in the field.

DNA and fluorescein tracer tests to study the recharge, groundwater flowpath and hydraulic contact of aquifers in the Umbria-Marche limestone ridge (central Apennines, Italy)

The purpose of this paper is to highlight the hydrogeological contact among aquifers in karst and fissured systems and study the different flowpaths present in said aquifers; given the complex hydrogeological and tectonics settings, detailed surveys in the Umbria-Marche limestone ridges and tracer field tests were used to achieve this goal. DNA and fluorescent tracers were injected into a sinkhole and thereafter recovered at different points, allowing both for the identification of contact among aquifers, as well as the main and secondary directions of groundwater. The tracer tests have shown that the majority of the groundwater flow is directed towards the axis of the tectonic structures, emerging in more depressed areas. In addition, they have confirmed the influence of karstification on the recharge, which allows for a more detailed characterisation of water circulation in the unsaturated zone of the Maiolica and the Calcare Massiccio limestone aquifers thus offering confirmation of the hydrogeological survey results, and providing additional information that was previously unknown. Furthermore, the DNA tracer provided good results in the field especially in the karst systems and fissured rocks, thus confirming its appropriacy for flowpath investigations and vulnerability analyses of springs. In particular, DNA is suitable for very large amounts of groundwater owing to its very low detection limit. Further investigations and studies are, however, required to assess its validity also for the evaluation of hydrogeological parameters.