INTERCOMPARISON OF DIFFERENT TRACERS IN THE EVALUATION OF GROUNDWATER DYNAMICS IN HETEROGENEOUS POROUS AQUIFERS: A STUDY IN THE ALLUVIAL PLAIN OF VENICE

摘要

The paper deals with experiments carried out with artificial tracers on a site of the alluvial plain of Venice. The area has 13 boreholes 5-15 m in depth. The aquifer is very permeable and consists of gravel and coarse sand, the thickness of which reaches 450 m within the area. The experiments were made using ~(131)I, ~3H, NH_4Cl, LiCl and Rhodamine WT. Because of the absence of fine matrix in the sediment, the tracer behaviour in the aquifer is nearly the same for all the tracers used; however the results are affected by the different detection methods and sensitivities. In practice ~(131)I and ~3H were detected at levels of 5 × 10~(-10) Ci·L~(-1), while LiCl and NH_4Cl were measured at levels of 10~(-8) and 10~(-6) kg·L~(-1). Rhodamine WT also gave good results; its detection limit was 10~(-9) L·L~(-1).