APPLICATION OF A REACTIVE TRANSPORT MODEL FOR INTERPRETING NONCONSERVATIVE TRACER EXPERIMENTS - THE RIO-MAIOR CASE-STUDY

The application of analytical groundwater solute transport models is p resented in a case-study in the white-sand aquifer of Rio Maior, Portu gal. Two simultaneous experiments were performed using a conservative and non-conservative tracer. The experiments were carried out using an innovative technique developed by Lobo-Ferreira (1988, 1989). A measu red quantity of two different tracers one being considered an ideal tr acer and the other a non-conservative tracer were injected simultaneou sly in 1 m(3) of water from the aquifer into a piezometer, during a me asured period of time. A injection of 1 m(3) of fresh water from the a quifer was injected immediately afterwards. Under regional groundwater flow the tracer returned back to the piezometer where the concentrati on was monitored for both tracers. The purpose of the experiment is to analyze the different behaviour of two tracers with different propert ies, under the same hydrogeological conditions, using a reactive trans port model. The ideal tracer experimental results obtained served to t est if the experimental hydrogeological properties of the aquifer, i.e . the velocity and the longitudinal dispersivity, used in the model, f it with the experimental results. As the model performance was shown t o be very accurate, the data obtained for the aquifer hydrogeological properties were used in the non-conservative tracer modelling. The res ults for the non-conservative modelling were adjusted to the field mon itoring by changing the initial settings and comparing with the field curve by an inverse problem procedure. This allowed us to calibrate th e non-conservative parameters of the tracer. The results obtained in t his study illustrate the different behaviour between conservative and non-conservative tracers. The two models, CANALX, which computes solut e spatial profiles, and CANALT, which computes the solute breakthrough curve, provide quantitative tools to analyze the behaviour and the da ta for adsorbing solute transport in groundwater. Given parameters unc ertainties and experimental limitations, we consider the model perform ance to be very encouraging in this application.