FARKLI KIRIKLI-ÇATLAKLI AKİFER SİSTEMLERİNDE KİRLETİCİ TAŞINIM PARAMETRELERİNİN BELİRLENMESİ

Abstract

The high degree of heterogeneity in fractured aquifers is a major challenge to quantify flow and contaminant transport parameters. It is, however, extremely important to characterize contaminant transport processes and estimate the transport parameters in these aquifer systems, due to their vulnerability to pollution problem. Within this framework, in this study it is mainly aimed to estimate the contaminant transport parameters in fractured aquifers. Additionally, it is targeted to demonstrate how fractured aquifers differ from porous media aquifers in terms of parameter estimation on the basis of conceptual modelling approaches. To achieve this, four case study were conducted in different fractured aquifer systems to quantify the main transport parameters. The first case study consisted of the Single Well Injection-Withdrawal Test (SWIW)-tracer test, experimented in fractured basalt aquifer with using Uranine tracer dye. Bimodal breakthrough curve (BTC) was obtained from the tracer test. To estimate the transport parameters, bimodal BTC was fitted by Gaussian and Lorenzian (Cauchy) probability distribution function, being conceptualized by Dual Porosity Model (DPM) and Equivalent Porous Media (EPM) modelling approaches, respectively. Therefore, it was concluded that the appropriate modelling approach for fractured basalt aquifer to quantify transport parameters was DPM, because of permitting the evaluation of double porosity based transport mechanism. Furthermore, the origin of bimodal breakthrough curve (BTC) was evaluated in terms of its shape and size to understand transport mechanism in the fractured aquifer. With the help of BTC’s early time, transition time and late time, the transport mechanism of aquifer was defined upon BTC. In the second case study, two-well tracer test was applied in fractured dolomitic limestone aquifer to quantify the transport parameters. The BTC of Rhodamine WT exhibited multi-peaked shape. The regional transport parameters were fundamentally characterized by Gaussian distribution function, based on EPM modelling approach. It is also noted that three distinct local peaks in multi-peaked BTC were evaluated to be as secondary flow pathways mainly permitting contaminant transport, therefore the local advective velocity of each path was calculated. Within the third case study, in order to estimate aquifer hydraulic parameters, drawdown results of three wells drilled into fractured limestone aquifer were assessed with diagnostic plots. Moench, 1984 and Barker, 1988 model solutions were selected to characterize double porous aquifer. Thereby, the hydraulic conductivity and storativity parameters of fracture and matrix for each well were calculated. Moreover, the derivative graph of PK2 well was analyzed by unconfined, confined, and single fractured aquifer types based on the estimation of transmissivity parameter to demonstrate the importance of aquifer type selection in drawdown curve analysis. With derivative analysis, the possible flow regimes of dual porous aquifer were demonstrated in the vicinity of pumping well. Therefore, the early time, transition time, and late time behaviors were described with demonstration of possible transport process in these time periods. In the last case, the distribution coefficient (Kdm) of different matrix materials were determined by laboratory static batch tests. The retardation factors (Rdm) of matrix materials were calculated by using determined Kdm values and their bulk densities.