Aquifer parameter estimation in fractured-rock aquifers using a combination of hydraulic and tracer tests

[摘要] English: Water resources in South Africa are already being stressed and the country is slowlybecoming a water-scarce country. This presents a challenge to all water resourcemanagers to ensure that the basic water needs of every South African are met. A goodestimation of the aquifer parameters is the basis of managing groundwater resourcesand understanding groundwater flow and transport processes. Because most of thesuitable groundwater resources in Southern Africa occur in fractured rock aquifers,this thesis focuses on aquifer parameter estimation in fractured rock aquifers.A guideline for aquifer parameter estimation in fractured rocks is derived, based on acombination of hydraulic and tracer tests. The methods included account for theunknown flow geometry and the resulting uncertainty by introducing the non-integerflow dimension, which can be calculated from hydraulic and / or tracer test data. Theguideline includes:o New methods for conducting and analysing tracer tests accounting for non-integerflow dimension prevailing during the tests in fractured aquifers.G A new method for estimating the kinematic porosity from single-well tracer tests.�?Description and comparison of the use of a three-dimensional numerical model foraquifer parameter estimation .�?The software TRACER-PLAN to enable the geohydrologist to conduct effectivetracer tests. Depending on the type of test and the geological structure the test setup,such as discharge rates, amount of tracer and duration of the test, can beoptimised.�?To simplify and unify the analysing procedure the software TRACER enables theuser to choose the correct analysing method depending on the test set-up and theconceptual model of groundwater flow. Most of the analysing proceduresmentioned in this thesis are included.While the approaches for estimating the hydraulic parameters from pumping test dataare commonly used methods, which are adapted to the situation in Southern Africa,new approaches to analyse tracer test data are developed, which account in a moregeneral way for the unknown geometry.A combination of hydraulic and tracer tests including analysing procedure isproposed, which enables the hydrogeologist to estimate important hydraulic andtransport parameters from the results of one test rather than conducting different tests.Depending on the purpose of the investigation, two types of combined tests aredeveloped. As minimum requirement conducting and analysing a single-well test issuggested. If an observation borehole in the vicinity is available, a multiple-well testshould be conducted.The proposed methods were used in case studies with different geological settings andcompared to each other. From the results of the case studies and theoretical models itcan be concluded thatG analytical methods for estimating the hydraulic properties of fractured rockaquifers must be used with precaution, even when the correct conceptual model ischosen,I) for more accurate estimation numerical models, preferable a three-dimensionalnumerical model, should be used,Q the developed methods for analysing tracer test data, using the concept offractional flow dimension, will yield more accurate and normally higher values forthe flow velocity than the common methods, using the length of the tested sectionand a flow dimension of2,lil the developed methods for analysing tracer test data, using the concept offractional flow dimension, are applicable in different geological settings,o the developed method for estimating the kinematic porosity from a single-welltracer test is generally applicable in both the fracture zone and the matrix, but theaccuracy depends upon the correct conducting procedure,e the validity and accuracy of the results depends mainly on the quality of theconducting procedure and the correct conceptual model for the analysingprocedure.The requirement for the analysing procedure can be summarised as:�?From the hydraulic test data the conceptual model should be derived, usingdiagnostic plots and derivatives, as integrated in the software TRACER or in othersoftware programs such as FC and TPA�?The hydraulic data should be analysed applying the approach of non-integer flowdimension, as integrated in the software TRACER.�?If necessary numerical models should be used for complete parameter estimation.lil The tracer test data should be analysed, applying the approach of non-integer flowdimension, as integrated in the software TRACER.The effect of matrix diffusion on solute transport in fractured aquifers is immanent,but no existing method is able to simulate it properly. Further research in estimatingthe impact of matrix diffusion on the plume movement and in developing a suitablemethod to simulate and quantify its effect is therefore strongly recommended.

[发布机构] University of the Free State