OVERVIEW

The Hydrogeochemistry course aims to address the equilibria that are established between aqueous solutions such as rain, groundwater, surface water and mineral phases that make up rocks and soils, through the presentation of appropriate theoretical and computational tools of a high scientific standard. The course includes a section dedicated to the equilibria of high ionic strength waters such as sea water, brine and mixing with groundwater, a condition typical of coastal areas.

AIMS AND CONTENT

LEARNING OUTCOMES

The aim of the Course is oriented to help a future professional in the interpretation of the water-rock interactions between aqueous solutions stored in a geological reservoir. Having the global water cycle in mind an environmental technician should understand at glance what is happening in an aquifer by means of water sampling, graphical interpretation of diagrams and processing of water analyses. This is done in the first part of the Course. The second part is devoted to show a series of tools useful to prepare the numerical modeling of a reactive transport simulation by finite difference method showing how some numerical techniques (i.e. Newton-Raphson method for system of linear equations) enable the solution of 3D models built by field geological informations. Changing observation scale, both in space and in time, some finer features of the inter- and intra-aquifer dynamics with other compartments of hydrosphere will be enlightened by the use of the imprinting of stable isotopes of hydrogen and oxygen. The meaning of the isotopic fractionation factor will be presented here. The Course ends with the presentation of techniques of aqueous solution speciation calculations in thermo-baric condition characteristic of shallow groundwaters throwing the intimate relations between water and mineralogical nature of of the geological aquifer system. Some practical water sampling and data measurement issues will be shown directly in the field. The theory presented in the Course will be coupled with computational practice helping the students to how convert an idea, based on (hydro)geological field experiences, to a useful model expanding the geochemical knowledge of systems.

AIMS AND LEARNING OUTCOMES

The course is designed to cover, in as balanced a manner as possible, various aspects of the investigation of a water system in the broadest sense in the field of professional and research activities. In particular, at the end of the course, students will be able to:

- describe the fundamental components of a heterogeneous, multi-component water-rock system with the aim of numerically modelling its main aspects;
- critically evaluate the choices made in selecting variables for the description of a simplified water-rock system, including those representative of the water-sediment interface in coastal areas;
- generate input for specific calculation codes that reflect the project requirements and operational resources and meet the needs for accuracy, precision and solvency;
- correctly acquire the labile chemical-physical parameters in the field that can be used later in modelling;
- integrate information from other specific fields relevant to geology in order to solve the problem.

PREREQUISITES

Teaching is based on continuous exchange between lecturers and students and requires the application of principles already learned in other courses.

In order to effectively attend the course, students must have a solid knowledge of the courses taken during their Bachelor's degree programme, particularly in Geochemistry.

TEACHING METHODS

The course consists of lectures and guided practical lessons on PCs. As there are learning tests, activities to apply the knowledge acquired, practical and methodological activities, attendance at lectures and laboratory exercises is strongly recommended. Classroom lectures are delivered using multimedia presentations. Guided practical lessons are aimed at the immediate application of the theoretical knowledge acquired during the lesson. Simulation laboratory exercises take place in the DISTAV computer lab. 

SYLLABUS/CONTENT

The Hydrogeochemistry course [IGCH-65685] aims to provide future professionals with the foundations for correctly interpreting the interactions between the water contained in a reservoir and the solid matrix that constitutes it. The relationships between the various compartments within the general water cycle are highlighted through sampling, diagrammatic interpretation and the processing of data derived from laboratory analytical reports.

The interest in the evolutionary dynamics of an aquifer in terms of quality leads in the second part to addressing the basic issues for the preparation of a flow and transport simulation (including reactive transport). In this regard, the basic concepts of finite difference modelling, basic numerical resolution techniques and calculation stability conditions in simulation will be presented.

The fine inter-aquifer dynamics and the temporal evolution in relation to the adjacent compartments (atmosphere and seawater) are investigated through the isotopic study of O and H, so part of the programme will focus on the isotopic fractionation of these elements.

The acquisition of knowledge related to the course will be completed through computational practice in the speciation calculations of aqueous solutions under thermo-baric conditions typical of shallow aquifers and the presentation of case studies of interest in water geochemistry.

Part of the programme will be conducted in the field with exercises in sampling water from springs and surface waters. Each theoretical topic presented will be supported by computational practice in guided lessons using OpenSource software.

Introduction

Definitions of aquifer and water body: physical limits and legal characteristics. Reference legislation on water (EU, national). Regional Water Protection Plan (PTA). Water cycle: chemical-physical and isotopic footprint of water in various compartments (rainwater, surface water, groundwater, karst water, marine water). In and out of the water budget of an aquifer. Saturated zone and establishment of an aquifer. Characteristics of the transfer of inorganic and organic pollutants from the surface to the aquifer. Workflow of a hydrogeochemical project.

Sampling

Definition of survey and monitoring (surveillance, operational, investigation): observation scale in the space-time domain. Issues of budget, accuracy and synchronisation of acquisition. Preparation of a field trip for water sampling. Calculation of spring flow rates. Preliminary flushing of a drainage well. Instruments for measuring T, pH, Eh, EC, TDS, O2, alkalinity, pCO2: calibration and maintenance. Continuous logging of a well. Problems with the use of sound-sensitive sensors in seawater.

Data interpretation

Units of measurement for concentration and chemical-physical quantities. Conversion relationships between various units and quantities. Electron neutrality of a water analysis. Bivariate diagrams. Ficklin diagram. Triangular diagrams. Piper diagram. Langelier-Ludwig (LL) diagram. Quick analysis of a laboratory analysis report.

Aqueous solutions in a porous medium

Nature of the “numerical” porous medium: relations with geological reality. Porosity and Darcy's law, hydraulic gradient, permeability. Hydraulic conductivity tensor. Anisotropy and heterogeneity of the aquifer depending on the scale of observation. Movements of an aqueous solution in a porous medium: advection, diffusion, dispersion. Correct Fick's laws. Tortuosity. Dispersion coefficients. Direct interaction between solute-solvent and solid matrix: adsorption isotherms (Langmuir and Freundlich). Delay factor. Ion exchange between solution and solid matrix. The water mixing process: the norm, not the exception. Numerical models of flow and reactive transport: main characteristics. Laplace and Poisson equations. Finite difference method. Principles of the NR method for solving systems of linear equations. Boundary conditions of a finite difference model. Conditions for numerical stability of flow and reactive transport calculations.

Stable isotopes of H and O

Isotopic dimension of the Periodic Table. Stable isotopes of greatest interest for hydrogeochemistry: H, O. Reference standards (SMOW, V-SMOW). Isotopic fractionation: why, where and under what conditions it occurs. Fractionation factor. Global (MWML) and local isotopic meteor line. Effects of temperature, altitude, precipitation and “continentality” on fractionation.

Speciation calculations

Why perform a speciation calculation. Basic geochemistry refresher: thermodynamic activity, Henry's constant, fugacity, ionic strength, reaction and equilibrium constants, conditional constants, thermodynamic affinity at equilibrium, saturation index. Types of water-rock reaction models. Equilibrium vs. disequilibrium. Reaction kinetics. Thermodynamic databases for speciation calculations: structure and content. Why there are multiple thermodynamic databases. Impact of database choice on calculation results. Workflow for calculating the speciation of an aqueous solution. Eh-pH diagrams and dependence on the thermodynamic database: ATLAS Eh-pH (Japan).

Software
Phreeqc3.0 [ http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/ ]
PHAST/P4W [ http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phast/ ]
PhreePlot [ http://www.phreeplot.org ]

RECOMMENDED READING/BIBLIOGRAPHY

The slides used during the lessons are not available as they are designed as a teaching tool to help the teacher follow a logical thread and allow students to follow the lesson, the contents of which are reported in full in the recommended texts. The texts listed below are suggested as reference texts, but students may also use other university-level texts.

Vetuschi Zuccolini M. (2011) Appunti di Idrogeochimica.
Ottonello G. (1991) Principi di Geochimica. Zanichelli Editore
Clark I (2015) Groundwater Geochemistry and Isotopes. CRC Press.

TEACHERS AND EXAM BOARD

LESSONS

Class schedule

The timetable for this course is available here: Portale EasyAcademy

EXAMS

EXAM DESCRIPTION

The exam consists of a personalised test sent by email by the lecturer and completed independently by each student at a time and in a manner of their choosing. It is submitted and discussed on the exam date in front of the Commission. The exam is passed if the student obtains a grade greater than or equal to 18. There will be 3 exam sessions in the winter session (January-February) and 3 exam sessions in the summer session (June, July, September). Working students and students who are not currently enrolled may request the activation of extraordinary sessions.

ASSESSMENT METHODS

Details on how to prepare for the exam will be provided during the first lesson, together with a presentation of the course as a whole. The level of detail required for each topic will be provided during the lessons. The exam will be based mainly on the discussion of the results of the test provided by the lecturer. Based on the quality of the answers, the Commission will take the opportunity to explore other topics covered during the lessons and not directly addressed in the test. The ability to present topics clearly and with correct terminology will also be assessed.