Hydrogeochemical forecasting

The foundation of model hydrogeochemical forecasting is a mathematical model. All its parameters are represented by numerical values and the correlations between them are expressed algebraic operations in formulae. The reason is that major processes associated with them are impossible to observe in nature. 

This book is the second part of a course, Fundamentals of Hydrogeochemistry. It reviews spontaneous processes responsible for the formation of ground water composition and properties. It includes four major sections. The first section introduces the basics of thermodynamics and provides the concept of properties of chemical reactions. The second section is devoted to basic processes of the formation of natural waters properties and composition in the geological environment. The main attention is devoted to the water mass exchange with rock, subsurface gas, non-polar liquids and biochemical processes. The third section reviews processes of mass-transfer in the geological medium. In the fourth section methods of hydrogeochemical forecasting are described. 

And lastly, chapter four gives an idea of hydrogeochemical forecasting and modeling methods. 

The conditions are described by the type, size, configuration, structure and properties of a hydrogeochemical object within whose bounds is solved the set forecast problem. 

Distance at the scale of space, time or events to the point, for which the forecast parameters are determined, is called forecast period. By the nature of final results are distinguished the state forecast and interval or process forecast. In the former case of interest is the state of a hydrogeochemical object at a specific point of the scale and in the latter, change in the nature and direction of this state. 

Its substance is in setting problem forecast objectives, i.e., questions, which are necessary to answer through modeling. As a rule, they have an ecological or research nature. In the former case the problem to be solved is associated with underground water or geological environment quality protection as a whole. In the latter case, with the study of hydrogeochemical environment, its processes and their role in formation economic mineral deposits. 

The content and interrelation of the above submodels determine the structure of the hydrogeochemical model as a whole the first one determines the substance of the hydrogeochemical model, the second and third, its conditions. At that, the hydro-geodynamical submodel characterizes variable conditions associated with ground water flow, the geological submodel characterizes unchangeable conditions in the forecast area. The content and interrelation of two former submodels determine the type of hydrogeochemical model as a whole. 

For instance, V.N. Ozyabkin (1995) subdivides them depending on the complexity and dimension of the forecast object. J.Rubin (1983), W. Kinzelbach (1992), S.R. Kraynov et al. (2004) base the classification on phase uniformity of the medium and velocity of chemical processes. In this connection they distinguish thermodynamical, transport and kinetic models. In Europe and the USA are broadly used classifications based on typization of local problems (Chen Zhu, Anderson G., 2002, Bethke C. M., 2008, etc.). In connection with this all hydrogeochemical models are subdivided there into three groups speciation-solubility models or batch models, reaction path modelsor mass transfer models reactive transport models or couplet mass transport models. In the second group of this classification is non-uniquely identified the role of mass transfer kinetics. 

SI. equal to 0 and concentration, temperature and pressure gradients are absent. They are similar to periodical action reactors, in which chemicals are loaded, mixed under assigned stable conditions and instantaneously brought to total chemical equilibrium. This type of models are intended for a forecast not of processes but the state of hydrogeochemical medium when the flow time At. and chemical relaxation time At are equal to 0. For this reason they are often called zero-dimension models (Ozyabkin, 1995 Chen Zhu, Anderson, 2002). In the Western literature they are called... 

Solution of other types of hydrogeochemically imbalanced systems in most cases requires discretization of the forecast area and two-step sequence of mathematical computations. 

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