Groundwater-lake systems approaches

Hydrogeologists take a variety of approaches in quantifying the rates of groundwater exchange with lakes. These approaches can be physically or chemically based isotopic approaches are one example of the chemical methods. The application of stable isotopes to the study of groundwater-lake systems is the primary focus of this chapter. 

The purpose of this chapter is not to promote the replacement of traditional physically based methods of assessing groundwater-lake systems with isotopic methods, but rather to demonstrate the utility of isotopic techniques. Physically based methods can provide more detailed information on the spatial and temporal variability of a groundwater-lake system than isotopic approaches can provide. Regardless of the method chosen, however, an adequate number of piezometers is necessary to ensure that groundwater samples are collected from upgradient areas. 

Physical Approaches. Groundwater-exchange rates with lakes are traditionally estimated by careful measurements of hydraulic potentials within the groundwater system, followed by application of Darcy s law in the form of flow-net analysis or numerical modeling. However, these measurements can be time-consuming and costly, and can require monthly to weekly measurements at many piezometers to examine the three-dimensional nature of the hydraulic-potential field. In addition, characterization of the hydraulic conductivity of the aquifer is critical to physical approaches and typically leads to results with large uncertainties (I, 2). 

This chapter is written with two objectives (1) to discuss field, laboratory, and modeling results in which the kinetics of particle aggregation and deposition in natural aquatic systems are developed and tested and (2) to indicate approaches for studying the kinetics of such reactions in these and other aquatic systems in practice and in research. The chapter begins with a consideration of the kinetics of particle deposition in groundwater aquifers. This is followed by an assessment of particle aggregation and sedimentation in lakes. A modeling approach for the kinetics of particle-particle interactions in aquatic systems is then presented. 

Our analysis describes virus adsorption from the standpoint of chemical equilibrium. Since adsorption equilibrium appears to be approached closely in our systems in less than or equal to 2 hr, and since the residence time of viruses in natural water systems is greater than 2 hr for many cases (for example, lakes, groundwaters, rivers, etc.), equilibrium considerations are entirely appropriate. In other situations, where residence times of the virus in the system are small compared to expected times required for adsorption to approach equilibrium (for example, sand filters in water treatment, water distribution systems, etc.), the DLVO-Lifshitz theory may still be applied directly. The work of Fitzpatrick and Spielman (57) concerning filtration and that of Zeichner and Schowalter (58) concerning colloid stability in fiow fields demonstrate this clearly. Their developments of hydrodynamic trajectory analysis coupled to DLVO-Lifshitz considerations can be extended... 

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