Introduction

Abstract

The chemical and biological constituents contained in groundwater depend on two factors: the natural environment of groundwater storage and move­ment, and human activities. Precipitation infiltration and surface water per­colation are the natural sources of groundwater. The total dissolved solids (TDS) of precipitation is generally very low, but its chemical components will be changed when infiltrated through soil beds by a series of actions, such as solution, oxidation, reduction, ion exchange, and so on. The infiltration and percolation water will be involved in groundwater movement in both the vertical and the lateral directions in the aquifer. During this process, the TDS of groundwater will continually increase as rocks and minerals are dissolved into the water. Human activities may change the natural process and cause groundwater to contain organisms, hydrocarbons, heavy metals and other harmful matter. Groundwater, therefore, should be looked upon as a multicomponent fluid. The content of each component in groundwater can be expressed by its concentration, i.e., a mass of certain component contained in unit volume of water (M/L ³). If the concentration of component a is written as C _a , then the standard of water quality for a certain use can be written in the following common form: $\begin{gathered} {C_{\alpha ,\min }}\, < \,{C_\alpha }\, < {C_{\alpha ,\max }}, \hfill \\ \,\,\,\,\,\,\,\left( {\alpha \, = \,1,\,2,\,...,\,n} \right) \hfill \\ \end{gathered}$ where C_α,min and C_{α, max} are the given lower and upper limits, respectively, of the concentration of component α, and n is the total number of components considered. According to the actual situation, the components may refer to either single ions or multi-ion compositions.