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CITY OF LINO LAS 10/24/94 Water Quality Program possible to quantitatively compare alternative solutions of complex water resource problems. As modeling continues to be refined, the decision - making process will be improved considerably. The process leading to pollution must be understood to develop and apply a mathematical quality model representing these processes. Pollution is transported by water through the soil (infiltration and surface evaporation) and by surface or overland flow. Chemical interaction and transformation determine the transported pollutant concentrations. Most chemicals will exist in two forms (1) the soluble form, where the chemical(s) is transported in solution (groundwater or surface water) or (2) absorbed (attachment) to soil particles, transported only when soil particles move. The form of a particular pollutant is highly variable. Some forms are more soluble than others, some more easily absorbed, some more toxic than others. All of these variables add to the complexity of water quality modeling. Types of Models Generally, there are two types of models: empirical models and physical process (casual) models. Empirical models represent cause and effect modeling, transforming a set of input variables into a description of output without describing the processes taking place. Physical process or casual models attempt to describe the physical, chemical and biological processes without requiring excessive or unavailable input data. Empirical models are fairly simple, requiring less data than physical process models. Though cost effective, empirical models are limited in the range of data used in their development, and are often misapplied. The result can be misleading data regarding cause and effect. Physical process models on the other hand, require considerable data to develop and a great deal of research to test. These models can predict watershed response, assess the effects of environmental change, coordinate and structure research, and point out ways to improve and develop empirical models. However, because of the extensive data requirements, short cuts are often taken in their application. Local Water Management Plan SEH No. A- LINOL9402.00 Reference Document Page 45