Proceedings of the International Workshop, Tehran, 29-31 October 2006
The depth to water table is less than 100 m in the north and around 5 m in some areas in the south. In the latter case, the water table is influenced by evaporation. As it is shown in Figure 5, in a big part of the city (mainly to the southern part) water table is situated in a depth not more than 30 m. Especially in Rey area, water table is almost close to the surface and continuous pumping operations are performed to make live possible there.
Groundwater quality According to ground water type maps, the pattern of bicarbonate, sulfate and chloride water types through the plain is not as expected in a plain in a typical situation. In most cases, the bicarbonate water type is the dominant type in upstream areas. Getting farther from recharge source, the sulfate and the chloride water types are expected to be the dominant type, in the midbasin and in the downstream areas respectively. This pattern is somehow changed in Tehran aquifer (Figure 6). The chloride water type has developed to southern, western and even some central parts of the city, reflecting the effect of industrial and urban wastewater pollution [Haj Hariri et. al, 1995]. According to an assessment on the extent and magnitude of biological and chemical contamination of the Tehran aquifer by the Tehran Water Authority during 1987-1991, the aquifer was divided into two main areas; the highly contaminated and the low contaminated areas. The highly contaminated area was mainly concentrated in the central parts of the aquifer and comparing the extents of this area in 1990 and 1992 showed that this zone was spreading from central parts to other parts of the aquifer [Taher Shamsi, 1999]. Further studies during 1993-1996 indicate more increase in pollutants in the Tehran aquifer. Most of samples taken from the eastern half of the aquifer have shown pollution to microelements such as iron, cadmium, chrome and lead as indicators of industrial wastewater pollution, in 1996 [Haj Hariri et. al, 1995]. Pollution
Figure 6. Water type in Tehran aquifer in two successive years 1994 and 1995 [Haj Hariri et. al, 1995]
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