chemical quality characteristics of ehran ground water aquifer

there are 3700 wells in tehran city, of which 850 are deep wells. to determine tehran ground water quality, as a pretest we selected 102 wells by simple random sampling; water analyses were made according to the latest edition (1985) of the standard methods. comparisons of the obtained results with who standards show that only 0.98% of the samples go beyond the maximum desirable concentration of 0.2 mg detergent/l. the mean of total hardness of all samples (223.82 mg/l) shows that all water are in the range of hard waters, with 2.97% of samples being above the maximum permissible concentration (500 mg/i) for hardness; in 24 permissible and maximum desirable level, according to w.h.o standards. the concentrations of heavy metals determined in thes survey are not more that the standard except for chromium, which showed an undesirable increase in two percent of the cases.