Temporal changes in the physical properties and chemical composition of the municipal water supply of Shahrood, northeastern Iran

A systematic monitoring program was implemented in 1999 to evaluate the temporal changes in the physical properties and chemical composition of water from the Shahrood Qanat, which provides 30% of Shahrood's municipal water needs. A qanat is a near-horizontal gallery which yields water by gravity. The results show that the physical properties, in contrast to the concentration of ions, are in an almost steady state condition and the slight variations are due to the travel time of water in the qanat gallery, the mixing of qanat water, the seasonal temperature fluctuation, and the likely unavoidable errors associated with long-term monitoring. They also show that severe drought during the past nine years has not yet affected the groundwater quality. The TDS of the qanat water is relatively low and the water is of the calcium-bicarbonate type. However, the above average concentrations of nitrate (14.9 mg/L) and phosphate (0.105 mg/L) may reflect the impact of the excessive use of fertilizers in the capture zone of the qanat. High Ca, Mg, pH, and a higher-than-recommended hardness value reflect the influence of carbonate-rock formations on the groundwater composition. The study shows that systematic monitoring is required to identify the erroneous data, to optimize the monitoring program and to characterize the water quality trend.