Evaluation of groundwater quantity and quality in the Kashan Basin, Central Iran

This paper investigates groundwater changes in the Kashan Basin quantitatively and qualitatively. According to the data obtained from 53 observation wells, it is found that the mean water table is decreased about 7.93 m between 1990 and 2006, indicating a mean water table decline of 0.496 m/year. To study groundwater quality, 21 samples are analyzed for their physicochemical characteristics such as pH, hardness, chloride (Cl), electrical conductivity (EC) and total dissolved solid (TDS) values. Comparing the results with drinking water quality standards issued by World Health Organization (WHO), it is found that most of the water samples are not potable. Hydrochemical facies using Piper diagram indicate that in most part of this basin, the chemical character of water is dominated by NaCl. However, Na% values indicate that just 53% of samples are permissible for irrigation. The chloride–bicarbonate ratios reveal that salt lake intrusion to this basin is the main source of salinity. It is also found that functional relationships between EC and Cl are logarithmic.

Research Highlights
► Because of uncontrolled discharge in the Kashan Basin, the mean water table has decreased about 7.93 m between1990 and 2006, indicating an average water table decline of 0.496 m/year.
► The quality of groundwater in this basin is affected by the Salt Lake intrusion to this basin. According to the ratio of Cl/HCO3, a total of 80% of samples are contaminated by saltwater intrusion.
► The piper diagram shows the dominant cations are in order of Na > Ca > Mg > K and the dominant anions are in order of Cl > SO4 > HCO3. So, the hydrochemical facies of water in the Kashan Basin is dominated by Na Cl.
► Functional relationships show a logarithmic relation between EC and Cl in this basin.