Hydrochemical changes over time in the Zahedan Aquifer, Iran.

Groundwater in the Zahedan Aquifer located in the arid southeast of Iran was chemically characterized to understand both the nature of the alluvium aquifer and the effect of human activities, specifically sewage disposal on groundwater quality. Concentrations of major cations and anions in the Zahedan Aquifer are much higher than concentrations observed in groundwater of similar settings. Although the nature of the aquifer and climatic parameters have affected the chemistry of groundwater, human impacts on the groundwater quality are more significant. The electrical conductivity in some areas of the Zahedan aquifer increased up to 7,500 microS/cm in 25 years. Human influences in some areas are so prevalent, that the groundwater type changed from a Na(+)-HCO(3) (-) in 1976 to a Na(+)-Cl(-) type in 2000. The impact of human influences on the groundwater quality is also indicated through observed nitrate concentration up to 4.81 meq/L in the urban area.