Surface and Groundwater Quality in Taftan Geothermal Field, SE Iran

摘要

Geochemical characteristics and potentially toxic element contents of groundwater, thermal springs, and cold springs of Taftan area in the southeast of Iran examined in two different seasons in order to assess their quality and possible contamination source. Groundwater and spring water samples were collected in May and September 2012 and analyzed for major parameters, anions, cations, and potentially toxic elements. Groundwater is the local source of drinking water and along with cold springs is used for agricultural irrigation. Thermal springs are mainly used for bathing and balneological purposes. For both wells and springs under study, boron was found to have the higher concentration than the specifications in WHO standards except for PF spring. Arsenic, Fe, Mn, Pb, and Ni in thermal springs and most of groundwater samples and cold springs indicate higher concentration than those of WHO standard. The low Na/Ca and Na/K ratios in STS and TTS thermal springs confirm these waters associated with up-flow zones, while higher Na/K ratios for cold springs reveal effects of lateral flows. Conservative elements indicate that thermal springs fall within the hydrothermal field, indicating magmatic affiliation of the thermal waters. High concentrations of trace elements and major ions in well water, thermal springs, and acidic cold springs provide evidences for water-rock interaction processes and the presence of active deep circulations. Saturation indices (SI) show that thermal waters are oversaturated with respect to quartz, chalcedony, alunite, gypsum, celestite, and barite, evident by precipitation of sulfate and siliceous minerals in the most recent precipitates of the geothermal system. The cold springs and groundwater are oversaturated with chalcedony, quartz, hematite (four water wells), and goethite (two water wells), slightly highlighting the mixing of the groundwater with thermal and acidic springs. The SI indicates that the Fe-phase minerals could control mobility of As in the groundwater of the Taftan area. The present study is addressing a significant risk of toxic elements in groundwater resource management, in the volcanic regions in the southeast of Iran, and suggests some preventive measures for controlling adverse effects of using such waters for drinking and irrigation.