هيدروشيمي منابع آب زيرزميني در مناطق بزمان، ايرانشهر و اسپكه، جنوب شرق ايران

Hydrochemical characteristics of groundwater in the Bazman, Iranshahr and Espake area, southeast of Iran

در اين پژوهش منابع آب زيرزميني منطقه آتشفشاني بزمان و مناطق نزديك به آن، به تعداد 69 محل چشمه و چاه كشاورزي با استفاده از روش هاي گرافيكي، نسبت يوني و شاخص هاي كيفي مورد ارزيابي قرار گرفتند. نتايج نشان مي دهد، پنج تيپ Na-Cl، Na-Cl-SO4، Na-Cl-HCO3، Na-SO4 و Na-HCO3 در آب زيرزميني منطقه وجود دارد و نوع غالب عمدتاً آب هاي كلرو بيكربناته سديك و كلرو سولفاته سديك هستند. علاوه برآن تمامي نمونه ها نسبت به انيدريت، هاليت، تنارديت و اكثر نمونه هاي آب زيرزميني نسبت به كلسيت، دلوميت، ژيپس و آراگونيت تحت اشباع بودند. نتايج حاصل از نسبت هاي يوني نشان مي دهند كه هر سه نوع كاني هاي كلسيت، دولوميت و ژيپس در منطقه، خصوصيات هيدروژئوشيميايي آب زيرزميني منطقه را كنترل مي كنند. بر مبناي نمودارهاي تعيين منشا شوري، عامل شوري آب زيرزميني چشمه هاي منطقه، انحلال كاني هاي نمك تشخيص داده شد. با توجه به نمودار شولر مشاهده مي گردد كه اكثريت نمونه هاي آب چاه ها و بيشتر نمونه هاي آب چشمه ها به جز چشمه هاي S4، S5، S11 و S14 از نظر شرب در محدوده ي خوب و قابل قبول قرار مي گيرند؛ در حاليكه بر خلاف انتظار بر اساس نمودار ويلكوكس، بيشتر نمونه هاي آب زيرزميني جهت كشاورزي مناسب نيستند. دليل اين امر، نسبت بالاي جذب سديم در آب هاي با هدايت الكتريكي پايين است، كه سبب تخريب بافت خاك مي شود.

In this research، 69 water samples taken from springs and production wells were evaluated to assess the groundwater quality in the Bazman، Iranshar and Espake area. Investigations were carried out using graphical methods such as Piper، Stiff، Schoeller and Wilcox and various qualitative indicators to identifying water facies and specific uses. The groundwater samples، therefore، were categorized into five water types including Na-Cl، Na-Cl-SO4، Na-Cl-HCO3، Na-SO4 and Na-HCO3. It was also found that most of the samples are undersaturated with respect to anhydrite، halite، thenardite، calcite، dolomite، gypsum and aragonite minerals. According to diagrams، halite minerals dissolution is the source of the salinity of groundwater for study area. In addition، calcite، dolomite and gypsum minerals control hydrochemical chractrestices of the groundwater in this area. According to the Schoeller diagram، some of the groundwater sample، except N3، B8، S4، S5، S11 and S14، are suitable for dinking. While، Wilcox digram shown groundwater resources are not appropriate to irrigation use. It is due to high sodium adsorption ratio (SAR) in groundwater of study area; because of its direct relation to the adsorption of sodium by soil. Introduction: Bazman، Iranshahr and Espake regions are located in Sistan and Baluchestan province، southeastern of Iran. In this volcanic area، there are several thermal and cold springs. The use of geothermal water resources for irrigation is not commom world wide as these resources are limit. These groundwaters having a different hydrogeochemistry. Therefore، this research investigates the hydrochemistry of hot and cold groundwater resources in this volcano area. Materials and methods: In order to measure concentration of ions in groundwater، water samples were collected from 14 springs and 53 production wells. The wells in the study area relate to the three areas of Bazman، Iranshahr and Espake. The water samples were poured into acid-washed polyethylene bottles which had been carefully washed out with the water of each sampling point. Then the samples were quickly moved to the laboratory and were put in a refrigerator. Electrical conductivity، pH، redox potential (Eh)، and temperature were measured in situ using a portable digital EC (AQUA-TC 485) and pH (WalkLAB-TI900) meters which were calibrated before being used. The samples were then filtered to separate the suspended particles. The major ions were analyzed by using standard methodologies. Results and discussion: EC of the water samples ranges from 507 to 10250 μmhos/cm. The Piper and Stiff diagrams suggested that the groundwater samples could be classified into five “water types”; namely، Na-Cl، Na-Cl-SO4، Na-Cl-HCO3، Na-SO4 and Na-HCO3. It was found that the groundwater samples were chiefly of Ca-HCO3 type. The water type in western springs of the study area is NaCl-HCO3. Bicarbonate shows the presence of carbonate bearin minerals in the groundwater from Jamal formation. In most groundwater samples، the molar ratio of Na/Cl shows which this ratio is more than 1. This is due to the fact that the dissolution of sodium-containing silicate minerals especially by weathering and cation exchange has increased the ratio. The molar concentrations of HCO3- versus Ca2+ and HCO3- versus Ca2+ + Mg2+ are plotted. When calcite or dolomite dissolves in groundwater، water samples must be plotted on a 2:1 line. However، this did not happen which indicates that Ca2+ and/or Mg2+ decreased by direct cation exchange. Conclusion: The hydrochemical compositions of the geothermal springs are different than those for the cold waters. Both geothermal springs have Na-Cl water type، with chlorine concentration mole more than sodium. This may be due to that the high-depth circulation of the meteoric water in the area provides an enough time for water to achiving the thermodynamic equilibrium. Then exchange of the sodium cation with the medium occurred and therfore sodium mole ratio is much less than chlorine. However the springs to western part of the study area have a NaCl-HCO3 water type، while concentration of chlorine is lower than the sodium. Bicarbonate shows the presence of carbonate bearin minerals in the groundwater. In addition، the eastern springs of Bazman which located in sedimentary rocks، have a Na-SO4 water type. It is due to sulfur bearing minerals. Also، salinity in the groundwatr is resulted from mixing and evaporate formationed. According to the Schoeller and Wilcox diagram، the water samples except S4، S5، S11 and S14 are usable for drinking، while are not sutable to irrigation use. It is due to high sodium adsorption ratio (SAR) in groundwater of study area; because of its direct relation to the adsorption of sodium by soil.