نوع مقاله : مقاله پژوهشی
1 گروه زمین شناسی، دانشگاه آزاد اسلامی واحد لاهیحان
2 گروه زمین شناسی، دانشگاه آزاد اسلامی واحد لاهیجان
3 گروه زمین شناسی، دانشگاه پیام نور
عنوان مقاله [English]
One of the most important subjects in hydrology is water quality. Groundwater quality is one of the most important aspects of hydrogeochemistry, which discusses the chemical description of water, the spatial distribution of various chemical structures, the suitability of water for various purposes such as drinking, agriculture and industry. Because each of them has certain quality characteristics and criteria in terms of quality. Therefore, by examining them qualitatively, the contamination of these resources can be prevented (Alley, 1993). One third of the world's population uses groundwater for drinking, so investigating and monitoring of groundwater quality can play an important role in achieving sustainable development (Mosaferi et al. 2014). The purpose of this study is to investigate the characteristics and factors affecting the water quality of springs from the west of Rasht (near Fooman and Soomeesara) and in this regard, classification of springs based on the major anions and cations, to determine the quality of water in the region in terms of variables Physicochemical BOD, PH, Eh, Ec, TDS, major cations and anions and some trace elements, study of possible effects of geological units on the water quality of springs in the study area, detecting of physicochemical properties and quality of spring water in terms of drinkability, the study of water contamination in the study area based on the microbial indicators of Total Coliforms and Fecal ColiForm. Study areas is located in Gorgan-Rasht zone in terms of divisions of geological and structural units of Iran (Nabavi, 1355), which is part of the Alborz zone and is situated between of 49˚ 17’ to 49˚ 30’ of Eastern longitudes and 37˚ 12’ to 37˚ 20’ of Northern latitudes in 1/100000 geological sheet of Bandar e Anzali. The studied springs are located in Rasht and Soomehsara.
After Sampling, samples were stored at 4 ° C and sent to Rasht Science and Technology Park Laboratory (Zist Danesh Azma Company) for evaluating of physicochemical properties, measuring the concentration of anions, SO42-, HCO3- (NO3, Cl- and major cations (K +, Mg2 +, Ca2 +) (Na +), total hardness, heavy metals (Al, Cu, Hg, Pb, As Fe,), total dissolved solids (TDS) (mostly containing inorganic salts such as carbonates, bicarbonates, chlorides, sulfates, phosphates and calcium nitrates, magnesium, sodium, potassium, iron and small amounts of organic matter (Kotaiah and Swamy, 1994) and biochemical oxygen (BOD), acidity (pH), electrical conductivity (EC) (measurement of water-soluble ions such as chloride cations, sulfate , Sodium, Magnesium, Calcium, Iron (Rao and Rao, 2010) and microbial studies. Element concentrations measured by atomic absorption spectrophotometry (AAS) method using graphite furnace. Evaluation of the concentration of anions was conducted by titration and potentiometry. Aq.QA software according to the standard (WHO 2011) was used to analyze the data and the type of water and its quality. The effect of geological formations on the water quality was evaluated and interpreted by chemical water diagrams including (Piper, Stiff, Durov, Ion balance). The quality of drinking water was also assessed using Schoeller (1995), metal index (MI), and heavy metal pollution index (HPI).
After evaluating the amounts of ions and chemical compounds in the water, we need to monitor and classify these amounts. Qualitative diagrams such as Piper, Stiff, Durov, Ion balance plotted by Aq-Qa software were used. Piper diagram (Piper, 1994) is used for geochemical evaluation of groundwater flow system (classification of samples and determination of chemical type and water facies). The position of hydrogeochemical data of springs in the western region of Rasht (Gilan province) on the Piper diagram indicates the presence of three different hydrogeochemical types including (Ca-Cl) type in Abbas Ali Faraj Poor spring, (Ca-HCO3) type in Abkar springs, Agha Seyed Javad tomb and Nazar Mhaleh spring and (Ca-SO4)type in the spring of Mohammad Ali Abbast. Due to the predominant type of water in the region, which is calcium bicarbonate and the predominant element in all springs (calcium), these waters have a constant hardness and the concentration of alkaline earth cations (Ca2 +) and weak acid anions (HCO3-) in them is higher than strong acid anions (SO4-).
The Stiff diagram is used to assess water quality changes in a place and over a period of time (Arvidson, 2006). According to the Stiff diagram, the groundwater of the region is in the groups of calcium bicarbonate (M2, M5, M4 springs), calcium sulfate (M3 spring) and calcium chloride (spring M1), respectively.
One of the criteria for classifying water in terms of drinking is the Schoeller classification. According to Schoeller classification in Abbas Ali Faraj Pour and Mohammad Ali springs water class (except for calcium which is bad) in all cases is in the good to acceptable range, and Abkar spring is in the category of unsuitable (for calcium) but in all other cases is in the category of good and acceptable, and the springs of Agha Seyed Javad tomb and Nazar Mahaleh (except for calcium which is drinkable in emergency situations) are in the good and acceptable category in terms of drinking. According to the Gibbs diagram, West Rasht springs are mainly located in the area where the rock process is predominant. This represents the interaction between the chemistry of the rock and the chemistry of the rainwater that has penetrated into the ground. To determine the level of pollution of water resources in terms of the presence of heavy metals, the Metal Index (MI) is used to assess the ability to drink and the Heavy Metal Pollution Index (HPI) to examine the effect of heavy elements on human health. If the values obtained for MI were less than one, the water would be drinkable; if the MI were more than one, the water would be non-drinkable and if it were equal to one, it would be at risk (Tamasi et al. 2004). According to the results, all MI springs are less than one and so drinkable. If the HPI were higher than 100, the water would be contaminated with heavy metals; if the HPI were equal to 100, the water would be at risk of heavy metal contamination; and if the HPI were less than 100, the water would not be contaminated with heavy metals. By calculating the Heavy Metal Contamination Index (HPI), none of the studied sources are contaminated with heavy metals.
1- The position of hydrogeochemical data of springs in the western region of Rasht on the piper diagram indicates the presence of three different hydrogeochemical types including type (Ca-Cl), (Ca-HCO3) and type (Ca-SO4) in the studied springs.
2- According to Durov diagram, the amount of TDS in the spring of Mohammad Ali Abbast (M3) is the lowest and the spring of the tomb of Agha Seyed Javad (M4) is the highest.
3- According to the Stiff diagram, the groundwater of the region is abundant in the groups of calcium bicarbonate (and calcium sulfate and calcium chloride, respectively).
4- According to Schoeller diagram, all the studied springs are in good to acceptable range in terms of drinking (except for calcium).
5- Except for springs M1 and M5 with BOD more than 5 ppm (water purity is doubtful), other springs with BOD less than 5 ppm comply with Schoeller and 1053 standard of Iran and WHO and are pure water.
6- Except for spring M3, which is free of coliforms due to fecal coliform feces, all other four springs have fecal origin water pollution and all springs have bacteria originating from sewage and are placed in unsatisfactory water class.
7- According to Iranian standards, all springs are within the permitted range, but according to WHO, Abkar spring, except for chlorine ions, comply with other cases, and other springs comply with WHO standards and are within the permitted range.