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Groundwater Geochemistry in the Alisadr,Hamedan, Western Iran Aida Asgary NDSU Geol 628 Geochemistry 2010
Why Groundwater Quality is Important • In arid and semi-arid regions, agriculture is limited by the availibility of suitable irrigation water. • Groundwater is the main source of irrigation and drinking in these areas.
Study Area • Climate of study area is semi-arid. • The area is characterized by predominance of metamorphic rocks (sedimentary rocks) • Groundwater has been used for drinking, agricultural and domestic purposes. • Hydrogeochemical investigation was carried out in Alisadr area to identify groundwater geochemistry and its suitability for irrigation purposes.
Fifty nine samples were selected.The results show that major cations in order to their concentrations are Ca+, Mg2+,Na+,and K.Among anions Co32-, Hco3, Cl-, and No3- have the highest concentrations.Besed on dominant cations and anions water types were found.
Groundwater Quality, WHO Standards • World Health Organization Standards • Based on WHO’s drinking water standards, limit for No3 in drinking water is 50 mg/l. • Concentration of No3 in 15% of the samples were above the standards. • High values of NO3 are results of agricultural activities.
Groundwater Quality, Total Hardness • Hard water is the water that contains high levels of dissolved calcium, magnesium. • Hardness = 2.5(mg Ca/L) + 4.1(mg Mg/L) • The greater the amount of dissolved minerals in the water, the harder it is. • mg/L Degree of Hardness. 0 - 75 Soft, 75 - 150 Moderately Hard, 150 - 300 Hard, 300 and up Very Hard
Groundwater Quality, Total Hardness Ways in which total hardness and water quality are connected are : • Household plumbing. • Decrease in cleaning ability. • Water heaters can become less efficient. • Most of the water samples were in the categoray of hard and very hardwater.
Groundwater Quality, SAR • The sodicity hazard of water is described by Sodium Adsorption Ratio ( SAR). • High concentrations of Na+ are undesirable in water because Na+ is adsorbed in to the soil cation exchange sites, causing soil accumulations to disperse, reducing its permeability.
Groundwater Quality, SAR SAR=[Na]/([Ca+mg]/2)^0.5 Areas with high SAR, special management with salinity control may be required, only plants with good salt tolerance should be selected.
The Origin of Species • Compositional relations among dissolved species can reveal the origin of species and the process that generated the observed water compositions. • Possitive correlations indicates common resource.
The Origin of Species • Negative correlation between Ca and HCO3 shows that Calcite (CaCO3) can not be the source of Ca. • Calcium and So4 ions in groundwater are provided mostly by the dissolution of Gypsum(CaSO4:2H2O) • There is a strong correlation between Na and Cl that may explain the dissolution of halite(NaCl) in water can be the source. • Dissolution of Anorthite (CaAl2Si2O8) also can contribute to Ca ions in groundwater.
Inverse Modeling • Inverse modeling is used to estimate sets of minerals and gases that account for the differences in composition between the solutions. At least two solution is needed, but we can add as many as we want. • Inverse modeling can be used to predict the changes that may occur in concentration of elements in the flowpath, by indicating whether a mineral will disolve or precipitate.
Inverse Modeling Hypothesis: In this study correlation ratios were used to demonstrate possible origin of species, can inverse modeling provide the same results?
Inverse Modeling • 5 water solution were chosen. • Water solutions show increase in concentration of elements, with emphasizes on elements that cause quality problems for water.
Inverse Modeling INVERSE_MODELING 1 -solutions 1 5 -uncertainty 0.5 0.5 -phases Gypsum Calcite Anorthite Halite -balances pH 0.2 0.2 -tolerance 1e-010 -mineral_water true
Results of Inverse Modeling Positive mole transfers show dissolution of a mineral, and negative mole transfers shows precipitation of a mineral
1. Phase Mole Transfers Minimum Maximum Gypsum 9.770e-004 0.000e+000 0.000e+000 CaSO4:2H2O Calcite -3.565e-004 0.000e+000 0.000e+000 CaCO3 Anorthite 3.840e-005 0.000e+000 0.000e+000 CaAl2Si2O8 Halite 1.797e-003 0.000e+000 0.000e+000 NaCl 2. Phase Mole Transfers Minimum Maximum Calcite -3.565e-004 0.000e+000 0.000e+000 CaCO3 Anorthite 3.840e-005 0.000e+000 0.000e+000 CaAl2Si2O8 Halite 1.796e-003 0.000e+000 0.000e+000 NaCl 3. Phase Mole Transfers Minimum Maximum Gypsum 9.770e-004 0.000e+000 0.000e+000 CaSO4:2H2O Anorthite 1.336e-005 0.000e+000 0.000e+000 CaAl2Si2O8 Halite 1.797e-003 0.000e+000 0.000e+000 NaC 4. Phase Mole Transfers Minimum Maximum Anorthite 1.336e-005 0.000e+000 0.000e+000 CaAl2Si2O8 Halite 1.796e-003 0.000e+000 0.000e+000NaCl
Results of Inverse Modeling • Results indicates the dissolution of gypsum, anorthite and halite and precipitation od calcite. • Based on the results origin of species are found, and they support the results in the article.