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Groundwater Chemistry



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Groundwater Chemistry Natural water quality problems in Groundwater 1 Inorganics from natural geochemical sources As Se Ba 2 Radionuclides Radon 3 Hardness 4 Sulfate 5 Dissolved Iron and Manganese 6 Taste and Odor 7 Total Dissolved Solids Groundwater Chemistry Anthropogenic Water Quality Problems 1 Inorganics 2 Volatile Organic Carbons VOCs 3 Synthetic Organic Carbons SOCs Where do the major ions in Groundwater come from Major Cations Mineral Sources Major Anions Mineral Sources 1 Groundwater Chemistry Some Definitions Hardness Alkalinity Acid neutralizing capacity of a water The amount of strong acid needed to bring the pH of a water to near 4 7 Dissolved Organic Carbon Total Inorganic Carbon Ionic Strength Activity and Ionic Strength 2 Groundwater Chemistry is Carbonate Chemistry approx 360 ppm by volume of CO2 in clean atmosphere CO2 aq CO2 g KH 10 1 5 atm mol L CO2 aq H2O aq H2CO3 aq H2CO3 H HCO3 1 Ka1 10 6 3 HCO3 H CO3 2 Ka2 10 10 3 CO2 g H2O aq H aq HCO3 aq Groundwater Chemistry is Carbonate Chemistry 3 Carbonate Equilibrium in Different Environments Atmosphere pH pCO2 Unsaturated Zone Roots pH pCO2 Groundwater saturated zone carbonate dissolution pH pCO2 Chemistry along Groundwater Flow Path Ca2 ALK TDS I SO42ClGroundwater Flow Path Distance or Age of Groundwater 4 Bar Pie Diagrams to Represent GW Chemistry Check water analysis by checking charge balance Carbonate Equilibrium Calculations ALK TIC Combine with Equilibrium Expressions 5 Carbonate Equilibrium Calculations Is Groundwater Saturated wrt to a Mineral Important question because if it is 1 undersaturated then gw is dissolving aquifer material 2 supersaturated then mineral is precipitating in aquifer 6 Mineral Solubility Products Solubility Example A groundwater analysis reveals that there is 134 mg L of calcium Ca2 and 429 mg L of sulfate SO42 The ionic strength is 0 025 M Calculate the molar concentration and activity of each ion to estimate the ion activity product Is the groundwater is saturated



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