Hydro Week 3 Notes
Hydro Week 3 Notes GEOL 313
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This 4 page Class Notes was uploaded by Nimra Muhammad on Sunday September 20, 2015. The Class Notes belongs to GEOL 313 at George Mason University taught by Dr. Jules M Goldspiel in Fall 2015. Since its upload, it has received 34 views. For similar materials see Applied Hydrogeology in Geology at George Mason University.
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Date Created: 09/20/15
Groundwater chemical environment chemistry terms element an atom defined by its number of protons in nucleus ion charged atom or molecule anion and cation negative change and positive charge respectively ionic compound splits into ions ex nacl pbc03 cac03 compound molecule organic compounds molecules that contain carbon ex c02 c03A2 CN CH4 usually biological system inorganic compounds molecule that is not an organic compound usually geological system Mole unit for number of particle in a sample 602210quot23 molecular weight gmol concentration amount of constituent amount of total mixture mounts mass volume number units pph 1g100g o ppt 1g1000g o ppm 1 g1000000 g ppb 1 g1 000000000 g many ways to report concentration moll molarity gt liter of solution solventwater solute molkg molality gt kg of solvent activity effective concentration alpha yi mi yi activity coefficient mi molal concentration molg how many going to participate in a chemical reaction accounts for non ideal solutions constituents react with each other by concentration gt a 1 for pure liquid and solid a is unitless by convention a yimi mi implied conditionally m in molkg in general a alpha is about 1 for uncharged species in dilute solution alpha gt1 for uncharged species in concentrate solution alpha lt 1 for uncharged species in concentrate solution equivalent unit of electric charge for a given ionic species eq ion amount ion change magnitude 1 eq 1 mole of equot usually magnitude of 10quot 3 eq Na 1 m eq 1moCa22meq Typical groundwater compounds major ion Na Ca Mg K Cl SO4quot2 HCOS C032 90 o of groundwater has these 8 ions other common ions Fe2 Fe3 Sr2 Br3 N03 F 01 10 mgL silica Si02 1 mgL Key Influences on Groundwater temperature chemical reaction rates depends on temperature pressure phase liquid Vs gas rates slightly water flow rates Q KA dhdl hydraulic concentration permeability viscosity gravity rock matrix composition what s coming in contact and what dissolves is important eg limestone Vs granite electrical neutrality constraint electrically neutral solutions eg no lighting bulb total number of positive charges ve charges multiply concentration of multivalent ions eg Ca2 by charge gt Zm Ca2 Key influences on Groundwater Quality existing Groundwater composition natural inorganic content ions solids natural organic plant membrane animal residue micro organism containment infiltration and injection infiltration surface water into the ground natural inorganic content natural organic content containment infiltration industrial municipal water treatment oil and gas agriculture local chemical reaction dissolution and precipitation eg wind cave national park SD ionic compounds nacl cac03 dissociate when dissolved in water important for several environments limestone CaCOS Anhydrite CaSO4 gypsum Oxidation Reduction 4Fe3 302 gt2Fe203 4e reaction that involves transfer of electrons ex uranium mine near Moab UT Solubility Dissociation and Equilibrium General chemical reaction aAbB gt cC dD can define activity product K for reaction K products reactants Solubility reactions dissolution cac03 gt ca2 COB 2 Si022H20 gt H4SiO4 Equilibrium reaction at equilibrium aequilibrium rate of formal reaction same rate as of reverse K Keq by definition K activity product Not Equilibrium Reaction reactions moves in direction to bring it to equilibrium if KgtKeq reaction moves to left activity product if Klt Keq if K Keq Ksp solubility product equilibrium water dissociation equilibrium water dissociation H20 gt H OH k a a OH a H20 if in equil kKeq 1010quot14 at 250 a 10A4 kw is function of pressure C02 bicarbonatecarbonate dissolution and dissociation equilibrium K c02 H20 coz a H2c03 KHZCOB H2003 gt H HCOB KHCOB HCOB a H 003A2 Kw H20 gt H OH Equilibrium Vs Kinetics rates forward and back are same energy forward state Kinetics rate at which reaction occurs rate at which reaction approach equil may not equally reach equilibrium Summary of K types for Groundwater chemistry K activity product and K ion activity product not necessarily equilibrium Keq equilibrium constant Ksp solubility product equilibrium constant from specific dissociation reaction Kw water dissociation constant equilibrium constant for water dissociation K species dissociation constant for given species equilibrium constant Key Metrics of Groundwater Quality water quality acidity pH og10a H2 groundwater pH 685 rarely above pH of 9 Alkalinity measure of ability to neutralize an acid Salinity measure of total dissolved salts concentration in water frequently interchanged with total dissolved solids Hardness measure of multivalent cations concentration in water frequently reported as cac03 pic summary of surface water measurements Ionic strengths calculated from all ion charges and concentrations l 12 Emiziquot2 used for calculating activity Oxidation potential measure of the tendency of dissolved and solid Natural organic contents amount of natural organic matter isotope and their uses stable isotope Cf 2 behave as 013
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