GEOCHEMISTRY, GROUNDWATER AND POLLUTION,

Transcription

1 GEOCHEMISTRY, GROUNDWATER AND POLLUTION, 2 ND EDITION C.A.J. APPELO Hydrochemical Consultant, Amsterdam, the Netherlands D.POSTMA Institute 01Environment & Resources DTU, Technical University 01Denmark, Kgs. Lyngby, Denmark AA BALKEMA PUBLISHERS LeideniLondonINew York/Philadelphia/Singapore

2 Contents LIST OF EXAMPLES NOTATION XII XV INTRODUCTION TO GROUNDWATER GEOCHEMISTRY I 1.1 Groundwater as drinking water I Standards for drinking water I 1.2 Units ofanalysis Groundwater quality Sampling of groundwater Depth integrated or depth specific sampling Procedures für sampling of groundwater Chemical analysis ofgroundwater Field analyses and sampie conservation Accuracy ofchemical analysis FROM RAINWATER TO GROUNDWATER The hydrological cycle The composition of rainwater Sources and transport ofatmospheric pollutants Stable isotopes in rain Isotopic ratios and the 8 notation The Rayleigh process The isotopic composition ofrain Dry deposition and evapotranspiration Mass balances and ecosystem dynamics Water quality profiles in the unsaturated soil Overall controls on water quality FLOW AND TRANSPORT Flow in the unsaturated zone Flow in the saturated zone 64 VII

3 VIII Contents Darcy's law Flowlines in the subsoil Effects of non-homogeneity The aquifer as a chemical reactor 3.3 Dating of groundwater 3.4 Retardation The retardation equation Indifferent and broadening fronts Sharpening fronts Solid and solute concentrations 3.5 Diffusion Diffusion coefficients Diffusion as a random process Diffusive transport Isotope diffusion 3.6 Dispersion Column breakthrough curves Dispersion coefficients and dispersivity Macrodispersivity 4 MINERALS AND WATER 4.1 Equilibria and the solubility of minerals 4.2 Corrections for solubility calculations Concentration and activity Aqueous complexes Combined complexes and activity corrections Calculation of saturation states 4.3 Mass action constants and thermodynamies The calculation of mass action constants Calculation of mass action constants at different temperature 4.4 Equilibrium calculations with PHREEQC Speciation calculations using PHREEQC The PHREEQC database Mineral equilibration 4.5 Solid solutions Basic theory The fractionation factor for solid solutions Kinetic effects on the fractionation factor 4.6 Kinetics of geochemieal processes Kinetics and equilibrium Chemical reactions and rates Temperature dependency ofreaction rates Mechanisms of dissolution and crystallization Rate laws for mineral dissolution and precipitation

4 Contents IX 5 CARBONATES AND CARBON DIOXIDE Carbonate minerals Dissolved carbonate equilibria The carbonic acid system Determining the carbonate speciation in groundwater Carbon dioxide in soils Calcite solubility and Pco Calcite dissolution in systems open and closed for CO 2 gas Two field examples Carbonate rock aquifers Dolomite and dedolomitization Pleistocene carbonate aquifers Kinetics of carbonate reactions Dissolution Precipitation Carbon isotopes Carbon-13 trends in aquifers C and groundwater age Retardation by sorption and stagnant zone diffusion ION EXCHANGE Cation exchange at the saltlfresh water interface Adsorbents in soils and aquifers Clay minerals Exchange equations Values for exchange coefficients Calculation of exchanger composition Calculation of exchanger composition with PHREEQC Determination of exchangeable cations Chromatography of cation exchange Field examples of freshening Salinity effects on cation exchange Quality patterns with salinization Fronts and chromatographic sequences Modeling chromatographic sequences with PHREEQC Physical non-equilibrium Modeling stagnant zones The Gouy-Chapman theory of the double layer Numerical integration of the double layer equations Practical aspects of double layer theory Irrigation water quality SORPTION OF TRACE METALS The origin and occurrence of heavy metals in groundwater Sorption isotherms and distribution coefficients 315

5 X Contents Distribution coefficients from ion exchange Variable charge surfaces Titration curves with suspended oxide particles Surface charge and point ofzero charge, PZC Sorption edges Sorption, absorption, and coprecipitation Surface complexation Surface complexation models The ferrihydrite (Fe(OH)3) database Diffuse double layer concentrations in surface complexation models 7.5 Complexation to humic acids The ion association model Tipping and Hurley's discrete site model "WHAM" Distribution models Humic acids as carriers oftrace elements 7.6 Kinetics of surface complexation Extrapolation of adsorption kinetics for other metal ions 7.7 Field applications 8 SILICATE WEATHERING Weathering processes The stability of weathering products Incongruent dissolution of primary silicates The mass balance approach to weathering Kinetics of silicate weathering Field weathering rates Acid groundwater Buffering processes in aquifers REDOX PROCESSES Basic theory The significance of redox measurements Redox reactions and the pe concept Redox diagrams Stability of water The stability of dissolved species and gases: Arsenic The stability of minerals in redox diagrams Sequences ofredox reactions and redox zoning Decomposition of organic matter Oxygen consumption Pyrite oxidation Kinetics of pyrite oxidation Oxygen transport and pyrite oxidation Nitrate reduction Nitrate reduction by organic matter oxidation Nitrate reduction by pyrite and ferrous iron

6 Contents XI 9.6 Iron reduction and sources ofiron in groundwater Iron in aquifer sediments Reductive dissolution ofiron oxides 9.7 Sulfate reduction and iron sulfide formation The formation of iron sulfides 9.8 The formation ofmethane 10 POLLUTION BY ORGANIC CHEMICALS 10.1 Gas-water exchange Evaporation of a pure organic liquid 10.2 Transport of pure organic liquids through soil 10.3 Sorption of organic chemicals Sorption of charged organic molecules Sorption in stagnant zones Release from stagnant zones and blobs 10.4 Transformation reactions of organic chemicals Monod biotransformation kinetics 10.5 Kinetic complexation of heavy metals on organics 11 NUMERICAL MODELING 11.1 Numerical modeling of transport Only diffusion Advection and diffusion/dispersion Non-linear reactions 11.2 Examples of hydrogeochemical transport modeling Tritium-Helium age dating Toluene degradation in an aquifer Remediation of a BTEX polluted site Acid drainage from a Uranium mine In-situ iron removal from groundwater Arsenic in Bangladesh groundwater Fractionation of isotopes APPENDIX A: HYDROGEOCHEMICAL MODELING WITH PHREEQC APPENDIX B: ANSWERS TO PROBLEMS INDEX

7 List of Examples 1.1 Recalculation of concentration units 1.2 Effect of iron oxidation on analytical results 1.3 Estimating the reliability ofwater analyses 1.4 Analytical errors due to precipitation in the sampling bottle Calculate 1) 18 0 ofrain condensing from vapor 2.2 Calculate recharge using the CI- mass balance 2.3 Estimate the Cl- and NO] concentration in groundwater below agriculturalland Calculate the travel time from midway in the Vejen waste site to 125 m downstream 3.2 Calculate the water level in the Vejen river, 1km downstream from the waste site 3.3 Flushing of NO] from an aquifer 3.4 Retardation and isotherm slope 3.5 Analytical modeling of column elution 3.6 Retardation of a sharp front 3.7 Recalculate 10 ppm As in sand to solute concentration in mg/l pore water 3.8 Travel time of diuron in a soil 3.9 Calculation of a diffusion profile 3.10 Diffusive flux through a clay barrier (after Johnson et al., 1989) 3.11 Chloride isotope fractionation during diffusion 3.12 Dispersion coefficient from a single shot input 3.13 Front dispersion in a column 3.14 Pollutant spreading during transport in an aquifer 3.15 Longitudinal dispersivity in the Borden aquifer Gypsum addition to high fluor groundwater 4.2 Calculate ionic strength and ion activity coefficients 4.3 Solubility ofgypsum 4.4 Calculation of solubility products from Gibbs free energy data 4.5 Temperature dependency of the solubility product 4.6 Calculate the speciation of a water analysis using PHREEQC 4.7 Solubility ofquartz at 150 C 4.8 Equilibrate a water sampie with minerals 4.9 Ideal solid solution of Cd2+ in calcite 4.10 Non-ideal solid solution ofcd2+ in calcite 4.\\ Miscibility gap in the solid solution 4.12 Oxidation offe(2) 4.13 Dissolution of hydroxyapatite; transport or surface reaction controlled? XII

8 List o[examples XIII Dissolution rate of quartz Kinetic dissolution of quartz with PHREEQC Calculate TIC in water for a fixed CÜ2 pressure Calculation of the aqueous carbonate system with PHREEQC Manual calculation ofcarbonate speciation and SIe.leite PHREEQC calculation ofcarbonate speciation and SIe.leite Calculate mixing effects on calcite saturation state with PHREEQC PHREEQC calculation ofopen and closed system calcite dissolution Propagation of the calcite dissolution front in the R0m0 aquifer Dissolution ofdolomite in the Italian Dolomites Kinetic dissolution ofcalcite calculated with PHREEQC, comparing simplified and parent "PWP" rates PHREEQC calculation ofo 13 C during calcite dissolution PHREEQC calculation of 13C evolution during dedolomitization Groundwater age from 14C Estimate exchangeable carbonate on Chalk and the retardation of 14C Estimate the retardation of 14C by matrix diffusion Recalculate CEC (meq/kg soil) to concentration (meq/l pore water) Structural charge of smectite Exchange coefficients as a function of solution normality Calculate the cation exchange complex in equilibrium with groundwater Calculate the exchanger composition in contact with groundwater, using PHREEQC Calculate the exchanger composition, using the Rothmund-Komfeld equation Simulate the analytical measurement ofexchangeable cations Flushing of an exchange complex The water composition after passage of a salinity front during freshening Flushing of K + from a column PHREEQC model for Valocchi's field injection experiment Calculate the surface potential on montmorillonite Calculation of the Exchangeable Sodium Ratio (ESR) Calculation of SAR adjusted for calcite precipitation Freundlich sorption isotherm for Cd 2 + on loamy sand Estimate the distribution coefficient of Cd 2 + Distribution coefficient for S~+ Exchange coefficient of Cd 2 + vs Na+ on montmorillonite Calculate the specific capacitance of a -y-a12ü3 surface Calculate the surface potential on -y-a12ü3 Calculate the equivalent ionic strength for a constant capacity model Recalculate sites/nm 2 to mol/l Sorption ofcd 2 + to iron oxyhydroxide in loamy sand Estimate the spherical surface area ofa fulvic acid Sorption of Cd 2 + to organic matter in loamy sand Calculate heavy metal removal from groundwater with aeration and filtration Incongruent dissolution of K-feldspar Mass balance and the water chemistry ofthe Sierra Nevada (USA) Mass balance calculation of mineral weathering using PHREEQC Dissolution kinetics ofk-feldspar as calculated by PHREEQC Acid groundwater formation and gibbsite buffering Modeling acidification with PHREEQC Calculation ofredox speciation with the Nernst equation Calculate EO from LlG~

9 XIV List 0/examples 9.3 Calculation of redox speciation using the pe concept Calculation ofk from thermodynamic data Oxidation ofthe atmosphere's N 2 content to nitrate Calculation of redox zonation with PHREEQC Applying Henry's law to oxygen dissolution Compare oxygen flux and carbon productivity in a soil Modeling gas loss during pyrite oxidation with oxygen Construct a redox balance for nitrate reduction by organic matter oxidation I I Reaction ofbenzene with iron-oxide and methanogenesis ph butfering by pyrite and kinetically dissolving iron oxides Estimate the flux offreon-ii (CCI 3 F) into the sea Retardation oflindane and PCH Calculate sorption and ion exchange ofquinoline with PHREEQC Estimate the composition of a DNAPL pool in an aquifer Model the extraction ofa DNAPL pool with PHREEQC Estimate the hazard of groundwater pollution by methyl bromide PHREEQC model of phenol degradation Xylene degradation with biomass growth Speciation ofedta in Glatt river water Kinetic exchange offe(3)edta Il.l Calculation of aquifer pollution by waste site leachate A Pascal code to model Cl- diffusion from seawater into fresh water sediment Implicit calculation of diffusion Model the linear retardation of ')'-HCH in a laboratory column Etfect ofthe Freundlich exponent on breakthrough curves from a column