Groundwater Remediation Lecture NOTE 9 (Contaminant Hydrogeology)

1. Groundwater Remediation Lecture NOTE 9 (Contaminant Hydrogeology) Joonhong Park Yonsei CEE Department 2013. 11. 27

2. Sources of GW Contamination • Degree of Localization (point vs. nonpoint) • Loading History • Kinds of Contaminants

3. Light NAPL (non-aqueous phase liquid) contamination Tank LNAPL residual Vapor from LNAPL Capillary fringe LNAPL Free Phase Water table Dissolved LNAPL (plume) Groundwater Flow

4. Dense NAPL contamination Vapor from NAPL NAPL residual Capillary fringe Water table Dissolved NAPL (plume) Clay Layer Groundwater Flow Direction LNAPL Free Phase Groundwater Flow Bedrock

5. Contamination Loading History • Pulsed versus Continuous Loading • Variable versus Constant Concentrations • Figure 17.2 • Hysteresis issues

6. Types of Contaminants • Radioactive contaminants: Eh-pH (Fig. 16.8, p.334) • Trace Metals: Eh-pH (Fig.12.11, p.276) • Nutrients (Nitrate, ammonia, phosphorus species) • Other Inorganics (salinity, perchlorate, fluoride etc.) • Organic contaminants (hydrocarbons, halogenated aliphatics, halogenated aromatics, persistent organic pollutants [POPs]) • Biological contaminants (bacteria, fungi, virus etc.)

7. Organic Contaminants (Table 17.5) • Petroleum Hydrocarbons and derivatives: (i) fuels (BTEX, butane, phenol), alcohols, creosote (cresols), ketones (acetone) [aerobically degradable; mobile; light]; (ii) PAHs (acenaphthene, benzopyrene, benzoperylene) [little mobile] • Halogenated Aliphatic Compounds: (i) monochloride ethane; dichloroethane; trichloroethane (chloroform); (ii) monochloride ethene(VC), dichloroethene (DCE), trichloroethene (TCE), tetrachloroethene (PCE) [aerobically or anaerobically degradable; mobile; dense] • Halogenated Aromatic Compounds: brominated aromatics; polychloriated biphenyls and dioxins [aerobically or anaerobically degradable; little mobile; dense] • POPs (Persistent Organic Pollutants): PCBs, pesticides, dioxins; PAHs [very little mobile; dense]

8. Important Chemical Properties • Oxidation-Reduction potentials (Eh) • Hydrogen dissociation constant (Ka) • Solubility (Cs) • Solid Formation Constant (Ks) • Henry’s Constant • Vapor Pressure (p) • Specific Gravity • Octanol-Water Partitioning Constant (Kow)

9. 1.2 O2 H2O 0.4 Mobile species Eh Immobile species 0 H2O H2 0 pH 14

10. Aerobic degradation (산화) Sorption to Soil Organics Reductive dechlorination (환원) Sorption onto Subsurface Material Degradation Rate Monochlorinated Polychlorinated 0.25 4 Degree of chlorination

11. The most frequently detected groundwater contaminants in hazardous waste sites

12. Relative ease of cleaning-up of contaminated aquifers as a function of contaminant chemistry and hydrogeology (1=easiest; 4 = the most difficult) Contaminant chemistry Strongly sorbed, dissolved (degrades/volatilizes) Strongly sorbed, dissolved Separate Phase LNAPL Separate Phase DNAPL Mobile, Dissolved (degrades/ Volatilizes) Mobile, Dissolved Hydrogeology Homogeneous, single layer 1 1-2 2 2-3 2-3 3 Homogeneous, multiple layer 1 1-2 2 2-3 2-3 3 Heterogeneous, single layer 2 2 3 3 3 4 Heterogeneous, multiple layer 2 2 3 3 3 4 Fractured 3 3 3 3 4 4

13. Solute Plumes as a Manifestation of Processes • Transport Processes • Transformation Processes • Water table configuration or piezometeric surface • Region shape • Pumping • Pollutant loading function

14. Design of Sampling Networks • Close interval point sampling and sample locations. • Screen length issue: Differences in sampling (REVs) for hydraulic heads and contaminant concentrations. • Unfortunately, a system that is ideal for chemical sampling is usually not very good for measuring hydraulic heads with an electric tape (device). • The location of sampling points should account for the character and complexity of flow. • Defining the vertical extent of the plume is most difficult because often plumes are not very think. • A simple system: a line of samplers installed along the midline of the plume.

15. Assuring the Quality of Chemical Data Main problems and measures: • Contamination of samples with fluids that were used to drill the hole (use a tracer in drill fluids) • Changes in water quality caused by the presence of the well. (well materials) • Sample deterioration (environmental conditions change after collection of water samples. Use standard collection and preservation methods) • Sloppy field and laboratory practices. (for field work, use appropriate bottle washing, filtering or preservatives ; for laboratory works, use spiked controls, duplicate samples to different laboratories, and analysis of replicate samples)

16. Sampling Methods • Conventional Wells or Piezometers • Multilevel Samplers (Standpipe type, Bundle Piezometers, Suction type, Westbay-type Samplers, Gas-drive sampler) • Solid and Fluid Sampling: Cone Penetrometry (hydraulic heads, water samples with depth, unconsolidated sediment samples, GeoProbe) • Dissolved Contaminants in the Unsaturated Zone

17. Indirect Methods for Detecting Contamination • Soil-Gas Characterization • Industrial standard tech for tracing volatile organic compounds in groundwater (good for gasoline detection) • Limitation: Not detecting all organic pollutants (not good for detecting non volatile or too soluble volatiles); Presence of low permeability layers blocking gas flow. • Vapor pressure-Aqueous Solubility Plot (Figure 17.23) • Gas Chromatograph (GC) • Rapid and economic way of survey of large sites

18. Indirect Methods for Detecting Contamination • Geophysical Methods • Electrical methods (conductivity, electromagnetic methods) • Ground-Penetrating Radar (GPR) (water table, stratigraphic boundaries, NAPLs; less useful in clayed, moist lake clay or glacial till) • Magnetometry (variations in the Earth’s total magnetic filed; to locate containers and pipelines; no use for organic contaminants themselves) • Seismic Methods