Groundwater Remediation Lecture NOTE 9 (Contaminant Hydrogeology) Joonhong Park Yonsei CEE Department

Sources of GW Contamination (1)Degree of Localization (point vs. nonpoint) (2)Loading History (3)Kinds of Contaminants

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

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

Contamination Loading History (1)Pulsed versus Continuous Loading (2)Variable versus Constant Concentrations (3)Figure 17.2 (4)Hysteresis issues

Types of Contaminants (1)Radioactive contaminants: Eh-pH (Fig. 16.8, p.334) (2)Trace Metals: Eh-pH (Fig.12.11, p.276) (3)Nutrients (Nitrate, ammonia, phosphorus species) (4)Other Inorganics (salinity, perchlorate, fluoride etc.) (5)Organic contaminants (hydrocarbons, halogenated aliphatics, halogenated aromatics, persistent organic pollutants [POPs]) (6)Biological contaminants (bacteria, fungi, virus etc.)

Organic Contaminants (Table 17.5) (1)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] (2)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] (3)Halogenated Aromatic Compounds: brominated aromatics; polychloriated biphenyls and dioxins [aerobically or anaerobically degradable; little mobile; dense] (4)POPs (Persistent Organic Pollutants): PCBs, pesticides, dioxins; PAHs [very little mobile; dense]

Important Chemical Properties (1)Oxidation-Reduction potentials (Eh) (2)Hydrogen dissociation constant (Ka) (3)Solubility (Cs) (4)Solid Formation Constant (Ks) (5)Henry’s Constant (6)Vapor Pressure (p) (7)Specific Gravity (8)Octanol-Water Partitioning Constant (Kow)

pH 14 Eh H2 H2O O2 Mobile species Immobile species

MonochlorinatedPolychlorinated Degree of chlorination Sorption onto Subsurface MaterialDegradation Rate Sorption to Soil Organics Reductive dechlorination ( 환원 ) Aerobic degradation ( 산화 )

The most frequently detected groundwater contaminants in hazardous waste sites RankCompoundCommon sources Trichloroethene (TCE) Lead Tetrachloroethene (PCE) Benzene Toluene Chromium Methylene chloride Zinc 1,1,1-trichloroethane Arsenic Chloroform 1,2-dichloroethane trans 1,2-dichloroethene Cadmium Manganese Dry cleaning; metal degreasing Gasoline (prior to 1975);mining, construction materials (pipe), manufacturing Dry cleaning; metal degreasing Gasoline; manufacturing Metal plating Degreasing; solvents; paint removal Manufacturing; mining Metal and plastic cleaning Mining; manufacturing Solvents Degreasing; solvents By product of 1,1,1-TCA or TCE Mining; plating; battery Manufacturing; mining; natural occuring.

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

Solute Plumes as a Manifestation of Processes (1)Transport Processes (2)Transformation Processes (3)Water table configuration or piezometeric surface (4)Region shape (5)Pumping (6)Pollutant loading function

Design of Sampling Networks (1)Close interval point sampling and sample locations. (2)Screen length issue: Differences in sampling (REVs) for hydraulic heads and contaminant concentrations. (3)Unfortunately, a system that is ideal for chemical sampling is usually not very good for measuring hydraulic heads with an electric tape (device). (4)The location of sampling points should account for the character and complexity of flow. (5)Defining the vertical extent of the plume is most difficult because often plumes are not very think. (6)A simple system: a line of samplers installed along the midline of the plume.

Assuring the Quality of Chemical Data (1)Contamination of samples with fluids that were used to drill the hole (use a tracer in drill fluids) (2)Changes in water quality caused by the presence of the well. (well materials) (3)Sample deterioration (environmental conditions change after collection of water samples. Use standard collection and preservation methods) (4)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) Main problems and measures:

Sampling Methods (1)Conventional Wells or Piezometers (2)Multilevel Samplers (Standpipe type, Bundle Piezometers, Suction type, Westbay-type Samplers, Gas-drive sampler) (3)Solid and Fluid Sampling: Cone Penetrometry (hydraulic heads, water samples with depth, unconsolidated sediment samples, GeoProbe) (4)Dissolved Contaminants in the Unsaturated Zone

Indirect Methods for Detecting Contamination Soil-Gas Characterization (1)Industrial standard tech for tracing volatile organic compounds in groundwater (good for gasoline detection) (2)Limitation: Not detecting all organic pollutants (not good for detecting non volatile or too soluble volatiles); Presence of low permeability layers blocking gas flow. (3)Vapor pressure-Aqueous Solubility Plot (Figure 17.23) (4)Gas Chromatograph (GC) (5)Rapid and economic way of survey of large sites

Indirect Methods for Detecting Contamination Geophysical Methods (1)Electrical methods (conductivity, electromagnetic methods) (2)Ground-Penetrating Radar (GPR) (water table, stratigraphic boundaries, NAPLs; less useful in clayed, moist lake clay or glacial till) (3)Magnetometry (variations in the Earth’s total magnetic filed; to locate containers and pipelines; no use for organic contaminants themselves) (4)Seismic Methods