Further Information for Lecture 4
Hazardous Pollutants
The information provided on this page is to enhance your understanding of three aspects:
- The most common sources of these hazardous materials.
- What these hazardous compounds actually are and why their fate depends on factors like volatility, solubility and persistence.
- The affect no remedial action has: diseases and health risks - as occurred in the 'Love Canal'
Common Sources:
THE EIGHT CONTAMINANT GROUPS:
The hazardous materials can be separated into the following eight contaminant groups:
- Nonhalogenated volatile organic compounds (VOCs)
- Halogenated volatile organic compounds
- Nonhalogenated semivolatile organic compounds (SVOCs)
- Halogenated semivolatile organic compounds
- Fuels
- Inorganics
- Radionuclides
- Explosives.
1) Non-halogenated volatile organic compounds (VOCs)
A nonhalogenated compound is one which does not have a halogen (e.g., fluorine, chlorine, bromine, or iodine) attached to it. e.g. Alcohols, fuels, BTEX, and gas phase contaminants
Subsurface contamination by nonhalogenated VOCs potentially exists in four phases:
**Any of these phases may occupy the pore spaces in the unsaturated zone.
**Residual bulk liquid may occur through a number of mechanisms (volatilisation, advection and diffusion) and be retained by capillary attraction in the porous media (where NAPLs 'break' from their continuous phase, leaving isolated residual globules).
Insoluble organic contaminants may be present as NAPLs:
Sites where non-halogenated VOCs may be found include:
-burn pits, chemical manufacturing plants or disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive/mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas.
Subsurface contamination by nonhalogenated VOCs potentially exists in four phases:
- Gaseous phase: Contaminants present as vapours in unsaturated zone.
- Solid phase: Contaminants in liquid form adsorbed on soil particles in both saturated and unsaturated zones.
- Aqueous phase: Contaminants dissolved into pore water according to their solubility in both saturated and unsaturated zones.
- Immiscible phase: Contaminants present as non-aqueous phase liquids (NAPLs) primarily in unsaturated zone.
**Any of these phases may occupy the pore spaces in the unsaturated zone.
**Residual bulk liquid may occur through a number of mechanisms (volatilisation, advection and diffusion) and be retained by capillary attraction in the porous media (where NAPLs 'break' from their continuous phase, leaving isolated residual globules).
- Volatilisation from residual saturation or bulk liquid into the unsaturated pore spaces produces a vapour plume. Advection and diffusion processes may cause lateral migration of this vapour plume (independent of ground water movement).
- Advection: the vapour plume contaminants are transported by the movement of air - may result from gas pressure or gas density gradients.
- Diffusion: the movement of contaminants from areas of high vapour concentrations to areas of lower vapour concentrations.
- Advection: the vapour plume contaminants are transported by the movement of air - may result from gas pressure or gas density gradients.
- Volatilisation from contaminated ground water also may produce a vapour plume of compounds with high vapor pressures and high aqueous solubilities.
- Dissolution of contaminants into water (from residual saturation or bulk liquid) may occur in either the unsaturated or saturated zones, then move in the G.W flow. Even low-solubility organics may be present at low concentrations dissolved in water.
Insoluble organic contaminants may be present as NAPLs:
- Dense NAPLs (DNAPLs) have a specific gravity greater than unity and will tend to sink to the bottom of surface waters and ground water aquifers.
- Light NAPLs (LNAPLs) will float on top of surface water and ground water.
- The DNAPLs and LNAPLs may adhere to the soil through the capillary fringe and may be found on top of water in temporary or perched aquifers in the vadose zone.
Sites where non-halogenated VOCs may be found include:
-burn pits, chemical manufacturing plants or disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive/mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas.
2) Halogenated VOCs
A halogenated compound is one onto which a halogen (e.g., fluorine, chlorine, bromine, or iodine) has been attached, typically requiring more extensive treatment than nonhalogenated compounds. The more halogenated the compound (i.e., the more halogens attached to it), the more resistant it is to biodegradation.
Incineration of halogenated compounds requires specific off-gas and scrubber water treatment for the halogen, in addition to the normal controls that are implemented for nonhalogenated compounds.
Note: Contamination by VOCs potentially exists in the same four phases as for non-halogenated VOCs (Gaseous, solid, aqueous & immiscible), same transport processes can occur (see non-halogenated VOCs (above)) and again, can be present as NAPLs.
Sites where halogenated VOCs may be found include:
-burn pits, chemical manufacturing plants or disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive/mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas.
Incineration of halogenated compounds requires specific off-gas and scrubber water treatment for the halogen, in addition to the normal controls that are implemented for nonhalogenated compounds.
Note: Contamination by VOCs potentially exists in the same four phases as for non-halogenated VOCs (Gaseous, solid, aqueous & immiscible), same transport processes can occur (see non-halogenated VOCs (above)) and again, can be present as NAPLs.
Sites where halogenated VOCs may be found include:
-burn pits, chemical manufacturing plants or disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive/mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas.
3) Non-halogenated semivolatile organic compounds (SVOCs)
Nonhalogenated SVOC contaminants include PAHs (e.g. naphthalene, phenanthrene, anthracene, pyrene, fluoranthene) and pesticides (e.g. insecticides, fungicides, herbicides).
See non-halogenated VOCs for the phases, transport processes and contaminant locations (these are the same). Also, as for non-halogentaed VOCs, insoluble/low solubility organic contaminants may be present as NAPLs.
Sites where nonhalogenated SVOCs may be found include burn pits, chemical manufacturing plants and disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radiologic/mixed waste disposal areas, oxidation ponds/lagoons, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas and wood preserving sites.
See non-halogenated VOCs for the phases, transport processes and contaminant locations (these are the same). Also, as for non-halogentaed VOCs, insoluble/low solubility organic contaminants may be present as NAPLs.
Sites where nonhalogenated SVOCs may be found include burn pits, chemical manufacturing plants and disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radiologic/mixed waste disposal areas, oxidation ponds/lagoons, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas and wood preserving sites.
4) Halogenated semivolatile organic compounds
Halogenated SVOC contaminants include PCBs (e.g. Pentachlorophenol) and pesticides (e.g. insecticides, fungicides, herbicides).
See non-halogenated VOCs for the phases, transport processes and contaminant locations (these are the same). While the degree of volatilisation from halogenated SVOCs is much less than for halogenated VOCs, the same transport processes occur and insoluble/low solubility organic contaminants may be present as NAPLs.
Sites where halogenated SVOCs may be found include burn pits, chemical manufacturing plants and disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radiologic/mixed waste disposal areas, oxidation ponds/lagoons, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas and wood preserving sites.
See non-halogenated VOCs for the phases, transport processes and contaminant locations (these are the same). While the degree of volatilisation from halogenated SVOCs is much less than for halogenated VOCs, the same transport processes occur and insoluble/low solubility organic contaminants may be present as NAPLs.
Sites where halogenated SVOCs may be found include burn pits, chemical manufacturing plants and disposal areas, contaminated marine sediments, disposal wells and leach fields, hangars/aircraft maintenance areas, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radiologic/mixed waste disposal areas, oxidation ponds/lagoons, pesticide/herbicide mixing areas, solvent degreasing areas, surface impoundments, and vehicle maintenance areas and wood preserving sites.
5) Fuels
Fuel contaminants are generally nonhalogenated. The contaminants in the unsaturated zone exist in the same four phases (vapours in the pore spaces, sorbed to subsurface solids, dissolved in water & as NAPLs.
The nature and extent of transport are determined by the interactions among contaminant transport properties (e.g., density, vapour pressure, viscosity) and the subsurface environment (e.g., geology, aquifer mineralogy, and ground water hydrology).
The nature and extent of transport are determined by the interactions among contaminant transport properties (e.g., density, vapour pressure, viscosity) and the subsurface environment (e.g., geology, aquifer mineralogy, and ground water hydrology).
- Most fuel-derived contaminants are less dense than water and can be detected as floating pools (LNAPLs) on the water table.
- Typically, after a spill occurs, LNAPLs migrate vertically in the subsurface until residual saturation depletes the liquid or until the capillary fringe above the water table is reached.
- Some spreading of the bulk liquid occurs until pressure from the infiltrating liquid develops sufficiently to penetrate to the water table.
- The pressure of the infiltrating liquid pushes the spill below the surface of the water table.
- Bulk liquids less dense than water spread laterally and float on the surface of the water table, forming a mound that becomes compressed into a spreading lens.
- As the plume of dissolved constituents moves away from the floating bulk liquid, interactions with the soil particles affect dissolved concentrations. Compounds more attracted to the aquifer material move at a slower rate than the ground water and are found closer to the source; compounds less attracted to the soil particles move most rapidly and are found in the leading edge of a contaminant plume.
- More volatile LNAPL compounds readily partition into the air phase.
- Vapour-phase transport can be followed by subsequent dissolution into ground water.
6) In-organics
These include: metals (in the elemental form or as salts mixed in the soil), radioactive materials (radionuclides), arsenic and asbestos. Asbestos fibres require special care to prevent their escape during handling and disposal; permanent containment must be provided.
Metals cannot be degraded or readily detoxified and can pose a long-term environmental hazard. Treatment options for radioactive materials are limited to volume reduction/concentration and immobilisation.
The fate of the metal depends on its physical/chemical properties, the associated waste matrix, and the soil. Significant downward transportation of metals from the soil surface occurs when the metal retention capacity of the soil is overloaded, or when metals are solubilised (e.g., by low pH). As the concentration of metals exceeds the ability of the soil to retain them, the metals will travel downward with the leaching waters. Surface transport through dust and erosion of soils are common transport mechanisms. The extent of vertical contamination intimately relates to the soil solution and surface chemistry.
Sites where inorganic contaminants may be found include artillery and small arms impact areas, battery disposal area, burn pits, chemical disposal areas, contaminated marine sediments, disposal wells and leach fields, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive and mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, sand blasting areas, surface impoundments, and vehicle maintenance areas.
Metals cannot be degraded or readily detoxified and can pose a long-term environmental hazard. Treatment options for radioactive materials are limited to volume reduction/concentration and immobilisation.
The fate of the metal depends on its physical/chemical properties, the associated waste matrix, and the soil. Significant downward transportation of metals from the soil surface occurs when the metal retention capacity of the soil is overloaded, or when metals are solubilised (e.g., by low pH). As the concentration of metals exceeds the ability of the soil to retain them, the metals will travel downward with the leaching waters. Surface transport through dust and erosion of soils are common transport mechanisms. The extent of vertical contamination intimately relates to the soil solution and surface chemistry.
Sites where inorganic contaminants may be found include artillery and small arms impact areas, battery disposal area, burn pits, chemical disposal areas, contaminated marine sediments, disposal wells and leach fields, landfills and burial pits, leaking collection and system sanitary lines, leaking storage tanks, radioactive and mixed waste disposal areas, oxidation ponds/lagoons, paint stripping and spray booth areas, sand blasting areas, surface impoundments, and vehicle maintenance areas.
7) Radio-nuclides
Radionuclides should be considered to have properties similar to those of other heavy metals. Like metals, the contaminants are typically nonvolatile and less soluble in water than some other contaminants. The solubility, mobility and volatility of individual radionuclides will vary and some may volatilise when treated with processes at elevated temperatures (e.g., vitrification) requiring an off-gas treatment.
Radionuclides cannot be destroyed or degraded; therefore, the only remediation technologies applicable involve separation, concentration/volume reduction, and/or immobilisation. Because radionuclides are not destroyed, ex situ techniques will require eventual disposal of residual radioactive wastes. These waste forms must meet disposal site waste acceptance criteria.
Sites where radionuclide contaminants may be found are mainly radioactive and mixed waste disposal areas.
Radionuclides cannot be destroyed or degraded; therefore, the only remediation technologies applicable involve separation, concentration/volume reduction, and/or immobilisation. Because radionuclides are not destroyed, ex situ techniques will require eventual disposal of residual radioactive wastes. These waste forms must meet disposal site waste acceptance criteria.
Sites where radionuclide contaminants may be found are mainly radioactive and mixed waste disposal areas.
8) Explosives
The term "explosive waste" commonly is used to refer to propellants, explosives (e.g. TNT), and pyrotechnics (PEP). These materials are susceptible to initiation/self-sustained energy release when present in sufficient quantities and exposed to heat, shock, friction, chemical incompatibility, or electrostatic discharge.
Safety precautions must be taken at sites contaminated with explosive wastes to avoid initiation. The most important safety precaution is to minimize exposure, which involves minimising the number of workers exposed to hazardous situations, the duration of exposure, and the degree of hazard.
Sites where explosive contaminants may be found include military/artillery/impact areas, contaminated marine sediments, disposal wells, leach fields, landfills, burial pits, and TNT washout lagoons.
Safety precautions must be taken at sites contaminated with explosive wastes to avoid initiation. The most important safety precaution is to minimize exposure, which involves minimising the number of workers exposed to hazardous situations, the duration of exposure, and the degree of hazard.
Sites where explosive contaminants may be found include military/artillery/impact areas, contaminated marine sediments, disposal wells, leach fields, landfills, burial pits, and TNT washout lagoons.