SITE REMEDIATION Pedro A. García Encina Department of Chemical Engineering University of Valladolid
CONTAMINATED SITES In the past much wastes were dumped indiscriminately or disposed of in inadequate facilities. These problems went ignored as did spills of product or leaks from tanks. Theses practices contaminated sites with hazardous substances that pose a threat to human populations.
HAZARDOUS WASTE - Characteristics Corrosivity - waste that is highly acidic or alkaline, with pH <2 or pH >12.5. Ignitability - waste that is easily ignited. Reactivity - waste that is capable of sudden, harmful reaction or explosion. Toxicity - waste capable of releasing specified, toxic substances to water in significant concentrations.
HAZARDOUS WASTE - Major Categories Inorganic Aqueous Waste - liquid waste composed of acids, alkalis or heavy metals in water. Organic Aqueous Waste - mixtures of hazardous organic substances (pesticides, petrochemicals) and water. Oils - liquid waste composed primarily of petroleum derived oils (lubrication oils, cutting fluids). Inorganic Sludges/Solids - sludges, dusts, solids, non-liquid wastes containing hazardous inorganic substances (metal fabricating wastes). Organic Sludges/Solids - tars, sludges, solids and other non-liquid wastes containing organic hazardous substances (contaminated soils).
Toxicity Characteristics of Hazardous Wastes Acute Toxicity - results in harmful effects shortly after a single exposure, such as cyanide poisoning. Chronic Toxicity - may take up to many years to result in toxic effects, such as cancer or long-term illness.
HAZARDOUS WASTE TREATMENT • Source Reduction • Recycling • Treatment • Disposal
WASTE MINIMIZATION-PREVENTING TOMORROW´S REMEDIATION PROBLEMS Many of today´s contaminated sites are the result of accepted lawful waste-disposal practices of years ago
SITE REMEDIATION • Source Reduction (?) • Recycling (difficult) • Treatment • Disposal
SITE REMEDIATION METHODOLOGY · SITE CHARACTERIZATION · REMEDIAL ALTERNATIVES ANALYSIS · DESIGN, CONSTRUCT AND OPERATE
SITE CHARACTERIZATION - Definition Site Characterization is defined as the qualitative and quantitative description of the conditions on and beneath the site which are pertinent to hazardous waste management.
SITE CHARACTERIZATION - Goals The goals of site characterization are to: 1. Determine the extent and magnitude of contamination 2. Identify contaminant transport pathways and receptors 3. Determine risk of exposure
Identification of Receptors and Pathways receptors storage tank residual gasoline gasoline vapors Domestic well groundwater table floating gasoline groundwater flow
METHODS OF SITE CHARACTERIZATION • Remote Methods • Seismic Survey • Soil Resistivity • Ground Penetrating Radar • Magnetometer Survey • Direct Methods • Auger Drilling • Rotary Drilling • Soil Excavation
REMOTE SUBSURFACE CHARACTERIZATION Seismic Survey Shock wave propagates faster through rock than soil, depth to rock and rock type can be determined. Geologic Wave Material Velocity (m/s) Dry sand 500-900 Wet sand 600-1800 Clay 900-2800 Water 1400-1700 Sandstone 1800-4000 Limestone 2100-6100 Granite 4600-5800 Source Geophones Seismic wave Soil Rock
Resistivity Soil Type Range (ohm-m) Clays 1-150 Alluvium and sand 100-1,500 Fractured bedrock Low 1,000s Massive bedrock High 1,000s REMOTE SUBSURFACE CHARACTERIZATION Soil Resistivity Soil/rock type can be determined by soil resistivity. R=soil resistivity(ohm-m) s=electrode spacing (m) V=measured voltage (volts) I=applied current (amperes) Current Meter Battery Voltage Meter s Current flow lines
DIRECT SUBSURFACE CHARACTERIZATION Auger Drilling • Useful in unconsolidated geologic materials. • Sample collection easy, intact samples can be collected with hollow-stem auger. • Cannot be used where significant consolidated rock is present. • Does not alter subsurface geo-chemistry. Rod inside hollow stem for removing plug Flight Removable Plug Drill Bit
DIRECT SUBSURFACE CHARACTERIZATION Rotary Drilling • Useful in consolidated geologic materials, can drill through rock. • Subsurface samples contaminated with drilling mud. • Air-rotary may blow volatile contaminants into surrounding subsurface structures (basements). • Mud-rotary alters subsurface chemistry. mud pump mud pit
DIRECT SUBSURFACE CHARACTERIZATION Drilling through confining layers may allow the spread of contamination from one hydrologic unit to another. monitoring well leaking tank soil contaminated ground water confining layer (clay) uncontaminated water
DIRECT SUBSURFACE CHARACTERIZATION Soil Excavation Advantages Disadvantages • No specialized equipment, typically uses backhoe. • Subsurface samples can be collected directly. • Inexpensive. • Good source removal mechanism. • Useful only in unconsolidated geologic materials to a maximum depth of 10 meters. • Large surface disturbance. • Excavation not useful for long term groundwater monitoring.
SOIL CHARACTERIZATION Soil Contaminant Sampling • Performed during drilling or excavation. • Collection of samples from several depths within the soil profile. • Where volatile compounds are present, sampling should be done in air-tight glass containers. No headspace should be left in the containers. • Samples should be chilled for transportation to the laboratory.
GROUNDWATER CHARACTERIZATION Extent of Contamination: Successive wells should be drilled until the extent of the groundwater contaminant plume is defined.
AIRBORNE CONTAMINATION Source: Waste pile Release Mechanism: Volatilization Transport Medium: Air Exposure Mechanism: Inhalation or skin contact Exposure Point: May be distant from source, depends on concentration and wind speed
AIRBORNE CONTAMINATION Measurement Techniques Laboratory Analysis: Samples can be collected in the field in an air-tight bag (Tedlar™ ) and sampled in the laboratory. Field Analysis: Samples can be analyzed in the field via handheld instrumentation such as a photo-ionization detector for volatile organic compounds or a draw-tube collection device (such as a Drager™ tube).
AIRBORNE CONTAMINATION Reducing Airborne Hazards • Airborne Hazards Reduction can be accomplished through: • Source removal • Covering the source (prevents volatilization) • Dilution with clean air (if indoors)
ASSESSING EXPOSURE RISK Definition: Assessment of exposure risk seeks to determine the probability that contamination will migrate to a receptor (human or animal) and be ingested (eaten, inhaled, or absorbed by the skin).
EXPOSURE PATHWAYS 2 3 4 1
EXPOSURE PATHWAYS 2 Contaminated groundwater: exposure from drinking or from breathing contaminated vapors liberated during bathing 3 4 1
EXPOSURE PATHWAYS 2 3 4 Inhalation of airborne contaminants: volatilized from the source and carried by wind. 1
EXPOSURE PATHWAYS 2 3 4 Direct contact with contaminated soil: exposure from skin contact with contaminants in soil. 1
EXPOSURE PATHWAYS 2 3 4 Indirect contact: exposure to contaminant from crops or animals which have accumulated contamination from soil or groundwater 1
SITE REMEDIATION METHODOLOGY · SITE CHARACTERIZATION · REMEDIAL ALTERNATIVES ANALYSIS · DESIGN, CONSTRUCT AND OPERATE
DEVELOPMENT OF ALTERNATIVES • Identify general response to actions for each objective • Characterise media to be remediated • Identify potential technologies • Screen the potential technologies • Assemble the screened technologies into alternatives
ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost
ALTERNATIVE SELECTION • Qualitative assessment of how well an alternative meets the remedial action objective over the long term • To calculate by means of a complete analysis the residual risk (Risk represented by untreated contaminants or residuals remaining at the site) 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost
ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost • Is only a issue with the alternatives that leave untreated contaminants or treatment residuals at site at the conclusion of the implementation period • One tradeoff that require careful consideration at most sites is whether to treat or to contain
ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability Function of 4. Short term effectiveness 5. Cost • History of the demonstrated performance of a technology • Ability to construct and operate it given the existing conditions at the particular site • Ability to obtain the necessary permits from regulatory agencies
ALTERNATIVE SELECTION • Deals primarily with the effects on human health an the environment of the remediation itself during its implementation phase • Health and environmental risk • Worker safety • Implementation time 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost
ALTERNATIVE SELECTION • The weight given to the cost when evaluating alternatives depend upon the particular guidance of the agency • Capital costs (the cost to construct the remedy) • Operating and maintenance cost (O & M) (post-construction expenditures) 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost
TREATMENT ALTERNATIVES On site · In situ · Ex situ (Excavation) Off site (Excavation & Transportation)
HAZARDOUS WASTE TREATMENT METHODS Physical/Chemical Methods: Mass transfer and chemical transformation processes resulting in the removal or remediation of contamination by abiotic, not combustion means. Biological Methods: Transformation or binding of contaminants by microorganisms, principally bacteria. Waste Stabilization: Containment of wastes such that they pose no further threat to receptors. Combustion Methods: Transformation of organic wastes by burning.
SOIL VAPOR EXTRACTION Description - soil vapor extraction (SVE) uses a vacuum applied to soil to remove volatile organic compounds (VOCs) from the unsaturated zone. Uses - effective for contaminants with high vapor pressure, such as gasoline compounds, chlorinated solvents. Advantages - low cost, simple design and operation, efficient removal of VOCs from unsaturated zone. Disadvantages - not effective for non-volatile compounds, not effective in low permeability soils or where groundwater is close to the surface, may need to treat off-gas in another process, does not address groundwater contamination.
SOIL VAPOR EXTRACTION Vapor Extraction Pump contaminated soil air movement through contaminatedsoil Water Table Contaminated Groundwater
AIR STRIPPING Description - enhances volatilization of dissolved contaminants from water. Can be used for treatment of either process wastewater or groundwater pumped to the surface. Uses - remove volatile organic compounds (VOCs) from water. Advantages - simple operation, efficient removal of low concentrations of VOCs. Disadvantages - high capital cost, design intensive, may need to treat off-gas in another process.
Packed Column Air Stripper Water Inlet (contaminated) Air Outlet (contaminated) Types of Packing Materials Pall ring Raschig ring Berl saddle Intalox saddle Tri-pack Packing Material Water Outlet (clean) Air Inlet (clean)
Packed Column Air Stripper Typical Air-Stripping Column Specifications: Diameter: 0.5 - 3 meters Height: 1 - 15 meters Air/Water ratio: 5-200 Pressure drop: 200 - 400 N/m2 Stripping Column Off-gas Treatment System
CARBON ADSORPTION Description - carbon adsorption uses granular activated carbon (GAC) to remove organic contaminants from a water or vapor stream. Contaminated air/water is pumped through the GAC unit and contaminants adsorb onto carbon particles by electrostatic forces. Uses - effective for a wide range of organic contaminants. Is commonly used both for process waste treatment and for hazardous waste remediation. Advantages - easy to install, can completely remove many organics, can treat either water or vapor stream. Disadvantages - high operating expense, carbon must be changed periodically, contaminants are not mineralized.
SOIL WASHING OR FLUSHING Description - Excavated soil is flushed with water or other solvent to leach out contamination. Based on the principles of solid-liquid extraction Uses - remove organic wastes and certain (soluble) inorganic wastes Advantages - simple operation, efficient removal of organic contaminants (VOC, semi VOC and halogenated organics) . For metal, it has been successful at extracting organically bound metals (tetraethyl lead) Disadvantages - Longer washing times and soil-handling problems with lower-permeability clays and clay-like soils