1 site remediation pedro a. garcía encina department of chemical engineering university of...

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SITE REMEDIATION

Pedro A. García Encina

Department of Chemical Engineering

University of Valladolid

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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.

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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.

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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).

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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.

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HAZARDOUS WASTE TREATMENT

• Source Reduction

• Recycling

• Treatment

• Disposal

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POLLUTANT REDUCTION TECHNIQUES

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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

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SITE REMEDIATION

• Source Reduction (?)

• Recycling (difficult)

• Treatment

• Disposal

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SITE REMEDIATION

METHODOLOGY

· SITE CHARACTERIZATION

· REMEDIAL ALTERNATIVES ANALYSIS

· DESIGN, CONSTRUCT AND OPERATE

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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.

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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

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Zones of Contamination

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groundwatertable

groundwater flow

storagetank

floating gasoline

gasoline vaporsresidualgasoline

receptors

Domesticwell

Identification of Receptors and Pathways

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EXPOSURE PATHWAYS

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METHODS OF SITE CHARACTERIZATION

Remote Methods

•Seismic Survey•Soil Resistivity•Ground Penetrating Radar

•Magnetometer Survey

Direct Methods

•Auger Drilling•Rotary Drilling•Soil Excavation

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REMOTE SUBSURFACE CHARACTERIZATIONSeismic Survey

Geologic WaveMaterial 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

Geophones

Seismicwave

Soil

Rock

Source

Shock wave propagates faster through rock than soil, depth to rock and rock type can be determined.

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REMOTE SUBSURFACE CHARACTERIZATION

Soil Resistivity

ResistivitySoil Type Range (ohm-m)

Clays 1-150

Alluvium and sand 100-1,500

Fractured bedrock Low 1,000s

Massive bedrock High 1,000s

R sVI2

R=soil resistivity(ohm-m)s=electrode spacing (m)V=measured voltage (volts)I=applied current (amperes)

Current flow lines

s

BatteryCurrent Meter

Voltage Meter

Soil/rock type can be determined by soil resistivity.

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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.

Drill Bit

RemovablePlug

Flight

Rod inside hollow stem for removing plug

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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

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Drilling through confining layers may allow the spread of contamination from one hydrologic unit to another.


leakingtank

confining layer (clay)

uncontaminated water

contaminated ground water

soil

monitoring well

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Soil Excavation

•Useful only in unconsolidated geologic materials to a maximum depth of 10 meters.

•Large surface disturbance.

•Excavation not useful for long term groundwater monitoring.

•No specialized equipment, typically uses backhoe.

•Subsurface samples can be collected directly.

•Inexpensive.

•Good source removal mechanism.

Advantages Disadvantages

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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.

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GROUNDWATER CHARACTERIZATION

Extent of Contamination: Successive wells should be drilled until the extent of the groundwater contaminant plume is defined.

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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

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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).

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Reducing Airborne Hazards

Airborne Hazards Reduction can be accomplished through:

• Source removal

• Covering the source (prevents volatilization)

• Dilution with clean air (if indoors)

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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).

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EXPOSURE PATHWAYS

1

2

3

4

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EXPOSURE PATHWAYS

1

2

3

4

Contaminated groundwater: exposure from drinking or from breathing contaminated vapors liberated during bathing

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EXPOSURE PATHWAYS

1

2

3

4Inhalation of airborne contaminants: volatilized from the source and carried by wind.

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EXPOSURE PATHWAYS

1

2

3

4

Direct contact with contaminated soil: exposure from skin contact with contaminants in soil.

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EXPOSURE PATHWAYS

1

2

3

4

Indirect contact: exposure to contaminant from crops or animals which have accumulated contamination from soil or groundwater

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SITE REMEDIATION

METHODOLOGY

· SITE CHARACTERIZATION

· REMEDIAL ALTERNATIVES ANALYSIS

· DESIGN, CONSTRUCT AND OPERATE

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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

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ALTERNATIVE SELECTION

1. Long term effectiveness

2. Long term reliability

3. Implementability

4. Short term effectiveness

5. Cost

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3. Implementability


5. Cost

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)

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3. Implementability


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

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3. Implementability Function of


5. Cost

History of the demonstrated performance of a technology Ability to construct and operate it given the existing conditions at the particular siteAbility to obtain the necessary permits from regulatory agencies

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3. Implementability


5. Cost

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

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3. Implementability


5. Cost

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)

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TREATMENT ALTERNATIVES

On site

· In situ

· Ex situ (Excavation)

Off site (Excavation & Transportation)

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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.

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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.

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SOIL VAPOR EXTRACTION

contaminated soil

WaterTable Contaminated Groundwater

air movement throughcontaminated soil

Vapor Extraction Pump

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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.

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Packed Column Air Stripper

Intalox saddle

Raschig ring

Pall ring

Berl saddle

Tri-pack

Water Inlet (contaminated)

Air Inlet (clean)

Water Outlet (clean)

AirOutlet

(contaminated)

Packing Material

Types of Packing Materials

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Packed Column Air Stripper

Typical Air-Stripping Column Specifications:

Diameter: 0.5 - 3 metersHeight: 1 - 15 metersAir/Water ratio: 5-200Pressure drop: 200 - 400 N/m2

Stripping Column

Off-gas Treatment System

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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.

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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

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SCHEMATIC FLOWSHEET OF A SOIL WASHING SYSTEM

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CHEMICAL OXIDATION

Description - organic chemicals in extracted groundwater or industrial process wastewater are transformed into less harmful compounds through oxidation by ozone (O3), hydrogen peroxide (H2O2), chlorine (Cl2) or ultraviolet radiation (UV). UV is often used in combination with ozone or hydrogen peroxide.

Uses - effective for a wide range of organic contaminants such as VOCs, mercaptians, and phenols. Can also be used for some inorganics, such as cyanide. Process is non-specific, oxidant will react with any reducing agent present in the waste, such as naturally occurring organic matter.

Advantages - effective, reliable treatment for waste streams which contain a variety of contaminants, often used for drinking water purification.

Disadvantages - high operating expense, incomplete oxidation may create chlorinated organic molecules (if Cl2 is used), generation of oxidizing agent typically cannot vary with fluctuating contaminant concentrations.

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CHEMICAL OXIDATION Reactor

Configuration

H2O2 Storage

Influentflowmeter

EffluentControl System

Power System

Reaction Chamber

UV Lamps

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CHEMICAL OXIDATION - Results

Fract

ion

TC

E

Rem

ain

ing

Initial TCE =58 mg/L

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CHEMICAL OXIDATION - ResultsHalogenated aliphatic destruction by H2O2 and UV at 20oC.

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CHEMICAL OXIDATION - Design ConsiderationsThermodynamics: Free energy available from reactions

Oxidant Free Energy (E, volts)O3 2.07H2O2 1.78Cl2 1.36

Kinetics: Reaction must proceed to necessary completion within the residence time in the reactor vessel. Combination of UV with ozone or hydrogen peroxide increases reaction kinetics .

Design Steps:

1) Will oxidation reaction proceed with contaminants present?

2) What is the contact time necessary between the oxidant and the contaminants present?

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SUPERCRITICAL FLUID EXTRACTION

Description - contaminated liquid or solid is placed in a reactor vessel with the extraction fluid, which is heated and pressurised to the critical point (see chart). In treatment of hazardous wastes, fluids most commonly used are water and CO2, some organic solvents may also be used.

Uses - supercritical fluid extraction can be used to treat contaminated soils, sediments, sludges, solids or liquids.

Advantages - effective treatment for process wastes or extracted soil or groundwater which is either highly contaminated with organic compounds or with very recalcitrant (hard to treat) organics

Disadvantages - expensive, solids must be reduced in size to 100 um to pass through high pressure pumps.

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SUPERCRITICAL FLUID EXTRACTION Reactor

ConfigurationSchematic diagram of reactor for the extraction of organic compounds from water, CO2 is the extraction fluid.

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SUPERCRITICAL FLUID EXTRACTION Solvent Selection

CriteriaCost - water, CO2 are least expensive

Recoverability - solvent must be recoverable for process to be economical

Hazard in use - SFE involves high temperatures and pressures which reactor vessels must be built to withstand

Critical temperature and pressure - the higher the critical T and P of the solvent, the greater the operating expense

Distribution coefficient - determines the solvent/ contaminant ratio which can be used.

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MEMBRANE PROCESSES

Electrodialysis - separation of ionic species from water by direct-current electric field. Useful for removal of charged ions and metals from water.

Reverse Osmosis - solvent is forced through a semi-permeable membrane by the application of pressures in excess of the osmotic pressure. Useful for removal of metals and some organics.

Ultrafiltration - separates dissolved contaminants on the basis of molecular size. Lower limit for molecular weight is approximately 500.

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BIOLOGICAL PROCESSES

Description - biodegradation uses micro-organisms (bacteria) to remove organic contaminants from vapors, liquids or solids. Most organic contaminants are utilized by bacteria as both a carbon and energy source.

Uses - biological processes are effective on both process waste streams and remediation of soil and groundwater. Biodegradation systems for soil and groundwater can by designed either in-situ (in place) or ex-situ (removed from the ground).

Advantages - low cost, low site disturbance, effective for many organic contaminants.

Disadvantages - long clean-up times, not effective for inorganic contaminants, specialized conditions necessary for chlorinated solvent degradation.

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BIOLOGICAL PROCESSES

Necessary Constituents:• microorganisms capable of degrading contaminants• contaminants in aqueous (water) phase• available electron acceptor present

Aerobic Degradation: takes place in the presence of molecular oxygen (O2), the most energetically favorable electron acceptor.

Anaerobic Degradation: when O2 is not available, other compounds can act as electron acceptors for biodegradation processes, such as NO3, Fe+3, Mn+4, SO4, and CO2.

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Energy Available from Electron Acceptor Processes

Electron

Acceptor

Go (kJ/mol mineralized)

O2

NO3

Fe+3

SO-24

CO2

-3913-3778-2175-358-37

Toluene

-3566-3245-2343-340-136

Benzene

-

, Mn+4~ ~

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BIOLOGICAL PROCESSES - Remediation of soil and

groundwater

In-situ biodegradation:Natural attenuationEngineered systems

Ex-situ biodegradation:Pump and treat systems for groundwaterLandfarming systems for soil treatment

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--2

In-Situ Biodegradation - Natural Attenuation

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Typical Contaminant / Electron AcceptorTypical Contaminant / Electron AcceptorConcentrations with DistanceConcentrations with Distance

-2

-

-2

-

Natural Attenuation of Contaminants

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Aerobic Respiration

10% Denitrification14%

Iron (III) Reduction

8%

Sulfate Reduction

29%

Methanogenesis39%

Relative Importance of Electron Acceptor Processes at 25 Air Force Sites

Source: Wiedemeier et al., 1995

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Stoichiometric Conversion Example: Iron Stoichiometric Conversion Example: Iron ReductionReduction

BTEX + 36Fe+3 + 21H2O 36Fe+2 + 7CO2 + 7H2OAssume 20 mg/l Fe+2 observed in aquiferCalculate BTEX consumed per unit volume:(20 mg/l Fe+2 produced )

1 mmol Fe+256 mg Fe+2

( ) 1 mmol BTEX36 mmol Fe+2

( ) 92 mg BTEX1 mmol BTEX

( )= 0.9 mg/l BTEX consumed in aquiferCalculate groundwater flux and total BTEX consumed:Assume:

Vgw = 1 ft/day Plume width =

100’ Plume height = 10’

Flux = vwh = 1000 ft3/d = 7500 gal/d = 28x103 l/dBTEX consumed = (28x103 l/d) (0.9

mg/l) = 25 g

BTEX/day

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In-Situ Biodegradation - Engineered Systems

water/nutrientsupply tank

aircompressor

injectionwell

water table

contaminatedsoil

airsparger

confining layer

pump

Groundwater treatment unit

Air-sparging/nutrient addition system

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Infiltration gallery, recirculating system

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Combination air injection/extraction system

water table

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Air injection bioventing

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Ex-Situ Biodegradation - Pump and treat

Water Table

LiquidHydrocarbonContaminantSkimmer

Pump

VacuumAir removal

Oil/waterSeparator

Vacuum Pump

Liquid phaseBioreactor

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Ex-Situ Biodegradation - Biofiltration

Contaminated Soil

Vapor ExtractionWell

Blower

MoistureAddition Biofilter

Biofilter is colonized with bacteria capable of degrading contaminants. Media can be soil, peat, compost, or manufactured packing material.

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Ex-Situ Biodegradation - Biopiles

Gas Monitoring ProbesAir Intakes

Irrigation Piping

Weights

Aeration Pipes

Wood Chips

Tarp

CrushedStone

Soil

Curb

LeachatePipe

ImpermeableBase Aeration Pipe

Contaminated Soil

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Ex-Situ Biodegradation - Landfarming

Procedures:

• Excavated soils are spread onto the ground surface to a depth of less than 0.5 meters.

• Underlying soils should be low permeability, or a clay liner or impermeable membrane should be used to prevent contaminant migration to groundwater.

• Landfarmed soils should be tilled every 2-3 months and kept moist.

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WASTE STABILIZATION AND CONTAINMENT

Procedure: Excavated soils or process wastes are secured such that contaminant migration will not occur (containment), or are mixed with binding agents that solidify the waste and prevent leaching or release of the contaminants (stabilization).

Processes:

• Encapsulation

• Sorption processes

• Polymer stabilization

• In-situ vitrification

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COMBUSTION METHODS

Description: waste combustion can take place in hazardous waste incinerators, cement kilns, or industrial boilers. Most significant design parameter is the heat value of the waste. Many concentrated organic wastes will support combustion without supplemental fuel.

Applicable wastes: all organic wastes can be mineralized using combustion methods. Metals are oxidized in the combustion process and are either vented in gaseous form or are concentrated in ash. Metals prone to gaseous emission are arsenic, antimony, cadmium, and mercury.

Procedure: Wastes are graded for suitability for combustion. Waste analysis also indicates the proper fuel/air mixture for complete combustion.

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CONTAINMENT

Frecuently it is necessary to minimize the rate of off site contaminant migration employing containments technologies to minimize risk to public health and environment.

Containment technologies may be associated with other technologies to implement a long-term clean-up strategy for the site

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CONTAINMENT

Active system components require considerable effort and on-going energy in put to operate (For example pumping wells)

Pasive system components work without much attention, except maintenance (such a cover)

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BARRIER

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BARRIER

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SELECTION OF REMEDIAL ALTERNATIVES1. Data Needs

A. Site CharacterizationB. Regulatory DispositionC. Risk Assessment

2. Establishment of Site ObjectivesA. Clean-up Level NecessaryB. Long-term LiabilityC. Costs

3. Development and Analysis of AlternativesA. Development of Possible AlternativesB. Analysis of Alternatives for Effectiveness

4. Remedial Option Selection, Implementation, and MonitoringA. Remedial Option SelectionB. ImplementationC. Long term Site Monitoring

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SELECTION OF REMEDIAL ALTERNATIVES

Data Needs:

• Understand extent and magnitude of contamination. A thorough site characterization is necessary. Chemical fate and transport must be understood.

• Determine risk to potential receptors. This is necessary to correctly focus efforts where they are most needed. Typical exposure pathways include groundwater wells and airborne contaminants.

• Determine what limits or requirements are placed on the clean up by government regulations. It is important to insure that all participants understand and agree on the goal of the remedial effort.

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Establishment of Site Objectives:

• Establishment or negotiation of acceptable clean-up goals is necessary prior to selection of a remedial process.

• The extent of long-term liability for the site should be considered.

• Costs of each remedial option must be considered along with the financial means of the financially responsible party. Options for cost assistance should be considered at this stage (national and international).

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Development and Analysis of Alternatives:

• A list of potential remedial alternatives is compiled for further study based on their feasibility to clean up the site.

• Criteria for selection of a remedial alternative are effectiveness, reliability, cost, time to implementation, and time to clean up.

• Before a remedial solution is chosen, a detailed plan of implementation should be formulated to insure that the technique is capable of remediating the site to the goals prescribed.

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Remedial Option Implementation and Monitoring:

• After a remedial option is selected, construction contracts and engineering designs must be completed. Can be done by employee engineers or contractor engineers (must be familiar with technology chosen).

• Long term site monitoring should continue to insure that the solution is working, and that further contaminant migration does not occur. Monitoring should include all applicable media (groundwater, soil vapor, and air).

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CONTAMINATED SITES IN SPAIN

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ACTIONS TO BE CARRIED

OUT IN SPAIN

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LEY 10/98 DE RESIDUOS

CONTAMINATED SITES

· Depends of Comunidades Autónomas

· List of contaminated places (priority to clean-up)

· Need to clean-up the site

· The responsible of the contamination

· The owner of the site

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REGIONAL PLANS

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CONTAMINATED SITE (BOECILLO)

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1 site remediation pedro a. garcía encina department of chemical engineering university of...

Documents

plug slide

zones of contamination

risk of exposure slide

site characterization

goals of site characterization

hazardous waste management

waste minimization

reactivity waste