Remediation

Topics Covered

Clean up standardsSource ControlRisk AssessmentNatural AttenuationPump and TreatLimitations to Pump and TreatAlternatives

Introduction

Contaminated soil and GW most prevalent problems at HW sites

VOCs/metals most prevalent problem at NPL sites

SVE most widely used innovative techNPL Status ~ 1100 on NPLRCRA - 3000 sites $7.4-41.8 billion. primarily

corrosive/ignitable wastes, HM, org solvents, oil

General - Cont’d

UST - 161,000, 91% pet, 2% hazardous materials

DOD - 9300 potential petroleum, solvents, metals, pesticides, paints

DOE - 10,500 areas, VOCs and mixed wastes

700 Other federal sites30,000 state sites

Site Cleanup

Source Control Source removal and disposal Source containment Institutional control

Groundwater/soils cleanup

Groundwater Contaminant Cleanup

Physical containmentHydraulic containment/treatment (pump

and treat) pump to isolate contaminant zone

Required as long as source exists to meet cleanup standards

Typical Standards - Numerical Cleanup Criteria

Meet requirements of existing laws, or

Protective of human health or ecological receptors, or

Background concentration, orAnalytical limits

Fallacy of Numerical Clean up Criteria

Not the only way to protect (paving, capping, fencing)

treatment may reduce some contaminants but not all

May be over protective and too costly

May not be feasible

Technical Impracticability

Study recognized that pump and treat cannot restore all sites

Recommendations Categorize sites increase incentive to use innovative

technology use experts to determine technical

feasibility charge fee at these sites to fund research

Relative of Remediation 

HydrogeologyContaminant Chemistry

Mobile, Dissolved

Strongly sorbed, dissolved

LNAPL DNAPL

Homogeneous, single layer 1 2 2-3 3

Homogeneous, multiple layers 1 2 2-3 3

Heterogeneous, single layer 2 3 3 4

Heterogeneous, multiple layers 2 3 3 4

Fractured Bedrock 3 3 4 4

Risk Based Corrective Action

ASTM standards for conducting risk based assessment for corrective action

Risk Assessment Primer

Risk Assessment

Topics Covered

DefinitionsRisk Assessment ProcessUncertainty

Definitions

Risk is the probability that a specific negative outcome will occur

Safety is the complement of risk, or the probability that an adverse effect will not occur

Risk Values

Activity Annual RiskSmoking 10 cigarettes/day 1 x 10-3

Motor vehicle accidents 2 x 10-4

Manufacturing work accident 8 x 10-5

Pedestrian hit by automobiles 4 x 10-5

Drinking two beers/day 4 x 10-5

Person in a room with a smoker 1 x 10-5

Peanut butter (4 teaspoons/d) 8 x 10-6

Drinking water with EPA limit of Trichloroethene 2 x 10-9

Factors in Risk Acceptability

Voluntary vs. NonvoluntaryDegree of controlMagnitude of the outcomeAwarenessCatastrophic PotentialGroup involvementCost of alternatives

Process

H a z a r d

D a t a

I d e n t i f i c a t io n

D o s e - R e s p o n s e

R is k M a n a g e m e n t

W h a t a g e n t s a r e p o t e n t i a l l y h a r m f u l ?

W h o w i l l b e e x p o s e d t ow h a t a n d f o r h o w lo n g ?

H o w i s in t a k e o r d o s er e la t e d t o a d v e r s e e f f e c t s ?

W h a t e f f e c t s a r e l ik e l y o n h u m a n h e a l th a n d e n v i r o n m e n t?

Exposure

Assessment

Risk

Assessment

Characteristics

Hazard Identification

Toxicity assessment determines whether exposure to a chemical, physical, or biological agent can cause an increase in the incidence of an adverse effect.

Necessary condition for a health or safety riskPhysical, metabolic, and chemical properties of

the agent; Potential routes of exposure; toxicological

effects; results of animal studies; and site characteristics

Dose-Response Assessment

Relationship between the level of exposure and the extent of injury

Carcinogenic and non-carcinogenic effects

Responses vary from death to tumors, skin irritation, respiratory effects, genetic mutation, and fetal development problems

Dose-Response Curve

Response

Dose

X

X

X X

No Threshold, Linearat Low Doses

Slope = Cancer Slope Factor

Dose-Response CurveD

ose

Response

XX

XX

XRfD

NOAEL Threshold

Noncarcinogenic Reference Dose

SF

NOELRfd

Rfd: mg/kg-d

Safety Factor

Intrahuman variationsExtrapolation from animalssubchronic to chronicLOAEL to NOELIncomplete database

Exposure Assessment

Calculates the dose which an exposed individual receives

Delineates the affected population by identifying possible exposure paths

Exposure routes ingestion inhalation dermal absorption

Dose

Daily Dose (mg/kg-day) = (C)(I)(EF)(ED)(AF) (AT)(BW)C = Concentration, mass/volumeI = Intake Rate, volume/timeEF = Exposure Frequency, time/timeED = Exposure Duration, timeA = Absorption Factor, unitlessAT = Averaging Time, timeBW = Body weight, mass

Typical Exposure and Intake Rates for Risk Assessment

Variable Value

Soil Ingestion Rate 200 mg/day (children 1 through 6 years old)100 mg/day (age groups greater than 6 years old)

Exposure Duration Adult - 30 years at one residence (national 90thpercentile); Child - 6 years

Body Weight 70 kg adult; 10 kg child

Averaging Time noncarcinogens = exposure durationcarcinogens, 70 years

Water Ingestion Rate Adult - 2 L/d; Child (1-6) 1 L/d

Inhalation RateAdults 0.83 m3/hr; Child 0.46 m3/hr

Risk Characterization

Risk = Toxicity x Exposure

Risk Characterization

Probability of adverse incidence occurring under the conditions identified during the exposure assessment.

Carcinogens, the daily dose is multiplied by the CSF Risks are additive for multiple

carcinogenic contaminants.

Risk Characterization

Non-carcinogens, Hazard index (HI) is calculated by

dividing the daily dose by the RfD Where more than one contaminant is

present a hazard quotient (HQ) is determined by summing all of the HIs

A HI over one indicated an unacceptable risk

Risk Management

Regulatory actionDecision to mitigate riskAction level

Uncertainty

The risk assessment process is extremely conservative in nature and utilizes measurements which are uncertain.

insufficient data or information gaps often exist in characterizing the potential risk of an agent, necessitating the need for assumptions or educated guesses.

Uncertainty

Use computational tools from the field of decision analysis to account for the uncertainties in the process

These tools allow risk to be expressed as a probability distribution rather than a single number which can then be used to make a more informed decision during risk management

Natural Attenuation

Process whereby concentration and areal extent of contaminant plume is maintained or reduced over time by natural processes

Monitoring onlyNo physical encouragement of processUsually petroleum hydrocarbons

(Oregon permitted PCP to be naturally attenuated)

NA Considerations

Is the plume increasing, decreasing, or stable?

Has the source been removed? Is there free product?Will the plume affect off site properties?How long will the plume persist?Receptors?What mechanism(s) are controlling plume?

Mechanisms

Biological processesDispersion/dilutionSorptionVolatilizationChemical transformation

NA Verification

Plume characterization (delineation)Mass declines over timedecreasing concentration over timePlume stable or decreasing with timePlume movement slower than

predicted

NA Verification

Geochemical changesLaboratory microcosmsGW modelingBreakdown productsLoss of electron donors/receptors

NA of Chlorinated Solvent Plumes - Anaerobic systems

Due to biodegradation of anthropogenic organic carbon

drives reductive dechlorinationstrongly reducing conditionsH2 > 5 nanomolarRapid and extensive dechlorination

of PCE, TCE, TCA, and CT

NA of Chlorinated Solvent Plumes - Anaerobic Systems

Anaerobic conditions result from naturally occurring organic carbon

Coastal or stream/river deposits, shallow aquifers (swamps), natural oil seeps

NA of Chlorinated Solvent Plumes - Aerobic Systems

Well oxygenated, little organic carbon

no degradation of PCE, TCE; only VC and DCE

advection, dispersion , and sorption

NA of Chlorinated Solvent Plumes - Mixed Environments

Favors NASequential anoxic-oxic conditions

beneficial for complete degradation of chlorinated solvents

Pump and Treat System

Location of plume and/or NAPLDesign of capture system

Design of P/T System

mass reduction occurs when extraction and injection wells positioned in most concentrated portion

minimize distance that contaminant plume pulled to extraction well

design to produce convergent flow toward central extraction location

minimize divergent flow along periphery

Pump and Treat Systems

Installation of wells/monitoring pointsPumping to contain/remove contaminantTreatment of extracted waterRecharge to subsurface, treatment facility,

or surface water

Appropriate Site Characteristics

high hydraulic conductivityadequate possible flow rates to create

sufficient capture zonemobile contaminant

Inappropriate Sites

heterogeneous aquiferlow hydraulic conductivitysorbed or precipitated contaminant,

slowly desorbing, dissolvingimmobile NAPLs contributing to miscible

plume (residual saturation in aquifer)

Limitations

The need to reach drinking water standards (ppb at times) exacerbates physical problems

Asymptotic behavior

Con

cen t

rati

on

Time

Flushing from large pores

Flushing from smaller pores

Interrupted pumping, additional desorption

Drinking Water Standard

Limitation - Cont’d

Sorbed compoundsKinetic limits to desorptionEffects of geologic complexity immobile water zonesEffects of fugitive NAPLDesign failure to contain plumeOperational failures

EnhancementPulsed pumpingsurfactants - increase mobility of contaminant

(more following)Couple P/T with impervious or hydraulic

barriers (injection wells). Impervious more effective but more intrusive.

steam injection and vapor extractionPneumatic or hydrofracturing to increase

permeabilitysolvent mobilization

Surfactants

enhancement of DNAPL dissolution in water and/or reduction of interfacial tension and decrease capillary forces

Surfactant qualities nontoxic biodegradable low cost decrease interfacial tension mix or emulsify in water

Surfactant Flushing Technique

inject aquatic/surfactant solution through wells along perimeter of site

recovery well in center of site separate aquatic solution/DNAPL in

treatment tank NAPL disposal, solution reinjection

Field tests reduce interfacial tension from 19.8 dynes/cm to 2-

5 dynes/cm, at 2% concentration. DNAPL removal ranged from 9 to 82 % depending on surfactant

Alternatives to Pump and Treat for DNAPLs

Conventional bioremediationSequenced anaerobic/aerobic

biodegradationmethanotrophic bacteria air sparging/SVE

Alternatives to Pump and Treat for DNAPLs

metal catalysts in permeable wallPhytoremediationElectrokineticsInjection of steamIn situ electrodes