Overview

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Overview Remedial Technologies
Philip B. Bedient Rice University
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How Remediation Technology Evolves
Cost-Effective Technology
Proven Technology
Large-Scale Field Trials
Emerging Technology
Uncontrolled Pilot Trials
Prototypes and Controlled Field Experiments
Experimental Technology
Bench Studies Concept / Problem Identification
CONCEPTS
Source Cherry, 1992
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Original Paradigm 1980s Groundwater Pump and
Treat Will Remediate Sites
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Bad News
Conc
?
Cleanup Standard
Time
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EPAs 19 Site Study

19 Sites With Five Years of Operating
Data Restoration Slower Than
Expected Three Causes Hydrology, Design
Flaws, NAPLs Update At 20 of 24 Sites,
DNAPL Probably Present
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(No Transcript)
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Forming Residual NAPL
Snap-Off Mechanism
Other Mechanisms Bypass, Etc.
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NAPLs and Capillary Forces
NAPL
NAPL
NAPL
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Residual vs. Free-Phase DNAPL
Free-Phase DNAPL
Residual DNAPL
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Residual NAPL Long-Term Source

• Cant Remove Residual
• Dissolves Slowly
• Large Mass Compared to Dissolution Rate

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Recovering LNAPL
Separator
Saturated Zone
Screen
Sand Pack
Pump
DNAPL Pool
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Recovering LNAPL Other Configurations
Dual Recovery Wells Pump Cans Skimmers Adsorbants
Trenches
DNAPL Pool
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DNAPL Conceptual Model
DNAPL Entry Zone
Residual DNAPL
Sand
Fractured Clay
Sand
Dissolved Phase Plume
DNAPL Pool
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Recovering DNAPL
DNAPL / Water Separator
Pump
Saturated Zone
Screen
Sand Pack
DNAPL Pool
Impervious Barrier
Sump
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DNAPL Pumping Design Process

• Choose Location of DNAPL Wells
• Select Pumps and Materials
• Assess EOR Technologies
• Vacuum-Enhanced Pumping
• Waterflooding
• Surfactants
• Steam
• Design Treatment System

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Remediation Technologies
Introduction - Why Are We Here Product
Removal and Source Control Groundwater pump
and treat Remedial Technologies in Use
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Pump-and-Treat (Dissolution)

• Dissolves Residual NAPL
• Key Concept Number of Pore Volumes
• Takes a Long Time

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Applicability of Dissolution of NAPLs

• NAPLs in Saturated Zone
• NAPL with Very Soluble Components
• Sites With Low Amounts of NAPL
• Highly Permeable Aquifers

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Proven/Emerging Remediation Technologies

• Excavation and Disposal / Treatment
• Soil Vapor Extraction (SVE) / Bioventing
• In-Situ Biodegradation / Oxygen Releasing
  Compounds
• Air Sparging
• Barriers
• Containment
• RBCA / Natural Attenuation

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Excavation and Disposal / Treatment
Haul To Off-Site Landfill
On-Site or Off-Site Thermal Treatment
On-Site Physical / Biological Treatment
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Applicability of Excavation

• Standard Construction Practice to 25 Feet Depth
• Dewatering Required if Below Water Table
• Unconsolidated Material
• Best Technology for Small Volumes

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Soil Vapor Extraction
Vapor Treatment System (Where Required)
Blower or Vacuum Pump
Air / Vapor Manifold
Clay
Grout Seal
Screen
Sand Pack
Contaminated Soils
Water Table
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Applicability of SVE
Vapor Pressure (mm Hg)
Likelihood of Success
Soil Air Permeability
104
HIGH (Coarse Sand / Gravel)
Very Likely
Butane
103
102
Benzene
101
MEDIUM (Fine Sand)
Xylene
Somewhat Likely
100
10-1
LOW (Clay or Silt)
10-2
10-3
Less Likely
10-4
Aldicarb
Source CDM, 1988
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Design Basis Information SVE

• Air Permeability
• Estimated from Soil Properties
• Measured With Test in Field
• Contaminant Characteristics
• DNAPL Composition
• Volatility (Vapor Pressure, Henrys Law
  Coefficient)
• Air Flow
• Stratigraphy
• Need for Impermeable Cap
• Water Table and Need for Pumping

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SVE Design Process

• Choose Number of Vapor Extraction Wells
• Choose Well Spacing, Inlet Wells, Seals
• Design Well Screens and Construction
• Remember Vapor Treatment
• Check for Groundwater Upwelling

Source Johnson 1990
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Bioventing
Ref. Hinchee
Blower
If Air Injection Rate is Slow Enough No Vapor
Treatment Is Needed
Unsaturated Zone
Saturated Zone
Slowly Adds Oxygen to Unsaturated Zone for
Biodegradation
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Bioventing Process Overview

• Inject Air Into Unsaturated Zone
• Primary Process Aerobic In-Situ
  Biodegradation
• Injection Is Slow to Minimize Release of Organics
  to Surface or Buildings
• No Need to Treat Vapors

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Bioventing Design Approach

• In-Situ Permeability Test
• In-Situ Respiration Test (24 - 80 hrs)
• Install Wells and Inject
• Ususally 2 in. PVC Vent Wells
• Water Table lt 20 ft Screen 10 - 20 ft
• Water Table gt 20 ft Through Contaminated Zone
• Spacing 5 to 60 ft, Depends on Depth and Soil
  Type
• Injection Rate Variable

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Proven/Emerging Remediation Technologies

• Excavation and Disposal / Treatment
• Soil Vapor Extraction (SVE) / Bioventing
• In-Situ Biodegradation / Oxygen Releasing
  Compounds
• Air Sparging
• Barriers
• Containment
• RBCA / Natural Attenuation

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In-Situ Biodegradation
Oxygen Addition
To Treatment Treatment / Recycle Recycle
Recovery Well
Injection Well
Nutrient Addition
DNAPL
In-Situ Biodegradation Zone
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Applicability of In-Situ Biodeg.

• Sites With Non-Chlorinated Compounds
• BTEX
• Creosote Sites (Napthalene, PAHs)
• Coal Tar
• Sites With Depressed Oxygen in Plume Area
• Aquifers With High Permeability

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In-Situ Biodeg. Design Process

• Estimate Total NAPL Mass
• Calculate Required Mass of Oxygen to Be Injected
• Yield 2 gms Oxygen for 1 gm Hydrocarbon
• Select Method to Add Oxygen to Injection Water
• Bubble Air in Injection Water 10 mg/l
• Pure Oxygen 25 mg/l
• Hydrogen Peroxide 100 mg/l (?)
• Calculate Water Needed
• Size Recovery Well System

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Oxygen Releasing Compound (ORC)
Magnesium peroxide compound activated by
moisture Patented technology controls and
prolongs release Moderate pH levels Pure
oxygen source (more dissolved O2 than
sparging)
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Air Sparging
Air Compressor
Blower
Vapor Treatment
SVE Well
Tiny Bubbles
NAPL
Volatilizes Organics and Promotes In-Situ Biodeg.
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Air Sparging Process Review

• Air Pathway
• Forms A Few Small Channels
• Remarkably Sensitive to Heterogeneities
• Air Flow From Top of Screen
• Remediation Processes
• Volatilization of NAPLs
• Air Stripping of Dissolved Organics
• Oxygenation of Water Enhances In-Situ Biodeg.

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Air Sparging Design Issues

• Well Configuration
• Usually 1-2 inch PVC Wells, 2-5 ft Screens
• Spacing 10 - 20 ft (Billings)
• Spacing 50 - 75 ft (Brown)
• Spacing 5 - 15 ft (Newell)
• Injection Pressure 1-10 psig
• Air Flowrates
• lt 10 SCFM per well
• Helps to Cycle (Hours, Not Days)

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Air Channel Pattern at Moderate Air Injection
Rate in a Medium Mixture of Two Bead Sizes With
38 of 0.75 mm and 62 of 0.3 mm
Overburden with 4 mm beads
Mixture of two size beads
Source Ji et al, 1993
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Air Channels at Low Air Injection Rate in 0.75
mm Uniform Bead Medium
Overburden with 4 mm beads
0.75 mm beads
Source Ji et al, 1993
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Short Circuiting in Air Sparging System
Air Flow
Contaminated Zone
Low Permeability Zone
Air bubble
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Proven/Emerging Remediation Technologies

• Excavation and Disposal / Treatment
• Soil Vapor Extraction (SVE) / Bioventing
• In-Situ Biodegradation / Oxygen Releasing
  Compounds
• Air Sparging
• Barriers
• Containment
• RBCA / Natural Attenuation

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Physical Barriers

• Purpose
• Prevent Outward Migration of Organics
• Reduce Inflow of Groundwater
• Design
• Types
• Keyed Into Confining Unit
• Partial vs. Complete Enclosures
• Construction
• Routinely Installed Down to 50 feet
• Cost 10 - 20 per sq. ft. for Slurry Wall

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Cutoff-Wall Keyed into Clay
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Cutoff Wall Hanging
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Hydraulic Containment
Pumping Well
Streamlines
Plume
Capture Zone

• Design Methods
• Javendahl Capture Zone Curves
• Computer Models
• Operational Factors
• Well Efficiency
• Seasonal / Annual Effects

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Hydraulic Containment With Slurry Wall
Slurry Wall
Slurry Wall
Well
Frac. Clay
Aquifers
Unfract. Clay
Drinking Water Aquifer
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Funnel and Gate Systems
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SKIMMING NAPLs IN SOURCE ZONES

• Interceptor trenches - collect free product
• Single pumping system
• Dual pumping system
• Combined water and product pumps
• Oil water separator at surface

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Typical NAPL Migration Pattern
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Interceptor Trench for DNAPL
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NAPL PLUME FROM FUEL SPILL
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NAPL RECOVERY SYSTEMTWO WELLSTWO PUMPS
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NAPL RECOVERYSYSTEM ONE WELLTWO PUMPS
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Natural Attenuation A New Approach

• Horizontal Wells

Basic Philosophy We Know It is Difficult to
Remove All Contaminants..... But We Can Predict
What Happens to Them.
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Overview of Natural Attenuation
Destruction of Contaminants via
Biodegradation Observed at Numerous Field
Sites Studied in Detail at Several Research
Sites Policy Guidance Now Recognize Natural
Att. Scientific Understanding is Rapidly
Increasing
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Natural Attenuation Under RCRA
Proposed Subpart S Preamble Natural Attenuation
Could Be the Most Appropriate Approach At Many
Sites and May Play a Major Role Conditions
Standards Achieved in a Reasonable Time
Likelihood of Exposure Is Minimal
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Obstacles to Natural Attenuation
? Associated with No Action ? Preference for
Zero Plume Growth ? Preference for Rapid
Remediation
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Evidence of Natural Attenuation
Criteria
? Plume stable or shrinking ? Plume is shorter
than would be expected ? Depletion of measurable
electron acceptors (OXYGEN, NITRATE OR SULFATE)
observed ? Metabolic by-products (FERROUS IRON
AND METHANE) observed ? Presence of active,
heterotrophic bacteria
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Evidence of Natural Attenuation
No BTEX
Map and Perform Mass Balance on Electron
Acceptors and Byproducts Oxygen Nitrate
Iron Sulfate CO2
BTEX
BTEX
Oxygen
Dissolved Oxygen
No Oxygen
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RISK-BASED CORRECTIVE ACTION
GROUNDWATER SERVICES, INC. John A. Connor,
P.E. Charles J. Newell, Ph.D., P.E. J. Peter Nevin
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Risk Assessment Fundamentals
Risk Management
Transport
RECEPTOR
SOURCE
Minimize risk by preventing exposure.
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Risk-Based Corrective Action Procedures
RISK-BASED APPROACH
TRADITIONAL APPROACH
Remedial Investigation
Remedial Investigation
Risk Assessment
Corrective Measure Study
Corrective Measure Study
Corrective Measure Implementation
Corrective Measure Implementation
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GRBCA(Gut-Feel Risk Based Corrective Action)
BAD
NOT SO BAD
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Baseline Risk Calculation
Exposure Concentration
x
Exposure Factors

Health Risk
x
Toxicity
Source Conc.
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Groundwater Services RBCA Tool Kit
www.gsi-net.com
Exposure Concentration
x
Exposure Factors

Health Risk
x
Toxicity
SOURCE CLEANUP LEVEL
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ASTM Guide for RBCA
ASTM RBCA Program
Site Classification and Response
? Classification Classify site per immediacy
and magnitude of risk, based on current snap
shot.
? Response Implement appropriate response
action for each class.
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Groundwater Exposure Pathway
3) Soil Leaching to Groundwater Ingestion
On-Site
Off-Site
Affected Soil
Affected Groundwater
4) Dissolved or Free-Phase Groundwater Plume
Ingestion
Potential Point of Human Exposure (i.e.,
on-site or off-site).
Affected Groundwater
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Proven/Emerging Remediation Technologies

• Excavation and Disposal / Treatment
• Soil Vapor Extraction (SVE) / Bioventing
• In-Situ Biodegradation / Oxygen Releasing
  Compounds
• Air Sparging
• Barriers
• Containment
• RBCA / Natural Attenuation