Overview
Remedial Technologies
Philip B. Bedient
Rice University
How Remediation Technology Evolves
Cost-Effective Technology
Proven
Technology
Large-Scale
Field Trials
Emerging
Technology
Experimental
Technology
Uncontrolled
Pilot Trials
Prototypes and
Controlled Field Experiments
Bench Studies
Concept / Problem Identification
CONCEPTS
Source: Cherry, 1992
Original Paradigm: 1980s
Groundwater Pump and Treat
Will Remediate Sites
Bad News
Conc
?
Cleanup Standard
Time
EPA’s 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
Residual saturation
of LNAPL in soil
from spill
Dissolved
contaminant plume
Free phase layer in
saturated zone
Ground water flow
Forming Residual NAPL
Snap-Off Mechanism:
Other Mechanisms: Bypass, Etc.
NAPLs and Capillary Forces
NAPL
NAPL
NAPL
Residual vs. Free-Phase DNAPL
Free-Phase DNAPL
Residual DNAPL
Residual NAPL: Long-Term Source
• Can’t Remove Residual
• Dissolves Slowly
• Large Mass Compared to Dissolution Rate
Recovering LNAPL
Separator
Sand Pack
Screen
Pump
DNAPL Pool
Saturated
Zone
Recovering LNAPL: Other Configurations
Dual Recovery Wells
Pump Cans
Skimmers
Adsorbants
DNAPL Pool
Trenches
DNAPL Conceptual Model
DNAPL Entry Zone
Residual DNAPL
Sand
Fractured Clay
Sand
Dissolved Phase
Plume
DNAPL Pool
Recovering DNAPL
DNAPL / Water Separator
Sand Pack
Pump
Screen
DNAPL Pool
Sump
Saturated
Zone
Impervious
Barrier
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
Remediation Technologies
• Introduction - Why Are We Here
• Product Removal and Source Control
• Groundwater pump and treat
• Remedial Technologies in Use
Pump-and-Treat (Dissolution)
• Dissolves Residual NAPL
• Key Concept: Number of Pore Volumes
• Takes a Long Time
Applicability of Dissolution of NAPLs
• NAPLs in Saturated Zone
• NAPL with Very Soluble Components
• Sites With Low Amounts of NAPL
• Highly Permeable Aquifers
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
Excavation and
Disposal / Treatment
Haul To Off-Site Landfill
On-Site or Off-Site
Thermal Treatment
On-Site Physical /
Biological Treatment
Applicability of Excavation
• Standard Construction Practice to 25 Feet Depth
• Dewatering Required if Below Water Table
• Unconsolidated Material
• Best Technology for Small Volumes
Soil Vapor Extraction
Air / Vapor
Manifold
Blower or
Vacuum Pump
Vapor Treatment System
(Where Required)
Clay
Grout Seal
Screen
Sand Pack
Contaminated Soils
Water Table
Applicability of SVE
Vapor Pressure
(mm Hg)
Likelihood of
Success
Soil Air
Permeability
104
Butane
103
Benzene
102
Xylene
101
100
10-1
Aldicarb
Very
Likely
Somewhat
Likely
HIGH
(Coarse Sand /
Gravel)
MEDIUM
(Fine Sand)
10-2
LOW
10-3
(Clay or Silt)
10-4
Less
Likely
Source: CDM, 1988
Design Basis Information: SVE
• Air Permeability
– Estimated from Soil Properties
– Measured With Test in Field
• Contaminant Characteristics
– DNAPL Composition
– Volatility (Vapor Pressure, Henry’s Law Coefficient)
• Air Flow
– Stratigraphy
– Need for Impermeable Cap
– Water Table and Need for Pumping
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
Bioventing
If Air Injection Rate is
Slow Enough No Vapor
Treatment Is Needed
Ref.: Hinchee
Blower
Unsaturated
Zone
Saturated
Zone
Slowly Adds Oxygen to Unsaturated Zone for Biodegradation
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
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 < 20 ft: Screen 10 - 20 ft
Water Table > 20 ft: Through Contaminated Zone
Spacing: 5 to 60 ft, Depends on Depth and Soil Type
Injection Rate: Variable
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
In-Situ Biodegradation
Oxygen
Addition
To:
• Treatment
• Treatment / Recycle
• Recycle
Injection
Well
Nutrient
Addition
Recovery
Well
DNAPL
In-Situ Biodegradation
Zone
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
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
– Pure Oxygen
– Hydrogen Peroxide
• Calculate Water Needed
• Size Recovery Well System
~ 10 mg/l
~ 25 mg/l
~ 100 mg/l (?)
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)
Air Sparging
Air
Compressor
Blower
Vapor
Treatment
SVE
Well
NAPL
Tiny
Bubbles
Volatilizes Organics and Promotes In-Situ Biodeg.
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.
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
– < 10 SCFM per well
– Helps to Cycle (Hours, Not Days)
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
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
Short Circuiting in Air Sparging System
Air Flow
Contaminated Zone
Low Permeability
Zone
Air
bubble
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
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
Cutoff-Wall – Keyed into Clay
LOW PERMEABILITY
WALLS
AQUITARD
FL OW
DNAPLs
AQUIFER
Cutoff Wall – Hanging
LOW PERMEABILITY
WALLS
AQUITARD
FL OW
DNAPLs
AQUIFER
Hydraulic Containment
Pumping Well
Streamlines
Plume
Capture Zone
• Design Methods
– Javendahl Capture Zone Curves
– Computer Models
• Operational Factors
– Well Efficiency
– Seasonal / Annual Effects
Hydraulic Containment With Slurry Wall
0'
Slurry Wall
Well
Slurry Wall
PITS
Pits
Frac. Clay
35'
Aquifers
DNAPL
Unfract. Clay
70'
Drinking Water
Aquifer
Funnel and Gate Systems
Funnel
Plan View
Contaminant
Plume
Plume Without
Critic al Contaminants
Gate
Keyed Gate
Fill
Vertical Slice
Aquifer
Plume
Treated
Plume
Reac tive medium
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
Typical NAPL Migration Pattern
Interceptor Trench for DNAPL
TREATMENT
UNIT
EXTRACTION
BACKFILL
CONTAMINATION
ZONES
GRAVEL
BACKFILL
TRENCH
NAPL PLUME FROM FUEL SPILL
NAPL RECOVERY
SYSTEM
TWO WELLS
TWO PUMPS
NAPL RECOVERY
SYSTEM
ONE WELL
TWO PUMPS
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.
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
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
Obstacles to Natural Attenuation

Associated with No Action

Preference for Zero Plume Growth

Preference for Rapid Remediation
NATURAL
ATTENUATION
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
Evidence of Natural Attenuation
No BTEX
BTEX
BTEX
Oxygen
Dissolved
Oxygen
No Oxygen
Map and Perform
Mass Balance on
Electron Acceptors
and Byproducts:
•
•
•
•
•
Oxygen
Nitrate
Iron
Sulfate
CO2
RISK-BASED CORRECTIVE ACTION
GROUNDWATER
SERVICES, INC.
John A. Connor, P.E.
Charles J. Newell, Ph.D., P.E.
J. Peter Nevin
Risk Assessment Fundamentals
Risk Management
Transport
SOURCE
RECEPTOR
Minimize risk by preventing exposure.
Risk-Based
Corrective Action Procedures
TRADITIONAL APPROACH
Remedial Investigation
RISK-BASED APPROACH
Remedial Investigation
Risk Assessment
Corrective Measure Study
Corrective Measure Study
Corrective Measure
Implementation
Corrective Measure
Implementation
GRBCA
(Gut-Feel Risk Based Corrective Action)
BAD
NOT SO BAD
Baseline Risk Calculation
Exposure x Exposure x Toxicity
Concentration
Factors
Source
Conc.
Calculation
=
Health Risk
Groundwater Services RBCA Tool Kit
www.gsi-net.com
Exposure x Exposure x Toxicity
Concentration
Factors
SOURCE
CLEANUP
LEVEL
Calculation
=
Health Risk
ASTM Guide for RBCA
ASTM RBCA Program
Release
Notification
Site Assessment
Site Classification
and Interim
Response
Tiered RBCA
Evaluation
Remedial Action
Compliance
Monitoring
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.
GOAL: Control near-term hazards as site
evaluation proceeds. Target resources
toward high-risk sites.
No Further Action
Groundwater Exposure Pathway
3) Soil Leaching to Groundwater: Ingestion
OnSite
Affected Soil
OffSite
Drinking Water Well
Affected Groundwater
4) Dissolved or Free-Phase Groundwater Plume: Ingestion
=
Drinking Water Well
Affected Groundwater
Potential Point of
Human Exposure
(i.e., on-site
or off-site).
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