Groundwater Remediation
• Thanks to Phil deBlanc, Groundwater Services, Inc.
Corrective Action Process
RESULTS:SITE-SPECIFIC EVALUATION
Release Assessment
Conceptual Exposure Model
Risk-Based Target Limits
Remedial Action
No Further Action
Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection.
Compliance Monitoring
Conceptual Exposure Model: Key Questions
Waste or contaminant “hot spots”
RECEPTORSOURCE Migration in air or water Humans,
ecological species
Transport
Conceptual Model Development
KEY POINT:
Must have YES to all 3 questions to have complete exposure pathway.
SOURCE: Is it toxic, flammable, explosive, or otherwise harmful?
TRANSPORT: Is it in unsafe location or could it move to unsafe location?
RECEPTOR: Could humans or ecological receptors be exposed to hazardous chemicals?
?
?
?
Risk is a function of exposure concentration, intake, and toxicity.
KEY POINT:
X X =Exposure
Factors Toxicity Health RiskExposure Concentration
Corrective Action Fundamentals
Source POE
Risk-Based Approach: General Procedure
Calculation of Target Levels
Calculation
ExposureConcentration x
ExposureFactors = Health Riskx Toxicity
Safe cleanup limits at source are back-calculated based on allowable risk level at receptor.
KEY POINT:
POE = Point of Exposure
Corrective Action Process Overview
StartEnd
Source POE
Corrective Action Process
RESULTS:SITE-SPECIFIC EVALUATION
Release Assessment
Conceptual Exposure Model
Risk-Based Target Limits
Remedial Action
No Further Action
Provides site-specific classification, risk-based evaluation, remedy selection, and cost projection.
Compliance Monitoring
Remedy Selection Guidelines
Remediation Options
Natural Attenuationconfirm stable /
diminishing condition
KEY POINT:
Remedy should serve to prevent risk by controlling exposure.
Removal/Treatment:remediate source
RECEPTORSOURCE
Containment:prevent transport
Institutional Controls:control exposure activity
Transport
Soil Excavation at PST site
Remedial Action: Soils
PST = Petroleum Storage Tank
Excavation and Disposal / Treatment
On-Site or Off-Site
Thermal Treatment
On-Site Physical / Biological Treatment
Haul To Off-Site Landfill
Active Engineered Remedies
TREATMENT / DISPOSAL OPTIONS
Soil Vapor Extraction
Blower or Vacuum Pump
Vapor Treatment System (Where Required)
Air / VaporManifold
Clay
Grout Seal
Sand Pack
Affected Soils
Water Table
Screen
Active Engineered Remedies
Air vacuum extracts volatile contaminants from affected soil.
Soil Vapor Extraction: Applicability
Likelihood ofSuccess
104
103
102
101
100
10-1
10-2
10-3
10-4
Source: CDM, 1988
COCVapor Pressure
(mm Hg)
Butane
Benzene
Xylene
Aldicarb
Soil AirPermeability
HIGH(Coarse Sand /Gravel)
MEDIUM(Fine Sand)
LOW(Clay or Silt)
Active Engineered Remedies
VeryLikely
SomewhatLikely
LessLikely
Soil Vapor Extraction (SVE) System at Former Gasoline Station
Remedial Action: Soils
SVE Wells and
Collection Headers
Vapor Treatment
System
REMOVAL / TREATMENT OPTIONS
GW Remediation Options
GW Pump & Treat Air Sparging Dual Phase Extraction
Hydraulic Containment (pumping)
Barrier Walls
CONTAINMENT OPTIONS
Affected Soil
GW INGESTION
Affected Groundwater
Active Remediation Technologies
Use continuous GW extraction to reduce COC concentrations in GW to applicable target levels.
GOAL
APPLICABILITY
GW Extraction:Recovery wells / submersible pumps; wellpoint systems.
GW Treatment:GAC, air stripper, biological, etc.
Moderate-to-high permeability groundwater units (K > 10-4 cm/s), low COC concentrations (CRF < 100), and no NAPL plume.
GW Pump & Treat: Overview
DESIGNOPTIONS
NAPL
CRF = COC Reduction Factor = (Current COC Conc./Target Level); K = Hydraulic Conductivity (cm/s)
GW Remediation Options
COC = Chemical of Concern
GW Pump & Treat: Well Installation
GW Remediation Options
Recovery Well Installation
Well Screen
Centralizer
Driller’s Knee
Driller’s Helper
Sand-Gravel Filter Pack
Wire-Wrapped Well Screen
Material: Corrosion & contaminant resistant. Options = PVC, SS, teflon, FRP.
Large enough to fit pump, usually 4-in or 6-in.
GW Pump & Treat: Recovery Well Design
FRP = Fiberglass reinforced plastic PVC = Polyvinyl chlorideSS = Stainless steel
CasingProtective casingConcrete surface pad
Bentonite pellet seal
Cement/bentonite grout
Select sand backfill
Casing
Well screenŠ10 ft
Varies
Š 3 ft
10 in
2 ft
Š1 ftSump with plug
To collection pipe
Centralizer
Centralizer
GW Remediation Options
GW Pump & Treat: Recovery Well Design
PVC = Polyvinyl chlorideSS = Stainless steel
Material: Typically same as casing. May use SS screen with PVC casing to economize.
Length: 30-50% of saturated thickness for unconfined unit; 70-80% of saturated thickness for confined unit
Placement: Adjust to match plume thickness, floating or sinking plume.
Diameter: Prevent excessive head loss through screen by evaluating screen open area and pumping rate.
Slot Size: Retain 90% of sand pack, slot size ≥ D10 of sand pack.
Well ScreenProtective casingConcrete surface pad
Bentonite pellet seal
Cement/bentonite grout
Select sand backfill
Casing
Well screenŠ10 ft
Varies
Š 3 ft
10 in
2 ft
Š1 ftSump with plug
To collection pipe
Centralizer
Centralizer
GW Remediation Options
Purpose: Stabilize formation, minimize fines in well, & maximize screen slot size.
Thickness: 3-8 in thickness between well screen and borehole wall.
Material: Clean, uniform, silica sand/gravel.
Sand PackProtective casingConcrete surface pad
Bentonite pellet seal
Cement/bentonite grout
Select sand backfill
Casing
Well screenŠ10 ft
Varies
Š 3 ft
10 in
2 ft
Š1 ftSump with plug
To collection pipe
Centralizer
Centralizer
Material: Portland cement/bentonite mix.
Configuration: At ground surface, sloped to drain rainwater away from well casing.
Grout Seal
GW Pump & Treat: Recovery Well DesignGW Remediation Options
Groundwater P&T: The Bad News
CO
C C
on
c. i
n G
W
Time
?Cleanup Standard
KEY POINT: USEPA study shows that GW P&T cannot cleanup to DW standard at most sites.
WHY NOT? Complex hydrogeology, design flaws, and NAPL.
GW Remediation Options
GW Pump & Treat: Tailing and Rebound
Source:From W, R, N, & W.
Regulatory Cleanup Level
C
t
C
t
Regulatory Cleanup Level
Pump Shut-Off
T
Continuous Pump and Treat Resulting in Tailing
Rebound After Pump and Treat System Shut-Off
GW Remediation Options
GW Pump & Treat: Wrap-Up
• Capable of providing hydraulic containment
• May be required tosatisfy regulators
• Incapable of attaining drinking water standards
• Must treat or dispose of recovered GW
• Long-term commitment
10
PRO CON
GW Remediation Options
Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels.GOAL
APPLICABILITY
GW Extraction:Recovery wells / submersible pumps; wellpoint systems.
Vapor Extraction: Blower, dual phase wellpoint pump.
Water Treatment: GAC, airstripper, biological
Vapor Treatment, GAC, catalytic furnace.
Low to moderate permeability groundwater units (K = 10-5 to 10-3 cm/s)
Dual-Phase Extraction: Overview
DESIGNOPTIONS
vapor
PumpGW
vapor
GW
GW Remediation Options
Dual-Phase Extraction: Design Options
Separate Air & Water Headers:Equip each well with submersible pump. Run SVE vacuum header to each wellhead.
Combined Air/ Water Header:Use dual-phase air/water vacuum pump and run single suction header to each wellhead with drop tube to water.
Dual-phase pump extracts both air
and water
Air
GW
GW Remediation Options
Inject air to volatilize organics and promote in-situ biodegradation, as needed to reduce COCs in GW to applicable target levels.
GOAL
APPLICABILITY
Air Injection:Air compressor with multiple small injection points.
Vapor Recovery: If needed, use SVE wells to recover and treat vapors.
Moderate to high-permeability GW units (K > 10-4 cm/s)
Air Sparging: Overview
DESIGNOPTIONS
Air
GW Remediation Options
• Well Configuration– Injection Points: 1-2 inch diam.
PVC Wells, 2-5 ft Screen length– Typical Spacing: 5 - 20 ft centers
• Injection Pressure: 1-10 psig• Air Flowrates
– < 10 SCFM per well– Helps to Cycle injection periods (Hours, Not
Days)
Air Sparging: Design Issues
Air Injection
Points
GW Remediation Options
Limitations
Air Sparging: Process Review
Air
Remediation Processes
GW Remediation Options
Volatilization of NAPLs
Air Stripping of Dissolved Organics
Oxygenation of Water Enhances In-Situ Biodegradation
Effectiveness may be reduced if a few small channels are formed
Very sensitive to heterogeneities
If air flow from top of screen only, entire groundwater bearing unit not treated
GW Remediation Options
In-Situ Biodegradation: Overview
Solid magnesium peroxide compound activated by moisture to slowly release O2 to GW. Can achieve higher dissolved O2 levels than air sparging, theoretically.
Inject ORC into aquifer or place in monitoring wells. Requires moderate GW pHlevels (e.g., pH 6-9).
Applicable if GW plume notexpanding & aggressivetreatment not needed tomeet remediation goals.
WHAT
HOW
WHEN O2 O2 O2
Oxygen Release Compound (ORC)
Use physical or hydraulic barrier system to prevent migration of affected GW to point of exposure.
GOAL
APPLICABILITY
Physical Barrier:Slurry wall, asphalt wall
Hydraulic Barrier:GW P&T system, cut-off trench
Applicable to all GW units and COCs. Physical barrier walls limited to 100 ft depth. Hydraulic containment (P&T) limited by water treatment requirements.
GW Containment: Overview
DESIGNOPTIONS
slurry wall
Affected GW zone
GW Remediation Options
GW Containment: Hydraulic Containment
GW Pumping Well
Streamlines
Plume
Hydraulic Capture Zone
PLAN VIEW
n Design Methods- Javendahl Capture Zone Curves
n Computer Models
n Operational Factors- Well Efficiency - Seasonal / Annual Effects- Produced Water Treatment
GW Flow
GW Remediation Options
GW Containment: Physical Barriers
• Purpose– Prevent Migration of COCs
from Affected Zone– Reduce Inflow of Clean Groundwater
• Design– Partial vs. Complete Enclosures– Can be Keyed Into Underlining
Confining Unit• Construction
– Routinely Installed Down to 50 feet– Cost: ~ $ 5 per sq. ft. for Slurry Wall
slurry wall
Affected GW zone
GW Remediation Options
GW Containment: Physical Barrier
0’
35’
70’
DNAPLDrinking WaterAquifer
Unfract. Clay
Frac. Clay
Aquifers
Slurry Wall
Slurry WallWell
tPi s
GW Remediation Options
Hydraulic Containment by Slurry Wall
Installation of Bentonite-
Slurry Barrier Wall
Remedial Action: Groundwater
Permeable Reaction Walls
Ref: Gillham
Funnels Dissolved Organics Through Reaction Wall
Funnel:ImpermeableBarrier Wall
Gate: Permeable Reaction Wall - Fill With Iron
FilingsFunnel:ImpermeableBarrier Wall
Installation of Permeable Treatment Trench
Remedial Action: Groundwater
– Dispersion
– Sorption kd = (Koc)*(foc)
NON-DESTRUCTIVE PROCESSES
– Biodegradation
– Volatilization
– Dilution
DESTRUCTIVE PROCESSES
Reduction in contaminant mass or concentration in groundwater over time or distance due to natural processes:
– Abiotic Reactions (hydrolysis)
O2 Fe +2
NO
3
CH
4
CO
2HydrocarbonSO
4
Natural Shrinking of GW Plume Over Time
What is “Natural Attenuation”?
Common Applications of MNA
A. SHRINKING PLUME
GW POE
B. STABLE PLUME
GW POE
MOST COMMON USE:
Affected GW plume is stable or shrinking with no impacted groundwater receptors.
Therefore, no risk of exposure.
No risk to
existing user.
No risk to
existing user.
MNA= Monitored Natural Attenuation
Today’s Focus
Soil Excavation SVE
Soil Excavation (smear zone)
Continuous Recovery
Periodic Recovery (bailing, High-Vac)
Air Sparging
NAPL IN UNSAT. SOIL ZONE
NAPL IN GW ZONE
NAPL Removal Options
Active Remediation Technologies
NAPL in Soil
NAPL in GW
Dissolved GW Plume
NAPL Removal Options: Key Factors
Soil Remediation Options
n Vertical distribution of NAPL
n Permeability of soil to NAPL
n Relative soil permeability to water & NAPL
Key Factors Influencing NAPL Removal
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Hydrocarbon Saturations
0
100
200
300
400
500
600
700
Ele
vati
on
Ab
ov e
Oil
/ Wat
er
Inte
rfac
e (c
m)
NAPL
Well
H2O
KEY POINT:
NAPL concentrates in “smear zone” atop GW table.
NAPL Removal Options
NAPL Removal Options: Vertical NAPL Distribution
NAPL = Non-aqueous phase liquid.
NAPL = Non-aqueous phase liquid. Source: Beckett & Huntley, 1999
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102
Hydraulic Conductivity of Soil to NAPL (m/day)
0
100
200
300
400
500
Ele
va
tio
n A
bo
ve
Oil
/Wa
ter
Inte
rfa
ce
(c
m)
Fine/Med Sand (Ksat = 4 m/d)Silty Sand (Ksat = 0.4 m/d)Silt (Ksat = 0.1 m/d)
Coarse Sand (Ksat = 43 m/d)
KEY POINT:
NAPL easier to remove in coarse-grained dry soils.Hard to remove in fine-grained wet soils.
NAPL Removal Options
NAPL Removal Options: Effects of Soil Type
Soil Type vs. Permeability of Soil to NAPL
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Water Saturation of Soil
Irreducible Water Saturation
NAPL Removal Options
NAPL Removal Options: Relative Permeabilities
KEY POINT:Soil saturated with waterhas low permeability for NAPL, so NAPL easierto removefrom dry soil.
Re
lati
ve
Pe
rmea
bili
ty
Relative Permeabilities of Soil to Water & NAPL
Soil K for NAPL
Soil K for Water
Continuously recover NAPL to reduce source mass, stabilize NAPL plume (e.g., daily operation).
GOAL
APPLICABILITY
DESIGNOPTIONS
Recovery wells & skimmer pumps
Interceptor trench &skimmer pump
Multi-phase recovery system
Sites with significant mobile NAPL plume atop GW (e.g., >> 1 ft thick).
Continuous NAPL Recovery Methods
NAPL
Pump
NAPL
NAPL Removal Options
Multi-Phase NAPL Recovery
Groundwater and NAPL
Soil Vapor
Smear Zone Dewatered Remediated Through Air Flow
NAPL Removal Options
Multi-Phase Recovery: Wrap-Up
• May be effective in low to moderate permeability settings.
• Fast where It works: 2 months to 2 years.
• Vapor and GW treatment can be very expensive.
• Will not achieve low cleanup levels in groundwater.
• Can be impossible to dewater smear zone in certain hydrogeologic setting
NAPL Removal Options
PRO CON
Remove periodic accumulation of NAPL from observation wells to reduce NAPL mass and mobility (e.g., weekly to quarterly operation).
GOAL
APPLICABILITY
Periodic bailing of wells
Periodic skimmer pump operation in wells or trench.
Periodic High-Vac recovery
Sites with minor NAPL accumulations and/or non-mobile NAPL plumes.
Periodic NAPL Recovery Methods
DESIGNOPTIONS
Bailer
NAPL
NAPL Removal Options
AtmosphericAir Bleed Valve
Periodic NAPL Recovery: High-Vacuum
VacuumGauge
Two-PhaseFlow
NAPL / GW Collection
Operational Water Table
Saturated Zone
Soil VaporFlow
Suction Pipe
GW and NAPL Flow
Vacuum Truck
Vapor Treatment
discharge
clean air
Conduct periodic vacuum extraction to recover NAPL (e.g., monthly or quarterly for 8-hour episode).
NAPL Removal Options
Groundwater /NAPL P&T System
Vacuum Pump
Recovery Well
Control Panel
Vapor Control System
Fluid Separation
Tank
Remedial Action: Groundwater
Remove NAPL smear zone by means of in-situ “air stripping.”GOAL
APPLICABILITY
Air Sparging:Periodically inject air to volatilize NAPL.
Sites with minor NAPL accumulations of volatile NAPL material in coarse-grained soils.
Air Sparging of NAPL Plume
DESIGNOPTIONS
Air
NAPL
NAPL Removal Options
Air Sparging System
Volatilizes Organics and Promotes In-Situ Biodeg.
GW Remediation Options
Air Compressor
Blower
Vapor Treatment
Tiny Bubbles
Affected GW zone
SVE Well(Optional)
Air Sparging of NAPL Plume
NAPL Recovery Options
Silt
Smear Zone
Air Channels
Water Table
KEYPOINT:
Air pathways affected by subsurface heterogeneities. Can result in inconsistent removal.
Air Sparging: Wrap-Up
• Has the potential to remove NAPL from the saturated zone without dewatering
• Less expensive than many alternatives
• Not applicable in many hydrogeologic settings
• Requires closely spaced wells• Often requires concurrent SVE• No reliable pilot test criteria
NAPL Removal Options
PRO CON
NAPL Removal: Is It Worthwhile?
• May help abate further spreading of NAPL plume
• Initially, the lowest $/lb. recovered
• May not significantly reduce source longevity
• Large fraction of NAPL left behind
• Slow• Often requires groundwater
pumping
NAPL Removal Options
MAYBE MAYBE NOT
You can
switch to
RNA if:
Remedy Completion: When is “Enough” Enough?
No Impacts: No current or potential receptor impacts.
Stable Plume: Affected GW plume stable or shrinking.
Not Time Critical: No rush to meet final COC target levels.
No Benefit: Further active remediation not likely to significantly reduce COC levels.
RNA = Remediation by Natural Attenuation
Active Remediation Technologies
No Further
Action
Required If:
Target Levels Achieved: COC levels reduced to applicable target levels in all media.
Compliance Monitoring: Follow-up monitoring (if needed) confirms remedy completion.
Institutional Controls: If needed. institutional controls in place. No COCs > target
levels
Remedy Completion: When is “Enough” Enough?
Active Remediation Technologies