Transcript No Slide Title

Remedial Action: Soils
Excavation and Disposal / Treatment
TREATMENT /
DISPOSAL OPTIONS
Haul To
Off-Site
Landfill
On-Site
or Off-Site
Thermal
Treatment
On-Site
Physical /
Biological
Treatment
Soil Vapor Extraction
Air / Vapor
Manifold
Air vacuum
extracts
volatile
contaminants
from
affected
soil.
Blower or
Vacuum
Pump
Vapor
Treatment
System
(Where Required)
Clay
Grout Seal
Screen
Sand Pack
Affected Soils
Water Table
Active Engineered Remedies
Soil Vapor Extraction: Applicability
COC
Vapor Pressure
(mm Hg)
104
Butane
Benzene
103
HIGH
(Coarse Sand /
Gravel)
Likelihood of
Success
Very
Likely
102
101
Xylene
Soil Air
Permeability
100
MEDIUM
(Fine Sand)
Somewhat
Likely
LOW
(Clay or Silt)
Less
Likely
10-1
10-2
10-3
Aldicarb
10-4
Source: CDM, 1988
Soil Vapor Extraction (SVE) System
at Former Gasoline Station
Vapor
Treatment
System
SVE Wells
and
Collection
Headers
GW Remediation Options
REMOVAL / TREATMENT OPTIONS
GW INGESTION
Affected
Soil
 GW Pump & Treat
 Air Sparging
 Dual Phase Extraction
CONTAINMENT OPTIONS
 Hydraulic Containment
(pumping)
Affected Groundwater
 Barrier Walls
GW Pump & Treat: Overview
GOAL
Use continuous GW extraction
to reduce COC concentrations in
GW to applicable target levels.
APPLICABILITY
Moderate-to-high permeability
groundwater units (K > 10-4 cm/s), low
COC concentrations (CRF < 100), and
no NAPL plume.
NAPL
DESIGN
OPTIONS
 GW Extraction:
Recovery wells /
submersible pumps;
wellpoint systems.
 GW Treatment:
GAC, air stripper, biological, etc.
CRF = COC Reduction Factor = (Current COC Conc./Target Level);
COC = Chemical of Concern
K = Hydraulic Conductivity (cm/s)
GW Pump & Treat: Well Installation
Recovery Well
Installation
Well Screen
Centralizer
Wire-Wrapped
Well Screen
Sand-Gravel
Filter Pack
GW Pump & Treat: Recovery Well Design
To collection pipe
Protective casing
Concrete surface pad
Casing
 Material: Corrosion & contaminant
resistant. Options = PVC, SS,
teflon, FRP.
 Large enough to fit pump, usually
4-in or 6-in.
Cement/bentonite grout
Casing
Varies
•
2 ft
Bentonite pellet seal
Š 3 ft
Centralizer
Well screen
Š10 ft
Select sand backfill
Centralizer
Sump with plug
Š1 ft
FRP = Fiberglass reinforced plastic
PVC = Polyvinyl chloride
SS = Stainless steel
10 in
GW Pump & Treat: Recovery Well Design
Well Screen
 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.
PVC = Polyvinyl chloride
SS = Stainless steel
To collection pipe
Protective casing
Concrete surface pad
Cement/bentonite grout
Casing
Varies
•
2 ft
Bentonite pellet seal
Š 3 ft
Centralizer
Well screen
Š10 ft
Select sand backfill
Centralizer
Sump with plug
Š1 ft
10 in
GW Pump & Treat: Recovery Well Design
Sand Pack
To collection pipe
Protective casing
Concrete surface pad
 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.
Cement/bentonite grout
Casing
Varies
•
2 ft
Bentonite pellet seal
Š 3 ft
Centralizer
Grout Seal
 Material: Portland cement/bentonite mix.
 Configuration: At ground surface,
sloped to drain rainwater away from well
casing.
Well screen
Š10 ft
Select sand backfill
Centralizer
Sump with plug
Š1 ft
10 in
Dual-Phase Extraction: Overview
GOAL
APPLICABILITY
DESIGN
OPTIONS
Use aquifer dewatering and soil venting to
reduce COC concentrations in GW to
applicable target levels.
Low to moderate permeability groundwater units
(K = 10-5 to 10-3 cm/s)
 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.
GW
vapor
vapor
GW
Pump
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
Air Sparging: Overview
GOAL
Inject air to volatilize organics and
promote in-situ biodegradation, as
needed to reduce COCs in GW to
applicable target levels.
APPLICABILITY
Moderate to high-permeability
GW units (K > 10-4 cm/s)
DESIGN
OPTIONS
 Air Injection:
Air compressor
with multiple small
injection points.
 Vapor Recovery:
If needed, use SVE
wells to recover
and treat vapors.
Air
Air Sparging: Design Issues
• 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
Injection
Points
Air Sparging: Process Review
Remediation Processes



Volatilization of NAPLs
Air Stripping of Dissolved Organics
Oxygenation of Water Enhances InSitu Biodegradation
Limitations



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
Air
In-Situ Biodegradation: Overview
Oxygen Release Compound (ORC)
WHAT
HOW
WHEN
 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 pH
levels (e.g., pH 6-9).
 Applicable if GW plume not
O2 O2 O2
expanding & aggressive
treatment not needed to
meet remediation goals.
GW Containment: Overview
GOAL
Use physical or hydraulic barrier
system to prevent migration of affected
GW to point of exposure.
APPLICABILITY
Applicable to all GW units and COCs.
Physical barrier walls limited to 100 ft
depth. Hydraulic containment (P&T)
limited by water treatment requirements.
DESIGN
OPTIONS
 Physical Barrier:
Slurry wall,
asphalt wall
 Hydraulic Barrier:
GW P&T system,
cut-off trench
slurry
wall
Affected GW zone
GW Containment: Hydraulic Containment
PLAN VIEW
GW Pumping Well
Streamlines
GW Flow
Plume
Hydraulic Capture Zone
 Design Methods
- Javendahl Capture
Zone Curves
 Computer Models
 Operational Factors
- Well Efficiency
- Seasonal / Annual Effects
- Produced Water Treatment
GW Containment: Physical Barriers
• Purpose
– Prevent Migration of COCs
from Affected Zone
– Reduce Inflow of Clean Groundwater
• Design
slurry
wall
– 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
Affected GW zone
GW Containment: Physical Barrier
Hydraulic Containment by Slurry Wall
0’
Slurry
Wall
Well
Slurry Wall
Pits
Frac. Clay
35’
Aquifers
DNAPL
70’
Unfract. Clay
Drinking Water
Aquifer
Installation of
BentoniteSlurry
Barrier Wall
Permeable Reaction Walls
Ref: Gillham
Funnel:
Impermeable
Barrier Wall
Gate: Permeable
Reaction Wall Fill With Iron
Filings
Funnel:
Impermeable
Barrier Wall
Funnels Dissolved Organics Through Reaction Wall
Installation of
Permeable
Treatment
Trench
NAPL Removal Options
NAPL IN UNSAT. SOIL ZONE
 Soil Excavation
 SVE
NAPL IN GW ZONE
NAPL in Soil
NAPL in GW
Dissolved GW Plume
 Soil Excavation
(smear zone)
 Continuous Recovery
 Periodic Recovery
(bailing, High-Vac)
 Air Sparging
Today’s
Focus
NAPL Removal Options: Key Factors
Key Factors Influencing
NAPL Removal
 Vertical distribution of NAPL
 Permeability of soil to NAPL
 Relative soil permeability to
water & NAPL
NAPL Removal Options: Vertical NAPL
Distribution
Well
700
600
KEY POINT:
500
400
NAPL
300
200
100
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Hydrocarbon Saturations
NAPL = Non-aqueous phase liquid.
H2O
NAPL
concentrates
in “smear
zone” atop
GW table.
NAPL Removal Options: Effects of Soil Type
Elevation Above Oil/Water Interface (cm)
Soil Type vs. Permeability of Soil to NAPL
500
Silt (Ksat = 0.1 m/d)
Silty Sand (Ksat = 0.4 m/d)
Fine/Med Sand (Ksat = 4 m/d)
Coarse Sand (Ksat = 43 m/d)
400
KEY POINT:
300
200
100
0
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
NAPL easier to
remove in
coarse-grained
dry soils.
Hard to remove
in fine-grained
wet soils.
10
Hydraulic Conductivity of Soil to NAPL (m/day)
NAPL = Non-aqueous phase liquid.
Source: Beckett & Huntley, 1999
NAPL Removal Options: Relative Permeabilities
KEY POINT:
Soil saturated
with water
has low
permeability
for NAPL, so
NAPL easier
to remove
from dry soil.
Relative Permeability
Relative Permeabilities of Soil to Water & NAPL
1
Irreducible Water
Saturation
0.8
0.6
Soil K for NAPL
0.4
Soil K for Water
0.2
0
0
0.2
0.4
0.6
0.8
Water Saturation of Soil
1
Continuous NAPL Recovery Methods
GOAL
Continuously recover NAPL to reduce
source mass, stabilize NAPL plume
(e.g., daily operation).
APPLICABILITY
Sites with significant mobile NAPL
plume atop GW (e.g., >> 1 ft thick).
DESIGN
OPTIONS
 Recovery wells &
skimmer pumps
 Interceptor trench &
skimmer pump
 Multi-phase
recovery system
NAPL
NAPL
Pump
Multi-Phase NAPL Recovery
Soil Vapor
Smear Zone Dewatered
Groundwater
and NAPL
Remediated Through Air Flow
NAPL Removal Options
Multi-Phase Recovery: Wrap-Up
PRO
• May be effective in low to
moderate permeability
settings.
• Fast where It works: 2
months to 2 years.
CON
•
•
•
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
Periodic NAPL Recovery Methods
GOAL
Remove periodic accumulation of
NAPL from observation wells to
reduce NAPL mass and mobility
(e.g., weekly to quarterly operation).
APPLICABILITY
Sites with minor NAPL accumulations
and/or non-mobile NAPL plumes.
 Periodic bailing
of wells
DESIGN
OPTIONS
Bailer
 Periodic skimmer
pump operation in
wells or trench.
 Periodic High-Vac
recovery
NAPL
Periodic NAPL Recovery: High-Vacuum
Vacuum
Gauge
Atmospheric
Air Bleed
Valve
TwoPhase
Flow
discharge
clean air
Vacuum Truck
NAPL / GW Collection
Vapor
Treatment
Suction
Pipe
Soil
Vapor
Flow
Conduct periodic vacuum
extraction to recover NAPL
(e.g., monthly or quarterly
Saturated Zone
for 8-hour episode).
GW and NAPL Flow
Remedial Action: Groundwater
Groundwater /NAPL P&T System
Recovery
Well
Vacuum
Pump
Fluid
Separation
Tank
Control Panel
Vapor
Control
System
Air Sparging of NAPL Plume
GOAL
Remove NAPL smear zone by means
of in-situ “air stripping.”
APPLICABILITY
Sites with minor NAPL accumulations
of volatile NAPL material in coarsegrained soils.
DESIGN
OPTIONS
 Air Sparging:
Periodically inject
air to volatilize
NAPL.
Air
NAPL
Air Sparging System
Air
Compressor
Blower
Vapor
Treatment
SVE Well
(Optional)
Affected
GW
zone
Tiny
Bubbles
Volatilizes Organics and Promotes In-Situ Biodeg.
Air Sparging of NAPL Plume
Water Table
Smear
Zone
Air Channels
Silt
KEY
POINT:
Air pathways affected by subsurface
heterogeneities. Can result in inconsistent
removal.
Active Remediation Technologies
Remedy Completion:
When is “Enough” Enough?
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