52. Remedial Action: Soils

53. Excavation and Disposal / Treatment
TREATMENT / DISPOSAL OPTIONS
Haul To Off-Site Landfill
On-Site or Off-Site
Thermal Treatment
On-Site Physical /
Biological Treatment

54. Soil Vapor Extraction
Blower or
Vacuum Pump
Air / Vapor
Manifold
Vapor Treatment System
(Where Required)
Air vacuum extracts volatile contaminants from affected soil.
Clay
Grout Seal
Screen
Sand Pack
Affected Soils
Water Table

55. Soil Vapor Extraction: Applicability
Active Engineered Remedies
Soil Vapor Extraction: Applicability
COC Vapor Pressure
(mm Hg)
Soil Air
Permeability
Likelihood of
Success
104
HIGH
(Coarse Sand /
Gravel)
Very
Likely
Butane
103
102
Benzene
Somewhat
Likely
101
MEDIUM
(Fine Sand)
Xylene
100
10-1
10-2
LOW
(Clay or Silt)
Less
Likely
10-3
Aldicarb
10-4
Source: CDM, 1988

56. Vapor Treatment System SVE Wells and Collection Headers
Soil Vapor Extraction (SVE) System at Former Gasoline Station
Vapor Treatment System
SVE Wells and Collection Headers

57. GW Remediation Options
REMOVAL / TREATMENT OPTIONS
Affected Soil
GW INGESTION
Affected Groundwater
 GW Pump & Treat
 Air Sparging
 Dual Phase Extraction
CONTAINMENT OPTIONS
Slide Topic: GW remediation options
GW pump and treat
Air spraging
Dual-phase extraction
Hydraulic containment
Barrier walls
Key Presentation Points: Introduce the technologies to be covered.
 Hydraulic Containment (pumping)
 Barrier Walls

58. GW Pump & Treat: Overview
Use continuous GW extraction to reduce COC concentrations in GW to applicable target levels.
GOAL
Moderate-to-high permeability groundwater units (K > 10-4 cm/s), low COC concentrations (CRF < 100), and no NAPL plume.
APPLICABILITY
NAPL
 GW Extraction: Recovery wells / submersible pumps; wellpoint systems.
 GW Treatment: GAC, air stripper, biological, etc.
Slide Topic: GW Pump and Treat: Overview
Goal: Use GW extraction to meet target levels
Applicability: High permeability homogeneous aquifers with low COC concentrations (no NAPL)
Options: submersible pumps or well point system
Key Presentation Points: Introduce GW Pump and Treat
Groundwater pump and treat systems are generally effective at achieving target levels only at high permeability sites where initial COC concentrations are less than 100x the target level.
DESIGN OPTIONS
CRF = COC Reduction Factor = (Current COC Conc./Target Level); K = Hydraulic Conductivity (cm/s)
COC = Chemical of Concern

59. Recovery Well Installation
GW Pump & Treat: Well Installation
Recovery Well Installation
Well Screen
Centralizer
Wire-Wrapped Well Screen
Slide Topic: GW Pump and Treat: Well Installation
Well Screen
Gravel Pack
Centralizer
Key Presentation Points: Point out key components of a recovery well.
Sand-Gravel Filter Pack

60. GW Pump & Treat: Recovery Well Design
Casing
 Material: Corrosion & contaminant resistant. Options = PVC, SS, teflon, FRP.
 Large enough to fit pump, usually 4-in or 6-in.
Slide Topic: GW Pump & Treat: Recovery Well Design
Material: PVC or Stainless Steel
Size: 4” or 6” (monitoring wells are often 2”)
Key Presentation Points: Point out key components of a GW recovery well.
FRP = Fiberglass reinforced plastic
PVC = Polyvinyl chloride
SS = Stainless steel

61. GW Pump & Treat: Recovery Well Design
Well Screen
 Material: Typically same as casing. May use SS screen with PVC casing to economize.
 Length: % 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.
Slide Topic: GW Pump & Treat: Recovery Well Design
Material
Length
Placement
Diameter
Slot Size
Key Presentation Points: Review the key design considerations in planning a recovery well (Continued on next slide).
PVC = Polyvinyl chloride
SS = Stainless steel

62. GW Pump & Treat: Recovery Well Design
Sand Pack
 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.
Grout Seal
Slide Topic: GW Pump and Treat: Recovery Well Design
Sand Pack:
Stabilize borehole and filter fine material from aquifer
Grout Seal:
Prevents contamination of well from ground surface or other water-bearing units.
Key Presentation Points: Discuss the design and function of sand pack and grout seal.
 Material: Portland cement/bentonite mix.
 Configuration: At ground surface, sloped to drain rainwater away from well casing.

63. Dual-Phase Extraction: Overview
Use aquifer dewatering and soil venting to reduce COC concentrations in GW to applicable target levels.
GOAL
Low to moderate permeability groundwater units (K = 10-5 to 10-3 cm/s)
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.
vapor GW
DESIGN OPTIONS
Slide Topic: Dual Phase Extraction: Overview
Goal: Use aquifer dewatering and soil vapor extraction to remove COCs from below the natural water table.
Applicability: Low to moderate permeability aquifers.
Options: Submersible pump and blower or dual-phase wellpoint pump
Key Presentation Points: Introduce dual-phase extraction.
Dual-phase extraction will not be effective at sites where high permeability prevents dewatering of the affected aquifer.
vapor GW
Pump

64. Dual-phase pump extracts both air and water
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
Slide Topic: Dual-Phase Extraction: Design Options
Separate Air & Water Headers
Combined Air/Water Hearers
Key Presentation Points: Discuss the design options for dual-phase extraction.

65. Air Sparging: Overview
Inject air to volatilize organics and promote in-situ biodegradation, as needed to reduce COCs in GW to applicable target levels.
GOAL
Moderate to high-permeability GW units (K > 10-4 cm/s)
APPLICABILITY
 Air Injection: Air compressor with multiple small injection points.
 Vapor Recovery: If needed, use SVE wells to recover and treat vapors.
Air
Slide Topic: Air Sparging: Overview
Goal: Inject air below water table to promote volatilization and biodegradation.
Applicability: Moderate to high permeability GW units.
Key Presentation Points: Introduce air spagring
DESIGN OPTIONS

66. Air Sparging: Design Issues
Air Injection Points
Well Configuration
Injection Points: 1-2 inch diam. PVC Wells, 2-5 ft Screen length
Typical Spacing: ft centers
Injection Pressure: psig
Air Flowrates
< 10 SCFM per well
Helps to Cycle injection periods (Hours, Not Days)
Slide Topic: Air Sparging: Design
Injection points may be small diameter wells.
Air flow rates typically <10 SCFM
Pulsing of air flow (with off cycle of several hours) helps to better distribute in aquifer. Continuous flow creates preferential flow pathways.
Key Presentation Points: Describe the design of air sparging system.

67. Air Sparging: Process Review
Remediation Processes
 Volatilization of NAPLs
 Air Stripping of Dissolved Organics
 Oxygenation of Water Enhances In-Situ Biodegradation
Air
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
Slide Topic: Air Sparging: Process
Limitations:
Air flow mostly from top of well screen. Lower portion of aquifer is not treated.
Preferential flow pathways result in only small area of aquifer being treated.
Even minor heterogeneities cause preferential flow pathways.
Key Presentation Points: Discuss the limitations of air sparging as a remedy for GW.

68. In-Situ Biodegradation: Overview
Oxygen Release Compound (ORC)
 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 expanding & aggressive treatment not needed to meet remediation goals.
WHAT O2
HOW
Slide Topic: Oxygen releasing compound (ORC)
What: Solid which slowly releases oxygen when put in aquifer
How: Inject ORC into aquifer or place in monitoring wells
When: May be used to create a reactive barrier to prevent plume migration
Key Presentation Points: Introduce the use of ORC to promote biodegradation.
The total mass of oxygen released into the aquifer by ORC is usually very small relative to the mass on contaminants. Mass transfer limitations often prevent the oxygen from reaching the contaminants.
However, ORC is relatively inexpensive and may satisfy a regulatory requirement for an “active” remedy at a site where natural attenuation alone would otherwise be effective.
WHEN

69. GW Containment: Overview
Use physical or hydraulic barrier system to prevent migration of affected GW to point of exposure.
GOAL
Applicable to all GW units and COCs. Physical barrier walls limited to 100 ft depth. Hydraulic containment (P&T) limited by water treatment requirements.
APPLICABILITY
 Physical Barrier: Slurry wall, asphalt wall
 Hydraulic Barrier: GW P&T system, cut-off trench
slurry wall
Affected GW zone
Slide Topic: GW Containment: Overview:
Goal: Prevent migration of affected groundwater
Applicability: All GW units
Options: Barrier wall, Hydraulic containment
Key Presentation Points: Introduce GW containment as a remedy.
With GW containment the goal is to prevent migration of affected groundwater rather than to achieve low target level throughout the plume.
DESIGN OPTIONS

70. GW Containment: Hydraulic Containment
PLAN VIEW
GW Pumping Well
Streamlines
GW Flow
Plume
Hydraulic Capture Zone
Slide Topic: Hydraulic Containment
Objective: Pump sufficient GW to prevent further migration of the affected GW plume.
Design: Capture zone calculation or computer model
Operational factors: seasonal fluctuation, water treatment
Key Presentation Points: Discuss the design of GW hydraulic containment systems.
n Design Methods - Javendahl Capture Zone Curves
n Computer Models
n Operational Factors - Well Efficiency - Seasonal / Annual Effects - Produced Water Treatment

71. 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
Slide Topic: Physical Barriers
Purpose: Reduce/prevent migration of COCs from affected GW zone
Design: Partial or complete enclosure around plume
Key Presentation Points: Introduce use of physical barriers for GW containment.

72. GW Containment: Physical Barrier
Hydraulic Containment by Slurry Wall 0’
35’
70’ D N A P L
Drinking Water
Aquifer
Unfract. Clay
Frac. Clay
Aquifers
Slurry Wall
Slurry Wall
Well t i s
Slide Topic: Physical barrier: Overview
Key Presentation Points: Point out key component of physical barrier for GW containment.
Pumping of GW is usually required in conjunction with the physical barrier in order to ensure complete containment of contaminants. However, the physical barrier greatly reduces the volume of water that must be pumped in order to obtain hydraulic containment.

73. Installation of Bentonite-Slurry Barrier Wall

74. Permeable Reaction Walls
Ref: Gillham
Gate: Permeable Reaction Wall - Fill With Iron Filings
Funnel:
Impermeable
Barrier Wall
Funnel:
Impermeable
Barrier Wall
Funnels Dissolved Organics Through Reaction Wall

75. Installation of Permeable Treatment Trench

77. NAPL Removal Options Today’s Focus  Soil Excavation  SVE
NAPL IN UNSAT. SOIL ZONE
 Soil Excavation
 SVE
Today’s Focus
NAPL IN GW ZONE
NAPL in Soil
 Soil Excavation (smear zone)
 Continuous Recovery
 Periodic Recovery (bailing, High-Vac)
 Air Sparging
Slide Topic: NAPL technologies.
Soil excavation
Soil vapor extraction
Continuous recovery
Periodic recovery
Air sparging
Key Presentation Points: Introduce the NAPL technologies covered in this presentation.
NAPL in GW
Dissolved GW Plume

78. NAPL Removal Options: Key Factors
Key Factors Influencing NAPL Removal
n Vertical distribution of NAPL
n Permeability of soil to NAPL
n Relative soil permeability to water & NAPL
Slide Topic: NAPL Removal: Key Consideration
Vertical distribution of NAPL
Permeability of soil to NAPL (absolute and relative to water)
Key Presentation Points: Introduce key considerations in design of a NAPL recovery system.
At many sites, soil and NAPL properties make it impossible to recover a significant percent of the total NAPL at the site. An active NAPL recovery should not be installed unless the system will recover enough NAPL to improve the prospect of achieving the overall site remediation goals.
The next slides will provide details on the factors listed in this slide.

79. Elevation Above Oil/Water Interface (cm)
NAPL Removal Options: Vertical NAPL Distribution
Well
700
600
KEY POINT:
NAPL concentrates in “smear zone” atop GW table.
500
Elevation Above Oil/Water Interface (cm)
400
NAPL
300
200
Slide Topic: NAPL Recovery: Vertical NAPL Distribution
LNAPL thickness in a monitoring well does not correlate well with the portion of the aquifer that has high LNAPL saturation. LNAPL saturation is generally low directly above the water table (where the water from the capillary fringe prevents high LNAPL saturation). LNAPL saturation generally increases further above the water table until the top of the LNAPL layer is reached.
Key Presentation Points: Discuss the vertical distribution of LNAPL in the aquifer.
The low LNAPL saturation at the groundwater interface results in a low soil permeability for LNAPL at this interface and limits LNAPL recovery.
100
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
H2O
Hydrocarbon Saturations
NAPL = Non-aqueous phase liquid.

80. NAPL Removal Options: Effects of Soil Type
Soil Type vs. Permeability of Soil to NAPL
500 S i l t ( K = . 1 m / d ) s a t
KEY POINT:
NAPL easier to remove in coarse-grained dry soils. Hard to remove in fine-grained wet soils. S i l t y a n d ( K s = . 4 m / )
400 F i n e / M d S a ( K s t = 4 m ) C o a r s e S n d ( K t = 4 3 m / )
300
Elevation Above Oil/Water Interface (cm)
200
Slide Topic: NAPL Recovery: Effect of Soil Type
The soil permeability for NAPL is a function of both NAPL saturation and soil type. NAPL is easier to recover from course grained soils.
Close to the water table, low NAPL saturation results in very low permeability for all soil types.
Key Presentation Points: Discuss the impact of soil type on soil permeability for NAPL.
100 1 - 9 1 - 8 1 - 7 1 - 6 1 - 5 1 - 4 1 - 3 1 - 2 1 - 1 1 1 1 1 2
Hydraulic Conductivity of Soil to NAPL (m/day)
NAPL = Non-aqueous phase liquid.
Source: Beckett & Huntley, 1999

81. Relative Permeabilities of Soil to Water & NAPL
NAPL Removal Options: Relative Permeabilities
Relative Permeabilities of Soil to Water & NAPL
0.2
0.4
0.6
0.8 1
Water Saturation of Soil
Irreducible Water Saturation
KEY POINT:
Soil saturated with water has low permeability for NAPL, so NAPL easier to remove from dry soil.
Relative Permeability
Soil K for NAPL
Soil K for Water
Slide Topic: NAPL recovery: Relative permeability
The permeability of the soil for NAPL or water is a function of the saturation of the fluid. Therefore, soil saturation with water has a low permeability for NAPL. Therefore, as NAPL recovery progresses and the NAPL saturation decreases, the permeability for NAPL also decreases and additional NAPL becomes more difficult to recover.
This process often limits the ability to recover a significant amounts of NAPL from an aquifer. The yield of the NAPL recovery system drop dramatically even though significant amounts of NAPL are still trapped in the aquifer.
Key Presentation Points: Discuss how the relationship between saturation and relative permeability limits NAPL recovery.
NAPL flow models or empirical recovery curves can be used to estimate NAPL recovery levels for different soil types/NAPL thicknesses. These should be used to determine whether NAPL recovery efforts are justified.

82. Continuous NAPL Recovery Methods
Continuously recover NAPL to reduce source mass, stabilize NAPL plume (e.g., daily operation).
GOAL
Sites with significant mobile NAPL plume atop GW (e.g., >> 1 ft thick).
APPLICABILITY
 Recovery wells & skimmer pumps
 Interceptor trench & skimmer pump
 Multi-phase recovery system
NAPL
DESIGN OPTIONS
Slide Topic: Continuous NAPL Recovery:
Goal: reduce NAPL mass, stabilize NAPL plume
Applicability: High permeability sites with significant NAPL thickness.
Options: Skimmer pump, trench, dual (or multi)-phase recovery
Key Presentation Points: Discuss continuous NAPL recovery systems.
System operation should be terminated when recovery goals met or NAPL recovery volume decreases to low level.
NAPL
Pump

83. Remediated Through Air Flow
Multi-Phase NAPL Recovery
Groundwater and NAPL
Soil Vapor
Smear Zone Dewatered
Remediated Through Air Flow
Slide Topic: Multi-phase NAPL recovery:
Draw-down of water table may increase NAPL flow gradient and recovery rates. Vapor recovery removes volatile chemicals from the unsaturated zone.
Key Presentation Points: Introduce multi-phase NAPL recovery.

84. Multi-Phase Recovery: Wrap-Up
NAPL Removal Options
Multi-Phase Recovery: Wrap-Up
PRO
CON
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
Slide Topic: Multi-phase recovery
Pro:
More effective than other technologies in low to moderate permeability soils.
Most mass removal occurs in first months of operation. (If it works, it will work quickly).
Con:
Expensive of GW and vapor treatment needed.
Will not achieve low GW standards (i.e. drinking water limits).
Dewatering of smear zone not possible in higher permeability units.
Key Presentation Points: Discuss Multi-phase NAPL recovery.
Bottom line: Multi-phase recovery is the most effective NAPL recovery technology for low permeability soils, however, at these site no technology is likely to achieve meaningful levels of NAPL recovery. (i.e., a large percent of the NAPL will remain trapped in the aquifer.)

85. Periodic NAPL Recovery Methods
Remove periodic accumulation of NAPL from observation wells to reduce NAPL mass and mobility (e.g., weekly to quarterly operation).
GOAL
Sites with minor NAPL accumulations and/or non-mobile NAPL plumes.
APPLICABILITY
 Periodic bailing of wells
 Periodic skimmer pump operation in wells or trench.
 Periodic High-Vac recovery
Bailer
DESIGN OPTIONS
Slide Topic: Periodic NAPL recovery.
Goal: Reduce NAPL mobility and/or mass
Applicability: Sites with lower permeability soil and/or minor NAPL accumulations
Options: Bailing, skimmer pump/trench, High-Vac recovery.
Key Presentation Points: Introduce periodic NAPL recovery.
Periodic NAPL recovery typically does not result in recovery of large NAPL volumes. However, periodic recovery should be considered at sites where regulatory requirements are driving NAPL recovery but site conditions (i.e. low permeability or NAPL thickness) are likely to limit the ability to recover significant volumes of NAPL.
Periodic NAPL recovery operations should be terminated when recovery yields drop to low levels.
NAPL

86. Periodic NAPL Recovery: High-Vacuum
Two- Phase
Flow
Vacuum Truck
discharge clean air
Vacuum
Gauge
Atmospheric
Air Bleed Valve
NAPL / GW Collection
Vapor Treatment
Suction Pipe
Soil Vapor
Flow
Slide Topic: Periodic NAPL Recovery: High-Vac
Vacuum truck is used to periodically remove a large volume of NAPL and groundwater. Rest period in between recovery operations allows time for NAPL to flow back into the vicinity of the well.
Key Presentation Points: Introduce High-Vac recovery.
Although High-Vac recovery is more cost effective than continuous recovery at many sites, costs can become significant if High-Vac recovery is continued for a long period of time.
Conduct periodic vacuum extraction to recover NAPL (e.g., monthly or quarterly for 8-hour episode).
Operational Water Table
Saturated Zone
GW and NAPL Flow

87. Remedial Action: Groundwater
Groundwater /NAPL P&T System
Fluid Separation Tank
Recovery Well
Control Panel
Vapor Control System
Vacuum Pump

88. Air Sparging of NAPL Plume
Remove NAPL smear zone by means of in-situ “air stripping.”
GOAL
Sites with minor NAPL accumulations of volatile NAPL material in coarse-grained soils.
APPLICABILITY
 Air Sparging: Periodically inject air to volatilize NAPL.
Air
NAPL
DESIGN OPTIONS
Slide Topic: Air sparging of NAPL
Goal: Remove NAPL through volatilization followed by biodegradation in the vapor phase.
Applicability: Minor NAPL thicknesses in course grained aquifers.
Key Presentation Points: Introduce air sparging of NAPL.

89. Air Sparging System Volatilizes Organics and Promotes In-Situ Biodeg.
Compressor
Blower
Vapor
Treatment
SVE Well (Optional)
Affected GW zone
Tiny
Bubbles
Volatilizes Organics and Promotes In-Situ Biodeg.

90. Air Sparging of NAPL Plume
Silt
Smear
Zone
Air Channels
Water Table
KEY POINT:
Air pathways affected by subsurface heterogeneities. Can result in inconsistent removal.

91. No COCs > target levels
Active Remediation Technologies
Remedy Completion: When is “Enough” Enough?
 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 Further Action Required If:
No COCs > target levels
Slide Topic: Remedy Completion: Active remedy
No additional monitoring is required if:
Target levels achieved and/or compliance monitoring indicates no potential impacts in the absence of monitoring
Key Presentation Points: Discuss criteria for not further monitoring at a corrective action site.