LNAPL AND SHEEN MANAGEMENT Rick Ahlers September 29, 2016
LNAPL AND SHEEN MANAGEMENTRick AhlersSeptember 29, 2016
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About the Presenter
c 760.214.4768e [email protected]
RICK AHLERSTechnical Expert, NAPL Management Global CoP Lead
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Is This the Appropriate Response?
LNAPL Basics
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What is LNAPL?
Light Non-Aqueous Phase Liquid
Air/LNAPL Interface
LNAPL/Water Interface
LNAPL In-Well Thickness
Monitoring Well
Water
LNAPL/Water Interface
Air/LNAPL Interface
Air
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LNAPL Body DevelopmentTime 1 Time 2
Time 3 Time 4
LNAP
L Sa
tura
tion
Hi
Lo
LNAPLHead
Soil pore resistance
Buoyancy
After ITRC, 2009
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Soil grain
Water
Air
LNAPL
Vadose Zone
Saturated Zone
Pore Scale LNAPL Distribution
ITRC, 2009
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non-wetting fluid (air or NAPL)
Soil grains
wetting fluid (water)
(From Wilson et al., (1990); and API 2003)
1mm
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Residual NAPL is NAPL Trapped by Capillary Pressure(From Wilson et al., (1990); and API 2003)
1mm
PNAPL Pwater
Pwater
Capillary PressureMobile: PNAPL > Pc + PwaterResidual: PNAPL ≤ Pc + Pwater
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LNAPL Body Stability
Release volume is finite, so LNAPL extent stabilizes then shrinks
Time 4 Time 5
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LNAPL “Smearing”
Traps LNAPL above and below the mobile LNAPL interval
01
0 1
higher 2-phase
residual LNAPL
saturation
sn
low 3-phase
residual LNAPL
saturation
sw
After Chevron 1996
Elev
atio
n
01
0 1
sn
sw
01
0 1
low 3-phase
residual LNAPL
saturation
residual water
sn
sw
LNAPL immobile
01
10
sn
higher 2-phase
residual LNAPL
saturation
sw0 1
01sn
low 3-phase residual LNAPL
saturation
residual water
sw
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LNAPL flow toward edges of body is balanced by natural losses
Natural Source Zone Depletion
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Risk-Based LNAPL Management
Respond to Actual LNAPL Risk
Csa
t
Recoverable (MEP)
Migrating
ResidualLNAPL present,
but cannot flow into wells
MobileLNAPL can flow into wells
NAPL is Source of Dissolved and Vapor Plumes
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Is LNAPL Recovery Worthwhile?
0.01
0.1
1
10
100
1000
0 500 1000 1500 2000 2500 3000
Operating Time(Days)
LNAP
L R
ecov
ery
Rat
es(G
allo
ns/D
ay)
High LNAPL Transmissivity
Low LNAPL Transmissivity
NSZD
Natural Source Zone Depletion (NSZD)
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• MNA for dissolved phase plumes
• NSZD for LNAPL source zones
NSZD is not MNA
Dissolved Mass
LNAPL Mass
Sorbed Mass
99.9%
0.09%
0.05%
99.9%
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NSZD in the Saturated Zone
• Mass loss by:• Dissolution • Biodegradation
Groundwater Flow
Dissolution and BiodegradationElectron Acceptor
Flux
Electron Acceptor Depletion
Mobile or Residual LNAPL
After ITRC, 2009
<10% of total NSZD
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NSZD in the Vadose Zone
Biodegradation
Dissolved Plume
Groundwater Flow
Oxygen Transport
Volatilization of CH4 and HCs
Mobile or Residual LNAPL
Methanogenesis
Modified from ITRC, 2009 and Ririe, 2013
>90% of total NSZD
Mass loss by:
• Volatilization
• Biodegradation• Aerobic in vadose
zone• Methanogenic in
vadose and saturated zones
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NSZD Rates in Perspective
Not affected byactive recovery
RC
1-acre LNAPL body
Recoverable
Mobile
Residual
• NSZD (1,000 gal/acre/yr)• Acts on 100% of
LNAPL Body • 5 Skimmers
• 0.2 ft LNAPL • Tn = 0.1 ft2/day• 74 gal/yr
• 13 more Skimmers • 266 gal/yr• ¼ NSZD
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LI-COR CO2 flux chamber
E-Flux passiveCO2 traps
Nested Soil Vapor Probes
Temperature Profile
Methods for Quantifying NSZD
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Soil Gas Gradient
After ITRC 2009
O2in
CO2out
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Dynamic Closed Chamber: Instantaneous CO2 Flux
• Measures CO2 build-up in chamber over about a minute
• Rapid site survey• Identify LNAPL &
background areas
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Traps: Time-Integrated CO2 Flux
CO2 Sorbent canisters placed on in-ground receiver
CO2 sorbent canisters placed on in-ground receiver
Source: CSU 2011
• Deploy CO2 traps for two weeks • above LNAPL body • in background locations
• Differentiate atmospheric from fuel carbon
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Pre-existingPreferential Pathways Trap = Preferential Pathway
• Surface Conditions/Caps• Subsurface Heterogeneities• Wind Conditions• Impacts at great depth• Need for Intrusive Work
Challenges with Soil Gas Methods
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Temperature Profile
• Measure Temperature Profile in Existing Wells• No Intrusive Work Required
LNAPL Seepage and Sheens
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What Are Sheens?• Very thin layer of NAPL on water surface
• May be liquid, waxy semi-solid or solid material
• Biogenic sheens derived from breakdown of natural organic material
• “Petroleum” sheens derived from crude or refined petroleum
Petroleum Sheen Biogenic Sheen
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Why Do Sheens Matter?
Clean Water Act of 1972
(“Sheen Rule”)
Looks like “pollution”
Property damage
Potential odors
Interference with recreation
Ecological risk Natural
Resource Damage?
Aesthetics, stigma
Apparent risk
“Uncontrolled release”
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Sheen Optics Incoming Rayof Light
LNAPL Layer0.3 – 5 microns
Water
Air
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Why Do Many NAPLs Spread Out On Water?
• Air-water surface tension "pulls" NAPL layer across interface
• Spreading coefficient
NAPL
After API (2007)
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SOIL
NAPL
LNAPL Seepage
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High Water
Low Water
SOIL
NAPL
LNAPL Drainage at Low Water
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SOIL
NAPL
Ebullition
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SOIL
NAPL
LNAPL Wicking
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LNAPL Seep Mitigation
Groundwater-Surface Water Interface Remedies
Upland Remedies
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Seep Mitigation Conceptual Model
• Upland Barriers
• Adsorption• NAPL-wetting
• Enhance Natural Depletion
• GSI Barriers
After Chalfant 2015
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Seep Mitigation ApproachesActive Passive
Hydraulic Control
Recovery Well
Recovery Trench
Physical
Adsorption
Reactive Core Mat
Permeable/Impermeable
SorptiveBarrier
Hanging/Foot Wall (Barrier
Wall)
Sheet Pile Bentonite
Capillary Barrier
OleophilicBio Barrier
Excavation
Mulch Bio-Wall
NAPL-Wetting & Enhanced Depletion
Isolation Cap
GSI Approach
Upland Approach
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Oleophilic Bio Barrier (OBB)
10 cm
Oleophilic = NAPL WettingThe OBB material prefers to be coated with a film of NAPL rather than a film of water
Chalfant 2015
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NAPL Wetting Capacity• Dip & Drip
• 3.1 L/m2 NAPL (diesel)• Dip & Spin
• 2.4 L/m2 NAPL (diesel)• Column
• 3.2 L/m2 NAPL (diesel)
Chalfant 2015
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Treatment Mechanisms• NAPL Wetting
• Aerobic Biodegradation
Lines of Evidence• Visual & UV mat inspections
• Geochemical sampling
• Analytical chemistry
• Microbial sampling
Chalfant 2015
OBB Pilot Test - Rensselear
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OBB Enhances Assimilative Capacity• Fluorescence testing
of geocomposite • NAPL observed on outer textile layer
• Biodegradation • Aerobic compared to sediments
Chalfant 2015
• Microbial Population Enhanced
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OBB Prevented Seeps
Seeps and sheens observed adjacent to OBB pilot
No sheens observed along OBB
Chalfant 2015
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LNAPL flow toward seepage face is reduced by natural losses
NSZD and NAPL Seepage
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Thank You!
Questions?