LNAPL AND SHEEN MANAGEMENTA68D389E-4186... · Light Non-Aqueous Phase Liquid. Air/LNAPL Interface....

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LNAPL AND SHEEN MANAGEMENTRick AhlersSeptember 29, 2016

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About the Presenter

c 760.214.4768e rick.ahlers@arcadis.com

RICK AHLERSTechnical Expert, NAPL Management Global CoP Lead

Is This the Appropriate Response?

LNAPL Basics

What is LNAPL?

Light Non-Aqueous Phase Liquid

Air/LNAPL Interface

LNAPL/Water Interface

LNAPL In-Well Thickness

Monitoring Well

LNAPL/Water Interface

Air/LNAPL Interface

LNAPL Body DevelopmentTime 1 Time 2

Time 3 Time 4

LNAPLHead

Soil pore resistance

Buoyancy

After ITRC, 2009

Soil grain

Vadose Zone

Saturated Zone

Pore Scale LNAPL Distribution

ITRC, 2009

non-wetting fluid (air or NAPL)

Soil grains

wetting fluid (water)

(From Wilson et al., (1990); and API 2003)

Residual NAPL is NAPL Trapped by Capillary Pressure(From Wilson et al., (1990); and API 2003)

PNAPL Pwater

Pwater

Capillary PressureMobile: PNAPL > Pc + PwaterResidual: PNAPL ≤ Pc + Pwater

LNAPL Body Stability

Release volume is finite, so LNAPL extent stabilizes then shrinks

Time 4 Time 5

LNAPL “Smearing”

Traps LNAPL above and below the mobile LNAPL interval

higher 2-phase

residual LNAPL

saturation

low 3-phase

residual LNAPL

saturation

After Chevron 1996

low 3-phase

residual LNAPL

saturation

residual water

LNAPL immobile

higher 2-phase

residual LNAPL

saturation

low 3-phase residual LNAPL

saturation

residual water

LNAPL flow toward edges of body is balanced by natural losses

Natural Source Zone Depletion

Risk-Based LNAPL Management

Respond to Actual LNAPL Risk

Recoverable (MEP)

Migrating

ResidualLNAPL present,

but cannot flow into wells

MobileLNAPL can flow into wells

NAPL is Source of Dissolved and Vapor Plumes

Is LNAPL Recovery Worthwhile?

0 500 1000 1500 2000 2500 3000

Operating Time(Days)

High LNAPL Transmissivity

Low LNAPL Transmissivity

Natural Source Zone Depletion (NSZD)

• MNA for dissolved phase plumes

• NSZD for LNAPL source zones

NSZD is not MNA

Dissolved Mass

LNAPL Mass

Sorbed Mass

NSZD in the Saturated Zone

• Mass loss by:• Dissolution • Biodegradation

Groundwater Flow

Dissolution and BiodegradationElectron Acceptor

Electron Acceptor Depletion

Mobile or Residual LNAPL

After ITRC, 2009

<10% of total NSZD

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

NSZD Rates in Perspective

Not affected byactive recovery

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

LI-COR CO2 flux chamber

E-Flux passiveCO2 traps

Nested Soil Vapor Probes

Temperature Profile

Methods for Quantifying NSZD

Soil Gas Gradient

After ITRC 2009

CO2out

Dynamic Closed Chamber: Instantaneous CO2 Flux

• Measures CO2 build-up in chamber over about a minute

• Rapid site survey• Identify LNAPL &

background areas

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

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

Temperature Profile

• Measure Temperature Profile in Existing Wells• No Intrusive Work Required

LNAPL Seepage and Sheens

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

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”

Sheen Optics Incoming Rayof Light

LNAPL Layer0.3 – 5 microns

Why Do Many NAPLs Spread Out On Water?

• Air-water surface tension "pulls" NAPL layer across interface

• Spreading coefficient

After API (2007)

LNAPL Seepage

High Water

Low Water

LNAPL Drainage at Low Water

Ebullition

LNAPL Wicking

LNAPL Seep Mitigation

Groundwater-Surface Water Interface Remedies

Upland Remedies

Seep Mitigation Conceptual Model

• Upland Barriers

• Adsorption• NAPL-wetting

• Enhance Natural Depletion

• GSI Barriers

After Chalfant 2015

Seep Mitigation ApproachesActive Passive

Hydraulic Control

Recovery Well

Recovery Trench

Physical

Adsorption

Reactive Core Mat

Permeable/Impermeable

SorptiveBarrier

Hanging/Foot Wall (Barrier

Sheet Pile Bentonite

Capillary Barrier

OleophilicBio Barrier

Excavation

Mulch Bio-Wall

NAPL-Wetting & Enhanced Depletion

Isolation Cap

GSI Approach

Upland Approach

Oleophilic Bio Barrier (OBB)

Oleophilic = NAPL WettingThe OBB material prefers to be coated with a film of NAPL rather than a film of water

Chalfant 2015

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

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

OBB Enhances Assimilative Capacity• Fluorescence testing

of geocomposite • NAPL observed on outer textile layer

• Biodegradation • Aerobic compared to sediments

Chalfant 2015

• Microbial Population Enhanced

OBB Prevented Seeps

Seeps and sheens observed adjacent to OBB pilot

No sheens observed along OBB

Chalfant 2015

LNAPL flow toward seepage face is reduced by natural losses

NSZD and NAPL Seepage

Thank You!

Questions?

LNAPL AND SHEEN MANAGEMENTA68D389E-4186... · Light Non-Aqueous Phase Liquid. Air/LNAPL Interface....

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