LNAPL AND SHEEN MANAGEMENTRick AhlersSeptember 29, 2016

© Arcadis 2016

Disclaimers and NoticesThe materials herein are intended to furnish viewers with a summary and overview of general information on matters that they may find to be of interest, and are provided solely for personal, non-commercial, and informational purposes. The materials and information contained herein are subject to continuous change and may not be current, correct, or error free, and should not be construed as professional advice or service. You should consult with an Arcadis or other professional familiar with your particular factual situation for advice concerning specific matters.

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About the Presenter

c 760.214.4768e rick.ahlers@arcadis.com

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?