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Is Hydraulic Recovery Of LNAPL Always a Wise Decision?

Sanjay GargCurt Stanley

Shell Global Solutions (US) Inc.

© 2007 Shell Oil Company. All rights reserved.

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LNAPL in a Regulatory Nut Shell• LNAPL present at thousands of site• Perceived as significant environmental threat • Technical and regulatory complexity• Typically no clear policy/regulation framework for decision

making– RCRA, CERCLA, …LNAPL not specifically addressed– UST 40 CFR 280.64 (1988): “…remove free product to the maximum

extent practicable as determined by the implementing agency…”• Many states developed/determined prior to current State of Knowledge• Federal Statute, State Statute/Regulation, Policy, Guidance Document Ranges from…

– Remove all detectable levels of LNPL at all sites , – Defined measurable amount (.01’-1/8”), – Risk based/Site Specific– No clear requirement

• Multiple policies within same State - Project Manager to Project Manager

• Unresolved LNAPL issues hold up site closure• Unending LNAPL management costs can dominate the limited

resources

Source: Interstate Technology and Regulatory Council (ITRC)

Similar regulatory

situation around the world

Similar regulatory

situation around the world

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Today’s Scope

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What is Different When LNAPL is in a Monitoring Well?

If groundwater, vapor or soil impacts are present, most likely LNAPL is present in the subsurface

– It may or may not flow into a monitoring well– Traditional fate-and-transport approaches

(e.g., RBCA) are commonly accepted when LNAPL is not in a monitoring well

If groundwater, vapor or soil impacts are present, most likely LNAPL is present in the subsurface

– It may or may not flow into a monitoring well– Traditional fate-and-transport approaches

(e.g., RBCA) are commonly accepted when LNAPL is not in a monitoring well

What is different when LNAPL flows into monitoring wells?

–More pores are occupied by LNAPL

–How does it affect groundwater and vapor?

–What other risks?

–How do risks change after LNAPL is removed from wells?

What is different when LNAPL flows into monitoring wells?

–More pores are occupied by LNAPL

–How does it affect groundwater and vapor?

–What other risks?

–How do risks change after LNAPL is removed from wells?

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Mythbuster

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View at an LNAPL Site Subsurface• LNAPL

–Above and/or at LNAPL residual saturation*

• Dissolved phase

• Vapor Phase• Sorbed

Lower Limit of Smear Zone

* Fraction of pore space occupied by LNAPL that cannot be mobilized under an applied gradient

After ASTM

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LNAPL in a Monitoring Well

Lower Limit of Smear Zone

After ASTM

LNAPL Saturation0 1

• When LNAPL saturation is greater than residual saturation it will flow into a well

• All soil pores are not occupied with LNAPL

• Fraction of pore space occupied by LNAPL depends on well thickness, and soil type

– Can be from a few % in fine-grained soils to a few tens of % in coarse sand and gravel

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No LNAPL in Well• LNAPL

– At residual saturation

• Dissolved phase

• Vapor Phase• Sorbed

LNAPL Saturation0 1

Residual LNAPL Saturation

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Limit of Recoverable NAPL

• 280 samples from 3 sites• Residual LNAPL

determined by centrifuging at 1000g’s

• Most samples from fine to medium sand

• Area above the green line was able to be drained from the core at 1000g’s

# Samples0 50 100 150 200 250

LNA

PL S

atur

atio

n

0

10

20

30

40

Initial SaturationResidual Saturation

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LNAPL and Dissolved Phase

0

2

4

6

8

10

12

0 0.1 0.2 0.3 0.4LNAPL Saturation

Equi

libri

um G

roun

dwat

er

Con

cent

ratio

n (m

g/L)

Ben

zene

AB

C

Similar behavior for soil gas

50 % Reductionin So

50 %

Red

uctio

nin

C_o

il_be

n

A

B

C

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LNAPL: How Much or WhatWhich is a more important question?

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1Relative Time

Rel

ativ

e G

W C

once

ntra

tion

So<Sor

So>Sor

Post Hyd. Rec

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1Relative Time

Rel

ativ

e G

W C

once

ntra

tion

So>Sor

Post AS/SVE (e.g.)

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Risks & Problem Statement

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Why be concerned about LNAPL?

• NAPL composition– Explosive hazards– Dissolved phase concentration– Vapor phase concentration– Soil direct contact or ingestion

• NAPL Saturation– Mobility through soil or preferential pathways– Longevity of dissolved phase and vapor phase plumes– Aesthetic

Should evaluate LNAPL from two perspectives: what and how much

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Darcy Law

If there is more than one fluid in the pore space, then Darcy Law is applicable to each fluid separately (e.g., GW & NAPL)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.1 0.2 0.3 0.4 0.5

LNAPL Saturation

NA

PL C

ond/

Hyd

. Con

d GasolineDiesel

qN = KN iN

q = K i

For a finite LNAPL volume in the pore space, iN and KN will continually decrease as the LNAPL migrates

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NAPL Migration

Large volume release on known date from a crude oil pipeline

time = 0 − 0+ 3 months 6 months 9 months 1 year 2 year 3 year

LNAPL Plume Genesis

Data from API Interactive LNAPL Guide

• High LNAPL saturation and high LNAPL gradient result in ‘fast’initial velocity

• Low saturation & flat LNAPL gradient result in slowing down of the LNAPL plume and pore-entry pressure results in ultimate stoppage of the plume

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Exposure Scenarios at an LNAPL Site

3a

2

3b

45

Drin

king

wat

er w

ell

1

LNAPL Risk ScenariosWhen LNAPL in the Ground(evaluated using RBCA)

2 Groundwater (dissolved phase)

3a

Groundwater to vapor3b

LNAPL to vapor

Direct Skin ContactNot Shown

Additional considerationsWhen LNAPL in Wells(not evaluated using RBCA)

4 LNAPL mobility (offsite migration, e.g. to surface water, under houses)

5 LNAPL in well (aesthetic, reputation, regulatory)

LNAPL Emergency issuesWhen LNAPL in the Ground(not evaluated using RBCA)

Vapor accumulation in confined spaces causing explosive conditions

1

Direct LNAPL migration to surface waterDirect LNAPL migration to underground spaces

Not shown

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Three Scenarios

So<Sor

h>hNc

h

1. No LNAPL in wells• Traditional fate-and-transport frameworks work well

(e.g., RBCA)

3. LNAPL in wells and mobile

h

h<hNc

2. LNAPL in wells and immobileWe do not always

differentiate Cases 2 & 3

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Lines of evidence of LNAPL Footprint Stability• Monitoring Results

– No appearance of LNAPL in previously LNAPL-free wells– No increasing LNAPL thickness at edge of LNAPL plume

• Ensure thickness is not increasing because the well is new and has not reached equilibrium• Ensure changes in LNAPL thickness are not related to water table fluctuations

– Stable or Shrinking dissolved phase plume

• Calculated Velocity– Perform baildown test to get Ko at peripheral wells

• Alternatively Ko can be estimated if Khyd is known– Measure io– qo = Ko io

• Age of the release– Timing of release – Weathering indicators

• Recovery rates– Decreasing LNAPL recovery rates

• Petrophysical lab tests– Measured saturation less than or slightly greater than residual saturation values

h

h<hNc

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Time to Reflect

– We cannot remove any significant amount due to technology limitations

– It does not alter groundwater concentrations

– The plume is stable– It does not provide net environmental

benefit• Sometimes more co-pollution than

cleanup

Why do we perform hydraulic recovery of LNAPL if:

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Time to Reflect

– When the release is new (prevents LNAPL footprint from expanding)

– If LNAPL is mobile (most older LNAPL plumes are stable!)

– Regulatory requirement

When does it make sense to perform hydraulic recovery of LNAPL?

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LNAPL Management Approach

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An Approach• Stop release• Address safety and risk issues

• Evaluate LNAPL plume stability. If plume is mobile, take measures to arrest expansion (e.g hydraulic recovery, physical barriers).

• Perform risk assessment (e.g., RBCA) and mitigate or manage risks– Conventional remediation methods

• Consider institutional controls

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LNAPL velocitySpecific Volume

Fraction LNAPL Recoverable

Intersected drains

Management plan focuses on • elimination/repair of drains • barrier walls • limited hydraulic recovery • institutional controls

• Several acre, old LNAPL plume near the coast

• No dissolved phase risk• Approach based on evaluating

LNAPL migration risk to harbor

Progressive LNAPL Management

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Progressive LNAPL Management

EXPLANATION

Benzene Content in LNAPLValue

High : 0.005814

Low : ND

SCALE

1:7,800

1 inch equals 650 feet

0 650

Benzene in LNAPL

SCALE

1:7,800

1 inch equals 650 feet

0 650

Explanation

LNAPL Mobility

LNAPL Mobility

EXPLANATION

Percent of Measurements0%

0-25%

25-50%

50-75%

75-100%

SCALE

1:7,800

1 inch equals 650 feet

0 650

No DataLNAPL Persistence in Wells

SCALE

1:7,800

1 inch equals 650 feet

0 650

12

3 45

67

8 9 1011

12

Management Areas

Active Remediation Areas

Courtesy : Beckett & Lyverse

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Ways to define Extent Practicable

Mass Removal

GW/vapor Risk Reduction

Mobility Reduction

Mobility

GW/vapor Conc

Dist to receptor

LNAPL Saturation

$/gal

Objective Start Criteria

# years

Gal/time

End CriteriaSame as start +LNAPL Well

ThicknessAesthetic

Transmissivity

Specific Volume

Recoverability

Water/Oil Ratio

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0

1

2

3

4

5

6

7

0.00 0.10 0.20 0.30LNAPL Saturation

Ft a

bove

wat

er-L

NA

PL

inte

rface

0.20 0.40 0.600

1

2

3

4

5

6

7

0.00 0.10 0.20 0.30LNAPL Saturation

Ft a

bove

wat

er-L

NA

PL

inte

rface

0.20 0.40 0.60

MW MW

LNAPL Groundwater

Pre- Hydraulic Recovery Post- Hydraulic Recovery

Residual Saturation

0

1

2

3

4

5

6

7

0.00 0.10 0.20 0.30LNAPL Saturation

Ft a

bove

wat

er-L

NA

PL

inte

rface

0.20 0.40 0.600

1

2

3

4

5

6

7

0.00 0.10 0.20 0.30LNAPL Saturation

Ft a

bove

wat

er-L

NA

PL

inte

rface

0.20 0.40 0.600.20 0.40 0.600

1

2

3

4

5

6

7

0.00 0.10 0.20 0.30LNAPL Saturation

Ft a

bove

wat

er-L

NA

PL

inte

rface

0.20 0.40 0.600.20 0.40 0.60

MW MW

LNAPL Groundwater

Pre- Hydraulic Recovery Post- Hydraulic Recovery

Residual Saturation

m m0.3

0.6

0.9

1.2

1.5

1.8

2.1

0.00.3

0.6

0.9

1.2

1.5

1.8

2.1

0.0

RBCARBCA

RBCA +potential mobility

Key PointsLNAPL and Risk

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Key PointsWe know how to address Scenario 1

– Traditional RBCA and remediation

h>hNc

h

h

h<hNc

We always do not distinguish between Scenarios 2 and 3

– We assume if LNAPL flows into wells then it must be mobile

All 3 scenarios can be addressed by traditional remediation (SVE, IAS, DPE etc)

– Scenario 3 may require additional LNAPL recovery and hydraulic control.

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Progress

Geared to large-scale sites

A management framing document

Training material

How to construct an LCSM

Remediation metrics

Remedial objective

ASTM

RTDF

Tools to help frame the LCSM

Calculation tools

Educational materials, parameter

Lookup tables

API

Texas TRRP 32

British Columbia (Canada)

State/OtherGuidances

LARWQCB/WSPA

ITRC

Ongoing

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ResourcesCompleted

API Website: www.api.org/lnapl

NAPL Cleanup Alliance: www.rtdf.org/public/napl

ASTM: www.astm.org

ASTM LNAPL Decision Guide (E50.04 July 2005)

SABCS British Columbia http://www.sabcs.chem.uvic.ca/docs.html

Texas Commision of Environmental Quality TCEQ – NAPL Evaluation and Recovery (TRRP 32)

OngoingITRC: http://www.itrcweb.org/teampublic_LNAPLs.asp

Los Angeles Regional Water Quality Control Board / Western States Petroleum Association LNAPL work group

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Obrigado

Thank you