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FRACTURED ROCKCharacterization and RemediationAllan HornemanSeptember 30, 2016

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About the Presenter

c 207 553 0072

e allan.horneman@arcadis.com

ALLAN HORNEMAN, PHDPrincipal Geologist | Area Focus Leader: Fractured Rock

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Learning ObjectivesAfter attending this presentation, you should be able to:

• Identify Appropriate Fractured Rock Investigation Strategies;

• Assess Key Fate and Transport Themes Based on Rock Type; and

• Distinguish Between Fractured Rock Source and Plume Remedial Strategies and Goals.

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Agenda• The Fractured Rock Challenge

• Investigation Tools

• Know Your Rock – Fate and Transport Considerations in different rock types

• Remedial Approach – Focus on the Mass that Matters

• Case Studies

• Summary

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Fractured Rock and the Matrix Diffusion Challenge

Overcoming industry-wide pessimism

After Beth Parker et al.

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Fractured Rock Storage vs Transport

Advective Zones – Pure Advection

Advective / Storage Zones – Slow Advection

Storage Zones – Static Water / Storage

Highly Fractured zones(Mobile Fraction)

Low Fracture Density/Blind Fractures(Immobile Fraction)

Rock Matrix/Highly Weathered Rock(Storage Fraction)

Hydraulic Conductivity > 10-4 cm/sec

10-6 cm/sec < Hydraulic Conductivity < 10-4 cm/sec

Hydraulic Conductivity < 10-6 cm/sec

Mobile Fraction θm

Immobile Fraction θi

Stationary Fraction θs

Mass Transfer

Diffusion

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The Advances in Site Characterization

• Complex fracture network• Absence/presence of matrix porosity• Source mass vs mass that moves• Vertical gradients and aquitards

CSM based on monitoring well data?

CSM based on targeted tools to reduce uncertainty:Geophysical methodsFLUTe liner technologiesDFN approachCORETM

Rock coring Short screened monitoring wellsTracersPassive flux meters

Fractured Rock Investigation Toolbox

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It All Start With a CSM• Publications – USGS, maps,

publications;

• Prior site work and reports;

• Initial site visit – Take a good look at the road cuts and topography.

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Rock Coring & CORETM

• Logging of rock and fractures;

• Assessment of mass in unfracturedrock matrix;

• Physical property estimates:– TOC– Matrix porosity– Tortuosity

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FLUTeTM Liner & Hydraulic Profiling Tool

Identify High K (Advection) and Low K (Aquitards – Low Advection/Diffusion) Zones)

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FACT LINER – (FLUTe Activated Carbon Technique)• Concentration Profiling;• Mass Flux;• Refine CSM and Inform In-

situ Remedy.

164 ft

175 ft

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Passive Flux MeterDeveloping technology utilizing tracers.

- Provide flux and fracture orientation information comparable to combined FACT and hydraulic profiling tool.

Klammler et al., 2016

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Bulk Conductivity / VAP Data Interval Conductivity (FLUTe)

Acoustic Televiewer

Downhole Geophysics

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Other Geophysical Tools

Lithology vs Inferred Fate & Transport

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Volcanic Rock Fate & TransportRapid cooling, formation of obsidian, highly susceptible to weathering – primary porosity and more permeable zone

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Volcanic Rock Investigation/Remediation Focus

“Mass that Matters” Focus in Line with “Do No Harm”

Low K

High K

Low K

High K

Low K

Focus on high K zones

Don’t short-circuit low K zones

MassThat

Matters

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Sedimentary Rock Fate & Transport

> 99% of mass present within the unfractured rock matrix

• Matrix porosity (up to 20%) – Significant Storage;

• Bedding important – fracturing, flow and advective transport

• Zones of reduced fracture density control vertical extent of contamination.

DiffusionHalo

Extremely Fracture Zone

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µg VOC / g rock

Sedimentary Rock: Sourcing, Aquitards & PartitioningD

epth

(ftb

gs)

Source rock porewater: 100,000s µg/L

Groundwater: 1,000s µg/L

Groundwater: 1µg/L

Aquitard

Sorbed93%

Primary Pore Water

7%

Fracture Water0.1%

PartitioningMass Partitioning

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Metamorphic rock

SlateCleavage and foliationComplex jointingMatrix porosity low

Fate & transport Complex – some similarities to sedimentary rock

Biotite gneissMineral foliationComplex jointingMatrix porosity very low

Fate & transport Complex – some similarities to e.g. granite.

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Metamorphic Rock Fate and Transport• Mass bleeds into discrete fracture/fracture sets• Moves within fracture system – here primarily

oriented NE-SW.• Primary transport may be un-related to apparent

hydraulic gradient.

MW-301

MW-302

Overburden

SE

NW Hall

Rd

Alternating fine &

pegmatitic granofels

Schist/SchistyGneiss

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Karst – and now things get tricky• Unique aquifer

structure

• Water and contaminants often move fast and far

• Traditional characterization approaches alone will often be misleading

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Karst Porosity• Matrix (Primary)

• Fracture/joints (secondary)

• Chemical dissolution (channels) (tertiary) joints

major channels

open bedding planewith channels shown

“First Do No Harm”

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“First Do No Harm” Concept

Long open borings + Large hydraulic gradient = Injecting contaminant at depth

Typically strong vertical hydraulic gradient;

Historic long open borings allows for significant vertical transport of mass over time;

1,180

1,200

1,220

1,240

1,260

1,280

1,300

1,320

1,340

1,360

1,380

1,300 1,320 1,340 1,360 1,380

Mon

itorin

g Po

rt E

leva

tion

(ft re

lativ

e to

mea

n se

a le

vel)

Total Head (ft relative to mean sea level)

Remediation of Fractured Rock

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General Investigation/Remediation Trends

2000 2010

Pre-2005:Investigation: Monitoring wells

2001: Revised remedial Approaches - Early adaptors In-situ bio in source zones.

2005 and onwards: Next Gen supplemental investigations. Source zone vs. plume goals, targeted source zone remedies. Revised source zone remedial goals.

2010s: In-situ plume remedies

2014: Closure of U.S. large plume fractured rocksite.

Pre-2000s: Remedial Strategy: P&T and limited excavation

Post 2005: Risk driven goals

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Drivers for Fractured Rock Remediation

Source Zone

VI Mass Discharge

Plume – Risk Drivers

VIMass

Discharge to surface water

Protection of Water

supplies

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Fractured Rock Site Closures

Large Plume (2,000 ft) –Fractured

Sandstone. Cost Savings

$8MRisk Based Remedial

Goals

Focus on High Concentration / Mass

FluxAdaptive Approach

Large Plume 5,000 ft) –Fractured

Chalk. Cost Savings $6M

SITE Closure

Remediation – Case Studies

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Example 1: Source Reduction and Plume Closure

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Example 1: Overcoming Matrix Diffusion

Post Remediation After Remediation

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Example 1: Adaptive Approach

Site Closure Reflecting:• Regulatory/Risk Based Goals

• Focus on Mass Recovery/Destruction

• Adaptive Approach

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Example 2: Karst Site - Risk Based Site Closure

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Limited Bedrock data

Bedrock Well

1,1 DCE Concentration (µg/L)

MCL

20

40

60 1. Only 1 bedrock well at site – exhibits increasing 1,1 DCE trend

2. RM-2 Guidance requires estimation of POE concentration (hypothetical offsite domestic well):

− “For sites in unique geologic environments not suited for the Domenico Model (such as karst…), another, more appropriate, model…should be applied.”

No such model exists for karst!

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Assessment of Risk Based Standards

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No Further Action - Site Closure

LPOE

Distance (ft)

QPOE Flow

(gal/d)Void Space

M1,1-DCE Source Concentration in Bedrock (µg/L)

1850 150 0.10% 1091850 150 0.24% 461850 300 0.10% 1701850 300 0.24% 701500 150 0.10% 963000 150 0.10% 149

Range of computed “acceptable” 1,1 DCE values

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SummaryThe challenge of fractured rock remediation can be overcome by:

• Appropriate risk based remedial goals;

• Focus on high concentrations and flux zones; and

• Adaptive remedial approach.

An appropriate and targeted remedial approach based on sufficient site understanding is the key to cost and risk uncertainty reduction.

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ContactsAllan Horneman, PhDPrincipal GeologistPortland, Maineallan.horneman@arcadis.com

Michael Cobb, P.G.Principal GeologistPortland, Mainemichael.cobb@arcadis.com

Keith White, P.G.Principal GeologistSyracuse, New YorkKeith.white@arcadis.com

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Q&A

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