The Discrete Fracture Network (DFN) Field Approach for Investigating

Contaminated Sites in Fractured Sedimentary Rock

Beth ParkerNSERC Industrial Research ChairProfessor, School of Engineering

Solinst SymposiumGeorgetown, ONOctober 29, 2010

(shortened version for distribution)

Discrete Fracture Network Approach

PCE

Mackay and Cherry, 1989

DNAPLs Commonly Pass Through Overburden Into Bedrock

DNAPL source zone initial condition

Interbedded sandstone and shaleSandstone with shale interbeds

FracturedPorous Rocks

Bedding planes and joints in dolostone

Small Fracture Porosity and Large Matrix Porosity0.1 to 0.001% 2 to 25%

A

Microscopicview of rock

matrix

mineral particleDETAIL A

PLUMEZONE

SOURCEZONE

vadosezone

groundwaterzone

PLUMEFRONT

Nature of Contamination inFractured Sedimentary Rock

Requires a Different Approach

Matrix Diffusion Causes Plume Front Retardation

No DiffusionSolute front

With Diffusion and Sorption

non-porousmatrix

porousmatrix

With Diffusiont = 1

t = 1

time = 1

retardationporousmatrix

(Freeze and Cherry, 1979)

Critical Issues

Fracture network characteristics• Fracture aperture, spacing, • length and connectivity

Matrix properties• transport, storage and reactions

Discrete Fracture Network Field Approach

Use chlorinated solvent plumes as tracersNatural flow system conditions

DFN numerical models with appropriate (DFN) field and laboratory data for input / verification can realistically

represent and predict plumes in sedimentary rock

Premise

Questions: How many active fractures?

What is their Interconnectivity?

DenseNetwork

SparseNetwork

Sparse Fracture Network Yields Rapid Transport of TCE and Distant Plumes

South North2000

1500

1000

500

CA Site

Feet

abo

ve s

ea l

evel

0 5000 ft

Strong Retardation Restricts Expansion of TCE Plume

0 5000 ft

South North

2000

1500

1000

500

CA Site

Feet

abo

ve s

ea le

vel

Data Acquisition Framework for Site Characterization

Drill Corehole

Core Hole

Contaminant Analysis

Physical / Chemical Properties

Geophysics / Hydrophysics

Packer TestsK-Profiler

Multilevel Systems

Rock Matrix Fracture Networkuse lined holes almost exclusively

Obtain Data while Drilling

vadosezone

groundwaterzone

Core Hole for Rock Core Analyses in Areas of Previous DNAPL Occurrence

coredhole

0 1 10 100TCE mg/L

rock core

non-detect

Fractures withTCE migration

1

2

3

4

5

6

fractures coresamplesanalyzed

cored hole

Core Sampling for Mass Distribution &Migration Pathway Identification

DNAPL Disappearance from Fractures by DiffusionParker et al., Ground Water (1994)

Fracture Aperture2b

FractureSpacing

φfφm

H O2

DNAPLφf φm

DissolvedPhase

φfφm

DissolvedPhase

Early Intermediate Later Time

FORMER SOURCEZONE

vadosezone

groundwaterzone

PLUMEZONE

Current Site Condition: No DNAPL Remains and Plume Expands Very Slowly

Waterloo (Solinst) Removable

Modular System :

Installation in Progress

1998

California Site

Casing is Moved Towards Hole with Cables and Tubes Inside

Transducer & Double Valve Pump Attached to Each Port

Comparison of Multilevel and Rock Core Data:

Total TCE (μ g / g)

200

250

300

350

0.01 0.1 1 10

Pore water TCE (mg / L)

Dep

th (

feet

)0.01 0.1 1 10 102

multilevelzone

non-detects

Zone6

5

4

3

21

6

5

4

3

21

rock core35Bsimilar

dissimilardue to cross-contamination

Sterling et al. GW (2005)

Rock Core Results Show…

Numerous migration pathways hydraulically active, interconnected fractures

Open boreholes cause cross-contamination

ThereforeUse Rock Core AnalysisAvoid cross-connection

Prevention of Borehole Cross-Connection

Three methods exist

• FLUTe Liner

• Solinst Continuous Modular Packer

• Conventional Packers

FLUTe LinerUrethane Coated Nylon Fabric

Cherry, Parker and Keller (2007) GWMR

FLUTe liner pressed tightly against borehole wall to seal

without liner with liner

P.Pehme, 2006

Cross-Connected Not Cross-Connected

Depth Discrete Multilevel SystemsUse maximum number of ports!

FLUTe WestbaySolinst“Waterloo”

Westbay System

ExceptionallyDetailed

Head Profiles

38 ports

Abrupt inflectionsindicate unitboundaries

J.Meyer et al. 2009

FRACTRAN Simulations

Matrix for each unit has the same properties

Km = 10-6 cm/s

η = 15%

Average horizontal gradient ~ 0.01

Average vertical gradient ~ 0.03

Bulk Kh ~ 3.0 x 10-3 cm/s

Bulk Kv ~ 2.1 x 10-5 Meyer et al 2008

FRACTRAN SimulationsHead Profiles

0

5

10

15

20

25

30

35

40

45

7.0 7.5 8.0 8.5 9.0 9.5 10.0

Hydraulic Head (m)

Z (m

)

X=50mX=100mX=150m

Unit 1

Unit 2

Unit 3

Unit 4

Key Points

HGUs are partitions of the groundwater flow domain that are hydraulically consistent

HGUs are the framework for numerical modeling of groundwater flow and contaminant transport

Detailed head profiles are essential for delineating hydrogeologic units

J.Meyer et al. 2009

Summary

• Essential Methods for Contaminant Site Characterization in Sedimentary Rock

• Rock Core • Multi-Level Monitoring• Temporary Borehole Seals

• K-profiling• Temperature profiling in sealed boreholes

with lots of detail

minimize openhole conditions

Funding & Acknowledgements

Funding provided by site owners, NSERC and University Consortium for Field-Focused Groundwater Contamination Research

Support / collaboration with Westbay®, FLUTe™, and Solinst

The datasets presented are part of a larger research program and were collected by many graduate students, field technicians, research associates, and lab staff at the UoGuelph and UWaterloo

Key collaborators include John Cherry, Steve Chapman, Jessi Meyer

ReferencesCherry, J.A., B.L. Parker, and C. Keller. 2007. A new depth-discrete multilevel monitoring approach for fractured rock. Ground Water

Monitoring & Remediation 27, no.2: 57-70.

Keller, C.K., J.A. Cherry, and B.L. Parker. in submission. New method for continuous hydraulic conductivity profiling in fractured rock. submitted to Ground Water.

Meyer, J.R., B.L. Parker, and J.A. Cherry. 2008. Detailed hydraulic head profiles as essential data for defining hydrogeologic units in layered fractured sedimentary rock. Environmental Geology 56, no.1: 27-44.

Parker, B.L. 2007. Investigating contaminated sites on fractured rock using the DFN approach. In Proceedings of 2007 U.S. EPA/NGWA Fractured Rock Conference: State of the Science and Measuring Success in Remediation, September 24-26, 2007, Portland, Maine, Westerville, Ohio: National Ground Water Association.

Parker, B.L., J.A. Cherry, and B.J. Swanson. 2006. A multilevel system for high-resolution monitoring in rotasonic boreholes. Ground Water Monitoring and Remediation 26, no.4: 57-73.

Parker, B.L., S.W. Chapman, and J.A. Cherry. 2010. Plume persistence in fractured sedimentary rock after source zone removal.Ground Water, in press.

Pehme, P.E., B.L. Parker, J.A. Cherry, and J.P. Greenhouse. 2010. Improved resolution of ambient flow through fractured rock with temperature logs. Ground Water 48, no.2: 191-205.

Sterling, S.N., B.L. Parker, J.A. Cherry, Williams, Lane and Haeni. 2005. Vertical x-connection of TCE in a borehole in fractured sandstone. Ground Water 43, no.2: 557-573.

Sudicky, E.A. and R.G. McLaren. 1992. The Laplace transform Galerkin technique for large-scale simulation of mass transport in discretely fractured porous formations. Water Resources Research 28, no.2: 499-514.