Understanding the Role of Matrix

Diffusion When Evaluating

Remedial Options

Seth Pitkin

Vice President

Stone Environmental, Inc.

Environmental Business Council of New England

Energy Environment Economy

Understanding Matrix Diffusion

In Porous and Fractured Media

Seth Pitkin

EBC Site Remediation and Redevelopment Program

Advances in Site Remediation

12 November 2013

3

Dual Porosity Systems

■ Systems in which there are (relatively) high and low

permeability units.

■ Nearly all advective flow takes place through the pores in

the high permeability materials (mobile porosity)

■ Water in the saturated pore spaces in the low permeability

materials (immobile porosity) is dominated by diffusive,

rather than advective flux

■ Pore water in the low permeability materials essentially

serves as storage for solutes

4

Source Zone Plume Phase/Zone

Low Permeability

Transmissive

Transmissive

Low Permeability

Vapor

DNAPL

NA NA

Aqueous

Sorbed

Complex Processes 17 potentially relevant fluxes

Sale et. al., 2007

Dual Porosity Systems

•EARLY STAGE

5

Precision Site, Coco Beach, FL Site Hydrogeology

Modified from Guilbeault, 1999

Sand / silt / shells

v ~ 5-20 cm/d

10 m

0 m

15 m

Coquina lenses

Property boundary

v ~ 1-10 cm /d

Beach Sand 5 m

clay layers

0 ft

50 ft

25 ft

6

Sand Aquifer with Clay Lenses and Underlying Aquitard

Steve Chapman –University of Guelph

7

Persistent Plume after Source Isolation

due to Back Diffusion from Aquitard and Clay Lenses

Steve Chapman –University of Guelph

8

9

Where the Mass is Cocoa, FL

IK Log

Low K Unit

Profiler Samples Soil Samples

Bundle Samples

10

Soil Coring and Sampling

•Investigation &

Remediation

Group

•Investigation & Remediation Group

11

Subsampling for VOCs

0 4 in

Sorbed

mass

Dissolved

mass

Stainless steel

sampler (3/4” ID)

plunger

sample

volume

Sample location

Guilbeault, 1999

12

Fractured Rock and the Discrete

Fracture Network Approach

B.L. Parker B.L. Parker

13

Small Fracture Porosity and Large Matrix Porosity

0.1 to 0.001% 2 to 25%

A

Microscopic

view of rock

matrix

mineral particle

DETAIL A

B.L. Parker

14

Types of Flow Systems

■ Type 1 – Conductivity and storage in fractures with

negligible matrix porosity (Single porosity system)

■ Type 2 - Conductivity in fractures, high storage negligible

conductivity in matrix porosity (dual porosity system)

■ Type 3 – Conductivity and storage in the matrix porosity with

conductivity enhanced by fractures (dual permeability

system)

■ Type 4 – highly conductive matrix where fractures are

present but do not add appreciably to the volumetric flux of

the system

Nelson, R. 2001. Geologic Analysis of Naturally Fractured Reservoirs. Second

Edition. Gulf Professional Publishing. 332 p.

15

Microfractures Can Act Like Primary Porosity

89.0 89.5 90.0

B.L. Parker

16

DNAPL Disappearance from Fractures by Diffusion

Parker et al., Ground Water (1994)

•Fracture Aperture 2b

•F •racture •S •pacing

f •m

H2O

DNAPL

f •f f

•m

•D Dissolved

•P •hase

f •f f •m

•D Dissolved •P •hase

Early Intermediate Later

Time B.L. Parker

17

Diffusion Into Rock Matrix

Porous Rock Matrix

Diffusion Halo

Fracture

B.L. Parker

18

•x

1.0

0.8

0.6

0.4

0.2

0 20 40 60 80 100

Distance into matrix (cm)

Rel

ati

ve

con

cen

trati

on

(C

/ C

o)

•TCE •90 cm

Time: 22 years

diffusion profile

TCE Diffusion Profile in Sandstone

Porosity = 10%

foc = 0.1%

R = 3

Sw = 1420

B.L. Parker

19

PCB Diffusion Profiles in Shale

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

X (cm)

C/C

o

25

50 years

Parameters:

Co = 0.2 mg/L

De = 2.5 x 10-8

cm2/s

R = 2550

fm = 0.05

B.L. Parker

20

21

Vadose

zone

Groundwater

zone

Rock Core in Areas of Previous DNAPL Occurrence

Cored hole

B.L. Parker

22

•0 1 10 100

TCE mg/L rock core

non-detect

Fractures with

TCE migration

1

2

3

4

5

6

fractures Core

sample

s

analyze

d

cored hole

Rock Core Sampling for Mass Distribution

and Migration Pathway Identification

23

Comparison of Multilevel and Rock Core Data

Santa Susana Field Laboratory, CA

Total TCE ( g / g)

200

250

300

350

0.01 0.1 1 10

Pore water TCE (mg / L)

Dep

th (f

eet)

0.01 0.1 1 10 102

multilevel zone

non-detects

Zone

6

5

4

3

2

1

6

5

4

3

2 1

rock core 35B similar

dissimilar

due to cross-

contamination

Sterling et al. GW (2005)

24

Open Hole Cross - Connection of TCE

Hole-35B

6

5 4

3

2 1

Zone

0

100

200

300

De

pth

(f

ee

t )

Casing

~ 0.1 gpm

zone 6 zone 3

B.L. Parker

25

Utility of Rock Core VOC Analyses

■Migration pathway determination

■Mass distribution in dual porosity system

both vadose and saturated zones

nearly all mass in low K matrix

■Not affected by cross-connection

■Mass transfer to rock matrix causes

DNAPL disappearance and source attenuation

plume front retardation and plume attenuation

■Remediation controlled by diffusion

rebound if treatment only addresses fractures

26

1. Core

Extraction

2. Full Core

3. Sampled Core

5. Methanol

Extraction

4. Rock

Crushing

1.

2.

3.

4.

5.

3.

COREDFN Sampling and Preservation

27

Importance of Field Preservation (TCE)

■Higher concentrations

■ Field preservation necessary for accuracy

Concentration (µg/g wet rock)

Ele

va

tio

n(m

asl)

10-4

10-3

10-2

10-1

315

320

325

330

335

340

Shake-flask (Lab Preserved)

Shake-flask (Field Preserved)

Lab Preserved Field

Preserved

Lab Preserved (µg TCE/ g wet rock)

Fie

ldP

rese

rve

d(µ

gT

CE

/g

we

tro

ck)

10-4

10-3

10-2

10-1

10-4

10-3

10-2

10-1

1:1 Line

28 Concentration ( µg TCE/ g rock )

Ele

va

tio

n(m

asl)

10-4

10-3

10-2

10-1

315

320

325

330

335

340

Purge & Trap

■EPA SW846 8260

■Elevated method detection limit

■ Incomplete extraction

■Volatile losses

■Not suitable for VOCs in this rock formation

Comparison of two standard methods

Purge

& Trap

Shake-flask

Non-Detect

29

Long extraction time for shake-flask method (field samples)

Data from Yongdong Liu (2005)

Time (days)

Co

nce

ntr

atio

n(µ

g/L

me

tha

no

l)

0 7 14 21 28 35 42 490

20

40

60

80

100

120

140Sample 54

Sample 246

Sample 254

Sample 290TCE

Guelph Samples

30

Microwave Assisted Extraction is Fast

■ Microwave sample for 40 min

■ Extraction at higher temperature and pressure

Increases diffusion rate and analyte desorption rate

Elevated boiling point (temperatures ~ 120ºC)

Increased solvent penetration

31

Spill Area

Core 36

Rock Matrix

Sampling and

Analysis Results

32

Core 35

Packer Test

Result

Well Cluster

Result

Matrix pore

water conc.

33

LVRR-35 Core (75 – 80 ft bgs) TCE Concentrations in Unfractured 5-ft. Run

ND 94 ug/L

2200 ug/L 94 ug/L

1800 ug/L 900 ug/L

34

■ Concentrations decline

by 1.5 Orders of

magnitude 1 ft into matrix

from fracture in core run

from 75 to 80 ft bgs

(shown at right)

Core 35

35

Which Sample Do You Pick as Representative of This Core Run?

Core 35

<4 ug/L TCE 3,000 ug/L TCE <4.6 ug/L TCE

36

4 km

Downgradient

of

Spill Area

Core 33

37

Mass Distribution in the Rock Matrix

3100

9.7

220

0.75

45

0.27

1.6

0.29

0.78

0.049

0.041 1.1

0.082

0.71

0.059

0.048

Core

33

Core

35

Core

36

38

Conclusions

■ In porous media transport occurs in high K zones

■ In porous media most of the mass may be in the low K

zones

■ In fractured media transport occurs in fractures

■ In fractured media the vast majority of the mass may be

present in the matrix (primary) porosity

■ It is necessary to investigate the low K zones and primary

porosity to determine the mass present

■ Failure to remediate the mass in the low K zones will likely

result in failure to reach remedial objectives