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