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Effect of Salinity Changes on Particle Release and Hydraulic Conductivity in Sediments

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Title: Effect of Salinity Changes on Particle Release and Hydraulic Conductivity in Sediments


1
Effect of Salinity Changes on Particle Release
and Hydraulic Conductivity in Sediments
  • MS Defense
  • Theresa Blume
  • Bioresource Engineering

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5
Overview
  • Introduction
  • What are Colloids?
  • Why are they important?
  • How are Colloids released?
  • Part I Determination of Critical Salt
    Concentration
  • Part II Permeability Changes as a Result of
    Particle Release
  • Conclusions

6
What are Colloids?
after Stumm 1992
7
Why are Colloids important?
  • They are abundant in the subsurface
  • Large surface area
  • high potential for contaminant absorption

8
Colloid Facilitated Contaminant Transport
9
The Hanford Site, Washington
10
The Hanford Formation
11
Overview
  • Introduction
  • What are Colloids?
  • Why are they important?
  • How are Colloids released?
  • Part I Determination of Critical Salt
    Concentration
  • Part II Permeability Changes as a Result of
    Particle Release
  • Conclusions

12
How can Colloids Become Mobile?
  • Shear stress
  • Dissolution of cementing agents
  • In-situ precipitation
  • Increasing repulsion forces as a result of
    changes in solution chemistry (pH, salinity)

13
The Electric Double Layer
after Elimelech et al. 1995
14
Expanding Double Layers
Grain Surface
Particle
Grain Surface
Particle
Overlapping double layers
15
The DLVO Theory
after Ryan and Elimelech 1996
16
Critical Salt Concentration
17
Overview
  • Introduction
  • What are Colloids?
  • Why are they important?
  • How are Colloids released?
  • Part I Determination of Critical Salt
    Concentration
  • Part II Permeability Changes as a Result of
    Particle Release
  • Conclusions

18
Sediments
Silica Sand
Coarse Hanford Sediment
19
Column Experiment I Determining CSC
20
Methods used to Determine the CSC
Sediment
Salt Solution
Mesh
Batch Experiments
Column Experiments
21
Batch Results I
COARSE SEDIMENT
SILICA SAND
Detached particles (mg/g)
Detached particles (mg/g)
NaNO3 (mol/l)
NaNO3 (mol/l)
22
Batch Results
COARSE SEDIMENT
SILICA SAND
Detached particles (mg/g)
Detached particles (mg/g)
NaNO3 (mol/l)
NaNO3 (mol/l)
23
Column Results
NaNO3 (mol/l)
Particle concentration (mg/ml)
Particle concentration (mg/ml)
NaNO3 (mol/l)
Pore volumes
Pore volumes
SILICA SAND
COARSE SEDIMENT
24
Comparison of CSCs
Experiment Silica Sand Hanford Sediment
Batch 0.015-0.032 mol/l 0.11-0.17 mol/l
Batch (with mesh) 0.015-0.020 mol/l 0.10-0.11 mol/l
Column 0.028-0.042 mol/l 0.10-0.13 mol/l
25
Hanford Sediment
untreated
after freshwater shock
acid washed
26
Consequences of Colloid Release
  • Contaminant Transport
  • Permeability Changes
  • Irrigated Sodic Soils
  • Coastal Aquifers
  • Formation Damage

27
Overview
  • Introduction
  • What are Colloids?
  • Why are they important?
  • How are Colloids released?
  • Part I Determination of Critical Salt
    Concentration
  • Part II Permeability Changes as a Result of
    Particle Release
  • Conclusions

28
Particle Release and Entrapment
29
Swelling Clays
30
Particle Release caused by Swelling Clays
Flow
after Mohan et al. 1993
31
Column Experiment II Permeability Changes
32
Particle Size Distribution of Fine and Coarse
Hanford Sediments
33
Coarse Hanford Sediment vs. Glass Beads
Coarse Sediment
Manometers
Fine Sediment
Fine Sediment
Glass Beads
34
Permeability Reduction
Ki/Ki0
Ki/Ki0
Pore volumes
Pore volumes
Glass Beads
Coarse Hanford Sediment
35
Permeability Reduction
Coarse Matrix Ki0 (initial) KiF (final) KiF /Ki0
Coarse Sediment 0.013 0.0009 0.07
Coarse Sediment 0.015 0.003 0.17
Coarse Sediment 0.023 0.002 0.09
Glass beads 0.005 0.0017 0.31
Glass beads 0.004 0.0007 0.20
Glass beads 0.0013 0.00017 0.13
36
Permeability of the Fine Layer vs. Overall
Permeability
Ki (cm2)
Pore volumes
37
WHY did the permeability decrease?
38
Particle Release from Coarse and Fine Hanford
Sediments
COARSE
Particle concentration (mg/ml)
NaNO3 (mol/l)
Pore volumes
Particle concentration (mg/ml)
NaNO3 (mol/l)
FINE
Pore volumes
39
Reversibility
A salt solution (0.2 mol/l NaNO3), B salt pulse
(5 mol/l NaNO3) C freshwater shock (0.0001
mol/l NaNO3) D second salt pulse (5 mol/l, then
0.2 mol/l NaNO3)
40
Summary and Conclusions
  • Particle release from sediments was studied
    under two different aspects
  • (1) at what salt concentration does particle
    release occur and how can this salt concentration
    be determined and
  • (2) does particle release have an effect on
    sediment permeability?

41
Summary and Conclusions, continued
  • CSC determination with batch experiments is
    possible.
  • CSC (Silica Sand) 0.03 mol/l NaNO3
  • CSC (Hanford Sediment) 0.13 mol/l
    NaNO3

42
Summary and Conclusions, continued
  • Significant decrease of hydraulic conductivity
    (layered system)
  • up to 90 for the Hanford Sediment
  • up to 80 for the glass beads
    experiments.
  • Processes in the fine layer control the system

43
Possible Implications for the Hanford Site
  • The high CSC determined for the Hanford Sediment
    emphasizes that colloid detachment could be an
    issue also at the Hanford Site.
  • Studies of these phenomena should take into
    account layered systems as permeability decreases
    in fine layers could inhibit vertical flow while
    enhancing lateral flow and thus also contaminant
    transport.

44
Acknowledgements
  • A big thank you to
  • John Selker
  • Noam Weisbrod
  • Roy Haggerty Skip Rochefort
  • Reed Glasmann
  • Dalia
  • Faculty, Staff Grad Students of BRE
  • esp. David, Melissa France

45
Thank you all for coming!
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47
Changes in pH
A
B
C
D
Q (cm3/sec)
EC (mmho/cm) and pH x 10
Pore volumes
A salt solution (0.2 mol/l NaNO3), B salt pulse
(5 mol/l NaNO3) C freshwater shock (0.0001
mol/l NaNO3) D second salt pulse (5 mol/l, then
0.2 mol/l NaNO3)
48
Column Experiment
49
Types of Subsurface Colloids
  • Clays (kaolinite, illite, smectites and
    vermiculites)
  • Colloidal humic acids
  • Iron hydrous oxides, iron and manganese oxides
  • Biological colloids such as microorganisms and
    viruses
  • Anoxic sediments sulfide and polysulfide colloids

50
Chemical and Physical Parameters
Sediment K ppm Ca meq/100g Mg meq/100g Na meq/100g Mn ppm Fe ppm d60/d10 d50 mm CEC meq/ 100g
Silica Sand lt39 lt0.1 lt0.1 lt0.1 0.1 2.5 1.2 0.36 -
Hanford Coarse 121 4.9 1.4 0.63 0.4 4.6 3.03 0.67 4.1
Hanford Fine 222 12.4 2.7 1.29 0.5 5.0 4.92 0.07 9.7
51
Size Distribution of Released Particles
52
Sediment Mineralogy
  • Hanford Coarsedominated by basaltic rock
    fragments, plagioclase rich (lt 10 clay minerals)
  • Hanford Fineenriched in quartz and mica compared
    to Coarse, otherwise similar (30-35 clay
    minerals)
  • Released Particles enriched in clays relative to
    the Sediments 40-50 clay minerals (includes
    smectite, mica, Fe-Mg chlorite, and kaolinite)
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