Title: Effect of Salinity Changes on Particle Release and Hydraulic Conductivity in Sediments
1Effect of Salinity Changes on Particle Release
and Hydraulic Conductivity in Sediments
- MS Defense
- Theresa Blume
- Bioresource Engineering
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5Overview
- 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
6What are Colloids?
after Stumm 1992
7Why are Colloids important?
- They are abundant in the subsurface
- Large surface area
-
- high potential for contaminant absorption
8Colloid Facilitated Contaminant Transport
9The Hanford Site, Washington
10The Hanford Formation
11Overview
- 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
12How 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)
13The Electric Double Layer
after Elimelech et al. 1995
14Expanding Double Layers
Grain Surface
Particle
Grain Surface
Particle
Overlapping double layers
15The DLVO Theory
after Ryan and Elimelech 1996
16Critical Salt Concentration
17Overview
- 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
18Sediments
Silica Sand
Coarse Hanford Sediment
19Column Experiment I Determining CSC
20Methods used to Determine the CSC
Sediment
Salt Solution
Mesh
Batch Experiments
Column Experiments
21Batch Results I
COARSE SEDIMENT
SILICA SAND
Detached particles (mg/g)
Detached particles (mg/g)
NaNO3 (mol/l)
NaNO3 (mol/l)
22Batch Results
COARSE SEDIMENT
SILICA SAND
Detached particles (mg/g)
Detached particles (mg/g)
NaNO3 (mol/l)
NaNO3 (mol/l)
23Column Results
NaNO3 (mol/l)
Particle concentration (mg/ml)
Particle concentration (mg/ml)
NaNO3 (mol/l)
Pore volumes
Pore volumes
SILICA SAND
COARSE SEDIMENT
24Comparison 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
25Hanford Sediment
untreated
after freshwater shock
acid washed
26Consequences of Colloid Release
- Contaminant Transport
- Permeability Changes
- Irrigated Sodic Soils
- Coastal Aquifers
- Formation Damage
27Overview
- 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
28Particle Release and Entrapment
29Swelling Clays
30Particle Release caused by Swelling Clays
Flow
after Mohan et al. 1993
31Column Experiment II Permeability Changes
32Particle Size Distribution of Fine and Coarse
Hanford Sediments
33Coarse Hanford Sediment vs. Glass Beads
Coarse Sediment
Manometers
Fine Sediment
Fine Sediment
Glass Beads
34Permeability Reduction
Ki/Ki0
Ki/Ki0
Pore volumes
Pore volumes
Glass Beads
Coarse Hanford Sediment
35Permeability 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
36Permeability of the Fine Layer vs. Overall
Permeability
Ki (cm2)
Pore volumes
37WHY did the permeability decrease?
38Particle 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
39Reversibility
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)
40Summary 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?
41Summary 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
42Summary 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
43Possible 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.
44Acknowledgements
- 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
45Thank you all for coming!
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47Changes 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)
48Column Experiment
49Types 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
50Chemical 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
51Size Distribution of Released Particles
52Sediment 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)