Sodium Bicarbonate Injection
for Remediation of
Acidic Groundwater
Tennessee Department of Environment Conservation
Solid Hazardous Waste Conference
Gatlinburg, Tennessee
April 19, 2007
Christina B. Brown, P.E.
AquAeTer, Inc.
Brentwood, Tennessee
Introduction
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Problem Background
Site Overview
Feasibility Study
ƒ Field Work
ƒ Bench Scale Testing
ƒ Continuous Testing
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Pilot Study
ƒ Design
ƒ Results
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Future Plans
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Problem Background
Former chemical manufacturing site
o Natural ravine used for chemical dumping
o Slurry wall and pump and treat system installed
in 1980’s to remediate groundwater
o
ƒ Phenolics
ƒ BTEX
ƒ Sulfuric acid
o
Treatment successfully reduced phenolic and
BTEX concentrations below regulatory limits
ƒ Groundwater remained highly acidic
o
The pH in monitoring wells exterior to the
slurry wall began to drop after 2000
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Site Overview
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Site Map
N
Flow
River
Groundwater flow
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Site Photo
River
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Impoundment
Cross Sectional View
Approximate Existing Ground Surface
0 ft
Fill
Silty Sand
Silty Clay
Silt
Clayey Silt
Trace of Sand
Interbedded
Silt and Clay
Clayey Silt
River
Alluvial Sands
60 ft
Shale Bedrock
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Feasibility Study
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Feasibility Study
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Goal: Evaluate remedies to prevent acidic
groundwater (pH < 5.5) from reaching river
Options Considered
ƒ Passive Neutralization Barrier
• Limestone
ƒ Injection of Soluble Alkaline Chemical
• Sodium Bicarbonate
• Sodium Hydroxide
o
Selection Criteria
ƒ Technical Feasibility
ƒ Cost
ƒ Lifetime
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Feasibility Study
o
Field Studies
ƒ Additional sampling (wells and piezometers)
ƒ Slug testing
ƒ Collected water for laboratory studies
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Acidity Contours
River
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Feasibility Study – Bench Scale
o
Determine the optimal neutralization agent for
field application based on:
ƒ Precipitate (solids) formation
• Properties
• pH range
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Impact of anoxic environment
Off-gassing
Heat generation
pH endpoint control
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Titration Curves
9
Hydroxide - atm.
Bicarbonate - atm
Bicarbonate - Nitrogen
Hydroxide - Nitrogen
8
7
pH
6
Buffered Region
5
4
3
2
0
10
20
30
40
mMoles alkali added
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50
60
70
Precipitate Volume Comparison
Sodium Hydroxide
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Sodium Bicarbonate
Bench Scale Summary
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No significant heat or gas generation during
any test
Bicarbonate precipitate was 1/3 the volume of
hydroxide and settled much more rapidly
Anoxic environment has minimal impact on the
variables of concern
ƒ Titration curve is nearly identical in region of concern
ƒ Precipitate volumes and properties are similar
o
Limestone has a very slow reaction rate and
armours easily
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Feasibility Study - Continuous Testing
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Alkaline Injection - Precipitate behavior in porous
medium
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Site water with sodium bicarbonate
Site water with sodium hydroxide
Passive Barrier – Fouling and efficiency
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Limestone rock with site water
Limestone sand with site water
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Limestone Columns
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Sodium Bicarbonate Column Versus Sodium
Hydroxide Column
Bicarbonate
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Hydroxide
Progression Of Precipitate Plume In Sodium
Hydroxide Column
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Effluent Precipitate
Bicarbonate Effluent
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Hydroxide Effluent
Continuous Testing Conclusions
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Limestone beds are rendered ineffective very
quickly due to precipate
Precipitate from bicarbonate moves through
small pore spaces more easily
Test Results + Cost Analysis
Bicarbonate Injection
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Sodium Bicarbonate Injection Benefits
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Soluble chemical will follow groundwater path
Costs for treatment are significantly less than limestone
wall
Costs for re-treating or moving treatment are minimal
Maximum pH of 8 – endpoint control
Smaller volume of precipitate with better properties for
aquifer transport
Remediate soil surface to eliminate rebound issues?
Plugging of aquifer??
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Pilot Injection
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Pilot Injection
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Install additional injection and monitoring
wells to north of slurry wall
Perform titrations with soil and groundwater
from borings
Develop cost effective injection system
Begin Injection
Monitor
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Injection / Monitoring Wells
Slurry Wall
Existing Monitoring Wells
New Monitoring Wells
Shallow Injection Well
Deep Injection Well
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Injection System
Head values will be equal during gravity feed.
Estimated
rate of
injection 0.05
and 6.0 gpm
Vented Well Cap
Optional PVC Riser
250-Gallon Tote
containing bicarbonate
solution
Monitoring Well
0.5” Tubing
Pallet
Unconsolidated Soils
Alluvial Sands
Shale Bedrock
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Installation
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General pH Trends
9
Injection Started
8
7
pH
6
5
4
3
2
6/19/2005
9/27/2005
1/5/2006
4/15/2006
7/24/2006
Date Sampled
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11/1/2006
2/9/2007
5/20/2007
Specific pH Trends
MW-18
MW-17
MW-21
Groundwater flow
Shallow IW
P-4
Deep IW
Slurry wall
MW-18
MW-17
8
9
Injection Started
Injection Started
Top pH
7
7
6
pH
pH
Bottom pH
8
6
5
5
4
4
3
3
1/1/06
2/20/06
4/11/06
5/31/06
7/20/06
9/8/06
Date
10/28/06
12/17/06
2/5/07
3/27/07
2
1/1/06
5/16/07
4/11/06
5/31/06
7/20/06
9/8/06
10/28/06
12/17/06
2/5/07
3/27/07
5/16/07
10/28/06
12/17/06
2/5/07
3/27/07
5/16/07
Date
MW-21
9
2/20/06
P-4
9
Injection Started
Injection Started
8
8
7
7
pH
pH
6
6
5
5
4
4
3
2
01/01/06
02/20/06
04/11/06
05/31/06
07/20/06
09/08/06
10/28/06
12/17/06
02/05/07
03/27/07
05/16/07
Date
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3
1/1/06
2/20/06
4/11/06
5/31/06
7/20/06
9/8/06
Date
Bulk Chemical Delivery System
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Slug Testing
Prior to Injection:
10-3 – 10-6
After Injection:
10-4 – 10-6
Material
Hydraulic Conductivity
cm/s
Clay
10-9 - 10-6
Silt, sand silts, clayey sands, till
10-6 - 10-4
Silty sands, fine sands
10-5 - 10-3
Well sorted sands, glacial outwash
10-3 - 10-1
Well sorted gravel
10-2 - 10-1
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Future Plans
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Increase the number of injection locations
Consider interior remediation
Collect samples from borings in area of
remediation to determine impacts to soil
properties
Continue monitoring
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Conclusions
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Sodium bicarbonate injection is showing
promising results
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Moving through aquifer and raising pH to acceptable levels
within 45 days and up to 100 feet
Minimal impact on aquifer conductivity
Simple to implement
Highly cost-effective
Understanding groundwater chemistry and site
hydrogeology are key to success
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AquAeTer, Inc.
optimizing environmental resources – water, air, earth
Chrisie Brown
[email protected]
(615) 373-8532
Visit us at booth #114