cleaning up a salt spill · 2021. 4. 6. · introduction • site located in central alberta. •...
TRANSCRIPT
Cleaning Up a Salt Spill:
Predictive Modelling and Monitoring Natural Attenuation to Save Remedial Costs
Outline
• Introduction• Remedial Alternatives• Alternate Approach: Site Assessment and Predictive
Modelling• Importance of Predictive Modelling for Remediation by
Natural Attenuation
Introduction
• Site located in central Alberta.• Pipeline break on September 6, 2002 caused by corroded
pipe.• Approximately 5,250 m2 affected area.• Initial spill response (by others):
– standing fluid (produced water and oil) removed by vacuum truck;
– trenches excavated along and downslope of spill area;– limited soil and trench water quality data collected; and– geophysics survey (EM 38).
• Shallow groundwater table present.
Site Plan
Remedial Alternatives (16,000 m3 in situ)
• Traditional dig and dump ($2.1M to $2.5M).• Pump and deep well disposal ($1.0M to $1.3M).
EM38 Survey (September 2002)
Base: ESSIS 2002 EM38
EM38 Survey (September 2002, 2003)
Site Assessment
– Electromagnetic (EM) survey 2004.– Groundwater flow regime.– Soil and groundwater quality data.– Vegetation survey.– Predictive modelling vs. observed water quality.
Site Assessment: EM Survey (2003, 2004)
Site Assessment: Groundwater Flow Regime
K=1 m/dayI = 5%
Site Assessment: Groundwater Flow Net
Site Assessment: Soil Quality Data
• Fall 2002 (spill response info in source area):– maximum chloride (Cl) concentration of
39,100 mg/Kg; and– maximum sodium adsorption ratio (SAR) of
49.7 dS/m and electrical conductivity (EC) of 29 dS/m.
Site Assessment: Soil Chloride Concentration (Spring 2005)
(source area) (high EM38 area)
Site Assessment: Soil SAR Concentration (Spring 2005)
(source area) (high EM area)
Site Assessment: Groundwater Quality Data
Spring 2005• Spill Area:
– chloride in shallow well (523 mg/L); and– chloride in deep (bedrock) well (27 mg/L).
• High EM38 Area:– chloride in shallow well (747 mg/L); and– chloride in deep (bedrock) well (6 mg/L).
Site Assessment: Dissolved Chloride Concentration Profile Along Plume
C o ncentrat io n vs D istance
05MW10
05MW0905MW06
05MW04
05MW11
0
100
200
300
400
500
600
700
800
900
0 20 40 60 80 100 120 140 160 180 200D istance fro m pipeline break area
2005
Site Assessment: Vegetation Assessment
• White spruce trees dying because of waterlogged conditions.
• Waterlogged conditions predate 2002 pipeline spill.• Some regeneration occurring, but growth is inhibited
because of salt water spill.• Restoration plan for site reclamation provided to
client.
Site Assessment: Air Photo Review
Drainage direction
Site Assessment: Air Photo Review
Site Assessment: Air Photo Review
Site Assessment: Air Photo Review
So How Will We Clean Up This Site?
• Trees not killed by salt spill.• Chloride concentrations not affecting bedrock aquifer.• Chloride plume moving, but decreasing over time.• What’s the process? Can this be sustained and at
what rate?
Conceptual Salt Leaching Model
Chloride in soil and
groundwater
Chloride in soil and
groundwaterMixing Zone
Chloride Transport rate
Q(infiltration rate)
Conceptual Transport Model
Groundwater Flow into Centroid = Vi Final
Volume = Vi + Vr +Vu
Infiltration Through Recharge = Vr
Upward Groundwater Flow = Vu
Mi/Vi C1
Vr,1
Vu,1
C3
Vu,2 Vu,3
C2
Vr,2 Vr,3
Conceptual Transport Model
Time Step 1 Time Step 2 Time Step 3
Model Calculation Results
Dissolved Chloride Concentration Profile Along Plume
39100
5661
706
61
20
1
10
100
1000
10000
100000
0 50 100 150 200Distance from Pipeline Break Area
Chl
orid
e C
once
ntra
tion
(mg/
L)
Drinking Water Guidelines
Fall 2002 (Estimated)
Fall 2003 (Predicted)
Fall 2004 (Predicted)
Fall 2005 (Predicted)
Fall 2006 (Predicted)
Groundwater Quality
Dissolved Chloride Concentration Profile Along Plume
05MW11
05MW04
05MW06 05MW09
05MW10
0100200300400500600700800900
0 50 100 150 200Distance from Pipeline Break Area
Chl
orid
e C
once
ntra
tion
(mg/
L)
Spring 2005
Spring 2006
Fall 2006
Drinkingw ater Guidelines
Model Calculation Results (Comparison to Analytical Data)
Dissolved Chloride Concentration Profile Along Plume
05MW11
05MW04
05MW06 05MW09
05MW10
0100200300400500600700800900
0 50 100 150 200Distance from Pipeline Break Area
Chl
orid
e C
once
ntra
tion
(mg/
L)
Spring 2005
Spring 2006
Fall 2006
Drinkingw ater Guidelines
Fall 2004 (Predicted)
Fall 2005 (Predicted)
Fall 2006 (Predicted)
Fate and Transport: What processes are occurring?
• Upward vertical groundwater flow direction (Vu):– salts not being transported deeper; and– enhances soil flushing.
• Horizontal flow 45 m/year (Vi):– provides natural flushing capacity.
• Infiltration rate (Vr):– provides groundwater recharge; and– enhanced by ponding (drainage course
disrupted).
Fate and Transport: So what does this tell us?
• Met remedial objectives within four years of the spill.• Natural attenuation effective for remediating this salt
spill.
Revisit to Remediation Options
• Traditional Dig and Dump ($2.1M to $2.5M).• Pump and Treat $1.0M to $1.3M.• Natural Attenuation:
– $50,000 for site assessment;– $10,000 for predictive modelling; and– $20,000 for ongoing EM survey and groundwater quality
monitoring (3 years).• Preferred Remediation Option?
– cost Saving of $900,000 to $2.3M;– remediation complete within 4 to 6 year timeframe; and– minimal surface disturbance.
Important Considerations for Predictive Modeling
• Site Assessment: EM survey and attenuation with time (mass spreading with time).
• What’s the process? Can this be sustained and at what rate?
• Impact of Cl off site?
Next Steps for the Site
• Continue monitoring (EM survey, groundwater quality).• Evaluate EC/SAR in soils and need for amendments.• Engage stakeholders [Alberta Environment (AENV)/landowner].• Implement restoration plan:
– improve surface drainage after remediation goal achieved; and
– revegetate area and weed control .
Questions??