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/day I = 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 ncentratio n vs D istance
900 800
2005
700
05MW06
05MW09
600 05MW11
500 400 300
05MW10
05MW04
200 100 0 0
20
40
60
80
100
120
140
D istance fro m pipeline break area
160
180
200
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
Q (infiltration rate)
Mixing Zone
Chloride Chloride ininsoil soiland and groundwater groundwater
Chloride Transport rate
Conceptual Transport Model
Infiltration Through Recharge = Vr
Groundwater Flow into Centroid = Vi
Final Volume = Vi + Vr +Vu
Upward Groundwater Flow = Vu
Conceptual Transport Model
Mi/Vi
Vr,1
Vr,2
C1
C2
Vu,1
Time Step 1
Vu,2
Time Step 2
Vr,3
C3
Vu,3
Time Step 3
Model Calculation Results Dissolved Chloride Concentration Profile Along Plume Drinking Water Guidelines
Chloride Concentration (mg/L)
Fall 2002 (Estimated) Fall 2003 (Predicted)
100000
Fall 2004 (Predicted)
39100
Fall 2005 (Predicted)
10000
Fall 2006 (Predicted)
5661
1000
706
100
61 20
10 1 0
50
100 Distance from Pipeline Break Area
150
200
Groundwater Quality Dissolved Chloride Concentration Profile Along Plume Chloride Concentration (mg/L)
Spring 2005 Spring 2006
900 800 700 600 500 400 300 200 100 0
Fall 2006 Drinkingw ater Guidelines
05MW06
05MW09
05MW11 05MW10
05MW04
0
50
100 Distance from Pipeline Break Area
150
200
Model Calculation Results (Comparison to Analytical Data) Dissolved Chloride Concentration Profile Along Plume
Spring 2005
Chloride Concentration (mg/L)
Spring 2006 Fall 2006
900 800 700 600 500 400 300 200 100 0
Drinkingw ater Guidelines Fall 2004 (Predicted) Fall 2005 (Predicted)
05MW06
05MW09
Fall 2006 (Predicted)
05MW11 05MW10
05MW04
0
50
100 Distance from Pipeline Break Area
150
200
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??
