Application of Enhanced Reductive Dechlorination (ERD) to Degrade Chlorinated Hydrocarbons within a MultiAquifer Environment
Jonathan Miles, PhD; David Atkinson; Thomas White; Pieter Dols ; Anil Waduge, PhD AquaConSoil, 16-19 April 2013 Barcelona, Spain
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Content
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• • • •
ERD Theory Field Application – Conceptual Site Model Field Application – Pilot Trial Design Field Application - Results
The Theory
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Reductive Dechlorination
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Terminal Electron Accepting Processes
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Selection of Electron Donor
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Molasses: • • • • • • •
Waste product, cheap Sustainable, green solution Highly soluble in water Used as a 5 to 10% solution in water Low pressure injections Easy to handle No evidence of well fouling
In situ Reactive Zone (IRZ)
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Application in the Field
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Site setting
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• Automotive component supply factory • Located in Wales, UK • Site underlain by Alluvium and Bedrock (“Marl”) • Groundwater flow toward river beyond site boundary within Marl • Historical releases of trichloroethene in centre of site, following use as a solvent • Reducing conditions
Complex Conceptual Site Model
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Contaminant Distribution
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Trichloroethene in groundwater – primary mass in the Marl Multi-level monitoring undertaken Transformation to cis 1,2 dichloroethene and vinyl chloride observed More than 200m from source to edge of site Primary concern – potential discharge of contaminated groundwater to river (50m from site boundary)
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Pilot Trial Design
Objectives • To assess ERD as a full scale remedial solution for the cVOCs in the Alluvium and Marl • Obtain site specific design information including hydraulic parameters for the site through tracer testing Basic Design • Multiple injection and monitoring wells across discrete geology • 4 injections over a period of 10 months Other Considerations • External layout, manage vinyl chloride vapours • Manage TOC injections to control pH
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Pilot Trial Layout
Bedrock
Response Wells
Dose
Ground level
Injection Wells
Simplified horizontal cross section
Drift Phase Wells
Alluvium MW7
RMW1 RMW2
Approximately 5 m bgl
Weathered Marl Groundwater flow Approximately 12m bgl
Competent Marl
IW1 to IW6
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Horizontal distances not to scale
MW504 MW503
MW601 S/D MW602S/D
MW401 MW402
Injection Scope Injections Into Alluvium
Injection
Volume of Molasses Injected (litres)
Month 0, Injection 1
7,000
Month 3, Injection 2
14,000
Month 6, Injection 3
20,000
Month 9, Injection 4
8,000
Injections Into Marl
Injection
Volume of Molasses Injected (litres)
Month 0, Injection 1
7,000
Month 3, Injection 2
14,000
Month 6, Injection 3
6,000 (water)
Month 9, Injection 4
9,000
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Tracer Testing •
The variation of electrical conductivity and TOC through the aquifer following molasses injection used as a tracer
Mobile Porosity Calculations
Aquifer
Mobile Porosity
Alluvium
0.015%
Upper Marl
0.35% to 1.0%
Lower Marl
1% to 3.9%
Groundwater Velocity Calculations
Aquifer
Groundwater Velocity
Alluvium
0.03 to 0.5 m/day
Upper Marl
0.9 m/day
Lower Marl
0.2 to 0.8 m/day
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IRZ Establishment & Maintenance (Marl) pH
Total Organic Carbon
Methane
• pH stable between 6 and 8 for majority of trial • TOC increase proportional to distance from injection point (log scale) • Strong methanogenisis indicated from trial mid point Imagine the result
ERD Performance - Alluvium
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ERD Performance - Marl Shallow Marl
Deep Marl
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Full Scale System?
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Conclusions
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Success: • Anaerobic conditions can be enhanced and sustained beneath the site by injection of molasses solution. • All geologic units responded well to the pilot trial. • Periodic injection of molasses enabled the establishment of a long lived IRZ within the pilot trial area with elevated levels of TOC recorded up to approximately 32 m from the injection point. • The pilot trial gained hydraulic data to facilitate the design of a full scale system.
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[email protected]
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