Hydrocarbon Plume Characterisation & Remediation in a Densely Abstracted Chalk AquiferAdrian Bhreathnach MBA MSc PgDip BSc PIEMA
Director m: 07743 319710
Telling a Story
• Background
• Objectives
• The Challenges
• Implementation & Progress
• Lessons Learned
Background – The Sites
• Active Salad Growing
• Site A• Glass Area 38,500 m2
• Two Groundwater Abstractions
• >80,0000 litre Kerosene Fuel Storage
• Site B• Glass Area 13,000 m2
• One Groundwater Abstractions
• >40,0000 litre Kerosene Fuel Storage
• Glass Area 13,000 m2
• New Pit Chalk
• East Anglia
• Groundwater Source Protection Zone 2
Site A
Site B
Background – The Release
• Site B – Pump in Abstraction Well located at 25m bgl - Kerosene
• Subsequently – Kerosene identified in Site A Abstraction Well (220m upgradient)
• Loss of kerosene heating oil – 4No OST’s - >500 litres / hr usage @ <5oC
• Source of kerosene identified as underground fuel oil delivery line over approximately 6 years
Stop kerosene LNAPL migration towards identified receptorsStop
Reduce dissolved concentrations of speciated petroleum hydrocarbons to below remedial target levels
Reduce
Remove LNAPL from aquiferRemove
Objectives
Overcoming Obstacles & Design (1)The Sites • Business Continuity
• Glass Houses
• Groundwater >20m bgl
The Regulations • Environmental Permit Regulations & Position Statement 3A
• Water Resources Act 1991
• Zero Capacity
The Discharge• No Foul Sewer within 1km
• No Surface Water
• Contaminated Chalk Aquifer
Overcoming Obstacles & Design (2)Data Inconsistencies• Consultant Well Sampling – Inconsistent Results & Trends
• Historical water table levels
Contaminant Transport Routes• Fracture Flow
• Migration Flux Rate (750,000 litres / day)
• Migration Depths (~22m & ~24m bgl)
Stage 1
•Plume Management (Groundwater)
•Low-Flow Fracture Plume Containment
Stage 2
•Source Management (Soils)
•Excavation & Soil Vapour Extraction
Stage 3
•Active Removal – Free Oil & Dissolved Phase
•Targeted Flow Abstraction & Optimisation
Stage 4
•Enhanced Biodegradation (O2 Injection)
•Natural Attenuation
Remediation Stages480,000 litres / day 854,000 litres / day
Key
Free Phase Plume (2017) 67,000m2
Key
Free Phase Plume (2018) 25,000m2
LNAPL Area
2017
LNAPL Area
2018
Progress & Next StepsSite A• LNAPL removed – Awaiting rebound assessment
• Stage 4 – Enhanced O2 biodegradation ongoing
• >99.9% Reduction in dissolved hydrocarbon concentrations
Site B• LNAPL recovery ongoing
• Delays due to reinjection limitations now resolved
• Implementing system amendments on western boundary to increase LNAPL recovery area and rates
Site A
Site B
Take Forward Messages
• Timely regulator engagement and enforcement flexibility is critical to effective pollution control.
• Critical project data informing decision making needs to be consistent, reliable and that any ‘irregularities’ need to be understood prior to remediation design.
• Innovative site characterization techniques can also be deployed during remediation to provide effective low-flow and targeted groundwater treatment solutions in Chalk aquifers.
• A great example of the time and financial benefits of prioritising conceptual understanding, effective characterization and remediation design.