Hydrocarbon Plume Characterisation & Remediation in a ...

Hydrocarbon Plume Characterisation & Remediation in a Densely Abstracted Chalk AquiferAdrian Bhreathnach MBA MSc PgDip BSc PIEMA

Director m: 07743 319710

e: [email protected]

Telling a Story

• Background

• Objectives

• The Challenges

• Implementation & Progress

• Lessons Learned

BACKGROUND

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

Site A

Site B

Background - The Source

Chilcott. HPA, 2006.

Background -The Receptors

OBJECTIVES

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

THE CHALLENGES

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)

IMPLEMENTATION &PROGRESS

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

Key

>100 µg/l

>1,000 µg/l

>10,000 µg/l

>100,000 µg/l

Dissolved Phase Contamination Plume (2017)

Dissolved Phase Contamination Plume (2018)

Key

>100 µg/l

>1,000 µg/l

>10,000 µg/l

>100,000 µg/l

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

Lessons Learned

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.