Dr Frank Dennis Associate - Royal Society of Chemistry · OBJECTIVES Provision of basic information...
28
CONTAMINANT HYDROGEOLOGY AT NUCLEAR SITES Dr Frank Dennis Associate
Transcript of Dr Frank Dennis Associate - Royal Society of Chemistry · OBJECTIVES Provision of basic information...
CONTAMINANT HYDROGEOLOGY AT NUCLEAR SITES
Dr Frank DennisAssociate
CONTENTS
Introduction
Objectives
Background
Regulatory setting
A bit about contaminants
A bit about their management/treatment
Summary
INTRODUCTION
International consulting engineers specialising in ground engineering and environmental science
Established in 1960 in Canada, offices in the UK since 1973
Offices in 85 countries, completed projects in more than 120 countries
6,500 staff worldwide, around 250 staff in the UK
Key environmental consultant to UK nuclear industry
OBJECTIVES
Provision of basic information regarding
contaminant hydrogeology at nuclear sites
Encourage thought on the issues associated
with groundwater contaminant management
BACKGROUND – TYPES OF OPERATIONS
Operating (and planned) nuclear power
e.g. BE/EdF; some Magnox
Decommissioning sites
Old UKAEA and BNFL sites
Some private sites (e.g. GE Healthcare sites)
MoD sites
e.g. AWE, Devonport, etc
Waste/repository programmes
Surface/near surface LLW
Deep ILW
BACKGROUND - NUCLEAR SITE LOCATION
BACKGROUND – GEOLOGICAL CONTEXT
CONTAMINANTS OF CONCERN
Radionuclides Fingerprint generally unique at each site
• Dounreay – 137Cs; 90Sr
• Sellafield - 90Sr; 137Cs; 99Tc, 3H
• Aldermaston – long-lived α; 3H
“Conventional” Contaminants More common than you might think
• DNAPL
• LNAPL
• Acid
• Heavy Metals
• TNT
COC’s EXAMPLE 1
Western Storage Area, Harwell
25 unlined chemical waste (solvent) pits excavated into Chalk
Detection of significant off-site contamination in 1980’s
Contaminant plume extends many km
Containment plant operational 1993
Replacement plant operational 2007
5.75 tons of contaminant removed from groundwater since 1993
COC’s EXAMPLE 2
Shaft, Dounreay
ILW disposal in 65m deep, 4m diameter shaft
Inventory poorly understood but dominant CoC’s include 137Cs; 90Sr
Migration from unlined shaft into host rock and ultimately to sea
Extensive programme to hydraulically isolate shaft complete
COC’s EXAMPLE 3
Anonymous site
Surface radionuclide contamination of concrete
Scabbling to remove concrete
Cleaned concrete crushed and used for landscaping site
Hydrocarbons picked up in groundwater
GROUNDWATER MANAGEMENT - REGULATORS
Understand the law and the regulatory environment
Confusing regulatory regime Environment Agency
Health and Safety Executive
Local Authority
GROUNDWATER MANAGEMENT - STAKEHOLDERS
Understand the Stakeholder’s requirement
Engage with Stakeholders early
Be prepared to impress Stakeholders with solutions and not just present them with problems
GROUNDWATER MANAGEMENT - STAKEHOLDERS
GROUNDWATER MANAGEMENT
Understand the nature of the problem and act immediately
Phase the investigations to continually:
Reduce uncertainty
Refine the conceptual model
Refine the risk assessment
Define the best remedial solution
GROUNDWATER MANAGEMENT - REMEDIATION
Remediation techniques
Natural attenuation
Pump and treat
Permeable reactive barriers
Cut off walls
REMEDIATION - PUMP AND TREAT SYSTEMS
REMEDIATION - PUMP AND TREAT SYSTEMS
TREATMENT OF CONTAMINATED DISCHARGES
Temporary groundwater treatment plant
• Floculation and settlement
• Granular activated carbon
• Air stripping
• Ion exchange
PERMEABLE REACTIVE BARRIERS (PRBs)
Relatively new technology in UK, lack of track record over full design life
Another slow process – design life measured in decades
Design can be complex, no active pumping so understanding of existing groundwater conditions are fundamental
Not maintenance free- fouling/encrustation reactors- exhaustion of treatment media
Several processes covered by patents
IN-GROUND PERMEABLE REACTIVE BARRIERS (PRBS)
PRB EXAMPLE – NORTHWEST ENGLAND
Funnel and gate system
slurry wall barrier
mechanical in ground gate constructed of steel containing iron filings (“zero valent iron”)
iron filings reacting with Chlorinated Solvents
Source: Arup
Source:Envirometal Technologies Inc.
PRB EXAMPLE – NORTHWEST ENGLAND
Source:Arup
Reactor vessel ready for installation
Reactor vessels in place in PRB gate
ENVIRONMENTAL IMPACTS FROM GROUNDWATER CONTROL
Impact 1: Abstraction- e.g. impact on water sources
Impact 2: Pathways for groundwater flow- e.g. increased risk of aquifer pollution
Impact 3: Barriers to groundwater flow- e.g. changes in groundwater level
Impact 4: Discharges to groundwater- e.g. risk of fuel spills, etc
Impact 5: Discharge to surface water- e.g. risk of pollution of surface waters
TIMING OF REMEDIAL ACTIVITIES
Dependant on type of site
Two schools of thought for decommissioning
sites:
Treatment at the end of decommissioning
programme;
Integrate ground and groundwater management
fully into the programme (best practice guidance
from IAEA)
NEW BUILD
Risk from contaminants already on site
Risk of contamination from near surface
construction activity
Risk from off-site sources
NEW BUILD - IMPACTS OF GROUNDWATER CONTROL
Effect on Aquifer Quality
Pumping from dewatering systems changes natural hydraulic gradients and velocities
This can cause the migration of plumes of polluted water associated with adjacent contaminated sites
SUMMARY
Complicated regulatory regimeCoC’s are not limited to
radionuclidesVariety of treatment options
availableFully understand the contaminant
system and act
