contaminated sites investigations in fractured bedrock
TRANSCRIPT
CONTAMINATED SITES INVESTIGATIONS IN FRACTURED BEDROCK SETTINGS -
INFORMATION AND EXAMPLES OF WHEN AND HOW TO INVESTIGATE THEM
CSAP Fall Professional Development Workshop
November 23, 2016 - Vancouver, BC
Presented by : Stephen Munzar and Annette Mortensen
OUTLINE! Introduction
! Regulatory Requirements
! Important Considerations
! Components of Bedrock Investigations
! Techniques
! Data Analysis
! Use of Conceptual Site Models
! Summary and Conclusions
INTRODUCTION
Why investigate bedrock?
! Regulatory requirements
! Many potable water supply wells are constructed in bedrock
! Flow/transport through bedrock can act as a significant pathway to sensitive receptors
! Groundwater flow and contaminant transport behave differently in bedrock
INTRODUCTION (CONT’D)
Some common misconceptions about bedrock:
! Bedrock is an an impermeable barrier
! Groundwater does not flow in bedrock
! Contaminants do not migrate in bedrock
! Bedrock is not fractured
Reality is:All bedrock is fractured!
INTRODUCTION (CONT’D)
Several conceptual models for fractured flow:
1. Dual porosity
2. Single fracture
3. Equivalent porous media
REGULATORY REQUIREMENTSWhen are Bedrock Investigations Required?! Regulatory requirements:
! Ensure that groundwater at a site is suitable for current and future uses and is of adequate quality to protect adjacent water uses
! If contamination is identified or suspected, site investigations of all relevant media for each PCOC are required
! Define the nature and extent of contamination to provide information necessary for conducting a risk assessment and/or develop a remediation plan
CONCEPTUAL SITE MODEL
REGULATORY REQUIREMENTSHow to Investigate Bedrock
! No “specific” ministry guidance on bedrock investigations! Protocol 21, Water Use Determination ! Technical Guidance 6, Assessment of Hydraulic Properties for Water Use
Determinations! Technical Guidance 8, Groundwater Investigation and Characterization! Technical Guidance for Contaminated Sites. Groundwater Investigation in Site
Assessment, Golder, June 2010! Fractured Bedrock Field Methods & Analytical Tools, SABCS, October 2010
! Advice of a qualified professional should be obtained to plan and conduct a bedrock aquifer investigation
PROTOCOL 21Water Use Determinations
! Bedrock! Drinking water use
PROTOCOL 21Drinking Water Use Determinations in Bedrock
! DW automatically applies to bedrock units when:
! Current use within 500 m
! Aquifer mapped in the BC Water Resource Atlas
1.5M 1.5M
Natural ConfiningBarrier
5 m
BEDROCK CURRENT USE
SAND KMAX = 1E-5 M/S
DW
No DW
No DW
CLAY KMAX = 1E-8 M/S
DW5 m
BEDROCK MAPPED AQUIFERNO CURRENT USE
SAND KMAX = 1E-5 M/S
DW
DW
SILT KMAX = 5E-7 M/SDW
PROTOCOL 21Future Drinking Water Use Evaluation in Bedrock
! Bedrock investigations required when: ! Contamination in soil and groundwater
> DW standards extends to the bedrock surface
BEDROCK NOT MAPPED AQUIFER
1.5MSAND KMAX = 1E-5 M/S NO DW
SILT KMAX = 5E-7 M/SCONTAMINATION < DWAT BEDROCK SURFACE
!"#$%
PROTOCOL 21Future Drinking Water Use Evaluation in Bedrock
! Bedrock investigations must include:
! Hydraulic conductivity- Kgeomean if ! 6 wells- Kmax if " 5 wells
! Yield (sustain pumping at 1.3 L/min)
! Utilize nearby data:
! TG6: Bedrock data within 500 m
! Imap: Borehole Map
BEDROCK NOT MAPPED AQUIFERNEARBY SITE:Kmax = 2E-8 m/sYIELD < 1.3 L/min
1.5MSAND KMAX = 1E-5 M/S
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NO DW
SILT KMAX = 5E-7 M/SCONTAMINATION > DWAT BEDROCK SURFACE
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PROTOCOL 21MOE Borehole Mapping Project! >900 contaminated sites borehole logs in BC
PROTOCOL 21Natural Confining Barriers
! P21 definition: NCB’s are unconsolidated geological units
! Bedrock as a natural confining barrier
! Where bedrock investigations indicate that part of the bedrock unit operates as a natural confining barrier protecting the deeper more permeable bedrock unit, a site-specific director’s determination of water use can be obtained
- Detailed bedrock investigation
- Contaminant free
! Preapproval to not delineate
! Not practicable / feasible to delineate
SOME IMPORTANT CONSIDERATIONS! Requires greater evaluation of the geology and
hydrogeology e.g. lithology, porosity, structure (fracturing), hydraulic properties, flow
! May require specialized drilling and well installation methods
! Greater training and management of field staff
! Staff with specialized expertise in geology and hydrogeology
! If planned well can be completed relatively economically
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COMPONENTS OF BEDROCK INVESTIGATIONS
Main Components:
1. Geology and hydrogeology data collection
2. Data analysis
3. CSM development
4. Additional investigation (if required)
5. CSM refinement
BEDROCK INVESTIGATION GOALS
! Define the geology (lithology and structure)
! Identification of flow features (primary and secondary porosity – e.g. fractures)
" If possible, determine which fractures are flowing" Screen over the flowing fractures (if discrete fracture flow
model)
TECHNIQUES
! Desktop research (review regional geology maps)
! Map the surface geology at outcrops:! Lithology and structure (fracture identification,
fracture density, orientation - strike/dip)
! Collect rock samples for lithology
TECHNIQUES (CONT’D)
! Bedrock drilling methods:
! ODEX, Air Rotary, Sonic – all provide an “open” borehole
! Diamond drilling provides open borehole and rock core
! Core drilling good option if not performing borehole geophysics to find fractures
TECHNIQUES (CONT’D)
! Borehole geophysics:
! Temperature, resistivity, caliper logs! Acoustic and optical televiewer! Flow meter
! Good option on “open” boreholes to identify fractures
TECHNIQUES (CONT’D)
! Monitoring well installation: ! Slotted PVC, Flute Sampler, Solinst Packers/Waterloo Multilevel
Sampling, CMT, Westbay Multilevel Systems
! Hydraulic testing:! Slug tests / packer tests / pumping tests
! Lateral and vertical hydraulic head distributions i.e. flow determination
! Groundwater chemistry sampling
! Tracer studies
DATA ANALYSIS
! Determine lithology and porosity
! Define structural geology (e.g. number of fracture sets/orientations, etc.)
! Geophysical data - which fractures are flowing, directions and rates
! Hydraulic data - fracture transmissivity/conductivity / connectivity –gradients and flow directions, probable fracture model type
CONCEPTUAL MODEL DEVELOPMENT
! Geologic model
! Physical hydrogeology! Hydrostratigraphy, flow boundaries, flow directions, hydraulic conductivities,
hydraulic gradients and velocities/fluxes, recharge/discharge areas
! Contaminant hydrogeology! Source area(s), source properties (physical and chemical), release
mechanisms, transport mechanisms
BEFORE INVESTIGATION
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INITIAL INVESTIGATION
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EXAMPLE CSMS
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Unconsolidated Soil and Bedrock Contaminated Site Adjacent to Marine Environment
SUMMARY AND CONCLUSIONS
! Several circumstances when bedrock should be investigated
! Investigations can be done relatively economically
! Requires thorough evaluation of geology and hydrogeology
! Flow and transport in bedrock often behaves very differently
! Development of CSMs can assist in establishing the flow and contaminant transport regime and remedial planning
! Can be a significant pathway to a receptor
THANK YOU!QUESTIONS?
Presenter Contact Information:
Stephen Munzar MSc, PGeo Annette Mortensen, Phd, PEng
Senior Hydrogeologist / Partner Senior Contaminated Sites Officer
Core6 Environmental Ltd., BC Ministry of environment