Environmental Tracers to Delineate Recharge and Flow ......Environmental Tracers to Delineate...
Transcript of Environmental Tracers to Delineate Recharge and Flow ......Environmental Tracers to Delineate...
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Environmental Tracers to Delineate Recharge and Flow Processes in the Gibsons Aquifer, British Columbia
Presented by: Jessica Doyle, UBC M.Sc. Student
Water Technologies Symposium April 12, 2013 – Fairmont Banff Springs
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Presentation Overview Project Team Town of Gibsons and Study Objectives Approach to Aquifer Mapping Study Conceptual Hydrogeological Model Environmental Tracers Numerical Groundwater Modeling Future Groundwater Scenarios Aquifer management and sustainability
April 12, 2013 Water Technologies Symposium 2013
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Project Team Waterline Resource Inc.
Project Development and Management University of British Columbia
Environmental Tracer Study Numerical Modeling Supervisors: Uli Mayer and Tom Gleeson (McGill)
Gordon GroundH2O (Gibsons) Community Outreach
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Gibsons, British Columbia Located on the Sunshine Coast, BC Humid, Mediterranean-like climate 1500 mm precipitation/year
70% during winter months Snow at high elevation
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Google Earth 2012
Howe Sound
Strait of Georgia
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Home of The Beachcombers!
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Town of Gibsons Voted “World’s Most Livable Town” – 2009
International Awards for Liveable Communities. Award program endorsed by the United Nations.
Voted “World’s Best Drinking Water” - 2005 Berkley Springs International Water Tasting Contest
4,300 residents 2/3 rely on groundwater Untreated
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Plan for Growth Bedroom community to
Vancouver; Expected population increase
from 4,300 to 10,000 by 2026; 73% (7,300) supplied by
groundwater; Demand up from 2,000 to 4,200
m3/day.
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Source: Town of Gibsons Official Community Plan, Neighbourhood Areas, Oct. 2003
Gospel Rock Neighborhood Plan Area
Harbour Plan Area
Upper Gibsons Plan Area
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Aquifer Mapping Study - Approach Phase 1 (2011 – 2013)
Data Compilation, field work, initial conceptual model
Phase 2 (2011-12): Refine conceptual model UBC Involved (NSERC)
Environmental Tracers Numerical Modeling
Community Outreach Report (April 2013)
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Topo and Study Area Boundary
April 12, 2013 Water Technologies Symposium 2013 Source: Elevation data from Sunshine Coast Regional District, 2012
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Bedrock Geology
Source: Bedrock Geology: (Journey and Monger, 1997)
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Source: Surficial Geology Modified from (McCammom, 1975)
Surficial Geology
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101 wells in BC MOE database
15 monitoring wells
15 Geophysical Soundings
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Source: Surficial Geology Modified from (McCammom, 1975)
Geo-model Input
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Cross Section A-A’ (NW-SE)
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3D Conceptual Model: Bedrock Layer
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Mount Elphinstone
Lower Gibsons
Gibsons Creek
Chaster Creek
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3D Conceptual Model: Pre-Vashon (Aquifer)
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Gibsons Creek
Lower Gibsons
Chaster Creek
Mount Elphinstone
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3D Conceptual Model: Vashon Till/Basal Capilano
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Mount Elphinstone
Gibsons Creek
Lower Gibsons
Chaster Creek
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3D Conceptual Model: Capilano Layer
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Mount Elphinstone
Gibsons Creek
Lower Gibsons
Chaster Creek
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Aquifer Extent
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UBC Research Use environmental tracers to delineate recharge locations and
processes into the Gibsons aquifer Integrate tracer results into a numerical groundwater flow
model to calculate recharge rates Model future groundwater scenarios to predict and guide
sustainable groundwater use for future growth
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Environmental Tracers Groundwater samples
analyzed for: Chlorofluorocarbons (CFCs) Sulfur-hexafluoride (SF6) Tritium (3H) Noble Gases (He, Ne, Ar, Kr, Xe) Stable Isotopes (18O, 2H)
Limitations with CFCs/SF6 method Discuss noble gas, tritium results
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(Newman et al., 2010)
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Atmospheric Noble Gases
Concentrations based on Henry’s Law; Function of temperature, elevation (pressure) and salinity at time of
recharge
Take measured gas concentrations to solve for unknown recharge parameter – temperature Assume: Salinity = 0 mg/L, Elevation (ground elevation at each well).
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Naturally occurring; Dissolve into
groundwater at time of recharge;
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Tritium/Helium Dating Tritium (3H) in atmosphere
from thermonuclear testing in the 1950’s and 60’s
3H decays to tritogenic helium (3He) 3He determined in noble gas
analysis t1/2 = 12.3 years
3H/ 3He ratio = apparent groundwater age
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WL10-01 MW06-2 WL10-02 MW06-1
TW #2 TW
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“Mountain Block”
“Bench”
3H/3He Ages and Noble Gas Temperatures
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Mountain Block Recharge (MBR) Tracer results suggest significant amount of MBR
How much? How do we assess recharge along the mountain where
there is no physical information? No wells, drill holes, bedrock permeability info, water table
depth, etc…
Approach Noble gas temperatures to estimate recharge elevation Recharge elevation as a calibration target in numerical
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Elevation vs. Temperature
MW06-1A
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MW06-2B
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Chaster
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Strata
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Elev
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Max recharge elevation Min recharge temp
Min recharge elevation Max recharge temp
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Atmospheric Lapse Rate (-6.5˚C/1000m)
2˚C below atmospheric lapse rate
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Recharge Elevation Calibration Targets
Recharge ranges used in model calibration process
Also calibrated to observed water levels
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Elev
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Upper Mountain
Mid-Mountain
Bench
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MODFLOW Model Domain
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N 45˚
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MODFLOW Model Grid
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N 45˚
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Boundary Conditions
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Zones of Hydraulic Conductivity
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Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
N 45˚
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Hydraulic Head Calibration
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Recharge Elevation Calibration
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Groundwater in the Gibsons Aquifer consists of two recharge end members: 55% MBR
Pre-modern, cold (>50 years, ~5C) that recharges high up on Mt. Elphinstone flows through bedrock fractures and into the aquifer
45% Bench Modern, warm water (
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Can the Gibsons Aquifer Supply Enough Water for Future Growth – Sustainably? Predictive modeling shows that the Aquifer can
sustainably supply up to 4,200 m3/day, BUT Current wells can only supply up to 3,500 m3/day based
on calculated sustainable yield If any climate change or variability leads to more than
5% decrease in recharge– begin to deplete aquifer, May lead to salt water intrusion
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Conclusion Environmental tracer results improved our understanding
groundwater recharge to the Gibsons Aquifer – MBR! Also provided calibration targets in mountain where no physical
data exists
Numerical modeling suggests two end-members of recharge; 55% MBR 45% Bench
Predictive modeling suggests that the Gibsons Aquifer can support growth to full built out, however the Town needs to take measures to decrease water use if climate change or variability results in decrease recharge
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Thank You - Questions?
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Contact: [email protected]
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Aquifer Recharge
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Where ? Capilano Fluvial
deposits? Recharge
Windows - creeks, holes in the Vashon Till
Fault system ? How much?
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Water Chemistry
Group 1: Gibsons Aquifer, Gibsons and Chaster Creek
Group 2: Capilano Aquifer and Charman Creek
Group 3: Upper Reaches of Gibsons Deep aquifer
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Stable Isotopes
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δD v
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δ18O vs VSMOW
Global Meteoric Water Line
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STRATA
CHASTER
FDLW
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Charman Creek
Chaster Creek
Gibsons Creek
Springs
Victoria Precipitaion (20 masl)
Saturna Island Precipitation (178 masl)
Estimate of Local Meteoric Water Line
Charman
Groundwater
Chaster Creek and Gibsons Creek
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Numeric Engines MODFLOW – 2000
Visual MODFLOW 2009.1
Finite Difference Solver
PCG-2 Steady State – long
term averages
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http://wi.water.usgs.gov/glpf/images/cs_st_model_modflow_grid.jpg
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Hydraulic Head Calibration
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Recharge Elevation Calibration
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Town of Gibsons Growth and Future Groundwater Use
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4,535 4766 5009
5,657
6,400
7,242 7,034
8,559
10,743
2,601
2,675 3,140
3,732 3,906 4,182 4,473
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1981 1986 1991 1996 2001 2006 2011 2016 2021 2026
Low Growth (1%)
Medium Growth (2.5%)
High Growth (4%)
Measured Population by CanadianCensus
Current = 2,000 m3/day
3,000 m3/day
Full Build-Out = 4,200 m3/day
Environmental Tracers to Delineate Recharge and Flow Processes in the Gibsons Aquifer, British Columbia Presentation Overview Project TeamGibsons, British ColumbiaHome of The Beachcombers!Town of GibsonsPlan for GrowthAquifer Mapping Study - ApproachTopo and Study Area BoundarySlide Number 10Slide Number 11Slide Number 12Slide Number 133D Conceptual Model: Bedrock Layer3D Conceptual Model: Pre-Vashon (Aquifer)3D Conceptual Model: Vashon Till/Basal Capilano3D Conceptual Model: Capilano LayerSlide Number 18UBC ResearchEnvironmental Tracers Atmospheric Noble GasesTritium/Helium Dating3H/3He Ages and Noble Gas TemperaturesMountain Block Recharge (MBR)Elevation vs. TemperatureRecharge Elevation Calibration TargetsMODFLOW Model DomainMODFLOW Model GridBoundary ConditionsZones of Hydraulic ConductivityHydraulic Head CalibrationRecharge Elevation CalibrationModeling ResultsCan the Gibsons Aquifer Supply Enough Water for Future Growth – Sustainably?ConclusionThank You - Questions?Aquifer RechargeSlide Number 38Stable IsotopesNumeric EnginesHydraulic Head CalibrationRecharge Elevation CalibrationTown of Gibsons Growth and Future Groundwater Use