Salt Water Intrusion in Coastal Aquifers · Indicator parameters of SWI 4. What is happening in our...
Transcript of Salt Water Intrusion in Coastal Aquifers · Indicator parameters of SWI 4. What is happening in our...
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Salt Water Intrusion in Coastal AquifersMarch, 2015L. Pilgrim, P.Geo.
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Agenda
1. What is SWI?2. What are the causes?3. Indicator parameters of SWI4. What is happening in our region?5. Conclusions
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What is Salt Water Intrusion?
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Natural Conditions of Groundwater Flow
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SWI
Process where seawater infiltrates a coastal aquifer impacting the groundwater
Highly due to density
Greatly affected by the characteristics of the aquifer
Direct relationship between recharge rate and SWI
Saltwater - fresh water interface
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SWI
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What Causes Salt Water Intrusion?
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SWI
Factors that affect the saltwater - fresh water interface:
1) Sea level rise2) Subsidence3) Decrease in recharge4) Increase in pumping/extraction
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Causes – Global Scale
Rising of Sea Water Level► Caused by global warming, resulting in increase in the quantity of salt
water putting pressure on fresh water aquifers
Change in Precipitation► Slower recharge rate to replenish the amount of fresh water in the
aquifer, making it more susceptible to the inland movement of salt water
Climatic ChangesCO2 emissions + surface water temperature = evaporation rate
(decrease in recharge)
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Causes – Regional Scale
Soil Type► permeability
Bedrock Type► fractures
Thickness of water bearing zone
Topography► Areas with moderate slope potentially more susceptible
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Causes – Local
Increase Consumption of Water► Increase in fresh water demand (groundwater and surface water)
Pumping► Increase in fresh water demand and longer duration of pumping from an
aquifer increases the potential for drawing in salt water along coastal aquifers
Agriculture/Processing► Human activity requiring an abundance of fresh water
Increase in Development► Paved surfaces etc., prevent the natural recharge of an aquifer► Greater potential for impacts► Aging infrastructure may lead to impacts infiltrating into potable wells and
pumping systems
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SWI induced by pumping conditions
SWI
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Causes
Saltwater can contaminate freshwater aquifers when one or more of the following mechanisms occur:
► Lateral or horizontal intrusion occurs when excessive water withdrawals from an aquifer cause saline water from the coast to move inland
► Vertical movement or upconing of saltwater can occur near a discharge well when water moves toward the wellhead and saltwater in the deeper aquifers rises up
► Cross-aquifer contamination can be caused by wells that are open to multiple aquifers or have casings that have been corroded or broken.
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Indicator Parameters
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Indicator Parameters
Need an understanding of the aquifer conditions► Bedrock and surficial geology► Transmissivity
Need an understanding of the well construction► Screen placement► Distance from coast► Groundwater elevation
Need to obtain baseline monitoring data!!!!!
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Indicator Parameters
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Parameter CDWQGChloride > 250 mg/L
Bromate 0.01 mg/L
Sodium < 200 mg/L
TDS < 500 mg/L-
Conductivity -
► Transition zone typically characterized by: TDS = 1000 – 35,000 mg/LChloride = 250 – 19,000 mg/L
► Typical Bromide concentration in seawater is ~ 45-65 mg/L.
► Aesthetic Objectives
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Indicator Parameters
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Parameter CDWQGChloride > 250 mg/L
Bromate 0.01 mg/L
Sodium < 200 mg/L
TDS < 500 mg/L-
Conductivity -
Cl/Br ratio► Chloride
► Essential element► Highly mobile► Very soluble and not easily
removed from potable water supplies
► Bromide► Could be a result of SWI,
dissolution from sedimentary bedrock or human activities/discharge
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Groundwater Monitoring
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► Strong correlation between conductivity and chloride
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What is Happening in Our Region?
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Atlantic Canada
Atlantic Canada has the largest length of populated coastline in Canada
Minimal studies conducted to date
No regional trends to date
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Atlantic Canada
Warmer temperatures and more precipitation expected, affecting the recharge rate
Sea level rise is projected to be~ 60 cm by 2100
Land is subsiding in Atlantic Canada by ~20 cm/100 years
Will result in vulnerability along the coastline and to infrastructure
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Atlantic Canada
Regional Adaptation Collaborative (RAC)► Federal program focused on climate change ► Initiative for all provinces and territories
Atlantic Climate Adaptation Solutions Association (ACASA)► Focus on Atlantic Region ► Collaborative effort between 4 Atlantic Provinces► Different government departments and universities► Also studying effects on coastal erosion, flooding and groundwater
management
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Atlantic Canada
New Brunswick► SWI due to over pumping in coastal aquifers (Point du Chene, NB)► SWI due to over pumping for processing
Prince Edward Island► Vulnerable to SWI due to natural conditions including subsidence, increased
tidal action and large estuaries
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Atlantic Canada
Newfoundland► SWI case study on southwest coast of NL conducted by NLDEC► Provide baseline data
Nova Scotia► ACASA conducted studies in Pugwash and Wolfville, NS.► NS has significant groundwater flow towards the coast ► Sandstone bedrock, low permeability► Pugwash - salinity likely due to dissolution of gypsum► Wolfville - salinity likely due to human impacts
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Concluding Statements
Increase risk of SWI due to demand for freshwaterRequires a better understanding of existing conditionsRequires more monitoring and studyExpected to become a more significant issue with climate change.Need to plan for the future!
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Contact us
Lynn Pilgrim, P.Geo.Environmental Geoscientist
Amec Foster WheelerFredericton, NB
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