Seatwater Intrusion and Groundwater Conservation-Webinar Presentation

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Seawater Intrusion and Groundwater 
Conservation
Islands Trust Webinar -March 5, 2025
Jessica Doyle, P.Geo, BSc
Water Protection Section Head
Colin McKenzie, P.Geo, BSc
Regional Hydrogeologist
Nicole Fulcher, MSc
Groundwater Protection Officer

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Outline
•Introductions
•Seawater Intrusion
•What is SWI
•Why it matters (why people should 
care)
•What we know about SWI 
•What can we do (prevent, manage)
Groundwater Conservation
•Why?
•Conservation practices
•Storage
•Rainwater Harvesting
•Monitoring and Sampling
•Resources
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Seawater 
Intrusion

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What is Seawater Intrusion?
•Occurs when saline water is drawn 
into a freshwater aquifer
•This can affect one well or multiple 
wells in an area
•Can be from natural processes or 
caused by human activities
•Sea level rise
•Storm surges
•Pumping
•Overuse
•Leaks
•Freshwater floats like a lens above 
seawater with a transition zone 
between the freshwater and seawater

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What is Sea Water Intrusion?

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Transition Zone
https://pubs.usgs.gov/fs/old.2000/fs-057-00/
https://pubs.usgs.gov/circ/2003/circ1262/
Fun fact: Seawater is denser than freshwater due to the salinity, this results in 
more complex flow dynamics 
 -> density-dependent flow

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Activities that can Contribute to Intrusion
•Groundwater 
pumping
•Dewatering 
excavations
•Decreased 
groundwater 
recharge
•Exacerbated by 
climate change 
and sea level 
rise 
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Coastal Island Vulnerability
•High density in certain areas
•Small parcels
•High volume of well users close to the 
coast
•Higher risk of storm surges and floods
•Less recharge capacity
•Sea level rise
•Peninsulas
•Bedrock aquifers
•Increased seasonal use during summer 
from visitors (during drought)
•Low to moderate slope
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Image Credit: Klassen and Allen 2016

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Why does Seawater Intrusion Matter and why 
Should I Care?
•We are seeing more wells with sea water intrusion & at-risk areas being developed
•Changing climate is causing more impacts (i.e. deepening groundwater levels due to longer 
drought periods)
•Has impacts to well owners and operators
•This can be very difficult and expensive to reverse (well may have to sit, trucking in water, 
additional monitoring and testing...)
•It is a growing issue 
•Well operation causing sea water intrusion violates Water Sustainability Act S.58 (any well 
use)
•Can affect single wells or wells in an area
http://rdnwaterbudget.ca/islands/datagaps/

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How Can It Affect Well Owners/Operators
•Health risks to those at risk (hypertension, elderly, young children)
•Impacts to property values
•Possible damage to plumbing
•Possible damage to garden and landscaping or not being able to use 
water for watering (risks to your food security)
•Costs of trucking and storing freshwater if needed
•Affecting the aquifer and others that use it like your neighbours
•Impacts to your water source can be complicated, expensive and 
timely to reverse

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Seawater Intrusion & Drinking 
Water
•Aesthetic objectives
•Chloride ≤ 250 mg/l
•Sodium ≤ 200 mg/l
•TDS of ≤ 

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