January 21, 2021 Sabina Montgomery-Swan
(Last Updated On: )

How to Protect the Aquifer & Your Well

Most islanders depend on well water for sustained water supply. But as the demand for water increases and more water is pumped from the aquifer new challenges arise with well water quality like sulfur taste and odour, low yields, or saltwater intrusion.

What is saltwater intrusion?

The freshwater aquifer near the coast or on islands like the Gulf Islands is becoming more at risk of saltwater intrusion. Especially in areas close to the coast with a high density of wells, the risk of seawater intrusion into the freshwater aquifer is higher.

Close to the coast, groundwater consists of a freshwater aquifer that sits above the higher density seawater with a transition zone (a mix of fresh and saltwater) in between. Mobile: click on image for description:

Saltwater Intrusion - Figure 1

Figure 1: Under non-pumping conditions there is an equilibrium established between fresh and saline groundwater at depth.

The aquifer is affected by

  • seasonal variations in groundwater levels,
  • amount of groundwater recharge from the rain, and
  • the rate of groundwater pumping.

When the pumping rate is too high or when the well is too deep, it can result in saltwater intrusion into the well.

Saltwater Intrusion - Figure 2

Figure 2:Pumping or other disturbances (e.g. sea level rise, reduced recharge) can lead to upcoming or inland movement of the freshwater-saltwater interface. If a single well is over-pumped or multiple wells are pumping, a large area of the aquifer may be impacted by salinity.

In fracture bedrock, saltwater can find its way to the well via a single fracture.

Saltwater Intrusion - Figure 3

Figure 3: In a fractured bedrock aquifer a single fracture can deliver saltwater to the well.

Once seawater intrusion occurs, changes in the aquifer may be irreversible or may take many years to recover.

Find out more about saltwater intrusion from the Government of British Colombia’s website which gives advice about Best Practices for Prevention of Saltwater Intrusion.

How can you protect your well and the freshwater aquifer?

Saline water is harmful to people with high blood pressure and can cause damage to soil and vegetation. An increase in island population or farming can lead to wells over-pumping and cause saltwater intrusion into the freshwater aquifer.

If you have issues with seawater intrusion into your well or a low water yield, find out more about the recommended well management practices and consider implementing the following solutions:

  • installing a water storage tank (cistern) and pumping in water from the well in the wet season (winter) for use in drier periods (summer),
  • installing a rainwater collection system, collecting rainwater during the wet season, and augmenting your well-water supply with rainwater during the summer.

We can help determine how big your storage tank should be to meet your water demand for gardening or hosting relatives and visitors during the summer.

1660 gallon poly cistern for water storage

1660 gallon poly cistern for water storage

Learn more about groundwater and wells on your island. Click on this link to find out if your well is located in an area at high risk of seawater intrusions.

Coast off Gabriola Island

Coast off Gabriola Island

by Grazyna Chrobok, M.Eng.,P.Eng.