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  • Writer's pictureSimona

Managing Whidbey Island's Aquifers: Preventing Saltwater Intrusion


A significant portion of newcomers to Whidbey Island have little to no prior experience living with a well. Apart from the City of Oak Harbor and NAS Whidbey Island, which receive their drinking water through pipelines from the Skagit River (fun fact: it passes beneath the Deception Pass bridge), the remainder of the island relies on accessing our narrow island's network of underground aquifers.


WHAT IS AN AQUIFER?

Imagine an aquifer as a reservoir of freshwater, similar to a saturated sponge. Below the earth's surface, often reaching considerable depths, these reservoirs possess sufficient permeability to absorb incoming water seeping through layers of soil, rock, and gravel. Moreover, they can retain ample water to prevent depletion. Perhaps a visual representation would clarify this concept...

Illustration depicting an aquifer underground, resembling a sponge filled with freshwater, surrounded by layers of soil, rock, and gravel. The aquifer is shown as a reservoir with water seeping into it from above.

The issue with the above illustration concerning Whidbey Island is that we aren't situated on bedrock, and our island lacks substantial lakes. Instead, we're encompassed by saltwater, which poses a genuine concern for saltwater intrusion when excessive freshwater extraction from an aquifer occurs hastily.


WHAT IS SALTWATER INTRUSION?

Saltwater intrusion is when saltwater infiltrates an aquifer, compromising the freshwater supply. This intrusion happens when excessive water is extracted from the aquifer too quickly. The decrease in pressure draws in saltwater from the nearby shoreline, leading to the contamination of freshwater. Refer to the graphic below for a clearer depiction.

Illustration demonstrating saltwater intrusion into an aquifer, with saltwater infiltrating the freshwater reservoir due to excessive extraction. The decrease in pressure draws saltwater from nearby shorelines, contaminating the freshwater supply.

To mitigate saltwater intrusion, a method involves gradually and consistently extracting freshwater from the aquifer, storing it for times of increased demand, such as summer. This approach prevents excessive suction from the aquifer, which could draw in saltwater. Visualize it as delicately sipping from a straw inserted into a freshwater pocket—if you exert too much force, it could inadvertently draw in salt water from the surrounding sea.

Another crucial measure involves regularly monitoring wells across the island and gathering sufficient data to identify signals indicating wells at higher risk of saltwater intrusion compared to others.


In Island County, we were immensely fortunate to have Doug Kelly, a full-time hydrogeologist. Doug occupied a rare and vital role, instrumental in developing a data collection system and monitoring program. This initiative offers Island County residents early indicators if their well faces risks and provides actionable steps to avert potential issues.


Island County's website hosts an incredible resource known as ICGeo, a comprehensive database accessible to everyone. By activating the well layer, users can pinpoint the locations of all wells on Whidbey Island. Within a few clicks, users can generate a report, aiding in informed decision-making regarding Whidbey Island aquifer management. Users can generate the report hyperlinked with various supplementary details, complemented by an intuitive color-coding system. This allows for a swift and thorough assessment of water health status.

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Excellent article

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