Groundwater flows not significant | Letter to the editor

To the editor:

Here are corrections to the misinformation about Bainbridge Island’s groundwater supply published in a recent letter: The following quote is not accurate.

“… much of the water pulled from municipal wells (on Bainbridge) originates in the Olympic Peninsula, traveling in aquifers under the Sound.”

It is a fact there are similar aquifer bearing geologic units on the Kitsap Peninsula and Bainbridge Island. However, it is only inferred that these units are connected, and groundwater in the Kitsap Peninsula aquifers travels to Bainbridge aquifers below the Puget Sound uninterrupted. There is no direct evidence of a “magic underground river” flowing from the Olympic Mountains, which are approximately 30 to 40 miles to the west beyond the Kitsap Peninsula and the Puget Sound.

The city hired the U.S. Geological Survey (USGS) to evaluate the water supply, which is primarily from groundwater. The 2011 USGS report concluded the following (p. 91):

“Groundwater flow to Bainbridge Island accounted for about 1,000 acre-ft/yr, or slightly more than 5 percent of the recharge amounts.” This means that, at most, only about 5 percent of the groundwater recharge to Bainbridge aquifers could be coming from Kitsap Peninsula aquifers.

Moreover, the USGS further predicts that as growth continues to 2035, the groundwater flow direction in the deep Fletcher Bay Aquifer (which currently supplies 1/3 of Bainbridge’s drinking water) will likely reverse and move east to west, meaning the inferred 5 percent contribution from Kitsap Peninsula could be negligible.

Lastly, there is an enormous amount of pumping already in progress from production wells on the Kitsap Peninsula. Just 60 of the many Kitsap Peninsula production wells are producing approximately 30,000 gallons per minute. This extraction with projected growth severely reduces the potential migration of groundwater to Bainbridge Island.

Therefore, based on the USGS study and current Kitsap Peninsula pumping data, it is clear there is no significant contribution of groundwater from the Kitsap Peninsula — or any other off-island source — that Bainbridge residents can rely on. This is why Bainbridge is classified as an EPA Sole Source Aquifer.


Bainbridge Island

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