July 21, 2021
Have enough water? San Juan prepares to find out, with USGS study
Heather Spaulding

Lopez Island aquifers logged some of the highest recharge rates in the county when water supply was last studied. A new study next year will provide important data for managing supply as well as planning for the future as the population continues to grow. (Amy Nelson photo © 2021)

July 21, 2021
Have enough water? San Juan prepares to find out, with USGS study
Heather Spaulding

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Over the last 50 years, San Juan County has grown from a year-round population of 3,856 to 18,040 and has attracted a growing number of seasonal visitors and part-time residents. 

As the population has grown, water usage also has increased, at times overwhelming capacity in some systems. Summer drought conditions in recent years have necessitated rationing in some larger water systems, while some wells go dry for a period each summer. (Read more: “San Juan Islands’ fresh-water supply sustainability is in question,” Salish Current, Jan. 7, 2020.) 

A study funded by the state legislature and the U.S. Geological Survey (USGS) will address a major barrier in both predicting San Juan County’s future water needs and managing current systems: the capacity of wells in the county is unknown.

Last year, the legislature appropriated $92,000 for the county’s public health department to contract with USGS to update the most recent study. That survey was completed in 2002, when the county’s year-round population stood at 14,077, and was based on field work done in 1997 and 1998.

“The total cost of the [new] study for San Juan County is $150,000, with USGS providing a share of $58,000,” said environmental health specialist Ethan Schmidt. 

The county has had some extra time to anticipate the work, Schmidt suggested: “We actually were supposed to start the program this year, but COVID delayed it.”

Dependent on rain

The study has three main focal points, Schmidt explained.

First, geologists will evaluate ground and surface water, as well as meteorological data, primarily evaporation and precipitation. 

Next, they will analyze how long it takes aquafers to recharge, as done in the 2002 study. 

Aquifer recharge refers to the amount of surface water that actually percolates downward and becomes groundwater, available to be drawn up by a water well,” Kyle Dodd, San Juan County environmental health manager, said.

The island county’s aquifers are entirely rain-replenished. While the quantity of water coming into the island systems is both limited and not fully measured, what is known is that not more than 10% of total precipitation is absorbed into water systems, Dodd said. (Read more: “Water concerns spark funding request for groundwater studies for San Juans, Guemes,” Salish Current, Jan. 21, 2020.)

Different rock, different recharge

The 2002 study estimated groundwater recharge from precipitation in glacial-deposit (crushed and mixed rock fragments) and fractured-bedrock aquifers in selected areas of the county.

The report focused on Lopez, Shaw, Orcas and San Juan islands, the largest and most populated of the archipelago, and described how soil types, temperature, amount of precipitation, water evaporation and run-off affect aquifer recharge. It noted that determining the rate of aquifer recharge from precipitation is key to determining groundwater availability.

Weather, soil conditions and vegetation were assessed on a daily basis to estimate groundwater recharge over larger areas.The study also measured atmospheric chloride deposition, precipitation, stream flow and groundwater chloride concentrations in specific areas.

1997 U.S. Geological Survey report on Lopez Island notes that the United States Environmental Protection Agency advises that water with high chloride content — one effect of rising sea levels and saltwater intrusion into aquifers — may cause high blood pressure, taste salty and corrode or discolor pipes and appliances, among other effects.

Among the four islands, the 2002 study found that Lopez has some of the highest recharge rates — from 3 to 9 inches annually in various areas — due to a large area of glacial deposits covering bedrock. In contrast, Shaw has some of the lowest recharge rates, at about an inch or less annually.

Watch this space

Updating the county’s water balance information is the third task of the upcoming study. Water balance data is calculated based on water availability and use over a period of time, Schmidt explained. This data is included in an array of groundwater reports and is key to gauging where water shortages may crop up. 

Because water is such an important commodity, citizens have shown concern about and interest in local water issues, Schmidt said. He hopes the public will take an interest in the outcome of this study as well.

Dodd said the USGS is currently working on scheduling the study and plans to complete the project by the end of 2022. 

“The islands are completely dependent on rainwater,” Schmidt said, “So it’s important to see where we are at this point in time.”

For more on water supplies in the San Juan Islands:

— Reported by Heather Spaulding

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