Vashon appears to have enough water to meet Islanders’ needs over the next several years, but bigger questions remain about both the quality of that water and whether there’s enough to fully support salmon, birds and other wildlife, a far-reaching report by King County shows.

The report, seven years in the making, reflects a major milestone in the county’s understanding of the Island’s hydrology, said Jim Simmonds, supervisor of the Water Quality and Quantity Unit in the county’s Department of Natural Resources and Parks.

Its findings — a number of scenarios developed from years’ worth of data and with the help of sophisticated modeling tools — show Vashon’s groundwater levels will like decline very modestly over the next several decades due to population growth and the expected impacts of climate change.

Those findings could be seen as encouraging, Simmonds said.

“The amount of water that we’re using or plan on using Islandwide isn’t so much that we expect to run out of water,” Simmonds said.

But the results also give rise to other questions, he added. First, the model can’t pinpoint where the declines will occur, suggesting some private wells could run out years from now while other wells remain flush. What’s more, the model shows modest declines in summertime stream levels, which could affect animals, plants and the Island’s overall ecology, he said.

“At a macro level for the Island, it’s not about whether there’s enough. It’s about balance,” said Simmonds, who lives on Vashon.

A one to two percent decline in stream flow in Judd Creek, for instance, might make salmon restoration more difficult, he noted. “Some might say that’s no big deal. Others might say that’s a huge deal,” he said. “It’s a very subjective issue.”

The report, funded with money from surface-water management fees, was presented last week to the Vashon-Maury Island Groundwater Protection Committee, a group of Islanders empaneled to work with the county to protect Vashon’s groundwater.

In a lively give-and-take at the committee’s quarterly meeting last week and in interviews later, members said the report gives the Island an important look at an issue many have not fully understood. Some also said its findings were encouraging, while others noted that it underscores the need for their committee to begin exploring the harder issue of the quality of the Island’s water and how that might change over time.

“When you look at these results, they’re rather comforting,” said John Gerstle, a member of the committee. “There’s no catastrophe predicted out of this. It does show some degradation to stream flows, which can be harmful to fish. But there’s no show stopper.”

But Gerstle, noting that water quantity has long been a subject of spirited debate on the Island, said the report doesn’t mean it’s time to change Vashon’s restrictive zoning and begin aggressive development.

The 10 different scenarios in the report included ones where the Island experienced a population growth of 1,000 over the course of several years and others with an increase of 2,000, according to Simmonds.

“Implicit in this model is that our Island stays rural,” Gerstle said.

Michael Laurie, a water conservation expert who is stepping down as chair of the committee, concurred with Gerstle, adding that the report is only the beginning of a much bigger discussion.

“We need to think about not how we preserve what we have but how to create a vision of what is a sustainable Vashon and what kind of changes we think are needed to create a more sustainable Island,” he said. “When you look at it that way, the report doesn’t really give us any good solid answers, because we need to dig a little deeper.”

The report builds on a groundbreaking study written 25 years ago by J.R. Carr, known as the Carr Report, which demonstrated that the Island’s water supply comes from one aquifer and that it is recharged only by precipitation.

That report, with its implicit recognition that Vashon’s water supply is a limiting factor on the Island, became a touchstone for some who wanted to slow Vashon’s development; the county later looked to it when it rezoned Vashon to its current scenario, allowing only one house per five or 10 acres across much of the Island, said Jim Garrison, an Islander active in water resource issues.

But the Carr Report didn’t go far enough, because it looked only at groundwater levels, not the more complex issue of the Island’s overall hydrology and the interplay between groundwater and surface water, said Donna Klemka, another member of the committee.

Klemka, who’s been working on groundwater issues for 20 years, called the latest study “a significant milestone.”

“This is evidence that we’ve accumulated enough data to be able to say what our hydrological system looks like underground. And it demonstrates most intelligently the connection between groundwater and surface water,” she said.

“We can now say what science is telling us,” she added. “We’re not guessing.”

Like other committee members, she added that more work now lies before them as they and others work to understand the harder issue of the Island’s water quality.

“We’ve known since the Carr Report that our first constraint will probably be water quality,” she said.

Nitrates from failing septics, livestock manure and natural sources are a growing issue on the Island, she added.

“We’re way below the state level. But the question for us as a community is: Do we want to pollute up to the state level? And how do we stop the trend from continuing upwards?” she said. “Once this train gets going, how do you ever stop it? That’s a huge question.”

More information

The Vashon-Maury Island Groundwater Protection Committee meets four times a year. Its next meeting is Jan. 28. The panel’s members are appointed by the King County Council. The county is currently looking for someone to represent farming interests on the committee. Contact Laurence Stockton at Laurence.Stockton@kingcounty.gov with suggestions.

To read the full report on Vashon’s hydrology, visit www.kingcounty.gov/environment/waterandland/groundwater/management-areas/vashon-maury-island-gwma/vashon-island/WRE-Phase2-modeling-report.aspx.