The culprit behind Dockton Water’s 400,000 gallon mystery leak: A maple tree

A water leak last week on Maury Island that likely lost more than 400,000 gallons of water had an unlikely culprit: A tree.

That’s according to Dave Stoltz, general manager and operator of the Dockton Water Association (DWA), one of Vashon-Maury’s seven large Group A water districts.

On Tuesday, March 19, Stoltz and fellow operator Skylar Hornick discovered that a leak somewhere in the Dockton water system was rapidly losing thousands of gallons of water.

Hornick had discovered the leak during his routine daily check of the water silos. The silos had dwindled from 36 feet, an expected amount Monday morning, to only nine feet on Tuesday morning.

Stoltz said that means that over around 24 hours, the silos had lost nearly 300,000 gallons of water.

The 475-foot Sandy Shores well is Dockton’s backup water source, which usually shuts down periodically in the winter to save on chlorine and electricity. The primary source is Dockton Springs, a field of 26 shallow (10-12 feet deep) well-points.

The flow from those well points collectively reaches about 85 gallons per minute of water, which is chlorinated and then collects in a basin before being pumped out to residents. But Dockton Springs can only be operated an hour at a time, Stoltz said, and needs an hour in between pumping for the contact basin to fill up again.

So on March 19, when the leak was draining well over 100 gallons per minute — closer to 150, Stoltz said — and Sandy Shores was offline, the water was draining faster than Dockton Springs could hope to replace it.

“As you can imagine, 100 gallons a minute, every other hour, is not cutting the cheese,” Stoltz said. “Couple that with regular demand (for water) out there. Yeah, it took the 300,000 gallons out really quick.”

Stoltz sent Hornick to turn on Sandy Shores to get an additional 95 gallons per minute into the system — giving them enough flow to barely begin refilling the silos. In the meantime, the Water Association worked with Voice of Vashon and VashonBePrepared to alert homeowners in the area of the emergency and ask them to limit their water use.

Then it was time to go leak-hunting, checking for obvious signs of water coming out of the ground.

“He and I are driving around, looking,” Stotlz said. “With that much water gone, you think ‘Okay, it’s going to be really obvious where this break is at.’ “

But by the end of Tuesday, they’d found nothing. Desperate to find the leak, they even started reading meters at homes where they knew there weren’t residents living there full-time. No dice.

By late Tuesday afternoon, “We just finally had to give up … and say, we’ve got to regroup tomorrow and come up with a different plan.”

The big clue came Wednesday morning when Hornick, checking a four-pump booster station on 99th Avenue, discovered that Pump 3 — which gets little use this time of year — had been running for 22 hours straight.

“That’s a pump that normally doesn’t run this time of year, and if it does, it’s very, very, very little,” Stoltz said. “That told us where to look for the problem.”

So the duo took off to the south end of 99th Avenue toward 285th Street and started turning valves, hearing rushing water.

They reached the dead end of the road at 288th Street, where a fire hydrant and sample station sit atop “a gnarly cliff” overlooking Maury Island’s southern tip.

They turned a valve there. Nothing. Where on earth was the leak?

Stoltz backed up to the corner of 97th and 288th, where a large maple tree sat next to the valve, far off the road and out of the way.

He checked the valve there, heard gurgling, and “I knew, instantly, that the leak was there,” Stoltz said. He kicked a few leaves off the ground and saw the water coming out of the ground six feet away from the valve.

The area was “really sandy,” ensuring that the water slipped straight into the ground, unseen and undetected. (Sandy soil absorbs less water than soils made mostly of clay or silt and thus drains water faster.)

“Even walking that area, you’d never see that water, ever,” he said. “It was a perfect storm, basically.”

The maple tree had quietly grown over the top of a water extension there, and broken a plastic fitting in a two-inch water line feeding a customer meter.

However long the tree had been slowly growing there, the relentless forces of nature had finally forced their way through that Tuesday.

Stoltz slowed the leak by turning down the nearest valve, called in for permission to perform emergency digs, and turned to island contractor Frank Zellerhoff, Jr. to fix the leak.

By Wednesday afternoon, the leak had been isolated and the silos were refilling. By 5:30 p.m. on Thursday, the leak was finally, fully, fixed, Stoltz said.

Many water leaks are caused by tree roots growing around and eventually breaking water lines, Stoltz said. But that’s not the kind of problem that’s on the forefront of most homeowner’s minds, and many don’t even know where their water lines are, he said.

“These things are always an afterthought, right?” Stoltz said. “It’s out of sight, out of mind. It’s always like this with water, power, or even your sewer. … You don’t think about those things at all until it’s a problem.”

So there’s a lesson to take away from the experience, he said, it’s this: “Do not plant things in and around water lines, period. … If you’re gonna plant a tree, and you know you got a water line in that area, plant it at least 10 feet away from the waterline.”

And in general, homeowners should document and map out their water lines, take pictures when they’re installed and keep track of how their system works for future generations, he said: “Hand that information down, because it’s invaluable.”

Stoltz estimated that altogether, the system lost around 400,000 to 450,000 gallons of water. But the silver lining is that the break affected was in a place that couldn’t damage any homes, and where the water could easily drain. And the entire ordeal helped Stoltz update and correct errors in his water system map which frustrated the initial search for the break.

Another silver lining: Homeowners voluntarily reduced their water usage when asked, Stoltz said.

Dockton Water Association board president April Wilkinson “was fantastic” in reaching out over social media and with Voice of Vashon to warn people of the emergency, he said.

“Once the word got out like that, we made a little bit of gain before we even found that water leak,” Stoltz said. “That tells me that people were listening and doing the right thing.”