Seattle Press on Line - Broadview Sewer Repair Hits a Rock in Carkeek Park

Broadview Sewer Repair Hits a Rock in Carkeek Park

By Jeff Boone

Seattle Public Utilities at work laying pipe across Venema Creek in Carkeek Park.

Oct 06, 1999 -- The second part of a $1.02 million sewer repair project, intended to keep sewage in the pipe and out of Carkeek Park's creeks, literally got stuck in a rock last month, postponing completion of the project until next year. Seattle Public Utilities' Broadview/9th Avenue NW sewer repair project, announced in March and expected to be completed by July 7, is now in its sixth month.

The project was already behind schedule when Dames & Moore, a contractor in the employ of Seattle Public Utilities (SPU), finished replacing sewer pipes in the Broadview neighborhood above Carkeek Park and started the second phase of the project, the installation of a parallel line beneath Venema Creek. In order to lessen construction impact to Carkeek Park, SPU and Dames & Moore decided to tunnel beneath Venema Creek, employing a method known as underground directional drilling. It was, according to SPU, the fastest and most cost effective method. (The Venema Creek line will separate the eastern half of the Broadview basin from the western half. This separation will redistribute the load traveling downhill through the park to the Metro pumping station, preventing sewage overflows in the park and backups into Broadview basements. The park's pumping station collects sewage from northwest Seattle neighborhoods and pumps it to the West Point treatment facility in Discovery Park.)

Dames and Moore awarded the drilling contract to a sub-contractor, HDD. Drilling started the week of July 5, two months later than anticipated. Within a week, vibration from the drill created a sinkhole in the steep slope beneath the park's visitor center, on the hill adjacent to the main road into the park. Despite several soil borings, neither SPU or the two contractors detected wet sand, which was present beneath the topsoil. Nor did the borings indicate the amount of rock present in the park. The collapse of the sand layer created a 40-foot deep, 20-foot wide sinkhole.

Drilling continued.

On July 20, at 11:15 a.m., a "frackout" occurred. The drill's vibration collapsed sand beneath the bottom of Venema Creek, opening a hole in the creek bottom. Bentonite and drilling debris spewed into the creek. (Bentonite is a fine sediment used to lubricate a drill. It is also used as a water sealant; Bentonite expands and solidifies when it comes into contact with water.)

It was purely a coincidence that a visitor to the park, Gary Holcombe, who also happens to be president of the Carkeek Park Advisory Council, and Erin Powell, a park employee, witnessed the spill. The mocha color of the creek alarmed the pair, and, aware that drilling was in progress, indicated the cause. The pair found the drilling team and told them to stop. The drilling continued for twenty minutes while HDD verified that the drill had put a hole in the creek bottom.

The creek was cleaned up, and drilling resumed.

In late August, the drill hit a rock and stuck. Drilling stopped.

"They could have asked the neighbors," said Gloria Butts, a member of the Carkeek Park Advisory Council. "We know all about the cobblestones in the ground around here. They could come and look at the boulder in my yard. But," added Butts, "this project started out with the right intent."

"We're sorry," said Tim Kroll of SPU.

SPU has abandoned directional drilling and will now cut a trench through the park and Venema Creek to finish the first half of phase two, which means pipe as far as the Venema Creek manhole. However, SPU has to be out of the creek by October 15 because spawning salmon return to the creek around Thanksgiving. That does not leave SPU enough time to bring the Venema Creek line all the way to the pumping station.

The real problem lies with the increased pipe capacity in the Broadview neighborhood and the approaching monsoon season. According to Tim Kroll of SPU, Broadview's new and bigger pipes will expedite sewage flow down the hill into the park. And flow from Seattle's fast-growing northwest neighborhoods has only increased; in 1988, dry season low flow was half a million gallons daily, today it is 2 to 3 million gallons daily. SPU will apply Visqueen to the lids of the manholes and bolt them down, optimistic that this battening of the hatches will prevent the sewage overflows that plagued the park from November to March. Members of the Carkeek Park Advisory Council have adopted a wait-and-see attitude, remembering that last winter's surcharges blew manholes sky high nine times, decorating the boughs of cedar and fir with tampons and toilet paper.

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