Conveyance inspectors Grant Miller, left, and Jim Giger coordinate sewer cleaning work at a maintenance hole in Black Diamond.
Along a quiet residential street in Black Diamond, a large industrial truck draws curious looks from neighbors on a recent sunny morning. King County Wastewater Treatment Division’s new sewer cleaning truck has arrived.
“We’re basically pressure washing the pipe at 12 to 15 feet underground,” says Jim Giger, a conveyance inspector at WTD.
The Conveyance Inspection team lowers a suction hose and jet nozzle into the sewer line to remove sediment, wipes, and other debris that can clog pipes and equipment.
Into a maintenance hole, WTD’s Conveyance Inspection team lowers a powerful hose with a jet nozzle that sprays at 110 gallons per minute, blasting away debris from inside the pipe such as sediment, gravel, wipes and tissues, and congealed fats, oil and grease. The crew also guides a separate suction hose that vacuums up the debris into the truck’s tank.
It’s all part of WTD’s routine maintenance of 380 miles of county-owned pipes that stretch across a 424-square-mile service area in King County and parts of Pierce and Snohomish counties. That day, the team was cleaning a 400-foot section of the county’s 16-inch-diameter Black Diamond sewer line.
Originally installed in 1992, the line connects flows from Black Diamond to Covington, sending wastewater from homes and businesses in those communities to South Treatment Plant in Renton where it is treated and sent as cleaned water to Puget Sound.
A 6-mile stretch of this pipe will eventually be improved as part of WTD’s Black Diamond Sewer Upgrade Project, which will increase capacity for the area’s growing population through 2070.
The Black Diamond Sewer Upgrade Project will increase capacity to serve the growing community through 2070.
In the meantime, keeping sewer pipes clean today extends their lifetime until the pipe replacement project can be completed and keeps debris from costly damages to downstream pumps and equipment.
The vehicle, outfitted to handle a wide range of sewer pipe sizes in our regional system — anywhere from 2.5 inches to 9.5 feet wide — can clean up to 600 feet of pipe at a time without interrupting service or requiring a temporary bypass pipe to be installed.
Unlike traditional vacuum trucks that rely on large amounts of fresh water, the custom-built GapVax Recycle Sewer Cleaner truck uses up to 300 gallons of filtered wastewater to do its work. A built-in screening system filters debris from the wastewater (mainly water with a fraction of impurities) so that the truck can operate for longer periods before it needs to be emptied out at one of the King County facilities.
Conveyance inspector Grant Miller uses a handheld remote control to maneuver the recycler truck’s powerful cleaning system with precision.
“This is an amazing piece of equipment,” says Giger, who has worked with traditional vacuum trucks for 15 years. “This truck runs much quieter, gets the job done faster, and takes out most of the back-breaking labor. The hardest part now is lifting the 125-pound maintenance hole lid to get into the pipe!”
The Sewer Cleaning Program is an added service for the Conveyance Inspection team, which previously relied on contractors to do this vital work, while focusing on surveying and repairing these lines.
“We’re excited to build on our team’s success by taking on maintenance of our own pipes and structures,” says Mike Sands, WTD’s Conveyance Inspection supervisor. “Over the long term, this will help us reduce contractor and operational costs while gaining greater transparency and predictability across our system.”
Operating the truck is a passionate crew eager to take on the challenge. Grant Miller, a conveyance inspector, joined WTD two years ago at age 19. He attended a two-week hands-on training at the truck manufacturing facility in Pennsylvania, where he learned the ins and outs of the equipment. Now, Miller maneuvers the cleaning system with precision using a handheld remote control.
“Helping launch this program has given me a sense of ownership and pride,” says Miller. “I’m grateful for this opportunity to build my expertise and to train others on how to operate and maintain the truck.”
WTD’s Conveyance Inspection team sets up along a residential street in Black Diamond with their new sewer cleaning truck.
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