Sewage erupting 18 to 24 inches above ground near Lake Union waterfront brought City of Seattle crews on the double. The spill flowed over the curb, across the narrow street and down the steep hillside to flood neighboring yards.

After dye testing by Public Utilities workers confirmed that a 6-inch lateral serving four condominium buildings was the culprit, the city fined the homeowner association and ordered the breach repaired. The property management company that owned the buildings called Don Armenta, underground plumbing manager for Fischer Plumbing in Seattle.

“We scrambled a crew and within 24 hours had the green light to do the job,” he says. “Project managers from three large plumbing companies looked at it, referred us, and walked away.”

The repair involved pipe bursting, hydroexcavating, concrete demolition and working on a hillside with a ski-slope grade. The four-week project, which strained men and machinery, repaired the line and saved the management company $150,000.

Phase one, bid one

The condominiums are 50 feet above the street. A 50-foot-wide rectangular swimming pool, surrounded by lifted landscaped areas within retaining walls, is 20 feet above the street. An 8-foot-wide expanse of overgrown vegetation begins at the curb and ends against a 30-foot-high retaining wall.

After a one-call service verified that no utilities were in the way, Fischer’s crew excavated a 14- by 7- by 15-foot-deep shaft in the center of the street. Subcontractor Tom Lavelle of Lavelle Vac and Drainage in Seattle potholed the remaining 5 feet down to the combination sewer and lateral tie-in with his Vactor hydroexcavator. One traffic lane remained open.

“When we exposed the 6-inch clay lateral, it was completely clogged with rock, hardpan soil, and chunks of pipe,” says Armenta. “So, we excavated a second shaft closer to the retaining wall and saw some flow.” The men jetted, vacuumed and cabled the line until they restored half its capacity, enabling sewage to flow throughout the repair.

An inspection with a RIDGID SeeSnake push camera revealed no broken sections. “That puzzled us because we didn’t know why the pipe was full of debris,” says Armenta. “Then we started cleaning upstream from the wall and found 15 feet of 6-inch ductile under it. Then it switched to asbestos. Using the camera’s transmitter, we tracked the line 20 feet up the slope and over the edge of the pool.”

The pipe maintained a 20-foot depth, but the camera televised four laterals, two per condominium, coming in 15 to 20 feet deep and intersecting the pipe at 45-degree angles. The junctions were under the pool’s shallow end (three feet).

Because the lateral from the combined sewer to the wall was old, Armenta opted to burst it size-on-size using a 40-ton Pipe Genie system and PVC pipe. The burst was uneventful and fast.

Phase two, bid two

After draining the pool, Lavelle’s crew used 90-pound jackhammers to break up the two semicircular concrete steps, walls and floor, while Fischer’s men threw the chunks over the wall and into a dump truck parked below. They removed 20 cubic yards of concrete in five days.

During the process, the men found aggregate concrete under the pool deck. A maintenance man said that every five to 10 years, a foundation repair company jacked the slab back into place. Armenta counted at least five different lift points.

“The hydroexcavator made the next stage possible,” says Armenta. “Strategically, getting anything into that area was a nightmare, and damaging a retaining wall was always a risk.” The driver parked the truck on the street or in the condo parking lot. Fischer’s men worked the wands and suction hose, resting for most of the 90-minute intervals in which the truck driver emptied loads.

“Besides dragging hoses, the guys jackhammered the hardpan to free it for vacuuming,” says Armenta. “They also built and moved 1/4-inch plywood shoring back and forth. It was labor-intensive work.” It took five days to vacuum the soil and expose the large holes in the asbestos pipe at the lateral junctions. That’s when Armenta formulated his theory.

“The pool was probably illegal, because even the city had no record of it,” he says. “I believe the backhoe clipped the pipe while excavating the terrace. Since then, the ground had been hour-glassing under the pool, and every flush washed down more debris. The clay lateral allowed some sewage to escape into the soil, but eventually enough head pressure built up to cause the eruption.”

Traditional solution

Because the hillside was open-trenched, Fischer’s men laid 6-inch PVC pipe from the ductile section under the wall up to the pool, and replaced five or six feet of each lateral at the junction. To backfill, a concrete-truck driver reversed his truck against the condominium parking lot retaining wall, positioned the boom over it, and dropped the load 30 feet into the hole.

“We did a controlled-density backfill with lightweight cement slurry,” says Armenta. “The men built wooden structures to deflect the weight of the material so it wouldn’t damage the pipe.” It took nine cubic yards to fill in 15 feet. Then another company reinforced and restored the rest of the pool.

“This was one of the most technical projects of its kind performed in this market in recent times,” says Daryl Miller, owner of Fischer Plumbing. “Our expertise, equipment, and confidence carried the day profitably and without any issues. I am proud of our group.”