Sewer Rehab in Rose Canyon

Major rehab project saves failing sewer main and overcomes environmental concerns without excavation.

Sewer Rehab in Rose Canyon

Each joint was air-tested to ensure it was watertight.

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Innumerable joints in a sewer main lost their integrity, threatening leakage from miles of pipe beneath a scenic canyon in Southern California. The joints needed to be repaired without tearing up the canyon floor and disturbing riparian habitat.

The San Diego office of GHD, a multinational professional services firm, engineered and oversaw the rehabilitation project. Its oversight involved decisions that delicately balanced construction solutions and environmental preservation. In the end, it all worked out, but not in a purely linear fashion.

Initial failure

The Rose Canyon trunk sewer line, constructed in 1996, is a reinforced concrete structure with a PVC liner. To create the continuous pipe structure, 20-foot-long sections of 54- and 60-inch pipe were joined end to end with the interior liners fused using weld strips applied with heat and pressure. It was the discovery downstream of remnants of the weld strips that flagged the joints’ failing condition. Subsequent visual inspection by city of San Diego officials revealed general failure, with many of the welded strips loosening and, in some cases, becoming detached entirely.

Such seal failure was not unheard of, according to Casey Raines, the Rose Canyon project manager for GHD. Early generations of the welded seal product didn’t always work unless they were meticulously installed. “From our experience and in talking with others, when these weld strips were introduced, failure was kind of a chronic issue. It appears the Rose Canyon contractor didn’t have the proper experience.”

By the same token, San Diego officials inspecting the installation also lacked experience with the product in 1996 and were unable to distinguish a sound application of the strips from a faulty one. “The city pretty quickly started seeing weld strip materials downstream and in manholes. It was like ‘Uh-oh … ’”

The failure of the seals produced a threat of leakage and structural damage. The bad seals exposed the concrete pipe to corrosive hydrogen sulfide, which produces sulfuric acid and can corrode concrete and steel, thus turning a drip into a stream of escaping effluent.

This threat was distressing because Rose Canyon is not an insignificant feature in the region’s terrain. The canyon is a miniature valley with sloping sides covered by native grasses. Rose Creek runs through its bottom in the shade of oak and sycamore trees. Public and private properties are contained by the canyon walls, and the trunk line runs adjacent to the creek and the creek’s federally protected wetlands.

Measured approach

A significant sewage spill in Rose Canyon would be consequential. On the other hand, such a threat was not imminent, so in 2014 the city and GHD began systematically planning a fix. Studies, field surveys and assessments were undertaken to determine the temporary and long-term impact of the rehab work. The process took three years.

“There were a lot of changes during the design stage of the project, and a lot of permitting was involved, including with a railroad company,” Raines says about the long run-up to actual rehab work. GHD carefully weighed the results of the various studies and prior maintenance agreements with the railroad and with highway and street departments.

In a subsequent presentation to the North American Society for Trenchless Technology, Raines and her boss, GHD project manager Greg Watanabe, remarked that the project was “important to the trenchless industry because it not only used an innovative approach to repair the failing large-diameter sewer that had been recently constructed, but the rehabilitation and bypass design that was developed considered the environment and the community and ultimately determined the best way to minimize their impacts.”

Thus stated, the comprehensive process comes across as a neat, straightforward series of coordinated decisions leading to a cost-effective, efficient fix. In reality, getting from point A to point B also involved sashaying between points B and C and occasional retreats to point A.

For example, the construction of a temporary 42-inch-diameter bypass pipeline was envisioned to divert sewage flow during repair of 500 feet of 54-inch-diameter pipe upstream from a juncture structure.

Several trailer-mounted, engine-driven pumps were to be installed to divert flow from that section of the sewer main into an aboveground bypass line, with rehab work ensuing for an estimated three months. The presenters called the bypass solution a “notable” engineering feature of the project.

You know what they say about the best laid plans of mice and engineers: The bypass never happened. Raines says, “Shortly after the contract was awarded and the bypass plan was being developed, the Public Utilities section of the city told us they had changed the operation of an upstream pump station. It changed the flow and would require a larger bypass than planned.”

The practical implications were that GHD had to return to square one on rehabbing that section. It was no longer feasible to use a manhole as a collection point for the bypass. Instead, excavation would be required along with a wet well. “It all became very complicated and expensive,” Raines says. “It was not worth the money for such a short segment.” Stop logs were employed exclusively to regulate flow and allow rehab work in that segment of pipe.

Sealing the deal

Coming together on a solution also proved problematic. Raines and her GHD colleagues recommended that a full-on cured-in-place liner be inserted in the pipe, giving the sewer main a brand-new seamless interior. “Our original design recommendation assumed all the joints had failed,” Raines says, noting that the presumed condition of the pipe was a worst-case scenario predicated on “pretty old information.” To be on the safe side, the full relining was proposed.

City officials didn’t embrace the idea. The CIPP recommendation was, according to Raines, cheaper on a per-linear-foot basis, but more expensive overall. The city preferred something less costly on the assumption that the failure of joints wasn’t general enough to warrant an entire relining.

“Other factors weighed heavier for the city,” Raines says. “Cost was one, and the other was the impact on the surface. We were going to have to excavate to insert the liner rather than just use the manholes. A lot of the city’s concern was about restoration of the area after the job was completed. Those items of concern weighed heavier in their evaluation.”

Consequently, the contractor that was awarded the job — the San Diego office of Abhe & Svoboda — proceeded to rehab each individual joint using an internal mechanical seal. The selected repair method came from Cretex Specialty Products. The Cretex HydraTite internal joint seal is comprised of a rubber sleeve of varying widths and stainless steel expansion bands. Together they create a watertight compressed seal. Abhe & Svoboda is a certified installer of Cretex HydraTite internal seals.

The project addressed slightly fewer than 1,200 joints, each one categorized as to its condition — poor, bad or severe. The latter were divided further according to the type of Cretex seal to be employed, with more damaged joints requiring wider seals. The four widths were classified as standard, extra-wide, double-wide and the double-wide sleeve, which is made up of multiple interlocked seals. They varied from 11 inches wide to 58 inches. By far, the double-wide solution was the most employed, which testifies to the severity of the general joint failure.

Raines describes the installed seals as “fairly low profile,” yet they obviously are not as smooth as the surface of a continuous CIPP liner. It follows that over time some debris collection may occur at the joints, but the product has a long, proven history in a variety of pipe repair applications.

Safe completion

The repair work was undertaken by the contractor during dry-weather seasons to avoid the possibility of work crews producing environmental damage to the canyon floor during rainfalls. This meant that work was limited to an April-to-October window. Crews began work in April 2018, a full year after the winning bid was awarded. They pulled out in October of that year and returned in April 2019, finishing in August.

Laborers in the pipe were protected against fumes by small blowers that kept the air moving. Each crew member wore a sensor to warn of excess exposure to hydrogen sulfide, carbon dioxide and other sewage gases. All the sensors were monitored via Bluetooth for further safety against a sudden spike in fume content. No crew safety incidents were reported.

Ultimately, the completed project was more expensive than anticipated. The winning bid by Abhe & Svoboda came in at just under $7 million, but design changes and other unanticipated charges ran up the bill for the 4.5-mile project to more than $8 million.

Mastering the process

Systematically repairing more than a thousand leaking joints in 54- and 60-inch pipe was no small feat. The sheer number of joints spread over 4.5 miles was somewhat daunting to anticipate, and the logistics of moving people and materials in and out of a temporarily emptied pipe added to the challenge.

It all came together for a crew from Abhe & Svoboda, a full-service restoration contractor, which was assigned the job of removing hundreds of PVC weld strips from joints and replacing them with mechanical internal seals. Fewer than a dozen employees were involved in the rehab job, but they were utilized in what Casey Raines termed “an assembly line.” Raines was project engineer on the job for GHD, a multinational professional services firm.

Rather than swarm all over a joint to repair it, two-person Abhe & Svoboda teams worked on an individual joint in sequence, each team completing an assigned task before making way for a successor team. They all utilized hand tools for their work. Those who needed air or water for a task were supplied via hoses run into the pipe from manholes.

“The first two-man crew cleaned the area around the joint, and a second crew assessed damage and measured to determine what seal would be used,” Raines says. A third crew removed the damaged PVC weld strip from the joint. A follow-up team repaired any damaged concrete and leveled the area around the joint with mortar to ensure a tight seal. An epoxy was applied to the edges of the joint area.

“Then a team would enter the pipe, bringing down the rubber and stainless steel components. It would install the seal, hydraulically expand the retaining bands, lock them in place and do an air test to ensure it was installed properly.” A final team with cameras then would enter the pipe and document the completed work.

The tedious but coordinated labor in San Diego’s Rose Canyon proceeded steadily, and crews grew more productive as they progressed. Raines says, “They did about eight joints a day at first, but the contractor was able to complete almost 14 a day on average as the work continued.”

When the work began, 1,110 joints were assumed to need fixing. That estimate was based on the standard 20-foot length of a segment of the sewer main. But the pipe was curved in some places, meaning joints were closer together where shorter segments of pipe were employed, so the final count was closer to 1,200.


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