In 2010, the Carpinteria Valley Water District (CVWD) began installing a new water transmission pipeline to increase groundwater distribution for the City of Carpinteria, Calif.

The project began with the replacement of a failed well in the city’s El Carro Park, dormant since 2004. The second phase involved the installation of an approximately 3,800-ft water transmission pipeline that would carry the higher-quality water to downtown Carpinteria.

The CVWD retained civil engineering firm Flowers & Associates Inc., of Santa Barbara, Calif., for the design of the water transmission pipeline. After weighing the options of an open-trench installation vs. trenchless, in regards to cost and disruption to the surrounding area, the project team chose to go the trenchless route.
“We had reason to believe that a trenchless installation would be more economical and we were looking to minimize the project’s impact on the community,” says Vern Williams, principal at Flowers & Associates. “The pipeline route runs in front of a school, through a residential area and two parks, underneath U.S. Route 101, and passes underneath a creek. Considering these factors, we decided that using horizontal directional drilling to install the pipe would be the best decision for minimal disturbance to the surrounding area.”

Specialty Construction Inc., of San Luis Obispo, Calif., won the general contractor bid for the pipeline installation and subcontracted the directional drilling work to Ventura Directional Drilling, Inc., of Ventura, Calif. The next step was choosing a pipe material for the project. Flowers & Associates specified CertainTeed Certa-Lok C900/RJ restrained-joint PVC pipe, preferring not to use fusible pipe on the project.
“We didn’t want to use [fusible pipe] because it would have tied up the streets too much during the fusion process,” Williams says.

Certa-Lok pipe is easily assembled in 20-ft lengths with spline-locked couplings as the pullback continues, allowing pipe installation to keep moving at a steady pace and take up less space than fused lengths of pipe.
The job called for 2,460 ft of 12-in., DR 18 C900/RJ pipe, 740 ft of 12-in., DR 14 C900/RJ pipe and 600 ft of 8-in., DR 18 C900/RJ pipe. Ventura Directional Drilling used a Ditch Witch JT 3020 directional drill with 30,000 lbs of pullback, Ditch Witch FX 25 vacuum truck, CETCO drilling fluids and John Deere backhoes and excavators. The project start date was dictated by Carpinteria Elementary School, situated along the pipeline route, which mandated that the job not be done while school was in session.

“We had a small window of time available for this project,” says Bob McDonald, district engineer for CVWD. “It was either wait till winter break or wait till the following summer. We’d been ready to do the project for some time and wanted to get moving, so we chose to begin in the middle of last December while the school was closed for winter break.”

Unfortunately, rainfall in December was almost three times the average, forcing the crew to work through heavy rains and face the challenges of drilling through saturated light clay soil.

“The groundwater was very high when we dug our pits — about 2 ft deep in some areas,” says John Fields, president of Ventura Directional Drilling. “We had one section where you could see the pit filling up while you were looking at it. It was hard keeping up with the mud flows, too. We had to haul a lot more mud off the jobsite under these conditions.”

The wet weather also led to a few minor cave-ins on boreholes during drilling. Ventura Directional Drilling quickly addressed these obstacles, however, removing the excess mud with their vacuum truck, creating only a minimal slowdown in the project.

The crew consisted of four workers — one for operating the directional drill, one for performing utility locations, one for mixing drilling fluid and one for transporting excess mud to the disposal location. The crew made 10 bores at an average depth of 6 ft. They were supported by a crew from Specialty Construction, which handled entry and exit excavations for the boreholes and pipe assembly.

DR18 pipe was used in the majority of the project, especially for areas where there were tight radius bends. The maximum bore depth was 15 ft, when the crew had to drill underneath a large creek. Despite all of the obstacles presented by the rain and wet soil, the restrained-joint PVC pipe performed well during installation.
After Ventura Directional Drilling finished the pipeline installation, Specialty Construction completed the project with 200 ft of tie-ins, all done open-trench. In all, the project took approximately two months. The new pipeline passed pressure testing this past February with no leaks.

“The Certa-Lok pipe performed perfectly during pressure testing,” Fields says. “They tested the entire system —3,800 ft — and they had no leaks. When you test that long of a pipeline all at once, there’s potential for everything to go sideways, but this test was successful.”

Though the project was a success there were some lessons learned. Most importantly, CVWD plans to avoid scheduling pipe infrastructure improvements during rain seasons.

“The project had its complications, mainly because we were hit by this torrential rainfall and so much mud,” McDonald says. “I think it would have gone a lot smoother if we had done it during the dry season. I also now feel like it’s wise to plan for a lot of mud, regardless of the forecasted weather, and arrange for a disposal location with ample space. We were lucky that we had a disposal location this time with enough capacity to handle all of the unanticipated mud.”

All in all, CVWD was pleased with its choice of a trenchless pipeline installation over an open trench installation.

“Our main goal was to make only a small footprint on the community, and we achieved that,” McDonald says. “The average citizen didn’t see a lot of construction activity going on. Cost-wise, it ended up being pretty close to what an open trench would have been. The key benefit was the low profile nature of the directional drilling. There were some areas where we would have made a pretty big mess if we had gone with a conventional open trench installation.”

John Coogan is marketing and business development manager for CertainTeed Corp.

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