Dudek Helps in Wastewater Siphon Replacement Project

The City of Laguna Beachwas concerned about a siphon section of its primary wastewater transmission main that was constructed of steel pipe. They were also interested in evaluating the serviceability of contiguous fiberglass pipeline sections.

The fiberglass pipeline had changed ownership, and records of the material type and fabrication methods were lost. This made it essential that the project approach be well planned.

After deciding to replace one deteriorated siphon section, we thought it would be useful to inspect other parts of the system to better understand its overall life expectancy and condition. Except for the deteriorated siphon section, the system was found to be in good condition.”

The city enlisted Dudek to provide project management expertise and design services for the complex siphon project.

Approximately 1,000 linear feet of 24-inch fiberglass-reinforced pipe (FRP) was replaced with 20-inch fusible PVC pipe using a combination of cut-and-cover and slip lining techniques.

The most complex portion of the project was crossing a Caltrans bridge with only 20 inches of cover. Using experience from a recent Orange County Sanitation District project, Dudek engineers designed a unique pipeline solution and pre-purchased 316 stainless steel trifurcation specials that were manufactured according to our specifications. The trifurcations combined with Caltrans’ approval saved the city in excess of $500,000.

Additionally, a temporary bypass system was designed using hot taps and line stops. This is one of just a few times FRP has been successfully hot tapped. Dudek modeled and sized the temporary bypass system with 100 percent redundancy using the city’s existing pump station so no additional on-site pumps were necessary.

Factors that helped the project succeed were:

  • Well-planned, well-coordinated efforts. Highway 1’s center divide served as the construction staging area. As such, there was virtually no lay-down area for the contractor. Dudek engineers planned for this and worked with the contractor to sequence construction.
  • Significant community outreach. The city held meetings in advance of construction and notified businesses and residents of the upcoming work. Additionally, the city maintained beach access and kept traffic flowing. This was especially important around a nearby K-12 school.