The AWP Program is utilizing Horizontal Directional Drilling, a trenchless construction method for the installation of wastewater pipelines.
This technique is being used instead of conventional open cut construction in order to minimize the impacts to the three waterways this project crosses including the San Diego River and a nearby golf course.
Wastewater pipelines installed using HDD are typically up to 2,000 feet in length. This project however, is 3,500 feet with 36-inch, 18-inch, and 8-inch diameter High Density Polyethylene (HDPE) plastic pipes. The 36-inch pipe with its 4.5-inch thick walls is particularly uncommon.
All three sizes of pipe will be pulled into two HDD bore holes, which run from the East Mission Gorge Pump Station near State Route 52 to the first lake at Santee Lakes.
In early December, the team completed fusing the 8-inch pipeline. This involved the heating, melting and joining of plastic pipe. The fusing process began by shaving the end of the pipe. The end was then pressed against a hot plate and after that, the plate was removed and two ends were joined together. This fusing method eliminates joints in the finished pipe, preventing future leaks. It also allows the pull of the pipeline through the bore hole to happen in one continuous action.
The fusing of the 36-inch pipe took about one month and was completed in June 2023. The 18-inch pipe is also complete. 10,500 total feet or 2 miles of pipe have been fused, marking the completion of the fusing process. The next step is pulling the pipelines through the bore holes in spring of 2024.
Interesting fact: The deepest portion of the HDD alignment reaches 80 feet below the ground surface!