Desalination Plant Reactivation
June , 2018
In response to a prolonged drought and water crisis in the late 1980’s, the City of Santa Barbara constructed a seawater desalination plant that came online in the summer of 1992. After operating only a couple of months, it was shut down and placed in “standby mode” due to a large amount of rainfall that winter.
With the region experiencing another prolonged drought, in 2015 it was decided to reactivate the desalination plant and expand the capacity using updated technology not available in the early 1990’s. Unfortunately, possibly due to the fast track construction schedule for the original system, detailed as-builts (particularly in regard to the offshore intakes) were not available, and many components had been removed when the plant was place in standby. Because of this, the project was characterized as a “design-build”.
Global was contracted by Kiewit Infrastructure West to mobilize a derrick barge and dive crew to set large concrete top packages over the two open intake structures, install two connecting spool pieces to the intake pipeline running 2500 feet to the beach, pull new power cables through the pipeline from the shore, and perform other miscellaneous tasks. The work was estimated to take less than two weeks to complete.
Phase I Offshore Work (July 2016 – September 2016)
Global was tasked with performing an initial 3-4 day inspection to obtain measurements and confirm existing conditions at the pipe termination and two concrete intake structures. Working from the Danny C, a Santa Barbara based workboat; the crew found that the location where an offshore transition section split the pump power cables to the intakes was completely encased in a formed concrete pour. In addition, steel pipe spools left encased in the concrete structures had suffered heavy corrosion and needed to be replaced. Two other FRP “Y” pipe sections that were to branch off the intake structure connecting pipe sections were determined by the engineers to need replacement.
The dive crew worked for weeks at the transition section, exposing the steel formwork by hand jetting/dredging, burning the form away, and removing the concrete and steel reinforcing from the encased FRP fitting using chippers, drills, and a hydraulic concrete splitter. The engineers wanted to preserve the fitting for design evaluation and original dimensions, so the demolition was done carefully to recover the fitting intact. After removal of the two “Y” sections and the transition piece, video documentation and measurements were taken of the existing concrete intake structures for construction of the new top packages.
Phase II Offshore Work (October 2016 – February 2017)
The DB San Diego with dive crew and equipment was mobilized from Long Beach, and set up on a four point anchor spread at the desalination plant intake structure. The two concrete top structures, each weighing 90,000 pounds, were staged on deck. These structures would have to be placed on the top of the existing intakes with enough precision to line up sixteen corresponding 2” diameter bolt holes, after which large intake pumps would have to be lowered through a narrow slot at the top of the concrete structure.
Other notable tasks performed by Global included the first ever underwater installation of an HDPE Victaulic coupling of two 42” sections of pipe, which required precise milling of several grooves on each side of the pipe to allow a leak proof coupling. Global worked with the Victaulic Corporation closely to ensure the rotating hydraulic milling tool was adapted for safe and effective use underwater by divers. Victaulic sent a technical team to offshore to document the procedure.
The dive team also:
- Installed cable conduits and pulled thousands of feet of pump power and control cables from the transition vault on the beach.
- Designed and installed a vinyl sheet pile form around one the existing intake structure that was found to have significant scouring under the base. The sheets were driven into the sand bottom using custom tooling, were further supported by tensioned wire holdbacks to the structure fastened to concrete anchors, and temporarily backfilled with gravel until permitting allows concrete placement.
- Formed and pumped high strength grout around new HDPE pipe penetrating the concrete structure. The old, corroded steel spools were removed by burning and concrete chipping, which created large annular space subsequently filled by the grout operation.
- Chipped out old pump concrete footings, and installed the steel check valves, spool pieces, and pumps in a plumb and level position.
- Designed adjustable pipe spool templates to account for various misalignments between the intake pipeline and both intake structures. The templates featured flanges at both ends and a telescoping pipe section that was installed, welded to fix the alignment, and recovered to the surface. The HDPE pipe supplier then used the steel templates to fabricate a perfect fit for the HDPE spools.
- Worked closely with environmental monitors, both afloat and on the barge, to ensure there was no impact to marine mammals or the marine environment. Other than a young sea lion that briefly adopted the barge as a resting place, the desalination plant reactivation project continued without any interruption due to environmental impact.