Surf’s up and clean in Southern California thanks to Oldcastle and the Santa Monica “Clean Beaches” stormwater cistern. Located at the base of the world-famous Santa Monica Pier, the Deauville basin will be used to harvest up to 1.6 million gallons of stormwater runoff from the pier’s downtown drainage basin.
The harvested runoff will then be diverted for treatment at the Santa Monica Urban Runoff Recycling Facility and distributed for non-potable uses. Overflows from the tank will be discharged into the sanitary sewer system.
The project was scoped in May 2017 and originally designed as a standard modular StormCapture® system. After evaluation of the project’s unique design and specification requirements, Oldcastle proposed the use of a StormCapture PV precast panel vault system in lieu of the conventional modular StormCapture system as a value-engineered solution.
The challenge was to design a system 262-feet long by 78-feet wide by 12-feet tall (inside depth), or “very close to the size of a football field,” said Selim Eren, project engineer with the city of Santa Monica. Plus, the system was going to be erected on sandy soil, with a water-table at grade, and able to withstand 15-feet of compacted backfilled soil while supporting a surface parking lot over the entire basin. The system also needed to be water-tight when filled with 1.6 million gallons of stormwater while passing a mandatory 24-hour leak-test.
To complete the test, groundwater was pumped into the tank, then measurements were taken two days later to document any water loss. “With this type of structure some water loss is expected,” Eren said. However, the tank met the acceptable limit of losing no more than 0.01% of water. “That would amount to half an inch from the whole 1.6 million-gallon tank,” he explained. After the structure passed the leak test, the water was later used during the construction phase, such as preparing the backfill for compaction.
To reduce the project’s energy footprint, rather than installing pumps that require both ongoing maintenance and power, the project relies on gravity to transfer water from the pier outfall to the 1.6 million-gallon cistern. However, that meant placing the cistern well below grade.
“In our case, we were going extremely deep; there would not only be traffic loading from the top but heavy soil pressure, as well as water table pressure and buoyancy from the shallow water table that is kind of acting against it. We really needed to have a specially designed system,” Eren said. “During design, we were deciding whether the structure should be precast or cast in place. The ground level is at the beach level, and the water table is very shallow. It varies seasonally, changing between 5 and 10 feet and depending on the tides as well. Also, the footprint of the site is very small, so there is no way to cut and slope the edges of the excavation that would be needed to get approximately 30 feet below the surface.”
Complicating matters, Eren said the Santa Monica Pier “is actually busy all year, with some of the busiest days right around Christmas time. We needed to stay outside of the summer season as much as possible.” Therefore, building a form and then casting the structure in place would have added an unacceptable duration to the construction schedule. “We decided to use the StormCapture PV panel vault system from Oldcastle,” Eren said.
To fully comply with leak-test requirements, the basin was designed to withstand hydrostatic (water pressure) loads and the hydrodynamic (seismic) loads during the test, without any external support or backfill. Oldcastle’s ability to recognize the need for pursuing an alternative solution that was both practical and economical was key in securing the project.
The successful design-build project was the result of an early and ongoing collaborative effort between Kube Engineering, Corrpro Companies, ACME Construction, and Oldcastle’s sales and engineering teams in Southern California and Auburn, Washington. Relying on the Auburn team’s vast experience with the design and manufacturing of panel vault systems was invaluable in developing the solution.
Eren said the goal of the “Clean Beaches” initiative was simple and direct, “to prevent any of the polluted stormwater from the city from contributing to degrading the quality of the water on Santa Monica beaches.” And the only way to achieve that goal for the Santa Monica Pier watershed was “to eliminate most of the runoff and stormwater from reaching the ocean.”
Overall, the project consisted of 191 precast wall panels and roof slabs. Production at the Oldcastle plant in Fontana, California began on January 30th, 2018 and was completed on March 26th, 2018. On-site installation of the system started on March 13th, 2018 with the last roof panel installed on April 3rd, 2018. In addition to the precast basin supplied by the Oldcastle plant in Fontana, the general contractor also chose to use a proprietary OneLift® pump station supplied by the Oldcastle plant in Chandler, Arizona.