Orinda Water Treatment Plant Upgrade

Project Update

Servicing over 800,000 San Francisco East Bay residents, the Orinda Water Treatment Plant is at the heart of East Bay Municipal Utility District’s (EBMUD) water system. Water is piped 90 miles (145 km) from the Pardee Dam in the Sierra Nevada Mountains to the plant in Orinda. Originally constructed in 1935, the historic plant is located east of the Caldecott Tunnel in the Berkeley Hills and connects to the east end of the Claremont Tunnel. The treatment plant has gone through multiple construction upgrades through the decades, and Delve Underground has a history with its growth, tracing back to inspection of the Claremont Tunnel in 2002 and the award-winning Claremont Tunnel Seismic Upgrade Project, which was completed in 2007.

For the current upgrade, EBMUD is adding an underground ultraviolet disinfection facility and chlorine contact basin (UV-CCB) which will reduce the formation of disinfection byproducts that currently form when chlorine reacts with naturally occurring organic matter in water, thereby improving the current water treatment process. This upgrade includes a new below-grade structure to host the new UV-CCB facility, as well as new piping connections to the existing filter effluent lines and the Claremont Tunnel. EBMUD Project Manager Tim Karlstrand notes that “the new UV-CCB facility is an engineering marvel built completely underground to allow the water system to continue operating by gravity all the way from our Pardee Reservoir to the majority of our customers with no pumping.”

As a subconsultant to Carollo Engineers, Delve Underground oversaw the geotechnical investigation effort and developed geo­technical baselines and the design for the support of excavation reference and ground treatment options. Delve is now providing engineering services during construction, including technical review and field observations to EBMUD as the subject expert for geotechnical instrumentation monitoring, support of excavation, and trenchless technologies.

The $267 million construction contract was awarded to Flatiron West Inc., and construction started in the winter of 2022. Flatiron teamed up with Drill Tech Drilling and Shoring (DTDS) to install the support

of excavation system for the UV-CCB facility. The support of excavation system consists of a secant pile tieback system and soil nail walls at localized deeper excavations to accommodate the final structure. On February 22, 2023, DTDS installed the first secant pile on the project site. Three Bauer drill rigs, a BG50, BG40, and BG28, were mobilized to facilitate the installation of secant piles. The secant pile installation for the UV-CCB support of excavation was completed in May 2023, and the contractor is progressing with the mass excavation and tieback installations.

Geotechnical instrumentation was installed in multiple phases prior to and after the secant pile operation. The contractor proposed a flexible installation and monitoring plan to accommodate different construction activities that conflicted with site access constraints. Delve Underground is supporting EBMUD in discussions with the contractor to adjust the instrumentation plan as needed.

“One of the most exciting things about this project is the variety of specialty scopes of work. The project has secant piles, tiebacks, internal bracing, trenchless tunneling, spiles, compensation grouting, permeation grouting, and jet grouting…it really showcases our firm’s expertise across different disciplines.” – Keith Bryant, Associate Engineer on Delve Underground’s Orinda team

Project construction started in 2022 and is expected to complete in 2027. Two smaller excavations will follow the UV-CCB, utilizing secant piles and internal bracing. The work also includes modifications to an existing underground structure to construct the new pipelines tying into the Claremont Tunnel. Delve Underground will continue to collaborate actively with the EBMUD and the contractor team to facilitate creative engineering solutions to each unique challenge.