Thousand Oaks Water Treatment Plant
Under contract to Calleguas Municipal Water District, Fugro conducted geotechnical engineering design and provided construction monitoring services for a 50 mgd water filtration plant on a 17-acre site near Lake Bard in the City of Thousand Oaks.

Legislation passed by the California legislature in 1992 required all municipal water reservoirs to be covered or the water treated prior to consumption. Because the relatively large size of their reservoir (Lake Bard) precluded covering, the Calleguas chose to construct a new treatment plant to comply with the regulations. The water treatment plant included a 3-million-gallon clearwell, filters, clarifiers, ozone contractors, waste water and sludge basins, chemical treatment facility, and administration building.

Fugro excavated and downhole logged 16 bucket drill holes and about one dozen backhoe test pits to characterize the site geology. Cut slopes as high as 80 feet and engineered fill slopes as high as 50 feet were required to construct the water treatment plant. Deepened footings and selective overexcavation and recompaction were required to minimize settlement potential in areas where mat foundations for the clearwell, filters, clarifiers, and wash water recovery basins encroached upon cut/fill lines.

Stability of the cut slopes, which were excavated from the Sespe Formation that is prone to sliding, was a concern. Mitigation measures that were designed included adjusting the slope inclination, removing unstable materials, and planting appropriate slope vegetation.

Fugro also conducted a fault study to estimate the potential for ground surface rupture and probabilistic and deterministic seismic hazard analysis to estimate the ground shaking potential at the site.

Fugro also provided geotechnical observation and field density testing during rough grading of the site that included over 300,000 cubic yards of earthwork.