Retention systems, Ground Improvement & Dewatering at WWTP.
Malcolm Drilling was contracted for Phase 1: Site Preparation of the Wastewater Treatment Plant Nutrient Removal and Wet Weather Flow Management Upgrade and Expansion Project. A major component of the Clean Water Program, the Wastewater Treatment Plant (WWTP) expansion represents one of the largest rehabilitation efforts undertaken at the San Mateo WWTP since the 1970s. Upgrading the WWTP will allow it to manage heavy rainstorms, up to 78 million gallons per day, and produce high-quality treated water.
Malcolm provided a design-build temporary shoring wall to support the 20-foot-deep excavation of the new below-grade treatment facilities. Starting with the installation of a continuous triple-auger cement deep soil mixed (CDSM) shoring wall around the perimeter, 65 feet deep with wet-set steel soldier beams. The wall was laterally supported by one row of tie-backs angled steeply downward to develop bond capacity below the 30-foot-thick layer of Bay Mud soil.
In addition to the temporary shoring, Malcolm also provided a design-build groundwater control plan and installed deep wells that properly dewatered the excavation and depressurized the lower aquifers to provide a stable and dry excavation.