Project Details

Owner: City of Soledad

Contract value: $49,553,440


The existing Soledad Wastewater Plant consisted of three sets of ponds, including aerated ponds, secondary ponds and a polishing pond. The upgrade and expansion converted the former location into a mechanical plant that includes headworks pretreatment, primary, secondary, tertiary and residuals treatment. The plant effluent is used as reclaimed water or flows to rapid infiltration basins for disposal. Plant solids flow to stabilization basins for thickening, then to a screw press system for dewatering, before moving into drying beds.

The plant is made up of 23 unique structures and building areas including headworks, biological nutrient removal (BNR), aeration, clarifiers, pump stations, flocculators, filters, ultraviolet disinfection, chemical/polymer injectors, and solids drying. Included within these areas is specialized equipment that consists of the following: grit removal system, compressible media filtration system, ultraviolet disinfection, and a screw press system for dewatering sludge. These features are interconnected by 7,000 linear ft of process piping and monitored by electronic devices, programmable logic controllers (PLC) and SCADA.

Several key construction activities were critical to the successful and timely completion of the project. A soil-bentonite wall was installed around the perimeter of the open excavation to allow a system of dewatering pumps to lower the water table below the construction. This value engineering proposal avoided the most of the shoring originally required on the project and provided a significant credit to the owner. Stone columns were used to compensate for the liquefiable soil in areas where it was too close to levees to excavate and replace the soil under some of the structures.