Sonora Regional Wastewater Treatment Plant Upgrades

Sonora, CA


PACE performed a facility assessment and prepared an upgrade design for the Sonora Regional Wastewater Treatment Facility to address the facility’s declining effluent performance. The conventional trickling filter secondary process was converted to an extended aeration activated sludge (EAAS) process utilizing the Parkson Biolac® mixing and aeration process for improved functionality and performance. The upgraded facility is capable of treating 5.0 million gallons per day (MGD) maximum day flows and 10.0 MGD peak hour flows. In addition, the upgrades ensure regulatory compliance with the Waste Discharge Requirement (WDR) permit limits for biochemical oxygen demand (BOD) and total suspended solids (TSS).


The project was funded through a U.S. Department of Agriculture (USDA) grant, which required expeditious analysis and mapping to establish base flood elevations and demonstrate to the USDA that the project could be designed and constructed with Federal Emergency Management Agency (FEMA) approval. PACE performed complete hydrologic and hydraulic analyses of the detailed expansion design. The analyses demonstrated that the project would not be in the 500-year floodplain and would not cause upstream or downstream impacts.


Key Features:

  • 90,000 cubic yards of earthwork in balanced cut-fill construction with enhanced stormwater conveyance
  • Finished grade above FEMA floodplain
  • High-quality process equipment, including:
    • Parkson Biolac extended aeration configuration with variable freeboard for system equalization
    • Kaeser (Pillar) Mag-Bearing high-efficiency aeration blowers to provide constant dissolved oxygen
    • Ovivo submerged launderer clarifiers with tertiary feed pumps at constant flow downstream
    • Veolia Hydrotech 10-micron polyester filters for consistent low-turbidity effluent
    • FKC screw press for dry secondary thickened WAS dewatering
  • USDA grant-funded project
  • 9,000-square-foot administration building, civil improvements, and recycled water fill station
  • Renovated digester building with repurposed aerobic digesters for solids processing

Tuolumne Utilities District

Wastewater Treatment