Easterly Wastewater Treatment Plant Tertiary Treatment Improvements
City of Vacaville, California

West Yost completed facility master planning and design to address changing regulatory requirements for the City’s Easterly Wastewater Treatment Plant. This project includes $130 million of improvements required to meet new regulatory requirements and to abandon the old North Plant and replace it with capacity in the New South Plant.

The Tertiary Improvements Project will comply with new regulatory requirements that mandate stringent ammonia and nitrate limits, eliminate blending, and comply with dry weather filtration/Title 22 reclamation and potential trihalomethane (THM) limits. It is critical that the improvements be completed to meet the compliance schedule in the NPDES permit.

Major facilities and improvements that are currently being designed include:

  • Secondary process expansion, including aeration basins/blowers and clarifiers. Aeration basin reactors are being converted from anaerobic/aerobic to anoxic/aerobic with mixed liquor recycle to facilitate denitrification.
  • Tertiary filters required to meet summer discharge Title 22 standards.
  • Chlorine contact tank expansion required to provide Title 22 advanced disinfection.
  • Flow equalization facilities required to equalize primary effluent during peak storm events.
  • Administration and laboratory space expansion required to house increasing City staff.
  • Demolition and restoration of the old North Plant.