Regional Wastewater Treatment Plant Planning and Design
City of Atwater, California

West Yost provided planning and design for the City of Atwater’s new Regional Wastewater Treatment Plant (WWTP). The new plant was required to increase average flow capacity to 6 mgd (expandable to 12 mgd ultimate) and comply with new regulatory requirements for advanced treatment. West Yost evaluated upgrades to existing treatment plant facilities as well as alternatives involving abandoning the existing plant and constructing new facilities on a City owned site five miles from town. Constructing new facilities on a City owned site five miles from the town allowed the City to replace aging facilities, eliminate odor problems for commercial businesses and nearby residents, eliminate chemical deliveries through the heart of town, and make valuable land available for other City or community uses.

The West Yost design includes the following major treatment unit-processes:

  • Headworks including screening, grit removal and odor control provisions.
  • Two biological nutrient removal oxidation ditches with secondary clarifiers providing for effluent ammonia below 2 mg/L and nitrates below 10 mg/L. Effluent BOD and SS will be consistently below 10 mg/L. Provisions for supplementary carbon addition, which might be required to fuel the nitrification process, are also provided.
  • Effluent filtration/UV disinfection facilities.
  • Office/laboratory space.
  • Sludge digestion/dewatering facilities, including cake storage.

Project planning and design were completed on a fast track schedule, and construction was substantially completed in July 2012, three months ahead of schedule.

Planning and preliminary (30%) design also included a new 12 mgd (expandable to 24 mgd) pump station with odor control facilities and flow surge protection, and six miles of twin 30-inch diameter force mains to the new advanced treatment plant. West Yost has been responsible for ongoing discharge permitting and for permitting the new discharge location, including Regional Board coordination.

Design for Energy Savings

The City of Atwater Regional WWTP was designed by West Yost to include a variety of energy efficiency measures to minimize energy consumption. West Yost coordinated these design initiatives with PG&E’s Savings by Design program and was effective in securing a PG&E incentive payment to the City for over $224,000. PG&E recognized the final project for achieving energy reductions of 294 kW and 2,160,963 kWh. Eligible features of Atwater’s WWTP design included: high efficiency heating, ventilation, and air conditioning (HVAC) units at the plant’s electrical and administration buildings; the use of rotary fan press technology for biosolids dewatering; high efficiency surface aerators in the oxidation ditches; automatic control of dissolved oxygen levels using variable speed motors for the oxidation ditch surface aerators; the use of a low-pressure, high-intensity UV disinfection system; and use of a high-efficiency aeration system for the plant’s aerobic digesters. 

Design for Cost-Effective Future Expansion

Facilities at the new treatment plant were designed in a modular layout. This will minimize the future cost of expanding the plant and provide additional needed capacity to meet ever-evolving regulatory requirements.

Significant Savings During Construction Includes Less Than 0.3% in Change Orders.

The design team, City staff, and construction management team worked together to assure a high quality project and to control construction costs for the City. Their resulting efforts were successful with a $42 million construction project finishing with less than one-percent in change orders. In addition, construction was completed six months ahead of schedule.

Industry Awards

  • Environment, American Public Works Association, Sacramento Chapter 2013 Project of the Year 
  • American Society of Civil Engineers, Sacramento Section 2012 Environmental Project of the Year