The metropolitan Bakersfield area is located in the eastern portion of the southern San Joaquin Valley in central California, about 120 miles north of downtown Los Angeles. Bakersfield has been one of the fastest growing cities in California for many years, and it had a Year 2000 census of 246,889. Bakersfield expects that its population will continue to grow between 2% and 3% a year, resulting in a projected Year 2025 population increase to 507,500. Wastewater flows are expected to increase proportionally in Bakersfield’s service area.

Bakersfield currently owns and operates two wastewater treatment and disposal facilities. Wastewater Treatment Plant 2, serving the eastern half of the city, was expanded recently and has adequate capacity. However, Wastewater Treatment Plant 3, serving the western half, has not been upgraded in more than 10 years and has reached capacity.

Existing Plant 3 odor-control facility near headworks

Earth-moving activities at Plant 3 site

Plant 3’s existing facilities provide treatment capabilities for both liquid and solid streams with an average daily flow capacity of 16 million gallons per day (mgd). At present, the liquid stream treatment facilities consist of one headworks, four primary clarifiers, four trickling filters, four secondary clarifiers, one overflow/equalization lagoon, and four storage reservoirs. For most of the year, the treated effluent is transported through an 8.5-mi-long, outfall line to Los Angeles’ Green Acres Farm, west of Interstate 5. During periods of wet weather, Plant 3 temporarily stores excess effluent that cannot be accepted by the farm. The solid stream treatment facilities consist of four primary and three secondary sludge pumps, six anaerobic digesters, and 24 sludge-drying beds. Trucks haul the dried sludge to the city-owned farm associated with Plant 2, where it is applied to the soil as a fertilizer supplement.

In response to Bakersfield’s need to upgrade and expand Plant 3 (because of the increasing wastewater flow and more stringent regulatory requirements), the city hired Parsons in 2004 to prepare a master plan for the plant expansion and then design the necessary facilities. In the master plan, Parsons evaluated several expansion scenarios and ultimately recommended that the size of Plant 3 be doubled to provide a total wastewater treatment capacity of 32 mgd. Parsons also recommended that a new activated-sludge biological treatment process replace the existing trickling filters and that all other existing treatment facilities be upgraded and/or expanded. From a future total flow of 32 mgd, an anticipated 14-mgd secondary effluent will continue to flow to the Green Acres Farm and 16 mgd will be percolated onsite. The remaining 2 mgd will receive tertiary treatment (in accordance with California Title 22 standards) to be reused locally for in-plant use and landscape/turf irrigation.

In April 2007, Parsons completed the design for the Wastewater Treatment Plant 3–2007 Expansion, providing more than 800 drawings and thousands of pages of specifications. After a 4-month, bid-and-award period, a notice to proceed was issued on September 17 to the successful construction contractor. In accordance with established city procedures, a separate firm was hired as construction manager for the project. Parsons will continue to provide engineering services during construction.

Plan view of proposed facilities

The upgraded and expanded Plant 3 will include the following constructed facilities:

• The new 40-mgd-capacity McCutchen/Gosford lift station that replaces an existing offsite pump station and a new interceptor sewer to convey wastewater to the treatment plant.
• A new septage and grease-receiving station.
• A new headworks that includes facilities for screening the plant’s influent wastewater, pumping the wastewater to two vortex-type grit-removal tanks, and washing and dewatering the collected screenings and grit, as well as new structures for distributing the flow to the primary clarifiers.
• Four new primary clarifiers to be converted from the existing four secondary clarifiers to work in conjunction with four existing primary clarifiers.
• Two new organic media biofilters to be converted from existing trickling filters.
• Ten new aeration tanks and four new secondary clarifiers, together with one return and one waste-activated sludge pumping system for biochemical oxygen demand and nitrogen removal.
• Six new percolation basins for disposal/reclamation of treated wastewater.
• New 2-mgd-capacity tertiary treatment, including filtration and disinfection.
• A reclaimed water storage reservoir and pump station for in-plant use and landscape/turf irrigation.
• Two dissolved air flotation units to thicken secondary sludge.
• An upgraded boiler/heat exchanger system to augment the heating capacity of the existing six anaerobic sludge digesters.
• Two new fixed-cover anaerobic digesters to increase Plant 3’s solids-processing capacity.
• A new sludge-dewatering system to house several centrifuges, sludge cake pumping facilities, and truck-loading facilities.
• A new cogeneration system that uses digester gas to generate electrical power.
• A new odor-control system that includes three odor-removal biofilters (two converted trickling filters and one completely new biofilter unit).
• New administration, laboratory, operations, and maintenance buildings to support the upgraded and expanded plant.
• Extensive landscaping around the new buildings and on a 6-ft-high berm surrounding the perimeter of the plant.

Workers place reinforcing steel in wall of McCutchen/Gosford lift station

Bakersfield is using the Plant 3–2007 Expansion project to spearhead two other improvements immediately adjacent to the plant. For the first project, Parsons is providing a design that will upgrade the four roads surrounding Plant 3 into arterial streets for the city. These arterials will have three lanes of traffic in each direction, enhanced signalized intersections, and landscaped medians. For the second improvement, a large portion of the processed plant effluent will be reclaimed to irrigate the Bakersfield Sports Village—an ambitious project currently in the planning phase that will create a family-oriented recreation and retail environment for the entire community.

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