BACKGROUND

The City owns and operates the existing wastewater treatment plant (WWTP) under California Regional Water Quality Control Board (CRWQCB) Waste Discharge Requirements (WDR) Order No. 94-184. This State regulation requires that the City begin planning for WWTP expansion once treatment volumes reach 80 percent of the plant’s design capacity. The treatment volumes at the existing wastewater treatment plant are in excess of 70% capacity, prompting consideration of new or expanded facilities.

The City of Coalinga is undertaking the construction of a new wastewater treatment and sewer trunk line as well as decommissioning of the existing wastewater facility in order to provide additional capacity to support growth in the area and allow development within the parameters identified in the City’s General Plan.  The City intends to use proven technology to treat wastewater for beneficial reuse.  Design-Build entities will be requested to submit on a selected technology identified by the City and will also have the opportunity to submit alternative technology solutions that the entity feels may be in the City’s best interest to implement from a capital cost and long-term operation and maintenance standpoint.

PROJECT DESCRIPTION

The site proposed for the new wastewater treatment plant (WWTP) is located southwest of the intersection of Jayne Avenue (Highway 33) and Alpine Avenue (Highway 33), outside the current city limits of the City of Coalinga.  The property is approximately 477 acres, encompassing Assessor Parcel Nos. 085-02-036, 085-02-037, and 085-02-029. Jacalitos Creek crosses the northwest corner of the property. Based on information developed during preparation of the Environmental Impact Report (EIR) for the Project, the treatment facilities and effluent storage ponds would be located on approximately 90 acres south of Jacalitos Creek on the western side of the property.  The selected Design-Build Contractor would develop final configuration of the proposed treatment facilities.  The existing WWTP occupies approximately 11 acres on City-owned property at the confluence of Los Gatos Creek and Warthan Creek, north of Jayne Avenue at the eastern City limits, located on Assessor Parcel Nos. 070-07-023, 071-02-026, and 071-02-043, with effluent disposal by agricultural irrigation on adjacent property.  Proposed piping to connect the City sewer collection system to the new WWTP would be constructed within easements located over private property from the existing WWTP to Jayne Avenue and then east along the north side of Jayne Avenue within the City/Caltrans right-of-way to the proposed WWTP property.  The proposed Project would include construction of the new treatment facilities and sewer trunk line as well as the decommissioning of the existing WWTP.

In accordance with information presented in the City’s EIR, the proposed WWTP design would be based on population and wastewater projections to serve the area, which would be accomplished in incremental capacities through the planning year 2025.  The City anticipates that the initial average daily design flow for the WWTP would be 1.5 mgd, with a peak factor of 1.75 for maximum hourly flow. Average daily wastewater flow identified in the EIR for the year 2025 is projected at 2.36 mgd.  General planning documents prepared by the City identify an ultimate treatment capacity requirement of approximately 5.0 mgd based on population projections for the existing service area as well as projections associated with the potential annexation area available to the City.

The EIR identifies aerated lagoon reactors as the biological treatment process proposed for the new WWTP.  Further definition of the baseline influent flows and treatment process will be provided in the solicitation documents for the Project.  The City may modify the treatment process to be identified as the baseline project in the solicitation documents at its sole discretion.  The City prior to issuing the Request for Proposals for the Project will prepare any amendments to the environmental documents, if required.  It is the intent of the City’s solicitation process to use the final baseline project to define the scope of the work during the proposal process, however, alternative treatment processes that have shown extensive successful performance at municipal facilities with similar characteristics to that of the City may be considered at the sole discretion of the City. It is anticipated that treated wastewater from the proposed facility type would be treated to an effluent quality categorized as “undisinfected secondary” according to Part 40, Code of Federal Regulations (CFR) Title 22. Effluent from the facility would be delivered for reuse in accordance with regulatory limitations.  Plant performance requirements will be fully defined in the City’s Request for Proposals.

A new sewer trunk line would be installed to connect the existing sewer collection system to the proposed WWTP. Based on information presented in the City’s EIR for the proposed infrastructure, approximately 2,700 L.F. of 24” sewer line would be installed south from the existing WWTP through easements on private property to Jayne Avenue.  Installation of the trunk line would continue east along the north shoulder of Jayne Avenue with approximately 5,200 L.F. of 24” sewer pipe and would then complete the distance to the western property line of the WWTP property with approximately 12,000 L.F. of 30” pipe. Trunk line pipes would be sized to accommodate peak flow at planning projections to be identified by the City.  The pipeline would require crossing at Jacalitos Creek and the associated flood plain proximal to the new WWTP.  New connections between existing sewer mains and the new trunk line would be required in order to divert flow from the existing WWTP to the new facility.

Based upon the final scope of services to be determined by the City, the Project may include the decommissioning of the existing wastewater treatment plant, including demolition of buildings, ponds and other facilities as well as grading of the property to return the land to natural contours.