Innovative Design-Build Implementation of CSO Storage in Lewiston, Maine

The Lewiston Auburn Water Pollution Control Authority (LAWPCA) is required to construct a combined sewer overflow (CSO) storage tank to reduce the frequency and volume of CSO discharges into the Androscoggin River from Structure B and Outfall 002 located at the Wastewater Treatment Plant (WWTP). This project will be implemented using a conventional design build (DB) approach. The WWTP is designed to handle an average daily flow of 14.2 million gallons per day (MGD) but currently treats an average daily flow of about 8 MGD. During wet weather the collection systems from Auburn and Lewiston can deliver flows approaching 50 MGD to the WWTP. Excess wet weather flow, above the peak flow capable of being treated through the full WWTP treatment process, overflows from Structure B to the Androscoggin River via a 48-inch outfall leading to Outfall 002. Control of overflows from Structure B is the OBJECTIVE of this DB project. The WWTP currently has sufficient influent pumping capacity to pump and treat a peak flow of 32 MGD. LAWPCA is currently advancing plans to increase the firm WWTP peak flow pumping and treatment capacity to 38 MGD and the 2.1-million-gallon (MG) CSO Storage Facility capacity is based on a 38 MGD WWTP capacity. Purpose of Paper and Presentation: The purpose of this paper and presentation is to convey how LAWPCA structured their conventional DB RFP to provide proposers with considerable latitude to develop and offer LAWPCA a best value solution to their needs while requiring CSO storage site utilization that will preserve options for expanding CSO storage if required in the future. Project Scope: The services in this DB project include engineering, design, permitting, and procurement of materials and equipment, construction, testing, start-up, and commissioning of the LAWPCA CSO Storage Facility. Overflow from downstream of Structure B and upstream of the Outfall 002 discharge location will be intercepted at a Diversion Structure and conveyed to a CSO Storage Pump Station with a firm capacity of 30 MGD. The CSO Storage Pump Station will pump to the Storage Tank(s). Following each storm event, the Storage Tank(s) will be dewatered by gravity to the WWTP for full treatment. The Diversion Structure, CSO Storage Pump Station, and Storage Tank(s) are required to be located within limits shown on an indicative drawing included in the DB procurement document (see attached figure). Major facilities, components, and functions that make up the CSO Storage Facility include the Diversion Structure, CSO Storage Pump Station, Storage Tank(s), ancillary piping (e.g., Diversion Structure to CSO Pump Station, CSO Pump Station to Storage Tank, Storage Tank drain, process water, etc.), Support Building including a garage bay and an Electrical and Control Room, and replacement of an existing stand-by generator. Examples of how the project technical requirements for selected facilities, components, and functions that make up the CSO Storage Facility provide proposers with flexibility while preserving LAWPCA with operational and future flexibility are presented in Table 1. Status of Completion: The design-build RFP, which is the subject of this abstract submittal, was completed in August 2023. Selection of a design builder will be completed by early 2024 with design and construction of the LAWPCA CSO Storage Facility underway by the time this conference takes place in April 2024. Benefits of Presentation: The primary benefit to those attending this presentation will be the opportunity to learn how LAWPCA was innovative in developing their conventional DB RFP to both provide latitude to proposers while preserving their options for future CSO storage expansion. The paper and presentation will expand on the examples in Table 1, above. Additional benefits will include learning how DB can be used to implement time-sensitive wet weather projects and how excess wet weather flow storage can be cost-effectively integrated into an active wastewater treatment plant process and site. Conclusion: The LAWPCA CSO Storage Facility is an important project in attaining regulatory compliance in accordance with long-term CSO control plan requirements and for improving the water quality of the Androscoggin River. Project financing and affordability are important to LAWPCA and citizens of Auburn and Lewiston. ARPA funds, which must be expended by the end of calendar year 2026, will be used to reduce the local cost burden. Selection of conventional DB for implementation of this CSO Storage Facility project will enable LAWPCA to meet that date and take advantage of a best value solution while preserving options for potential future CSO storage needs.