Re-Routing of a Major Urban Trunk Sewer to Expand Water Reclamation

The City of Irvine, CA (City) uses reclaimed water produced at its Michelson Water Reclamation Plant (MWRP) for landscape irrigation and sanitary flushing, and is planning to increase production capacity from current 18 million gallons per day (mgd) to 33 mgd.In order to ensure sufficient wastewater feed for the planned expansion at MWRP, the Harvard Avenue Trunk Sewer (HATS), which currently flows to the Orange County Sanitation District (OCSD), must be re-routed to the plant. IRWD currently pays OCSD to treat the HATS flow at its wastewater treatment Plant No. 1 facility in Fountain Valley, CA.The re-routing of the 9 mgd build-out flow of the HATS to MWRP would have the dual benefit of providing the wastewater feed needed at MWRP to produce the additional reclaimed water, plus eliminating the payment of fees to OCSD. This makes the economics of this project particularly attractive.This paper is an account of the various schemes that were evaluated to re-route the HATS flow to MWRP. The fully developed urban project area required collaborative brain storming sessions with the Client to identify the potentially feasible alternative schemes. Alternatives included: pump station and forcemain, gravity line and lift station, and gravity line alone, at various locations and alignments.Diurnal flows were updated using data collected over 6 months to generate design diurnal curves for the project (Figure 2). The curves were used to estimate the current and future inflows to the system and identify available unused capacities in existing trunk sewers. The Storm Water Management Model (SWMM) was used extensively to analyze the hydraulics of the various alternatives, identify bottlenecks and surcharge locations, and to size and optimize the components of the proposed schemes. The final selected alternative consists of a diversion structure, gravity line to a pump station equipped with dual odor control facilities, forcemain that leads to a vortex drop structure, and a junction structure to connect to an existing trunk sewer.The project was so attractive that the City expedited implementation by opting for the “design-build” method of project delivery so as to have the project on-line by February 2008. The Engineer prepared the design-build RFP package, which specified the Design Basis and the 15% design of the selected alternative. The project was awarded in April 2007, with a contractual completion date of July 2008.This project is a show-case example of how thorough Engineering Studies combined with a collaborative approach with the Client can lead to effective implementation of the optimized solution in a timely manner.