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Owner: Irvine Ranch Water District (IRWD)
Final Contract Amount: $4,095,000
Completion Date: December 2008

The Harvard Avenue Trunk Sewer (HATS) Diversion project diverts up to 16.5 MGD of wastewater flow from the western part of the City of Irvine, which went to the Orange County Sanitation District facilities, to the IRWD’s Michelson Water Reclamation Plant. The project consists of a diversion structure, 2,200 linear feet of sewer line, the 16.5 MWD pump station, and a junction structure.

Orion and the designers of the project, CDM Engineers, collaborated closely on construction to ensure the owner’s aggressive schedule was maintained, this required close coordination at all levels of management and craft workers during the construction of the pump station concrete structure and installation of the pump station mechanical and electrical components. This close collaboration resulted in the ASCE Orange County Chapter’s 2009 Project Achievement of the Year Award

Orion began the project by excavating 4 large pits, some in excess of 40 feet deep. Starting from the below grade diversion structure the gravity sewer alignment extends under 4-lane city streets and mature landscaped green belt approximately 1,000 LF to the pump station. The gravity line was constructed applying micro tunneling, a trenchless construction technology. The piping material used was 36” polycrete pipe made from aggregate and polyester resin. The 24” force main section starts at the pump station and runs for 1,000 LF along the edge of the Westpark housing development and Cal-Trans landscape freeway easement and was constructed using open cut trench methodology. The forcemain connected to the downstream sewer in a below grade vortex-style drop structure. This was the most effective design minimizing air entertainment and odor.

The project was undertaken on a fastrack schedule to avoid increased sewage treatment costs at OCSD wastewater treatment plant and to take advantage of the available capacity at the IRWD Water Reclamation facility. This required close coordination with IRWD and the City of Irvine Engineering and Building Departments in the permitting process and the further approval of the following local, regional and state agencies:

• Orange County Fire Authority
• State Water Resources Control Board
• South Coast Air Quality Management District
• California Occupational Safety and Health Agency