Designed by Brown and Caldwell, an environmental engineering and construction firm, Hawaii’s largest ever wastewater system upgrade has been officially completed.
The upgrade improves Windward Oahu’s sewage collection and treatment system by connecting the Kaneohe Wastewater Pre-Treatment Facility (KWWPTF) to the Kailua Regional Wastewater Treatment Plant (KRWWTP) via a three-mile long, 10-foot diameter gravity sewer tunnel. Wastewater flows via gravity from a depth of 39-feet below ground level at the KWWPTF to a depth of 77-feet below ground at the KRWWTP. The route travels under the Oneawa Hills in order to avoid Kaneohe Bay and any sewage overflows into the environmentally sensitive public resource.
Brown and Caldwell also designed a 45 million gallons per day Tunnel Influent Pump Station to lift wastewater to the surface for treatment at KRWWTP. The project also includes a new 15 million gallons per day replacement for the existing Kailua Influent Pump Station, a generator and headworks buildings, and odor control facilities.
Because the new tunnel system conveys wastewater via gravity rather than pressure, three upstream pump stations and a three-mile long force main (all potential community overflow points) were able to be eliminated.