The city expects to begin work next spring on a two-year, $80 million project to install a major new sewer line that will run the length of one of the busiest thoroughfares in the Kalihi business district.

The gravity-flow trunk line would run the length of Waiakamilo Road, from Nimitz Highway to North King Street, and then continue mauka along Houghtailing Street to North School Street. It’s a distance of about 6,000 feet, or 1.3 miles.

A draft environmental assessment for the project was submitted to the state Office of Environmental Quality Control last week. The city still needs to obtain several approvals, including a special-management-area use permit. The city expects the project to begin in March and take about two years, said Lori Kahikina, director of the city Department of Environmental Services.

The project will run through a bustling hodgepodge of restaurants, bars, mechanic shops, office space, factories, housing and car dealerships. They include Damien Memorial School, Honolulu Ford, Paradise Flooring, Honolulu Sign Co., Menehune Mac Factory Gift Center, the Waiakamilo Shopping Center and the Aloha T-shirt Factory.

Kahikina said the city is working with state and city agencies to ease congestion in part by ensuring two lanes are flowing in both directions at all times, particularly the section of Waiakamilo Road between Dillingham and North King. The six-lane road section now allows parking on both sides. (The section of Waiakamilo between Nimitz and Hart Street is state-owned.)

“What we’re going to have to do is use the middle of Waiakamilo so that we can have the two lanes in either direction, but it is going to have some impact,” Kahikina said.

A traffic study included with the draft environmental study states the project will “cause temporary closures to traffic lanes, parking lanes and sidewalks. Traffic detours will need to be implemented at particular locations and adjoining streets.”

Hank Erwin, owner of Hank’s Tax Service, said he’d rather the project not take place during his busy season between February and April. Erwin, who’s been at his Waiakamilo location for about five years, said his business should be OK as long as customers can drive in and out of his parking area.

“It just needs to happen in such a way that it doesn’t put me out of business,” Erwin said, citing the horror stories he’s heard about businesses having a hard time as the rail project moved through the Pearl City-Aiea section of Kamehameha Highway. He urged the city to keep area businesses in the loop about how and when they will be affected.

Next door to Erwin’s office, K. Ifuku Radiator owner Darick Shinsato said he expects some impact but believes his business will weather it. But like Erwin, Shinsato said city officials need to “come and talk story with us and let us know what’s going on.”

According to the city’s plans, the pipe diameter of the Waiakamilo line would vary between 30 and 54 inches. The city intends to use subsurface micro-tunneling in depths of 10 to 30 feet for most of the project.

The project is designed to divert roughly 40 percent of the wastewater that now goes to the Awa Street Wastewater Pump Station to the Hart Street Wastewater Pump Station. A 2010 consent decree reached with the U.S. Environmental Protection Agency and the state deemed the Awa station “at risk for potential sewer spills and or overflows due to the volume of sewer flows received at that facility,” the draft environmental assessment said.

On the makai end, the new line would connect with the existing Nimitz sewer main and take the effluent to the Hart station, where it would then be pushed to the Sand Island Wastewater Treatment Plant for treatment and disposal.

The 2010 consent decree requires the city to undertake a series of upgrades to its sewer system with a total price tag of about $5.5 billion in 2010 dollars, Kahikina said.

The Waiakamilo trunk line project is among the last of the improvements required of the island’s sewer collection system, she said. The focus will soon shift to the conversion of two sewage treatment plants to secondary treatment capability, which could cost $4 billion by themselves. The Honouliuli plant is supposed to be upgraded by 2024 and the Sand Island facility by 2035, she said.