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The city will attempt to avoid laying pipes in Tryon Creek on a major upcoming project by employing horizontal directional drilling.

The Portland City Council on Wednesday approved use of the construction manager-general contractor method for an upcoming $54 million upgrade of the Tryon Creek Wastewater Treatment Plant.

City staffers are beginning to design the project. A preconstruction contract will soon be awarded to a contractor experienced in horizontal directional drilling and wastewater plant construction.

The Tryon Creek Wastewater Treatment Plant serves Southwest Portland and parts of unincorporated Multnomah and Clackamas counties. Last year the plant treated 2 billion gallons of wastewater. The facility, which provides secondary treatment for activated sludge, was built in 1965 and expanded 11 years later. It’s run by the city, but located in Lake Oswego, where Tryon Creek joins the Willamette River.

The upcoming project will replace aging equipment and convert open-air processing areas to enclosed ones. It will increase capacity and improve efficiency, according to Jim Brown, a Bureau of Environmental Services project manager. Additionally, the headworks will be moved to a higher elevation to allow gravity to power wastewater flowing through the plant.

The current headworks is located above-ground in lower Tryon Creek. The upgrade to a gravity-flow system will allow BES to remove above-ground sections of the interceptor in Tryon Creek.

鈥淎t this stage it appears that horizontal directional drilling replacement of the lower, 2,500-feet Tryon Creek Interceptor is a viable alternative that could provide significant long-term benefits,鈥� Brown told the City Council. 鈥淚t would be drilled in much deeper ground 鈥� not in hard rock, not under the riverbed at all.鈥�

颅BES plans to begin formal design and permitting in fall 2018, with construction occurring from spring 2019 to fall 2021. Goals for minority participation on the project include 22 percent of hard construction costs going to DMWESB subcontractors, 31 percent to apprentices and 28 percent to journey-level workers.

The CM-GC method will allow the city to work closer with its construction contractor and start working with it at the point most beneficial to the design, according to Scott Gibson, BES’ principal engineer for the project.

鈥淲e’re examining options, so we expect it to evolve,鈥� he said. 鈥淲e’ve asked for the alternative delivery method because we believe it will help us come up with the right project for the city.鈥�

An amendment proposed by Commissioner Nick Fish added an emergency clause to the ordinance so the project could begin sooner.

In other business on Wednesday:

The City Council shuffled money to begin purchasing affordable housing via the $258 million affordable housing bond approved by Portland voters in November.

An interfund loan of $51 million in unappropriated reserves to the Portland Housing Bureau was approved. A loan was needed because property is available and it’s unlikely that bond proceeds or grant money will be sufficient before the latest closing date.

Earlier this month, the City Council approved the purchase 鈥� up to $47 million 鈥� of the Ellington Apartments for use as affordable housing. The sale is expected to close in February 2017. The difference between the approved price and the loan amount is due to closing costs and repairs needed on the property, said Karl Dinkelspiel, a housing program manager.