The city of Spokane has awarded a $30 million, eight-year contract to the Spokane office of Denver-based CH2M Hill Inc., for engineering, design, and construction management on the second phase of upgrades to Spokane's wastewater treatment plant.

CH2M Hill will oversee $100 million in planned upgrades over that period of time, and will provide planning at the beginning of the process, along with process engineering and plant engineering over the course of the contract. Lars Hendron, the city's principal wastewater management engineer, says numerous subcontractors will be used for various engineering work under the CH2M Hill contract.

"We have a target that approximately 40 percent of the total contract price would go to subconsultants," Hendron says.

The contract is being awarded just as the city is finishing up its first phase of upgrades to the plant, which cost about $130 million over a 10-year period. One project that had been designed during phase one is scheduled to be constructed next spring, as the first phase-two project, Hendron says.

In that project, which could cost between $3 million and $4 million, the plant's headworks screen system will be upgraded. Hendron says the current bar-style screen that filters wastewater as it enters the plant will be replaced with a perforated-style screen that will filter out more large debris before it gets to the main treatment facility. That debris, such as branches, bottles, and other large items, is rinsed clean, compacted, and disposed of, he says.

One of the projects that will be included in phase two is a planned upgrade of the primary treatment system at the facility, which is the main step of treatment in separating as much solid waste out of the wastewater as possible. The preliminary estimate for that project is about $8 million, Hendron says.

In another project, the city plans to make improvements to four of the facility's aeration basins, adding additional walls to the open-style basins to control the aeration process more precisely to meet stringent regulations better.

In another project, the city plans to spend about $2 million adding a cogeneration facility to the plant. It will convert some of the excess gas produced by the digesters to electricity, which then will be used by the plant, Hendron says. Currently, some of the plant's excess gas is used to make steam heat, but when less steam is needed the gas is released, he says.

The city also plans additional odor-control projects at the plant. They will involve constructing a way to capture air as it comes off the treatment processes and pump it through a biofilter basin, which will be full of bark chips. The bark chips will support a layer of microbes that will consume the odor-producing components, Hendron says.

Also during phase two, the city plans to conduct a pilot study of ultraviolet disinfection systems at the wastewater treatment plant, Hendron says. The city recently converted the plant's disinfection system to liquid chlorine from chlorine gas, but with new filtering units that are planned for 2014 in a later phase of work, it hopes to be able to convert the plant to an ultraviolet disinfection system.

Toward the end of the eight-year second phase, the city anticipates building two more digesters at a combined cost of about $50 million, Hendron says. It currently has two new digesters and two older-style digesters, and would eventually discontinue use of the older ones, which can't process as much solid waste.

Hendron says that though the city hasn't planned future projects beyond phase two, it likely will need to launch a third phase of work to start replacing some of the equipment it installed around the beginning of phase one, back in 1998.