Hoffman Contractors Inc., of Spokane, is the apparent low bidder, with a bid of $5.4 million, for a city of Spokane contract to upgrade portions of the city's wastewater treatment plant.

Bids for the project came in well below a city estimate of up to $7.9 million, largely because the estimate was done last year when material costs were higher, says Lars Hendron, the city's principal wastewater management engineer. A contract is expected to be awarded early next month, and work is begin soon after that.

The year-and-a half-long project will include a number of upgrades, primarily related to improving the plant's system for screening out debris in wastewater before it enters the plant's headworks, Hendron says. The headworks is the entry point for the plant's main treatment facility.

The main component of the work will be replacing a bar-style screen that filters out debris such as tree branches, bottles and large pieces of garbage with a system of perforated screens that will catch more debris. Hendron says the new system likely will capture about three times as much debris as the bar-style screens.

To accommodate that anticipated increase of debris, two related upgrades will be included in the project. One of those involves construction of a bypass channel to divert wastewater, in the event that the screens become clogged, around the headworks building and allow it to reenter the flow beyond the screen system.

The other is an upgraded washing and compacting system that will deal with debris screened out of the wastewater, Hendron says. Now, the debris is rinsed off before being disposed of as solid waste. The new system will wash the debris more thoroughly and compact it, making it suitable to be incinerated at the city's waste-to-energy plant.

Under the same contract, Hoffman will modify what's called a septage dumping area at the plant. Septage is partially treated waste stored in septic tanks. Currently, septic-tank pumping trucks must drive up a ramp to unload their collected waste, then back down the ramp to turn around and exit the facility. The ramp will be removed and a level, "drive through" septic-dumping area will be created to ease access and egress for such trucks.