Starting this year and continuing through the next five years, the city of Spokane's wastewater management department plans to invest around $300 million into upgrades intended to greatly reduce the volume of combined stormwater and untreated sanitary sewer wastewater going into the Spokane River.

Those efforts will translate into opportunities for some Inland Northwest-based construction companies to bid on contracts for substantial work here.

Companies that have been awarded contracts from the city for recent wastewater management projects associated with the sewer overflow abatement include Davenport, Wash.-based Halme Construction Inc., and Clearwater Construction & Management LLC, of Spokane.

The U.S. Environmental Protection Agency and the Washington state Department of Ecology are mandating that by the end of 2017, combined sewer overflows (CSOs) into the river must be reduced to one overflow event per discharge site per year, says Dale Arnold, director of wastewater management for the city.

During heavy rain storms and rapid snowmelt, stormwater runoff going into the city's combined sewer system can overload the capacity of the sewer lines, which take wastewater to the Riverside Park Water Reclamation Facility, located at 4401 N. Aubrey L. White Parkway.

To relieve the combined sewer system during a big rain or melt-off, some untreated stormwater runoff that's combined with sanitary sewer waste flows directly into the river.

As an example of how weather can impact combined sewer overflow events, during the first quarter of this year the total volume of overflow was recorded at 46 million gallons, with 92 separate overflow events, the wastewater management department reports. About 37 million gallons of that overflow volume occurred during March—the wettest March on record for the Spokane area, says Lars Hendron, principal engineer with the wastewater department.

Last year, the combined sewer system overflowed into the Spokane River a total of 183 times at 22 separate overflow sites along the river, and the total volume of those events was around 19.5 million gallons.

"If it didn't do that, untreated wastewater would come up out of the manholes during a storm," Arnold says. "The water has to be relieved, or it would be uncontrolled."

The city has installed signs at each of those overflow sites, called outfalls, to notify citizens of where untreated wastewater could at times be spilling into the river. Each of those signs notes the CSO outfall site number and a phone number to call and notify the city of an active outfall event. The sign also advises people not to go into the river or to fish if there is wastewater coming out of the outflow pipe.

While those signs ask citizens to notify the wastewater management department if they see an outfall event, Arnold says the combined sewer system still is monitored remotely for any overflows 24 hours a day by the employees at the Riverside Park Water Reclamation Facility. The wastewater department also maintains and updates a page on its website, www.spokanewastewater.org, with the day and time of any overflow events that have occurred within the past 48 hours.

When the city's original wastewater disposal system was built in the early half of the 20th century, storm runoff and household wastewater were carried by the same pipes, Arnold says. Also, before the wastewater treatment plant was built in the late 1950s, all of that wastewater went directly into the Spokane River and Latah Creek.

Starting in the 1980s, however, the city spent more than $50 million to address the high volumes of untreated, combined wastewater that was flowing into the river—between 900 million gallons and 1 billion gallons each year, Arnold says.

He says that during the majority of that decade and into the early 1990s, the city completed work in areas of Spokane north of the river and mostly west of Division Street to separate stormwater and wastewater into separate pipes. That project reduced the number of combined sewer outfalls along the river from around 42 to about 24 that existed before the city recently began work to further reduce overflow, Arnold says.

"We addressed the huge amount of stormwater on the north side that was causing so many of the outfalls" into the river, Arnold says.

As part of that project, he says the city also constructed several catch basins for the runoff that's collected by the stormwater-only line, and connected those basins to the river so that in the event of a heavy rain or melt-off, only stormwater would flow into the river.

In all, those upgrades to the North Side's sewer system in the '80s and early '90s reduced combined wastewater flows into the Spokane River by 85 percent, which, at the time, met some newly enacted EPA guidelines, Arnold says.

Today, however, Arnold says that most neighborhoods in the city located south of the river still are served by a combined sewer system. That part of the citywide system wasn't upgraded when the North Side was, he says, because separating the combined sewer system on the south side would be more difficult and costlier.

During the last eight years, the annual volume of combined sewer overflows from those remaining locations has ranged between a high of 116 million gallons, in 2006, to a low of around 19 million gallons, in 2008 and last year. Those outfall volume totals depend upon a number of factors, including weather and precipitation totals, Arnold says.

The planned upgrades between now and 2017 will address the remaining 22 discharge sites, and Arnold says the goal is to reduce the total annual volume of untreated overflows from those points to less than 10 million gallons a year.

To put that number into perspective, city administrator Theresa Sanders says the city of Indianapolis, which is nearly four times larger than Spokane, has a goal to get its combined sewer overflows into nearby waterways below 440 million gallons a year by the EPA deadline, down from the several billion gallons of untreated sewage overflow that now occurs there annually.

Gerry Gemmill, acting director of the city's public works and utilities department, says, "It's not just a Spokane issue—it's all over the country, and part of it is the fact that the price tags for these things are enormous. We are looking at this and trying to balance the need to meet regulations and to keep it affordable to ratepayers."

Arnold says that funds for the city's six-year combined sewer overflow abatement efforts will come mostly from wastewater service fees paid by residents. The current monthly fees for wastewater service as listed on the city's website total about $53 a month for single-family residences inside city limits, and $79 a month for residences outside the city's boundaries.

Arnold says the city of Spokane has been working since the early '90s on a plan to reduce each of the remaining outfalls to just one wastewater discharge event per year. The city also plans to eliminate eight more of the remaining outfall sites by the end of 2017.

One method the wastewater management department is using to reduce combined wastewater discharges is constructing combined sewer overflow basins, which are massive underground tanks designed to hold the mixed wastewater during a storm so that it doesn't flow into the river. After the amount of storm runoff into the system has subsided, the combined wastewater gradually is piped from the CSO basin back to the main interceptor pipe, which carries it to the wastewater treatment facility.

So far, Arnold says the city has constructed four CSO tanks, and it will have completed or started work on four more basins by the end of this year. By the end of 2017, the city plans to have installed a total number of 37 CSO basins mostly on the south side of the river, he says.

Two new CSO basins that currently are being constructed at a cost of $4.1 million in southeast Spokane, along east South Riverton Avenue, will eliminate the need for two outfall points nearby, CSO 39 and CSO 40. Work on that project is expected to be complete this fall, and its contractor is Halme Construction, of Davenport.

Later this year or early next year, the city's wastewater department expects to begin work nearby on another new CSO basin on the north side of the river, along Upriver Drive between Rebecca and Freya streets. Construction of that new control system is estimated to be about $5 million, Arnold says. A tank also is planned to be installed in the 900 block of East Sprague, he says.

In determining the schedule of when improvements to the combined sewer system would be made, Arnold says the city decided first to tackle some of the outfall points that have had the most frequent discharge events.

In 2010, the most frequent outfall events occurred at CSO 26, located at Avista Utilities' Monroe Street Dam; CSO 24, located in Peaceful Valley and just downstream from the Monroe Street Dam, and at CSO 34, located just south of the East Trent Avenue Bridge.