Sewer holding tank construction begins

Construction started this week on the first in a series of Spokane wastewater improvements that eventually will stop discharges of diluted sewage into the Spokane River.

Workers for Clearwater Construction of Spokane will be installing a 200,000-gallon concrete tank next to Riverside Avenue in High Bridge Park west of downtown.

The tank will gather a combination of storm and wastewater during high flows and hold the water for later treatment at the city-county sewer plant downstream, said Dale Arnold, wastewater director for Spokane.

The $1.6 million project is the first in a series of tanks being planned by the city to prevent overflows during high runoff periods, which occur during thunderstorms and quick snowmelts.

Two sewer lines coming from the Sunset Boulevard and Grove Road areas will be connected to the tank. Currently those two lines have overflowed an average of 14 times a year, dumping an estimated 2 million gallons of combined storm and wastewater into the river.

Once the tank is installed, the combined sewage will be held in the tank until the runoff slows and then be pumped to the wastewater plant for treatment.

Under a clean-water agreement with the state, the city is planning to install as many as 20 underground holding tanks along the river to collect the excess sewage during rainstorms and snowmelts. The cost of building those tanks is estimated at $221 million.

Because the tank at High Bridge Park is being installed in an area known for early Native American encampments, the city was required to undertake an archaeological dig of the site at a cost of $430,000 in 2005.

Archaeologists from Eastern Washington University found thousands of artifacts that proved that the site was used by native people as early as 8,000 years ago.