A $30,000 contract with the Lands Council may help the city of Spokane siphon off some of the potential $350 million cost of separating and treating stormwater runoff.
It’s a pittance, but if successful could be one of several steps the city hopes will whack $100 million off that treatment bill.
Council representatives have already begun canvassing the Shadle area, looking for homeowners and businesses willing to allow installation of a stormwater garden on their property. The gardens will collect runoff from streets and other impermeable surfaces, then filter out oil and other crud using engineered soil and bio-char, a residue from heating farm and forest waste.
Char, like more familiar charcoal filters, absorbs impurities, perhaps even PCBs.
The cleansed water permeates back into the soil where it undergoes further, natural filtration before entering the Spokane River or Spokane Valley-Rathdrum aquifer.
Natural treatment is, potentially, a much less expensive alternative to tanks the city has installed in several places to simply hold runoff. Some of that water also contains sewage, and that brew is eventually pumped to the Spokane wastewater treatment plant. Where stormwater and sewage are not mixed together, the runoff with all its dirt goes straight into the river.
The tanks and other associated changes in infrastructure came with that $350 million price tag; one Mayor David Condon has refused to accept since his election in 2011.
Lands Council Executive Director Mike Peterson was on Condon’s infrastructure transition team, and the council in April 2012 produced a white paper that suggested stormwater gardens might help avoid construction of more tanks.
The contract, a first between the city and the Lands Council, will give the organization a chance to prove the idea works.
Once three or four sites are identified, the council will design the gardens with the assistance of AHBL, a regional engineering firm. Peterson says construction could start next spring, and the Lands Council is committed to garden upkeep for four years.
If acceptable to the landowners, that work might be done by Airway Heights inmates trained in landscaping by the council.
Peterson says the council will monitor the volume and purity of the water going into and out of the gardens to assure they are effective, and cost-effective. Although they work, other tests of biofiltration on Lincoln Street and Broadway Avenue are too expensive to help the city cut costs, he says.
There have been complaints about the condition of the Lincoln stormwater gardens, but Peterson says he wants the Lands Council versions to become showpieces more landowners will adopt, diverting still more water.
By year-end, city officials expect to submit an amended plan for combined stormwater management to the Washington Department of Ecology, with more details that will include green strategies to follow in January. If stormwater gardens prove effective, fewer and smaller tanks will be needed.
That would be a great outcome for the council and the city.