The City of Silverton, Oregon, was planning a constructed wetland to solve a stream thermal overload problem involving its Schemmel Lane Wastewater Treatment Plant. The Oregon Association of Nurseries was looking for place to build a botanical garden.

Through collaboration and cooperation, both solved their problems and came out as winners.

Invasive species, such as sweet autumn clematis and English ivy were choking Silver Creek, a 16-mile stream that flows through downtown Silverton and is the receiving stream for the treatment plant, a 2.5 mgd (design) secondary facility with average flows of 2.2 mgd in winter and 0.9 mgd in the summer.

Cooling down

“In 1995, we had a thermal overload problem as established by our total maximum daily loadings and had to get our effluent out of Silver Creek in summer,” says Steve Starner, water quality supervisor. To solve the problem by further treating and cooling the effluent naturally, the city purchased a 240-acre horse ranch about 1.5 miles from the plant as a site for the wetlands.

“Since the city had the land and the nurserymen’s association needed a botanical garden location with lots of water, it made sense to combine the two,” Starner says. The world-class botanical garden, known as The Oregon Garden, was designed as an 80-acre educational venue with more than 20 specialty gardens, each focused on a theme.

Among them is a children’s garden that includes animal-shaped bushes and shrubs, a treehouse and an area similar to a dinosaur dig. A rose garden displays more than 40 varieties arranged by color, and a sensory garden highlights plants and flowers with therapeutic scents, such as lavender, oregano, coneflower and rosemary. A conifer garden displays more than 400 species, including a large collection of dwarf and miniature conifers and varieties of companion plants such as Daphnes, Japanese maples, heathers and heaths.

Bringing the water

Irrigation for all the gardens is provided through a series of cascaded ponds and strategically located holding tanks. More than 1 mgd of effluent is pumped from the plant through a 16-inch force main with a 60 hp vertical turbine pump (Goulds Water Technology, a Xylem brand). Three complexes at the wetland and gardens, with a combined 25 cells, are gravity-fed and passively provide three final filtration functions.

“The Oregon Garden is one of only a few anywhere that reuses wastewater for a water feature,” Starner says. Landscaping of the Axis Garden, a pattern of turf lined with trees and bushes that display seasonal colors, includes a waterfall-style fountain at one end and the Oregon Garden Resort hotel and conference center at the other. The 106-room hotel was built in 2006, six years after the garden opened, to boost tourism.

The Schemmel Lane plant received a 2018 Award for Excellence from the WateReuse Association, recognizing Silverton’s creation of the wetland to lower discharge temperatures to meet state standards and to further treat wastewater through creation of the garden.

Starner says, “It all just came together at the right time.”