California's Mouse-Shaped Wetlands Cleans Effluent and Provides Habitat

A wetland shaped like an endangered small mammal provides effluent polishing and wildlife habitat in Petaluma, California.
California's Mouse-Shaped Wetlands Cleans Effluent and Provides Habitat
Overhead view of the plant showing the mouse-shaped polishing wetlands near the top and in relationship to the rest of the facility.

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The image of an endangered species has a major presence at the Ellis Creek Water Recycling Facility in Petaluma, California. A constructed wetland consisting of four ponds in the shape of a mouse covers more than 30 acres and serves as a polishing filter for the 8 mgd (average) advanced treatment plant.

“The architect designed the polishing wetlands in the shape of the endangered salt marsh harvest mouse,” says Matt Pierce, operations supervisor. “From an aerial shot, you can see what looks like an outline of the mouse.”

Bird shelters

The wetland ponds are separated by earthen berms that define the mouse’s image. Each pond has small islands that shelter nesting birds and direct the flow toward the outfall at the Petaluma River. A walking trail that represents the mouse’s tail connects the wetlands to a water conservation garden and a 1.8-million-gallon concrete-lined reservoir near the plant.

The facility recycles about 40 percent of its effluent for reuse (100 percent during summer). Two golf courses, the city parks, nearby farmland and a vineyard are the primary users. The facility uses its own reclaimed water year-round for landscape irrigation, fire protection, plant process water and toilet flushing.

Advanced process

Wastewater receives several stages of treatment before it reaches the mouse-shaped wetlands. After conventional treatment and time in an aerated lagoon, effluent flows for about a month through eight 18-acre oxidation ponds, ending in a separate treatment wetland populated with bulrushes.

Three 50 hp submersible pumps (Flygt – a Xylem brand), controlled by a flow setpoint in the SCADA system, deliver water from the treatment wetlands to either the polishing wetlands or the tertiary treatment process for advanced treatment before reuse.

Petaluma began recycling in the 1980s by pumping effluent into the oxidation ponds from a treatment plant that was decommissioned and replaced by the Ellis Creek Facility in 2009. The ponds were retained and the polishing wetlands were added. “The oxidation ponds are off-limits to the public, but the polishing wetlands are accessible and very popular,” Pierce says.

Rich environment

Hikers, bicyclists and bird watchers enjoy more than 4 miles of trails that traverse the wetlands. A variety of birds including pelicans, egrets, herons, sandpipers, red-tailed hawks and marsh wrens call the wetlands home. Western pond turtles are also found there, and swans and Canada geese frequent the oxidation ponds.

A connecting trail at the wetlands leads to more than 7 miles of additional trails that link to a city park, a marsh and the Petaluma River. The trail system provides public access to nearly 230 acres of wildlife habitat used for educational programs, nature study and tourism.

Top of Form

To demonstrate sustainability, two green roofs were part of the Ellis Creek construction project. With a combined area of nearly 13,000 square feet, the roofs of the administration and maintenance buildings were planted with more than a dozen species of ground cover. Birds including killdeer have used the roofs for nesting.

Both green roofs are irrigated with recycled water from the facility’s holding pond. Stormwater overflow from the roofs drains into ground-level rain gardens and bioswales, visible from nearby roads and the wildlife viewing areas. Vines cover the façade of the buildings. One green roof was used to support a university professor’s native bee study research, investigating the ecological importance of living roofs in relation to native bee populations.

“We are proud of our facility,” says Pierce. “It was designed to meet ever-increasing performance standards in a sustainable manner. It also benefits the community in terms of wildlife habitat and recreational opportunities.”


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