Final phase of irrigation upgrade begins

Work began last week to install a 12-inch pipe down North Douglas Avenue, which will eventually allow effluent to run to city parks for irrigation.

The City of Cottage Grove utility crew began installing a 12-inch pipe down North Douglas Avenue last week, marking the third and final phase of an upgrade to the city’s irrigation system.

The pipe, which will extend from the city’s wastewater treatment plant to Trailhead and Bohemia parks, will allow treated effluent to flow to the parks and replace the current use of treated drinking water for irrigation in those areas.

The new line is scheduled to be completed late 2022 or early 2023 and will likely see its first use in the summer of 2023.

Eventually, the effluent may be used to irrigate Coiner and other parks in the city, said Public Works and Development Director Faye Stewart.

Effluent is wastewater which has been treated to remove contaminants. In Cottage Grove, it is discharged either by way of irrigation or released into the Coast Fork of the Willamette River.

Middlefield Golf Course, owned by the city, had until recently been the only site used for effluent irrigation, but has not always been enough to handle heavy flows.

With limited options, the city run afoul of a few Department of Environmental Quality (DEQ) violations over the years as discharge into the river raised the water temperature or added particulate above DEQ standards.

DEQ’s requirements have also become more stringent, city staff have said, thus requiring an expansion of area to release the effluent through irrigation.

Most recently, the city has upgraded its irrigation system at the exit 174 I-5 interchange to use the effluent as well, adding about 15 acres to its irrigation area.

“With the expansion of the interchange, and then down to the other city parks, we’re hopeful that we’ll be able to utilize all the effluent that we produce in the summer months and we don’t have to put it back into the river,” said Stewart.

The irrigation project, along with the completion of a roughly 10-million-gallon storage pond, is expected to create a long-term solution to relieve the city issues around the discharge the recycled water.

The upgraded system will also be more in line with the city’s steps toward a “greener” future, a request many in the public have made to the city.

For one, replacing drinking water for effluent as irrigation will have a net benefit on energy consumption.

“We are already treating the effluent at the sewer treatment plant,” said Stewart. “We’re not adding any more energy consumption (by using effluent), but we are reducing the amount of energy consumed to treat drinking water.”

Effluent also has a benefit to vegetation, said Stewart, as there are some minerals and nitrates still left in the water which feeds the grass and other flora, which in turn means less fertilizer is needed to keep the grass green.

The golf course, for example, has seen a drastic reduction in the amount of fertilizers that have been used, Stewart said.

Ideally, the irrigated water which is not utilized by the vegetation will seep down into the water table and cool off as it finds its way back into the aquifer and the area’s water system.

A reduction in the amount of treated drinking water, which is in heavy demand during the summer months, may also allow for more water to remain in the Row River to support aquatic life.

While the concept of treated wastewater being sprayed across public land may be offputting for some, city staff have repeatedly expressed confidence in the level of safety in the city’s effluent, placing it just one level below typical drinking water.

“[The effluent] is considered treated to a Class A treatment, which allows everything except for human consumption,” said Stewart. “So if we were to actually put the treated effluent back through our treatment system at the water treatment plant, it would technically be treated to a level that could be utilized by humans to drink. It’s actually treated to a level where the water is cleaner than the water that’s in the rivers today.”

Fire safety will also see an upgrade with the completion of the irrigation project as the new main line being installed down Douglas Avenue will include additional fire hydrants.

“And last year, we were able to offer the large 10-million-gallon storage pond that we have for the effluent,” said Stewart. “We made it available to the Oregon Department of Forestry, the fire department and private timberland owners in case there was a wildfire and, if they had their helicopters with their water buckets, they could dip out of that reservoir for a fire locally.”


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