Flood wall built to protect Santa Rosa treatment plant

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Santa Rosa is putting the finishing touches on a $200,000 wall surrounding vital sections of the Laguna wastewater treatment plant in an effort to prevent El Niño-fueled flood waters from inundating the low-lying facility.

Workers this week maneuvered into place the final few 4,000-pound concrete blocks that will make up most of a 950-foot-long wall designed to keep the waters of the Laguna de Santa Rosa at bay in the event of serious storms.

“It’s a little bit like Legos,” explained Mike Prinz, director of operations at the Llano Road plant, describing the construction process.

The location of the city’s wastewater treatment plant alongside the Laguna leaves it vulnerable to flooding. In the winter of 2005 and 2006, for example, floodwaters entered the plant and swept away an estimated 50,000 gallons of partially treated wastewater. For that and other violations, the city was fined $194,500 by the North Coast Water Quality Control Board.

So plant officials have been thinking for a few years about building a permanent flood protection wall to keep the plant safe from 100-year or even 500-year floods, Prinz said. But that project is still being studied and has yet to be funded.

Global warming is part of the calculation behind the need for a permanent wall. The Laguna won’t be affected by rising sea levels anytime soon, as it drains into the Russian River near Forestville, about 20 miles inland and about 50 feet above sea level. But experts expect a warmer planet will result in more intense storms, which could increase the frequency of local flooding, Prinz said.

As a strengthening El Niño last year increased the likelihood of a wet winter, city officials decided to move forward with a smaller temporary flood wall. They decided to ring some of the lowest areas of the plant with a structure that should protect against a 15-year flood, Prinz said.

Crews have taken about 250 blocks that are 5 feet long and 2.5 feet high, set them in mortar and stacked them two high in some places. There are gaps in the wall in a few areas that cross roads and paths. When needed, those areas will be closed off with inflatable, water-filled flood barriers known as Tiger Dams.

The wall doesn’t go around the entire plant, just around key portions of the treatment process, including massive clarifying tanks, filters that remove remaining particles, and the ultraviolet lights that serve as the final step to disinfect the water.

When waves of Laguna water pour into that finely tuned process, the system becomes overwhelmed.

“The plant wasn’t designed to take all that additional water,” Prinz said.

At $200,000, the project is actually one of the least expensive upgrades done in recent years at the plant. Roughly speaking, the project amounts to one-tenth of 1 percent of the plant’s roughly $200 million value, he noted.

Keeping that unwanted water out will protect the environment against spills and save ratepayers from fines in a tighter regulatory environment, Prinz said.

“Should we pay more money in violations, or should we put that money into something that will prevent violations?” he said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. On Twitter @srcitybeat.

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