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How a massive tank could protect Sacramento from sewage overflows

The City of Sacramento plans to build a massive tank under McKinley Park to handle Sacramento’s mixed sewage and rain runoff. How it would change the city’s flooding problem.
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The City of Sacramento plans to build a massive tank under McKinley Park to handle Sacramento’s mixed sewage and rain runoff. How it would change the city’s flooding problem.

McKinley Park in East Sacramento is one of the city’s busiest summertime playgrounds. It may soon become a gathering spot in winter for a less savory visitor – sewage.

City officials are talking about building a massive storage tank beneath the park’s baseball field as a temporary detention basin for rain and sewage during bad storms to reduce street flooding, city officials say. The water vault, or cistern, could be as deep as three or four stories underground.

The $30 million project would be partly funded by a 2016 city utility fee hike, which the city has used to help finance decades-long upgrades of one of its worst infrastructure shortcomings, an antiquated plumbing system that carries stormwater and sewage mingled together in the same pipes.

This combined system has landed the city in trouble with state water control and health officials. It gets backed up during the biggest winter deluges, causing water and sewage to flow out of storm drains, flooding some streets. It also has resulted in untreated sewage flowing into the Sacramento River.

The proposed cistern would connect to the city’s subterranean pipes and store up to 1 million cubic feet of water. That water would be pumped back into the pipes afterward to flow to the regional wastewater treatment plant near Elk Grove. The cistern would not be needed to collect water during smaller rainstorms.

City officials say water and sewage street floods are less frequent now, thanks to years of storm and sewer upgrades, but they still happen in low-lying areas. Sewage flowed this winter onto low-lying residential streets adjacent to McKinley Park’s panhandle, at the site of a former slough, forcing city crews to respond to clean the streets.

Kathleen Mannion, who lives near McKinley Park, said at times she has not been able to get home via the regular route because that end of the street was flooded. A photo distributed by the city and taken by a resident of a heavy storm some time in the last decade shows water shooting up, fountain-like, from displaced manhole covers in the center of the street.

“It makes you nervous,” she said. She welcomes the water vault. “It strikes me as common sense, something neighbors hope would have been done sooner.”

But the water vault idea has prompted concern on social media. Some residents on the Nextdoor East Sacramento community forum said they do not believe the project is needed. Others expressed concerns about major construction in a public park. One noted that city may build a small facility above ground to contain potential odors from air that vents out of the underground tank as water pours in.

City utilities engineer Brett Grant said several smaller underground cisterns are already in use in the city, including at 42nd and R streets in East Sacramento and another under a soccer field and community garden at the Oak Park community center. He said he has heard of no odor complaints or problems so far.

East Sacramento City Councilman Jeff Harris supports the project, but said he wants community discussion of its design, features, timing and exact location.

“It is a big deal if you put sewage in people’s basements or in the river,” Harris said. “We’re subject to some pretty big fines if we don’t get on top of our sewer outflows.”

He said there may be money in the project budget to replace the park’s sprinkler system and do other park upgrades.

The cistern will be sized to prevent street flooding during what are called 10-year storms. Those are storms that have a 10 percent chance of happening in any given year. Streets in that area could still flood if heavier rains hit.

The project’s tentative construction start date is March 2019. The baseball field portion of the park likely would be torn up through late 2020.

City officials have been working since 1995 on upgrades to what city officials call the “combined storm and sewer system,” a single conveyance system built progressively over time starting more than a century ago in the original areas of town, including downtown, midtown, north Land Park and Oak Park.

That work stemmed from a cease-and-desist order from the Central Valley Regional Water Quality Control Board, which was concerned by flooding on city streets and by the city’s periodic discharges of untreated sewage into the Sacramento River when the antiquated system was overwhelmed during storms.

City officials say they decided early on it would be too expensive and disruptive to separate the storm and sewage systems. Instead it has been bolstering the old system with bigger pipes, pump stations and a wet-weather wastewater treatment facility on the river. Harris calls that a “long-term band-aid,” but the best option the city had. The city has been spending an estimated $10 million a year most years since 1995 on upgrades.

City data show that street flooding has been cut in half since 1990. Nevertheless, computer modeling shows that in a major storm, right now, as much as 3 million cubic feet of water would flood into city streets in the central part of the city – mainly spot flooding in lower-lying neighborhoods.

The McKinley Park cistern is on a list of 28 additional projects, costing an estimated $300 million, that the city hopes to build in the next 30 years to continue reducing the amount of street flooding.

Tony Bizjak: 916-321-1059, @TonyBizjak

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